Nematode (Roundworm) Skin Infestations

Nematodes (roundworms) are parasitic worms with long, cylindrical bodies. Roundworm infections are widespread throughout the world, but particularly in tropical climates. There is a separate article discussing Nematode Infections in general.

• An estimated 17.7 million people are infected with the most serious of these, onchocerciasis (river blindness).
• Most of these are in Africa but also found in, Latin America and Arabia.
• The risk of blindness has been reduced since the introduction of ivermectin therapy.¹

• Onchocerca volvulus mainly causes infections in West, Central, and East Africa but also in Central America and South America.
• Larvae enter blood during meal taken by infected female blackfly.
• In 1-3 months, larvae develops into adult worm, capable of releasing up to 2,000 microfilariae/day for approximately 10 years. These are found mainly in the lymphatics of the subepidermis. Also enter the eye, mainly in the anterior chamber.
• In heavily infected person there may be 100 million microfilariae. These are well tolerated whilst alive but invoke an intense inflammatory reaction on dying.

Presentation

• In mild form localised maculopapular rash with itching. These may clear spontaneously or go on to chronic and generalised form with severe itching.
• Larvae develop into adult worms within palpable nodules usually found over bony prominences of thorax, pelvic girdle or knees. Also found on head of children. May heal with hyperpigmentation. Lichenified, hyperkeratotic lesions can be very distressing as widespread and intensely itchy.
• A localised form in Arabia causes chronic papular dermatitis, often in one extremity only.
• In long-standing infection, destruction of elastic fibres in the skin makes it thin with wrinkled, cigarette-like appearance. Skin begins to sag and depigmentation of the pretibial areas is typical in older people living in endemic areas and called 'leopard skin'.
• Light-skinned patients infected on visiting a country may appear a year or so later with intensely itchy, red macular or maculopapular lesions that may be localised to one area of the body or more generalised.
• May also be fever, muscle or joint pain.
• Rash sometimes lasts for several months after treatment.
• Also associated with weight loss, musculoskeletal pain and lymphadenitis.
• Ocular changes include intraocular microfilariae, punctate keratitis, sclerosing keratitis, anterior uveitis, chorioretinitis, optic neuritis, optic atrophy, glaucoma, blindness (river blindness).

Investigation

• Skin snips are immersed in normal saline and microfilariae can be seen swimming free within 24 hours.
• Examination of excised nodules show adult worms.
• More sensitive techniques include enzyme immunoassay and PCR (polymerase chain reaction).

Treatment

• Ivermectin: single dose clears microfilariae from skin for several months. Repeat dose every 6-12 months prevents progression.²
• Treatment is often associated with increased itching, swelling of face or extremities, headache and body pains, which usually occur after the first treatment.

Prevention

Control of blackfly by spraying. Mass distribution of ivermectin.

• Can occur in the temperate zones in the warmer months of the year, but infection is most commonly found in tropical and subtropical climates.
• Ancylostoma braziliense is the most common cause but can be caused by the larvae of various nematode parasites.
• Eggs are passed from animal faeces into warm, moist, sandy soil, where the larvae hatch. Larvae penetrate through follicles, fissures, or intact skin of the new host.
• In their natural animal hosts (e.g. dogs and cats), the larvae are able to penetrate into the dermis and are transported via the lymphatic and venous systems to the lungs.
• Humans are accidental hosts and the larvae are unable to penetrate the basement membrane to invade the dermis. The disease therefore remains limited to the skin when humans are infected.

Presentation

Lesions are most often found on the dorsa of the feet, the interdigital spaces of the toes, the anogenital region, the buttocks, the hands, and the knees. Diagnosis is usually made by the clinical appearance of the track.

• Itching and red papules
• Serpiginous (snake-like), 2-3 mm wide, slightly elevated, erythematous tunnels tracking 3-4 cm from the penetration site
• Oedema and acute inflammation
• Scars
• Secondary infection

Treatment

• Thiabendazole is currently considered the agent of choice. Topical application is used for early, localised lesions. The oral route is preferred for widespread lesions or unsuccessful topical treatment.
• Other effective alternative treatments include albendazole, mebendazole, and ivermectin.

• Loa loa is distributed in West and Central Africa.
• Transmitted by the Chrysops fly in West Africa. The larvae burrow into human skin during feeding.
• Adult migrates through the skin at approximately 1cm/minute and sometimes crosses the eye.
• Occasionally, infection causes sudden transitory localised inflammatory reaction known as Calabar swellings.

Presentation

• May appear several years after infection.
• Calabar swelling appearing, often on the forearms or wrists, sometimes after heavy exercise. Can appear on the face, breasts or legs.
• Oedematous lesions are red and itchy.
• May also be fever and irritability.
• Swelling subsides after a few hours or 1-2 days maximum.
• Can see migrating worm under the skin.

Investigations

• Full blood count: eosinophilia (may exceed 70%).
• Daytime blood sample shows microfilariae.
• Polymerase chain reaction (PCR) and ELISA methods are more sensitive.³

Treatment

• Diethylcarbamazine kills microfilariae and many adult worms.
• In heavy infections there may be a febrile reaction, and in heavy Loa loa infection there is a small risk of encephalopathy. In such cases treatment must be given under careful in-patient supervision and stopped at the first sign of cerebral involvement.
• Patient also likely to have onchocerciasis and so careful monitoring for severe eye and skin inflammation is essential.

Prevention

Avoid Chrysops fly bites.

• Dracunculiasis occurs mainly in Africa, the Middle East, India, and other tropical areas.
• The larvae reside in an intermediate host, a tiny fresh-water crustacean or copepod, of the genus Cyclops.
• Ingestion of contaminated water containing infective larvae causes the infection. The larvae are released in the stomach or small intestine, and then penetrate the mucosa to mate and mature.
• After maturation is complete, the female Dracunculus reaches lengths of up to 1 metre and slowly migrates from the gastrointestinal tract into subcutaneous tissue, most commonly to a lower extremity.

Presentation

• Allergic manifestations: erythema, urticaria, pruritus, nausea, vomiting, giddiness, syncope, fever (occasionally).
• Local lesions: papule, sterile blister, ulceration, abscesses, worm protrusion from skin.

Treatment

• The adult worm is extracted from the patient using a stick at the skin surface and wrapping or winding the worm a few centimeters per day.
• This slow process can take many days and, in some cases, up to a few weeks, but is required to avoid breakage and leaving behind a portion of the worm.
• Metronidazole or thiabendazole (in adults) is used as an adjunct to stick therapy, facilitating the extraction process.

Prevention

Treatment and filtration of water supplies in endemic areas.

• Transmitted by Culicoides midges in tropical climates, they are of very limited clinical significance.
• Only M. streptocerca causes recognised cutaneous symptoms.

Presentation

• Chronic papular lesions often with post-inflammatory hyperpigmentation.
• Less commonly causes lichenification.

Investigations

• Microfilariae shown in blood or skin (distinctive 'walking stick' shape to tail).

Treatment

• If asymptomatic then no treatment is required.
• Otherwise ivermectin is effective.