Introduction
Peste des petits ruminants (PPRs) is a notifiable viral transboundary disease, highly contagious for domestic and wild small ruminants [1]. PPR virus, a member of the genus morbillivirus and family Paramyxoviridae, is the source of this acute, and usually deadly disease of sheep and goats [2,3]. The genome has a molecular weight of 5.8 × 106, and the virion’s diameter is between 150 and 300 nm. According to Gebre et al. [4] and Dundon et al. [5], the virion is extremely susceptible to heat, lipid solvents, non-ionic detergents, formaldehyde, and oxidizing agents [4,5].
PPR disease is clinically characterized by fever, biocular and nasal discharge, coughing, sneezing, sporadic mouth lesions, foul foul-smelling diarrhea with a high morbidity and mortality rate in the infected flock or herds. Transmission of the disease requires close contact between susceptible animals and infected animals in the febrile stage. Fine infective droplets are released into the air from these secretions and excretions, particularly when affected animals cough and sneeze and animals in close contact inhale the droplets and become infected [6,7]. Although close contact is the most important way of transmitting the disease, it is suspected that infectious materials can also contaminate water, feed troughs, and bedding, turning them into additional sources of infection. Intensive fattening and trade in small ruminants, at markets where animals from different sources are brought into close contact with one another, enhances transmission of the disease [8].
PPR causes a high mortality rate which severely restricts the production of sheep and goat’s production. As a result, it is regarded as one of the worst animal diseases throughout Asia, the Middle East, and Africa. The Food and Agricultural Organization with the World Organization for Animal Health lists it as one of the priority diseases for sheep and goats in the global framework for the progressive control of trans-boundary animal diseases programs [9].
In Ethiopia, PPR was clinically suspected to be present in 1977 and was confirmed late in 1991 [10]. It continues to cause the death of millions of sheep and goats annually and is a constant threat to the livelihoods of subsistence farmers in many agro-ecological zones of the country [11,12]. The disease is associated with high mortality and morbidity rates in naïve populations [13], significant economic losses, reduced production and productivity as well as high control costs [11]. The geographic distribution of the PPR disease has increased rapidly in recent years, as it has in much of Eastern Africa, with the emergency of lineage IV during the 2010 outbreak in the country [14].
Understanding PPR disease occurrence is crucial for the integrated, risk-based, and effective prevention and control program of the disease and it can be identified either by conducting sero surveillance in unvaccinated populations or by retrospective studies of PPR disease occurrence from compiled monthly reports or from outbreak investigated data. PPR disease sero surveillance was conducted in a few weredas of the region and revealed the seroprevalence ranges from 0% to 4.93% [15,16,4]. Retrospective PPR disease occurrence information showing spatial, temporal, and other risk factors for the occurrence of the disease is crucial for the integrated, and effective PPR disease prevention, control, and elimination program, based on its epidemiological unit, however, in South West Ethiopia People Region (SWEPR) not such kind of study was conducted, so to fulfill this gap, this study has been conducted.
General objective
- Identifying risk factors for the occurrence of PPR disease outbreak and appraising its control and prevention activities conducted in the South West Ethiopia region.
Specific objectives are
- To determine temporal, spatial, and animal-related risk factors, and also prevalent risk factors linked to the production system for the occurrence of PPR disease in the study area.
- Assess activities conducted for the prevention and control of PPR disease occurrence
Materials and Methods
Study area
The SWEPR is one of the regional states of Ethiopia, established on 23 November 2021 after a successful referendum from the former Southern Nations, Nationalities, and peoples, Region. Currently, the region consists of six zones, and within it, there are 39 districts and 5 town administration states as shown in Figure 1. Temperate climate prevails in areas having elevations ranging from 620 to 2,780 meters above sea level. Crop-livestock production is the major farming practice in the region which accounts for 2,176,310, sheep, and 3,145,732 goats (South West Region, Bureau of Agriculture, 2021; Personnel communication).
