Background

Lymphatic filariasis, commonly known as elephantiasis, is caused by three species of thread-like nematode worms, known as filariae – Wuchereria bancrofti, Brugia malayi and Brugia timori. Adult worms lodge in the lymphatic system and disrupt the immune system. The worms can live for an average of 6-8 years, and produce millions of microfilariae (immature larvae) that circulate in the blood. Mosquitoes are infected with microfilariae by ingesting blood when biting an infected host. Microfilariae mature into infective larvae within the mosquito. When infected mosquitoes bite people, mature parasite larvae are deposited on the skin from where they can enter the body. The larvae then migrate to the lymphatic vessels where they develop into adult worms, thus continuing a cycle of transmission.

Lymphatic filariasis infection involves acute/chronic symptoms or an asymptomatic condition. Many cases of infection are asymptomatic. These asymptomatic infections still cause damage to the lymphatic system and the kidneys as well as alter the body's immune system.

Acute episodes of local inflammation involving skin, lymph nodes and lymphatic vessels often accompany the chronic symptoms. Some of these episodes are caused by the immune response to the parasite, but most are the result of bacterial skin infection where normal defenses have been partially lost due to underlying lymphatic damage. When lymphatic filariasis develops into chronic conditions, it leads to lymphoedema (tissue swelling) or elephantiasis (skin/tissue thickening) of limbs and hydrocele (scrotal swelling). This mostly affects the legs, but can also occur in the arms, breasts, and genitalia.

Filarial infection can also cause tropical pulmonary eosinophilia syndrome. This syndrome is typically found in infected persons in Asia. Clinical manifestations of this syndrome include cough, shortness of breath and wheezing. The eosinophilia is often accompanied by high levels of IgE (Immunoglobulin E) and antifilarial antibodies.

Epidemiology

Currently, 882.5 million people in 44 countries worldwide remain threatened by lymphatic filariasis and require preventive chemotherapy to stop the spread of this parasitic infection.

Before 1960s, people living in Taiwan, Kinmen, and Penghu were at risk of infection with lymphatic filariasis. A long term program of prevention and treatment had been implemented since 1958. The number of cases of lymphatic filariasis had decreased year after year. There are no cases of lymphatic filariasis in Taiwan.

Prevention and Control

Travel advices of avoiding mosquito bites for passengers heading out to endemic areas of lymphatic filariasis:

1. Attire with long sleeve shirt and long pants at night, and avoid wearing dark clothing.
2. Use of epidermal mosquito repellent.
3. Avoid going out at dawn or dusk.
4. Stay in accommodations that are installed with screened door/window and fitted with adequate sanitation amenities.
5. Sleep with an insecticide-treated bednet. Check for any probable holes in the bednet, or any mosquito trapped inside the net. Use insect spray or mosquito repellent in the bedroom.
6. Sleep in an air-conditioned room reduces the risk of mosquito bites due to the lowered room temperature.

FAQs

1. What is lymphatic filariasis?
   • Lymphatic filariasis is caused by three species of thread-like nematode worms, known as filariae – Wuchereria bancrofti, Brugia malayi and Brugia timori. Adult worms lodge in the lymphatic system and disrupt the immune system. Many cases of infection are asymptomatic, but the infection usually causes damage to the lymphatic system and sometimes leads to lymphoedema (tissue swelling) or elephantiasis (skin/tissue thickening) of limbs and hydrocele (scrotal swelling).
2. How is lymphatic filariasis transmitted?
   • The pathogen of lymphatic filariasis is transmitted only via the bites of infected female mosquitoes. Mosquitoes are infected with microfilariae by ingesting blood when biting a person who has lymphatic filariasis. Microfilariae develop into infective larvae within the mosquito. When infected mosquitoes bite people, the microscopic mature microfilariae pass from the mosquito through the skin, and migrate to the lymphatic vessels where they develop into adult worms. An adult worm lives for about 6–8 years. The adult worms mate and release millions of microfilariae into the blood. People with the microfilariae in their blood can give the infection to others through mosquitoes.
3. Who is at risk for infection?
   • Short-term tourists have a very low risk of contracting the disease. Long-term residents in tropical or sub-tropical regions where the disease is endemic are at the greatest risk for infection.
4. What are the signs and symptoms of lymphatic filariasis?
   • Lymphatic filariasis infection involves asymptomatic, acute and chronic conditions. Many cases experience no symptoms. Acute episodes of local inflammation involving skin, lymph nodes and lymphatic vessels. Some inflammation is caused by the immune system response to the parasite, but some is largely the result of bacterial skin infection. When lymphatic filariasis develops into chronic conditions, it leads to lymphoedema (tissue swelling) or elephantiasis (skin/tissue thickening) of limbs and hydrocele (scrotal swelling). This mostly affects the legs, but can also occur in the arms, breasts, and genitalia.
5. How do I know if I have filariasis for sure?
   • The standard method is the identification of microfilariae by microscopic examination. This is not always feasible because microfilariae are nocturnally periodic, which means that they only circulate in the blood at night. For this reason, the sample has to be taken during the night to ensure the microfilariae are present in the bloodstream. The blood can also be studied to check for the presence of antibodies (antifilarial IgG4). A new method involving a highly sensitive "card test" has been developed to detect antigens without laboratory equipment using finger-prick blood droplets taken of anytime of the day.

More Information

1. WHO∣Filariasis
2. USA CDC∣Lymphatic Filariasis

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