Ticks (order Ixodida) are parasitic
arachnids that are part of the
mite
Mites are small arachnids (eight-legged arthropods). Mites span two large orders of arachnids, the Acariformes and the Parasitiformes, which were historically grouped together in the subclass Acari, but genetic analysis does not show clear evid ...
superorder
Parasitiformes. Adult ticks are approximately 3 to 5 mm in length depending on age, sex, species, and "fullness". Ticks are external
parasite
Parasitism is a close relationship between species, where one organism, the parasite, lives on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The entomologist E. O. Wilson has ...
s, living by
feeding on the blood of mammals, birds, and sometimes reptiles and amphibians. The timing of the origin of ticks is uncertain, though the oldest known tick fossils are from the
Cretaceous
The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of th ...
period, around 100 million years old. Ticks are widely distributed around the world, especially in warm, humid climates.
Ticks belong to two major families, the
Ixodidae or hard ticks, and the
Argasidae, or soft ticks. ''
Nuttalliella,'' a genus of tick from southern Africa, is the only member of the family Nuttalliellidae, and represents the most primitive living lineage of ticks. Adults have ovoid/pear-shaped bodies (idiosomas) which become engorged with blood when they feed, and eight legs. Their
cephalothorax
The cephalothorax, also called prosoma in some groups, is a tagma of various arthropods, comprising the head and the thorax fused together, as distinct from the abdomen behind. (The terms ''prosoma'' and ''opisthosoma'' are equivalent to ''cepha ...
and abdomen are completely fused. In addition to having a hard shield on their dorsal surfaces, known as the scutum, hard ticks have a beak-like structure at the front containing the mouthparts, whereas soft ticks have their mouthparts on the underside of their bodies. Ticks locate potential hosts by sensing odor, body heat, moisture, and/or vibrations in the environment.
Ticks have four stages to their lifecycle, namely egg,
larva
A larva (; plural larvae ) is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle.
The ...
,
nymph
A nymph ( grc, νύμφη, nýmphē, el, script=Latn, nímfi, label=Modern Greek; , ) in ancient Greek folklore is a minor female nature deity. Different from Greek goddesses, nymphs are generally regarded as personifications of nature, are ty ...
, and adult. Ticks belonging to the Ixodidae family undergo either a one-host, two-host, or three-host lifestyle.
Argasid ticks have up to seven nymphal stages (
instar
An instar (, from the Latin '' īnstar'', "form", "likeness") is a developmental stage of arthropods, such as insects, between each moult (''ecdysis''), until sexual maturity is reached. Arthropods must shed the exoskeleton in order to grow or ass ...
s), each one requiring blood ingestion, Argasid ticks undergo a multihost lifestyle. Because of their hematophagous (blood-ingesting) diets, ticks act as
vectors of many serious diseases that affect humans and other animals.
Biology
Taxonomy and phylogeny
![Tick in amber carrying spirochetes](https://upload.wikimedia.org/wikipedia/commons/d/df/Tick_in_amber_carrying_spirochetes.jpg)
Ticks belong to the
Parasitiformes, a distinctive group of mites that are separate from the main group of mites, the
Acariformes. Whether the two groups are more closely related to each other than to other arachnids is uncertain, and studies often recover them as not closely related. Within the Parasitiformes, ticks are most closely related to the
Holothyrida, a small group of free living scavengers with 32 described species confined to the landmasses that formed the supercontinent
Gondwana
Gondwana () was a large landmass, often referred to as a supercontinent, that formed during the late Neoproterozoic (about 550 million years ago) and began to break up during the Jurassic period (about 180 million years ago). The final stages ...
.
Fossilized ticks have been discovered from the end of the Early Cretaceous onwards, most commonly in amber. The oldest discovered tick fossils are an argasid bird tick from Late Cretaceous (
Turonian
The Turonian is, in the ICS' geologic timescale, the second age in the Late Cretaceous Epoch, or a stage in the Upper Cretaceous Series. It spans the time between 93.9 ± 0.8 Ma and 89.8 ± 1 Ma (million years ago). The Turonian is preceded by t ...
~94-90 million years ago) aged
New Jersey amber
New Jersey Amber, sometimes called Raritan amber, is amber found in the Raritan and Magothy Formations of the Central Atlantic (Eastern) coast of the United States. It is dated to the Late Cretaceous, Turonian age, based on pollen analysis of th ...
,
and various ticks found in
Burmese amber, including ''
Khimaira'' and ''
Deinocroton'', which do not belong to any living family of tick, and members of the living ixodid genera ''
Amblyomma'' and ''
Ixodes'' dating the earliest
Cenomanian
The Cenomanian is, in the ICS' geological timescale, the oldest or earliest age of the Late Cretaceous Epoch or the lowest stage of the Upper Cretaceous Series. An age is a unit of geochronology; it is a unit of time; the stage is a unit in the s ...
stage of the Late Cretaceous, around .
An undescribed juvenile tick is known from late
Albian Spanish amber
Spanish might refer to:
* Items from or related to Spain:
**Spaniards are a nation and ethnic group indigenous to Spain
**Spanish language, spoken in Spain and many Latin American countries
**Spanish cuisine
Other places
* Spanish, Ontario, Cana ...
, dating to 105 million years ago.
The younger
Baltic
Baltic may refer to:
Peoples and languages
* Baltic languages, a subfamily of Indo-European languages, including Lithuanian, Latvian and extinct Old Prussian
*Balts (or Baltic peoples), ethnic groups speaking the Baltic languages and/or originati ...
and
Dominican amber
Dominican amber is amber from the Dominican Republic derived from resin of the extinct tree ''Hymenaea protera''.
Dominican amber differentiates itself from Baltic amber by being nearly always transparent, and it has a higher number of fossil incl ...
s have also yielded examples that can be placed in living genera. A phylogenetic analysis suggests that the last common ancestor of all living ticks likely lived around 195 million years ago in the Southern Hemisphere, in what was then Gondwana.
