Intestinal human parasites can be grouped into two categories---protozoa and helminths. Protozoa are single-celled organisms capable of reproducing inside the body, resulting in potentially serious infections. Protozoan parasites are typically transmitted through contact with feces in soil, water or food. Helminths are multicellular animals that use the human body for a single stage of their often complex life cycles. Internal parasites can live in your body for years before they produce any symptoms, if they ever do.
Intestinal Parasites
Frequently observed protozoan intestinal parasites include Entamoeba histolytica and Giardia lamblia, the most common human parasitic infection worldwide. Both G. lamblia and E. hotolyitica cause severe diarrhea, vomiting and weight loss. Common helminths include the many species of tapeworms, hookworms, roundworms and pinworms which are known to cause sleep disturbances, fever, diarrhea and gastrointestinal obstruction. The best means by which to keep from contracting an intestinal parasites is to eat peeled raw foods, drink bottled or treated water, and keep food preparation areas sanitary.
Bloodborne Parasites
Bloodborne parasites are characterized by the two qualities. The first is that they use the infected person's circulatory system to get to other specific regions of the body where they congregate. Secondly, they may be transmitted to another person through blood, either by transfusion or an insect intermediary such as a mosquito.
The bloodborne parasites in the United States that warrant concern are protozoans. Chagas disease, also called American trypanosomiasis and characterized by fever, constipation and abdominal pain, is caused by Trypanosoma cruzi and spread by the bite of infected reduvid bugs. The many species of the Leishmania protozoa are spread by the bite of a tiny sandfly, producing disfiguring lesions on the face. Both of these ailments are more common in and near the tropics. Two protozoan parasites that specifically infect red blood cells are Babesia, which is spread by ticks throughout the United States; and the malaria-causing Plasmodium, which is tranmitted solely by mosquitoes of the genus Anopheles.
Parasites of Other Body Regions
Trichomoniasis is the most common pathogenic parasitic infection in the United States, according to the Centers for Disease Control & Prevention or CDC. It is caused by the flagellated protozoan Trichomonas vaginalis, and lives in the prostrate and urethra of infected males and the lower genital system of infected females. Another site of attack by internal human parasites is the central nervous system. Several species of protozoan amoeba are so specialized that they only attack the components of the central nervous system. A person infected by the amoebic parasite Naegleria fowleri develop encephalitis within one to 14 days and usually succumb to the disease three to seven days later.
References
- Centers for Disease Control & Prevention: Division of Parasitic Diseases
- US Department of Health and Human Services: Centers for Disease Control and Preventions: Bloodborne Parasites
- University of Maryland Medical Center: Medical Reference: Intestinal parasites
- US National Library of Medicine and National Institutes of Health: Chagas disease
- World Health Organization: Leishmaniasis
- GItract.info: A list of human intestinal parasites
