Pathway to Peste des Petits Ruminants Virus Elimination - methods for complex ecosystems

Lead Research Organisation: Royal Veterinary College
Department Name: Pathology and Pathogen Biology

Abstract

The emergence of the viral disease, peste des petits ruminants (PPR) across Asia and Africa, affecting some of the poorest and most challenged human communities on earth, demands urgent action to mitigate its immediate and ongoing insidious impacts on domestic and wild ruminants. PPR is a very severe disease of sheep and goats that is very common in East Africa causing high mortality of up to 100%, and loss of milk and meat. It threatens the food security and livelihoods of pastoralists and small-holder farmers. It also threatens wildlife resources, as die-off of rare and endangered wild caprines in Asia has shown. Over the past few years there has been much discussion at international and national levels about the control and possible eradication of PPR, and in early 2015 a global PPR eradication programme was launched.
Since the emergence of PPR in Kenya and Tanzania in 2006-2008, there have been several vaccination campaigns to limit its impact on livestock keepers but outbreaks continue to occur, and lack of effective surveillance means that it is unclear how and where the virus is persisting. Vaccination is usually applied in response to outbreaks if funds are available, which helps to reduce livestock keepers' immediate losses due to the disease, but low levels of vaccination coverage could be contributing to virus persistence. A more pragmatic but research-driven approach is needed to halt PPR virus persistence and spread in East Africa, as well as in infected and at-risk areas of Africa, Asia and Europe.
The project aims to study the wildlife and livestock populations in the Greater Serengeti ecosystem, how they interact with each other, and how the interaction of multiple susceptible species might contribute to persistence of PPR infection making disease control more challenging in a multi-host compared to a single host system.
Based on our previous studies we know that some common wildlife species can be infected with PPR virus, such as buffalo, wildebeest, gazelles and others. We do not know whether they are becoming infected by contact with sheep and goats, or whether the virus is circulating independently among wildlife.
The project will map the livestock and wildlife populations, their numbers, how they move and the type of contact between wildlife and livestock. It will measure the level of PPR infection in the wildlife by conducting a blood-sampling survey to test for PPR antibodies. It will measure the frequency of disease outbreaks in sheep and goat flocks as reported by farmers and through interviews with farmers and flock visits, in sites with different levels and patterns of livestock-wildlife contact. Putting all this information together, we will be able to plan the best way to carry out PPR vaccination in the sheep and goat population to eliminate infection in a short period of time, and the best way to carry out surveillance in both small stock and wildlife to monitor PPR infection and disease.
The project will be carried out by researchers from the Royal Veterinary College, University College London and CIRAD, France, working together with Kenyan and Tanzanian veterinary services, researchers and wildlife authorities and local institutions, and the local livestock keeping communities.
The valuable information gained from this study will be the first step towards eliminating PPR from this ecosystem and the lessons learned will be applicable in other parts of Africa and Asia. In addition to the new knowledge gained, reducing the impact of diseases like PPR will allow farmers, particularly women, in these areas to be more productive, to improve their food security and livelihoods. This comes at a critical time of transition to other livelihoods, with simmering tensions around land use, agriculture and biodiversity conservation, and the increasing effects of climate change and drought. Better disease control will allow people to be more resilient during this socio-economic transition.

