Cryptosporidium and Cyclospora first

Cryptosporidium strikes over 400,000 people in Milwaukee! Cyclospora causes diarrhea in more than 1,000 residents of the USA and Canada! Such dramatic outbreaks have enhanced our awareness of the potential for food-and waterborne microbes to affect large numbers of people in the USA. According to the latest World Health Report, "Almost half the world's population suffers from diseases associated with insufficient or contaminated water and is at risk from waterborne and foodborne diseases, of which diarrhoeal diseases are the most deadly" (1). As these recent outbreaks demonstrated, the USA is not an island and our citizens are also vulnerable to food-and waterborne pathogens. What are these unfamiliar organisms and where have they come from? Parasitic protozoa are not common in developed countries. Few people, even in the medical establishment, knew much about Cyclospora and Cryptosporidium until recently. At one time it was thought that Cyclospora was a blue-green alga because it appeared to share some structural and chemical features with this group of prokaryotes. Later observations revealed that Cyclospora is a eukaryotic organism related to the coccidian parasites Cryptosporidium and Isospora and more distantly related to the microsporidia Septata and Enterocytozoon. Although some of these protozoa were isolated long ago from a variety of animal hosts and a few were known to cause human diarrhea in some tropical countries, it has only been during the past few decades, with the increase in numbers of immunocompromised persons (transplant patients, those undergoing chemotherapy, and AIDS victims) that they have become widely recognized as significant causes of human diarrhea. As recent outbreaks have demonstrated, however, immunocompetent individuals are also at risk for infection. All of these protozoa have a similar life cycle and are likely disseminated by some variation of the fecal–oral route, possibly involving contaminated water and food (2). When the oocysts (infectious stages) of Cryptosporidium, Cyclospora, and Isospora are ingested by an individual, they pass to the small intestine where they excyst, releasing sporozoites. These cells invade the enterocytes (epithelial cells lining the small intestine) and undergo a cycle of asexual reproduction to form merozoites. When the merozoites are released from the enterocytes, they disperse to infect other intestinal cells. There may be one or many cycles of this type of asexual reproduction and then a cycle of sexual reproduction producing gametes. Fertilization results in the formation of oocysts, which are then passed out with the feces. In some protozoa, such …