''Echinostoma'' is a
genus
Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...
of
trematodes (flukes), which can infect both humans and other
animal
Animals are multicellular, eukaryotic organisms in the Kingdom (biology), biological kingdom Animalia. With few exceptions, animals Heterotroph, consume organic material, Cellular respiration#Aerobic respiration, breathe oxygen, are Motilit ...
s. These intestinal
flukes have a three-host life cycle with
snails
A snail is, in loose terms, a shelled gastropod. The name is most often applied to land snails, terrestrial pulmonate gastropod molluscs. However, the common name ''snail'' is also used for most of the members of the molluscan class Gastrop ...
or other aquatic organisms as
intermediate hosts
In biology and medicine, a host is a larger organism that harbours a smaller organism; whether a parasitic, a mutualistic, or a commensalist ''guest'' (symbiont). The guest is typically provided with nourishment and shelter. Examples include a ...
,
[ ] and a variety of animals, including humans, as their
definitive hosts.
''Echinostoma'' infect the
gastrointestinal tract
The gastrointestinal tract (GI tract, digestive tract, alimentary canal) is the tract or passageway of the digestive system that leads from the mouth to the anus. The GI tract contains all the major organ (biology), organs of the digestive syste ...
of humans, and can cause a disease known as echinostomiasis. The parasites are spread when humans or animals eat infected raw or undercooked food, such as
bivalve molluscs
Bivalvia (), in previous centuries referred to as the Lamellibranchiata and Pelecypoda, is a class of marine and freshwater molluscs that have laterally compressed bodies enclosed by a shell consisting of two hinged parts. As a group, bival ...
or
fish
Fish are aquatic, craniate, gill-bearing animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish as well as various extinct related groups. Approximately 95% of li ...
.
Taxonomy
There has been debate about the number of species in this group, with estimates as high as 120 unique species of ''Echinostoma'',
however, currently 16 species have been accepted as valid species with another 10 to be validated
''Echinostoma'' are difficult to
classify Classification is a process related to categorization, the process in which ideas and objects are recognized, differentiated and understood.
Classification is the grouping of related facts into classes.
It may also refer to:
Business, organizat ...
based on morphology alone. Many species look alike and can be considered
cryptic species
In biology, a species complex is a group of closely related organisms that are so similar in appearance and other features that the boundaries between them are often unclear. The taxa in the complex may be able to hybridize readily with each oth ...
(different lineages are considered to be the same species, due to high morphological similarity between them).
Many
species
In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...
of ''Echinostoma'' have been re-classified several times. For example, the species now known as ''
Echinostoma caproni
''Echinostoma caproni'' is a species of 37-spined Egyptian echinostome. It is naturally found in Cameroon, Congo, Egypt, Madagascar, and Togo.
''Echinostoma caproni'' uses different snails species as first and second intermediate hosts, like ' ...
'', was previously known by a variety of names including ''E. liei'', ''E. parasensei'' and ''E. togoensis''.
Methods for classifying ''Echinostoma'' species, such as the ''
Echinostoma revolutum
''Echinostoma revolutum'' is a trematode parasites, of which the adults can infect birds and mammals, including humans. In humans, it causes echinostomiasis..
Distribution
''Echinostoma revolutum'' is the most widely distributed species of the ...
'' group, were devised by Kanev.
The ''Echinostoma'' species in this group are now classified according to their shared
morphological and biological characteristics, such as the presence of 37 collar spines.
Molecular methods, such as sequencing
mitochondrial DNA
Mitochondrial DNA (mtDNA or mDNA) is the DNA located in mitochondria, cellular organelles within eukaryotic cells that convert chemical energy from food into a form that cells can use, such as adenosine triphosphate (ATP). Mitochondrial D ...
and
ribosomal DNA
Ribosomal DNA (rDNA) is a DNA sequence that codes for ribosomal RNA. These sequences regulate transcription initiation and amplification, and contain both transcribed and non-transcribed spacer segments.
In the human genome there are 5 chromos ...
, are also used to distinguish between species of ''Echinostoma'' as an alternative to morphological classification methods.
