Cryptosporidiosis in calves

Cryptosporidiosis is a widespread zoonotic parasitic disease affecting livestock all over the world. Despite its prevalence, there is very little evidence about transmission routes to young calves, and how it could affect them long-term. Many commonly used disinfectants on farm are unable to inactivate Cryptosporidium oocysts, and some commercially available disinfectants, which claim to work, do not appear to have sufficient evidence available to the research and farming community. This work shows multiple commercial disinfectants which have been directly compared against each other for their efficacy against Cryptosporidium oocysts. The idea that transmission could occur from adult cattle via direct contamination of calf pens with faecal material has been disputed in scientific literature. Older research suggests that adult cattle are not infected with the same species that the calves have, however more recent research with new oocyst concentration techniques has found this not to be the case. It is essential therefore that the genotypes of Cryptosporidium are determined to see if adult cattle pose a risk to their calves. Genotyping using microsatellite analysis gives a more in-depth look at the type of C. parvum present. The aim was, therefore, to determine the risk that adult cattle pose to their calves with regard to C. parvum oocyst transmission on both a dairy and a beef farm in Scotland. Using these methods, it was discovered that adult dairy cattle are unlikely to play a major role in the transmission of C. parvum to their calves. Most of the adult cattle on the dairy farm were predominantly shedding C. parvum however calves on the same farm presented with different multilocus genotype. On the beef farm, however, many of the adult cattle did share the same multilocus genotype as their calves, and so pose more of a risk for oocyst transmission to their calves. The species and genotypes of Cryptosporidium present in Scottish wildlife has very few published studies, therefore the aim was to determine the prevalence of C. parvum in samples from rabbits and pheasants in Scotland. Rabbit faecal samples collected from 18 farms from across Scotland revealed C. parvum to be the most prevalent species; an unusual discovery as it was previosuly believed that C. cuniculus was the most prevalent species in wild rabbits. Despite this the DNA was very difficult to genotype which may indicate that the oocyst load in the faeces of rabbits was small, or that the PCR may have been affected by inhibition. If there is little DNA present, rabbits are unlikely to pose a major threat to calves with regard to C. parvum oocyst transmission. The pheasants also presented with C. parvum as the most prevalent species, although very few shared the same genotype that was present in the calves at the pheasant samples location. Very few oocysts are required to cause cryptosporidiosis in a calf, so even if co-located wildlife do not appear to be shedding high numbers of oocysts, there is still a small risk of transmission present. Young calves affected with cryptosporidiosis tend to make a full recovery under the right management, and the clinical signs clear up within a couple of weeks. It is not known whether or not there is a long-term effect on the calves ability to gain weight following infection with the parasite. Therefore the aim was to compare calves with different levels of clinical cryptosporidiosis to calves with no signs of clinical disease and weigh these animals periodically until they went to market at 6 months of age. It was found that calves with severe disease gained significantly less weight than those with no clinical disease and even animals with mild cryptosporidiosis suffered reduced weight gain over 6 months. This result demonstrates the economic cost that the parasite could have to the farming community on a long-term basis. Commonly used disinfectants are typically ineffective against Cryptosporidium oocysts, and those that are on the market have very little evidence to support their efficacy. Therefore, seven commercial disinfectants were tested for their efficacy to inactivate Cryptosporidium oocysts based on excystation rate and sporozoite to shell ratio. It was identified that hydrogen peroxide and hydrogen peroxide-based disinfectants are the most successful at inactivating oocysts, but only when the disinfectant is freshly prepared. Testing the efficacy of disinfectants once the disinfectant had been made up for 7 days showed that the best performing disinfectant with regard to having the least degradation over seven days was KENOTMCOX. As many farmers are unlikely to make disinfectant up fresh every time it is used, it is useful to know that despite the high efficacy of some products, time since the product was prepared significantly reduces this. It was also found that pens contaminated with faecal material are likely to reduce the efficacy of hydrogen peroxide-based disinfectants and so it is important to clean pens before disinfection. Therefore, this PhD has addressed the knowledge gaps in the literature regarding the role of adult cattle, rabbits and pheasants in the transmission of C. parvum to calves. Neither one poses a major risk due to the low oocyst output and mixed C. parvum genotypes present. It is more likely therefore that calves maintain infection through widespread environmental contamination caused by other infected calves. This work has shown how infection with C. parvum in the first few weeks of life has a significant effect on the weight gain achieved over a 6-month period and so cryptosporidiosis has a significant effect on livestock production and on the profitability of the farm business. The efficacy of commercial disinfectants has provided the advice that disinfectants should be made up fresh and used on an area that has already been cleaned of faecal material in order to inactivate as many of the oocysts as possible.