Assessing the potential of plains zebra to maintain African horse sickness in the Western Cape Province, South Africa.
Authors: Porphyre Thibaud, Grewar John D
Journal: PloS one
Summary
# Editorial Summary: African Horse Sickness Persistence in Zebra Populations African horse sickness (AHS) represents a significant trade barrier for equine exports from endemic regions, and South Africa's Western Cape Province—currently disease-free except for sporadic outbreaks—faces a potential risk from zebra populations, which are considered the natural reservoir for AHS virus. Porphyre and Grewar developed a sophisticated hybrid mathematical model incorporating age and sex structure in plains zebra populations, with transmission dynamics driven by local rainfall and temperature conditions, to determine whether zebra could sustain AHS circulation year-round. Their modelling revealed critical population thresholds: coastal zebra populations would need to exceed 2,500 individuals for AHS to persist beyond two years, while inland populations would require a minimum of 500 individuals, and the coastal population would need at least 50,000 zebras for true endemicity to become established. Since existing zebra populations in the Western Cape fall well below these critical thresholds across both coastal and inland regions, the probability of AHS establishing itself following a single introduction into local zebra is extremely low, effectively eliminating zebra as a realistic long-term infection reservoir for domestic horses in the province. For equine professionals operating in or trading from the Western Cape, this modelling provides valuable reassurance that zebra populations do not pose a significant endemic risk to horse health, though continued surveillance remains prudent given the sporadic outbreak history.
Read the full abstract on PubMed
Practical Takeaways
- •The presence of zebra populations in the Western Cape is not a significant epidemiological barrier to disease control efforts for AHS in horses
- •Current zebra population sizes in the Western Cape do not support ongoing AHS circulation, reducing the risk of sporadic horse outbreaks from wildlife reservoirs
- •Trade and movement restrictions for equids from the Western Cape based on zebra-maintained AHS risk are not scientifically justified by population dynamics
Key Findings
- •Plains zebra populations in the Western Cape Province are too small to maintain endemic AHS circulation from a single introduction event
- •Coastal zebra populations would require >2,500 individuals for AHS to persist >2 years, even with infectiousness >50 days
- •Inland zebra populations would need ≥500 individuals or unrealistic infectiousness duration for AHS to become endemic
- •Risk of AHS persistence in local zebra populations is extremely low and unlikely to serve as a year-round infection source for horses