Study population
All outbreaks of PPR cases and PPR vaccinations were conducted in all ages and breeds of sheep and goat’s population and notified by monthly disease outbreak and vaccination activity report (DOVAR) to Mizan Regional Veterinary Laboratory Center (MiRVLC).
Source of data
PPR is a notifiable disease in Ethiopia, and all cases should be reported monthly to the national epidemiology directorate of the Federal Ministry of Agriculture. For this study, data were taken from the monthly disease outbreak and vaccination activity report, which was sent to the Mizan Regional Veterinary Laboratory Center from January 2018 to December 2022 from all districts of the South West Ethiopia Region were included.
Operational definition
Temporal PPR outbreaks event were divided into four seasons, with the spring or early dry season lasting from September to November, the summer or late dry season lasting from December to February, the early rainy or early autumn season lasting from March to May, and the winter or rainy season lasting from June to August. The spatial distribution of the PPR outbreak is taken as the longitude and latitude coordinates for a single outbreak location. Confirmed outbreaks were created and delivered by DOVAR when a case was examined and diagnosed by a regional laboratory using a rapid PPR test and immunocapture enzyme-linked immuno sorbet assay, and a positive result was found, whereas suspected outbreaks were made and sent by DOVAR based on a presumptive diagnosis without a laboratory test result. Animal species infected by the outbreak were divided into caprine, ovine, or mixed caprine and ovine species. Age groups that were affected were determined using data that was categorized as being less than 1 year old, greater than 1 year old, or all age groups if both age groups were affected. The population at risk is the number of animals of the same species present in the same area during the outbreak, which is considered by the epidemiological unit. The sexes of the animals infected were recorded and classified as male, female, or both if both were affected. The term “control vaccination” refers to the number of animals that are vaccinated to stop an outbreak of the disease while prophylactic vaccination refers to the number of animals vaccinated for preventative purposes before an outbreak.
Study Design and Sample size
Retrospective study design was used to describe the extent of the PPR outbreak in animals, its location and time, as well as other risk factors for its occurrence, and to assess PPR vaccination that was carried out in the region.
Figure 1.
Number of PPR outbreak reported from 2018 to 2022 in South West Ethiopia Region.
Study variable
The number of animals at risk, the number of deaths and cases of animals due to PPR, the month and year of the outbreak, the district and zone in the region, the age and species of the affected animals, and the agricultural system where sheep and goats raised were the primary variables considered in this study. The impact of PPR will be assessed by its morbidity, mortality, and case fatality rate (CFR). The animal level morbidity rate was calculated as the number of animals infected by a PPR outbreak during a given time divided by the total number of animals at risk at that time multiplied by a hundred. The mortality rate was calculated as the number of animals that died due to a PPR outbreak during a given time divided by the total number of animals at risk at that time multiplied by a hundred. CFR was determined as the number of animals that died due to a PPR outbreak during a given time divided by the total number of animals infected multiplied by a hundred. In addition, the PPR vaccination conducted was assessed.
Data management and analysis
The data were entered into a Microsoft Excel sheet and analyzed by using a Pivot table. The trend and distributions of PPR cases by animal, place and time, and other associated risk factors related to PPR outbreak and vaccination, were presented using graphs and tables. The spatial distribution of PPR outbreak occurrences in the region was displayed by a point map. Mendeley desktop was used as a reference manager for citation and reference [17].
Results
According to Figure 1, between January 2018 and December 2022, 1900 DOVAR reports were submitted to the Mizan Regional Veterinary Laboratory Centre; of these, 1,888 (99.34%) were zero reports, and 12(0.66%) PPR outbreaks report with a total of 528 number cases and 212 number deaths were recorded, of which seven (n=7, 58.33) had been confirmed by a laboratory test and the remaining five (41.67%) were reported as suspected PPR outbreaks.
Figure 2.
Seasonal occurrence of PPR disease outbreak by months of the year.
Table 1.
