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The human flea (''Pulex irritans'') – once also called the house flea – is a
cosmopolitan Cosmopolitan may refer to: Internationalism * World citizen, one who eschews traditional geopolitical divisions derived from national citizenship * Cosmopolitanism, the idea that all of humanity belongs to a single moral community * Cosmopolitan ...
flea Flea, the common name for the order (biology), order Siphonaptera, includes 2,500 species of small flightless insects that live as external parasites of mammals and birds. Fleas live by hematophagy, ingesting the blood of their hosts. Adult f ...
species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...
that has, in spite of the
common name In biology, a common name of a taxon or organism (also known as a vernacular name, English name, colloquial name, country name, popular name, or farmer's name) is a name that is based on the normal language of everyday life; and is often con ...
, a wide host spectrum. It is one of six species in the genus '' Pulex''; the other five are all confined to the
Nearctic The Nearctic realm is one of the eight biogeographic realms constituting the Earth's land surface. The Nearctic realm covers most of North America, including Greenland, Central Florida, and the highlands of Mexico. The parts of North America ...
and
Neotropical realm The Neotropical realm is one of the eight biogeographic realms constituting Earth's land surface. Physically, it includes the tropics, tropical Ecoregion#Terrestrial, terrestrial ecoregions of the Americas and the entire South American temperat ...
s. The species is thought to have originated in
South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a considerably smaller portion in the Northern Hemisphere. It can also be described as the southern Subregion#Americas, subregion o ...
, where its original host may have been the
guinea pig The guinea pig or domestic guinea pig (''Cavia porcellus''), also known as the cavy or domestic cavy ( ), is a species of rodent belonging to the genus ''Cavia'', family Caviidae. Animal fancy, Breeders tend to use the name "cavy" for the ani ...
or peccary.


Morphology and behavior

''Pulex irritans'' is a holometabolous insect with a four-part lifecycle consisting of eggs, larvae, pupae, and adults. Eggs are shed by the female in the environment and hatch into larvae in about 3–4 days. Larvae feed on organic debris in the environment. Larvae eventually form pupae, which are in cocoons that are often covered with debris from the environment (sand, pebbles, etc.). The larval and pupal stages are completed in about 3–4 weeks when the adults hatch from pupae, then must seek out a warm-blooded host for blood meals. Adults lack genal and pronotal ctenidia. The flea eggs are about 0.5 mm in length. They are oval-shaped and pearly white in color. Eggs are often laid on the body of the host, but they often fall off in many different places. The larvae are about 0.6 mm in length. They are creamy white or yellow in color. Larvae have 13 segments with bristles on each segment. The larvae feed on a variety of organic debris. The pupa are around 4 x 2 mm. After undergoing three separate molts, the larvae pupate, then emerge as adults. If conditions are unfavorable, a cocooned flea can remain dormant for up to a year in the pupal phase. The adults are roughly 1.5 to 4 mm in length and are laterally flattened. They are dark brown in color, are wingless, and have piercing-sucking mouthparts that aid in feeding on the host's blood. Both genal and pronotal combs are absent and the adult flea has a rounded head. Most fleas are distributed in the egg, larval, or pupal stages.


Host species

The most common hosts for ''P. irritans'' are carnivores and less occasionally pigs. Humans are not frequently parasitised in the developed world.