Species
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 most known ''Echinostoma'' species based on the
mitochondrial
A mitochondrion (; ) is an organelle found in the cells of most Eukaryotes, such as animals, plants and fungi. Mitochondria have a double membrane structure and use aerobic respiration to generate adenosine triphosphate (ATP), which is use ...
nad1 sequences:
Further confirmed species are ''
E. lindoense''
Sandground & Bonne, 1940 and ''
E. luisreyi''
Maldonado, Vieira & Lanfredi, 2003, these are not included in the phylogeny because of a lack of genetic material.
Unconfirmed species are ''
E. acuticauda'', ''
E. barbosai'', ''
E. chloephagae'', ''
E. echinatum'', ''
E. jurini'', ''
E. nudicaudatum'', ''
E. parvocirrus'', ''
E. pinnicaudatum'', ''
E. ralli'', and ''
E. rodriguesi''.
Morphology
''Echinostoma'' are internal
digenea
Digenea (Gr. ''Dis'' – double, ''Genos'' – race) is a class of trematodes in the Platyhelminthes phylum, consisting of parasitic flatworms (known as ''flukes'') with a syncytial tegument and, usually, two suckers, one ventral and one oral. ...
n
trematode
Trematoda is a class of flatworms known as flukes. They are obligate internal parasites with a complex life cycle requiring at least two hosts. The intermediate host, in which asexual reproduction occurs, is usually a snail. The definitive host ...
parasites which infect the intestines and
bile duct
A bile duct is any of a number of long tube-like structures that carry bile, and is present in most vertebrates.
Bile is required for the digestion of food and is secreted by the liver into passages that carry bile toward the hepatic duct. It ...
of their
hosts
A host is a person responsible for guests at an event or for providing hospitality during it.
Host may also refer to:
Places
*Host, Pennsylvania, a village in Berks County
People
*Jim Host (born 1937), American businessman
*Michel Host ( ...
.
The length and width of adult ''Echinostoma'' varies between species, but they tend to be approximately 2-10mm × 1-2mm in size.
Adult ''Echinostoma'' have two
suckers: an anterior oral sucker and a ventral sucker.
They also have a characteristic head collar with spines surrounding their oral
sucker.
[
] The number of collar spines varies between ''Echinostoma'' species, but there are usually between 27 and 51.
These spines can be arranged in one or two circles around the
sucker, and their arrangement may be a characteristic feature of an ''Echinostoma'' species.
''Echinostoma'' have a digestive system consisting of a
pharynx
The pharynx (plural: pharynges) is the part of the throat behind the mouth and nasal cavity, and above the oesophagus and trachea (the tubes going down to the stomach and the lungs). It is found in vertebrates and invertebrates, though its struc ...
,
oesophagus
The esophagus (American English) or oesophagus (British English; both ), non-technically known also as the food pipe or gullet, is an organ in vertebrates through which food passes, aided by peristaltic contractions, from the pharynx to the ...
and an excretory pore.
''Echinostoma'' are
hermaphrodite
In reproductive biology, a hermaphrodite () is an organism that has both kinds of reproductive organs and can produce both gametes associated with male and female sexes.
Many Taxonomy (biology), taxonomic groups of animals (mostly invertebrate ...
s,
and have both male and female reproductive organs. The
testes
A testicle or testis (plural testes) is the male reproductive gland or gonad in all bilaterians, including humans. It is homologous to the female ovary. The functions of the testes are to produce both sperm and androgens, primarily testoster ...
are found in the posterior part of the fluke's body, in the area furthest from the
mouth
In animal anatomy, the mouth, also known as the oral cavity, or in Latin cavum oris, is the opening through which many animals take in food and issue vocal sounds. It is also the cavity lying at the upper end of the alimentary canal, bounded on ...
.
The
ovary
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. ...
is also found in this location, close to the testes.
The
egg
An egg is an organic vessel grown by an animal to carry a possibly fertilized egg cell (a zygote) and to incubate from it an embryo within the egg until the embryo has become an animal fetus that can survive on its own, at which point the a ...
s (ova) of ''Echinostoma'' are operculate
and vary in size, but are typically in the range of 80-135μm × 55-80μm.
Geographic distribution
The
genus
Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...
''Echinostoma'' has a global
distribution Distribution may refer to:
Mathematics
*Distribution (mathematics), generalized functions used to formulate solutions of partial differential equations
* Probability distribution, the probability of a particular value or value range of a vari ...
