Study GuideMicrobiology–Diseases of the Digestive System1.Protozoal Diseases of the Digestive SystemProtozoa are single-celled organisms that can infect the digestive system when contaminated food orwater is consumed. These infections often cause diarrhea and abdominal discomfort and can beespecially dangerous for people with weakened immune systems. Below are the most importantprotozoal diseases of the digestive tract.1.1Amoebic DysenteryAmoebic dysentery is caused by the amoebaEntamoeba histolytica.In the environment, this protozoan exists in acyst form, which allows it to survive outside the body.Humans become infected by eating food or drinking water contaminated with these cysts.Once inside the body, the cysts releasetrophozoites, which are the active, feeding forms. Thesetrophozoites invade theintestinal lining, causing tissue damage. From there, they may enter thebloodstream and spread to other organs, especially theliver and lungs.Infected individuals pass cysts in their stool and may remaincarriers for long periods, even ifsymptoms are mild or absent. Treatment is usually effective with the drugmetronidazole.1.2GiardiasisGiardiasis is caused byGiardia lamblia, a protozoan that moves using flagella.The organism enters the body in itscyst formthrough contaminated food or water. In the intestine,the cysts release trophozoites, which attach to the intestinal wall and multiply.Symptoms commonly include:•Foul-smelling, watery diarrhea•Abdominal pain•Intestinal discomfortPeople who enjoy outdoor activities such ashiking, backpacking, and campingare at higher risk.This is because untreated mountain streams may contain Giardia cysts from wild animals.The infection is treated withmetronidazole, which is usually very effective.Preview Mode
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