Overview
- Cryptosporidiosis is a highly prevalent gastrointestinal parasitic disease caused by protozoan species of the genus Cryptosporidium that infect a wide range of animals, including people, throughout the world. Cryptosporidiosis is of considerable importance in neonatal ruminants, in which it is characterized by mild to severe diarrhea, lethargy, and poor growth rates. In infected individuals, Cryptosporidium oocysts can be detected in Ziehl-Neelsen–stained fecal smears. Treatment is supportive, with antidiarrheal remedies and replacement of fluids and electrolytes. Strict hygiene is cardinal to preventing infections.
Clinical signs
- C parvum is a common cause of calf diarrhea, and cryptosporidial oocysts have been detected in the feces of 70% of 1- to 3-week-old dairy calves. Infection can be detected as early as 5 days of age, with the greatest proportion of calves excreting organisms between days 9 and 14. Many reports associate infection in calves with diarrhea occurring at 5–15 days of age.
- Cryptosporidial infection in foals appears less prevalent and is seen at a later age than in ruminants, with excretion rates peaking at 5–8 weeks old.
- Infection can be associated with severe outbreaks of diarrhea, with high case fatality rates in lambs 4–10 days old and in goat kids 5–21 days old.
Pathogenesis and transmission
- The source of cryptosporidial infection is oocysts that are fully sporulated and infective when excreted in the feces. Large numbers are excreted during the patent period, resulting in heavy environmental contamination. Transmission may occur directly from calf to calf, indirectly via fomite or human transmission, from contamination in the environment, or by fecal contamination of the feed or water supply. A periparturient rise in the excretion of oocysts may occur in ewes. C parvum is not host-specific, and infection from other species (eg, rodents, farm cats) via contamination of feed is also possible.
Life cycle
- The life cycle of Cryptosporidium consists of six major developmental events. After ingestion of the oocyst, there is excystation (release of infective sporozoites), merogony (asexual multiplication), gametogony (gamete formation), fertilization, oocyst wall formation, and sporogony (sporozoite formation). Oocysts of Cryptosporidium spp can sporulate within host cells and are infective when passed in the feces. Infection persists until the host’s immune response eliminates the parasite. In natural and experimentally produced cases in calves, cryptosporidia are most numerous in the lower part of the small intestine and less common in the cecum and colon. Prepatent periods are 2–7 days in calves and 2–5 days in lambs. Oocysts are usually passed in the feces of calves for 3–12 days.
Summary
- Cryptosporidiosis is a gastrointestinal parasitic disease of vertebrate animals and people.
- The disease is noteworthy in young ruminants, in which it causes mild to severe diarrhea and retarded growth. Cryptosporidium oocysts can be detected in Ziehl-Neelsen–stained fecal smears of infected animals.
- No fully-effective therapeutic drugs exist, but fluid and electrolyte replacement, as well as nutritional support, are indicated. Control involves strict hygiene to eliminate or reduce contamination of the environment by Cryptosporidium oocysts.