Filariasis is a parasitic infection caused by thread-like worms known as filariae. These worms are transmitted to humans through the bites of infected mosquitoes. The infection is most common in tropical and subtropical regions, particularly in Africa, Asia, and South America.

Symptoms of filariasis can vary depending on the stage of the infection. In the early stages, there may be no symptoms at all. As the infection progresses, however, common symptoms include:
Swelling of the legs and genitals (elephantiasis)
Skin rashes and itching
Fever
Headaches
Tiredness

If left untreated, filariasis can lead to serious complications such as chronic lymphedema, which is characterized by the chronic accumulation of lymph fluid in the limbs and genitals, leading to severe swelling and disfigurement.

Diagnosis of filariasis is typically made through a combination of blood tests and physical examinations. The most common test used to diagnose filariasis is called the microfilaria test, which looks for the presence of microfilariae (the immature form of the worm) in a blood sample. Other tests that may be used include antibody tests and imaging studies such as ultrasound or CT scans.