A major outbreak of Streptococcus equi subsp. zooepidemicus infections in free-range chickens is linked to horses.

The study delves into an outbreak of Streptococcus equi subsp. zooepidemicus infections in free-range chickens, where it was discovered that horses were a likely source of infection. The infection led to a high mortality rate and changes in observed lesions, with the first detection of small-colony variants (SCVs) linked with the chronic phrase of the disease.

Outbreak of Infection

• The researchers reported a significant outbreak of Streptococcus equi subsp. zooepidemicus infections affecting 11,000 free-range chickens at the age of 47 weeks. This is remarkable as such infections in poultry have been rare in recent decades.
• The outbreak initially appeared as acute, turning into a chronic stage. It produced a steep mortality rate of approx. 80% within just 21 weeks. The swift nature of the outbreak and the high mortality rate indicates a severe health issue in the chicken population.

Introduction of Small-Colony Variants (SCVs)

• For the first time, the study reports on the small-colony variants (SCVs) of S. equi subsp. zooepidemicus associated with the chronic phase of the outbreak.
• SCVs may explain the sudden change in the lesions observed in the infected poultry, a development that the researchers probed to understand.

Source of Infection

• The researchers carried out comparison of partial sequences of rpoB, multilocus sequence typing and pulsed-field gel electrophoresis to determine the source of the outbreak. They found the isolates from chickens to be identical to the ones in horses kept on the same farm.
• These evidence led to the conclusion that horses were a probable source of the outbreak, indicating the potential of interspecies transmission of this disease.

Conclusions and Implications

• The findings of the study underscore the critical need for protecting free-range chickens from contact with other animals and birds that are known to host pathogens of significance to poultry.
• This enforces the importance of closely managing and monitoring inter-animal contact in farm environments, to prevent such cross-species transmission of diseases from happening in the future.