Following a request from the European Commission, the EFSA Panel on Animal Health and Welfare (AHAW Panel) was asked to deliver a scientific opinion on peste des petits ruminants (PPR), in order to provide an update on the characterisation of the disease; to assess the risk of introduction into the European Union (EU) and the speed of spread, the risk of becoming endemic and its impact; and to determine if further measures are justified. This request is linked to PPR being currently reported in Turkey and several other Northern African countries. If the virus were to enter the EU, it could cause severe direct losses related to important mortality rates in naive populations.
In particular, EFSA was asked to (i) characterise the disease and provide an update on the global occurrence of PPR and changes in the distribution during the last 10 years; (ii) map the region of concern and other countries of the Mediterranean Basin and Black Sea, displaying identified, or likely, major live animal trade routes; (iii) evaluate all possible pathways of introduction of PPR into the EU, ranking them on the basis of their level of risk, with a view to enhancing preparedness and prevention; (iv) assess the risk of introduction and speed of propagation of PPR into the EU and neighbouring countries; (v) assess the risk of PPR becoming endemic in animal populations in the EU; (vi) assess the impact PPR would have if it were to enter the EU, considering different scenarios as regards the effectiveness of surveillance and control measures; and (vii) review the feasibility, availability and effectiveness of the main disease prevention and control measures (diagnostic tools, biosecurity measures, restrictions on movement, culling).
Regarding disease characterisation, the AHAW Panel reported that PPR is a severe viral disease of small ruminants caused by a Morbillivirus closely related to rinderpest virus. It is widespread in Africa, the Middle East and Southern Asia. It is one of the priority animal diseases whose control is considered important for poverty alleviation in those regions. PPR causes severe disease in its acute form, with fever, respiratory symptoms, congestion and necrosis of mucous membranes, diarrhoea, abortion and immunosuppression. The mortality can range between 10 and 90 %, depending on host status, and if animals recover there is no persistent infection or carrier state. PPR virus (PPRV) resistance is extrapolated from its similarity with rinderpest virus. The virus is considered sensitive to heat, ultraviolet light and pH lower than 5.5 and higher than 10, and it does not survive in the environment, unless in shaded conditions, where it can survive for up to 72 hours. In fresh and chilled meat, it may survive for a few days. PPR transmission is usually via contact with infected animals, or with their fresh secretions or faeces. The virus is found in all kinds of secretions from approximately 3 to 22 days post infection. Goats are considered more susceptible than sheep, and in the latter PPR may circulate undetected for some time. Cattle and pigs can be infected with the virus and then develop specific antibodies, but show no clinical signs. Camels and several wild ruminants can be infected and show clinical disease, although their role in the epidemiology of PPR, in particular in further eliminating the virus, needs to be clarified.
Considering the identified or probable animal movements in the regions of concern, the movements of small ruminants related to trade (both legal and illegal) are the most likely cause of the spread of PPR across borders, as movements often occur between East Africa and the Arabian Peninsula, where the sudden and large increase in livestock movements owing to religious festivity can negatively affect the containment of the disease. The movement of live animals from third countries in the Mediterranean Basin and Black Sea areas into the EU is currently forbidden, according to EU animal health legislation on the import of live animals from countries where PPR is endemic. However, illegal movements of animals cannot be quantified. The illegal movement of animal products, including meat products, carried by tourists and visitors from countries that are at high risk of PPR and communicable animal diseases is large and underestimated.
Regarding the main possible pathways for PPR introduction into free areas, the introduction of infected animals is largely the most efficient pathway to introduce PPR into a country. In the EU, this could occur by the illegal transport of infected animals. In addition, the introduction of PPRV into the EU through infected animal products may occur, in particular when illegally or intentionally carried to spread the virus (e.g. bioterrorism), although the risk of this is low and the further spread of PPR via this route is unlikely. Of less importance is the introduction of PPRV via fomites into the EU, which is considered to be unlikely. This could occur when vehicles carrying livestock return to the EU after the delivery of animals in infected areas or farms and where no biosecurity measures are applied.
In order to estimate the risk of introduction of PPR into the EU via the illegal movement of animals, a model was used to assess the probability of an individual being infectious in a given shipment size. For example, for a level of seroprevalence in the country of origin equal to 37 %, the number of animals that would need to be moved to have a probability of introduction greater than 0.95 or lower than 0.05 to introduce PPR into Europe would be 421 and 8, respectively. On the other hand, if the seroprevalence is 8 %, the number of animals that would need to be moved to have a probability of introduction greater than 0.95 or lower than 0.05 to introduce PPR into Europe would be 1 952 and 34, respectively.
