July 1999
DANA POINT, Calif. - In parasitic infections, it is important to differentiate between infection and disease. In this protozoan world many people have infections without symptoms, said James S. Seidel, MD, PhD, professor of pediatrics, University of California Los Angeles.
"Approximately 30% of you are infected with Toxoplasma, approximately 2% with Giardia and approximately half a percent with Entamoeba histolytica," he said at the Infectious Diseases in Children Symposium West, recently held here. A problem arises, said Seidel, when disease is present.
It is also important to differentiate between equilibrium and nonequilibrium states, he said. "Only when you have a change in the host immunity or a huge parasite burden do you get disease, and that is why disease is more manifest in developing countries than in the United States."
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---Cryptosporidium
In this country, said Seidel, there is a major problem with Cryptosporidium." Anywhere from 60% to 95% of our ground water that has been tested is infected with Cryptosporidiumcysts." This contamination puts a large population at risk for serious disease, he said.
This at-risk population includes those infected with HIV, chemotherapy patients and people with collagen vascular disease. "We do not often think about these people in relation to the water and what we should recommend in terms of their drinking water."
Many patients say they drink bottled water, he said. "This has to do with the feeling that bottled water is safer." The caveat to bottled water, he said, is that much of it is just filtered tap water, which does not eliminate this parasite. "So there is a problem of what kind of bottled water people use."
Cryptosporidium cysts are resistant to chlorination, they have variable success with filtration and the prevalence rate is somewhere between 3% and 6% of people with diarrhea illness in this country.
A major outbreak occurred in Milwaukee, where there were 416,000 reported cases and 92 deaths. Fecal matter from cows in Wisconsin contaminated the ground water.
The attack rate within households was approximately 5%. "People did not transmit it to each other within households, they got it from the primary source, which at that time was water."
Seidel said Cryptosporidium has a high mortality rate in immunocompromised patients. "Patients with Cryptosporidium should always be considered high on the list with people who are immunosuppressed. It is a cause of travelers diarrhea and it is an important cause of day care diarrhea outbreaks," said Seidel.
In a normal host, the parasite produces a severe, but self-limited enterocolitis. The hallmark of Cryptosporidium and its full-blown manifestations is cholera-like, watery diarrhea. There is occasionally mucous flecks, but there is not much else. It is fairly fulminant, and patients can have anywhere from five to 40 movements a day, he said.
Diarrhea can persist for weeks and cause severe dehydration and loss of electrolytes, particularly in people with HIV. Gall bladder disease can also occur, and there has been one reported case of pancreatitis occurring, he said.
"Interestingly enough, there have been several cases of HIV-infected people in whom Cryptosporidium has been recovered from the sputum of patients with respiratory disease," he said. Whether the parasite was the cause of the respiratory disease or whether the sputum was contaminated with contents from below is really not known, he said. "These were all patients with CD4 counts less than 50, which is the general rule for being at risk for all opportunistic infections."
The variability in a laboratory's ability to make the correct diagnosis of parasites is important, particularly with the protozoa, Seidel explained. "A technician who looks at one specimen every week is not going to be able to do the stains properly or to identify the parasites properly. Testing by polymerase chain reaction (PCR) will not be accurate if the technician does not do many of them."
He also said that physicians must be aware of where the parasite specimens are sent because this is an expensive test, and many commercial laboratories are not good at the tests, he said. "A public health department is often a good source for laboratory diagnosis of parasites."
Cryptosporidium diagnosis can be made using a modified acid-fast stain looking directly at the stool. He said it is currently a time-consuming diagnosis. "You have to put the stools in a special sugar solution, float it, make your smears and then stain it properly."
There is no truly effective treatment. Recent data indicate azithromycin (Zithromax, Pfizer) and other macrolides show that the parasite is sensitive to high-dose therapy. "Cryptosporidiumonly partially responds to some therapies, and it often requires long-term prophylaxis to effect at least a clinical cure."
---Cyclospora
Cyclospora is similar to Cryptosporidium in its clinical course, said Seidel. Like Cryptosporidium, his parasite is transmitted by contaminated water or food, and not from person to person.
Cyclospora is a major public health problem in Nepal, India, where 3% of the population carry the parasite, and prevalence rates of 11% have been reported during the rainy season.
Major U.S. outbreaks have resulted from contaminated berries and water supplies. In 1997 and 1998, raspberries imported from Guatemala were contaminated and led to an outbreak that resulted in 1,400 reported cases of diarrhea illness from Cyclospora.
The differences between Cyclospora and Cryptosporidium are that Cyclospora is slightly larger and not quite as acid-fast on stain, and it can be treated with double doses of trimethoprim-sulfamethoxazole (TMP-SMX). Immunosuppressed patients often have to go on prophylactic therapy, he added.
Cyclospora have a worldwide distribution, a variable incubation period and a long clinical course. "People infected can have diarrhea for weeks and weeks and weeks," he said.
Like Cryptosporidium and Cyclospora, Isospora belli is a new emerging parasite. Isosporiasis, a coccidian protozoa, at one time was only seen in cats and dogs, but now I. belliis the only I. species transmittable to humans. Until the last decade, infection was rare, but it is now commonly found in immunosuppressed individuals and in travelers, according to Seidel.
Diarrhea resulting from I. belli tends to be cyclic. Patients will experience bouts of watery diarrhea, then cessation for a few days, then a reoccurrence of the same symptoms with cramping and profuse diarrhea. "Cyclic diarrhea probably has to do with the life cycle, the way the parasite in the intestine mucosa is multiplying and then releasing," he said. This can occur in immunocompromised and normal hosts.
Treatment is difficult in immunosuppressed patients who have CD4 counts less than 50. It can be treated with TMP-SMX, but a prolonged course of therapy may be required.
Giardia lamblia is one of the most prevalent U.S. parasitic infections. This parasite, according to Seidel, has a worldwide distribution with prevalence rates ranging from 1% to 20%.
It is a problem in the national park system because it is always present in the parks. It comes from water, from the animals in the valley, and from people defecating in open areas. Campers should treat water with iodine solution, Seidel suggested.
Cross-species transmission has been demonstrated and may be responsible for infection in campers. G. lamblia results in an infection in the small intestine. The cysts are always excreted in varying quantities at various times, not uniformly. The peaks occur in the first two weeks, and then after four weeks few parasites are found.
Unlike many other parasitic infections, patients infected with G. lamblia may not have diarrhea; it is only present in 12% of those infected.
"If you have a patient who just feels lousy all the time, feels bloated and is having a terrible time with weight loss, you should always include giardiasis in your differential and get a stool antigen for Giardia."
All patients who pass cysts should be treated because of the public health implications of the illness. "This parasite has the potential to cause disease in all patients and should always be treated," he said. Albendazole (Albenza, SmithKline Beecham), although not indicated for use with this parasite, it is effective when given as a five-day course, according to Seidel.
For more information:
- Seidel JS. Intestinal parasitic infections in children: Newly emerging pathogens. Presented at the Infectious Diseases in Children Symposium West. May 22-23. Dana Point, Calif.
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