Peste des petits ruminants: model of transmission and elimination in Ethiopia

Peste des petits ruminants (PPR) is targeted for eradication through mass vaccination campaigns. While an efficacious vaccine exists, the level of PPR virus (PPRV) transmission in animal populations is unknown. By combining the results from a nationwide serological survey with a dynamic model simulating viral spread, researchers have estimated viral transmission potential in Ethiopia, where PPRV is endemic, and vaccination coverage required for disease elimination.

They report in PNAS that repeated vaccination campaigns targeting production systems acting as viral reservoirs would be the most effective way of eradicating the disease.

PPR is a deadly disease of sheep and goats threatening the livelihoods of farmers predominantly in Africa, the Middle-east and Asia, with some cases also recently reported in Bulgaria. The Food and Agriculture Organisation of the United Nations and the World Organisation for Animal Health have launched global efforts to eradicate this disease within the next 15 years.

The PPR eradication strategy relies on mass vaccination campaigns. Although a vaccine providing lifelong protective immunity exists, such campaigns are costly and logistically challenging, due in particular to the mobility and the lack of accessibility of small ruminant flocks, and the lack of accurate census data.

An international team, led by Dr Guillaume Fournié, Senior Research Fellow at the Royal Veterinary College, and initiated by CIRAD’s Dr Francois Roger, worked in Ethiopia to combine the results of a nation-wide serological survey with a dynamic model which simulated PPR spread. With this information, the team identified the pastoral production system as a reservoir of infection from which the virus could spread to other small ruminant populations in Ethiopia and neighbouring countries. They were able to estimate the vaccination coverage that would be required to suppress viral transmission.

Dr Guillaume Fournié said, “Identifying high-risk populations and tailoring vaccination strategies to local epidemiological contexts is essential. This would not only reduce the cost of PPR eradication, but also increase the likelihood of success by setting more achievable vaccination coverages.”

Dr François Roger added, “PPR causes huge economic losses and a very large number of families in low- and middle-income countries are at risk of losing their livelihoods, food security and employment. Considering the limited budgets allocated to the control of PPR and the numerous field constraints, decision effective making-tools are essential”.

Read article: A dynamic model of transmission and elimination of peste des petits ruminants in Ethiopia by Guillaume Fournié, Agnès Waret-Szkuta, Anton Camacho, Laike M. Yigezu, Dirk U. Pfeiffer, and François Roger published in PNAS, online ahead of print, 27 July 2018, doi: 10.1073/pnas.1711646115

[SOURCE: Royal Veterinary College]