Microfilaria Life Cycle

Microfilaria is a term used to describe the juvenile stage of any parasite that lives in the host's circulatory system. This term is used most frequently in relation to heartworm disease. Heartworms invade the circulatory system of mammals, primarily dogs, and live off the host animal until the parasite dies and is absorbed by the host's body.

Reproduction

Adult heartworms reproduce by sexual or asexual means, like many worm species, and release microfilariae, or pre-larvae, into the bloodstream of the host animal. These microfilariae circulate though the host's circulatory system until ingested by a feeding female mosquito. Once the microfilariae enter the stomach of the mosquito, they mature into a larval stage, ready to infect the new host.

Maturation

Once the larvae are ready, the intermediate host, the mosquito, will transmit the larvae to the new host by biting the unsuspecting victim. The infective larvae then travel through the host's circulatory system until they reach the heart, where they set up house and mature into adults and begin the process again.

About Microfilariae

Microfilariae are considered an advanced embryonic stage of the heartworm lifecycle and give the parasite the best possible chance for survival. Female heartworms will only release the microfilariae during certain times of the day, usually during early dusk hours, to increase the likelihood that they will be ingested by mosquitoes.

Development

Organs of the microfilariae are in the very early stages of development, and will not sustain a larva, though rapid development occurs immediately after ingestion by the intermediate host, usually completing within a two-week period. The microfilariae burrow into the stomach of the mosquito to remain within the intermediate host's system until they are fully mature and ready to invade the primary host's bloodstream.

Testing

Companion animals are routinely tested for the presence of heartworms through a simple occult antibody test. It is common to follow up a positive occult test with a filter test to confirm the presence of microfilariae.

A simple blood test can be performed on companion animals to detect microfilariae. A small sample of blood is drawn, filtered through a special filter, smeared across a microscope slide and stained. Magnification helps in seeing the microfilariae.

Treatment

Treatment for removal of the microfilariae from the host animal includes oral or injectable ivermectin, which kills the embryos. Prevention is key in controlling this parasite. A monthly regimen of oral ivermectin is 99.9 percent effective in preventing heartworm infection in cats and dogs.

References

• Heartworm Disease