A cross-sectional investigation of Leptospira at the wildlife-livestock interface in New Zealand.

There has been a recent upsurge in human cases of leptospirosis in New Zealand, with wildlife a suspected emerging source, but up-to-date knowledge on this topic is lacking. We conducted a cross-sectional study in two farm environments to estimate Leptospira seroprevalence in wildlife and sympatric livestock, PCR/culture prevalence in wildlife, and compare seroprevalence and prevalence between species, sex, and age groups. Traps targeting house mice (Mus musculus), black rats (Rattus rattus), hedgehogs (Erinaceus europaeus) and brushtail possums (Trichosurus vulpecula) were set for 10 trap-nights in March-April 2017 on a dairy (A) and a beef and sheep (B) farm. Trapped wild animals and an age-stratified random sample of domestic animals, namely cattle, sheep and working dogs were blood sampled. Sera were tested by microagglutination test for five serogroups and titres compared using a Proportional Similarity Index (PSI). Wildlife kidneys were sampled for culture and qPCR targeting the lipL32 gene. True prevalence in mice was assessed using occupancy modelling by collating different laboratory results. Infection profiles varied by species, age group and farm. At the MAT cut-point of ≥ 48, up to 78% of wildlife species, and 16–99% of domestic animals were seropositive. Five of nine hedgehogs, 23/105 mice and 1/14 black rat reacted to L. borgpetersenii sv Ballum. The sera of 4/18 possums and 4/9 hedgehogs reacted to L. borgpetersenii sv Hardjobovis whilst 1/18 possum and 1/9 hedgehog reacted to Tarassovi. In ruminants, seroprevalence for Hardjobovis and Pomona ranged 0–90% and 0–71% depending on the species and age group. Titres against Ballum, Tarassovi and Copenhageni were also observed in 4–20%, 0–25% and 0–21% of domestic species, respectively. The PSI indicated rodents and livestock had the most dissimilar serological responses. Three of nine hedgehogs, 31/105 mice and 2/14 rats were carrying leptospires (PCR and/or culture positive). True prevalence estimated by occupancy modelling in mice was 38% [95% Credible Interval 26, 51%] on Farm A and 22% [11, 40%] on Farm B. In the same environment, exposure to serovars found in wildlife species was commonly detected in livestock. Transmission pathways between and within species should be assessed to help in the development of efficient mitigation strategies against Leptospira. Author summary: Leptospirosis is a bacterial disease that can be transmitted through the urine of infected animals. Recently, the number of human cases of leptospirosis in New Zealand has increased, and wildlife is suspected to be an emerging source. To better understand this, a study was conducted on two farms in New Zealand. Wild animals, including mice, rats, hedgehogs, and possums, and domestic animals, including cattle, sheep, and working dogs, were captured, and tested for exposure to Leptospira. We found multiple serovars of leptospirosis throughout both livestock and wildlife, with important variation by species and age class. Reactions to Ballum were found in all domestic and wild species and all ages while domestic animals, possums, and hedgehogs commonly reacted to Hardjobovis. Cattle, sheep, hedgehogs, and possums also showed exposure to Tarassovi. These indicate potential multiple and complex pathways of disease transmission and dynamics among serovars and suggest that Leptospira infection in wildlife in New Zealand can pose a risk to both livestock and human health. Further research is needed to understand how the bacteria are being transmitted to effectively prevent the associated disease. [ABSTRACT FROM AUTHOR]