These fleas are nearly permanent parasites in the adult stage. The adults are distinguished by having a small thorax and short legs, and the abdomen of the female is greatly enlarged and filled with eggs. They are mainly tropical, but some species occur widely outside the tropics. The smallest flea that attacks humans is the unfed male and female of Tunga penetrans. However, when mated and the female is enveloped into the skin, she becomes the largest flea known to infest humans.

Chigoe, jigger, sand flea, Tunga penetrans (Fig. 16.2c, d)

Adults are about 1 mm long; the blood-engorged female is about 5 mm wide. The head is angular, the anterior margin straight, and the genal and pronotal combs are absent. Eyes are distinct. Eggs are deposited to the outside of the host, and hatching occurs in 3-4 days; fecundity is about200 eggs. Larvae drop to the ground and develop in 10-17 days away from the host. Larvae develop in the soil in locations frequented by the host. There are only two instars and development from egg to adult takes about 3 weeks. The newly emerged adults actively search for a host; the females attach to the feet of mammals, including humans and pigs. The male chigoe is free-living. It feeds with its head and body up to five abdominal segments inserted into the host. The female does not actually burrow into the skin, butis enveloped by surrounding skin tissue, with the end ofher abdomen remaining exposed. During the next 10 days, her abdomen distends and swells with eggs, which she ejects to the outside. Some eggs hatch within the skin cavity, but the larvae drop to the ground to develop. When the female dies, she remains in the skin of the host. The presence of an adult chigoe in the foot can cause a crippling injury, and the damage to the skin results in a secondary infection. Infestations are usually on bare feet, and the most common sites are between the toes and soles. This species occurs in hot and dry locations in neotropical regions of North and South America, West Indies, and Afrotropical regions, including Madagascar. It apparently originated in South America as a parasite of pigs, and was carried to Africa around 1872. This parasite is usually acquired by people traveling on dry roads, soiled by the excreta of domestic animals.

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