Cryptosporidium Parvum Volunteer Study: Infectivity and Immunity

This chapter reviews a Cryptosporidium parvum volunteer study in the context of infectivity and immunity. Cryptosporidium infections are widespread in most societies worldwide. Transmission is principally through drinking and recreational water supplies; however, it can also be contracted through person-to-person and animal-to-person contact. Recent advances in molecular techniques have identified two distinct Cryptosporidium genotypes associated with different transmission cycles. Genotype 1 is associated with human infections, whereas genotype 2 is zoonotic in nature and passed readily between humans as well as a variety of animal species. Because of the constraints in animal models, human subjects have been studied to understand many basic aspects of the infection and the disease. In 1993, Cryptosporidium volunteer study was carried out to better recognize the infectivity of the parasite, the illness attack rate, the natural history of the disease, and the host immune response. Healthy volunteers between the ages of 18 and 50 years were challenged with a single oocyst dose of known concentration, and they were monitored for six weeks. Four geographically-diverse, genotype 2 isolates-Iowa, TAMU, UCP, and Moredun-have been studied in volunteers who were seronegative by ELISA prior to challenge. The results showed that several parameters, including illness attack rate, and the severity of symptoms also vary among isolates, but do not directly associate with infectivity (ID₅₀). Increase in the Reactivity Index(RI) can be associated with oocyst shedding.