The development of lymphatic filariasis in humans remains an enigma: while the infection is generally acquired early in childhood, the disease may take years to manifest itself. Indeed, many people never have outward clinical manifestations of their infection. Studies have shown that such seemingly healthy patients may have hidden lymphatic pathology. Asymptomatic infection is frequently characterized by the presence of thousands or millions of larval parasites (microfilariae) in the blood and of adult worms in the lymphatic system.
The most severe symptoms of chronic disease generally appear in adults, and in males more often than in females. In endemic communities, some 10–50% of men suffer genital damage, notably hydrocele (fluid-filled enlargement of the sacs around the testes) and elephantiasis (gross enlargement) of the penis and scrotum. Elephantiasis of the entire leg or arm, the vulva and the breast may affect up to 10% of men and women in these communities.
Acute episodes of local inflammation involving the skin, lymph nodes and lymphatic vessels often accompany chronic lymphoedema or elephantiasis. Some of these episodes are caused by the body’s immune response to the parasite, but most are the result of bacterial skin infections, linked to the partial loss of the body’s normal defences as a result of underlying lymphatic damage. Careful cleansing is extremely helpful in healing the infected areas and in both slowing and, more remarkably, reversing much of the overt damage that has already occurred.
In endemic areas, chronic and acute manifestations of filariasis tend to develop more often and sooner in refugees or newcomers than in local populations. Lymphoedema may develop within 6 months and elephantiasis as quickly as a year after arrival.