Coccidiosis, caused by species of the apicomplexan parasite Eimeria, is a major disease of chickens, according to Lisa Luu of the University of Liverpool in the UK. Eimeria species are present worldwide, and are ubiquitous under intensive farming methods.

However, in a paper in BMC Veterinary Research, she and co-authors from other institutes in the UK and Ethiopia explain that the prevalence of Eimeria species is not uniform across production systems. In developing countries such as Ethiopia, a high proportion of chicken production occurs on rural smallholdings, i.e. 'village chicken production', where infectious diseases constrain productivity and surveillance is low. Coccidiosis is reported to be prevalent in these areas.

However, a reliance on oocyst morphology to determine the infecting species may impede accurate diagnosis, the researchers continue, so they used cross-sectional and longitudinal studies to investigate the prevalence of Eimeria oocyst shedding at two rural sites in the Ethiopian highlands.

Faecal samples were collected from 767 randomly selected chickens in May or October 2011. In addition, 110 chickens were sampled in both May and October. Eimeria oocysts were detected microscopically in 427 (56 per cent; 95 per cent confidence interval (95 per cent CI) 52 to 59 per cent) of the 767 faecal samples tested.

Moderate clustering of positive birds was detected within households, perhaps suggesting common risk factors or exposure pathways.

Seven species of Eimeria were detected by real time PCR in a subset of samples further analysed, with the prevalence of some species varying by region.

Co-infections were common; 64 per cent (23/36; 95 per cent CI: 46 to 79 per cent) of positive samples contained more than one Eimeria spp.

Despite frequent infection and co-infection overt clinical disease was not reported.

Eimeria oocysts were detected significantly more frequently in October (248/384, 65 per cent, 95 per cent CI: 60 to 69 per cent), following the main rainy season, compared to May (179/383, 47 per cent; 95 per cent CI: 42 to 52 per cent; P< 0.001).

Eimeria oocyst positivity in May did not significantly affect the likelihood of detecting Eimeria oocyst five months later, perhaps suggesting infection with different species or immunologically distinct strains.

Luu and co-authors concluded that Eimeria spp. oocysts may be frequently detected in faecal samples from village chickens in Ethiopia. Co-infection with multiple Eimeria spp was common and almost half of Eimeria positive birds had at least one highly pathogenic species detected. Despite this, all sampled birds were free of overt disease.

Although there was no evidence of a difference in the prevalence of oocysts in faecal samples between study regions, the researchers added that there was evidence of variation in the prevalence of some species, perhaps suggesting regional differences in exposure to risk factors associated with the birds, their management and/or location-specific environmental and ecological factors.

Reference

^{Luu L., J. Bettridge, R.M. Christley, K. Melese, D. Blake, T. Dessie, P. Wigley, T.T. Desta, O. Hanotte, P. Kaiser, Z.G. Terfa, M. Collins and S.E. Lynch. 2013. Prevalence and molecular characterisation of Eimeria species in Ethiopian village chickens. BMC Veterinary Research 2013, 9:208 doi:10.1186/1746-6148-9-208}

November 2013