Study on Molecular Characterization and Pathogenesis of Peste des Petits Ruminants Virus (PPRV) in selected sites of Ethiopia
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Date
2025
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Addis Abeba University
Abstract
Background: PPR has emerged as a significant and high-priority livestock disease in Ethiopia. A relatively recent study indicated that the disease leads to economic losses amounting to 14% of the yearly household income, posing a serious threat to the livelihoods of livestock owners. In connection to the worldwide significance of PPR, the FAO and WOAH developed a global strategy in 2015 to eradicate the disease by 2030. In alignment with this framework, countries such as Ethiopia have devised their own plans to achieve eradication by setting the same target year. However, over five years of control efforts, PPR outbreaks persist in Ethiopia and continue to expand into regions that were previously unaffected. This phenomenon coupled with others necessaitates to the need and urgency of investgating the factors that influence the continued presence of the virus in the field. One of the potential factors is the involvement of non-target host species, such as cattle, which may play a significant role in the epidemiology of PPR. Furthermore, much of the current understanding of PPR pathology and pathogenesis is derived from research on closely related viruses, such as the rinderpest (RP) virus signifying knowledge gap in the area. oreover, updated knowledge of circulating PPRV lineages/strains and their virulence profiles is essential for targeted and effective PPR control and eradication efforts in
Ethiopia. Objectives: This study aimed to identify factors hindering the success of ongoing PPR control and eradication efforts in Ethiopia and beyond. The first study addressed whether infected cattle shed enough PPRV to transmit the virus to seronegative small ruminants or other seronegative cattle while also evaluating the role of cattle in PPR epidemiology. The second study aimed to investigate PPRV tissue tropism, shedding patterns, pathogenesis, clinical progression, and comparative pathology in goats and cattle to support the development of more effective surveillance and control strategies. The third study aimed to identify circulating strains and compare their virulence in an experimental setting. Such insights could aid in strategic planning for more effective disease control. Methodology: The first experimental study aimed to investigate the role of cattle in PPR epidemiology by using both empirical and model-based approaches. The trial was conducted at the Animal Health Institute (AHI) experimental facility. Local virus strains, lineage IV isolate Ethiopia/Habru/2014) and animal breeds were used in the study. The first experiment consisted of five consecutive trials involving 15 sheep, 66 goats, and 37 cattle, with a total of 118 animals. To simulate natural transmission, sheep and goats were administered 1 ml of viral suspension, while cattle received 2 ml, all via the intranasal inoculation route. Similarly, the second experimental study was conducted using local breeds of goats and cattle, along with a locally circulating PPRV strain. A total of 32 animals, with 16 from each species, were included. Samples were collected from live animals, as well as postmortem samples from purposivelly sacrificed goats and cattle. In goats, sampling was performed daily, while in cattle, it was conducted at predetermined intervals. Finally, an experimental study was conducted on 21 goats, including both experimental and control groups, to assess the virulence of six PPRV strains
circulating in specific regions of Ethiopia. Samples were collected from both live and sacrificed goats at predetermined intervals for further analysis. All animals used in the experiments were serologically negative for PPR, allowed to acclimatize for 10–15 days, randomly assigned to experimental barns, and analyzed using various diagnostic techniques. Results: Studies on the role of cattle in the epidemiology of PPR demonstrated that the animals can naturally contract the virus through contact with infected goats, though they typically exhibited only mild and short-lived clinical symptoms. This indicates that cattle play a limited
role in PPRV transmission due to the fact, cattle-to-goat transmission being rare, even when the animals share the same space for extended periods. While qRT-PCR detected PPRV RNA in a virusinfected sentinel calf, attempts to isolate the virus were unsuccessful. Additionally, cattle that were experimentally inoculated or housed with PPRV-infected goats did seroconvert. These findings underscore the need for further investigation into the mechanisms that may restrict disease development and viral shedding in this species. A comparative pathology study of PPRV in goats and cattle revealed moderate level of clinical signs in goats while, no obvious symptoms among cattle. Instead, cattle experienced a subclinical infection, suggesting they could act as silent carriers of the virus. The significant difference in clinical manifestations between the two species (P-value = 0.0070) underscores the variation in host responses to PPRV infection. Although the successful isolation of live PPRV from cattle samples was limited, it raises the need to reassess the epidemiological role of cattle in PPRV transmission. These findings indicate that under certain conditions, cattle could serve as potential reservoirs or silent spreaders of the virus. However, further research is needed before applying these results to other PPRV lineages or regions beyond the currently circulating lineage-IV PPRV in Ethiopia. Investigation of comparative virulence of locally circulating PPRV strains in indigenous goats, demonstrated that five out of six strains displayed typical PPR clinical signs, with the exception of one lineage-IV strain (designated as 38920/19), which only caused a mild nasal discharge. Goats inoculated with viruses from two different lineages, lineage-IV and lineage-III, exhibited nearly identical clinical outcomes, indicating that lineage classification alone may not be a reliable predictor of disease severity. The observed reduction in virulence in one strain may be attributed to inherent biological differences or technical factors related to laboratory procedures. Conclusions: The present study considered in-depth examination of various factors and insights that could potentially affect theongoing PPR control and eradication efforts, highlighting key areas for further research and consideration. The study on the role of cattle in PPRV epidemiology suggests that local breed (zebu) in mixed-species environments play a limited role in transmitting PPRV to sheep and goats. The detection of PPRV RNA in a naturally infected sentinel calf, despite failed virus isolation attempts, highlights the need for further comparative studies on both cattle and goats. A comparative pathology study of PPRV in goats and cattle provides evidence of subclinical infections and live virus shedding in cattle, suggesting that
under certain conditions, cattle may play a more active role in PPRV epidemiology than previously recognized. However, the current study relied on a single local lineage (L-IV) limits the broader applicability of the findings to other strains and regions. To enhance understanding of PPRV, further research should investigate additional virus strains and their virulence characteristics. The comparative virulence study of Ethiopian PPRV strains reveals similar virulence profiles across lineages (L-III and L-IV) in local goats, indicating that lineage classification alone may not reliably predict clinical outcomes. This finding is essential for informing regional disease control strategies.
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Keywords
Cattle, comparative virulence, pathogenesis, experimental, goats, PPR, PPRV, strain characterization, virus transmission