Ticks belong to three different families. The majority of tick species belong to the two families: Ixodidae (hard ticks) and Argasidae (soft ticks). The third living family is
Nuttalliellidae, named for the bacteriologist
George Nuttall
George Henry Falkiner Nuttall FRS (5 July 1862 – 16 December 1937) was an American-British bacteriologist who contributed much to the knowledge of parasites and of insect carriers of diseases. He made significant innovative discoveries in immu ...
. It comprises a single species, ''Nuttalliella namaqua'',
[ Guglielmone ''et al.'' (2010)] and as such is a
monotypic taxon
In biology, a monotypic taxon is a taxonomic group (taxon) that contains only one immediately subordinate taxon. A monotypic species is one that does not include subspecies or smaller, infraspecific taxa. In the case of genera, the term "unispe ...
. ''Nuttalliella namaqua'' is found in southern Africa ranging from
Tanzania
Tanzania (; ), officially the United Republic of Tanzania ( sw, Jamhuri ya Muungano wa Tanzania), is a country in East Africa within the African Great Lakes region. It borders Uganda to the north; Kenya to the northeast; Comoro Islands and ...
to
Namibia
Namibia (, ), officially the Republic of Namibia, is a country in Southern Africa. Its western border is the Atlantic Ocean. It shares land borders with Zambia and Angola to the north, Botswana to the east and South Africa to the south and ea ...
and
South Africa
South Africa, officially the Republic of South Africa (RSA), is the southernmost country in Africa. It is bounded to the south by of coastline that stretch along the South Atlantic and Indian Oceans; to the north by the neighbouring countri ...
.
The Ixodidae contain over 700 species of hard ticks with a
scutum
The ''scutum'' (; plural ''scuta'') was a type of shield used among Italic peoples in antiquity, most notably by the army of ancient Rome starting about the fourth century BC.
The Romans adopted it when they switched from the military formati ...
or hard shield, which the Argasidae lack. The Argasidae contain about 200 species; the genera accepted are ''
Antricola
''Antricola'' is a genus of tick
Ticks (order Ixodida) are parasitic arachnids that are part of the mite superorder Parasitiformes. Adult ticks are approximately 3 to 5 mm in length depending on age, sex, species, and "fullness". Tick ...
'', ''
Argas
''Argas'' is a genus of tick.
Species
* '' Argas abdussalami'' Hoogstraal & McCarthy, 1965
* '' Argas acinus'' Whittick, 1938
* '' Argas africolumbae'' Hoogstraal, Kaiser, Walker, Ledger, Converse & Rice, 1975
* '' Argas arboreus'' Kaiser, Hoo ...
'', ''
Nothoaspis
''Nothoapis'' is a genus in the soft-bodied tick family, Argasidae
The Argasidae are the family of soft ticks, one of the three families of ticks. The family contains 193 species, although the composition of the genera is less certain, and m ...
'', ''
Ornithodoros
''Ornithodoros'' is a genus in the soft-bodied tick family, Argasidae.
Physiology
The opening between the midgut and hindgut has been lost, making the ticks unable to pass digestive waste products out of their bodies.
Taxonomy
The Linnean name ...
'', and ''
Otobius
''Otobius'' is a genus in the soft-bodied tick family, Argasidae. While similar to the genus ''Ornithodoros'' it is characterized by a vestigial hypostome in adults, despite being developed in nymphs, in addition to the absence of both eyes and h ...
''.
They have no scutum, and the
capitulum
capitulum (plural capitula) may refer to:
*the Latin word for chapter
** an index or list of chapters at the head of a gospel manuscript
** a short reading in the Liturgy of the Hours
*** derived from which, it is the Latin for the assembly known ...
(mouth and feeding parts) is concealed beneath the body.
The
phylogeny
A phylogenetic tree (also phylogeny or evolutionary tree Felsenstein J. (2004). ''Inferring Phylogenies'' Sinauer Associates: Sunderland, MA.) is a branching diagram or a tree showing the evolutionary relationships among various biological spec ...
of the Ixodida within the Acari is shown in the cladogram, based on a 2014
maximum parsimony
In phylogenetics, maximum parsimony is an optimality criterion under which the phylogenetic tree that minimizes the total number of character-state changes (or miminizes the cost of differentially weighted character-state changes) is preferred. ...
study of
amino acid
Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although hundreds of amino acids exist in nature, by far the most important are the alpha-amino acids, which comprise proteins. Only 22 alpha am ...
sequences of 12
mitochondria
A mitochondrion (; ) is an organelle found in the Cell (biology), cells of most Eukaryotes, such as animals, plants and Fungus, fungi. Mitochondria have a double lipid bilayer, membrane structure and use aerobic respiration to generate adenosi ...
l proteins. The Argasidae appear
monophyletic
In cladistics for a group of organisms, monophyly is the condition of being a clade—that is, a group of taxa composed only of a common ancestor (or more precisely an ancestral population) and all of its lineal descendants. Monophyletic gro ...
in this study.
Anatomy and physiology
![Amblyomma americanum tick](https://upload.wikimedia.org/wikipedia/commons/2/29/Amblyomma_americanum_tick.jpg)
Ticks, like
mites
Mites are small arachnids (eight-legged arthropods). Mites span two large orders of arachnids, the Acariformes and the Parasitiformes, which were historically grouped together in the subclass Acari, but genetic analysis does not show clear evid ...
, belong to the subclass Acari that lack their primary somatic segmentation of the
abdomen
The abdomen (colloquially called the belly, tummy, midriff, tucky or stomach) is the part of the body between the thorax (chest) and pelvis, in humans and in other vertebrates. The abdomen is the front part of the abdominal segment of the torso. ...
(or
opisthosoma
The opisthosoma is the posterior part of the body in some arthropods, behind the prosoma (cephalothorax). It is a distinctive feature of the subphylum Chelicerata (arachnids, horseshoe crabs and others). Although it is similar in most respects to a ...
), rather these parasitic
arachnids present a subsequent fusion of the abdomen with the
cephalothorax
The cephalothorax, also called prosoma in some groups, is a tagma of various arthropods, comprising the head and the thorax fused together, as distinct from the abdomen behind. (The terms ''prosoma'' and ''opisthosoma'' are equivalent to ''cepha ...
