The Terrible Effect of Tissue Nematodes to Human Health

Filariasis, onchocerciasis, loiasis, dracunculiasis are tropical diseases. Wuchereria affects about 200-300 million people. Onchocerca affects millions of people in Africa and Central America. What is the medical concern about these strange ailments?

Wuchereria bancrofti

This causes filariasis. It occurs in the tropics and its mode of transmission through biting by the females mosquito (especially Anopheles and Culex species) on the skin of Humans, depositing the infective larvae. The larva penetrates the skin, enter a lymph node, and after a year, mature to adults that produce mecrofilariae. These circulate in the blood, chiefly at night, and are ingested by biting mosquitoes. Within the mosquitoe, the micro filariae produce infective larvae that are transferred with the next bite. Humans are the only definitive hosts.

Adult worms in the lymph nodes cause obstruction of lymphatic vessels, causing edema of the legs and genitalia (elephantiasis). Laboratory diagnosis is based on blood smears taken from the patient at night to reveal the microfilariae. A yearly dose of drug therapy would kill the microscopic worms circulating in the blood. Drugs such as Diethylcarbamazine (DEC) and ivermectin are most trusted drugs for the effective treatment therapy of filariasis. Even if these drugs do not totally kill all the adult worms, they prevent the affected person from spreading it to someone else. But even after the death of all Adult worms, there could still be swellings of the genitals, breast, arms, legs etc. Management therapy can then be applied by

1. Daily cleaning up of swollen regions with careful administration of soap and water.

2. Application of anti-bacterial cream/ointment on any wounds.

3. Elevation and constant exercise of swollen limb to spread the fluid and improve lymph flow.

Prevention involves mosquito control with insecticides and the use of protective clothing, mosquito netting and repellents.

Onchocerca volvulus

This causes onchocerciasis. Vectors of Onchocerca volvulus (black flies) develop in rivers and people who live along those rivers are affected. Infection rates are often over 80% in endemic areas. Humans are infected when the female black fly simulium deposits infective larvae on the skin while biting. The larvae enter the wound and migrate into the subcutaneous tissue, where they differentiate into adults, usually within dermal nodules. The female produces microfilariae that are ingested when another black fly bites. The microfilariae develop into infective larvae in the fly to complete the cycle. Humans are the only definitive hosts.

Infalmmation occurs in subcutaneous tissue, and pruritic papules and nodules form. Microfilariae migrate through subcutaneous tissue, ultimately concentrating in the eyes. They cause lesions that can lead to blindness (“river blindness”). Laboratory diagnosis is based on Biopsy of the affected skin which would reveal microfilariae. Treatment is based on drug therapy. Drugs which can be used are as follows

1. Diethylcarbamazine (DEC)

2. Suramin (Antrypol)

3. Amocarzine (CGP-6140)

4. Ivermectin

5. Surgical (Nodulectomy) in severe cases.

Prevention involves control of the black fly with insecticides.