Parasitic and Protozoal Infection

There are a number of worms that parasitize humans. These can be divided into three major groups: roundworm (nematodes), tapeworm (cestodes), and flukes (trematodes). Only the most common infections that are likely to be seen in North and Central America will be discussed.


Pinworms are intestinal parasites transmitted by the ingestion of the egg form. This roundworm is called Enterobius vermiculari and is a small white worm about one-half inch in length. An estimated 200 million people in the world are infested with parasites, 18 million in the United States and Canada.

Children are particularly affected. Rectal itching is present, due to the unique nocturnal habits of the female parasite that nightly leave the anus to lay eggs on the skin surrounding it. Scratching leads to reinfection by ingestion. Usually all members of the family should be treated simultaneously.

The whipworm or Trichuris infection is more serious with invasion of the colon mucosa by the adult parasite. This is found more commonly in the tropics, especially in children. At times abdominal pain, diarrhea, and dysentery results with a chronic blood loss that may produce significant anemia.

The roundworm or Ascaris lumbricoides migrates first to the lungs and later lives in the intestinal tract. It is estimated that 25% of the world’s population is infected with this nematode. Ascaris worms are quite large and cylindrical in size. Muscular activity maintains them in within the small intestine.

Amazingly, the daily egg output of the female is estimated to be 200,000 per worm! Their larva is liberated into the small intestine, migrate through the wall, and are thus carried by the blood stream to the lungs. Thus, without specific treatment, the condition is quite chronic and debilitating. Ascaris is primarily a household infection of rural areas. Adequate toilet facilities, hand washing, and strict personal hygiene are good preventives.

Hookworm disease is a symptomatic infection caused by two parasites living in the Americas. Hookworm infestation causes significant suffering; an estimated loss of seven million liters of blood occurs daily in the 700 million people infected throughout the entire world.

Abundant rainfall, shade, and welldrained, sandy soil are conditions conducive to the development of the hookworm egg into an infective larval form. Walking barefoot in the area allows the larvae to migrate through the sole of the victim’s foot into his blood stream.

There it enters the lungs, is coughed up, and later is swallowed, thus reaching the intestines. The major manifestation of hookworm disease is iron deficiency anemia, due to chronic blood loss. Specific treatment must be followed by adequate iron and protein intake in the diet in order for an individual to completely recover.

Common eggs of the roundworm types as seen under the microscope. Their proper identification aids in treatment, as pictured below.

Several intestinal worms, including Toxicara (the dog and cat hookworms), produce visceral larva migrans, and a disease called creeping eruption or cutaneous larva migrans. In this situation the parasite migrates in the skin causing intense itching. Strongyloides stercoralis, another roundworm, causes a serious intestinal infection. The preventive measures are similar for all of these: wear shoes, wash hands, cook vegetables.


Trichinosis is one of the most common flatworm infections in North America. This intestinal and tissue infection of man is caused by the nematode Trichinella spiralis. The disease is characterized by diarrhea during the development of the adult worm in the intestine.

Later there is a syndrome of muscle pain, fever, prostration, edema of the eyelids, and occasionally by myocarditis or encephalitis during the stage of larval migration in the tissues. Trichinosis in humans is contacted by ingesting meat-containing larvae in its dormant stage called a cyst.

The meat has almost always been pork, but about 10% of cases reported in recent years have been attributed to bear meat. Butcher shops often use the same knife or cutting board for different kinds of meat, so cross contamination may occur. Humans are particularly susceptible to this infection.

Cooking the meat thoroughly usually kills the larva and reduces the risk of infection. Specific treatment has not always been available and the prevention of Trichinosis lies mainly in the observance of an ancient Biblical injunction to shun swine’s flesh as food.

Schistosomiasis or Bilharziasis can be produced by three closely related flatworms of the Schistosoma family. These parasites live in the blood vessels of humans who dwell in tropical countries. The organs most frequently affected are the colon, urinary bladder, liver, lungs, and central nervous system. The best attack on this disease is preventive.

Public health measures, including proper disposal of human excrement, provision of pure water supply, and snail control methods in the epidemic areas can be helpful. The parasite, which is harbored by snails, enters the body through the skin of people wading, planting rice, or working in gardens. Specific treatment is difficult and relapses are frequent.

Tapeworm infections are usually acquired through the mouth. Eating raw or undercooked beef will allow introduction of embryos of the cestode Taenia saginata. There is also a pork tapeworm, Taenia solium, and the dwarf tapeworm Hymenolepsis nana. A broad fish tapeworm, Diphyllobothrium latum, is also parasitic in humans and can rob the body of Vitamin B12.

Anemia and other symptoms of B12 deficiency can then result. The most practical control measure of the tapeworm is to avoid disposing of untreated sewage in fresh water lakes. Personal hygiene should be stressed. The contamination of food by rats and mice should be prevented.

Protozoal Infection

Protozoa are one-cell animals. They infect man usually when introduced by mosquitoes or other insects. These infections remain among the major causes of human sickness and death in the world today. Over 500 million people still live in malaria areas. It is estimated that 100 million of these are infected at any given time.

Of those infected one million die of malaria annually. One of the most lethal of all human diseases, sleeping sickness, is carried by the Tsetse fly. In South America, another related organism infects several million people leaving many with severe heart and gastrointestinal lesions (Chagas’ disease).