(or
prosoma
The cephalothorax, also called prosoma in some groups, is a tagma of various arthropods, comprising the head and the thorax fused together, as distinct from the abdomen behind. (The terms ''prosoma'' and ''opisthosoma'' are equivalent to ''cepha ...
).
[ The tagmata typical of other ]Chelicerata
The subphylum Chelicerata (from New Latin, , ) constitutes one of the major subdivisions of the phylum Arthropoda. It contains the sea spiders, horseshoe crabs, and arachnids (including Opiliones, harvestmen, scorpions, spiders, Solifugae, solif ...
have developed into the gnathosoma
The gnathosoma (from Greek , ' = "jaw" and , ' = "body") is the part of the body of the Acari (mites and ticks) comprising the mouth and feeding parts. These are the hypostome, the chelicerae and the pedipalps. It is also called the capitulum (howe ...
(head), which is retractable and contains the mouthparts, and idiosoma (body), which contains the legs, digestive tract, and reproductive organs. The gnathosoma is a feeding structure with mouthparts adapted for piercing skin and sucking blood; it is the front of the head and contains neither the brain nor the eyes. Features of the gnathosoma include two palps, two chelicerae, and hypostome
In zoology, the hypostome can refer to structures in distinct animal groups:
*Hypostome (trilobite), the ventral mouthpart plate in trilobites
*Hypostome (tick)
The hypostome (also called the maxilla, radula, or labium) is a calcified harpoo ...
. The hypostome acts as stabilizer and helps to anchor the tick's mouthparts to the host. The chelicerae are specialized appendages used for cutting and piercing into the host's skin while palps are leglike appendages that are sensory in function.
The ventral side of the idiosoma bears sclerites, and the gonopore is located between the fourth pair of legs. In the absence of segmentation, the positioning of the eyes, limbs, and gonopore on the idiosoma provide the only locational guidance.[
Most ticks are inornate and appear to be brown or reddish brown in color. However, some species are ornate and have distinctive white patterns on the scutum.
Larval ticks hatch with six legs, acquiring the other two after a blood meal and ]molting
In biology, moulting (British English), or molting (American English), also known as sloughing, shedding, or in many invertebrates, ecdysis, is the manner in which an animal routinely casts off a part of its body (often, but not always, an outer ...
into the nymph stage. In the nymphal and adult stages, ticks have eight legs, each of which has seven segments and is tipped with a pair of claws. The legs are sometimes ornamented and usually bear sensory or tactile hairs. In addition to being used for locomotion, the tarsus of leg I contains a unique sensory structure, Haller's organ
Haller's organ is a complex sensory organ possessed by ticks. Ticks, being obligate parasites, must find a host in order to survive; via olfaction and the sensing of humidity, temperature, and carbon dioxide, Haller's organ detects them. Haller' ...
, which can detect odors and chemicals emanating from the host, as well as sensing changes in temperature and air currents. Ticks can also use Haller's organs to perceive infrared
Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from around ...
light emanating from a host. When stationary, their legs remain tightly folded against the body.[ Sonenshine (2005)]
p. 14
/ref>[ Nicholson ''et al.'' (2009)]
p. 486
/ref>
Ticks are extremely tough, hardy, and resilient animals. They can survive in a near vacuum for as long as half an hour. Their slow metabolism during their dormant periods enables them to go prolonged durations between meals. During droughts, they can endure dehydration without feeding for as long as eighteen weeks, however, ticks with limited energy reserves may succumb to desiccation
Desiccation () is the state of extreme dryness, or the process of extreme drying. A desiccant is a hygroscopic (attracts and holds water) substance that induces or sustains such a state in its local vicinity in a moderately sealed container.
...
after thirty-six weeks. To keep from dehydrating, ticks hide in humid spots on the forest floor or absorb water from subsaturated air by secreting hygroscopic
Hygroscopy is the phenomenon of attracting and holding water molecules via either absorption or adsorption from the surrounding environment, which is usually at normal or room temperature. If water molecules become suspended among the substance ...
fluid produced by the salivary glands onto the external mouthparts and then reingesting the water-enriched fluid.
Ticks can withstand temperatures just above for more than two hours and can survive temperatures between for at least two weeks. Ticks have even been found in Antarctica, where they feed on penguins.
Ixodidae
In nymphs and adults, the is prominent and projects forwards from the body. The eyes are close to the sides of the scutum and the large spiracle Spiracle or spiraculum may refer to:
* Spiracle (arthropods), opening in the exoskeletons of some arthropods
* Spiracle (vertebrates), openings on the surface of some vertebrates
* Spiraculum, a genus of land snails in family Cyclophoridae
Cycl ...
s are located just behind the coxae of the fourth pair of legs.[ Molyneux (1993)br>p. 6]
/ref> The hard protective scutellum, a characteristic of this family, covers nearly the whole dorsal surface in males, but is restricted to a small, shield-like structure behind the capitulum in females and nymphs. When an ixodid attaches to a host the bite is typically painless and generally goes unnoticed. They remain in place until they engorge and are ready to molt; this process may take days or weeks. Some species drop off the host to molt in a safe place, whereas others remain on the same host and only drop off once they are ready to lay their eggs.
Argasidae
The body of a soft tick is pear-shaped or oval with a rounded anterior portion. The mouthparts cannot be seen from above, as they are on the ventral surface. A centrally positioned dorsal plate with ridges projecting slightly above the surrounding surface, but with no decoration are often present. Soft ticks possess a leathery cuticle
A cuticle (), or cuticula, is any of a variety of tough but flexible, non-mineral outer coverings of an organism, or parts of an organism, that provide protection. Various types of "cuticle" are non- homologous, differing in their origin, structu ...
as well. A pattern of small, circular depressions expose where muscles are attached to the interior of the integument. The eyes are on the sides of the body, the spiracles open between legs 3 and 4, and males and females only differ in the structure of the genital pore.
Nuttalliellidae
Nuttalliellidae can be distinguished from both ixodid and argasid ticks by a combination of a projecting gnathosoma and a soft leathery skin. Other distinguishing characteristics include the position of th
stigmata
the lack of setae, the strongly corrugated integument, and the form of the fenestrated plates.
