What Is Lymphatic Filariasis?
Lymphatic filariasis (LF), also known as elephantiasis, is a Neglected Tropical Disease (NTD) caused by an infection of filarial parasites which are transmitted to humans through different types of mosquitoes. Lymphatic filariasis is one of the most common vector-borne parasitic diseases, with an estimated 893 million people in 49 countries worldwide at risk of infection. It is endemic throughout the tropics and subtropics of Asia, Africa, the Western Pacific, and parts of the Caribbean and South America.
What Causes Lymphatic Filariasis?
Lymphatic filariasis is caused by three species of nematode worms, known as filariae: Wuchereria bancrofti, Brugia malayi and Brugia timori. The adult worms often cause inflammation of the lymphatic system resulting in lymphatic vessel damage, primarily in the lower limbs. Though most infections are acquired in childhood, symptoms often begin later in adulthood and are characterised by gross enlargement of an area of the body — especially the limbs (lymphoedema) or swelling of the groin (hydrocoele). The disease causes severe disability and stigma, and can result in mental illness. We are working with partners to seek solutions for the elimination of lymphatic filariasis.
History Of Lymphatic Filariasis
Lymphatic filariasis is an ancient infectious disease that is thought to have existed as early as 1500 B.C. in early Egyptian civilisation. The connection between microfilariae and lymphatic filariasis was made in the late 1860s, and the transmission method via the mosquito vector was determined in 1900.
Prevention and Treatment Of Lymphatic Filariasis
The elimination of lymphatic filariasis can be achieved by stopping the spread of infection through preventive chemotherapy.
The WHO-recommended preventive chemotherapy strategy for lymphatic filariasis elimination is mass drug administration (MDA). MDA involves administering an annual dose of medicines to all eligible people living in endemic areas. The medicines used have a limited effect on adult parasites but effectively reduce the density of microfilariae in the bloodstream and prevent the spread of parasites to mosquitoes. This means that MDA must continue for at least 10-15 years in order to be effective. The MDA regimen recommended depends on the co-endemicity of lymphatic filariasis with other filarial disease – understanding what other parasites a person might be exposed to helps inform the most effective treatment path. More than 7.7 billion treatments have been delivered to stop the spread of infection since 2000. With the development of treatment and prevention we are on the path to eliminate the spread of lymphatic filariasis dramatically. Another strategy to reduce transmission of not only lymphatic filariasis, but also other mosquito-borne infections, is vector control. Interventions such as insecticide-treated nets, indoor residual spraying, or personal protection measures also help protect people from infection.
Elimination Of Lymphatic Filariasis
Since 2012, 17 countries have eliminated lymphatic filariasis.
The global goal set by WHO is to eliminate and eradicate lymphatic filariasis as a public health problem by 2030.
Managing chronic disease
Morbidity management and disability prevention are vital for improving public health and are essential services that should be provided by the health care system to ensure sustainability. WHO suggests that success in 2030 will be achieved if people affected by lymphatic filariasis have access to the following essential package of care:
- Treatment for episodes of adenolymphangitis (ADL);
- Guidance in applying simple measures to manage lymphoedema to prevent progression of disease and debilitating, inflammatory episodes of ADL
- Surgery for hydrocele
- Treatment for infection
As of September 2017, the WHO approved a new treatment strategy: mass drug administration (MDA) of a combination of Ivermectin, Diethylcarbamazine citrate, and Albendazole (IDA), which reduces treatment time from five-to-seven years to one-to-two years. Recent evidence indicates that the combination of all three medicines, triple drug therapy, can safely clear almost all microfilariae from the blood of infected people within a few weeks, as opposed to years using the routine two-medicine combination.
Alternative strategies are under investigation for specific situations, such as areas co-endemic with Loa loa or onchocerciasis. For example, in areas co-endemic with Loa loa where DEC and ivermectin cannot be used, twice yearly albendazole and the use of bednets is an already approved strategy and early studies have shown it to be effective. In areas where there is no onchocerciasis, triple drug therapy is recommended by WHO to accelerate elimination of lymphatic filariasis.
Challenges faced in eliminating lymphatic filariasis
- Rapid diagnostic tests that are not cross-reactive with Loa loa
- IDA implementation and M&E especially in hotspots
- MMDP capacity in poor-resource countries
- Guidelines, tools/diagnostics and strategies for post-MDA and post-validation surveillance
- Integration into PHC and UHC
- Strategy for systematic non-adherence, urban MDA and community fatigue