Economic impact of a peste des petits ruminants outbreak and vaccination cost in northwest Ethiopia.

Peste des petits ruminants (PPR) is an important endemic disease of small ruminants in Ethiopia. While vaccination is widely used in the country to control the disease, quantitative estimates of the actual economic losses due to outbreaks and costs of vaccination are scarce. This study assessed the economic impact and costs of PPR vaccination in Metema district, northwest Ethiopia. The economic impact of the disease was estimated from an outbreak investigation including interviews with 233 smallholder farmers in PPR-affected kebeles (subdistricts). The cost of PPR vaccination was obtained from vaccination programs in six kebeles of the district and from secondary data in the district veterinary office. In the investigated PPR outbreak, animal-level PPR morbidity and mortality rates were 51% and 22%, respectively, in sheep and 51% and 25%, respectively, in goats. The flock level morbidity rate was 83% for sheep flocks and 87% for goat flocks. The mean flock level loss was Ethiopian Birr (ETB) 7835 (USD 329 in 2018 average exchange rate) (95% CI: 5954-9718) for affected sheep flocks and ETB 7136 (USD 300) (95% CI: 5869-8404) for affected goat flocks. The losses in all study flocks during the outbreak were ETB 319 (USD 13.4) per sheep and ETB 306 (USD 12.9) per goat. Mortality accounted for more than 70% of the total losses in both sheep and goat flocks. Vaccination costs for PPR were estimated at ETB 3 per correctly vaccinated animal. Based on the estimated animal-level direct economic losses and vaccination cost, it can be conjectured that vaccination will pay if a district PPR outbreak occurs more than once every 13 years. This does not account for additional benefits from vaccine-derived herd immunity reducing disease burden in the wider population. In conclusion, PPR caused high morbidity and mortality in the affected flocks and resulted in high economic losses, equivalent to 14% of annual household income, dramatically affecting the livelihoods of affected flock owners. The vaccination practised in the district is likely to have a positive economic return, with strengthened vaccination programmes bringing reduced economic impact and improved livelihoods.

Post-vaccination herd immunity against peste des petits ruminants and inter-vaccination population turnover in small ruminant flocks in northwest Ethiopia.

Vaccination is the main tool for control of peste des petits ruminants (PPR) because of the availability of effective and safe vaccines that provide long lasting protection. However vaccination campaigns may not always provide sufficient herd immunity needed to prevent disease outbreaks because of logistic problems with vaccination such as inappropriate cold chain and vaccine delivery methods, and the rapid population turnover of small ruminants. This study was carried out to assess post-vaccination herd immunity against PPR and inter-vaccination population turnover in small ruminant flocks in Metema district, northwest Ethiopia where frequent PPR outbreaks occur despite regular vaccination. A total of 412 serum samples were collected from selected small ruminants in 72 flocks (average flock size of 33.4 and standard deviation of 30) above three months of age in three kebeles immediately before a vaccination program. One month after the vaccination using freeze dried live attenuated vaccine, 359 serum samples were collected from randomly selected small ruminants in the same flocks. The collected serum samples were analyzed to determine the seropositivity using a monoclonal antibody-based C-ELISA. The pre-vaccination seropositivity of 72.3% (95% CI: 67.8-76.4) increased to 93.9% (95% CI: 90.9-95.9) post-vaccination (P < 0.001). The observed seropositivity following vaccination was above the recommended herd immunity threshold (80%) required to reduce the transmission of infection in the population sufficient to eliminate virus. A survey of sampled flocks six months post-sampling indicated only 68% of animals were still present in these flocks. This population turnover reduces the herd immunity to about 64% which is below the required threshold for control. The high level of herd immunity achieved post-vaccination indicates good vaccine quality, cold chain maintenance and effective vaccine delivery in the district's vaccination campaigns. The decrease in herd immunity associated with population turnover and annual vaccination intervals represents a challenge to effective control and suggests changes to the timing or frequency of the vaccination is required.