Diet and feeding
Ticks are ectoparasites and consume blood
Blood is a body fluid in the circulatory system of humans and other vertebrates that delivers necessary substances such as nutrients and oxygen to the cells, and transports metabolic waste products away from those same cells. Blood in the c ...
to satisfy all of their nutritional requirements. They are obligate hematophages, and require blood to survive and move from one stage of life to another. Ticks can fast for long periods of time, but eventually die if unable to find a host. Hematophagy evolved independently at least six times in arthropods living during the late Cretaceous
The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of th ...
; in ticks it is thought to have evolved 120 million years ago through adaptation to blood-feeding. This behavior evolved independently within the separate tick families as well, with differing host-tick interactions driving the evolutionary change.
Some ticks attach to their host rapidly, while others wander around searching for thinner skin, such as that in the ears of mammals. Depending on the species and life stage, preparing to feed can take from ten minutes to two hours. On locating a suitable feeding spot, the tick grasps the host's skin and cuts into the surface. It extracts blood by cutting a hole in the host's epidermis
The epidermis is the outermost of the three layers that comprise the skin, the inner layers being the dermis and hypodermis. The epidermis layer provides a barrier to infection from environmental pathogens and regulates the amount of water rele ...
, into which it inserts its hypostome
In zoology, the hypostome can refer to structures in distinct animal groups:
*Hypostome (trilobite), the ventral mouthpart plate in trilobites
*Hypostome (tick)
The hypostome (also called the maxilla, radula, or labium) is a calcified harpoo ...
and prevents the blood from clotting by excreting an anticoagulant
Anticoagulants, commonly known as blood thinners, are chemical substances that prevent or reduce coagulation of blood, prolonging the clotting time. Some of them occur naturally in blood-eating animals such as leeches and mosquitoes, where the ...
or platelet aggregation inhibitor.
Ticks find their hosts by detecting an animals' breath and body odors, sensing body heat, moisture, or vibrations.[ A common misconception about ticks is they jump onto their host or they fall from trees, however, they are incapable of flying or jumping. Many tick species, particularly Ixodidae, lie in wait in a position known as "questing". While questing, ticks cling to leaves and grasses by their third and fourth pairs of legs. They hold the first pair of legs outstretched, waiting to grasp and climb on to any passing host. Tick questing heights tend to be correlated with the size of the desired host; nymphs and small species tend to quest close to the ground, where they may encounter small mammalian or bird hosts; adults climb higher into the vegetation, where larger hosts may be encountered. Some species are hunters and lurk near places where hosts may rest. Upon receiving an ]olfactory
The sense of smell, or olfaction, is the special sense through which smells (or odors) are perceived. The sense of smell has many functions, including detecting desirable foods, hazards, and pheromones, and plays a role in taste.
In humans, it ...
stimulus or other environmental indication, they crawl or run across the intervening surface.
Other ticks, mainly the Argasidae, are nidicolous, finding hosts in their nests, burrows, or caves. They use the same stimuli as non-nidicolous species to identify hosts, with body heat and odors often being the main factors.[ Many of them feed primarily on ]bird
Birds are a group of warm-blooded vertebrates constituting the class Aves (), characterised by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweigh ...
s, though some ''Ornithodoros'' species, for example, feed on small mammal
Mammals () are a group of vertebrate animals constituting the class Mammalia (), characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region of the brain), fur or ...
s. Both groups of soft tick feed rapidly, typically biting painfully and drinking their fill within minutes. Unlike the Ixodidae that have no fixed dwelling place except on the host, they live in sand, in crevices near animal dens or nests, or in human dwellings, where they come out nightly to attack roosting birds or emerge when they detect carbon dioxide
Carbon dioxide (chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is transpar ...
in the breath of their hosts.[ Allan (2001)]
Ixodidae remain in place until they are completely engorged. Their weight may increase by 200 to 600 times compared to their prefeeding weight. To accommodate this expansion, cell division takes place to facilitate enlargement of the cuticle. In the Argasidae, the tick's cuticle stretches to accommodate the fluid ingested, but does not grow new cells, with the weight of the tick increasing five- to tenfold over the unfed state. The tick then drops off the host and typically remains in the nest or burrow until its host returns to provide its next meal.
Tick saliva contains about 1,500 to 3,000 proteins, depending on the tick species. The proteins with anti-inflammatory properties, called evasin
Evasins are a family of salivary proteins produced in parasitic ticks which are capable of shutting off the first steps of an immune response brought about by chemokines. These proteins are injected into a tick's host to prevent a painful inflammat ...
s, allow ticks to feed for eight to ten days without being perceived by the host animal. Researchers are studying these evasins with the goal of developing drugs to neutralise the chemokines that cause myocarditis
Myocarditis, also known as inflammatory cardiomyopathy, is an acquired cardiomyopathy due to inflammation of the heart muscle. Symptoms can include shortness of breath, chest pain, decreased ability to exercise, and an irregular heartbeat. The ...
, heart attack, and stroke.
Ticks do not use any other food source than vertebrate blood and therefore ingest high levels of protein, iron and salt, but few carbohydrates, lipids or vitamins. Ticks’ genomes have evolved large repertoires of genes related to this nutritional challenge, but they themselves cannot synthesize the essential vitamins that are lacking in blood meal. To overcome these nutritional deficiencies, ticks have evolved obligate interactions with nutritional endosymbionts
An ''endosymbiont'' or ''endobiont'' is any organism that lives within the body or cells of another organism most often, though not always, in a mutualistic relationship.
(The term endosymbiosis is from the Greek: ἔνδον ''endon'' "within" ...
