Prevalence of pathogenic Leptospira spp. in sheep in a sheep-only abattoir in New Zealand

Abstract

AIM: To determine the prevalence of the two most commonly diagnosed pathogenic Leptospira spp. serovars, Hardjobovis and Pomona, in sheep in a sheep-only abattoir in New Zealand, and to determine the prevalence of kidneys which were leptospire culture-positive collected from sheep seropositive or seronegative to the microscopic agglutination test (MAT).

METHODS: A repeated cross-sectional observational study was conducted of serological and kidney culture prevalences of Leptospira borgpetersenii serovar Hardjobovis and Leptospira interrogans serovar Pomona. Lines of sheep and individual sheep were systematically randomly selected at a sheep-only abattoir during 18 May 2004 to November 2004 and 06 December 2004 to 14June 2005. Additionally, a cross-sectional study examined prevalences in a purposively selected line of sheep from a flock with clinical evidence of an outbreak of leptospirosis.

RESULTS: In the study population of 15,855 sheep of which 2,758 were sampled, 5.7 (95% CI=4.9–6.7)% were seropositive to one or both serovars; 44.2 (95% CI=34.6-54.2)% of 95 lines of sheep and 44.9 (95% CI=35.0-55.3)% of 89 farms showed serological evidence of infection. The serological prevalence of serovar Hardjobovis was significantly higher than that of serovar Pomona both at line (33% and 4%, respectively) and individual (5% and 1%, respectively) levels. A low but persistent seroprevalence of Hardjobovis throughout both years suggested low-level endemicity to this serovar, whereas Pomona infections appeared to besporadic. Leptospires were isolated from kidneys of 8/37 (22%)Hardjobovis- and 1/6 (17%) Pomona-seropositive, and 5/499(1%) seronegative animals. Of the animals purposively sampled from a farm with a clinical outbreak of leptospirosis, all kidneys from the 13 seropositive animals were culture-positive, indicating a high risk of exposure of meat workers in outbreak situations. Kidneys of MAT-seropositive sheep were 21.7 (95% CI=7.6–61.9) times more likely to test culture-positive than kidneys from animals with negative MAT titres. In general, the results indicated that 13/1,000 sheep slaughtered were potentially shedding leptospires.

CONCLUSIONS: The study demonstrated the presence of a definite risk of occupational exposure of meat workers in a sheep-only slaughterhouse to the two most commonly diagnosed pathogenic Leptospira spp. serovars in New Zealand.

KEY WORDS:

• Leptospirosis
• sheep
• Harjobovis
• Pomona
• MAT
• meat workers

Acknowledgements

The authors would like to acknowledge MIRINZ Food Technology and Research Incorporated, the Massey University Research Fund, the Sheep and Beef Society of the New Zealand Veterinary Association, Schering-Plough Animal Health, and Virbac for funding this research. We also extend our appreciation and thanks to the management and staff of Lamb Packers Ltd, Feilding, New Zealand, for their support and cooperation during sampling; Gribbles Veterinary Pathology, Palmerston North, New Zealand, for serological testing; friends and colleagues from the Epicentre and Institute of Veterinary, Animal and Biomedical Sciences at Massey University for assisting in collecting samples; and three anonymous referees whose comments contributed to the final version of the manuscript.