Part I Protozoans

Parasitism: Two organisms living together One benefits from the relationship at the expense of the other

Three groups of parasites  Protozoan  Metazoan  Exoparasites All the parasites are eukaryotes.

All protozoans have 2 important stages of life:  Trophozoite – active, free swimming state of protozoan  Cyst – dormant phase. In most cases this is the infective stage.

Classified by the way they move. Amoeba (sarcodina) Flagellates (mastigophora) Ciliates (ciliophora) Sporozoans (apicomyplexa)

Sarcodina the largest phylum (11,500 living species) of protozoans. It comprises the amebas and related organisms; which are all solitary cells that move and capture food by means of pseudopods, temporary extensions of the cell. Most sarcodines are free living; others are parasitic. One of these parasites is the causative organism of amebic dysentery.

Most sarcodines are free living; others are parasitic. They are found in aquatic and terrestrial habitats. Entamoeba histolytica is the causative agent of dysentery.

Acanthamoeba is the etiology of amoebic keratitis and encephalitis. Encephalitis is caused by Acanthamoeba entering cuts or through the nares and spreading to the central nervous system.

Most of the approximately 1,500 species of Mastigophora are propelled by one or more flagella, and members of the group are referred to as flagellates.

Giardiasis, infection of the small intestine by a protozoan, Giardia lamblia. Giardia is spread via the fecal-oral route, most commonly by eating food contaminated by the unwashed hands of an infected person or by drinking groundwater polluted by the feces of infected animals such as dogs and beavers (hence the nickname "beaver fever" ). It attaches itself to the walls of the small intestine and there multiplies quickly.

Trichomoniasis is caused by a Trichomonas vaginalis and is passed almost 100% of the time through sexual contact. Trichomoniasis is primarily an infection of women's vaginal and urinary tracts. A woman is most susceptible to infection just after having completed her menstrual period. Men also may carry the organism unknowingly, since infection in men may cause mild or no symptoms.

Human African Trypanosomiasis, also known as sleeping sickness, is a vector-borne parasitic disease. The parasites concerned are protozoa belonging to the Trypanosoma Genus. They are transmitted to humans by tsetse fly (Glossina Genus) bites which have acquired their infection from human beings or from animals harbouring the human pathogenic parasites.

Chagas diseases occurs in 15 Central and South American countries. The symptoms of Chagas disease vary over the course of an infection. In the early, acute stage, symptoms are mild and usually produce no more than local swelling at the site of infection. As the disease progresses, over the course of many years, serious chronic symptoms can appear, such as heart disease and malformation of the intestines. If untreated, the chronic disease is often fatal.

The ciliates are a group of protists characterized by the presence of hair-like organelles called cilia. Cilia are identical in structure to Flagella but typically shorter and present in much larger numbers with a different undulating pattern than flagella.

Infection occurs when a host ingests a cyst, which usually happens during the consumption of contaminated water or food. Once the cyst is ingested, it passes through the host’s digestive system.

The Apicomplexa are a large group of protists, most of which possess a unique organelle called apicoplast and an apical complex structure involved in penetrating a host's cell. They are unicellular, spore-forming, and exclusively parasites of animals. They are non-motile protozoans and rely on the fluid structures of the body for movement.

Malaria is a vector-borne infectious disease caused by a eukaryotic protist of the genus Plasmodium. It is widespread in tropical and subtropical regions, including parts of the Americas, Asia, and Africa. Each year, there are approximately 350–500 million cases of malaria, killing between one and three million people, the majority of whom are young children in Sub-Saharan Africa.

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Toxoplasmosis is a parasitic disease caused by the protozoan Toxoplasma gondii. The parasite infects most genera of warm-blooded animals, including humans, but the primary host is the felid (cat) family. Animals are infected by eating infected meat, by ingestion of faces of a cat that has itself recently been infected, or by transmission from mother to fetus. Cats have been shown as a major reservoir of this infection.

Cryptosporidiosis, also known as crypto, is a parasitic disease caused by Cryptosporidium, a protozoan parasite in the phylum Apicomplexa. It affects the intestines of mammals and is typically an acute short-term infection. It is spread through the fecal-oral route, often through contaminated water; the main symptom is self- limiting diarrhea in people with intact immune systems.

In immunocompromised individuals, such as AIDS patients, the symptoms are particularly severe and often fatal. Cryptosporidium is the organism most commonly isolated in HIV positive patients presenting with diarrhea. Treatment is symptomatic, with fluid rehydration, electrolyte correction and management of any pain. Despite not being identified until 1976, it is one of the most common waterborne diseases and is found worldwide. The parasite is transmitted by environmentally hardy microbial cysts (oocysts) that, once ingested, exist in the small intestine and result in an infection of intestinal epithelial tissue.