noun, plural: microfilariae
The embryonic or early larval stage in the life cycle of certain parasitic nematodes especially of the family Onchocercidae
A microfilaria pertains to the embryonic or early larval stage of a filarial worm or of related genera of the family Onchocercidae.1 The family Onchocercidae is a family belonging to phylum Nematoda (nematodes). It includes parasitic worms of humans such as those causing filariasis, onchocerciasis, loiasis, etc.
The microfilaria develops from the egg. It is considered by others as the first larval stage.2 In most species of filarial worms that dwell in tissues at adulthood, the eggs hatch in utero thereby releasing the microfilariae. As for those species that dwell in blood, the microfilaria is regarded as that stage occurring within the embryonated egg. The egg would then hatch subsequently releasing the microfilaria upon the ingestion of an arthropod intermediate host. Within the intermediate host, the microfilaria develops into an infective larva, which can be transmitted to another definitive host (i.e. a vertebrate host).
1 Anderson, R.C. (2000) Nematode Parasites of Vertebrates: Their Development and Transmission. Second Edition. CABI Publishing: Wallingford, England, pp. 472-475.
2 Mehlhorn, H. (ed) (2001) Encyclopedic Reference of Parasitology: Biology, Structure and Function. 2nd Edition. Springer: Berlin. p.361.