One of the leading causes of disability around the world, Lymphatic filariasis (LF) is caused by three species of nematode worms (known as filariae) namely Wuchereria bancrofti, Brugia malayi and Brugia timori. The female Anopheles mosquito transmits microscopic filarial parasite from one person to another during its feeding process.
The adult worms cause inflammation of the lymphatic system that results in damage of the lymphatic vessel, primarily in the lower limbs. Usually, infections are acquired in childhood, however, symptoms often begin later in adulthood and are characterised by gross enlargement of a body area, especially the limbs (lymphoedema), or the groin (hydrocoele). This disease causes severe disability and stigma and can translate into mental illness.
Transmission Elephantiasis, known as Hattipaile in Nepali, is caused by parasites that are spread by mosquitoes. Firstly, mosquitoes become infected with roundworm larvae when they bite an infected human. Then they transfer the larvae to someone else, through the bloodstream. Finally, the worm larvae migrate to the lymphatics via the bloodstream and mature in the lymphatic system. Elephantiasis can affect both genders exposed to the parasites through mosquito bites. It gives rise to gross enlargement of the limbs and external genitals. And it is caused due to the obstruction of the lymphatic system that results in the accumulation of fluid in the affected areas.
As per reports, eighty one countries were considered endemic to lymphatic filariasis. An estimated 863 million people in 47 countries worldwide remain vulnerable to this disease and require preventive chemotherapy to stop its spread. Likewise, an estimated 120 million people belonging to tropical and subtropical areas of the world are infected with lymphatic filariasis. The global baseline survey has projected that Lymphatic filariasis caused hydrocoele among 25 million men and lymphoedema to over 15 million people. At least 36 million people are living with these chronic disease manifestations (WHO, 2022).
The elimination of lymphatic filariasis can be accomplished with the use of preventive chemotherapy which can help stop the spreading of the infection. The preventive chemotherapy strategy for lymphatic filariasis elimination is mass drug administration (MDA) as recommended by the World Health Organisation (WHO). The MDA envisions administering of an annual dose of medicines to all eligible people living in endemic areas.
The WHO approved a new treatment strategy in 2017 including mass drug administration (MDA) of a triple therapy of Ivermectin, Diethylcarbamazine citrate, and Albendazole. The combination therapy reduces treatment time from 5-7 years to 1-2 years. Recent studies have demonstrated that the combination of all three medicines (i.e. triple-drug therapy) is superior to the routine two-medicine combination as it can safely clear almost all microfilariae from the blood of infected people within a few weeks in comparison to years.
About 70 per cent of LF cases are found in four countries in the world, namely India, Indonesia, Bangladesh, and Nigeria. In the context of Nepal, 61 districts are considered LF endemic, corresponding to an estimated 25 million people at risk of infection and disease whereas nine districts have chronic cases of LF. Owing to the damage of the lymphatic system, people with elephantiasis have impaired immune function resulting in more bacterial infections of the skin. As a result, the skin is found to be dry, thick, and ulcerated with repeated infections. The repeated bacterial infections can cause fever and chills.
The risk of exposure to larvae is the greatest for people who live in tropical and subtropical regions, who live in unhygienic condition and who are regularly bitten by mosquitoes. The best approach to prevent elephantiasis is to escape from mosquito bites. People who visit or live in countries at risk should sleep under a mosquito net, cover up their skin with long sleeves and trousers, and use insect repellent.
The overall economic benefit of the MDA programme for 7 years (2000-2007) is estimated to be US$ 24 billion. Treatments done until 2015 are estimated to have averted at least US$ 100.5 billion of economic loss expected to have occurred over the lifetime of cohorts who have benefited from it. Since 2012, some 17 countries have eliminated lymphatic filariasis. Five additional countries have successfully implemented the WHO-recommended strategies, thus, stopping large-scale treatment, and are under surveillance to show that elimination has been achieved.
In 2013, the Government of Nepal developed a Plan of Action to eliminate LF by 2020 through the implementation of six MDA rounds in all endemic districts until 2018. The WHO has a target of eliminating and eradicating lymphatic filariasis as a public health problem by 2030.
Challenges Mosquito control is an additional strategy recommended by the WHO that helps reduce the transmission of lymphatic filariasis and other mosquito-borne infections. Measures such as insecticide-treated nets, indoor residual spraying, or personal protection may help protect people from infection. However, the use of insecticide-treated nets cannot be emphasised in areas where Anopheles is the primary vector for filariasis.
In conclusion, large-scale public awareness campaigns and strict adherence to mass drug administration are important methods for the prevention and eradication of filariasis. The main challenge is the implementation of MDA with strict drug adherence to cover most at-risk population. It is, thus, called upon all stakeholders to promote continued awareness campaign, community engagement, school health programmes, and mobilisation of female community health volunteers in addition to scaling up of the MDA campaign.
(Dr. Lohani is the clinical director at the Nepal Drug and Poison Information Centre. email@example.com)