Genomic Dissection of an Icelandic Epidemic of Respiratory Disease in Horses and Associated Zoonotic Cases

• Published in: mBio
• Main Authors: Sigríður Björnsdóttir, Simon R. Harris, Vilhjálmur Svansson, Eggert Gunnarsson, Ólöf G. Sigurðardóttir, Kristina Gammeljord, Karen F. Steward, J. Richard Newton, Carl Robinson, Amelia R. L. Charbonneau, Julian Parkhill, Matthew T. G. Holden, Andrew S. Waller
• Format: Article in Journal/Newspaper
• Language: English
• Published: American Society for Microbiology 2017
• Subjects: Icelandic horse; Streptococcus zooepidemicus; epidemiology; genome analysis; respiratory pathogens; zoonotic infections; Microbiology; QR1-502; Iceland
• Online Access: https://doi.org/10.1128/mBio.00826-17; https://doaj.org/article/0d6edb155b2d4c4ca3bb829aa21879f8

ABSTRACT Iceland is free of the major infectious diseases of horses. However, in 2010 an epidemic of respiratory disease of unknown cause spread through the country’s native horse population of 77,000. Microbiological investigations ruled out known viral agents but identified the opportunistic pathogen Streptococcus equi subsp. zooepidemicus (S. zooepidemicus) in diseased animals. We sequenced the genomes of 257 isolates of S. zooepidemicus to differentiate epidemic from endemic strains. We found that although multiple endemic clones of S. zooepidemicus were present, one particular clone, sequence type 209 (ST209), was likely to have been responsible for the epidemic. Concurrent with the epidemic, ST209 was also recovered from a human case of septicemia, highlighting the pathogenic potential of this strain. Epidemiological investigation revealed that the incursion of this strain into one training yard during February 2010 provided a nidus for the infection of multiple horses that then transmitted the strain to farms throughout Iceland. This study represents the first time that whole-genome sequencing has been used to investigate an epidemic on a national scale to identify the likely causative agent and the link to an associated zoonotic infection. Our data highlight the importance of national biosecurity to protect vulnerable populations of animals and also demonstrate the potential impact of S. zooepidemicus transmission to other animals, including humans. IMPORTANCE An epidemic of respiratory disease affected almost the entire native Icelandic horse population of 77,000 animals in 2010, resulting in a self-imposed ban on the export of horses and significant economic costs to associated industries. Although the speed of transmission suggested that a viral pathogen was responsible, only the presence of the opportunistic pathogen Streptococcus zooepidemicus was consistent with the observed clinical signs. We applied genomic sequencing to differentiate epidemic from endemic strains and to shed light on the rapid ...