Serological reactions against Leptospira interrogans serovars in New Zealand horses.

This research aims to determine the presence and frequency of Leptospira—a type of bacteria with several serovars or variants—in New Zealand horses. High concentration of certain serovars were found in tested horses, suggesting occasional infections, but there is no conclusive evidence of the horses being maintenance hosts for the bacteria.

Details of the Research

• The research was set off by a high concentration of the serovar ‘copenhageni’ of Leptospira interrogans bacteria, as well as lesser concentrations of others, found in a horse that recently had an abortion. Two associated horses also showed high concentrations of ‘hardjo’, another serovar.
• This discovery led scientists to conduct a more comprehensive study, as existing literature on Leptospira in New Zealand’s horses was limited.
• Three sets of serum samples were tested using the Microscopic Agglutination Test (MAT) against eight serovars to figure out the range of the bacteria in New Zealand horses. Among these serovars, ‘copenhageni’, ‘pomona’, ‘hardjo’, ‘tarrasovi’, as well as ‘ballum’, are usually found in New Zealand. The serovar ‘balcanica’, isolated from possums and known to cross-react with ‘hardjo’, was excluded from the study.

Sampling and Outcomes

• The first group of tested samples, numbering 380, were general submissions received by the Regional Animal Health Laboratories in 1988.
• The second group, consisting of 200 samples, were received by Ruakura Animal Health Laboratory between 1989 and 1990.
• The third group, with 182 samples, was received by the Central Animal Health Laboratory from January to May 1990.
• Based on the specificity of agglutination at 25% or higher, substantial reactions were detected against ‘pomona’, ‘copenhageni’, ‘hardjo’, and ‘bratislava’ serovars.
• Smaller reactions to other serovars, including the ones not known to be native to New Zealand, were also detected but these data were not conclusive.
• The research indicates that horses in New Zealand do occasionally experience Leptospira infections, though it is unlikely for them to serve as reservoir hosts for the bacteria.

Significance of the Research

• This is one of the few studies conducted about Leptospira in horses in New Zealand.
• The study sets a background for potential future research by providing data about the horse population’s exposure to leptospirosis.