Surging levels of leptospirosis infections in people have animal and human health authorities on alert in regions severely affected by flooding, as the disease lingers into the new farming season.
Disease monitoring by the Institute of Environmental Science and Research puts New Zealand’s current rate of human leptospirosis infection at 3.5 per 100,000 people, well up on last year’s 2.4 per 100,000. This is being driven strongly by infections in areas affected by long-term rainfall and Gabrielle’s flood impact.
From February to May this year Hawke’s Bay, Tairāwhiti and Waikato all reported significantly elevated levels of infection, with Hawke’s Bay reporting 25 cases in March alone.
Year to date, 106 people have been infected with the disease, with over half of those, 54, coming from Tairāwhiti and Hawke’s Bay district health regions. In March a higher-than-average number of patients were hospitalised by the disease.
At the current reported infection rate this year may prove the worst since 2017, when 140 people were affected.
The increased incidence in humans is another sting in Cyclone Gabrielle’s tail and confirms Massey University researchers’ concerns raised earlier this year about elevated disease risk.
They predicted that, a month after the flooding, rodent-borne disease outbreaks could start to appear with a strain of leptospirosis carried by rats, and livestock carrying several others.
The disease has the ability to survive in water and soil for several weeks after being shed in the carrier animal’s urine. It is not always easily detected in livestock, but it can be a debilitating disease when contracted by humans.
The significant lifts in the rate of human infections have prompted the Ministry for Primary Industries’ animal health endemic team to notify vets of the elevated risk of the disease spreading in livestock.
John Meban of Eastland Vets in Gisborne said the extended wet weather suffered by the region over the past 18 months does much to explain the increased incidence of leptospirosis.
“Our expectation is that will continue with all the surface flooding and water all around us”.
He said his suspicion is a leptospirosis strain is cycling through local sheep populations.
“You see sick animals when they pick up another strain, often the pig strain Pomona in cattle, which can cause abortion storms. We have seen a bit of leptospirosis in finishing lambs this year too.”
In Hawke’s Bay, VetsOne director and vet Mike Newall has also seen elevated levels of leptospirosis infections in traded lambs, and he has just had a dairy farming client hospitalised with it for four days.
“There are certainly more cases of it about than we have seen in the past.”
Both vets have been urging farmer clients to consider vaccination of their dairy and breeding cattle. Newall estimates 90% of his dairy clients have herds vaccinated but the rate is only 50% in beef herds.
Massey University veterinary epidemiologist Dr Emilie Vallee said Hawke’s Bay has always been a hot spot for leptospirosis infection, with meatworkers particularly susceptible. She said overseas experience suggests infection rates should drop after the flood event, usually after one to two months.
“These infections seem to be livestock related, judging by the strains being reported.”
She said human infection is a strong signal that the disease is present in the livestock population, with a traditional peak through early spring still to come.
Work by Vallee’s colleague Dr Jackie Benschop, funded by the Health Research Council, has shed more light on NZ’s leptospirosis transmission, and its effects.
Why worry about leptospirosis?
Leptospirosis is a bacterial disease transmitted through contact with the urine of infected animals to humans and consists of several strains carried by livestock and rodents.
The Health Research Council funded research conducted by Massey University that highlighted the disease’s debilitating effect on people.
The study was on 96 of the 244 people contracting leptospirosis between 2019 and 2021. The people affected by it were spread evenly across dairy, drystock, mixed, meat works and “other”.
Nearly all victims reported fatigue, fever, and headaches including hallucinations, and most also had nausea and diarrhoea. The majority of victims reported continuing problems with fatigue eight months after contracting the disease.
Two-thirds had to be hospitalised for an average of four nights, and 20% ended up in intensive care.
Massey University veterinary epidemiologist Dr Emilie Vallee said researchers hope to learn more from the Gabrielle experience to inform future flood responses.
She urged farmers to ensure livestock are vaccinated where possible, to make sure rodent control programmes are in place, to cover cuts, and to seek medical care when feeling unwell.