Cryptosporidium and Giardia in organic pig farms: a longitudinal study of seasonal- and age-related variation in species, genotypes and excretion levels

Summary

Although pigs are commonly infected with Cryptosporidium and Giardia duodenalis, and thus potential reservoirs of zoonotic species (or genotypes), little is known about age-related infection levels, seasonal differences and genetic variation in naturally infected pigs. Thus, to characterise seasonal and age-related variation in prevalence and intensity of infections at farm level, (oo)cyst shedding was monitored at quarterly intervals (September 2011 to June 2012) in piglets (n=152), young pigs (n=234), finishers (n=230) and sows (n=240) from three organic, Danish farms. (Oo)cysts were quantified by immunofluorescence microscopy; and representative Cryptosporidium (n=75) and Giardia (n=67) positive subsamples were characterized by amplification and partial sequencing of the SSU rRNA, hsp70, and gdh genes, respectively. Prevalence and intensity of infections varied significantly between age-groups with 53.3% piglets, 72.2% young pigs, 40.4% finishers and 2.9% sows testing positive for Cryptosporidium (p=0.0002) while 2%, 27.4%, 17.8%, and 5.0% tested positive for G. duodenalis in the same age-groups (p=0.0017). No significant differences were observed in the overall prevalence or intensity of infections between farms or seasons; and the prevalence within each age-group was stable throughout the year. Molecular analyses revealed C. scrofarum and C. suis in 69.0% and 29.3% and Giardia Assemblage E and A in 84.6% and 15.4% of successfully genotyped isolates. Presence of Cryptosporidium species was age-related with piglets exclusively hosting C. suis, apart from one exception, while young pigs and fatteners predominantly hosted C. scrofarum. In one sow, a new Cryptosporidium genotype was detected by partial sequencing of the hsp70 gene. Although C. scrofarum and C. suis are zoonotic, they are rare in humans. In contrast, human cases of G. duodenalis Assemblage A are common, whereas Assemblage E is restricted to livestock. As organic pigs are partly reared outdoors, environmental contamination with Cryptosporidium and Giardia is inevitable. However, the present data indicate that the potential public health risk associated with both parasites in Danish organic pig production is negligible.