Filarioses

Filarioses are a group of parasitic diseases caused by filarial nematodes that are transmitted to humans by arthropod vectors such as mosquitoes, blackflies, and biting midges. The main human pathogens are Wuchereria bancrofti, Brugia species (B. malayi and B. timori), Onchocerca volvulus, Loa loa, and various Mansonella species. Infections typically affect the lymphatic system, the skin and subcutaneous tissues, or the eyes, and disease manifestations range from asymptomatic to chronic and disabling.

The life cycle involves microfilariae circulating in the blood or skin, which are taken up by a feeding vector. Within the vector, the larvae mature and are transmitted to a new human host during a subsequent bite. Adult worms reside in lymphatic channels or subcutaneous tissues and release microfilariae that perpetuate the cycle. The periodicity of microfilariae in the blood varies by species and influences the time of day when diagnostic samples are most informative.

Clinical features vary by species. Lymphatic filariasis can cause lymphatic dysfunction, edema, and elephantiasis, as well as hydrocele. Onchocerciasis (river blindness) causes severe itching, skin changes, and ocular disease that can lead to blindness. Loiasis may present with Calabar swelling and transient symptoms, sometimes with ocular involvement. Many infections are mild or asymptomatic but can lead to chronic morbidity.

Diagnosis relies on detecting microfilariae in blood or skin specimens, or through serologic and molecular tests. Treatment regimens differ by species and include antiparasitics such as diethylcarbamazine, ivermectin, and albendazole, sometimes combined with doxycycline to target Wolbachia endosymbionts. Public health measures emphasize vector control and mass drug administration to reduce transmission and prevent disability.