Modelling the Dynamics of Post-Vaccination Immunity Rate in a Population of Sahelian Sheep after a Vaccination Campaign against Peste des Petits Ruminants Virus.
BACKGROUND
Peste des petits ruminants (PPR) is an acute infectious viral disease affecting domestic small ruminants (sheep and goats) and some wild ruminant species in Africa, the Middle East and Asia. A global PPR control strategy based on mass vaccination-in regions where PPR is endemic-was recently designed and launched by international organizations. Sahelian Africa is one of the most challenging endemic regions for PPR control. Indeed, strong seasonal and annual variations in mating, mortality and offtake rates result in a complex population dynamics which might in turn alter the population post-vaccination immunity rate (PIR), and thus be important to consider for the implementation of vaccination campaigns.


METHODS
In a context of preventive vaccination in epidemiological units without PPR virus transmission, we developed a predictive, dynamic model based on a seasonal matrix population model to simulate PIR dynamics. This model was mostly calibrated with demographic and epidemiological parameters estimated from a long-term follow-up survey of small ruminant herds. We used it to simulate the PIR dynamics following a single PPR vaccination campaign in a Sahelian sheep population, and to assess the effects of (i) changes in offtake rate related to the Tabaski (a Muslim feast following the lunar calendar), and (ii) the date of implementation of the vaccination campaigns.


RESULTS
The persistence of PIR was not influenced by the Tabaski date. Decreasing the vaccination coverage from 100 to 80% had limited effects on PIR. However, lower vaccination coverage did not provide sufficient immunity rates (PIR < 70%). As a trade-off between model predictions and other considerations like animal physiological status, and suitability for livestock farmers, we would suggest to implement vaccination campaigns in September-October. This model is a first step towards better decision support for animal health authorities. It might be adapted to other species, livestock farming systems or diseases.
UMR Contrôle des Maladies Animales Exotiques et Emergentes (Cmaee), Centre de coopération internationale en recherche agronomique pour le développement (Cirad), Campus international de Baillarguet, 34398 Montpellier, France.|UMR Cmaee 1309, Institut national de la recherche agronomique (Inra), Campus international de Baillarguet, 34398 Montpellier, France.
Pachka
http://orcid.org/0000-0002-7490-6257
P
Hammami
UMR Contrôle des Maladies Animales Exotiques et Emergentes (Cmaee), Centre de coopération internationale en recherche agronomique pour le développement (Cirad), Campus international de Baillarguet, 34398 Montpellier, France.|UMR Cmaee 1309, Institut national de la recherche agronomique (Inra), Campus international de Baillarguet, 34398 Montpellier, France.
Renaud
R
Lancelot
UMR Systèmes d'élevage méditerranéens et tropicaux (Selmet), Cirad, Campus international de Baillarguet, 34398 Montpellier, France.|UMR Selmet, Inra, Campus international de Baillarguet, 34398 Montpellier, France.|UMR Selmet, Montpellier Supagro, Campus international de Baillarguet, 34398 Montpellier, France.
Matthieu
M
Lesnoff
D000349:Africa; D000818:Animals; D001208:Asia; D006041:Goats / Q000276:immunology / Q000821:virology; D017589:Immunization Programs; D008877:Middle East; D029021:Peste-des-Petits-Ruminants / Q000276:immunology* / Q000517:prevention & control / Q000821:virology; D018107:Peste-des-petits-ruminants virus / Q000276:immunology* / Q000472:pathogenicity; D034561:Sheep, Domestic / Q000276:immunology / Q000821:virology*; D014611:Vaccination