Giardia and Cryptosporidium infections in domestic livestock: Zoonotic potential, transmission dynamics, and threat to drinking water

The main aims of this thesis were to obtain information on the prevalence of zoonotic and host-specific Cryptosporidium and Giardia in livestock on Prince Edward Island, Canada, to determine if the presence of cattle and pigs increase the levels of Giardia and Cryptosporidium in source water. Giardia genotypes and Cryptosporidium species in humans on PEI were also analysed to determine if they were the same as those found in cattle and pigs.

The role that dairy farms may play in contaminating source water on Prince Edward Island, Canada, with Giardia and Cryptosporidium is described in Chapter 2. Thirty-two percent and 14% of 752 fecal samples, and 100 and 55% of 20 herds, were positive for Giardia and Cryptosporidium, respectively. Most of the Cryptosporidium isolates belonged to C. andersoni and C. bovis. Giardia duodenalis assemblage E was predominant among all cattle age groups, while only 6 and 4% of isolates belonged to assemblages A and B, respectively. Giardia and Cryptosporidium were detected in 46 and 85% of surface water samples, respectively, while one groundwater sample was positive for Cryptosporidium. All four genotyped Cryptosporidium isolates from water were C. parvum. This study indicates that dairy cattle were predominantly infected with non-zoonotic species/genotypes of Cryptosporidium and Giardia. However, some surface water sources were contaminated with the zoonotic C. parvum and may represent a threat to the watershed and subsequent disease transmission to humans. Cattle >6 months of age were less likely to be infected with Giardia while there was no significant association between either the location of the farm or the housing type and infection with Giardia. Cattle >6 months of age in free-stall housing were more likely to be infected with Cryptosporidium species. While there was no impact of age, infection with Cryptosporidium tended to be higher in Queens County.

Chapter 3 describes the prevalence and genotypes of Giardia and Cryptosporidium on beef farms, including the water sources associated with the farms, and the risk factors for infection of cattle with these parasites. Giardia and Cryptosporidium were detected in 42% and 17% of 739 fecal samples, and 100 and 80% of 20 farms, respectively. G. duodenalis livestock genotype assemblage E predominated (89%). The zoonotic assemblages A and B were found in 4 and 7% of the fecal samples that were genotyped, respectively. Overall, the most common Cryptosporidium species detected in this study was C. andersoni. Giardia cysts and Cryptosporidium oocysts were detected in 14 and 93% of surface water samples of 14 farms, respectively. Cryptosporidium oocysts were detected in three (15%) ground water samples of 20 farms. Age of animals and location of the farm, were not associated with the risk of infection in cattle with either Cryptosporidium spp. or G. duodenalis. The presence of zoonotic species of Cryptosporidium and Giardia in beef cattle represents a potential threat to source water and subsequent disease transmission to humans from these parasites.

In Chapter 4, the prevalence of infection with Cryptosporidium and Giardia, and the genotypes and species of isolates, were determined in order to establish the zoonotic potential of pigs. Eighteen herds (86%) and 163 animals (26%; 95% CI: 22-29%) tested positive for Cryptosporidium, while just 3 herds (14%) and 6 animals (1%; 95% CI: 0.4-2%) tested positive for Giardia. The Cryptosporidium spp. most isolated among those successfully genotyped, belonged to pig genotype II (61%) and C. suis (36%). Pigs are not a major source of Giardia and the common occurrence of the host-specific genotypes and species of Cryptosporidium, indicate that domestic pigs, likely do not pose a significant health risk to humans from these parasites.

The species and genotypes of Cryptosporidium and Giardia in livestock were compared with those from humans to determine if zoonotic transmission of these species occurred, in Chapter 5. Overall 22% and 0.5% of human fecal samples were positive for Cryptosporidium and Giardia respectively. The species of Cryptosporidium found in humans were C.parvum and C hominis. C.parvum shedding in humans was more frequent than C. hominis. Sub-genotyping of C. parvum isolates from beef cattle revealed three sub-genotypes: IIaA16G2R1, IIaA16G3R1 and IIaA15G2R1. Two of these sub-genotypes: IIaA16G2R1 and IIaA15G2R1 were also found in humans. The results indicate that prevalences of the zoonotic species and genotypes of Cryptosporidium and Giradia in the herds sampled in this study were low. However, the data suggests zoonotic transmission of Cryptosporidium to humans on PEI and that cattle are the possible source of the parasite.