Toxoplasma gondii is a single-celled parasite that infects animals. Cyst forms wait in the muscle tissue of intermediate hosts to be eaten by a cat. In the cat the parasites reproduce to make large numbers of oocysts that are shed in the cat’s feces. Contact with these oocysts in the environment by other animals (e.g. rodents, pigs, humans, sheep) causes the animal to become infected. The parasites migrate to neural and muscle tissues to become cysts (1).
Plasmodium falciparum is a causative agent of malaria (along with other Plasmodium spp.). Humans become infected from the bite of an infected mosquito. The parasites first infect the liver cells where they develop into schizonts. These schizonts burst and release the blood stage of the parasite that infects red blood cells. The parasites replicate asexually inside the red blood cells to produce more schizonts. While this continues to happen, some red blood cell stage parasites develop into gametocytes. When a mosquito feeds on an infected human, it ingests some gametocytes with the blood meal. In the mosquito, the gametocytes undergo sexual reproduction and further development. The parasites make their way to the salivary gland to be released when the mosquito feeds (2).
Babesia bovis is a single-celled parasite of cattle that is transmitted by infected ticks. In the cow the parasites replicate asexually inside the red blood cells. Ticks that feed on an infected cow take in gametocytes in the blood, which reproduce sexually in the tick. The parasites then migrate to the salivary glands to be released when the tick feeds again (3).
Ixodid ticks from On The Grass.
Diplozoon paradoxum, Schistosoma mansoni, and Taenia solium from Valentine's Day.
Parasite Comics Team:
Dr. Chenhua Li (Lead, Ideas), Dr. Þórey Jónsdóttir (Illustrator, Ideas), Dr. Stephen Pollo (Writer, Researcher), Yuanzhe Wang (Digital Consultant).