Filarias

Filarias, or filarial nematodes, are a diverse group of thread-like parasites that cause filariasis in humans and animals. They are transmitted primarily by blood-sucking arthropod vectors such as mosquitoes, blackflies, biting midges, and deer flies. Adult worms typically inhabit lymphatic or subcutaneous tissues, while their offspring, microfilariae, circulate in the host’s bloodstream or reside in skin tissues depending on the species.

The principal human pathogens include Wuchereria bancrofti, Brugia species (B. malayi and B. timori) which cause lymphatic filariasis; Onchocerca volvulus which causes onchocerciasis (river blindness); Loa loa which causes loiasis; and various Mansonella species. Infections are often chronic and may be asymptomatic; symptoms, when present, result from the host inflammatory response to microfilariae or adult worms, or from tissue damage caused by long-standing infection.

Life cycle: microfilariae are ingested by a vector during a blood meal, develop into infective L3 larvae within the vector, and are transmitted to a new human host. L3 larvae mature into adults in target tissues and perpetuate the cycle by producing new microfilariae.

Diagnosis relies on detecting microfilariae in blood samples or skin snips, with consideration of species-specific periodicity (time of day when microfilariae are present in blood or skin). Serology, antigen tests, and PCR can aid in diagnosis, especially for low-density infections.

Treatment typically combines antiparasitic medicines such as diethylcarbamazine, ivermectin, and albendazole, sometimes with doxycycline to target Wolbachia endosymbionts. Management also includes control measures like mass drug administration, vector control, and disability care for affected individuals.