Hammami Pachka, Lancelot Renaud, Domenech Joseph, Lesnoff Matthieu
UMR 117 Animals, Health, Territories, Risks and Ecosystems (ASTRE), Centre de coopération internationale en recherche agronomique pour le développement (CIRAD), Campus international de Baillarguet, 34398 Montpellier, France.
UMR 117 ASTRE, Institut national de la recherche agronomique (INRA), Campus international de Baillarguet, 34398 Montpellier, France.
PLoS One. 2018 Jan 19;13(1):e0190296. doi: 10.1371/journal.pone.0190296. eCollection 2018.
Peste des petits ruminants (PPR) is a highly contagious and widespread viral infection of small ruminants (goats and sheep), causing heavy economic losses in many developing countries. Therefore, its progressive control and global eradication by 2030 was defined as a priority by international organizations addressing animal health. The control phase of the global strategy is based on mass vaccination of small ruminant populations in endemic regions or countries. It is estimated that a 70% post-vaccination immunity rate (PVIR) is needed in a given epidemiological unit to prevent PPR virus spread. However, implementing mass vaccination is difficult and costly in smallholder farming systems with scattered livestock and limited facilities. Regarding this, controlling PPR is a special challenge in sub-Saharan Africa. In this study, we focused on this region to assess the effect of several variables of PVIR in two contrasted smallholder farming systems.
Using a seasonal matrix population model of PVIR, we estimated its decay in goats reared in sub-humid areas, and sheep reared in semi-arid areas, over a 4-year vaccination program. Assuming immunologically naive and PPR-free epidemiological unit, we assessed the ability of different vaccination scenarios to reach the 70% PVIR throughout the program. The tested scenarios differed in i) their overall schedule, ii) their delivery month and iii) their vaccination coverage.
In sheep reared in semi-arid areas, the vaccination month did affect the PVIR decay though it did not in goats in humid regions. In both cases, our study highlighted i) the importance of targeting the whole eligible population at least during the two first years of the vaccination program and ii) the importance of reaching a vaccination coverage as high as 80% of this population. This study confirmed the relevance of the vaccination schedules recommended by international organizations.
小反刍兽疫（PPR）是小反刍动物（山羊和绵羊）的一种高度传染性且广泛传播的病毒感染病，在许多发展中国家造成了巨大的经济损失。因此，到2030年逐步控制并在全球根除该病被处理动物卫生问题的国际组织确定为一项优先事项。全球战略的控制阶段基于对流行地区或国家的小反刍动物群体进行大规模疫苗接种。据估计，在特定的流行病学单位中，需要70%的疫苗接种后免疫率（PVIR）来预防小反刍兽疫病毒传播。然而，在牲畜分散且设施有限的小农养殖系统中实施大规模疫苗接种既困难又昂贵。鉴于此，在撒哈拉以南非洲控制小反刍兽疫是一项特殊挑战。在本研究中，我们聚焦于该地区，以评估在两种不同的小农养殖系统中PVIR的几个变量的影响。
我们使用PVIR的季节性矩阵种群模型，估计了在为期4年的疫苗接种计划中，湿润地区饲养的山羊和半干旱地区饲养的绵羊的PVIR衰减情况。假设流行病学单位为免疫初免且无小反刍兽疫，我们评估了不同疫苗接种方案在整个计划中达到70% PVIR的能力。测试的方案在以下方面存在差异：i）总体时间表，ii）接种月份，iii）疫苗接种覆盖率。
在半干旱地区饲养的绵羊中，接种月份确实影响了PVIR衰减，而在湿润地区的山羊中则没有。在这两种情况下，我们的研究都突出了以下两点：i）至少在疫苗接种计划的头两年针对所有符合条件的群体进行接种的重要性，ii）达到该群体80%的疫苗接种覆盖率的重要性。本研究证实了国际组织推荐的疫苗接种时间表的相关性。
