Epidemiology of peste des petits ruminants in Uganda

Nkamwesiga, J. 2024. Epidemiology of peste des petits ruminants in Uganda. PhD thesis. Berlin, Germany: Freie Universität Berlin.

Peste des petits ruminants (PPR) is a viral disease that affects domestic small ruminants (goats and sheep) and some wild small ruminants. By 2015, more than 70 countries in Africa and Asia were confirmed as affected although the threat to Europe through Turkey and Bulgaria was quickly neutralised. In Uganda, PPR was first reported in 2007 the Karamoja subregion of northeastern Uganda in 2007, a region comprised of 9 different districts. PPR persisted in this region. Upon eradication of Rinderpest in 2011, PPR was identified as the next target for eradication because of how closely related their aetiologies and epidemiological situations were. Indeed, in 2016, the Food and Agriculture Organization of the United Nations (FAO) and the World Organisation for Animal Health (WOAH) launched a four-stage global PPR control and eradication (PPR-GCEP) by 2030. The control plan was set up to leverage on the momentum gained from PPR control activities to tackle other small ruminant diseases identified by small ruminant keepers through joint activities such as concurrent vaccination against multiple diseases. The PPR-GCEP demands that every PPR affected country complies with the program and implements respective activities to warrant progression from one stage to another until PPR is eradicated following a self-administered PPR Monitoring and Assessment Tool (PMAT). After all steps are achieved, countries will apply for declaration of freedom from disease and continue with activities aimed at maintenance of disease-free status. This thesis was designed to update the PPR epidemiological situation in Uganda, by generating data to fit into PPR-GCEP stage 1 (assessment stage) as well as identify areas for targeting of interventions – which is the cornerstone for the PPR-GCEP stage III (control stage), activities that directly contribute the PPR-GCEP. To achieve the set objectives, this study employed a range of advanced epidemiology, and social network analysis techniques to analyse archived PPR outbreak data and small ruminants movement data respectively. Additionally, the study employed molecular biology and molecular epidemiology techniques to identify the circulating PPR virus and other relevant coinfections in all cases of PPR-like disease reported in Uganda during the study period (202-2022).

Despite the disease persistence in this region for over a decade before it spread to other districts of Uganda, this study identified that the Karamoja subregion was now a diminishing hotspot whereas two new foci of transmission had come up in the central and southwestern regions of Uganda. Concentration of control interventions by government of Uganda and development partners in the Karamoja subregion coupled with rampant shipment of animals between districts from the northern, central, and western regions could have resulted in this shift in the disease focus. However, the districts in the pastoral production system (where the Karamoja subregion falls), had the highest levels of exposure to PPRV as compared to agropastoral and mixed cop-livestock production systems because of the stark difference in the small ruminant management practices amongst these systems. Small ruminants in the pastoral production system are allowed to roam freely on a large expanse of land whereas the those in the other systems are somewhat restricted in movement by fenced farms and or tethering by ropes which greatly protects limits their chances of contact with other flocks with potentially infected animals.

This study confirmed PPRV, CCPP, ORFV and GTPV coinfection among animals from 15 different reports of PPR-like disease that were investigated in this study. This observation further complicates field clinical diagnosis of PPR especially in countries without extensive laboratory diagnostics capacity such as Uganda. In conclusion, there is need to incorporate the detected coinfections in the panel of molecular diagnostics in Uganda to be able to achieve the target of effective PPR control of PPR and other small ruminant diseases. Furthermore, this study reports for the first-time coinfection of other important small ruminant diseases together with PPRV, an observation we believe will improve preparedness for proper disease management options such as chemotherapeutic treatment and vaccination to simultaneously target different disease pathogens. Animal movement control especially at international borders needs to be strengthened to reduce the likelihood of importing or exporting PPR infected small ruminants.

Findings of this study provide a basis for more robust timing and prioritization of control interventions such as vaccination to contribute to the global goal of control and eradication by 2030. For instance, these findings can be used to test a risk based PPR vaccination program by prioritising vaccination of small ruminants in PPR Up Trend districts. The districts that were identified as influential in the small ruminant networks can be good starting points to correctly institute animal disease control measures especially quarantine, vaccination and enhanced biosecurity. Such influential districts have previously been linked with the likelihood of driving the spread of infectious diseases in a very short time because of how quickly animals from them can potentially reach many districts in the country. The districts such as Kaberamaido, Lira, Nabilatuk that demonstrated high levels of connectivity especially by the different centrality measures should be prioritized for surveillance and control activities to increase the impact and effectiveness of such activities.

Districts such as Kampala, Mukono, Wakiso and Lira with high degree centrality and betweenness would increase the accuracy and sensitivity of active surveillance efforts other than blindly implementing such activities. This would in turn improve timely detection of disease outbreaks and reduce the spatial extent and impact thus improving the profitability of small ruminant production venture. Prioritization of interventions in terms of both space and time and for example districts with uptrend, drought-prone and those with high density of small ruminants and the time of the year when the amount of rainfall is low. Targeting PPR control interventions (vaccination and livestock movement control) to and from pastoral and agro-pastoral small ruminant production systems that are prone to PPR incursions is recommended to prevent PPRV spread to low-risk smallholder small ruminant production systems.