Schistosomiasis and fecal analysis
In my continuing effort to find timely and informative content for BIO230 students, I came across an article entitled “An in-depth analysis of a piece of shit,” published in the journal PLoS Neglected Tropical Diseases. The article title draws attention to the tropical disease schistosomiasis, and some of the difficulties in obtaining definitive diagnosis and epidemiological data for this disease. Although schistosomiasis is not found in the United States, the Center for Disease Control and Prevention estimates that over 200 million people worldwide are infected with the parasite that causes the disease. Infection with one of the helminth (worm) parasite species that causes the disease results a variety of widespread signs and symptoms such as fever, chills, aches, and rash, which are generally not life threatening. Without treatment, infections can last for years, and can lead to abdominal pain, liver dysfunction, and blood in the stool and urine. Treatment is readily accomplished on diagnosis using the anti-helminthic antibiotic praziquantel.
Members of genus Schistosoma demonstrate a complicated life cycle, with forms that move back and forth between humans and freshwater snails at times. Humans can become infected by simply being in water that is contaminated with the free-swimming cercaria stage of the organism, which can penetrate and burrow into the skin. After maturing into the worm stage, they migrate ultimately to the the abdomen and mate, and eggs are released into the blood, stool, and urine. It is actually the body’s reaction to the presence of eggs that leads to the majority of the signs and symptoms.
Which brings us full circle to the issues raised in “An in-depth analysis of a piece of shit.” Because early disease doesn’t show overt signs, proper diagnosis is important to prevent the later chronic health issues associated with long term infestation. Diagnosis is accomplished by fecal smears and microscopy, but is complicated by high rates of variability between individuals, the length of time of specimen collection, and how the specimen is prepared. The current study describes an initial attempt to examine and control this variability.
Initially, the authors standardized the fecal collection process, by educating volunteers on the proper method. The time of sample collection was noted, and slides were prepared from specified locations in individual stools using World Health Organization guidelines for Kato-Katz thick smear preparations for examination by microscopy. Fecal egg counts were then statistically analyzed for significance.
The authors found that Schistosoma fecal egg counts did not significantly decline during specimen storage, however there was variability in egg counts throughout an individual stool sample. The authors therefore recommend that samples are homogenized to minimize sample variability and increase the accuracy of detection. They do recommend that samples should be stored on ice or otherwise protected prior to examination to help prevent disintegration of the eggs of other intestinal parasites which may also be present.