Context: Lao People's Democratic Republic (PDR) becomes second country in 2023 after Bangladesh to eliminate lymphatic filariasis.

• According to the WHO progress report on the disease, Nineteen countries have been able to eliminate this disease.

• Of the 19 countries, 11 belong to the WHO Western Pacific Region (WPR). Lao PDR is 11th country in the WPR region to successfully eliminate LF.

• South-East Asia region: Bangladesh, the Maldives, Sri Lanka and Thailand. 

• Africa region: Malawi and Togo.

About Lymphatic filariasis

• Lymphatic filariasis is a neglected tropical disease (NTD), which occurs when filarial parasites mainly nematodes (roundworms) are transmitted to humans through mosquitoes.

• NTDs are a diverse group of tropical infections that are common in low-income populations in developing regions of Africa, Asia, and the Americas.

• Commonly known as elephantiasis, this infection is usually acquired in childhood and causes hidden damage to the lymphatic system.

• The painful and profoundly disfiguring visible manifestations of the disease (lymphoedema, elephantiasis and scrotal swelling) occur later in life and can lead to permanent disability.

Cause and transmission

Causes

There are 3 types of these thread-like filarial worms-

1. Wuchereria bancrofti is responsible for 90% of the cases.

2. Brugia malayi causes most of the remainder of the cases.

3. Brugia timori causes the disease.

Transmission

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

Symptoms

• Lymphatic filariasis infection involves asymptomatic, acute and chronic conditions.

• It many times does not show external signs of infection while contributing the transmission of the parasite.

• It can damage the lymphatic system and the kidneys and alter the body's immune system.

• When lymphatic filariasis develops into chronic conditions it leads to lymphoedema (tissue swelling) or elephantiasis (skin/tissue thickening) of limbs and hydrocele (scrotal swelling).

Treatment

• The WHO-recommended preventive chemotherapy strategy for elimination of lymphatic filariasis by using Mass Drug Administration (MDA).

• MDA administered an annual dose of medicines to the entire at-risk population.

• The medicines used have a limited effect on adult parasites but effectively reduces the density of microfilariae in the bloodstream and prevent the spread of parasites to mosquitoes.

• Currently there is no vaccine available to prevent this infection in human.