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Cryptosporidium (part 1 of 2) Page 4 of 13 �• �� 3 Transmission Accurate identification of the modes of transmission is of critical importance in evaluating the risks associated with cryptosporidiosis. Sources Reservoirs for Cryptosporidium include mammals, birds, fish, and reptiles. Species shed by one host can infect other hosts (e.g., cattle can infect humans). Animals that can carry Cryptosporidium include cattle, pigs, cats, deer, guinea pigs, mice, rats, and sheep. Young animals that are most likely to develop symptomatic infections and shed high quantities of infective oocysts. Exposure Routes There are a variety of exposure routes. Cryptosporidiosis is normally transmitted by the fecal route, when oocysts excreted by an infected animal or human are ingested by a susceptible person. A number of transmission routes exist because oocysts are capable of infecting other hosts immediately when released into the environment and after surviving in the environment for a period of time. These routes are: ■ From Animals - Transmission from animals to man has been documented by veterinarians and others working closely with sheep and cows. Gulls have been shown to be carriers. Pet animals such as dogs and cats have also been implicated in human cases.� ■ Person-to-Person - Person-to-person transmission is important. Cryptosporidiosis transmission can occur easily within families, play groups, nursery schools, day care centers, hospitals, and other institutions where precautions are not taken. Sexual transmission is also suspected, particularly in the gay community.z ■ From Water - Several major outbreaks in the last 10 years have shown that cryptosporidiosis can be contracted from contaminated water. Wastewater plants are not whotly effective in removing Cryptosporidium. Recreational contact with contaminated water in reservoirs, rivers, and other waters has been documented as a transmission source. Included in this category is an incident where 17 people contracted cryptosporidiosis while at a local wave pool. ■ Airborne - Some indications exist that airborne spread of Cryptosporidium occurs, although these have not been well documented. ■ Other - There have been a few reports of infection with Cryptosporidium following consumption of raw milk and raw sausages. In 1993, 160 people contracted cryptosporidiosis due to drinking contaminated apple cider at an agricultural fair in Maine. This has not been previously thought to be a significant route. Infectivity Uncertainty exists concerning the dose required to induce infection (not even http://sfwater.org/printContent.cfm/C_ID/446/ 10/19/2004 i .. ,r..