Epidemiology of parasitic protozoan infections in Soay sheep (Ovis ariesL.) on St Kilda

Abstract

The feral Soay sheep (Ovis aries L.) population on Hirta, St Kilda, is host to a diverse component parasite community, but previous parasitological studies of the population have only focussed on the metazoan species. This paper reports the first epidemiological study of the protozoan species comprising Cryptosporidium parvum, Giardia duodenalis and 11 species of Eimeria in Soay sheep across 3 years of varying host population density. Prevalence and intensity of almost all species of protozoa significantly decreased with host age, with the exception of E. granulosa, which increased in prevalence with host age. The prevalence of C. parvum appeared to vary positively with host population density but that of G. duodenalis did not vary significantly with density. Most species of Eimeria showed a distinct lag in infection level following the host population crash of 2002, taking up to 2 years to decrease. Mixed Eimeria species intensity and diversity were highest in 2002, a year of low host density. Parasite diversity decreased with host age and was higher in males. There were 5 positive pair-wise associations between protozoa species in terms of prevalence. The results of this study highlight the potential for protozoal infection to shape the evolution of parasite resistance in wild host populations harbouring diverse parasite species.

Subclinical Bovine Coccidiosis in Al -Baha Area, Saudi Arabia

“…Three positive pair-wise associations were found between Eimeria species. This finding is consistent with the finding of Craig et al [12], explained the positive pair-wise correlations between Eimeria species for one of two reasons. The first one is the overdispersion of parasites in natural populations, that is most individuals harbour few parasites and a few harbour many.…”

“…One hundred oocysts were randomly selected and identified to determine the percentages of each Eimeria species present in the fecal samples and then OPG per Eimeria species was counted Silva et al, 2011). An estimate of intensity of each Eimeria species was achieved by relating their proportions to the McMaster counts [12].…”

“…The co-infection is common with Eimeria species in cattle and in wild bovids [4,[7][8][9][10]. There is evidence for interactions between parasite species, highlighting the importance of understanding these relationships before devising control strategies against specific species in livestock systems [11,12]. In assessment of the dynamics of co-infections (either naturally, or following external perturbation), measures of abundance will be more sensitive than prevalence.…”

Genetic Diversity of Cryptosporidium spp. within a Remote Population of Soay Sheep on St. Kilda Islands, Scotland

“…Cryptosporidium parvum has been documented in domestic sheep (7), and Cryptosporidium species, presumed to be C. parvum, have been identified in Soay sheep by microscopic examination using modified ZiehlNeelsen staining (13). C. parvum sequence heterogeneity is known to exist (46,47), and variability was observed in all the St. Kilda locus 1 amplicons (46).…”

“…The Soay sheep population fluctuations and their isolation from human interference and other sheep have interested scientists since the 1950s, and much of the current research has focused on the parasites infecting the sheep (12). During an epidemiological study of protozoan parasites between 2001 and 2003, Cryptosporidium was first identified in the population by using ZiehlNeelsen staining (13). This test selectively stains the oocysts but is limited in its ability to differentiate between morphologically cryptic yet genetically diverse species.…”