This Lancet seminar gives a comprehensive overview of these tropical helminth infections. Both are transmitted by biting insects, and produce long-term chronic infections that have significant public health impact in affected regions.

Filariasis is caused by several parasitic nematodes with complex lifecycles; most require symbiotic Wolbachia bacteria for survival and the death of the parasite evokes an inflammatory response to the bacteria in the host. In lymphatic filariasis, this causes hydrocoele, lymphoedema, and elephantiasis, and in onchocerciasis, it causes skin inflammation and blindness (‘river blindness’).

Because the nematode is dependent on its endosymbiotic bacteria, an appropriate antibacterial agent (doxycycline) is effective as treatment. Other drugs used include diethylcarbamazine, ivermectin, and albendazole, usually in combination. Drug treatment may remove the infection, however this does not result in reversal of its effects and other measures may be needed. Control programmes have been set up to provide regular treatment to affected communities, with the aim of interrupting disease transmission and eliminating the burden on public health.