. The first appearance of ticks and their later diversification were largely conditioned by this nutritional endosymbiosis lasting for millions of years. The most common of these nutritional endosymbionts belong to the ''Coxiella'' and ''Francisella'' bacterial genera. These intracellular symbiotic microorganisms are specifically associated with ticks and use transovarial transmission to ensure their persistence. Although ''Coxiella'' and ''Francisella'' endosymbionts are distantly related bacteria, they have converged towards an analogous B vitamin-based nutritional mutualism with ticks. Their experimental elimination typically results in decreased tick survival, molting, fecundity and egg viability, as well as in physical abnormalities, which all are fully restored with an oral supplement of B vitamins. The genome sequencing of ''Coxiella'' and ''Francisella'' endosymbionts confirmed that they consistently produce three B vitamin types, biotin (vitamin B7), riboflavin (B2) and folate (B9). As they are required for tick life cycle, these obligate endosymbionts are present in all individuals of the tick species they infect, at least at early stages of development since they may be secondarily lost in males during nymphal development. Since ''Coxiella'' and ''Francisella'' endosymbionts are closely related to pathogens, there is a substantial risk of misidentification between endosymbionts and pathogens, leading to an overestimation of infection risks associated with ticks.
Range and habitat
Tick species are widely distributed around the world. They tend to flourish more in warm, humid climates, because they require a certain amount of moisture in the air to undergo metamorphosis
Metamorphosis is a biological process by which an animal physically develops including birth or hatching, involving a conspicuous and relatively abrupt change in the animal's body structure through cell growth and differentiation. Some inse ...
, and low temperatures inhibit their development of eggs to larvae.[ Nuttall (1905)]
The occurrence of ticks and tick-borne illnesses in humans is increasing. Tick populations are spreading into new areas, due in part to the warming temperatures of climate change
In common usage, climate change describes global warming—the ongoing increase in global average temperature—and its effects on Earth's climate system. Climate change in a broader sense also includes previous long-term changes to E ...
.
Tick parasitism is widely distributed among host taxa, including marsupial and placental mammals, birds, reptiles (snakes, iguanas, and lizards), and amphibians. Ticks of domestic animals
Ticks of domestic animals directly cause poor health and loss of production to their hosts. Ticks also transmit numerous kinds of viruses, bacteria, and protozoa between domestic animals. These microbes cause diseases which can be severely debilita ...
cause considerable harm to livestock through pathogenic transmission, causing anemia through blood loss, and damaging wool and hides. The Tropical Bont tick
''Amblyomma variegatum'', commonly known as the tropical bont tick, is a species of tick of the genus ''Amblyomma'' endemic to Africa. It has spread from its centre of origin to several countries, including the Caribbean islands, where it is kn ...
wreaks havoc on livestock and wildlife in Africa, the Caribbean, and several other countries through the spread of disease, specifically heartwater
Heartwater (also known as cowdriosis, nintas, and ehrlichiosis) is a tick-borne rickettsial disease. The name is derived from the fact that fluid can collect around the heart or in the lungs of infected animals. It is caused by ''Ehrlichia rumin ...
disease. The spinose ear tick has a worldwide distribution, the young feed inside the ears of cattle and various wildlife.
A habitat preferred by ticks is the interface where a lawn meets the forest, or more generally, the ecotone
An ecotone is a transition area between two biological communities, where two communities meet and integrate. It may be narrow or wide, and it may be local (the zone between a field and forest) or regional (the transition between forest and gras ...
, which is unmaintained transitional edge habitat between woodlands and open areas. Therefore, one tick management strategy is to remove leaf litter, brush, and weeds at the edge of the woods. Ticks like shady, moist leaf litter with an overstory of trees or shrubs and, in the spring, they deposit their eggs into such places allowing larvae to emerge in the fall and crawl into low-lying vegetation. The 3 meter boundary closest to the lawn's edge are a tick migration zone, where 82% of tick nymphs in lawns are found.
Ecology
In general, ticks are found wherever their host species occur. Migrating birds carry ticks with them on through their migrations; a study of migratory birds passing through Egypt discovered more than half the bird species examined were carrying ticks. It was also observed the tick species varied depending on the season of migration, in this study it is spring and autumn migrations, this is thought to occur due to the seasonal periodicities of the different species.
For an ecosystem to support ticks, it must satisfy two requirements; the population density of host species in the area must be great enough and it must be humid enough for ticks to remain hydrated.[ Wall & Shearer (2001)]
p. 55
/ref> Due to their role in transmitting Lyme disease
Lyme disease, also known as Lyme borreliosis, is a vector-borne disease caused by the ''Borrelia'' bacterium, which is spread by ticks in the genus ''Ixodes''. The most common sign of infection is an expanding red rash, known as erythema migran ...
, Ixodid ticks, particularly the North American ''I. scapularis'', have been studied using geographic information system
A geographic information system (GIS) is a type of database containing Geographic data and information, geographic data (that is, descriptions of phenomena for which location is relevant), combined with Geographic information system software, sof ...
s to develop predictive models for ideal tick habitats. According to these studies, certain features of a given microclimate – such as sandy soil, hardwood trees, rivers, and the presence of deer – were determined to be good predictors of dense tick populations.
Mites and nematodes feed on ticks, which are also a minor nutritional resource for birds. More importantly, ticks act as a disease vector and behave as the primary hosts of many different pathogen
In biology, a pathogen ( el, πάθος, "suffering", "passion" and , "producer of") in the oldest and broadest sense, is any organism or agent that can produce disease. A pathogen may also be referred to as an infectious agent, or simply a germ ...
s such as spirochaetes. Ticks carry various debilitating diseases therefore, ticks may assist in controlling animal populations and preventing overgrazing.
Ticks can transmit an array of infectious diseases that affect humans and other animals. Ticks that carry zoonotic pathogens often tend to have a wide host range. The infective agents can be present not only in the adult tick, but also in the eggs produced plentifully by the females. Many tick species have extended their ranges as a result of the movements of people, domesticated pets, and livestock
Livestock are the domesticated animals raised in an agricultural setting to provide labor and produce diversified products for consumption such as meat, eggs, milk, fur, leather, and wool. The term is sometimes used to refer solely to animals ...
. With increasing participation in outdoor activities such as wilderness hikes, more people and their dogs may find themselves exposed to ticks.
Life cycle
All three tick families ticks have four lifecycle stages: egg, larva
A larva (; plural larvae ) is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle.
The ...
, nymph
A nymph ( grc, νύμφη, nýmphē, el, script=Latn, nímfi, label=Modern Greek; , ) in ancient Greek folklore is a minor female nature deity. Different from Greek goddesses, nymphs are generally regarded as personifications of nature, are ty ...