. These parasites are particularly common in South East Asia, in countries such as
South Korea
South Korea, officially the Republic of Korea (ROK), is a country in East Asia, constituting the southern part of the Korea, Korean Peninsula and sharing a Korean Demilitarized Zone, land border with North Korea. Its western border is formed ...
and the
Philippines
The Philippines (; fil, Pilipinas, links=no), officially the Republic of the Philippines ( fil, Republika ng Pilipinas, links=no),
* bik, Republika kan Filipinas
* ceb, Republika sa Pilipinas
* cbk, República de Filipinas
* hil, Republ ...
.
[
] However, they are also found in some European countries,
and species such as ''Echinostoma trivolvis'' are found in
North America
North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and the Car ...
.
Life cycle
''Echinostoma'' have three
hosts
A host is a person responsible for guests at an event or for providing hospitality during it.
Host may also refer to:
Places
*Host, Pennsylvania, a village in Berks County
People
*Jim Host (born 1937), American businessman
*Michel Host ( ...
in their
life cycle: a first
intermediate host
In biology and medicine, a host is a larger organism that harbours a smaller organism; whether a parasitic, a mutualistic, or a commensalist ''guest'' (symbiont). The guest is typically provided with nourishment and shelter. Examples include a ...
, a second intermediate host and a
definitive host.
Snail
A snail is, in loose terms, a shelled gastropod. The name is most often applied to land snails, terrestrial pulmonate gastropod molluscs. However, the common name ''snail'' is also used for most of the members of the molluscan class Gastro ...
species such as ''
Lymnaea
''Lymnaea'' is a genus of small to large-sized air-breathing freshwater snails, aquatic pulmonate gastropod mollusks in the subfamily Lymnaeinae ( of the family Lymnaeidae, the pond snails.Bouchet, P.; Rosenberg, G. (2013). Lymnaea Lamarck, 179 ...
'' spp. are common intermediate hosts for ''Echinostoma'',
although
fish
Fish are aquatic, craniate, gill-bearing animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish as well as various extinct related groups. Approximately 95% of li ...
and other
bivalve molluscs
Bivalvia (), in previous centuries referred to as the Lamellibranchiata and Pelecypoda, is a class of marine and freshwater molluscs that have laterally compressed bodies enclosed by a shell consisting of two hinged parts. As a group, bival ...
can also be intermediate hosts for these parasites.
[ ]
''Echinostoma'' species have low specificity for their definitive
hosts
A host is a person responsible for guests at an event or for providing hospitality during it.
Host may also refer to:
Places
*Host, Pennsylvania, a village in Berks County
People
*Jim Host (born 1937), American businessman
*Michel Host ( ...
, and can
infect
An infection is the invasion of tissues by pathogens, their multiplication, and the reaction of host tissues to the infectious agent and the toxins they produce. An infectious disease, also known as a transmissible disease or communicable dis ...
a variety of different
species
In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...
of
animal
Animals are multicellular, eukaryotic organisms in the Kingdom (biology), biological kingdom Animalia. With few exceptions, animals Heterotroph, consume organic material, Cellular respiration#Aerobic respiration, breathe oxygen, are Motilit ...
, including
amphibian
Amphibians are tetrapod, four-limbed and ectothermic vertebrates of the Class (biology), class Amphibia. All living amphibians belong to the group Lissamphibia. They inhabit a wide variety of habitats, with most species living within terres ...
s,
aquatic birds
A water bird, alternatively waterbird or aquatic bird, is a bird that lives on or around water. In some definitions, the term ''water bird'' is especially applied to birds in freshwater ecosystems, although others make no distinction from seabi ...
,
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 and humans.
A definitive host which is infected with ''Echinostoma'' will shed unembryonated ''Echinostoma''
egg
An egg is an organic vessel grown by an animal to carry a possibly fertilized egg cell (a zygote) and to incubate from it an embryo within the egg until the embryo has become an animal fetus that can survive on its own, at which point the a ...
s in their faeces. When the eggs are in contact with
fresh water
Fresh water or freshwater is any naturally occurring liquid or frozen water containing low concentrations of dissolved salts and other total dissolved solids. Although the term specifically excludes seawater and brackish water, it does include ...
they may become embryonated, and will then hatch and release
miracidia.
The miracidia stage of ''Echinostoma'' is free-swimming, and actively penetrates the first intermediate snail host, which then becomes infected.
