The Biology of Tungiasis
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AGENT (CLASSIFICATION & TAXONOMY):

Kingdom: Animal
Phylum: Arthropoda
Class: Insecta
Order: Siphonaptera (fleas)

Tunga penetrans


A foot with severe complications due to tungiasis.
SYNONYMS:

Chigoe, jigger, pigue, nigua, pico, bicho de pie ("bug of the foot"), sand flea.

HISTORY OF DISCOVERY:

Gonzalez Fernandez De Oviedo y Valdes noted the earliest report of tungiasis at the turn of the 16th Century when Spanish conquerors of the crew of the Santa Maria were shipwrecked on Haiti and became infested with the disease. A few years later, the Spanish conqueror Gonzalo Ximenes de Quesada reported an entire village in Colombia that had been abandoned by its inhabitants due to this disease. Consequently, his soldiers became so infected with the disease that they could barely walk. In the 17th Century, Aleixo de Abreu, a Portuguese physician working in the Brazilian government, provided the world with the first scientific description of Tunga penetrans.

CLINICAL PRESENTATION IN HUMANS:

The first evidence of infestation by this sand flea is a tiny black dot on the skin at the point of penetration. Because the flea is a poor jumper, most lesions occur on the feet, often on the soles, the toe webs, and around or under the toenails. Among natives who frequently squat, however, the buttocks and perineum can be involved. A small, inflammatory papule with a central black dot forms early. Within the next few weeks, the papule slowly enlarges into a white, pea-sized nodule with well-defined borders between 4-10mm in diameter. This lesion can range from asymptomatic to pruritic to extremely painful. Multiple/severe infestations may result in a cluster of nodules with a honeycomb appearance.

Heavy infestations may lead to severe inflammation, ulceration, and fibrosis. Lymphangitis, gangrene, sepsis, the loss of toenails, autoamputation of the digits, and death may also occur. In most cases, however, this lesion heals without further complications.

Nonetheless, the risk of secondary infection is high. Tetanus is a common secondary infection that has reported associations with death.



TRANSMISSION:

The sand flea is normally found in the sandy terrain of warm, dry climates. It prefers deserts, beaches, stables, stock farms, and the soil and dust close to farms.

While both male and female sand fleas intermittently feed on their warm-blooded hosts, it is the pregnant female flea that burrows into the skin of the host and causes the cutaneous lesion. She does not have any specialized burrowing organs; rather, she simply attaches to the skin by her anchoring mouth and claws violently into the epidermis. Since this process is painless, it is thought that the flea may release some keratolytic enzymes. After penetrating the stratum corneum, the flea burrows to the stratum granulosum, leaving her posterior end exposed. The "black dot" of the nodule is this posterior end of the flea sticking out. The opening provides the flea with air and an exit route for feces and eggs. With its head in the dermis, the flea begins to feed on the host's blood and enlarges up to 1cm in diameter. Over the next two weeks, over 100 eggs are released through the exposed opening and fall to the ground. The flea then dies and is slowly sloughed by the host's skin.

The eggs hatch on the ground in 3-4 days. In the next 3-4 weeks, they go through their larval and pupal stages and become adults. The complete life cycle of a T. penetrans lasts about a month.

RESERVOIRS:

T. penetrans has many animal reservoirs including:

Humans, cattle, sheep, horses, mules, rats, mice, dogs, pigs, and other wild animals.
Tungiasis on a dog.
VECTORS:
n/a

INCUBATION PERIOD:

Signs of the bite will appear immediately or within days.

MORPHOLOGY:

T. penetrans is the smallest known flea, with a length of only 1mm. It is distinguished by its large angular, double-curved head and its narrow, short thorax region.




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