It is carried by the kissing bug, found in many homes of underprivileged people living in South America. Ten percent of the world’ s population, including 2-5% in the United States are infected with the intestinal protozoa (Entamoeba histolytica). Toxoplasmosis, giardiasis, and trichomoniasis are three cosmopolitan protozoan infections well known to American physicians. Some of the most common of these will be discussed briefly.

Amebiasis is an infection of the large intestine, produced by Entamoeba histolytica. It produces a disease ranging from chronic mild diarrhea to life— threatening dysentery. Liver abscesses may result, at times rupturing into the abdominal or chest cavities. These diseases are diagnosed primarily by an examination of the stool.

Careful microscopic investigation can disclose the presence of the cyst or adult form, a trophozoite. Treatment should be aimed at relief of symptoms, replacement of fluids, electrolytes, and blood loss, and eradication of the organism. The prevention of amebiasis is even more important.

For example, the avoidance of contaminated food and water, scalding of vegetables and the use of iodine release tablets in drinking water are important measures. Improvement in the general sanitation, detection of “cyst passers”, and their removal from food-handling duties, are general measures in prevention.

Malaria is a protozoal disease transmitted to humans by the bite of the Anopheles mosquito. It remains the major infectious disease problem in the world. Malaria is characterized by enlargement of the spleen, fever, anemia, and a chronic relapsing course.

Today malaria survives best in areas of South and Central America, Africa, and Asia, where the mosquito and the infected human population co-exist. The incidence of the disease has decreased since 1945, due to an active international cooperative program aimed at its eradication.

Several types of the organism, Plasmodium vivax, P. malaria, and P. falciparum exist. The cycles between the muscle aching, headache, and fever vary from 48—72 hour periods. “Cerebral malaria” can lead to paralysis, convulsions, delirium, coma, and rapid death. “Black water fever” is a type of malaria associated with P. falciparum.

Massive destruction (hemolysis) of red blood cells is followed by jaundice, kidney failure, and vascular collapse. The most important diagnostic test in the search for malaria parasites is the examination of a stained blood drop under the microscope. Final cure of malaria is difficult, but mild cases often respond to the timely use of fever therapy.

This is given as a rapid sweating steam or tub bath, bringing the body temperature up just as the chills begin, and before fever crests. The treatment should finish as usual with a cold mitten friction or a cool shower. Repeat this treatment on successive days if the chills return.

Performed faithfully in conjunction with a simple diet, extra rest, and other hygienic measures, control can usually be obtained. The prevention of malaria involves primarily mosquito control, using netting, repellents, and the draining of swampy areas to reduce their breeding potential. Travelers or missionaries to countries where resistant malaria is endemic may want to take preventive medication for added protection.

Leishmaniasis is seen in various forms in the new and old world. Trypanosomiasis or “sleeping sickness” is primarily a disease seen in Africa. Toxoplasmosis is a protozoa infection widely distributed among mammals and birds. In humans it can produce both congenital and acquired brain infections.

Specific diagnosis is important before determining the appropriate therapy. Minor protozoal diseases are a common nuisance, and at times are resistant to therapy. Trichomoniasis is a venereal infection caused by the protozoan Trichomonas vaginalis. This organism may survive in the bladder and the genital tract.

Itching, burning, and a profuse, malodorous creamyyellow discharge may persist for weeks. Usually the symptoms subside after the passage of time. Medicated douches as well as careful hygiene are important in the control.

Giardiasis is an unusual appearing organism. This protozoa infection is a significant cause of “traveler’s diarrhea”. It comes from drinking contaminated lake or river water, often while camping. Although the symptoms may persist for several weeks, most infections are asymptomatic and the symptoms are self-limited.

There are a number of other diseases resembling infectious processes where no organism has been identified. Sarcoidosis is one of these, often affecting the lungs and lymph nodes. Diagnosis is obtained by a skin test in association with chest x-ray or biopsies.

We have found fever therapy to be helpful in these cases, like many other infectious diseases of uncertain origin. Many other diseases can mimic the above described processes. With new organisms being discovered each year and new diseases being described, only a cursory review of the latest research is possible in the scope.

Some general principles can be helpful in the treatment of infections, however. Fever is one of the most common symptoms. It is usually thought to be a body defense against infection, since viruses do not multiply well at temperatures over 102 degrees F. Other germs are actually destroyed when the temperature reaches 104-105 degrees.

Unless the symptoms caused by the fever are severe, it should not be totally obliterated, but rather modified by such treatments as moist sponges, cool baths, or the wet sheet pack Hydrotherapy is an extremely valuable treatment for infections of the lungs and the gastrointestinal tract.

Hot and cold moist towels are used freely on the extremities and with the exception of tuberculosis, the same contrasting temperatures are useful in helping the lungs to increase their resistance and throw off the invaders. Many other diseases are self—limited if supportive measures, such as adequate fluids, rest, proper nutrition, sunlight, and judicious balance of all hygienic remedies are combined.

In spite of the many so-called “miracle drugs,” the increase of infectious diseases of uncertain origin and the emergence of resistant organisms continue to challenge patients, as well as physicians in the pursuit of simple remedies. I have been increasingly impressed with the potential of simple home remedies.

As the future ravages of infectious diseases will be more common, more virulent, and people increasingly susceptible to their invasion, everyone must find better ways to treat illness. Even more vital, perhaps, we must learn how to protect ourselves from the diseases of civilization.