Tungiasis

Tungiasis is the pathological condition resulting from infestation by fleas belonging to the genus Tunga. Although there are several species of Tunga, only the chigoe (T. penetrans) attacks humans. T. penetrans occurs in many tropical and subtropical zones but is especially common in the New World tropics, the West Indies, tropical Africa, and southern India. The first record of this flea was in 1492 from crewmen of Christopher Columbus stationed in Haiti. It apparently spread from the New World to other areas of the world by shipping commerce, being first recorded on the African continent in 1732 as a consequence of the slave trade.

Females of T. penetrans usually invade a site between the toes, beneath the toe nails, or on the soles of the feet. Other sites may include the arms, especially around the elbow, and genital region in heavy infestations. Sldn invasion by this flea can cause painful, subcutaneous lesions that often lead to more serious medical complications. The embedded chigoe (Fig. 7.13) invariably causes intense irritation and can result in secondary infections that ooze pus. When several chigoes attack an individual host at the same time, ulcerations often develop as the resultant lesions coalesce. Tetanus, cellulitis, and impaired blood flow to the site often lead to gangrene and may necessitate amputation of toes or, sometimes, an entire foot. Chigoe lesions therefore should receive prompt medical attention. Although the flea can be removed using a sterile needle or scalpel, it is important that lesions be thoroughly cleaned and dressed to avoid infection. This also applies to embedded dead fleas, which may rapidly cause affected tissues to fester and ulcerate if left untreated. The best defense against tungiasis is to avoid walking barefoot on beaches and other sandy soils in endemic regions where this flea develops.

Fleas as Intermediate Hosts of Helminths

Certain fleas are intermediate hosts for the cysticercoid stage of three species of tapeworms that occasionally infest humans. The most important of these is the double-pored tapeworm (Dipylidium caninum), the adults of which normally parasitize dogs. Gravid proglottids are released by D. caninum adults in the gut of the definitive host and are voided in the feces. The subsequently expelled eggs are ingested by flea larvae; the chewing mandibles of the larvae enable them to ingest the eggs, whereas the sucking mouthparts of adult fleas do not. Fleas such as Ctenocephalides felis, C. canis, and Pulex irritans play a significant role as intermediate hosts for this tapeworm. The dog chewing louse (Trichodectes canis) occasionally ingests D. caninum eggs and also can serve as an intermediate host.

The tapeworm develops slowly in flea larvae but rapidly in flea pupae. Cysticercoids can be seen in the body cavity of larvae and pupae, where they remain through development of the flea to the adult stage. Some flea mortality occurs in the pupal stage due to this helminth. Infestation of the human (definitive) host occurs when a person incidentally ingests an infested flea. The cysticercoid is liberated from the flea by digestive enzymes, after which it everts and attaches to the gut of its new host. Children playing with pets are especially susceptible to infestation by this tapeworm.

Two other tapeworms that utilize fleas as intermediate hosts are the rodent tapeworm (Hymenolepis diminuta) and the dwarf tapeworm (H. nana). Both infest rodents and occasionally parasitize humans, especially children. The development and transmission of these two cestodes are similar to that for D. caninum. Both H. diminuta and H. nana form viable cysticercoids in several species of fleas, especially C. canis, P. irritans, X cheopis, and N.fasciatus. They also infest several other arthropods, notably coprophagous beetles.

The zoonotic nematode Trichinella spiralis, which causes trichinosis, has also been found in fleas, although this is assumed to represent an accidental association.

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