Natural Heterobilharzia americana infection in horses in Texas.

Summary

# Editorial Summary: Natural Heterobilharzia americana Infection in Horses in Texas Heterobilharzia americana, a trematode parasite previously documented in dogs and wildlife across the southeastern United States, has recently emerged as a cause of hepatic granulomatous disease in horses. Researchers used molecular diagnostics (PCR amplification and DNA sequencing targeting the parasite's ribosomal RNA gene) to confirm H. americana infection in liver tissue samples from 12 horses presenting with hepatic granulomas identified either post-mortem or via surgical biopsy, with positive amplicons detected in 8 cases and confirmed species identity in 5 of those. Most notably, the parasitic granulomas were incidental findings in 10 of the 12 horses, suggesting that H. americana infection may be more prevalent in equine populations than previously recognised yet often subclinical or asymptomatic. For equine practitioners, this work establishes the need for heightened awareness of schistosome infection as a differential diagnosis in horses with unexplained hepatic pathology, particularly those in endemic regions, whilst also highlighting that such findings may not necessarily explain presenting clinical signs—requiring careful correlation between parasitological findings and clinical presentation.

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Key Findings

• •H. americana was identified in 8 of 11 horses (73%) with hepatic granulomas using PCR amplification and sequencing
• •Sequenced amplicons from 5 positive horses showed 100% identity with H. americana
• •Hepatic granulomas were incidental findings in 10 of 12 horses and not the primary clinical disease

Conditions Studied