Filarial parasites are transmitted to humans through mosquitoes

 

Articles:

This Week in PLOS Pathogens

 

The disease

Lymphatic filariasis, commonly known as elephantiasis, is a neglected tropical disease. Infection occurs when filarial parasites are transmitted to humans through mosquitoes. When a mosquito with infective stage larvae bites a person, the parasites are deposited on the person's skin from where they enter the body. The larvae then migrate to the lymphatic vessels where they develop into adult worms in the human lymphatic system.

Infection is usually acquired in childhood, but the painful and profoundly disfiguring visible manifestations of the disease occur later in life. Whereas acute episodes of the disease cause temporary disability, lymphatic filariasis leads to permanent disability.

Currently, more than 1.4 billion people in 73 countries are at risk. Approximately 65% of those infected live in the WHO South-East Asia Region, 30% in the African Region, and the remainder in other tropical areas.

Lymphatic filariasis afflicts over 25 million men with genital disease and over 15 million people with lymphoedema. Since the prevalence and intensity of infection are linked to poverty, its elimination can contribute to achieving the United Nations Millennium Development Goals.

Cause and transmission

Lymphatic filariasis is caused by infection with nematodes (roundworms) of the family Filariodidea. There are three types of these thread-like filarial worms:

  • Wuchereria bancrofti, which is responsible for 90% of the cases
  • Brugia malayi, which causes most of the remainder of the cases
  • B. timori, which also causes the diseases.

Adult worms lodge in the lymphatic system and disrupt the immune system. They live for 6-8 years and, during their life time, produce millions of microfilariae (small larvae) that circulate in the blood.

Lymphatic filariasis is transmitted by different types of mosquitoes for example by the Culex mosquito, widespread across urban and semi-urban areas; Anophelesmainly in rural areas, and Aedes, mainly in endemic islands in the Pacific.

Symptoms

Lymphatic filariasis infection involves asymptomatic, acute, and chronic conditions. The majority of infections are asymptomatic, showing no external signs of infection. 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 lymphoedema or elephantiasis. Some of these episodes are caused by the body's immune response to the parasite. However most are the result of bacterial skin infection where normal defences 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 (fluid accumulation). Involvement of breasts and genital organs is common.

Such body deformities lead to social stigma, as well as financial hardship from loss of income and increased medical expenses. The socioeconomic burdens of isolation and poverty are immense.

Treatment and prevention

The recommended regimen for treatment through mass drug administration (MDA) is a single dose of two medicines given together - albendazole (400 mg) plus either ivermectin (150-200 mcg/kg) in areas where onchocerciasis (river blindness) is also endemic or diethylcarbamazine citrate (DEC) (6 mg/kg) in areas where onchocerciasis is not endemic. These medicines clear microfilariae from the bloodstream.

Mosquito control is another measure that can be used to suppress transmission. Measures such as insecticide-treated nets or indoor residual spraying may help protect populations in endemic regions from infection.

Patients with chronic disabilities like elephantiasis, lymphoedema, or hydrocele are advised to maintain rigorous hygiene and take necessary precautions to prevent secondary infection and aggravation of the disease condition.

Join the conversation!

You are not Signed In. Sign In to Leave a Comment or Sign Up