Attachments
Introduction
Peste des petits ruminants (PPR) is a widespread, virulent and devastating animal disease of domestic small ruminants and wild artiodactyls, caused by the morbillivirus peste des petits ruminants virus (PPRV). Mortality rates may exceed 90%, particularly in immunologically naïve, malnourished and stressed populations. In endemic settings, the disease is more cryptic, but causes chronic loss of newborn animals as the virus circulates and persists in populations.
Economic losses are estimated at US$ 1.5 to 2.1 billion per year in locations where 80% of the world’s 2.1 billion sheep and goats are raised to provide livelihoods for more than 330 million of the world’s poorest people. In geographical terms, this is also where some of the world’s most endangered susceptible wildlife ungulate species share the landscape. Both the Food and Agriculture Organization of the United Nations (FAO) and World Organisation for Animal Health (OIE) adopted the Global Control and Eradication Strategy for PPR (PPR GCES) in 2015, with the aim of eradicating the disease globally by 2030. The GCES is underpinned by the international standards of the OIE Terrestrial Animal Health Code (OIE Terrestrial Code) and OIE Manual of Diagnostic Tests and Vaccines for Terrestrial Animals (OIE Terrestrial Manual). The OIE Terrestrial Code currently defines a case of PPR with reference to infection in sheep and goats. The Terrestrial Code notes that, even if some wild small ruminants can be infected, only domestic sheep and goats play a significant epidemiological role. Among other purposes, these guidelines are expected to assist with the systematic accumulation of evidence to evaluate the validity of this important assumption, since it has been challenged by a growing body of fieldbased experience.
Experiences in Asia suggest that wildlife can be adversely affected by the continuing presence or incursion of PPR in livestock with severe, periodic mortality events. These adverse impacts of PPR on wildlife populations and wildlife conservation efforts are greater than previously recognised. For example, outbreaks in Mongolia during 2016–2017 resulted in an estimated 80% decline in the endangered Mongolian saiga antelope (Saiga tatarica mongolica) population.
Furthermore, eradication efforts in livestock may be hampered by the occurrence of PPR in susceptible wildlife populations, since it remains possible, but not yet proven, that infected wildlife could reinfect livestock and thereby act as a reservoir or vector of PPRV. In Africa, PPRV infection appears to remain cryptic in wild ungulate species, with current evidence indicating widespread infection without apparent disease, which could also hamper eradication efforts in certain ecosystems on that continent. However, African ungulate species have expressed PPR disease in zoological collections in the Middle East, indicating a potential role for environmental or nutritional factors in disease expression. In summary, knowledge of the role that wildlife may play in PPR epidemiology (as maintenance, bridge or dead-end hosts) has increased and is currently improving, but there are still several knowledge gaps. However, there is now widespread agreement that wildlife must be considered and integrated within the next phase of the PPR Global Eradication Program (GEP) towards global freedom.
The Strategic Approach of the PPR GCES is based on four different stages. These stages correspond to a combination of decreasing levels of epidemiological risk and increasing levels of prevention and control. The stages range from stage 1, at which the epidemiological situation is being assessed, to stage 4, at which a country can provide evidence that there is no virus circulation, either at the zonal or national level, and is ready to apply for the official recognition by the OIE of its PPR-free status. At all four stages, surveillance is needed to assess the PPR epidemiological situation in domestic animals and wildlife throughout the national territory, as well as to identify the main risk factors for its introduction, maintenance and spread. Surveillance also assists in understanding PPR epidemiology in a country, as well as monitoring progress in control and eradication efforts.
Consequently, the PPR Secretariat, the OIE Working Group on Wildlife, and the PPR Global Research and Expertise Network (GREN) formed a joint Working Group to develop guidelines for PPR prevention, outbreak response, and control in wildlife, which can be used by countries to develop their PPR national strategic plans. These guidelines are intended to help countries in the development and implementation of PPR eradication programmes, including objectives, policies and strategies that can be adapted to the full range of national needs, and that facilitate the integration of the wildlife sector into the national strategic plan. Integration will enhance the conservation of wildlife populations, and facilitate management of diseases at the wildlife–livestock interface. The purpose of this document is to provide a conceptual framework that can be tailored to a particular national and epidemiological context. In addition, these guidelines, while specific to PPR eradication, can be adapted for any disease at the wildlife–human–livestock interface.