What is lymphatic filariasis caused by

Adult worms lodge in the lymphatic vessels and disrupt the normal functioning of the lymphatic system. The worms can live an average of six to eight years and throughout their life produce millions of small larvae microfilariae that circulate in the blood. When lymphatic filariasis becomes chronic, it causes lymphedema or elephantiasis swelling of the skin and other tissues of limbs and hydrocele.

It frequently affects the breasts and genital organs. Chronic lymphedema, or elephantiasis, is often accompanied by acute episodes of local inflammation of the skin and lymph nodes and vessels. Some of these episodes are caused by the body's immune response to the parasite. It is one of a group of conditions known as neglected tropical diseases NTDs.

The disease can cause abnormally enlarged body parts, which can be extremely painful and can lead to permanent physical changes. This condition, called lymphoedema, is highly stigmatised.

In men, it can cause hydrocele, a form of lymphoedema that causes the scrotum to swell, leading to pain and disability. The debilitating symptoms mean many people are unable to work, and children miss school to care for family members. The associated stigma can have a devastating impact on those affected, as well as their families and communities.

Source: World Health Organization. A combined dose of two medicines is given every year to people in high-risk areas by local volunteer community-directed distributors. Although people suffering from advanced lymphatic filariasis cannot be cured, the symptoms can be eased through surgery and care.

Research is undertaken to evaluate, inform and improve our programme strategies, helping to eliminate this disease more quickly and fairly. While river blindness is transmitted by the black fly and lymphatic filariasis by the mosquito, both diseases are caused by an infection of a filarial worm and often occur in the same places. In countries where river blindness in not co-endemic, lymphatic filariasis is treated using diethylcarbamazine, produced by Eisai, and albendazole tablets, donated by GlaxoSmithKline.

The disease spreads from person to person by mosquito bites. People get lymphatic filariasis from the bite of an infected mosquito. The microscopic worms pass from the mosquito through the skin, and travel to the lymph vessels.

In the lymph vessels they grow into adults. An adult worm lives for about 5—7 years. The adult worms mate and release millions of microscopic worms, called microfilariae, into the blood. People with the worms in their blood can give the infection to others through mosquito bites.

Repeated mosquito bites over several months to years are needed to get lymphatic filariasis. People living for a long time in tropical or sub-tropical areas like Fiji where the disease is common are at the greatest risk for infection. Short-term tourists have a very low risk. An infection will show up on a blood test. Lymphatic filariasis infection involves asymptomatic, acute, and chronic conditions. The majority of infections are asymptomatic, showing no external signs of infection.

Acute episodes of local inflammation involving skin, lymph nodes and lymphatic vessels often accompany the chronic lymphoedema or elephantiasis.