The pathology of experimental Corynebacterium equi infection in foals following intrabronchial challenge.

This research investigates the effect of Corynebacterium equi bacteria on foals (young horses), when administered directly into the bronchial airways. It shows that this can cause severe bronchopneumonia, and that vaccination does not protect against this. The study also details the various other damages caused by the bacteria, such as lung tissue destruction and inflammation. Further, it observes that large numbers of the bacteria are found in the lungs and lymph nodes even 17 days after infection.

Research Design and Methodology

• The experiment involved six foals, with some being injected directly into their bronchial tubes with a Corynebacterium equi bacterial solution. This direct application meant that the bacteria would directly affect the lung tissues and bronchial nodes of these foals.
• Half the foals were vaccinated against C. equi three weeks before being exposed to the bacteria. The other foals were not vaccinated and served as control subjects. By comparing between the vaccinated and unvaccinated foals, the efficacy of vaccination could be determined.

Experimental Outcomes

• All the foals developed severe bronchopneumonia, showing that vaccination against C. equi did not prevent the disease.
• Some foals were euthanized eight to nine days after infection for examination, while the others were euthanized at day 17. One control subject died at day nine due to disseminated intravascular coagulation, a condition where small blood clots develop throughout the bloodstream.
• The lungs and lymph nodes of the infected foals all had large numbers of C. equi bacteria, even the non-affected regions. These bacteria were also present in the spleen and liver, but in smaller quantities.
• The researchers noted some consistent effects of the bacteria: destruction of lung tissue, inflammation or edema, and inflammation of the lymph nodes. Oddly, one vaccinated foal developed pyogranulomatous colitis, an inflammatory bowel disease characterized by the formation of granulomas – clusters of immune cells formed in response to chronic inflammation.

Implications and Conclusions

• The lung lesions from the foals killed eight to nine days after infection were filled with various types of immune cells and the bacteria, indicating a vigorous immune response. Some small amounts of necrosis, or cell death, were noted in these regions.
• The lesions from the foals killed at day 17 showed extensive tissue destruction and a lack of fibrous tissue, which is usually indicative of healing. The fact that the same type of lesions was found in both the eight/nine-day and 17-day groups indicates a chronic and destructive effect of the bacteria in the lung tissues.
• The research concludes by comparing these results with those from naturally-infected foals, and suggesting that understanding these findings may help illuminate possible mechanisms of how the pneumonia develops in foals due to C. equi.