On the Crypto Hunt
Michael Fisher, Golden Plains Area Livestock Extension Agent
(Some of the research data reported here has a strong California slant. However, I believe the premise is still relevant to Colorado, both in the results that were discovered and the discovery of cattle versus wildlife implications.)
The protozoal species Cryptosporidium parvum is one of the causes of the parasitic disease cryptosporidiosis, also known as crypto. Completion of the crypto life cycle starts with the ingestion of C. parvum oocysts. Once ingested, the oocysts release sporozites which attach to the animals intestinal cells, triggering an immune response from the host. New oocysts develop. Those with a thick wall are transferred out of the animal in its feces, known as shedding, and can be ingested by other animals. The new oocytes that have a thin wall will rupture, offering the opportunity to re-infect the host animal.
Generally, calves that are affected by crypto will express signs within one to four weeks of age. The disease can cause calves to be weak and lethargic. They also are prone to severe watery diarrhea, which can lead to dehydration. Affected animals may have extended lowered performance long past the clinical signs of the disease. Additionally, shedding of the oocysts can continue for a few days beyond clinical signs, so isolated calves should not be returned to the herd as soon as their diarrhea ends.
Crypto is a zoonotic disease. This means that it can pass across species. It affects most mammals, including humans. It has been known to lead to death among young children, the elderly, and those people with a weakened immune system. Cryptosporidium parvum can resist many disinfectants and has the ability to withstand long periods of time in the environment. Being a waterborne parasite that can lead to human outbreaks of crypto, C. parvum mitigation within watershed management is becoming an increased area of concern.
Researchers from the University of California (Atwill et al, 2003) have been working to improve how estimates of low environmental loading and sporadic periparturient shedding of C. parvum are measured among adult beef cattle. If scientists can better understand the analysis and identification of these shedding events, it can further our protection of both the calf crop on the local ranch and human water supplies collected further down the watershed.
Atwill’s group found that 7.1 percent of the adult beef cattle that they tested were positive for C. parvum oocysts. While a greater number of these were discovered prior to calving, when compared to after calving, they determined the difference was not great enough to conclude a significant statistical difference. Further, it was determined to be unlikely that more than 1.4 percent of the test cattle that have had multiple calves were shedding moderate or high levels of oocysts. Using C. parvum shedding values of positive cattle and all test cattle combined, the research group determined that California beef cattle in the test population would have a C. parvum environmental load between approximately 3,600 and 9,200 oocysts per cow per day. When adjusted for stocking rate, the research group determined that roughly 650 to 1,625 oocysts could be shed upon a hectare of land per day by adult cattle. It is interesting to note in comparison, California ground squirrels which inhabited the same study areas as the beef cattle, had an average C. parvum oocyst shedding of 113,000. A hectare population density of these one-half pound squirrels can range from 8 to 94 adults.
References used for this article:
Atwill, E.R., B. Hoar, M. das Gracas Cabral Pereira, K. W. Tate, F. Rulofson, & G. Nader. (2003) Improved Quantitative Estimates of Low Environmental Loading and Sporadic Periparturient Shedding of Cryptosporidium parvum in Adult Beef Cattle. Applied & Environmental Microbiology. Pp 4604-4610.
Hodges, R. Cryptosporidiosis in Calves. Online publication accessed April 10, 2012; http://www.vet.k-state.edu/depts/VHC/agpract/articles/Crypto.pdf