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

• Published in: mBio Vol. 8; no. 4
• Main Authors: Björnsdóttir, Sigríður, Harris, Simon R, Svansson, Vilhjálmur, Gunnarsson, Eggert, Sigurðardóttir, Ólöf G, Gammeljord, Kristina, Steward, Karen F, Newton, J Richard, Robinson, Carl, Charbonneau, Amelia R L, Parkhill, Julian, Holden, Matthew T G, Waller, Andrew S
• Format: Journal Article
• Language: English
• Published: United States American Society for Microbiology 01.08.2017
• Subjects: Animals; Disease Outbreaks - veterinary; Epidemics; epidemiology; genome analysis; Genome, Bacterial; Horse Diseases - epidemiology; Horses; Humans; Iceland - epidemiology; Icelandic horse; respiratory pathogens; Respiratory Tract Infections - epidemiology; Respiratory Tract Infections - microbiology; Respiratory Tract Infections - transmission; Respiratory Tract Infections - veterinary; Streptococcal Infections - epidemiology; Streptococcal Infections - microbiology; Streptococcal Infections - transmission; Streptococcal Infections - veterinary; Streptococcus equi - genetics; Streptococcus equi - isolation & purification; Streptococcus zooepidemicus; Zoonoses; zoonotic infections; epidemiology; respiratory pathogens; zoonotic infections; Icelandic horse; genome analysis; Streptococcus zooepidemicus
• ISSN: 2161-2129; 2150-7511
• DOI: 10.1128/mBio.00826-17

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 subsp. ( ) in diseased animals. We sequenced the genomes of 257 isolates of to differentiate epidemic from endemic strains. We found that although multiple endemic clones of 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 transmission to other animals, including humans. 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 was consistent with the observed clinical signs. We applied genomic sequencing to differentiate epidemic from endemic strains and to shed light on the rapid transmission of the epidemic strain throughout Iceland. We further highlight the ability of epidemic and endemic strains of to infect other animals, including humans. This study represents the first time that whole-genome sequencing has been used to elucidate an outbreak on a national scale and identify the likely causative agent.