Role of small ruminants in the epidemiology of foot-and-mouth disease in Sudan

Abstract

Anti-3ABC activity was studied, using the Priocheck ELISA, in 1195 sheep and goats sera from four different states in Sudan; South and North Kordfan, Blue Nile and Kassala. Positive sera were screened by serum neutralization test (SNT) for serotype specific antibodies against known active FMD infections in the country; “O”, “A” and “SAT2”. Results were compared with those of 119 cattle sera; tested simultaneously. Regardless of the locality and the test system used, much lower activity was detected in sheep and goats than in cattle. Almost in every case, sero-prevalence of serotype specific antibodies in sheep and goats followed the same order that in cattle. Excluding the Blue Nile State, sero-prevalence of anti-3ABC antibodies in small ruminants (n=870) was 14.1% (C. I. 11.79%-16.41%) whereas that in cattle (n=89) was 53.9% (43.54%-64.26%). Unlike cattle, around 20% of small ruminants Priocheck positive sera failed to react in combined SNT while, concurrently, strong positive Priocheck reactors represented only 8.61% (n=1195). Apart from the Blue Nile state, sero-prevalence of serotype specific antibodies in small ruminants, in any instance, did not exceed 11%. Results were in agreement with the field observation in Sudan describing no clinical FMD in small ruminants. Infection of FMD in sheep and goats seemed largely secondary to that in cattle i.e. transmission within small ruminants’ herds was likely less significant than transmission from cattle. Sero-prevalence’s in goats, which generally reared more close to cattle, surpassed that in sheep (generally more susceptible), only, in Kassala state, where little grazing of cattle was practiced indicating also the insignificance of transmission within small ruminants herds. Diminished role of small ruminants in the epidemiology of FMD in Sudan is conceivable. Where higher FMD activity was detected, in the Blue Nile state, sero-prevalenc of anti-3ABC antibodies mounted to 37.8% (C. I. 32.53%-43.07%) in small ruminants (n=325) and to 83.3% (C. I. 69.95%- 96.65%) in cattle (n=30). Sero-prevalence’s of the mostly predominant type “O” reached 64% and 24% in cattle and small ruminants respectively. The no very good match between Priocheck ELISA and combined SNT positive reactors in small ruminants was likewise observed previously in wild life, in East Africa, when sero-prevalence estimates in the two test systems were low. Sheep, in Blue Nile and South Kordfan states where more multi-serotype conditions prevailed, showed statistically significantly different proportions (p= 0.0036) of such reactors. Likely, mild exposure (limited virus multiplication) to different serotypes resulted in boosting immune response to NSP but not to SP.