A mosquito vector transmits the microfilaria larval form of the worm from one host to another. Once inside the human host, the worm establishes itself in the lymphatics and lymph nodes - especially the inguinal group.
After 6 - 18 months sexual maturity is reached and following fertilisation the female liberates vast numbers of microfilariae into the blood.
Some filarial strains, particularly W. bancrofti, are termed periodic because the adult worm releases microfilariae particularly at night. Microfilaraemia is maximal at 1 am, about the same time that mosquitoes are most likely to bite. Subperiodic strains release microfilariae into the blood continually.
In the peripheral circulation the microfilariae may:
- re-enter the lymphatic system
- be taken up by a new mosquito vector
Last reviewed 01/2018