Christine Griebsch

University of Sydney photo

Dr. Christine Griebsch is a senior lecturer in small animal medicine at the University of Sydney.

Veterinarians in central Sydney are being urged to vaccinate dogs against leptospirosis amid a rare outbreak that has killed at least six pets in Australia's biggest city.

Leptospirosis is a bacterial infection that dogs typically pick up through contact with water contaminated by the urine of an infected animal, such as a rodent or other wildlife. The disease also may be transmitted through bites by or consuming an infected animal.

The disease can cause acute kidney failure and may also affect the liver. Survival rates vary, depending upon availability of treatment and severity of the infecting Leptospira type. Dogs can carry the bacterium without appearing ill. The bacterium can infect humans, too.

The six dogs confirmed to have contracted leptospirosis died or were euthanized, according to the University of Sydney. Two of the dogs succumbed to the disease last year; four more have died since May.

"The scientific literature suggests that more than 50% of infected animals usually survive an infection, though so far in Sydney the mortality rate is 100%," said Dr. Christine Griebsch, a senior lecturer in small animal medicine at the University of Sydney School of Veterinary Science.

It's unclear whether a particularly lethal type of Leptospira is at work or whether infected dogs with minor or no clinical signs simply have gone undiagnosed.

Of the six dogs that died, all experienced kidney problems. Of the two that were euthanized, one had seizures, and the other, bleeding.

The university has alerted all veterinarians in the city's central and inner western suburbs to encourage clients to bring in their dogs for leptospirosis vaccinations. Dog owners have responded with a surge in demand for the vaccine, according to Dr. Anne Fawcett, another lecturer at the School of Veterinary Science.

An investigative team at the university so far has collected at least 250 blood samples from healthy dogs presenting for vaccination and some potentially infected pets. Researchers aim to have the samples analyzed over the next few months. One serovar, or type — Leptospira copenhageni — already has been identified as the culprit in one of the six fatalities, Griebsch said. She stressed that more work needs to be done to assess whether other types are involved.

The inoculation currently being used in Sydney is based on the L. copenhageni serovar.

Investigators suspect the outbreak is linked to an ongoing bout of unusual construction activity, including on new major tram and train lines. The theory is that rats are being disturbed by the work and spilling out into residential areas.

Although it is possible that another animal could be transmitting the disease, rats are considered the most likely source.

The Sydney City Council has pledged to double the number of rat-bait traps in public areas.

The university is warning the public against laying their own rat poison due to the possibility that dogs will eat the poison (which happens with thousands of dogs in New South Wales state each year). Bait used by the council is encased in traps, typically posing a risk only to big dogs that can chew through the hard casings.

The outbreak has led to misinformation circulating among owners at dog parks about a "rat virus" and "rat AIDS," Fawcett told the VIN News Service.

"Dog owners are understandably concerned about the emergence of what they see as a 'new' disease," Fawcett said. "We are working hard to correct misconceptions."

Sydney's leptospirosis outbreak is a first for the city, although isolated infections have been reported in the past.

The rarity of the situation contrasts markedly from other parts of the world, such as Griebsch's previous home of Berlin, where leptospirosis is so common that canine vaccination is customary.

Triggers for outbreaks in other countries, such as Germany, have included heavy rainfall, which creates more puddles in which contaminated urine can collect, and in which dogs might play or drink.

New research shows that the health of rats themselves affects their risk of spreading the pathogen that causes leptospirosis. A study published in June by researchers at the University of Calgary in Canada — who sampled the rodents in Vancouver's improverished Downtown Eastside neighborhood — found that rats with illnesses or injuries, such as respiratory infections, heart disease, broken bones or bite wounds, were more likely to carry Leptospira. 

In humans, the bacterium can cause ailments ranging from a mild fever to kidney damage, meningitis, liver failure, respiratory distress and death, according to the U.S. Centers for Disease Control and Prevention. People are more likely to be infected in temperate or tropical climates and if they work outdoors or with animals.