Thomson, Sarah (2016) Cryptosporidiosis in farm livestock. PhD thesis. Submitted in fulfilment of the requirements for the Degree of Doctor of Philosophy, Institute of Biodiversity Animal Health and Comparative Medicine University of Glasgow 2016 http://theses.gla.ac.uk/7096/
This extensive and original research has highlighted some important features of Cryptosporidium parvum infections in calves based on the research completed in Scotland.
Some of the results may or may not have direct relevance to New Zealand farming conditions. In some instances they may be so relevant that they will challenge some of our current practices. Without some local (NZ) studies it is too early to make recommendations.
- Only one cow was shedding the genotypic strain variant that produced cryptosporidial scours for the calf shed. That cow calved early, and its calf developed cryptosporidial scours. These scours were apparently sufficient to spread the oocysts from that point on. While multiple genotypic strains occurred on the farm, it was only the one strain that emerged to be significant in the calf rearing environment.
- The PhD report included development of research study techniques that isolated Cryptosporidium parvum from cow dung, based on separation, concentration, identification and genotypic typing of the strains present. It confirms studies which suggest it is overwintering cows prior to calving potentially being the source of infection in a calf shed.
- No conclusions can be made of the shed being a source of infection between seasons. Within the season, the shed and farmer practices remains an important source for spread of infection between calves once the first calf has had cryptosporidial scours.
- The infective dose is an important element in determining the time of infection to the first signs on infection, with higher infective doses showing earlier and more severe signs.
- Strain (genotypic) variations exist which differ in severity of clinical signs. It is likely that strains producing more severe signs are contaminating the environment more successfully and ensuring their dominance as the ‘on-farm’ endemic type.
Comments: The actual output of crypto oocysts from a cow are below the detectable levels with current techniques routinely available without the research techniques of concentration that were used. Also the genotypic typing is a method that is not currently employed other than through the most advanced, specialised research laboratories.