, and adult.
Ixodidae
Ixodidae ticks have three different life cycles. Depending on the species, Ixodids can either possess a one-host lifecycle, two-host lifecycle, or three-host lifecycle.
= One-host ticks
=
In one-host ticks the tick remains on the host through the larval, nymphal, and adult stages, only to leave the host to lay eggs. Eggs laid in the environment hatch into larvae, which immediately seek out a host in which to attach and feed. Fed larvae molt into unfed nymphs that remain on the host. After engorging on the host's blood, the nymphs molt into sexually mature adults that remain on the host in order to feed and mate. Once a female is both fed and ready to lay eggs, only then does she leave the host in search of a suitable area to deposit her eggs. Ticks that follow this life cycle are called one-host ticks. The winter tick ''Dermacentor albipictus'' and the cattle tick ''Boophilus microplus'' are examples of one-host ticks.
= Two-host ticks
=
The lifecycle of a two-host tick often spans two years. During fall the pregnant female tick will drop off her second host and lay her eggs. The eggs hatch during winter, the following spring the larvae emerge and attach to their first host. Newly hatched larvae attach to a host in order to obtain a blood meal. They remain on the host then develop into nymphs. Once engorged, they drop off the host and find a safe area in the natural environment in which to molt into adults, this typically occurs during the winter. Both male and female adults seek out a host on which to attach, which may be the same body that served as host during their early development but is often a larger mammal. Once attached, they feed and mate. Gravid
In biology and human medicine, gravidity and parity are the number of times a woman is or has been pregnant (gravidity) and carried the pregnancies to a viable gestational age (parity). These terms are usually coupled, sometimes with additional te ...
females drop from the host to oviposit in the environment. Ticks that complete their life cycle in this manner are called two-host ticks, like ''Hyalomma anatolicum excavatum.''
= Three-host ticks
=
Most ixodid ticks require three hosts, and their lifecycles typically span three years. The female tick drops off its host, often in the fall, and lays thousands of eggs. The larvae hatch in the winter and emerge in the spring. When the larvae emerge, they attach and feed primarily on small mammals and birds. During the summer the larvae become engorged and drop off the first host to molt and become nymphs, this often occurs during the fall. The following spring the nymphs emerge and seek out another host, often a small rodent. The nymphs become engorged and drop off the host in the fall to molt and become adults. The following spring the adult ticks emerge and seek out a larger host, often a large mammal such as cattle or even humans. Females will mate on their third host. Female adults then engorge on blood and prepare to drop off to lay her eggs on the ground, while males feed very little and remain on the host in order to continue mating with other females.
Argasidae
Argasid ticks, unlike ixodid ticks, may go through up to seven nymphal stages (instars), requiring a meal of blood each time.[ Aeschlimann & Freyvogel, 1995]
p. 182
/ref> Often, egg laying and mating occurs detached from the host in a safe environment. The eggs hatch and the larvae feed on a nearby host for anywhere from a few hours to several days, this depends on the species of tick. After they feed the larvae drop and molt into their first nymphal instars, then the nymph seeks out and feeds on its second host, often this is the same as the first host, within an hour. This process occurs repeatedly and until the last nymphal instar occurs, thus allowing the tick to molt into an adult. Once an adult these ticks feed rapidly and periodically their entire lifecycle. In some species an adult female may lay eggs after each feeding. Their lifecycles range from months to years. The adult female argasid tick can lay a few hundred to over a thousand eggs over the course of her lifetime. Both male and female adults feed on blood, and they mate off the host. During feeding, any excess fluid is excreted by the coxal glands, a process that is unique to argasid ticks.
Nuttalliellidae
Nuttalliellidae is an elusive monotypic family of tick, that is, possesses a single species, ''Nuttalliella namaqua.'' There is little to nothing known about the lifecycle and feeding habits of ''N. namaqua'' but it is speculated this species of tick has multiple different hosts''.''
Relationship with humans
Tick-borne disease
Ticks are implicated in the transmission of a number of infections caused by pathogen
In biology, a pathogen ( el, πάθος, "suffering", "passion" and , "producer of") in the oldest and broadest sense, is any organism or agent that can produce disease. A pathogen may also be referred to as an infectious agent, or simply a germ ...
s such as bacteria
Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were among ...
, virus
A virus is a submicroscopic infectious agent that replicates only inside the living cells of an organism. Viruses infect all life forms, from animals and plants to microorganisms, including bacteria and archaea.
Since Dmitri Ivanovsky's 1 ...
es, and protozoa
Protozoa (singular: protozoan or protozoon; alternative plural: protozoans) are a group of single-celled eukaryotes, either free-living or parasitic, that feed on organic matter such as other microorganisms or organic tissues and debris. Histo ...
. A tick can harbor more than one type of pathogen, making diagnosis more difficult. Species of the bacterial genus ''Rickettsia
''Rickettsia'' is a genus of nonmotile, gram-negative, nonspore-forming, highly pleomorphic bacteria that may occur in the forms of cocci (0.1 μm in diameter), bacilli (1–4 μm long), or threads (up to about 10 μm long). The term "rickett ...
'' are responsible for typhus
Typhus, also known as typhus fever, is a group of infectious diseases that include epidemic typhus, scrub typhus, and murine typhus. Common symptoms include fever, headache, and a rash. Typically these begin one to two weeks after exposure.
...
, rickettsialpox
Rickettsialpox is a mite-borne infectious illness caused by bacteria of the genus ''Rickettsia'' (''Rickettsia akari''). Physician Robert Huebner and self-trained entomologist Charles Pomerantz played major roles in identifying the cause of the ...
, boutonneuse fever
Boutonneuse fever (also called, Mediterranean spotted fever, ''fièvre boutonneuse'', Kenya tick typhus, Indian tick typhus, Marseilles fever, or Astrakhan fever) is a fever as a result of a rickettsial infection caused by the bacterium '' Ricketts ...
, African tick bite fever
African tick bite fever (ATBF) is a bacterial infection spread by the bite of a tick. Symptoms may include fever, headache, muscle pain, and a rash. At the site of the bite there is typically a red skin sore with a dark center. The onset of sympto ...
