The prevalence of filarial infection in children has become better understood in recent years. Whereas the disease was once thought to affect only adults, it now appears that most infections are acquired in childhood. Initial infection is followed by a long period of subclinical disease, which progresses in later life to clinically manifest disease.
The adult filarial worms cause inflammation of the lymphatic system, resulting in lymphangitis and lymphadenitis. These conditions lead to lymphatic vessel damage, even in asymptomatic people, and lymphatic dysfunction, which predispose the lower limbs in particular to recurrent bacterial infection. These secondary infections provoke adenolymphangitis (ADL), commonly called “acute attacks”, which are the commonest symptom of lymphatic filariasis and play an important role in the progression of lymphoedema. It has been suggested that bacteria commonly gain access to damaged lymphatic vessels through “entry lesions”, often between the toes. ADL, which resembles erysipelas or cellulitis, is associated with local pain and swelling and with fever and chills.
Lymphoedema and elephantiasis
Lymphoedema and its more advanced form, elephantiasis, occur primarily in the lower limbs and are commoner in women. Several factors have been implicated in the progression of lymphoedema, including repeated episodes of ADL. Although lymphoedema due to filariasis should be distinguished from conditions such as heart failure, malnutrition, venous disease, podoconiosis and HIV/AIDS-associated Kaposi sarcoma, there is no agreement on its classification. In its most advanced form, elephantiasis may prevent people from carrying out their normal daily activities.
Scrotal hydrocoele is due to accumulation of fluid in the cavity of the tunica vaginalis. It has been suggested that true filarial hydrocoele occurs after the death of adult filarial worms, while a chylocoele is due to accumulation of fluid after the rupture of lymphatic vessels in the scrotal cavity.