The mere presence of swelling in the legs cannot be taken as an indication of filariasis. The diagnosis is made only if the clinical set up fits in, the patient belongs to an endemic area or has travelled to an endemic area (in India some districts of eastern UP, Bihar, Orissa, Andhra Pradesh, Tamil Nadu and Kerala), has had fever with increasing swelling in the legs which quite often begins from above and goes down to the feet. A definitive diagnosis is only by demonstrating parasites that cause the disease either in the blood or in the body fluid where swelling has occurred. There are some immunological tests that help confirm but they are not 100% sensitive. Recently a PCR (a special DNA test) has been developed and is reportedly sensitive. It is also reported that the parasite may be demonstrable in the lymphatics of spermatic cord in majority of infected men. All this needs evaluation by an experienced physician who had special expertise in parasitic diseases.I am not sure which part of the country you belong to but the kind of chronic swelling that I see commonly has nothing to do with filariasis. These are usually cases that have developed swelling because of venous thrombosis (clot formation in the veins of the legs), scarring from trauma, chronic swellings from persistent kidney, liver and heart failure and occasionally from malignancies involving lymph nodes in the groin.Keeping these in view do not accept the diagnosis of filariasis until your father has been fully investigated.