Pulex irritans

Taxonomic classification

Phylum: Arthropoda

Class: Insecta

Order: Siphonaptera

Genus: Pulex irritans (human flea)

There are over 1,600 species and subspecies of fleas that inhabit the earth’s diverse environment. Many of these fleas are parasites in the insect order Siphonaptera. Pulex irritans, also called the human flea, is not often seen in contemporary living quarters, but in the past this flea came in contact with all classes of people. Human blood is the preferred food of Pulex irritans, but it will feed on other mammals. Today, this species is most often found on pigs. Individuals that work with swine are some of the most likely people to become infested. In societies where personal hygiene is important, infestations by human fleas are not as common. Human fleas were extremely common before the development of modern standards in both hygiene and laundering. Most fleas, during that time, were found in a person’s bedding. In an attempt to decrease infestation, the Chinese placed warmed flea traps made of ivory or bamboo between the sheets before going to bed at night. During the Renaissance period, ladies frequently wore fur collars, called cravats, to catch the pestering fleas. The cravat could then be removed and shaken out to decrease the chance of coming in contact with any fleas. Pulex irritans is mainly a nuisance to humans. The flea's saliva contains enzymes and histamine-like substances, which may cause an allergic reaction in some of their victims. These allergic reactions may involve an intense itching sensation. The parasite can also be a vector of a variety of diseases. Even though Pulex irritans was not the primary species responsible for spreading the bubonic plague throughout Europe during the Middle Ages, it is capable of transmitting it. Pulex irritans may also transmit murine typhus, tularemia, and tapeworm, but the chances of this are relatively rare. One disease, in particular, that Pulex irritans is known to transmit is murine typhus. Murine typhus is a mild form of typhus caused by the bacterium Rickettsia typhi. The fleas become infected with the bacterium by feeding on a human who has the disease. The bacteria grow in the epithelial cells lining the flea's gut wall and are excreted in the insect's feces. After approximately twelve to eighteen days, the infection will kill the flea. Scratching of a fleabite will infect a person. Rubbing of the bitten area will spread the flea's infected feces into the wound. An infected person will experience headaches, marked prostration, malaise, chills, loss of appetite, nausea, and a rapid rise in temperature with fever after an incubation period of one to two weeks. Within four to six days after the initial symptoms appear a rash will form over most of the body.

Host spectrum

Humans, canids, felids, pigs, badgers, and rats may all become infested.

Geographic distribution

Pulex irritans is found worldwide.

Morphology

Adults –The adults are approximately 1.5 to 4 mm in length and are laterally flattened. They are dark brown in color, are wingless, and have mouthparts that aid in both the piercing of the skin and sucking of the host’s blood. Neither genal nor pronotal combs are present. The adult flea may have either a curved or rounded head. Only five percent of living fleas are in adult form at any given time. Most fleas are distributed in the egg, larva, or pupa stages.

Eggs – The flea eggs are about 0.5 mm in length. They are oval shaped and pearly white in color. Nonfertile females will produce eggs just as fertile females do, however, the eggs will be nonviable. Eggs are often laid on the body of the host, but since they are not sticky or cemented down, they can fall off in many different places.

Larvae – The larvae are approximately 6 mm in length. They are maggot-like, creamy/yellow in color, and have thirteen segments with bristles on each segment. The larva resembles a small legless caterpillar. The larvae will feed on a variety of debris, including dried excrement, dried blood, dead mites, dried bits of skin, and other organic remains. In some cases, the successful metamorphosis of a few species of flea larvae depends on the presence of fecal matter from the parent flea. In order to provide nutrition for the larvae during development, the parent flea will consume large amounts of blood. During this larval development period the parent flea consumes a great deal of blood (up to thirty times its own weight). The intake of blood will be used to produce a large quantity of feces to feed the larvae.

Pupae – The pupa, with a loosely woven debris-collecting cocoon, is approximately 4 x 2 mm. After undergoing three separate molts, the larvae will begin to spin silk cocoons. After days, weeks, or even months, the pupae will emerge from the cocoons as adults. If conditions are unfavorable, a cocooned flea can remain dormant for up to a year, waiting for the proper prey to become available.

Life cycle (stages)

Eggs may be either laid in the host's place of rest, often called environmental hot spots, or directly on the host. If the eggs are laid on the host, they will easily fall off due to their lack of stickiness. Larvae will hatch from the eggs and begin to feed. The larvae may remain in this stage for up to two hundred days. The pupae are the most tolerant and can last in this form anywhere from ten days to fifty weeks. The time span is dependant on various environmental conditions. The pre-emergent adults (pupae) may be stimulated to emerge by heat, carbon dioxide, or movement (both human and/or pet activity). If these specific stimuli are absent, the emergence of the flea will be delayed. The life span of adult fleas can range from only a few weeks to over an entire year.

Site of infestation

Pulex irritans will attach to and begin feeding on the skin.

Pathogenesis/clinical signs

Pulex irritans can lead to restlessness, and both irritation and scratching of the skin. Pulex irritans is also a vector of Yersinia pestis (plague).

Diagnosis

Diagnosis of Pulex irritans is accomplished by finding the fleas on the host.

Treatment

All animals in the household, especially cats and dogs, should be treated for Pulex irritans. In addition to flea removal, anti-inflammatory agents, and antibiotics for secondary pyoderma should be used. The environment should also be treated. Due to the development of new flea-control products, this is not always necessary except with cases of heavy infestations. Carpets should be shampooed and vacuum frequently. After vacuuming, the vacuum bag should be disposed of immediately. Room foggers may also be used in the house. The bedding or “environmental hot spot” should be washed in hot water, dusted, and sprayed, or have half a No Pest ^R Strip placed on the underside of the pet’s housing quarters. In the case of heavy infestations, a professional exterminator should be contacted. Pigs should be treated with pyrethroids or organophosphates and pet rats should have a No Pest ^R Strip placed above their cage.

Other control measures

Remember to treat both the environment and the host.

Public health significance

Pulex irritans can become a human parasite.

References Cited

http://www.cvm.missouri.edu/cvm/courses/vm556/Arthropods/Fleas/Fleas.htm#PULEX

http://icb.usp.br/~marcelcp/pulex.htm

http://www.olympusmicro.com/micd/galleries/darkfield/pulexirritans1.html

http://micro.magnet.fsu.edu/primer/techniques/dic/dicgallery/humanfleasmall.html

http://www.the-piedpiper.co.uk/th5a.htm