Forms of Lymphatic Filariasis and diagnosis
Although it rarely causes death, lymphatic filariasis is a major cause of suffering and disability. More than 1.3 billion people in 72 countries and territories (see map) live in areas where they are at risk of infection with filarial parasites.
The prevalence of 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. A re-evaluation of previous underestimations of the occurrence of infection in children will assist in redefining the global burden of the disease.
Until recently, the only method of diagnosis was through examination of thick smears of 20–60 μl of finger-prick blood. This blood has to be collected at a specific time – either at night or during the day, depending on the periodicity of the microfilariae. The method is inexpensive and feasible at individual and community levels. A more efficient, but cumbersome, method of diagnosis at the community level is filtration of 1 ml of intravenous blood and examination of the filtrate.
The development of an immunochromatographic card test (ICT) with high sensitivity and specificity for detecting W. bancrofti infection has simplified diagnosis, and test kits are commercially available. The test requires 100 μl of finger-prick blood drawn at any time, day or night.