Progression of Lymphatic Filariasis

Adult W. bancrofti worms with the smaller male on the left and larger female on the right. (Image 8)

Prepatent Period

The prepatent period is known as the period between the entrance of the infective larva into the human host and the first appearance of microfilaria within the human host (Reference 18). Because detection of low levels of microfilariae can be so difficult, the prepatent period will vary depending on the duration of time spent in an endemic area, and the amount of exposure to the vector (Reference 19). Little is known about the prepatent period in humans, but tests done on primates show a period of 7-8 months for W. bancrofti and 2 months for B. malayi (Reference 18).

Incubation Period

The incubation period is known as the period between the entrance of the infective larva into the human host and the presentation of clinical symptoms or observable signs. This period of time is completely variable, and can be as short as 4 weeks or as long as 8-16 months (Reference 18).

Chronic Stage of Lymphatic Filariasis

The chronic stage of lymphatic filariasis patients is also completely variable. In some patients it develops quickly, while in others it does not. Some patients develop chronic symptoms while they have living microfilariae in their circulatory system while other patients develop chronic symptoms long after microfilariae and adult worms have died. The high variability associated with the development of chronic symptoms is a mystery to many, and research is currently exploring causal relationships between levels of microfilaria and chronic symptoms (Reference 19).