Jigger, Jigger flea, Chigoe, Chigo, Chigoe flea, Chigo flea, Nigua, Niknik, Sand flea, Burrowing flea
Tunga penetrans is a species of flea also known as the jigger, jigger flea, chigoe, chigo, chigoe flea, chigo flea, nigua, niknik, sand flea, or burrowing flea. It is a parasitic insect found in most tropical and sub-tropical climates. In its parasitic phase it has significant impact on its hosts, which include humans and certain other mammalian species. A parasitical infestation of T. penetrans is called tungiasis. Jiggers are often confused with chiggers, a type of mite. Jiggers are native to Central and South America, and have been introduced to sub-Saharan Africa.
Synonyms for Tunga penetrans include Sarcopsylla penetrans, Pulex penetrates, and many others.
T. penetrans is most recognizable in its parasite phase. While embedded under the stratum corneum layer of the skin, it may reach up to 1 cm across. During the first day or two of infestation, the host may feel an itching or irritation which then passes as the area around the flea calluses and becomes insensitive. As the flea's abdomen swells with eggs later in the cycle, the pressure from the swelling may press neighbouring nerves or blood vessels. Depending on the exact site, this can cause sensations ranging from mild irritation to serious discomfort.
For the most part, the chigoe flea lives 2–5 cm below sand, an observation which helps explain its overall distribution. The temperature is generally too hot for the larvae to develop on the surface of the sand and the deeper sand does not have enough oxygen.
In a study of off-host stages, samples were taken from the top of the soil (to a maximum depth of 1 cm). The presence of T. penetrans in a soil sample was unaffected by soil temperature, air temperature or air humidity. No life stages of T. penetrans were found in any outdoor sample.
There is an observable drop in infestations during the wet season.
T. penetrans eggs, on average, are 0.6 mm long, The larva will hatch from the egg within one to six days, assuming the environmental conditions (e.g., moisture, humidity, etc.) are favorable.
After hatching, the flea will progress through two instar phases. This is unique in that most fleas go through three. Over the course of that development, the flea will first decrease in size from its just-hatched size of 1.5 mm to 1.15 mm (first instar) before growing to 2.9 mm (second instar).
About six to eight days after hatching, the larva pupates and builds a cocoon around itself. Because it lives mostly on and below the surface of sand, sand is used to stabilize the cocoon and help to promote its development. An environmental disturbance such as rain or a lack of sand have been shown to decrease incidence, most likely due to decreasing the environmental factors (i.e., sand) on which the flea depends for overall growth. Barring any disturbances to the cocoon, an adult flea will emerge from the puparium after 9–15 days.
Males are still mobile after a blood meal like other fleas, but the female flea burrows head-first into the host's skin, leaving the caudal tip of its abdomen visible through an orifice in a skin lesion. This orifice allows the flea to breathe, defecate, mate and expel eggs while feeding from blood vessels. It lives in the cutaneous and subcutaneous dermal layer.
Tungiasis lesions almost always occur on the feet (97%), but may occur on any part of the body. The toes are afflicted over 70% of the time, with periungual folds (around the toenail) a preferred site.
Only once the female burrows into the skin can reproduction occur, as the male and female show no interest in each other in the wild. The male flea dies after copulation. The female flea continues in vivo development, described in stages by the Fortaleza classification of tungiasis.
Over the next two weeks, its abdomen swells with up to several hundred to a thousand eggs, which it releases through the caudal orifice to fall to the ground when ready to hatch. The flea then dies and is often the cause of infection as the body rots under the thick scales its body chemistry created to protect it. The eggs mature into adult fleas within three to four weeks and the process begins anew.
