Salmonella Brandenburg - emergence of a new strain affecting stock and humans in the South Island of New Zealand

Abstract

AIMS: To report information on the spread of a new strain of Salmonella Brandenburg, which affected livestock and humans in the South Island of New Zealand, and a series of small case studies designed to investigate potential transmission of infection.

METHODS: Information on the occurrence and spread of S. Brandenburg in livestock was gathered from laboratory diagnostic submissions, from case studies on the faecal excretion rate in ewes, carrier status of black-backed gulls (Larus dominicanus), spread of S. Brandenburg organisms in sheep yards, infection in lambs going to meat plants, and from post-abortion pathological changes in the reproductive tract of ewes.

RESULTS: A newly recognised strain of S. Brandenburg was first diagnosed in aborting sheep from a flock in mid Canterbury in the South Island in 1996. Subsequently, the disease spread to other farms in mid and south Canterbury in 1997 and to Southland and Otago in the lower half of the South Island in 1998–2003. In 1999, the same strain was responsible for abortions in cattle and gastroenteritis in calves and adult cattle. The same strain of bacterium also caused disease in horses, goats, deer, pigs and humans. Spread of the disease on farms was strongly associated with aborting ewes, which resulted in considerable environmental contamination. During the abortion season, black-backed gulls appeared to spread the disease to other farms. Other potential sources of infection were carrier sheep, contaminated water sources and contaminated sheep-yard dust. Damage to the reproductive tract may affect the ability of surviving ewes to conceive.

CONCLUSION: Important features of this disease are its high morbidity and mortality within a flock or herd, rapid local spread and its role as an occupational, health and safety risk to farm workers and their families.

KEY WORDS:

• Salmonella Brandenburg
• epidemiology
• transmission
• sheep
• cattle
• horses
• goats
• deer
• dogs
• humans
• black-backed gulls

Acknowledgements

We wish to acknowledge the information provided by veterinary practitioners; the cooperation of the farmers involved in the projects and their veterinary practitioners; AgriQuality New Zealand staff for collecting samples; P Johnstone, AgResearch, Invermay, for statistical analysis; and MAF Policy for funding the projects. We also thank Meat NZ for allowing us to present some information from their programme; and to laboratory staff at LABNET Invermay Ltd, Labworks Animal Health Laboratory, ESR and Massey University for their contributions to these studies.