Parasites

A parasite is a micro- or macro-organism that needs to satisfy its vital nutritional requirements by feeding off certain host tissues or body fluids that contain the specific biochemicals that it needs.

Many of us have heard about parasites in humans such as giardia or amoebas, but we tend to overlook the relationship between these parasites and digestive and systemic diseases and disorders. The common belief that people in the US are free of parasites is a great illusion. Some estimate that about 50 million American children are infected with worm parasites; only a small portion of which is detected and reported. This is particularly worrisome when one recognizes that microscopic (single-celled protozoans), make up about 90% of all parasitic infections in the US according to the Centers for Disease Control and Prevention. If existing parasitic infections are evenly distributed, there would be more than enough parasites for every living person to have one. The most recent statistics of the worldwide prevalence of certain selected parasites follows:

Disease Human infections Annual deaths
Malaria 489 million 1-2 million
All worms 4.5 billion
Ascaris 1.0 billion 20 thousands
Hookworms 900 million 50-60 thousands
Whipworms 750 million
Filarial worms 657 million 20-50+ thousands
Schistosomes 200 million 0.5-1.0 million

This is only some of the examples of parasitism compromising human health worldwide. In temperate areas we are uneducated about the seriousness of parasitic diseases that reach their greatest impact in "tropical" countries from which many immigrate to the US. Contributing factors to parasitic diseases in the US, other than our own endemic parasites and immigration, include malnutrition, population density, economic conditions, sanitary practices, and life styles. Compounding factors in North America include the lack of media awareness, educational materials/counseling and training of the public, as well as in some cases, the professional community. It is in this spirit that this educational pamphlet is offered to you.

How we contract parasites.

A parasite is a micro- or macro-organism that needs to satisfy its vital nutritional requirements by feeding off certain host tissues or body fluids that contain the specific biochemicals that it needs. There are parasites for every single tissue of the human body, once they gain access. An intestinal parasite has to gain access via the oral cavity with contaminated food or drink if it is to cause infection. Other portals of entry are irrelevant. Eight ways by which humans can contract parasitic infections are briefly summarized below.

Drinking water :

Some of the most common microscopic human parasites (Protozoa) are transmitted via drinking water contaminated with fecal material from infected persons. This simple cycle occurs in water from running streams as well as from tap water in homes in large US and Canadian cities served by surface water treatment plants. Parasites transmitted in this manner include Cryptosporidium and Giardia

Skin contact with contaminated water :

This is the only method of infection available to certain parasites such as the schistosomes, some of the deadliest fluke (trematode) parasites of mankind. After emerging from the snail host, the infective larvae (cercariae) penetrate the skin of a person (swimmer, agricultural worker, children playing, etc.) and migrate in the human body ending up as adults in blood vessels (hepatic portal system). To get infected, one has to be exposed in an endemic area, ex., Africa, China, Mexico, Puerto Rico. At PCI, we have identified eggs in fecal samples from an isolated area near a stream in California nearby where a population of Vietnamese immigrants have settled.

Food :

Food intake is perhaps one of the most common ways of transmission of parasitic infections caused by microscopic (Protozoa) and macroscopic (worm, helminth) parasites alike. For example, Blastocystis and the cysts of the amoebas (both are protozoans) are infective when swallowed with contaminated food via the fecal-oral route. This can occur in a household setting or a restaurant. Similarly, the ingestion of the eggs of the human roundworm, Ascaris, readily occurs when fresh vegetables, ex., lettuce, grown in farms fertilized with infected human waste, are eaten without proper washing.

Insects :

Most blood sucking insects are capable of transmitting infectious agents via their bite as they attempt to feed on human blood. In the US, ticks transmit lyme disease, Rocky Mountain spotted fever, relapsing fever, Colorado tick fever, babesiosis, and rabbit fever; fleas transmit plague and endemic typhus, mosquitoes transmit malaria and dog heartworm, Triatoma (kissing) bugs transmit Chagas disease, and head lice can transmit epidemic typhus. If a person has had a history of a recent insect bite in any temperate or tropical part of the world, his/her blood should be tested for parasites. Insect-borne pathogens normally cause no harm to their natural (reservoir) hosts, ex., rodents, but become highly pathogenic in humans (their unnatural hosts).

Air :

Air-borne viruses, bacteria, and fungi are usually eliminated with the feces (occasionally orally) of a natural reservoir (usually wildlife) host but infect humans upon accidental inhalation. Examples in North America include histoplasmosis, Valley fever, and Hanta virus. These diseases are associated with bat guano, dust, and rodent feces, respectively.

Pets :

Despite what you may have been told, dogs, among other pets, are not man's best friend, parasitologically speaking. Dogs carry an intestinal tapeworm, Echinococcus, whose eggs spread all over their fur from the anal orifice during grooming. Unhealthy human contact with infected dogs, e.g., by kissing, brings the eggs into the human intestine which they penetrate as larvae and encyst in the body cavity, e.g., the liver or even the brain, as the life threatening hydatid cysts. Other worm parasites (helminths) are also readily transmitted from pets and other animals to man. Most notable are the beef and swine tapeworms, Taenia, by the consumption of beef and ham contaminated with larvae of these tapeworms.

People :

Close human-to-human contact is conducive to transmission of quite an assortment of sexually transmitted diseases including AIDS and herpes as well as other viruses causing cold and flu. Eating food in a restaurant or at home that may have been contaminated with Taenia eggs or Entamoeba cysts from the servers fecal through improper sanitary practices will surely produce infections with cysticercosis (appearing as lumps in the body or nerve organs) or amoebiasis (causing severe gastrointestinal distress, etc.), respectively. A recent inspection of an expensive restaurant in Los Angeles showed that 100% of all employees (not just servers) had fecal matter under their nails.

Soil :

Certain roundworm (nematode) parasites spend their transitional stages between one host and another as immature larvae in warm moist soil. Walking bare-footed or sitting on such fecally contaminated "seeded" soil in a wooded area or by a lake side, etc. will invite the larvae of hookworms or Strongyloides to penetrate the exposed skin and migrate in the body to finally become adults in the intestinal tract where the damage is done.

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