Authors: Greenwood Sarah, Chow-Lockerbie Betty, Ramsauer Sophie, Wachoski-Dark Garrett, Knight Cameron, Wobeser Bruce
Journal: Veterinary pathology
Summary
Equus caballus papillomavirus type 2 (EcPV-2) has long been implicated in equine genital squamous cell carcinomas, yet its broader epidemiology in asymptomatic populations remains poorly characterised. Greenwood and colleagues investigated EcPV-2 prevalence across Western Canadian horses by measuring seropositivity in 50 healthy animals, detecting EcPV-2 DNA via PCR across multiple tissue types collected at necropsy from 70 clinically normal horses, and localising active viral infection through RNA in situ hybridisation. The authors identified asymptomatic EcPV-2 infection in 29% of horses examined, with seropositivity indicating exposure in 36% of the healthy cohort; notably, viral RNA was concentrated in genital tissues (penis 35%, vulva 15%) but also detected in unexpected sites including the eyelid (12%), oral mucosa (11%) and muzzle skin (10%), whilst the discovery of infected fetuses provided the first evidence of vertical transmission in horses. This substantially higher prevalence compared to previous studies likely reflects the authors' use of deep tissue biopsies rather than superficial swabs, suggesting that EcPV-2 is far more widespread in asymptomatic horses than previously appreciated and that its pathogenic mechanisms in genital SCC development may be considerably more nuanced than the current literature implies. For practitioners, these findings underscore the need for heightened vigilance regarding subclinical EcPV-2 infection and its potential role in both reproductive disease and unexpected cutaneous or ocular lesions, whilst also raising important questions about transmission routes and disease progression in apparently healthy animals.
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Practical Takeaways
- •EcPV-2 infection is common and usually asymptomatic in horse populations—most infected horses will not develop clinical disease
- •Genital SCC development from EcPV-2 exposure appears to be multifactorial; infection alone does not predict cancer development
- •Tissue biopsy sampling is more sensitive than superficial swabs for detecting viral infection; consider this when investigating potential papillomavirus cases
Key Findings
- •EcPV-2 asymptomatic infection prevalence was 29% (20/70) in Western Canadian horses, higher than previously reported
- •Seropositivity to EcPV-2 was 36% (18/50) in healthy horses, indicating widespread exposure
- •EcPV-2 DNA was most prevalent in genital tissues (penis 35%, vulva 15%) but also detected in eyelid, oral mucosa, and muzzle skin (10-12%)
- •Evidence of vertical transmission documented for the first time, with EcPV-2 detected in equine fetuses