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Fleas

Category: Illness or disabilities

Type

Involuntary

Introduction and description

Fleas are small flightless insects that form the order Siphonaptera. Over 2,500 species of fleas have been described worldwide. The Siphonaptera are most closely related to the snow scorpionflies (Boreidae), placing them within the endopterygote insect order Mecoptera.  As external parasites of mammals and birds, they live by consuming the blood of their hosts.

Adults are up to about 3 mm (0.12 in) long and usually brown. Bodies flattened sideways enable them to move through their host's fur or feathers; strong claws prevent them from being dislodged. They lack wings, and have mouthparts adapted for piercing skin and sucking blood and hind legs adapted for jumping. The latter enable them to leap a distance of some 50 times their body length, a feat second only to jumps made by froghoppers. Larvae are worm-like with no limbs; they have chewing mouthparts and feed on organic debris.

Each species of flea is more or less a specialist on its host animal species: many species never breed on any other host, though some are less selective. Some families of fleas are exclusive to a single host group: for example, the Malacopsyllidae are found only on armadillos, the Ischnopsyllidae only on bats, and the Chimaeropsyllidae only on elephant shrews.

Disease vectors

 

Although ticks are recognised as significant carriers of disease, it appears to be almost ignored that fleas too can be the vectors for some truly awful diseases

The oriental rat flea, Xenopsylla cheopis, for example, is a vector of Yersinia pestis, the bacterium which causes bubonic plague. The disease is spread by rodents such as the black rat, which are bitten by fleas that then infect humans. Major historical outbreaks included the Plague of Justinian and the Black Death, both of which killed a sizeable fraction of the world's population.

Flea-borne zoonoses such as plague (Yersinia pestis) and murine typhus (Rickettsia typhi) caused significant numbers of human cases in the past and remain a public health concern. Other flea-borne human pathogens have emerged recently (e.g., Bartonella henselae, Rickettsia felis), and their mechanisms of transmission and impact on human health are not fully understood. PMID: 21888520

It may be worth adding that a considerable number of studies were undertaken during the first decade of the twenty-first century, because of renewed interest in potential agents of bioterrorism, including Y. pestis.

 

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References and further reading

  • Annu Rev Entomol. 2012;57:61-82. doi: 10.1146/annurev-ento-120710-100717. Epub 2011 Aug 29.
    Transmission of flea-borne zoonotic agents.  Eisen RJ1, Gage KL.1  Division of Vector-Borne Diseases, Centers for Disease Control and Prevention, Fort Collins, Colorado 30333, USA. dyn2@cdc.gov

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