Relationship with host


Direct effects of bites

Fleas are a pest species to their hosts, causing an itching sensation that results in discomfort and leads to scratching in the vicinity of the bite. Flea bites generally cause the skin to raise, swell, and itch. The bite site has a single puncture point in the center. Bites often appear in clusters or small rows and can remain inflamed for up to several weeks. This species bites many species of mammals and birds, including domesticated ones. It has been found on dogs and wild canids,
monkey Monkey is a common name that may refer to most mammals of the infraorder Simiiformes, also known as simians. Traditionally, all animals in the group now known as simians are counted as monkeys except the apes. Thus monkeys, in that sense, co ...
s in captivity,
opossum Opossums () are members of the marsupial order Didelphimorphia () endemic to the Americas. The largest order of marsupials in the Western Hemisphere, it comprises 126 species in 18 genera. Opossums originated in South America and entered North A ...
s,
domestic cat The cat (''Felis catus''), also referred to as the domestic cat or house cat, is a small Domestication, domesticated carnivorous mammal. It is the only domesticated species of the family Felidae. Advances in archaeology and genetics have sh ...
s, wild felids in captivity,
chicken The chicken (''Gallus gallus domesticus'') is a domesticated subspecies of the red junglefowl (''Gallus gallus''), originally native to Southeast Asia. It was first domesticated around 8,000 years ago and is now one of the most common and w ...
s, black rats and Norwegian rats, wild
rodent Rodents (from Latin , 'to gnaw') are mammals of the Order (biology), order Rodentia ( ), which are characterized by a single pair of continuously growing incisors in each of the upper and Mandible, lower jaws. About 40% of all mammal specie ...
s, pigs,
free-tailed bat The Molossidae, or free-tailed bats, are a family of bats within the order Chiroptera. The Molossidae is the fourth-largest family of bats, containing about 110 species as of 2012. They are generally quite robust, and consist of many strong-fly ...
s, and other species. It can also be an intermediate host for the flea tapeworm
cestode Cestoda is a class of parasitic worms in the flatworm phylum (Platyhelminthes). Most of the species—and the best-known—are those in the subclass Eucestoda; they are ribbon-like worms as adults, commonly known as tapeworms. Their bodies co ...
'' Dipylidium caninum''. Fleas can spread rapidly and move between areas to include eyebrows, eyelashes, and pubic regions. Hair loss as a result of itching is common, especially in wild and domestic animals. Anemia is also possible in extreme cases of high-volume infestations.


Vector capabilities

Plague, a disease that affects humans and other mammals, is caused by the bacterium ''
Yersinia pestis ''Yersinia pestis'' (''Y. pestis''; formerly ''Pasteurella pestis'') is a Gram-negative bacteria, gram-negative, non-motile bacteria, non-motile, coccobacillus Bacteria, bacterium without Endospore, spores. It is related to pathogens ''Yer ...
''. The human flea can be a carrier of the plague bacterium, although it is an exceptionally very poor vector of transmission. ''P. irritans'' is likely to have been the main vector for plague epidemics in Northern Europe due to the
Oriental rat flea The Oriental rat flea (''Xenopsylla cheopis''), also known as the tropical rat flea or the rat flea, is a parasite of rodents, primarily of the genus ''Rattus'', and is a primary Vector (epidemiology), vector for bubonic plague, plague and murine ...
having poor survival in cool climates.


Treatment and prevention

Common treatments include body shaving and medicated shampoos and combing. When preventing fleas, it is important to treat both the host and the environment. Household pets should be treated to prevent being infested. Carpets, and other floor surfaces, should be shampooed and vacuumed regularly to prevent fleas. When dealing with an infestation, bedding and clothing that may have been exposed should be washed thoroughly in hot water and kept away from other materials that have not been exposed. In extreme cases, extermination by a professional is necessary.


Phylogeny and Distribution

''Pulex irritans'' originated in Central and South America, where it evolved with only one host. Despite the origins of ''P. irritans'', it is now a
cosmopolitan Cosmopolitan may refer to: Internationalism * World citizen, one who eschews traditional geopolitical divisions derived from national citizenship * Cosmopolitanism, the idea that all of humanity belongs to a single moral community * Cosmopolitan ...
species, most likely due to the fur trade after the 18th century, and pet transport in more recent decades. Due to the cosmopolitan distribution of this group, research has been conducted to show that ''P. irritans'' individuals, when sampled from Spain and Argentina, only showed significant differences when comparing molecular data. The use of morphometric data, which is often the method for flea identification, showed no significant levels of divergence between the two populations. Combining both morphological and molecular data has identified the possibility of
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 ...
. This indicates a need to reconsider taxonomic classifications of these fleas. Studies in Europe and the Mediterranean also found this to be true. Human and cat fleas from Europe and the Mediterranean were studied and show such great variation within their own species that their taxonomy should be reevaluated based on mitochondrial gene heterogeneity.


References

{{Taxonbar, from=Q989263 Pulicidae Insects described in 1758 Taxa named by Carl Linnaeus Parasitic arthropods of humans