OBSERVATIONS OF LEPTOSPIROSIS IN FARMED DEER

Aims. Slaughterhouse and on-farm surveys were undertaken to investigat e some aspects of leptospirosis (Leptospira interrogans) in farmed dee r in the lower North Island of New Zealand. Methods. Blood samples and kidneys were collected at slaughter from 601 1-year and older red and red x Wapiti stags and 21 adult hinds from 53 farms (10 or 12 deer pe r farm). Serum samples were analysed for up to seven leptospiral serov ars. Gross and histological examinations of kidneys were undertaken. K idneys from 202 deer were cultured for leptospires. A follow-up postal questionnaire (68% response) indicated one herd had been vaccinated p rior to the survey. Serological analyses were also carried out on seru m bank samples from a previous on-farm survey involving male and femal e weaner, yearling and adult red deer from 16 commercial deer farms in March and November. Results. Serological reactions at titres greater than or equal to 96 to serovar hardjo were present in 73.6%, pomona in 41.5%, copenhageni in 11.3% and tarassovi in 15.1% of farms from the slaughterhouse survey. Antibodies to serovars australis, ballum and ba lcanica were present in three, one and four of six herds studied, resp ectively. Titre prevalence to hardjo was higher than that of pomona an d other serovars within farms. Cultures for Leptospira were positive i n 10 stags from six lines with similar prevalence across age groups. H istological examination showed many gross lesions were associated with mild interstitial cellular infiltration characteristic of subclinical leptospiral infections. Some sections from culture-positive kidneys c ontained spirochetes in renal tubules. The on-farm survey showed a 10- 30% within-herd prevalence of pomona and hardjo titres in 56% of 3-mon th-old deer herds, but, by 11 months of age, 100% of herds were titre- positive with high prevalences to one or both serovars. Concurrently, herds of 1-year-old and adult deer on the same farms were all seroposi tive. Conclusion. This study has shown that leptospiral infections are common in farmed deer in the survey area.