The prevalence of Dermatophilus congolensis in horses with pastern dermatitis using PCR to diagnose infection in a population of horses in southern USA.

This study aimed to investigate the link between D. congolensis, a bacteria usually associated with pastern dermatitis in horses, and the actual prevalence of infection in horses in southern USA. Using a reverse transcription quantitative PCR test, the researchers found that D. congolensis was uncommonly associated with pastern dermatitis in their test population.

Objective

The primary aim of this research was to identify whether D. congolensis is associated with pastern dermatitis in horses. The researchers sought to validate the common assumption that D. congolensis is implicated in the cause of pastern dermatitis.

• The involved horses were all client-owned, with 15 diagnosed as suffering from pastern dermatitis and 8 unaffected horses as controls.
• A cross-sectional study was performed, including a recording of each horse’s history and physical examination findings.
• In addition, samples were collected for cytological evaluation and RT-qPCR testing for D. congolensis.

Methods and Results

• The study followed a thorough methodology to gather a detailed dataset. Alongside RT-qPCR, dermatophyte culture and superficial skin scrapings were also conducted.
• Expectantly, 10 of the 15 horses suffering from pastern dermatitis had feathered pasterns.
• Contrary to popular belief, D. congolensis was found in only one nonfeathered horse, but not in any with feathered pasterns. This surprising finding was made through the RT-qPCR test.
• Cytology helped to identify bacteria in all horses but failed to detect any organisms resembling D. congolensis.
• The skin scrapings revealed that four feathered horses were positive for Chorioptes mites, a parasite of the skin.
• Interestingly, there were no observed dermatophytes on the fungal culture test.
• All the test results from the eight control horses were negative.

Conclusions

• The results led to the conclusion that D. congolensis was less commonly associated with pastern dermatitis in the studied population of horses than previously thought.
• On the other hand, Chorioptic mange, caused by Chorioptes mites, was commonly associated with pastern dermatitis in feathered horses and was, therefore, considered an important potential cause for this clinical presentation.