Chickens raised under village production systems are exposed to a wide variety of pathogens, and current or previous infections may affect their susceptibility to further infections with another parasite, and/or can alter the manifestation of each infection, according to lead author, Judy Betteridge of the University of Liverpool in the UK.

In a paper in Preventive Veterinary Medicine co-written with other researchers based in the UK and Ethiopia, she suggests that it is possible that co-infections may be as important as environmental risk factors. However, in cross-sectional studies, where the timing of infection is unknown, apparent associations between infections may be observed due to parasites sharing common risk factors.

Their study measured antibody titres to three viral (Newcastle disease, Marek's disease and infectious bursal disease) and two bacterial (Pasteurella multocida and Salmonella) diseases, and the infection prevalence of three families of endo- and ecto-parasites (Ascaridida, Eimeria and lice) in 1,056 village chickens from two geographically distinct populations in Ethiopia.

Samples were collected during four cross-sectional surveys, each approximately six months apart.

Constrained ordination, a technique for analysis of ecological community data, was used to explore this complex data-set and enabled potential relationships to be uncovered and tested despite the different measurements used for the different parasites.

It was found that only a small proportion of variation in the data could be explained by the risk factors measured.

Very few birds (nine out of 1,280) were found to be sero-positive to Newcastle disease.

Positive relationships were identified between Pasteurella and Salmonella titres; and between Marek's disease and parasitic infections, and these two groups of diseases were correlated with females and males, respectively. This may suggest differences in the way that the immune systems of male and female chickens interact with these parasites.

Betteridge and co-authors conclude that a number of infectious pathogens and their interactions are likely to impact village chicken health and production. Control of these infections is likely to be of importance in future development planning.

Reference

Bettridge J.M., S.E. Lynch, M.C. Brena, K. Melese, T. Dessie, Z.G. Terfa, T.T. Desta, S. Rushton, O. Hanotte, P. Kaiser, P. Wigley and R.M. Christley. 2014. nInfection-interactions in Ethiopian village chickens. Preventive Veterinary Medicine. Available online 12 July 2014. DOI: 10.1016/j.prevetmed.2014.07.002

August 2014