Wednesday, May 24 2017
Harrogate, United Kingdom
The Food and Agriculture Organization of the United Nations (FAO) and the World Organization for Animal Health (OIE) have developed a programme to eradicate PPR and the virus that causes it, by 2030. This program is termed the Peste des Petits Ruminants Global Eradication Programme or the PPR-GEP. This workshop was organized by the International Goat Association (IGA) to present multiple perspectives on the benefits and challenges of this massive undertaking. IGA has been the advocate of goat research, production and development to benefit humanity since 1982, and is a member of the PPR-GEP Advisory Council.
Summary from the Presenters
The participants congratulate FAO, OIE and other partners for the 2030 vision of global freedom of Peste des Petits Ruminants. Eradication will improve small ruminant production that can contribute to gender empowerment, food security, poverty alleviation and resilience as well as biodiversity conservation, if done correctly. We request each ISVC participant to advocate for this vision to donors and decision makers to financially support the implementation of PPR Global Eradication Programme.
PPR is the third viral disease targeted for global eradiation, after smallpox in humans, and rinderpest in cattle. The selection of PPR indicates the importance of small ruminants for human livelihoods and nutrition, and environmental impacts, and presents an opportunity for us to expand public knowledge and attitudes about sheep and goats for the future.
Session I - Technical Aspects of Peste des Petits Ruminants
Molecular Epidemiology of Peste des Petits Ruminants
Dr. Dalan Bailey
From this presentation, it is clear that PPR is a disease that is widespread, spreading and has devastating effects on animal health and on the economies of the poorest people in the poorest countries. Some facts offered by Dr. Bailey: PPR has now spread to over 70 countries in Africa, Middle East and Asia. More than 1.7 billion sheep and goats are at risk of PPR; this amounts to 80% of the global population of these species. Poor farmers rely on small ruminants; the estimated number is 330 million – the demand for small ruminant meat and milk continues to rise and by 2030 is expected to be at 177% of current numbers. Finally, PPR is estimated to cause 1.45 to 2.1 billion USD losses per year.
PPR is caused by a morbillivirus (PPRV) related to rinderpest (eradicated in 2011) of cattle and human measles. There is some evidence that there is cross-protection between the two livestock viruses. The acute disease is a systemic viral infection that attacks the epithelia and immune cells. Goats are more severely affected than sheep. When a region is first infected, morbidity is very high (100%) as is mortality. The signs are high fever, nasal discharge, erosive lesions of the respiratory tract, diarrhea, pneumonia, dehydration and high case fatality rate. Other diseases may appear similarly: contagious caprine pleuropneumonia (CCP), bluetongue (BT), orf, foot and mouth disease and pneumonia due to Mannheimia haemolytica. Asymptomatic infection of cattle frequently occurs with PPRV in the wild. The virus is quite simple – only 6 genes, and is an enveloped RNA virus.
Vaccination forms the backbone of a PPR control or eradication program. Dr. Bailey reviewed some of the requirements of an effective PPR vaccine. The vaccine must be able to confer life-long immunity and be safe, cheap and broadly available. It should be easy to administer (e.g. oral or intranasal instead of injectable). The dose should be a small volume to lessen the volume for transportation. It should confer protection very soon after vaccination and not allow carrier states. It should protect against all lineages. It should be safe and effective in very young animals as well as adults. Live attenuated vaccines often provide a better immune response but must be thermostable to break cold chain requirements. These vaccines must also be produced in facilities that can ensure Good Management Practices (GMP) standards are met and yet be responsive to changing and increasing demand for product. At this point, there is no DIVA PPR vaccine (DIVA = Distinguish naturally Infected from Vaccinated Animals). DIVA vaccines use genetically modified organisms – will this be an impediment to adoption? A DIVA vaccine is important to assure PPRV eradication has occurred, i.e. in the later stages of eradication as it will allow the ability to serologically differentiate vaccinated from naturally infected animals.
Diagnosis of PPR infections is important to understand the changing range of this disease – both geographically and species. This will impact how the PPR eradication program is executed in that particular country or region. Different methods are used: direct virus isolation using highly permissive cells lines; antigen detection using antigen capture ELISA (lateral flow device – research tool only at this point); genetic detection using Polymerase Chain Reaction (PCR), reverse transcriptase PCR (rtPCR), LAMP PCR (uses a florescent dye); and / or antibody detection using either Virus Neutralization (VN) or Competitive ELISA (C-ELISA).
When determining if PPR is the agent operating in the population, the OIE manual recommends the use of C-ELISA unless needing to confirm its presence in a clinical case in which virus isolation or PCR is recommended. Virus neutralization is the recommended method for detecting an immune response at the individual or population level. Immunocapture ELISA is used for confirmation of clinical cases.
Use of molecular epidemiology can be used to determine the source and spread of PPRV. There are four separate phylogenetic lineages – all are the same serotype and have no differences in pathogenicity or serological response. It appears that the Lineage IV virus is the one that has spread recently into north Africa and east Asia.
There have been many recent advances in PPRV diagnostics including the development of penside (i.e. point of care) tests and better understanding of the virus, the tissues it infects and the different immunological responses. Some of this research has shown that cattle may become infected with PPRV in some regions – there is debate on whether cattle may be carriers as well as other ruminant and non-ruminant wildlife. More work needs to be done including: improving vaccines and their implementation; developing more diagnostic capacity to improve surveillance activities; better understand the virus, host susceptibility and resistance, transmission and environmental stability; learn more about the impact of PPR and translate that for the public; and understand more about the role of co-morbidities (e.g. BT and sheep & goat pox) and how that will affect an animal’s immune response and thus control and eradication of PPR.