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The prevalence of antibodies against the three active infections of foot-and-mouth disease (FMD) in Sudan; “O”, “A” and “SAT2”, was studied in more than 1500 cattle sera, collected from 7 states in 2013, using a screening format of serum neutralization test (SNT). Prevalence’s detected were 60.16% ±2.25, 30.04%±2.19 and 12.31% ±1.59 for type “O”, “A” and “SAT2” respectively. The result indicated intense circulation and wide distribution of type “O” in the country as opposed to a likely significant introduction of type “SAT2” and “A”. The geographical distribution of FMD infections was defined as penetrating along the Nile basin, particularly, for “O” and “A” viruses and more favorable at Eastern and Western Sudan. Still more favorable conditions are to be expected North of Khartoum and in Darfur in the far West. Type “O” was intensely disseminated along the Nile basin and distribution decreased away from there. The Blue Nile state, at the South Eastern corner of the country, was an important route of entry of the three FMD viruses. Evidently, more risk factors were associated with intense traffic and movements of livestock related to national trade along and from the Nile basin than with movement of livestock associated with nomadic pastoralists in the East and West of the country. Nonetheless, movement of nomadic pastoralists in the East was associated with the potential risk of introduction of type “A” through the extended Eastern border of the country from Wad El Helew in Kassala to Aljabalein in the White Nilestate.Keywords: Foot-and-mouth disease; Sudan; epidemiology; Serum neutralization test; type “O”, “A” and “SAT2” viruses Séroépidémiologie de la fièvre aphteuse au SoudanLa prévalence des anticorps contre les trois infections actives de fièvre aphteuse au Soudan, à savoir «O», «A» et «SAT2», a été étudié dans plus de 1500 sérums de bovins, prélevés dans 7 États en 2013, selon un mode de dépistage du test de neutralisation du sérum (SNT). Les taux de prévalence détectés étaient de 60,16% ± 2,25, 30,04% ± 2,19 et 12,31% ± 1,59, respectivement pour les types «O», «A» et «SAT2». Le résultat est une indication d’une circulation importante et d’une large distribution du type «O» dans le pays, par opposition à une introduction probablement significative de «SAT2» et «A». En ce qui concerne la répartition géographique des infections à fièvre aphteuse, il a été déterminé que son inclusion se faisait le long du bassin du Nil, en particulier pour les virus «O» et «A», les conditions étant plus propices à l’est et au sud-ouest du Soudan. Des conditions encore plus propices sont à prévoir au nord de Khartoum et au Darfour dans l’extrême-ouest. Le type «O» a été intensément disséminé le long du bassin du Nil et sa distribution a diminué à partir de cette région. L’État du Nil bleu, au sud-est du pays, a été une voie importante d’entrée des trois virus de la fièvre aphteuse. De toute évidence, un plus grand nombre de facteurs de risque ont été associés à une circulation intense et à des mouvements de bétail résultant du commerce national le long et à partir du bassin du Nil, plutôt qu’avec des mouvements de bétail appartenant aux pasteurs nomades à l’Est et à l’Ouest du pays. Néanmoins, le mouvement des pasteurs nomades à l’Est a été associé au risque potentiel d’introduction du type «A» à travers la longue frontière orientale du pays, qui s’étend de Wad El Helew à Kassala jusqu’à Aljabalein dans l’État du Nil Blanc.Mots-clés : fièvre aphteuse, Soudan, épidémiologie, test de neutralisation de sérum; virus des types “O”, “A” et “SAT2”

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.

The performance of Chekit and Priocheck (Ceditest) 3-ABC ELISAs was evaluated in an area of endemicity using 196 sheep and 45 bovine sera. The Checkit ELISA failed to detect 8 positive sheep sera out of 10 detected by the Priocheck ELISA whilst both ELISAs detected 13 bovine sera as positive or borderline. The dissimilarity in the performance of the two ELISAs in testing sheep field sera, a target population, was shown to be consistent with their reported differences following experimental infection in cattle and was largely due to differences in their methodology. Sera expected to form high affinity and small immune complexes are better detected in the system of Priocheck-NS blocking ELISA while sera expected to form low affinity (recent infection) and large immune complexes are better detected in the latter system of Chekit ELISA. Identification of this aspect is crucial for optimization of these assays and for conclusive interpretation of their results. Prevalence in the test sheep group as detected by the Priocheck ELISA (8.47%) was more pertinent to the expected true prevalence than that detected by the Checkit ELISA (0.51%). The Checkit ELISA could prove to be useful for detection of relatively recent FMD virus circulation and, hence, control plans in enzootic areas.Key words: Foot-and-mouth disease; 3-ABC serology; Ceditest; Priocheck: Chekit ELISA; Blocking ELISA