The extended scheme, to be called Leptosure+, is a natural progression from the dairy programme which was launched in 2007, says NZVA veterinary advisor Roger Marchant.
“We would not be doing our job properly if we didn’t expand it from dairy,” he told Rural News.
The dairy version was recently revised with a key change being to start the vaccination programme with calves at 10-12 weeks after planned start of calving, as opposed to the traditional 6-month-old start (Dairy News, February 11).
It follows an NZVA-contracted review of the disease by Massey University which found some herd replacements are infected prior to vaccination and continue to shed the bacteria long after vaccination, putting people working with the animals at risk.
“We know that delayed vaccination is a risk because if an animal is exposed to the disease prior to vaccination, vaccination won’t eliminate the disease,” notes Marchant.
“And the longer we delay vaccination, the more chance the animal will be exposed to the bacteria.”
While most dairy herds are vaccinated, a pilot study suggests many will harbour a few of these cows that became infected before vaccination and consequently persistently shed the disease. That possibly explains a persistent residue of about 100 human cases/year since the late 1990s, after the toll had tumbled during the 1980s following the introduction of vaccines in the 1970s.
Marchant says a much larger study is planned to examine the risk such animals pose to farmers, farm staff, vets, and anyone else working with the stock.
“There’s no question about the efficacy of the vaccine; what we’re looking at is the efficacy of the vaccination programme.”
Given the lack of vaccination outside the dairy industry, young stock grazed on non-dairy farms may well be exposed to infection and if they haven’t had their sensitiser and booster vaccination, may contract it.
“On a good percentage of sheep and beef farms there’s evidence the animals have been exposed to leptospirosis at some stage,” notes Marchant.
Massey University’s Professor of veterinary epidemiology and infectious diseases, Cord Heuer, has collated the figures. Depending on the season and year, antibody tests show 60-90% of flocks have been exposed to leptospirosis, but that range is based on a sample of just 20 adult sheep per farm.
“If we tested whole flocks we’d probably find they’d all been exposed to some extent,” Heuer told Rural News.
“The bottom line is that there’s a very high rate of exposure in our drystock.”
Tests on sheep, beef and deer farmers themselves found about 6% had been exposed to the disease.
The most widespread strain of the disease, L.Hardjo, is more or less benign in cattle and sheep so it’s quite possible no ill-effect will be seen in livestock. However, if people working with the stock contract L.Hardjo, consequences can be severe, even fatal (Rural News, Feb 4).
Hence, Heuer says, the main reason for vaccination is protection of people working with stock.
“Overall there was very little effect on productivity from the disease in sheep and beef. We did find an effect in deer, in both reproduction and growth rate, which was sufficient to get a good return on vaccination, but we couldn’t find that on sheep and beef farms.”
Besides the human protection element of a vaccination programme on drystock farms, Heuer says it could be a selling point for farms looking to contract rear dairy grazers: an effective vaccination programme would mean reduced exposure risk for the dairy farmer’s youngstock.
Some sheep and beef stud flocks are already vaccinating against Leptospirosis but NZVA would like to see wider uptake with appropriate veterinary advice to ensure vaccination programmes are effective.
Increasing farm size and more corporate farming also means there’s greater demand for a quality assurance programme.
