African horse sickness in naturally infected, immunised horses.
Authors: Weyer C T, Quan M, Joone C, Lourens C W, MacLachlan N J, Guthrie A J
Journal: Equine veterinary journal
Summary
# Editorial Summary: African Horse Sickness in Vaccinated Horses Immunisation against African horse sickness (AHS) has long been considered protective, yet questions remain about breakthrough infections and their epidemiological significance in endemic areas. Researchers monitored 50 Nooitgedacht ponies in open camps over two years, collecting weekly blood samples and rectal temperatures whilst using real-time RT-PCR to detect AHSV RNA, thereby capturing both clinical and subclinical infections in vaccinated animals under natural field conditions. Over the study period, 16% of the immunised herd became infected with AHSV—with the concerning finding that half of these cases (8% of the total population) presented with no clinical signs whatsoever. This distinction matters considerably: subclinically infected animals may remain viraemic and potentially transmit virus to unvaccinated or naïve horses whilst escaping detection through conventional clinical monitoring. For practitioners working in endemic regions, these findings underscore the limitations of vaccination as a sole control strategy and suggest that immunised horses warrant closer epidemiological scrutiny, particularly when managing mixed or adjacent herds where disease status may be uncertain.
Read the full abstract on PubMed
Practical Takeaways
- •Vaccinated horses in AHS endemic areas can still become infected with the virus; vaccination reduces but does not eliminate infection risk, requiring continued disease surveillance
- •Subclinical infections in vaccinated horses represent a potential hidden reservoir for virus transmission; consider this when assessing herd immunity and disease control strategies
- •Regular testing of vaccinated horses for AHSV RNA may be warranted in endemic regions to detect and manage subclinical infections that could contribute to disease spread
Key Findings
- •16% of immunised horses in an AHS endemic area were infected with AHSV over a 2-year period despite vaccination
- •8% of the immunised horses experienced subclinical AHSV infection, demonstrating breakthrough infections without clinical signs
- •Half of all AHSV infections in vaccinated horses were subclinical, indicating silent viral circulation in immunised populations
- •Subclinical cases in vaccinated horses may have epidemiological significance for AHS transmission dynamics in endemic regions