This year, several graphic images of rodents in supermarkets across New Zealand, from Dunedin and Christchurch to Auckland, were revealed. Therefore, the Public Health Communication Centre Aotearoa has examined the ecology of rodents and their connection to human health.
Historically, rodents and humans have coexisted for years, and their existence was one of the early reasons for the domestication of cats.
Four species of rodents have been introduced into New Zealand: the house mouse (Mus musculus) and three species of rats: the kiore (Rattus exulans), brown rat (R. norvegicus), and black rat (R. rattus).
While the kiore is mostly restricted to a few offshore islands, the other three species are distributed across the main islands.
Rodents can harm human health in many ways. They contaminate food and the environment with their saliva, urine and faeces, which can carry pathogenic microbes.
The most commonly reported illness linked to rodents in the country is leptospirosis due to L. borgpetersenii sv Ballum and L. interrogans sv. Copenhageni.
Leptospirosis can vary from having no symptoms to a severe illness that may be life-threatening. Both mild and severe leptospirosis are highly underdiagnosed.
Mice and rats are the maintenance hosts for L. borgpetersenii sv. Ballum and L. interrogans sv. Copenhageni, respectively. Contact with rodent urine, such as farmers handling rodent-contaminated animal feed, people working in pest control, and the general population dealing with rodents in their homes are at risk.
Pet rodents are also increasingly popular. While there is no direct evidence linking a pet rodent to a case of leptospirosis in New Zealand, overseas reports suggest a possible relationship.
Supermarkets are very attractive for rodents because they contain a lot of food and hiding places. For every rodent seen during the day, 20 to 50 individuals are estimated to remain unseen.
Contaminated ready-to-eat foods carry an exceptionally high risk to human health. Bacterial pathogens such as non-typhoidal Salmonellae can grow on contaminated foods above 5.2°C. Climate change and extreme weather events will likely increase rodent populations and adversely impact humans.
Finding evidence of rodent activity in human food can be very upsetting, and all businesses involved in the food supply chain require pest management strategies combined with stringent food safety standards and a zero-tolerance policy for rodent sightings.
New Zealand has successfully eradicated rodents from approximately a third of its offshore islands; however, achieving the 2050 predator-free goal may require different approaches or technologies.
