Fleas (Siphonaptera)

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Fleas (Siphonaptera)
Diseases carried	Plague Typhus	Vector organisms	Xenopsylla cheopis (the Oriental rat flea) is the dominant vector for both diseases Plague can also be carried by X. astia in Asia and X. brasiliensis in the Southern hemisphere.
Life Cycle and Control	Eggs are usually laid in debris, not on animal hosts, in groups of about 3-25 a day with a female laying 300-1000 eggs over a life span that may be 10 days to more than a year. Eggs hatch after about 5 days (range 2-14 days depending upon local conditions). The larva that emerges avoids light and feeds actively on organic debris and may also feed on humans or animals. The length of the larval stage depends upon local conditions. The most important environmental variable is humidity and larvae may die if it moves outside a narrow range. After a period that may exceed 200days, the larvae pupate with the adult emerging after about 14 days. Most fleas can delay emergence if they do not detect a suitable host. Adult males and females can take several blood meals a day. They avoid light and hide in bedding and unwashed clothing. If the host dies, the flea moves almost immediately to a new one. Countermeasures are usually aimed at the adult flea. Infected animals and humans may be dusted with powdered insecticides (rather than liquids) and infested areas will also need to be treated. Repellents are also useful and good personal hygiene will also help control human infestation.		Many insecticides are effective against fleas. Those that have proven useful in treatment of animals include: carbaryl diazinon malathion permethrin
Other Countermeasures	Animal host populations need to be tested for infestation and aggressive animal control, especially of rats, is important. Pets, especially cats and dogs, should be given flea collars.		Benzyl benzoate DEET DIMP
Other comments	Yersinia pestis is transmitted by regurgitation of blood meals. This only happens after the bacterium has proliferated in the digestive tract and has blocked it. The regurgitated blood is injected into a host when the flea attempts to take a blood meal. The starving flea, unable to digest the blood meal, may feed much more frequently than an uninfected one. Bacteria secreted in feces may also enter a host through abrasions. In the case of typhus, the disease is only transmitted by rickettsia in feces, however, the agent can invade the ovary, leading to its transovarial transmission (via eggs).		Nosopyllus fasciatus, Leptopsylla aethiopica and Pulex irritans have also been implicated as plague vectors. L. segnis is also a typhus vector that can transmit the agent between animal hosts.
	Image source: Centers for Disease Control, Dr. Pratt Public Health Image Library Image #2069.		An example of Xenopsylla cheopis. The dark mass is Yersinia pestis that has blocked the digestive tract. Should the flea take a blood meal, it will regurgitate it back into the host and pass some of the bacteria into the host and cause infection.

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