Tungiasis: sand flea infestation of the feet

Most fleas bite and leave. The chigoe flea does not. According to the CDC, only the mated female burrows into the epidermis, where she causes a nodular swelling. She swells to about a centimetre across as her abdomen fills with eggs, sheds roughly 100 eggs over about two weeks, and then dies in the skin.

The eggs fall to the ground and develop into larvae and then adult fleas over a few weeks. This is why the problem persists where floors are made of earth or sand and where people and animals walk barefoot.

The CDC places the flea in tropical and subtropical regions including Mexico, South America, the West Indies and Africa, favouring sandy places such as beaches, farms and stables. The WHO describes tungiasis as a disease of impoverished communities in sub-Saharan Africa, South America and the Caribbean. Children aged 5 to 14 and older people are at greatest risk, as are people with disabilities, and unsealed earthen house floors are a recognised breeding ground.

Travellers are affected much less often, usually after walking barefoot on a beach or in farmland. A single lesion in a returning holidaymaker is the most typical picture in the UK.

DermNet describes a white patch with a central black dot, usually 4 to 10 mm across, mostly on the feet because the flea cannot jump high. The CDC says the initial penetration is typically painless. As the flea engorges, itching, irritation, inflammation and ulceration develop, and multiple foot lesions can make walking difficult.

The WHO notes that heavy infestation causes pain, itching and difficulty walking, sleeping and concentrating at school or work, and can lead to abscesses, tissue damage and nail loss. Some infections cause no symptoms at all, according to DermNet.

The main danger is infection of the opened skin. The CDC says secondary bacterial infection is frequent and can lead to serious conditions including tetanus and gangrene. Cellulitis is another recognised problem, according to DermNet.

For that reason, anyone who removes a flea should keep the area clean and make sure their tetanus protection is up to date. Seek review for spreading redness, increasing pain, pus, fever or a sore that does not heal.

Diagnosis rests on the appearance and travel history, and the CDC says laboratory identification relies on finding the adult flea and its eggs in a lesion. DermNet lists the options clinicians use: physically extracting the flea with sterile instruments, applying topical antiparasitic medication such as ivermectin, smothering the flea with wax or jelly, and freezing with liquid nitrogen. The flea dies naturally within about two weeks, so the aim is to prevent infection while it does.

The WHO states that the most effective treatment it cites is a dimeticone oil formulation. A UK clinician will choose from what is available locally. Home extraction with unsterilised needles is not recommended because it can leave parts of the flea behind and introduce bacteria.

DermNet gives the simplest advice: wear shoes when travelling in endemic regions. In communities, the WHO describes a combined approach that includes regular foot washing with soap, sealing or insecticide treatment of floors, and management of animal reservoirs, with coconut-oil-based repellents applied twice daily described as an effective preventive measure.

After a trip, inspect feet, especially between the toes and around the nails, and seek advice early if a small white lump with a dark centre appears.