Technical Summary

Peste des petits ruminants (PPR) is a transboundary viral disease of sheep and goats that is endemic in many countries of Africa and Asia, and is a major threat for pastoralist farmers, making a significant impact on food security, livelihoods and trade. PPR has recently been identified as a target for global eradication, but an important knowledge gap for the eradication effort is the role of wildlife in PPR epidemiology. The aim of this project is to improve understanding of the host-pathogen ecosystem of livestock, wildlife and PPR virus (PPRV) in the Greater Serengeti Ecosystem of Kenya and Tanzania to facilitate the design of effective and efficient surveillance and vaccination strategies for the elimination of PPRV. It is the first phase of a proposed five-year project that has the overall objective to test the hypothesis that the elimination of PPRV infection from domestic small ruminants leads to the elimination of PPRV infection from in-contact wildlife populations. The specific objectives are, in the Greater Serengeti Ecosystem; to define wildlife and small ruminant population spatial and temporal dynamics and their interface, to describe the spatial and temporal dynamics of PPR infection and disease in wildlife and domestic small ruminant populations, to develop surveillance and vaccination strategies for the elimination of PPRV from the ecosystem, and to strengthen coordination and build capacity to support cross-border disease surveillance and control policy and strategy. The project will develop a conceptual model of the ecosystem, integrate existing data and identify knowledge gaps to be addressed by qualitative and quantitative field studies in wildlife and livestock, including a serological survey to determine antibody prevalence in wildlife, strengthened disease reporting and investigation and active surveillance in livestock, and qualitative studies of small ruminant movements and trade, supported by laboratory diagnostics and molecular analysis.

Planned Impact

PPR is a disease of domestic sheep and goats and wild ruminants that is endemic across Asia and Africa, and in the past decade has expanded into southern and northern Africa, and central and eastern Asia. It causes high mortality in naïve populations (up to 100%), threatening food security, trade and biodiversity conservation, while in endemic areas there are frequent disease outbreaks that affect up to 50% of a flock causing high mortality, especially in young animals. Two thirds of sub-Saharan Africa are drylands where ruminant production is a central pillar of rural livelihoods and of particular importance to women, with small ruminants providing pathways out of poverty for pastoralists and agro-pastoralists. These are among the world's poorest people, commonly living on less than $1 per person per day. Their food security and future prospects are threatened by climate change and disease. Across sub-Saharan Africa there is a well-documented progressive species shift towards keeping small ruminants, linked to changes in climate, access to key resources and rising market demand. Controlling PPR can make a huge difference to the livelihoods of the poorest rural populations across sub-Saharan Africa and beyond. This project provides the foundation for demonstrating the elimination of PPR virus (PPRV) from a large complex multi-species wildlife-livestock ecosystem as pre-requisite for global eradication. It supports the first phase of a proposed five-year project by strengthening the necessary partnerships, improving understanding of the ecosystem, and developing surveillance and control methods and capacity. A key knowledge gap in global eradication centres on the role of wildlife in PPR epidemiology. If the proposed 5-year project is successful in eliminating PPRV from the ecosystem, it will demonstrate that wildlife is not a maintenance host for PPRV, and that elimination of PPRV from small ruminant populations will be sufficient to ensure eradication without intevention in wildlife populations. On the other hand, if the results show that wild animals are able to maintain PPRV infection, this will be crucial for initiating design of mitigation measures in these species. The role of wildlife in disease maintenance was a fundamental question during the rinderpest eradication programme: there was evidence that as incidence declined in cattle it also declined in wild animals in the Serengeti Ecosystem but with no systematic research the situation was uncertain even in the final stages of eradication. The results of this research will therefore provide evidence to support political will for eradication, increasing confidence of donors, Governments, communities and implementers in the global eradication process. This first phase will provide a case study of baseline data collection prior to embarking on PPR elimination; study design, qualitative and quantitative data collection methods, and data analysis. This will be relevant to extensive production systems in Africa and Asia, and will be disseminated through global PPR networks. It will provide useful information on other prevalent small ruminant diseases to support other disease control initiatives, and will strengthen communication between livestock keepers and veterinary authorities.
The project includes experienced skilled researchers in transboundary animal disease and virology (RVC, Pirbright, SUA), and draws on UCL anthropological expertise in local pastoralist systems. It will strengthen North researchers' collaboration with Africa and strengthen cross-border collaboration between veterinary services, wildlife and research organisations in Kenya and Tanzania, which will be extremely beneficial as PPR eradication efforts in Africa move forward. The PPR field test kit, developed by Pirbright Institute, will be used systematically as part of a surveillance system for real-time diagnosis which could accelerate elimination.

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