, Rocky Mountain spotted fever, Flinders Island spotted fever
Flinders Island spotted fever is a condition characterized by a rash in approximately 85% of cases.
It is associated with '' Rickettsia honei''.
See also
* Japanese spotted fever
* North Asian tick typhus
* List of cutaneous conditions
* Flinde ...
, and Queensland tick typhus
Queensland tick typhus is a zoonotic disease caused by the bacterium ''Rickettsia australis''.
It is transmitted by the ticks ''Ixodes holocyclus'' and '' Ixodes tasmani''.
Signs and symptoms
Queensland tick typhus is a tick-borne disease. Onse ...
(Australian tick typhus). Other tick-borne diseases include Lyme disease
Lyme disease, also known as Lyme borreliosis, is a vector-borne disease caused by the ''Borrelia'' bacterium, which is spread by ticks in the genus ''Ixodes''. The most common sign of infection is an expanding red rash, known as erythema migran ...
and Q fever, Colorado tick fever, Crimean–Congo hemorrhagic fever
Crimean–Congo hemorrhagic fever (CCHF) is a viral disease. Symptoms of CCHF may include fever, muscle pains, headache, vomiting, diarrhea, and bleeding into the skin. Onset of symptoms is less than two weeks following exposure. Complications ...
, tularemia, tick-borne relapsing fever, babesiosis
Babesiosis or piroplasmosis is a malaria-like parasitic disease caused by infection with a eukaryotic parasite in the order Piroplasmida, typically a ''Babesia'' or ''Theileria'', in the phylum Apicomplexa. Human babesiosis transmission via ti ...
, ehrlichiosis, Bourbon virus, and tick-borne meningoencephalitis
Tick-borne encephalitis (TBE) is a viral infectious disease involving the central nervous system. The disease most often manifests as meningitis, encephalitis or meningoencephalitis. Myelitis and spinal paralysis also occurs. In about one third ...
, as well as bovine anaplasmosis
Anaplasmosis is a tick-borne disease affecting ruminants, dogs, and horses, and is caused by ''Anaplasma'' bacteria. Anaplasmosis is an infectious but not contagious disease. Anaplasmosis can be transmitted through mechanical and biological vector ...
and the Heartland virus
''Heartland bandavirus'', sometimes called Heartland virus (HRTV), is a tick-borne ''phlebovirus'' of the ''Bhanja virus'' serocomplex discovered in 2009. The lone star tick transmits the virus to people when feeding on blood. As of 2017, only fi ...
. In the United States, Lyme disease is the most commonly reported vector-borne disease in the country.
Some species, notably the Australian paralysis tick, are also intrinsically venom
Venom or zootoxin is a type of toxin produced by an animal that is actively delivered through a wound by means of a bite, sting, or similar action. The toxin is delivered through a specially evolved ''venom apparatus'', such as fangs or a sti ...
ous and can cause tick paralysis
Tick paralysis is the only tick-borne disease that is not caused by an infectious organism. The illness is caused by a neurotoxin produced in the tick's salivary gland. After prolonged attachment, the engorged tick transmits the toxin to its host. ...
. Eggs can become infected with pathogens inside a female tick's ovaries
The ovary is an organ in the female reproductive system that produces an ovum. When released, this travels down the fallopian tube into the uterus, where it may become fertilized by a sperm. There is an ovary () found on each side of the body. T ...
, in which case the larval ticks are infectious immediately at hatching, before feeding on their first host. Tropical bont tick
''Amblyomma variegatum'', commonly known as the tropical bont tick, is a species of tick of the genus ''Amblyomma'' endemic to Africa. It has spread from its centre of origin to several countries, including the Caribbean islands, where it is kn ...
s transmit the heartwater
Heartwater (also known as cowdriosis, nintas, and ehrlichiosis) is a tick-borne rickettsial disease. The name is derived from the fact that fluid can collect around the heart or in the lungs of infected animals. It is caused by ''Ehrlichia rumin ...
, which can be particularly devastating in cattle.[ The ticks carried by migratory birds act as reservoirs and vectors of foreign infectious diseases. In the Egyptian migratory bird study, over 20 strains of pathogenic viruses were detected within the tick sample from autumn.][
Not all ticks in an infective area are infected with transmittable pathogens, and both attachment of the tick and a long feeding session are necessary for diseases to be transmitted.][ Consequently tick bites often do not lead to infection, especially if the ticks are removed within 36 hours. While adult ticks can be removed with fine-tipped tweezers or proprietary tick removal tools then disinfecting the wound,] there is growing consensus that ticks should be killed in-situ and frozen with either a custom spray or medical wart remover and left to fall out to avoid anaphylactic/allergic reactions. Professor Sheryl van Nunen
Sheryl van Nunen OAM MBBS FRACP, is an Australian allergy researcher and Senior Staff Specialist in the Department of Clinical Immunology and Allergy at Royal North Shore Hospital in Sydney, Australia, and Clinical Associate Professor at the Sy ...
, whose research in 2007 identified tick-induced mammalian meat allergy, famously said " tweezers are tick squeezers", referring to the tick toxins squeezed into people attempting to remove ticks with tweezers. Ticks can be disposed of by flushing them down the toilet, placing them in a container of soapy water or alcohol, or sticking them to tape that can then be folded over and thrown away.[
Bifenthrin and ]permethrin
Permethrin is a medication and an insecticide. As a medication, it is used to treat scabies and lice. It is applied to the skin as a cream or lotion. As an insecticide, it can be sprayed onto clothing or mosquito nets to kill the insects that t ...
, both pyrethroid
A pyrethroid is an organic compound similar to the natural pyrethrins, which are produced by the flowers of pyrethrums (''Chrysanthemum cinerariaefolium'' and ''Chrysanthemum coccineum, C. coccineum''). Pyrethroids are used as commercial and hou ...
s, are sometimes used as tick-control measures, although they have the disadvantage of being carcinogen
A carcinogen is any substance, radionuclide, or radiation that promotes carcinogenesis (the formation of cancer). This may be due to the ability to damage the genome or to the disruption of cellular metabolic processes. Several radioactive substan ...
ic and able to attack the nervous systems of other species besides ticks. Those who walk through tick-infested areas can make it harder for ticks to latch onto them by tucking their trousers into boots made of smooth rubber, which ticks have trouble climbing.
