Microbial Diseases Of The Digestive System

Fungal Diseases of the Digestive System

Mycotoxins are toxins produced by some fungi.

Mycotoxins affect the blood, nervous system, kidneys, or liver.

Ergot Poisoning

Ergot poisoning, or ergotism, is caused by the mycotoxin produced by Claviceps purpurea.

Cereal grains are the crop most often contaminated with Claviceps mycotoxin.

Aflatoxin Poisoning

Alfatoxin is a mycotoxin produced by Aspergillus flavus.

Peanuts are the crop most often contaminated with Alfatoxin.

Protozoan Diseases of the Digestive System

Giardiasis

Giardia lamblia grows in the intestines of humans and wild animals and is transmitted in contaminated water.

Symptoms of giardiasis are malaise, nausea, flatulence, weakness, and abdominal cramps that persist for weeks.

Diagnosis is based on identification of the protozoa in the small intestine.

Cryptosporiosis

Crytosporidium parvum causes diarrhea; in immunosuppressed patients, the disease is prolonged for months.

The pathogen is transmitted in contminated water.

Diagnosis is based in the identification of ocoysts in feces.

Cyclospora Diarrheal Infection

C. cayetanensis causes diarrhea; the protozoan was first identified in 1993.

It is transmitted in contaminated produce.

Diagnosis is based on the identifcation of oocysts in feces.

Amoebic Dysentery (Amoebiasis)

Amoebic dysentery is caused by Entamoeba histolyica growing the large intestine.

The amoeba feeds on red blood cells and GI tract tissues. Severe infections result in abscesses.

Diagnosis is confirmed by observing trophozoites in feces and by serological methods.

Helminthic Diseases of the Digestive System

Tapeworms

Tapeworms are contracted by the consumption of undercooked beef, pork, or fish containing encysted larvae (cysticerci). Types include:

When the cysticerci are ingested all but the scolex is digested in the stomach.

The scolex attaches to the intestinal mucosa of humans (the definitive host) and matures into adult tapeworm.

Eggs are shed in the feces and must be ingested by an intermediate host.

Adult tapeworms can be undiagnosed in a human.

Diagnosis is based on the observation of proglottids and eggs in feces.

Neurocysticercosis in humans occurs when pork tapeworm larvae are produced in humans, an infection that occurs when tapeworm eggs are ingested. (The human is then the intermediate host.) Larvae may then encyst in brain or eyes.

Hydatid Disease

Humans infested with the tapeworm Echinococcus granulosus might have hydatid cysts in their lungs or other organs.

Dogs and wolves are usually the definitive hosts, and sheep or deer are the intermediate hosts for E. granulosus.

Nematodes

Pinworms

Humans are the definitive host for pinworms, Enterobius vermicularis.

The disease is acquired by ingesting Enterobius eggs.

Hookworms

Hookworm larvae bore through skin and migrate to the intestine to mature into adults.

In the soil, hookworm larvae hatch from eggs shed in feces.

Ascariasis

Ascaris lumbricoides adults live in human intestines.

The disease is acquired by ingesting Ascaris eggs.

Trichinosis

Trichinella spiralis larvae encyst in muscles of humans and other mammals to cause trichinosis.

The roundworm is contracted by ingesting undercooked meat containing larvae.

Adults mature in the intestine and lay eggs; the new larvae migrate to invade muscles.

Symptoms include fever, swelling around the eyes, and gastrointestinal upset.

Biopsy specimens and serological tests are used for diagnosis.