Histological findings in corneal stromal abscesses of 11 horses: correlation with cultures and cytology.

The research involves a comparative study of histopathology, culture results, and cytology from horses diagnosed with corneal stromal abscess, with the objective to understand potential discrepancies between these tests and uncover the real extent of microbial infection in these conditions.

Methods and Sample Population

• The study was conducted in two veterinary teaching hospitals – Auburn University and Ohio State University.
• It involved 11 horses that were diagnosed with corneal stromal abscess.

Findings

• No bacteria were isolated in the culture or seen on histopathology in any of the horses, suggesting that routine testing methods may fail to detect certain bacterial infections.
• The absence of visible bacterial organisms in the histological sections doesn’t necessarily mean they aren’t present. This could be a result of destruction of bacteria by neutrophils, macrophages, and antibiotic therapy reducing their numbers.
• Out of the 11 horses, 4 (36%) were diagnosed with fungal keratitis via histopathology, while 7 (64%) exhibited keratitis without any known causative agent.
• Corneal stroma of 9 horses (82%) had a dense infiltration of neutrophils, and 2 (18%) showed a primarily pyogranulomatous reaction.

Inferences

• Out of the 4 horses that showed histological signs of fungal infection, only 2 were positive for identifiable fungi on culture and cytology. This indicates that traditional culture techniques can sometimes fail to identify an existing fungal infection.
• The other 2 horses, despite testing negative for fungal culture, were still considered pathogenic because fungal hyphae were observed in the deeper layers of the corneal stroma surrounded by an inflammation, providing histological evidence of mycotic keratitis.
• In 3 out of 6 cases where fungi were recovered on culture, they were considered contaminants due to lack of evidence in the histopathological sections, suggesting the importance of a diagnostic combination for accuracy.

Conclusions

• The study emphasizes the role of histopathology and application of special stains in interpreting culture and cytology results.
• This holistic approach can greatly enhance the accuracy of diagnosis in cases of corneal stromal abscess in horses.