Research since 2008 has documented red-meat allergies (mammalian meat allergy and Alpha-gal allergy
Alpha-gal allergy — or mammalian meat allergy (MMA) — is a type of meat allergy characterized by a delayed onset of symptoms (3–8 hours) after ingesting mammalian meat and resulting from past exposure to tick bites. It was first reported in ...
) in the U.S. due to lone star tick
''Amblyomma americanum'', also known as the lone star tick, the northeastern water tick, or the turkey tick, or the "Cricker Tick", is a type of tick indigenous to much of the eastern United States and Mexico, that bites painlessly and commonly ...
bites. The range of the problem has been expanding with the range of the tick. Other species of ticks are known for being responsible for meat allergies in other countries, including Sweden, Germany, and Australia.
Many tick-transmitted viruses, such as Crimean–Congo hemorrhagic fever virus, Kyasanur Forest disease virus, Alkhumra hemorrhagic fever virus
Alkhurma virus (ALKV) ( ar, فيروس الخرمة) is a zoonotic virus of the ''Flaviviridae'' virus family (class IV). ALKV causes Alkhurma hemorrhagic fever (AHF), or alternatively termed as Alkhurma hemorrhagic fever virus, and is mainly base ...
, and Omsk hemorrhagic fever virus
Omsk (; rus, Омск, p=omsk) is the administrative center and largest city of Omsk Oblast, Russia. It is situated in southwestern Siberia, and has a population of over 1.1 million. Omsk is the third largest city in Siberia after Novosibirsk ...
, are classified as dangerous enough to require biosafety level 4 precautions in laboratory environments. This includes five levels of containment, viz., storage vials within humidified desiccators, within environmental chamber
An environmental chamber, also called a climatic chamber or climate chamber, is an enclosure used to test the effects of specified environmental conditions on biological items, industrial products, materials, and electronic devices and components ...
s, within a tick suite, within a BSL4 laboratory. Precautions such as glove boxes, sticky pads, Vaseline barriers, safety suits, gloves, sticky tape, silicone vacuum grease, sticky trap paste, and micro mesh are used to safely contain ticks and prevent them from escaping.
Population control measures
With the possible exception of widespread DDT
Dichlorodiphenyltrichloroethane, commonly known as DDT, is a colorless, tasteless, and almost odorless crystalline chemical compound, an organochloride. Originally developed as an insecticide, it became infamous for its environmental impacts. ...
use in the Soviet Union
The Soviet Union,. officially the Union of Soviet Socialist Republics. (USSR),. was a transcontinental country that spanned much of Eurasia from 1922 to 1991. A flagship communist state, it was nominally a federal union of fifteen national ...
, attempts to limit the population or distribution of disease-causing ticks have been quite unsuccessful.[ Dennis & Piesman, 2005]
p. 3
/ref>
The parasitoid encyrtid wasp ''Ixodiphagus hookeri
''Ixodiphagus hookeri'', the tick wasp, is an encyrtid wasp which lays its eggs into ticks. It seems to use a symbiotic bacteria, ''Wolbachia pipientis'', to weaken the tick's immune system.
Description
''Ixodiphagus hookeri'' is a small wasp w ...
'' has been investigated for its potential to control tick populations. It lays its eggs into ticks; the hatching wasps kill their hosts.
Predators and competitors of tick hosts can indirectly reduce the density of infected nymphs, thereby lowering tick-borne disease risk by lowering the density and/or tick burden of reservoir-competent hosts. A study in the Netherlands found that the number of larval ticks on bank voles and wood mice was lower at sites with significant red fox ('' Vulpes vulpes'') and stone marten ('' Martes foina'') activity.[ ]
Material was copied from this source, which is available under
Creative Commons Attribution 4.0 International License
This supports the results of a study from the northeastern United States
The Northeastern United States, also referred to as the Northeast, the East Coast, or the American Northeast, is a geographic region of the United States. It is located on the Atlantic coast of North America, with Canada to its north, the Southe ...
, in which the incidence of Lyme borreliosis was negatively correlated with the density of red fox, possibly because foxes decrease the density of white-footed mice (''Peromyscus leucopus''), the most important reservoir-competent host for '' Borrelia burgdorferi''.
Another natural form of control for ticks is the helmeted guineafowl, a bird species that consumes mass quantities of ticks. Opossums groom themselves, swallowing many ticks; they are net destroyers of ticks, killing around ninety percent of the ticks that attempt to feed on them. More generally, high animal diversity has a strongly protective effect against tick-borne disease.
Topical tick medicines may be toxic to animals and humans. The synthetic pyrethroid
A pyrethroid is an organic compound similar to the natural pyrethrins, which are produced by the flowers of pyrethrums (''Chrysanthemum cinerariaefolium'' and '' C. coccineum''). Pyrethroids are used as commercial and household insecticides.
In ...
insecticide phenothrin
Phenothrin, also called sumithrin and d-phenothrin, is a synthetic pyrethroid that kills adult fleas and ticks. It has also been used to kill head lice in humans. d-Phenothrin is used as a component of aerosol insecticides for domestic use. It is ...
in combination with the hormone analogue methoprene was a popular topical flea and tick therapy for felines. Phenothrin kills adult ticks, while methoprene kills eggs. Some products were withdrawn, and others are known to cause adverse reactions.
See also
*Parasitology
Parasitology is the study of parasites, their hosts, and the relationship between them. As a biological discipline, the scope of parasitology is not determined by the organism or environment in question but by their way of life. This means it fo ...
*Ticks of domestic animals
Ticks of domestic animals directly cause poor health and loss of production to their hosts. Ticks also transmit numerous kinds of viruses, bacteria, and protozoa between domestic animals. These microbes cause diseases which can be severely debilita ...
* Tick-borne disease
Notes
References
Sources
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External links
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{{Authority control
Parasitic acari
Hematophages
Hazards of outdoor recreation