What are the Filarial Diseases?


lf_map_2014Lymphatic filariasis (Elephantiasis)
Over 67 million infected [1] 36 million disfigured or incapacitated [1] More than 1 billion people at risk in 73 countries [1] More than 25 million men with genital disease [2] More than 15 million people with lymphoedema or elephantiasis of the leg [2]


oncho_map_2014Onchocerciasis (River Blindness)
Over 37 million infected [3] About 187 million at risk in 36 countries [4] 4 million suffer from severe itching or dermatitis[5]
265, 000 are blind [5]




Loiasis – Loa Loa
Nearly 30 million at risk [6] About 13 million people infected [7]





Lymphatic filariasis (Elephantiasis) affects over 67 million people living in tropical areas of the world. About 80% of people at risk live in the following 10 countries:  Bangladesh, Democratic Republic of Congo, Ethiopia, India, Indonesia, Myanmar, Nigeria, Nepal, Philippines, and the Republic of Tanzania.

Onchocerciasis (River blindness) is almost exclusively confined to West and Central Africa, although there are localized infections in Yemen and some South American countries.

Loiasis (Loa loa infection) occurs in the rain forest and swamp areas of West Africa and in Central Africa.


Onchocerciasis (River blindness), Lymphatic filariasis (Elephantiasis) and Loiasis (Loa loa infection) are all caused by parasitic filarial nematode worms that are transmitted between humans by blood-sucking insects.

Onchocerciasis is caused by Onchocerca volvulus, transmitted by the bite of an infected female blackfly; lymphatic filariasis is caused by Wuchereria bancrofti (90% of cases), Brugia malayi (most of the remainder) and Brugia timori, and is transmitted by various mosquito species;  Loa loa worms are transmitted by the bites of Mango flies or by Deer flies (Chrysops spp.).

Social and economic impact

Filarial diseases are the most devastating of the neglected tropical diseases in terms of social and economic impact.  Families and communities have to bear the brunt of long-term healthcare, coupled with loss of productivity and earnings due to the incapacity to work.  The disabling and disfiguring effects on the individual lead to social stigmatization and isolation.


Filarial disease is not particularly life-threatening, but Onchocerciasis and Lymphatic filariasis cause long-term suffering and chronic disease with life-long disabilities in millions of people worldwide, such as blindness, severe itching and dermatitis (onchocerciasis), and swollen limbs and genitals (lymphatic filariasis). Loiasis is usually considered asymptomatic but can cause localized swellings associated with localized and generalized itching.

Patient treatments needs

Programs for the treatment and control of filarial diseases through mass drug administration (MDA) have been in place for over 20 years. However current treatments target the juvenile worm (microfilariae) and need to be repeated for 5 years in the case of lymphatic filariasis, and for 12-15 years in the case of onchocerciasis. Therefore, there is an unmet medical need for a drug that can kill the adult worms (macrofilaricide). A new, safe, short-course macrofilaricidal drug could be used in individual patient treatment and to help the elimination effort in MDA programmes and ideally also in patients with Loa loa co-infection.

Fact sheet

DNDi Filarial Diseases Fact Sheet




[1] Weekly Epidemiological Record (WER), (pp. 389–400), 13 September 2013

[2] WHO Epidemiology Lymphatic Filariasis 

[3] WHO “Weekly epidemiological record Relevé épidémiologique hebdomadaire Meeting of for Disease Eradication” June, pp. 197–208, 2007
WHO “Weekly epidemiological record (WER)”, Vol 91, 43, pp. 501-516, 28 October 2016
WHO Fact sheet N°95 – Onchocerciasis – river blindness
Zouré HGM, Wanji S, Noma M, Amazigo UV, Diggle PJ, et al. (2011) The Geographic Distribution of Loa loa in Africa: Results of Large-Scale Implementation of the Rapid Assessment Procedure for Loiasis (RAPLOA). PLoS Negl Trop Dis 5(6): e1210

[7] Hotez PJ, Kamath A. Neglected tropical diseases in sub-saharan Africa: review of their prevalence, distribution, and disease burden. PLoS Negl Trop Dis. 2009;3(8)
[8] WHO Lymphatic Filariasis Map