Morbidity, mortality, and CFR of PPR outbreak in the reported district.
| District reported PPR outbreak | Number of PPR outbreak | Population at risk | Number of cases | Number of deaths | Morbidity rate% | Mortality rate% | Case fatality rate % |
|---|---|---|---|---|---|---|---|
| Bero | 1 | 18972 | 46 | 13 | 0.24 | 0.07 | 28.26 |
| Gachit | 2 | 45995 | 66 | 20 | 0.14 | 0.04 | 30.30 |
| Gesha | 1 | 3000 | 6 | 0 | 0.2 | 0 | 0 |
| Gewata | 1 | 111038 | 80 | 60 | 0.07 | 0.05 | 75 |
| Gureferda | 1 | 12000 | 16 | 0 | 0.13 | 0 | 0 |
| Masha | 1 | 850 | 9 | 4 | 1.05 | 0.47 | 44.44 |
| Meenit Shasha | 1 | 6915 | 6 | 0 | 0.09 | 0 | 0 |
| Mizan Aman | 1 | 2500 | 23 | 11 | 0.92 | 0.44 | 47.83 |
| Yeki | 1 | 350 | 15 | 5 | 4.29 | 1.43 | 33.33 |
| Zaba gazo | 2 | 111433 | 261 | 99 | 0.23 | 0.09 | 37.93 |
| Grand total | 12 | 313053 | 528 | 212 | 0.17 | 0.07 | 40.15 |
Figure 3.
PPR reported outbreaks occurrence based on species category.
Table 2.
Age-associated risk factors for the occurrence of PPR outbreak in the study area.
| Age category | Sum of number of cases | Sum of number of deaths | Case Fatality Rate% |
|---|---|---|---|
| Young | 9 | 4 | 44.44 |
| Adult | 23 | 11 | 47.83 |
| All age | 496 | 197 | 39.72 |
| Grand total | 528 | 212 | 40.15 |
Relatively high numbers of PPR outbreaks were recorded in March, April, and July months of the year as shown in Figure 2 below. The morbidity, mortality, and CFR of the PPR outbreak varied from one district to the other, and it ranged from 0.07%–4.29%, 0%–1.43%, and 0%–75%, respectively. The impact of PPR disease outbreaks was summarized in Table 1 below by its mortality, morbidity, and CFR.
Figure 4.
Sex-associated risk factors for the occurrence of PPR outbreak in the study area.
Among the 12 PPR outbreaks reported in the study period 50% of them showed both caprine and ovine were affected (Fig. 3). Many of the reported PPR outbreaks revealed both male and female sexes and all age groups of sheep and goats were affected by the disease as shown in Table 2 and Figure 4 below. The majority of the PPR outbreaks were sent from the mixed crop-livestock farming system, as described in Figure 5. below.
Eight hundred and eighty-three thousand seven hundred and seventy-two (883,772) doses of PPR vaccination were administered in different zones of the region (551,800 doses as prophylaxis and 331,972 doses as controlling) as shown below in Figure 6. A high number of PPR outbreaks (n=6, 50%) were recorded in the western part of the region at Mirab omo and Bench Sheko zone.
Discussion
The present study shows except konta zone, PPR disease occurs in a sporadic outbreak form across all zones of the region. The spatial analysis demonstrated that a high number of PPR outbreaks were recorded in the Mirab omo and Bench Sheko zones, and these two zones accounted for 50% (n=6) of the regions, total PPR outbreaks. The high prevalence of PPR outbreaks in these areas might be, as the Mirab Omo zone geographically shares an international border with endemic and many PPR outbreak recorded countries, South Sudan, and vice versa uncontrolled livestock movement favors the transmission and emergence of frequent new outbreak in the area. This research supports the findings of Girma et al. [15], Gebre et al. [16], and Shichibi et al. [4] who showed that PPR is a significant disease in Mirab Omo and Bench Sheko zones indicating the circulation of PPR virus in many districts in that area. According to data on PPR outbreaks throughout the research period, the year 2022 had more outbreaks than any other year and this might be associated with the increased reporting rate of DOVAR by its quality as well as by quantity from the districts, and the increment of regional laboratory response for confirming reported suspected outbreak by laboratory diagnosis.
Figure 5.
