Filariasis

Lymphatic Filariasis Explained

Lymphatic filariasis, the cause of elephantiasis, is a tropical infection with microscopic roundworms, mainly Wuchereria bancrofti and, in parts of Asia, Brugia species. A mosquito picks up larvae when it bites an infected person and deposits them in the skin of the next person it bites. The larvae travel to the lymphatic vessels, which drain fluid from the tissues, and mature into adult worms that can live for several years, releasing millions of offspring called microfilariae into the bloodstream.

The disease occurs in parts of South and South-East Asia (including India), sub-Saharan Africa, the Pacific islands and a few places in the Americas, such as Haiti. Infection generally requires many bites over months or years, so short-stay travelers are at low risk.

Signs and Symptoms

Most infected people feel well for years, even though the worms are quietly damaging the lymphatic system. Visible disease develops in a minority:

• Lymphoedema: swelling of a leg, arm or breast that can progress to hard, thickened, folded skin (elephantiasis)
• Hydrocele: a fluid-filled swelling of the scrotum
• Acute attacks: fever, chills and a painful, hot, red, swollen limb, often triggered by bacteria entering through damaged skin
• Tropical pulmonary eosinophilia: a night-time cough and wheeze caused by an allergic reaction to microfilariae in the lungs

Diagnosis

Infection is confirmed with a blood test. In many regions the microfilariae circulate mostly at night, so traditional blood films are taken between about 10 pm and 2 am. Rapid antigen tests for W. bancrofti work at any time of day, and an ultrasound scan can sometimes show live adult worms moving within lymph vessels. Antibody tests are useful for travelers. Symptoms can appear years after leaving an endemic area, so always mention past travel or residence to your doctor.

How Filariasis Is Treated

Community treatment programs

The World Health Organization's Global Program to Eliminate Lymphatic Filariasis gives whole communities a single dose of combined medicines, usually once a year, to break the cycle of transmission. The combination depends on which other parasites occur locally:

The triple IDA combination clears microfilariae from the blood more completely than two-drug regimens, which is why WHO has recommended it in suitable areas since 2017.

Why ivermectin is given in combination

Ivermectin quickly clears circulating microfilariae, so mosquitoes can no longer pick up the infection, but it does little to the adult worms. On its own, therefore, it does not eliminate an established infection. For individual patients, specialists may use DEC where it is safe and sometimes a course of doxycycline, which targets bacteria the adult worms depend on. Treatment should always follow testing, especially for anyone who has been to areas with Loa loa or onchocerciasis, where some medicines can cause severe reactions.

Ivermectin Products

Doses are based on weight, or on height in mass programs. Precautions and side effects are covered in our ivermectin guide.

Caring for Lymphoedema

Medicines kill parasites but cannot undo lymphatic damage. Consistent daily care reduces painful acute attacks and helps stop swelling from getting worse:

• Wash the affected limb every day with soap and clean water, then pat it dry, especially between the toes and in skin creases.
• Treat cuts, cracks and fungal infections between the toes promptly, as they let bacteria in. Our antifungal creams can help with athlete's foot.
• Moisturize dry skin to prevent cracking.
• Raise the limb when resting and at night.
• Keep active and move your ankles and toes regularly to encourage lymph flow.
• Wear comfortable, well-fitting shoes, and use compression only if a specialist recommends it.
• Get prompt treatment for acute attacks, which often need antibiotics.

A hydrocele can usually be corrected with surgery.

Onchocerciasis: A Related Filarial Disease

River blindness is caused by Onchocerca volvulus, spread by blackflies that breed near fast-flowing rivers, mostly in sub-Saharan Africa. It causes relentless itching, skin changes and nodules, and can lead to blindness. Community-wide ivermectin, given once or twice a year, has greatly reduced the disease.

Prevention

In endemic areas, use an insect repellent containing DEET, sleep under a bed net and cover up in the evening. These steps also protect against malaria. Take part in community treatment rounds where they are offered.

Frequently Asked Questions

Can filariasis spread from person to person?

No. It is only transmitted through mosquito bites.

Will the swelling go away after treatment?

Early swelling can improve considerably with daily care and elevation. Advanced elephantiasis rarely reverses fully, but good care can stop it progressing and reduce attacks.

This page provides general information and is no substitute for assessment by a doctor experienced in tropical medicine. Ivermectin is a prescription medicine and should be taken only after proper testing and as part of a treatment plan agreed with your doctor.