Phylum: Nematoda
Filariasis is a parasitic disease caused by nematodes. (Nematodes are roundworms.) Filarial worms infect humans and animals worldwide. (Nematodes are not to be confused with other major types of parasitic worms. The three most common groups of parasitic worms include nematodes [roundworms], trematodes [flukes], and cestodes [tapeworms].)
Note: Two different diagnostic stages of the nematodes causing filariasis exist in the infected human:
- Adult worms - (most often, infections with Wuchereria bancrofti or Brugia malayi/Brugia timori present in the lymphatic system (lymphatic-dwelling) as lymphatic filariasis - but depending on the genus/species of those nematodes listed below, may present as filariasis in other locations of the body - this will be discussed in more detail throughout the course)
- Microfilariae (plural of microfilaria) - the embryo of the adult worm (or the intermediate stage between egg and larvae, also known as an early larval stage of a filarial worm); the smallest form of the filariae (usually present in the blood or tissues)
This course will focus primarily on the microfilarial stage of the following nematodes - which may be seen in the examination of human peripheral blood films or skin snips:
Nematode name (and preferred specimen type)
- Wuchereria bancrofti (blood)
- Brugia malayi (blood)
- Brugia timori (blood)
- Loa loa (blood)
- Onchocerca volvulus (skin snips)
- Mansonella ozzardi (blood)
- Mansonella streptocerca (skin snips)
- Mansonella perstans (blood)
1. CDC/Newton. Image #4637. "This photomicrograph depicts a glycerine mount, revealing the presence of the microfilarial pathogen, Onchocerca volvulus, in its larval form. O. volvulus is the filarial parasite responsible for causing the disease, onchocerciasis, or river blindness, and is transmitted to its human host through the bite of Simulium spp. of flies, including the black fly." PHIL public domain. Created 1975. Accessed April 6, 2023. https://phil.cdc.gov/Details.aspx?pid=4637
