New Zealand has the highest annual incidence of lepto in people among OECD countries. Massey University PhD student Emilie Valle said the disease posed a serious health issue to humans in NZ, with 70 cases diagnosed in people every year – 74% of which are farmers or meat workers.
Most of these infections are thought to arise from contact with livestock, with every second adult sheep and beef animal and every third deer being sero-positive.
Livestock data from a 2009-10 study of 161 sheep farms showed in a spot check of 20 animals a mob that 97% of mobs had evidence of infection, with at least one sero-positive animal – with a total of 51% of the animals antibody positive.
“So when you look from the roadside and see a sheep breeding flock, you can say infected, not infected, infected, not infected,” Heuer said.
“That’s the extent of leptospirosis in New Zealand. Almost all sheep have or have had an infection. And if you look at beef, it’s exactly the same. There is a massive presence of the bug.”
Heuer said that of the 50% sero-positive animals, 20-40% were shedding the bacteria, so 10-20% of all adult sheep and beef cattle were shedding the bacteria at any one time.
“So we have a high level of challenge in livestock and in exposure to people.”
Only a small fraction of incidences are reported with about 100 cases a year, with a possible 4000 cases that actually occur in the population.
When an animal is sero-postive it sheds on to the pasture and the bugs sit in the soil, surviving for several weeks until floods or high rainfall when higher levels of disease occur.
“In New Zealand there are many mixed farming systems, with sheep, beef cattle and deer often on the same pasture and when the water levels rise that’s when lepto cases come up.”
The number of contaminated carcases a meat worker was handling every day went up to 40-60 during a flood, Heuer said. “They have pretty massive exposure.”
He said research was still to be done on what effect lepto had on sheep production and reproduction.
“We don’t know the effect on sheep production. It’s thought to affect very early growth, but no effect later on.”
Research is also to be done on what wildlife is exposed to lepto and what role wildlife has to play in carrying the disease. “Are they just picking it up accidentally or are they maintaining it as a reservoir host?”
Heuer said it was important to do more research in this area to determine the effectiveness of control measures.