![Echinostomiasis Life Cycle no watermark](https://upload.wikimedia.org/wikipedia/commons/9/9f/Echinostomiasis_Life_Cycle_no_watermark.gif)
In the first intermediate host, the miracidium undergoes
asexual reproduction
Asexual reproduction is a type of reproduction that does not involve the fusion of gametes or change in the number of chromosomes. The offspring that arise by asexual reproduction from either unicellular or multicellular organisms inherit the fu ...
for several weeks, which includes
sporocyst formation, a few generations of
rediae and the production of
cercariae.
The cercariae are released from the snail host into water and are also free-swimming. The cercariae penetrate a second intermediate host, or they remain in the first intermediate host, where they form metacercariae.
Definitive hosts become infected by eating secondary hosts which are infected with metacercariae.
Once the metacercariae have been eaten, they excyst in the intestine of the definitive host
where the parasite then develops into an adult.
''Echinostoma'' are
hermaphrodite
In reproductive biology, a hermaphrodite () is an organism that has both kinds of reproductive organs and can produce both gametes associated with male and female sexes.
Many Taxonomy (biology), taxonomic groups of animals (mostly invertebrate ...
s. A single adult individual has both male and female reproductive organs, and is capable of self-fertilization.
Sexual reproduction
Sexual reproduction is a type of reproduction that involves a complex life cycle in which a gamete ( haploid reproductive cells, such as a sperm or egg cell) with a single set of chromosomes combines with another gamete to produce a zygote tha ...
of adult ''Echinostoma'' in the definitive host leads to the production of unembryonated eggs.
The life cycle of ''Echinostoma'' is temperature dependent, and occurs quicker at higher temperatures.
''Echinostoma'' eggs can survive for about 5 months and still have the ability to hatch and develop into the next life cycle stage.
Echinostomiasis
Infection
An infection is the invasion of tissues by pathogens, their multiplication, and the reaction of host tissues to the infectious agent and the toxins they produce. An infectious disease, also known as a transmissible disease or communicable dise ...
of humans with members of the family Echinostomatidae, including ''Echinostoma'', can lead to a disease called echinostomiasis. ''E. revolutum'', ''E. echinatum'', ''E. malaynum'' and ''E. hortense'' are particularly common causes of ''Echinostoma'' infections in humans.
Humans can become infected with ''Echinostoma'' by eating infected raw or undercooked
food
Food is any substance consumed by an organism for nutritional support. Food is usually of plant, animal, or fungal origin, and contains essential nutrients, such as carbohydrates, fats, proteins, vitamins, or minerals. The substance is inge ...
, particularly
fish
Fish are aquatic, craniate, gill-bearing animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish as well as various extinct related groups. Approximately 95% of li ...
,
clams and snails.
Infection with these parasites tends to be common in regions where cultural dishes require the use of raw or undercooked food that may be infected with ''Echinostoma''.
A mild infection may not have any
symptom
Signs and symptoms are the observed or detectable signs, and experienced symptoms of an illness, injury, or condition. A sign for example may be a higher or lower temperature than normal, raised or lowered blood pressure or an abnormality showin ...
s.
If symptoms are present they can include abdominal pain,
diarrhoea
Diarrhea, also spelled diarrhoea, is the condition of having at least three loose, liquid, or watery bowel movements each day. It often lasts for a few days and can result in dehydration due to fluid loss. Signs of dehydration often begin wi ...
, tiredness and weight loss.
Epidemiology of echinostomiasis
Echinostomiasis is
endemic
Endemism is the state of a species being found in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also found elsew ...
in South East Asia and the Far East, in countries including
China
China, officially the People's Republic of China (PRC), is a country in East Asia. It is the world's most populous country, with a population exceeding 1.4 billion, slightly ahead of India. China spans the equivalent of five time zones and ...
, Korea,
Taiwan
Taiwan, officially the Republic of China (ROC), is a country in East Asia, at the junction of the East and South China Seas in the northwestern Pacific Ocean, with the People's Republic of China (PRC) to the northwest, Japan to the nort ...
, Philippines,
Malaysia
Malaysia ( ; ) is a country in Southeast Asia. The federation, federal constitutional monarchy consists of States and federal territories of Malaysia, thirteen states and three federal territories, separated by the South China Sea into two r ...
