Parasites that infect humans are as old as antiquity. As a matter of fact, calcified parasitic eggs of schistosomes have been found in Egyptian mummies from as far back as 1200 B.C. In the United States human parasites are not a major issue because of good nutrition, sanitation and vector control, but in many parts of the world, parasites are a major affliction on nations in terms of deaths, economic woes and failure to thrive. The major human parasites belong to one of the following categories: roundworms, tapeworms, flukes or protozoa.
Ascaris Lumbricoides
Ascaris lumbricoides, or the giant intestinal roundworm (nematode), is a very common parasite transmitted through contaminated soil and is associated with poor sanitation. According to the Global Network for Neglected Tropical Diseases, Ascaris infections infect nearly a billion people worldwide at any one time, with 60,000 deaths annually.
Hookworm
Hookworm is a general term for two different species of the parasite. Hundreds of millions of people are infected with hookworm worldwide. The hookworm parasite infects humans through penetration of the skin (e.g. walking barefoot). Heavy infections of hookworm can lead to significant blood loss and anemia.
Pinworm
According to Ruth Leventhal, author of "Medical Parasitology," pinworm (Enterobius vermicularis) infection is the most common type of worm infection in the United States. Most common in children, the most significant symptom of pinworm infection is typically an itchy bottom. This is due to the adult female leaving the anus at night to lay her eggs.
Taenia Species
There are two species of the tapeworm (cestode) Taenia that infect humans; Taenia saginata (beef tapeworm) and Taenia solium (pork tapeworm). As the names imply, people get infected with these parasites through eating undercooked beef or pork. Taenia solium is significantly more serious due to the potential of cysticercosis.
Clonorchis Sinensis
The oriental liver fluke, or Clonorchis sinensis, is a flat, leaf-like parasite known as a fluke (trematode). This parasite is very common in the Far East and infection is due to the ingestion of undercooked or raw fish infected with the parasite. The oriental liver fluke has been implicated in bile duct cancer.
The Schistosomes
The schistosomes are a group of blood flukes that infect people throughout Africa, the Middle East, parts of South America and the Far East. The schistosomes infect people through skin penetration when the person is swimming or bathing in contaminated water. It causes both acute and chronic disease which include swimmer's itch, the production of granulomas in the liver or bladder, and distended abdomens from enlarged liver and spleen.
Plasmodium
Malaria is caused by the mosquito-borne protozoan parasite, Plasmodium. There are four species of plasmodium that infect humans with P. falciparum being the most serious. People get infected from the bite of a female Anopheles mosquito. The parasite goes through stages in the liver cells and then the red blood cells. Approximately 1 million people die from falciparum malaria annually in Africa. Symptoms of falciparum malaria include fever, chills, bloody urine and brain damage.
Trypanosoma Cruzi
T. cruzi is the causative agent of Chaga's disease. This parasite is only found in the Americas, particularly Central and South America where millions are infected. This protozoan parasite is transmitted to humans through the bite of a triatomine, or kissing bug. The bug usually bites while the person is sleeping, then it defecates and the itch from the bite wound causes the person to scratch it, introducing the parasite-infected feces into the wound. The main cause of death from this parasite is the resulting cardiac problems.
Giardia Intestinalis
This parasite is very prevalent in most areas of the world. Giardia intestinalis is a flagellated protozoa that is a cause of traveler's diarrhea in people. People usually get infected with Giardia through drinking contaminated water. It is also seen in outbreaks in places like day care centers.
Entamoeba Histolytica
This amoeba is the cause of amoebic dysentery. Contaminated water and food are the primary sources of infection. Many strains of this amoeba, up to 90 percent, cause little or no disease. However the other 10 percent is an invasive disease where it can produce a bloody, pus-filled diarrhea and end up producing abscesses in the liver and other organs.
References
- Global Network for Neglected Tropical Diseases-Ascaris
- "Medical Parasitology: a Self-Instructional Text;" Ruth Leventhal, Ph.D.; 1996
