Cryptosporidium parvum (thanks to www.sedico.net for this image) is one of the smallest parasites that lives in the water and resists chlorination. For most people it does not cause a problem as they only experience a minor stomach flu or no symptoms at all. In patients with a weak immune system Cryptosporidium becomes a major health threat.
Such patients (for instance aids patients) come down with cryptosporidiosis, a chronic form of cryptosporidium infestation. Several large U.S. and Canadian cities had sporadic waterborne outbreaks. After an incubation time of 7 days patients develop an explosive watery diarrhea. They have abdominal pains, feel sick, may have a low grade fever and a loss of appetite. After about 1 or 2 weeks of this symptoms disappear. As the patients are usually not vomiting, they do not get dehydrated, but some may have so much diarrhea that they need to be hospitalized for intravenous rehydration. In AIDS patients an infection specialist knowledgeable in this disease needs to be consulted. The same is true for microsporidiosis (infection with Microsporidia), which is another small parasite that affects up to about 30% of AIDS patients and causes chronic diarrhea.
Apart from the history, which is slightly different for the different underlying causes, stool cultures need to be ordered, in some patients blood cultures and when meningitis symptoms are present, a lumbar puncture may be required. The samples are cultured in special media to identify positively the offending agent. Special blood tests may have to be sent for heavy metal poisoning. From a public Health point of view, the doctor may need to alarm the health authorities to initiate epidemiological studies with analysis of food, water and the environment. In the meantime the physician will concentrate on treating his/her patient.
In the treatment of gastroenteritis there are always general measures for any case, which means that fluids, electrolytes and blood have to be replaced. Serial blood tests are used to determine that the body chemistry returns to normal.
For a minor viral gastroenteritis the treatment consists of avoidance of protein as this is most difficult to digest for a few days. So the intake concentrates mainly on carbohydrates (bread, noodles, rice), fat (butter or margarine) and fluids such as pop and chicken broth. When the diarrhea subsides, protein can gradually be reintroduced, first chicken, then pork and finally beef and milk products. If the tests came back identifying a cause, a decision needs to be made whether it is necessary to treat the offending agent. For instance, if it was a toxin that caused the illness, there is usually no reason to treat by the time the patient is recovering from the effect. Similarly the enteric viruses are usually self-limiting. However, when bacterial cultures show a positive result and the patient is still sick, the doctor likely will treat with appropriate antibiotics.
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