,
Indonesia
Indonesia, officially the Republic of Indonesia, is a country in Southeast Asia and Oceania between the Indian and Pacific oceans. It consists of over 17,000 islands, including Sumatra, Java, Sulawesi, and parts of Borneo and New Guine ...
and
India
India, officially the Republic of India (Hindi: ), is a country in South Asia. It is the seventh-largest country by area, the second-most populous country, and the most populous democracy in the world. Bounded by the Indian Ocean on the so ...
.
Echinostomiasis has also been reported in
Japan
Japan ( ja, 日本, or , and formally , ''Nihonkoku'') is an island country in East Asia. It is situated in the northwest Pacific Ocean, and is bordered on the west by the Sea of Japan, while extending from the Sea of Okhotsk in the north ...
,
Singapore
Singapore (), officially the Republic of Singapore, is a sovereign island country and city-state in maritime Southeast Asia. It lies about one degree of latitude () north of the equator, off the southern tip of the Malay Peninsula, borde ...
,
Romania
Romania ( ; ro, România ) is a country located at the crossroads of Central Europe, Central, Eastern Europe, Eastern, and Southeast Europe, Southeastern Europe. It borders Bulgaria to the south, Ukraine to the north, Hungary to the west, S ...
,
Hungary
Hungary ( hu, Magyarország ) is a landlocked country in Central Europe. Spanning of the Carpathian Basin, it is bordered by Slovakia to the north, Ukraine to the northeast, Romania to the east and southeast, Serbia to the south, Croatia a ...
and
Italy
Italy ( it, Italia ), officially the Italian Republic, ) or the Republic of Italy, is a country in Southern Europe. It is located in the middle of the Mediterranean Sea, and its territory largely coincides with the homonymous geographical re ...
.
The
prevalence of echinostomiasis varies between countries
but there tend to be foci of infection in areas where raw or undercooked hosts of ''Echinostoma'', such as snails or fish, are widely consumed.
Pathogenesis
''Echinostoma'' are not highly pathogenic.
Symptoms of greater severity tend to be seen in an echinostomiasis infection where there is a higher number of flukes.
The flukes cause damage to the intestinal mucosa, which leads to
ulceration and
inflammation
Inflammation (from la, wikt:en:inflammatio#Latin, inflammatio) is part of the complex biological response of body tissues to harmful stimuli, such as pathogens, damaged cells, or Irritation, irritants, and is a protective response involving im ...
.
Diagnosis
![Unstained Echinostoma egg](https://upload.wikimedia.org/wikipedia/commons/3/39/Unstained_Echinostoma_egg.jpg)
An ''Echinostoma'' infection can be diagnosed by observing the parasite eggs in the
faeces of an infected individual, under a
microscope
A microscope () is a laboratory instrument used to examine objects that are too small to be seen by the naked eye. Microscopy is the science of investigating small objects and structures using a microscope. Microscopic means being invisibl ...
. Methods such as the Kato-Katz procedure can be used to do this.
The eggs typically have a yellow-brown appearance, and are ellipsoid in shape.
To confirm which species is causing the infection adult worms must be recovered from the infected individual, such as with anthelmintic treatment.
Treatment and prevention
Echinostomiasis can be treated with the
anthelmintic drug
praziquantel, as for other intestinal trematode infections.
Side effects of anthelmintic drug treatment may include
nausea
Nausea is a diffuse sensation of unease and discomfort, sometimes perceived as an urge to vomit. While not painful, it can be a debilitating symptom if prolonged and has been described as placing discomfort on the chest, abdomen, or back of the ...
, abdominal pain,
headache
Headache is the symptom of pain in the face, head, or neck. It can occur as a migraine, tension-type headache, or cluster headache. There is an increased risk of depression in those with severe headaches.
Headaches can occur as a result ...
s or
dizziness
Dizziness is an imprecise term that can refer to a sense of disorientation in space, vertigo, or lightheadedness. It can also refer to disequilibrium or a non-specific feeling, such as giddiness or foolishness.
Dizziness is a common medical c ...
.
Echinostomiasis can be controlled at the same time as other
food-borne parasite infections, using existing control programmes.
Interrupting the parasite's lifecycle by efficient diagnosis and subsequent treatment of infected individuals, and preventing reinfection, may help to control this disease.
As echinostomiasis is acquired through the consumption of raw or undercooked infected food, cooking food thoroughly will prevent infection.
References
{{Taxonbar, from=Q3046987
Digenea genera
Plagiorchiida
Taxa named by Karl Rudolphi