By JOAN HENSON
In the last 12 months one Sydney vet diagnosed five of the six determined cases of inner city dog leptospirosis – a disease that kills canines – by performing advanced testing, despite rare reports of local cases.
Leptospirosis can be transmitted to animals and humans, and rodents are common carriers – but the source of Sydney’s outbreak is unknown, leaving the media speculating and experts perplexed.
The vet, Dr John Smith (not his real name), has presented his findings to researchers at the University of Sydney (USYD), who have commenced research into the outbreak.
Their study will identify any strains of leptospira bacteria involved, its source, and whether exposed dogs and cats are healthy shedders of the disease, or clinically infectious. The second stage, which will involve testing city rats and establishing their local density, is being planned.
Dr Smith says the first dog he diagnosed had vague symptoms: it was not eating, was quiet, and vomited occasionally. A blood test revealed the dog’s liver and kidneys were affected. “As I was driving to work, the potential for leptospirosis came to me. I had a couple of hundred dollars, maximum, to play with. I put the money towards that test because of the symptoms, and because the liver and kidneys were both affected. It was positive.”
He has diagnosed two cases in the last few weeks, and three last year. The 2018 cases were in Surry Hills, and the recent two were in Surry Hills and Darlinghurst. The sixth case was diagnosed in Glebe by USYD. All dogs died or were euthanised.
The City of Sydney has doubled public rat baits to 860 stations, while the RSCPA is offering free vaccines for one strain of leptospirosis until the end of August. Vaccines against multiple strains are offered overseas.
The media has speculated that flooding around light rail construction and more rats, may have fuelled the outbreak. Experts say it’s unlikely.
Professor Michael Ward from Sydney School of Veterinary Science, says “the classic big scale climate event that would precipitate a leptospirosis outbreak,” exposing people and animals to contaminated flood waters, has not occurred in Sydney. Further, leptospirosis is endemic to tropical and subtropical wildlife, but not known to be endemic to Sydney wildlife.
Peter Banks is a Professor of Conservation Biology at USYD. He says “there’s not really any evidence that we are seeing more rats,” as major drivers of rat numbers have not changed. He says that it is more likely that recently observed rats have been displaced.
The mark recapture study he expects to complete, as part of the USYD study into the outbreak, could indicate whether rat numbers have increased. He says this could be the first inner city study of rat numbers.
Professor Ward says that “if the leptospira bacteria is coming from rodents, something has prompted more exposure, either directly between rodents and dogs, or in a common environment.”
He says another possibility is that a Sydney wildlife species is reservoir to a strain of leptospirosis and has increased in population, thereby exposing dogs.
Scientists have limited information about leptospirosis because the bacteria is hard to isolate in samples, making it hard to study. There are over a thousand strains but only about six that are recorded as causing domestic animal and human disease.
Professor Ward says there is likely a lot more exposure in dogs than disease, because antibodies can exist in healthy dogs that will “shake off infection.”
Dr Smith says he consistently took precautions to work with relevant authorities as he diagnosed the leptospirosis cases, despite the fact that the disease is not legally notifiable for animals in NSW. He was also not aware in May that USYD had diagnosed a case of the disease.
He says “there is a chance this has been underdiagnosed,” as hepato-renal failure is often attributed to toxicity and other viral diseases.
USYD Lecturer Dr Christine Griebsch, from the School of Veterinary Science, is heading research into the outbreak.
She has invited pet owners to participate in the first stage of the study, which includes a “pilot regional blood sample… of leptospira exposure in healthy and in-contact dogs and cats.”
The invitation says that a preventative plan depends on identifying the causative strain and its distribution.
If the available vaccine does not match the strain, an overseas vaccine might be used, or in the case of a new strain, a new vaccine may need to be developed.
In the meantime, dog owners are being urged to vaccinate their dogs with the available vaccine.
Dr Smith says that he has been alarmed by the spread of inaccurate online information claiming that the vaccine is ineffective, and has tried to keep his clients and the public abreast of the facts.