New research from Massey University has shown that mice are a critical yet underestimated source of leptospirosis on farms.
While current control measures of leptospirosis are tailored for livestock strains, the study underlined the need for strategies that address rodent-associated strains of the disease.
Lead researcher Dr Marie Moinet said data from the study showed that the risk of getting leptospirosis remained significant regardless of fluctuations in mouse density.
Even at lower densities, roughly nine out of 10 mice were infected, indicating a persistent risk.
“Additionally, infected mice tend to roam more extensively, potentially spreading the disease further. Increased awareness of mice as a source of leptospirosis is essential, especially since we are often in closer contact with them than we realise. The recent trend of mice sighted in supermarkets is a good reminder of that.”
Led by researchers from Te Kunenga ki Pūrehuroa Massey University, in collaboration with ecologists from the University of Auckland and wildlife vets from Brazil, the study aimed to assess the density of infected mice within populations and understand their implications for disease transmission on a broader scale.
Conducted over two years in a farm setting, the study involved humane trapping and testing of mice for leptospira. While focused on a specific geographic area, the findings call for similar studies in urban settings to fully grasp the disease’s urban environments.
The research provides new insights into wildlife disease dynamics, with mice being underemphasised as disease carriers in New Zealand.
Given the ubiquitous presence of mice across the country, their population sizes often go unnoticed until they reach outbreak level. Moinet said it heightens the risk for infection but misconception around the disease can cause further complications.
“Leptospirosis cases and strains have historically been linked to livestock, creating the misconception that it’s only a farmer’s disease. Contact with infected mammal urine or contaminated water poses a significant transmission risk, with house mice harbouring the prominent Ballum strain in recent cases.
“The lack of awareness sets a dangerous precedent for those not in direct contact with livestock to be misdiagnosed or not receive proper treatment despite the need of a timely diagnosis.”
Infected people can show a wide range of symptoms, from asymptomatic to severe, including headache, fever, meningitis and kidney failure. Two-thirds of reported cases result in hospitalisation, averaging four nights, with half experiencing long-lasting symptoms. Early diagnosis and antibiotic treatment is critical.
“While current control measures of leptospirosis are tailored for livestock strains, our study underlines the need for strategies that address rodent-associated strains. “Awareness is the key to mitigation, particularly among health care providers, as anyone in contact with mice, including trampers, gardeners and urban residents, is at risk,” Moinet said.
Professor Jackie Benschop said the research shows the need for comprehensive strategies to mitigate leptospirosis risk.
“The data reinforces previous findings linking rodent activity to disease transmission, marking the need for greater attention to rodent control to safeguard public health. Pest control measures should not be limited to times of high density, and it’s likely climate change and our recent flooding incidents will aggravate the problem.”
