Friday, March 29, 2024

Late vaccination brings potential health risks

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Healthier stock, protected staff, and peace of mind are some big pluses for acting early when vaccinating calves this spring against leptospirosis.
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Dr Roger Marchant, veterinary advisor to the New Zealand Veterinary Association’s Leptosure programme, said NZ needed to continue to do more to drop its ranking from the top of the OECD for having the highest rate of human leptospirosis infections.

Recent data showed NZ had 100 cases of the notifiable disease reported annually. However the disease was estimated to be under-reported by as much as 40 times, and could be mistaken for a bad case of flu if not diagnosed properly.

“If that ranking was not enough to give pause for concern, then the recent research on how critical it is to vaccinate livestock early against the disease should be,” Marchant said.

Traditionally calves have not been vaccinated until about six months old.

However a pilot study conducted at Massey University in 2012 highlighted the risk of calves becoming infected with leptospirosis before vaccination.

If they were already infected, the vaccine wouldn’t protect either the infected animal or those working around it.

“That study was a wake-up call. It showed that the age of vaccination appears to be critical to the vaccine being able to do its job and prevent infection.”

“Extrapolating from the pilot study, a calf vaccinated at the traditional six-month mark could be up to eight times more likely to be shedding lepto as an adult, compared to a calf vaccinated at 10 weeks of age.”

A good rule of thumb in vaccinating earlier was to plan on giving the first vaccine shot 70 days after the planned start of AB calving, followed with the second booster vaccination four to six weeks later.

“You don’t want to start any sooner, or you run the risk that the protective antibodies from the mother will interfere with the vaccine’s effectiveness. Any later and they will have run out and the calf, if exposed to infection, is unprotected.”

Many calves were at risk of infection from a very young age as protection from colostrum was highly variable and short-lived in most calves. Delaying vaccination put calves at risk of infection and long-term shedding. This could result in infected cows entering the milking herd.

Marchant said vets, farmers, and farm staff faced the greatest risk of contracting leptospirosis from ineffectively vaccinated young stock.

Hamilton employment law expert and lawyer Andrea Twaddle said farmers were not always aware of their responsibilities regarding leptospirosis.

“Under the Health and Safety in Employment Act, employers have a general duty to take ‘all practicable steps to ensure the safety of employees while at work’”, she said.

They were required to identify and assess hazards, implementing controls or isolating those that might cause serious harm.

“It is practicable to vaccinate stock against leptospirosis, and therefore this should be considered by farmers on farms identified as at risk of the disease.”

Failing to take a basic step like vaccinating livestock for leptospirosis could make an employer liable for claims for health and safety breaches by a staff member, and the employer risked being pursued by Work Safe.

The new knowledge about needing to vaccinate early had been built into a revised leptospirosis “Leptosure” best practice plan.

It emphasised the earlier vaccination times, covered the risks for other livestock, and offered advice specific to an individual farm’s risk situation.

Backing up the Leptosure programme were vaccines proven to prevent leptospirosis if administered prior to infection.

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