Myonecrosis caused by double infection of S. equi subspecies zooepidermicus and Clostridium novyi type A in a horse

Summary: This case report describes the lesions and clinical findings in a horse sent to the Clinical Veterinary Hospital of the University of Extremadura for an infected wound, on the lateral aspect of the left hind limb. The infection was caused by Streptococcus equi subsp. zooepidemicus and Clostridium novyi type A, a bacterial co-infection that could eventually lead to synergistic infection and fatal myonecrosis. It is possible that prior infection with aerobic or facultative bacteria, such as Streptococcus equi subsp. zooepidemicus, as part of the bacterial flora of horses, may promote, by creating a low potential redox environment, the germination of Clostridium novyi type A spores. To the best of the authors' knowledge, this is the second report of Clostridium novyi type A as a causative agent of myonecrosis in horses. The anaerobic bacteria involved in clinical cases may be underreported due to the difficulty and inefficiency of culturing these microorganisms on some occasions.