Passive transfer of naturally acquired specific immunity against West Nile Virus to foals in a semi-feral pony herd.
Authors: Wilkins Pamela A, Glaser Amy L, McDonnell Sue M
Journal: Journal of veterinary internal medicine
Summary
# Editorial Summary: Passive Transfer of West Nile Virus Immunity in Foals When mares naturally exposed to West Nile Virus seroconvert, they develop humoral immunity that can be transferred to their foals through colostrum, potentially protecting neonates during their vulnerable early months; however, the efficacy of this naturally acquired maternal protection had never been formally evaluated. Researchers measured serum neutralisation titres against WNV and total IgG concentrations in 17 mare-foal pairs from a semi-feral pony herd in an endemic area where vaccination was not practised, using statistical correlation to assess the relationship between maternal and foal antibody levels. In foals with adequate passive transfer of immunity, maternal and foal WNV-specific titres showed exceptionally strong correlation (Spearman's rho = 0.84, R² = 0.91), with over 90% of foal titer variation explained by the dam's titer, though notably one foal failed to achieve adequate total IgG transfer entirely. These findings demonstrate that naturally acquired WNV-specific antibodies are reliably transferred to foals born to seroconverted mares, suggesting that in endemic regions, dams with natural exposure history may provide meaningful early immunological protection—though practitioners should recognise that this passive transfer depends critically on adequate colostral uptake, and protection will wane as maternal antibodies decline over the first months of life.
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Practical Takeaways
- •Foals born to mares with natural WNV exposure in endemic areas passively acquire specific immunity through colostrum, providing potential protection against clinical disease
- •The strong correlation between mare and foal antibody titers suggests dam serostatus can help predict foal protection levels in WNV-endemic regions
- •This natural passive immunity mechanism may influence vaccination strategies in endemic areas where multiple mares have seroconverted through natural exposure
Key Findings
- •Mare and foal WNV neutralization titers were significantly correlated (Spearman's rho = 0.84; P < 0.001) in foals with adequate passive transfer
- •Over 90% of foal titer variation was explained by mare titer (R² = 0.91; P < 0.001)
- •IgG concentration was not significantly different between seropositive and seronegative foals (P = 0.24)
- •Passive transfer of naturally acquired WNV-specific immunity occurs in pony foals born to seroconverted dams in endemic areas