In order to derive an estimate of the potential ranges of speed of propagation, outbreak data of PPR in Tunisia as reported to the World Organisation for Animal Health (OIE) were used to plot temporal and spatial linkages between outbreaks. According to this, the median speed of propagation was estimated to be 3.9 km/day, with a 95 % confidence interval of 0.3 to 65.5 km/day. Nevertheless, this result should be interpreted with caution without direct extrapolation to the potential epidemiological behaviour of PPR if it entered the EU. Because the control measures applied in the EU would aim at culling infected flocks and restricting movements, the spread of PPR in European situations would depend on farm density, travelling frequency and distance of small ruminants, and the duration of silent spread (high-risk period). In such conditions, long-distance transmissions would be more important for initiating new epidemics and thus for the spatial spread of the infection. The basic reproductive ratio calculated with data from a case study in Senegal and compared with other studies in Tanzania and Pakistan showed that PPR has a high within-flock transmission rate, and an outbreak would lead to infection of most animals in a herd. The between-herd transmission would be very variable in Europe, and common grazing grounds would be a major risk source and should be avoided when PPR is detected in the neighbourhood.
Regarding the risk of PPR becoming endemic in animal populations in the EU, although PPR is endemic in several countries neighbouring or close to the EU, owing to a lack of data regarding PPR transmission in the EU, the international data cannot be extrapolated directly to the European situation to make a quantitative assessment of the risk of endemicity. Given the control measures foreseen by the current EU policy, PPR would most likely not become endemic in the EU.
When assessing the impact and consequences of PPR entering the EU, from worldwide experience in endemic areas it can be assumed that, in the EU, goats would be more susceptible than sheep. Therefore, there might be a risk that, if PPR enters EU areas with dense sheep populations but low goat densities, such as Great Britain or Ireland, it would start circulating without being promptly detected, and would lead to widespread infection.
The main prevention and control measures for PPR have been assessed. In general, the AHAW Panel concluded that, as clinical signs of PPR are not disease specific and clinical diagnosis is not reliable, PPR should be confirmed by laboratory testing. The most common and reliable laboratory techniques for PPRV detection are polymerase chain reaction (PCR) and immunocapture enzyme-linked immunosorbent assay (ELISA). The latter is of choice where molecular techniques are not available or biological samples are poorly preserved, although this method is not as sensitive as PCR. Among serological tests, the one that is most used is competitive ELISA.
As far as vaccines for PPR are concerned, only live, attenuated vaccines are available, with high safety and efficacy, protecting against all known isolates of PPRV, but not supporting the differentiating infected from vaccinated animals (DIVA) principle. Possible DIVA vaccines based on recombinant techniques have been shown to be efficacious but are still at the experimental stage. Inactivated vaccines are not available and, owing to the immunological response to PPRV, would not be fully effective.
The lessons learnt from the PPR epidemics in Morocco are that PPR can be controlled in areas, such as Northern Africa, through mass vaccination campaigns implemented at the national level, provided that adequate means are available and correctly implemented. However, in endemic areas, assiduous vigilance is needed because there is a risk of PPR reoccurrence, especially with risk factors of continuous introduction such as the illegal cross-border movements of livestock. In general, early detection of (re)occurrence is a necessary condition for rapid response and the effective management of possible outbreaks of PPR.
Owing to several knowledge gaps about PPR and PPRV, the AHAW Panel recommends further investigation on (i) virus survival and infectiousness in different matrices (e.g. meat, milk) and under different environmental conditions (e.g. temperature, pH, humidity); (ii) the virulence of different virus isolates, the capacity of virus excretion and infectiousness in the same host animals, or of a single isolate in different host species, including European goat, sheep besides cattle, camels and pig breeds, to PPR; (iii) the collection and analysis of data on the transmission and spread within and between herds in different situations, including in a situation comparable to the EU; (iv) the knowledge on populations, movements and contact patterns of small ruminants; (v) the impact of socio-economic factors on the efficacy and efficiency of vaccination campaigns (e.g. vaccine delivery systems) in countries where PPR is endemic; and (vi) the development of safe, efficient and non-replicating DIVA vaccines against PPRV, as well as an associated diagnostic test.
In term of preparedness, the AHAW Panel recommends designing and implementing a regional PPR control strategy, especially in endemic countries or where PPR has occurred and been controlled (e.g. Morocco), relying on coordinated mass vaccination, and post-vaccination monitoring and efficient active surveillance measures.
Better knowledge of legal and illegal livestock and animal product movements should be sought, especially in areas at risk of or affected by PPR. Furthermore, adequate veterinary care and improved surveillance should be in place, in particular for transhumant flocks along the migratory routes in risk areas and especially for long-distance migrations. Awareness-raising campaigns and training for farmers and veterinary staff in recognising the disease under field conditions should be considered, especially for regions at higher risk of introduction of PPR (i.e. those bordering affected regions). Finally, if non-biological drivers of transmission of transboundary animal diseases will change (e.g. breakdown of veterinary infrastructures, human migration, political unrest), the risk of PPR introduction should be accordingly reassessed. Under this perspective, the cooperation of the EU with endemic countries should be encouraged for the prevention of introduction of PPR and other transboundary animal diseases and to enhance preparedness.
In terms of control, if PPR entered the EU, rapid detection, movement restriction, prompt culling of infected herds and disinfection measures should be considered effective measures in limiting the spread and impact of the outbreaks.