25 July 2002
Research projects commissioned by MAF and Ministry of Health into a disseminated outbreak of a 'new to New Zealand' strain of Salmonella between 1998 and 2002 have been completed.
The research was conducted by scientists from the Institute of Environmental Science and Research (ESR) and Massey University and covered both human and animal impacts of the outbreaks.
Matthew Stone, Exotic Disease Co-ordinator for the Ministry of Agriculture and Forestry (MAF) said the research provided a valuable insight into the risks associated with introduction of foreign salmonellae and why strong links between animal and human health scientists are required to investigate instances of disease transmission across species.
"This outbreak has provided an opportunity for MAF, Ministry of Health, Department of Conservation and research scientists from ESR and Massey University to be involved in an outbreak response and subsequent studies for a disease with clear human health and environmental implications."
Dr Stone said an important outcome from the study was the need to develop an integrated interagency approach to salmonellae surveillance in New Zealand.
"The research showed that there are limitations in the New Zealand surveillance of animal Salmonella infection. The systems in place for data collection on positive samples and isolates referred to the national salmonellae reference laboratory at ESR for definitive typing need to be strengthened. "
Although tests confirmed that the particular strain of Salmonella Typhimurium DT160 was new to New Zealand they were unable to show how the disease entered the country or its origin.
Dr Stone said possible means of introduction included migratory birds or imported contaminated animal feed, or human travellers.
"There is a reservoir of infection of DT160 in sparrows and probably other birds now. Infections in other animals and humans will continue as a result of infection acquired from this source," he said.
Because the strain is now widely dispersed in the environment, people should be reminded that safe food handling practices are essential, both in the home and in food businesses, to prevent food borne illnesses.
Douglas Lush from the Ministry of Health recommended that people avoid, where possible, contact with wild birds, including dead birds, or food and water contaminated with infected bird droppings. If contact is unavoidable they should wash their hands afterwards.
The symptoms of salmonella infection are stomach cramps, fever, vomiting and diarrhoea. Anybody with these symptoms should see a doctor.
Salmonella Typhimurium DT160 was first isolated from a child in Christchurch in 1998. Since then, it has rapidly become an important human infection. In 2001 the strain was the cause of 34% of the total cases of salmonellosis in New Zealand.
In 2000 the strain was determined as a cause of spring die-off in sparrows in Christchurch, and in subsequent years was associated with die-off in other regions. The strain has now been isolated from a wide range of other animals and birds.
MAF remains interested in investigating the cause of unusual bird deaths. Reports of unexplained bird mortality events involving more than 20 birds should be reported to the MAF Exotic Disease Hotline 0800-809-966.