PPR disease outbreak occurrence in different sheep and goat farming systems.
Figure 6.
Prophylactic and control PPR vaccination was conducted from 2018 to 2022.
Figure 7.
Map shown the spatial distribution of the PPR outbreak in South West Ethiopia Region.
The occurrence of PPR outbreaks in relation to age, sex, and species of animals shows no remarkable difference. Although there have been occasions when sheep have been more seriously affected than goats [18], generally, goats appear to be more vulnerable to and more significantly affected by clinical diseases than sheep [19].
More PPR outbreaks (n=6, 50%) than any other season of the year were noted during March to April. The movement of sheep and goats to market, particularly during the popular religious holidays ceremony of Easter for Christians and Arefa for Muslims, in March and April, may be linked to the occurrence of more PPR outbreaks in these months. The seasonality of animal movements could be responsible for the PPR incidence in Ethiopia, which mostly occurs between the months of March and June [20]. On the other hand, from April to August, there is a lot of rain, a number of sheep and goats are maintained on only a small area of land, and more animals will come into contact, which is conducive to the spread of the disease. This finding is in line with Mbyuzi et al. [21] who reported a significantly higher incidence of PPR as reported by farmers in the rainy season than dry season in Tanzania [21].
The current study showed that disease occurred in a higher proportion in mixed sheep and goat farming system than the pastoral and peri-urban farming system. This result is consistent with research by Ruget et al. [22], who showed that highlands had a higher risk of PPR outbreaks than lowland pastoral areas by asserting that the pastoral production system, which is mainly found in the lowlands, acts as a PPRV reservoir and that the virus frequently spreads to the highlands through herd movements.
The variation of PPR disease morbidity shown might be associated with the farming system, flock and herd size present, the biosecurity linked with the knowledge, attitude, and practice of disease prevention and control of the farmers. This finding is in agreement with Alzuheir [23] who reported a PPR mortality rate ranging from 0.9% to 3.5%, in Palastine. However, comparatively higher mortality and morbidity rates were reported by Jember [24] from north Ethiopia during an outbreak study with 50.3% and 21.6%, respectively, in sheep and 51.3% and 25.1%, respectively, in goats in the study flocks [24].
Commencement of PPR vaccination increased in the year 2021 and 2022. The increased commencement of PPR vaccination in the aforementioned year may be associated with controlling many outbreaks and for preventing the spread into the adjacent area by considering the risk analysis. Conducting PPR vaccination at endemic populations as well as high-risk areas using surveillance and epidemiological data is more advantageous compared to the commencement of vaccination to all susceptible sheep and goats as it requires huge cost [25].
Conclusion and Recommendations
PPR disease outbreak has been widely occurred and reported in 10 out of the 44 districts of South West Ethiopia Region in the study period. Many outbreaks of the diseases were recorded from March to July, which is more of the early rainy season of the year, and in the mixed crop-livestock farming system than the other production system. The economic impact associated with morbidity and case fatality of the disease is relatively high and varies among districts. Commencement and coverage of PPR vaccination in sheep and goats have increased in the region as more outbreak cases confirmed in recent years. Based on this conclusion the following recommendations are forwarded: -
- Precaution should be taken in these identified risk factors for the occurrence of PPR disease outbreaks.
- Strengthening surveillance and awareness creation to the producer and for kebele and district animal health officer for notifying suspected PPR outbreak immediately to the regional veterinary laboratory service for ensuring timely outbreak investigation to avoid reporting of suspected PPR outbreak by monthly DOVAR.
- Appropriate controlling and prevention strategies of PPR disease should be implemented as the outbreaks reported in most zones of the region.
- Further research on PPR disease epidemiology should be conducted.
Acknowledgments
The author is grateful to his adviser, Dr. Eskeziawu Binalfewu, for his support, advice, direction, insight, and constructive feedback on his research work.
The author also likes to thank the Ministry of Agriculture’s Epidemiology Directorate, FAO, and USAID for financial support for this study through the in-service applied veterinary epidemiology training Programs (ISAVET).
