Host determinants of peste des petits ruminants (PPR) pathogenesis

Thesis: M. Munir submitted this thesis for his Masters in Veterinary Microbiology at the Faculty of Veterinary Science, University of Agriculture Faisalabad, Pakistan.

Advisor: Professor Muhammad Siddique, Dean Faculty of Veterinary Science, University of Agriculture Faisalabad, Pakistan.

Abstract: Peste des petits ruminants (PPR) is a fatal and contagious morbillivirus infection of cloven-hoofed small ruminants (both wild and domestic), which is characterized by fever, pneumonia, profuse diarrhea, and inflammation of the mucous membrane of respiratory and digestive tracts. These clinical signs vary depending upon certain host factors such as species, age, sex, breed, immune status of the host, husbandry and seasons. This study was conducted to investigate the factors required to predispose the animal to PPR infection which, in turn, facilitates to understand the epidemiology of the disease and hence its control. Moreover, efforts were made to look into the prevalence of PPR in governmental livestock farms in northeast Pakistan, to ascertain differences in seroprevalence between imported versus local breeds. Extensive species surveys based on antibody detection indicated that the level of antibodies against PPRV N protein as detected by competitive ELISA was higher in sheep than in goats and it was also observed that goats are more susceptible to infection than sheep in terms of clinical signs. It was hypothesized, based on these results, that the difference in pathogenecity between sheep and goats may not be due to viral affinity but may be due to high recovery rate in sheep. It was concluded, based on serological surveys, that age is the main risk factor for the seropositivity in small ruminants. Furthermore, the vaccination of kids and lambs from 75-90 days of birth was suggested. Case fatality rate was also found to be higher in young goats than adults. The sex-based distribution of antibodies was hard to interpret because of early selling out of males and longer maintaining of female. In subtropical areas of study, the occurrence of the disease was reported to be more often during winter and rainy seasons. Confinement and restricted movement of the animals due to rainy seasons in tropical countries may affect the nutrition status of the animal and, hence, predispose to PPR infection. This variation probably explained by the region dependent differences in animal husbandry conditions and socio-economic status of the farm owner. Given the high prevalence of PPR among all breeds (local and imported), it is advisable to include PPR serology in the seromonitoring program to give a better indication of herd immunity and to establish appropriate PPR control measures in small ruminants, especially at the region where PPR is a threat to small ruminants.

Key words: PPR, seroprevalence, cELISA, pathogenesis, vaccination.

Correspondence to: Muhammad Munir, Department of Biomedical Sciences and Veterinary Public Health, Section of Virology, Swedish University of Agricultural Sciences, Ulls väg 2B, 751 89 Uppsala, Sweden. Phone: +46 18 67 4609. Email: muhammad.munir@bvf.slu.se