Friday, March 29, 2024

Lepto doesn’t differentiate

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Research on leptospirosis in New Zealand and the United Kingdom shows the disease is not picky or restricted to one farming sector.
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It doesn’t matter if you are a dairy farmer or a drystock farmer, the risk of contracting leptospirosis is on par according to a study from Massey University and the University of Warwick in England. And the flow-on effect puts meat workers at risk due to the poor vaccination uptake in drystock farming.

“Our main finding was that drystock farmers contributed approximately equal numbers of cases of leptospirosis as dairy farmers, but dairy farmers was a more frequently recorded class of occupation,” professor of veterinary public health and lead author of the study Jackie Benschop says.

“People contract leptospirosis from infected animal urine, and knowing the patient’s occupation is critical to combating the spread of the disease, such as by using livestock vaccination to reduce human contact with infected animal urine.”

They have also uncovered meat workers are most often notified with the two serovars most frequently contained in livestock vaccines – Hardjo and Pomona – and they have no agency in relation to the vaccination status of the stock they process.

“The lack of vaccinating in drystock inadvertently exposes meat workers to risk, as they come into direct contact through yarding, slaughtering and processing a large number of unvaccinated animals,” she says.

“Monthly data from our research shows that drystock farmer infections peak in August, which is likely due to increased animal contact at spring lambing and calving. The meat worker peak is in September and may be associated with the return of workers to begin processing the new season lambs after winter shutdown.”

Massey and Warwick Universities have been working on the research using routinely collected surveillance data from NZ’s notifiable disease database (EpiSurv) of cases from January 1, 1999 to December 31, 2016.

The new research has found the patient’s occupation was only recorded accurately in two thirds of cases in surveillance data taken between 1999 and 2016 when there were a total of 1557 cases. But when leptospirosis patients are interviewed to collect surveillance data and they identify their occupation as a farmer, there is a need to more finely differentiate their type of farming.

“This detailed occupational data collection is important as it has implications for leptospirosis prevention and control strategies. Livestock farmers, notably dairy and drystock, need to be differentiated as there are some specific risks,” she says.

Benschop says drystock farming encompasses the pasture grazing of beef cattle, sheep, deer for meat and wool and velvet production. In comparison, dairy cattle are often fed a pasture-based diet and supplement when required to balance their feed intake, are often milked twice daily for nine months of the year.

She says the dairy system relies on much more direct animal-human contact and although approximately 99% of dairy farms in NZ have a leptospirosis vaccination programme in place for their cattle, drystock vaccination rates are much lower.

“Although drystock farmers do not have daily contact with their animals, they are still exposed to the disease through calving cattle and deer,” she says.

“Our work provides important evidence for reassessing how little leptospirosis vaccinations are used in drystock. Vaccination programmes applied to drystock should help reduce the high proportion of meat workers and drystock farmers being infected with the serovars in the vaccines.

“The effectiveness of such a vaccination programme has been demonstrated to reduce the incidence of ‘dairy farm fever’ in dairy workers in the past 40 years,” she says.

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