Toxoplasma Gondii Life Cycle

Toxoplasma gondii belongs to genus Toxoplasma and shares the same class Coccidia with Plasmodium that causes malaria in humans. It is a parasitic protozoan, whose primary host is kittens or cats. Nevertheless, this parasite has the ability to infect majority of the warm-blooded animals, including birds and mammals. Upon infection, it tends to invade the cells of the brain and intestine. In humans, it causes varying degree of illnesses, depending upon the overall health of the patient. For better understanding about the mode of spreading, let's take a look at toxoplasma gondii life cycle and infection.

Toxoplasma Gondii Life Cycle

Toxoplasma gondii life cycle is categorized into two main stages, namely, the sexual and the asexual phase. Each of these require a specific host to complete its specific stages. For example, the sexual part of the toxoplasma gondii life cycle occurs in felines only (wild or domesticated cats); while the asexual part takes place in any of the prospective warm-blooded animals (birds, dogs, pigs, cattle, humans, etc.). Discussed below are the sexual and asexual stages in the life cycle of toxoplasma gondii:

Sexual Phase: The sexual cycle of toxoplasma gondii is marked by ingestion of tissue cysts by cats, probably after eating an infected rodent. Inside the body of felines, the cysts make their way to the stomach and intestines. Once toxoplasma cysts reach the intestines, they reside in the epithelial cells of the small intestinal lining. Then, the tissue cysts undergo sexual reproduction, which lead to the formation of oocysts. The sexual life cycle ends when oocysts are excreted by the cats in their feces within 3 - 10 days after ingestion of the tissue cysts. These oocysts can survive in the environment for more than one year, until they are ingested by an intermediate host.

Asexual Phase: The toxoplasma gondii oocysts present in the excreta of cats are ingested by other prospective hosts. Humans acquire this parasite after eating uncooked meat and contaminated foods (that contain oocysts) or through eating with unwashed hands. In the host's body, sporozoites are released that invade the macrophages of the intestine. The sporozoites are differentiated into motile tachyzoites which are then distributed to other parts of the body via blood circulation. The tachyzoites enter the bradyzoite stage, resulting in tissue cysts. These tissue cysts, upon ingestion by cats, will initiate the sexual life cycle again.

Toxoplasma Gondii Infection

Toxoplasmosis is the common disease name, caused due to infection by toxoplasma gondii in humans and also, other animals. People who have mental health problems are at a higher risk of getting exposed to toxoplasma gondii parasite than others. In a healthy individual, it is usually mild and subsides on its own within a few days, whereas toxoplasmosis in pregnancy can lead to serious medical problems, particularly in the baby. There have been reported cases, in which toxoplasmosis caused brain abnormalities in the developing fetus. In a very few cases, toxoplasma gondii infection results in miscarriage.

This was in brief about the life cycle and infection mode of toxoplasma gondii. According to scientific studies, sexual and asexual phases in toxoplasma gondii life cycle are independent to each other. The asexual tissue cysts can undergo several cycles in different intermediate hosts, until they enter cats (definitive host). Toxoplasma gondii in cats and dogs is of less concern, as the parasite does not cause severe medical problems.