Human Intestinal Parasites and Worms
In addition to bacteria and yeast, most of the world's four billion people are also colonized by human intestinal parasites and worms, and parasitic infection is not unusual in the U.S. population. It is a common occurrence, even among those who have never left the country.
Unlike bacteria, parasites appear to serve no useful function. The part of the immune system, which they stimulate, does not strengthen the organism to resist serious infection; instead it contributes to allergic reactions, so that parasitic infection increases allergic tendencies.
There are two general groups of intestinal parasites.
The first consists of intestinal worms -- tapeworms and roundworms -- that attach themselves to the lining of the small intestine, causing internal bleeding and loss of nutrients. People infested with worms may have no symptoms or may slowly become anemic.
The second category is the protozoa -- one-celled organisms like the amoeba, which caused John Gerard's colitis.
Antoine van Leeuwenhoek, the most famous of the early microscopists, discovered the first protozoa over three hundred years ago. When the inquisitive Dutchman set about to examine everything in the world that would fit under the lens of a microscope, he found organisms in his own stool that closely match the description later given to Giardia lamblia.
Giardia is the major cause of day-care diarrhea. Twenty to thirty per cent of workers in day care centers harbor Giardia. Most have no symptoms; they are merely carriers.
A study at Johns Hopkins medical school a few years ago demonstrated antibodies against Giardia in twenty per cent of randomly chosen blood samples from patients in the hospital. This means that at least twenty per cent of these patients had been infected with Giardia at some time in their lives and had mounted an immune response against the parasite.
Giardia contaminates streams and lakes throughout North America and has caused epidemics of diarrheal disease and chronic constipation in several small cities by contaminating their drinking water. One epidemic, in Placerville, California, was followed by an epidemic of Chronic Fatigue Syndrome, which swept through the town's residents at the time of the Giardia epidemic. Possibly, this epidemic was due to failure of some people to eradicate the parasite. In 1991, my colleagues and I published a study of 96 patients with chronic fatigue and demonstrated active Giardia infection in 46 per cent.
Sometimes, the intestinal damage produced by giardiasis persists for months after the parasite has been successfully treated. The impairment of digestion and absorption, which results from this damage, may cause fatigue and other symptoms.
The present decade has witnessed an increased awareness of parasitic infection as a common public health problem in the United States, thanks largely to Cryptosporidium, which recently achieved notoriety for contaminating Milwaukee's water supply, causing the largest epidemic of diarrhea in U.S. history, infecting 400,000 people and causing over one hundred deaths.
Most municipal water supplies in the U.S. today are home to protozoa like Giardia and Cryptosporidium and one in five Americans drinks water that violates federal health standards.
Every year, almost a million North Americans become sick from water-borne diseases; about one per cent dies. Further epidemics are inevitable. A recent epidemic occurred in Clark County, Nevada, despite state-of-the-art municipal water treatment.
If this is the case in a well-developed First World Country like America, one wonders at the state of water supplies of "lesser-developed" countries.