Unseen Threats in the Water

Understanding the Pathogen

Leptospirosis is caused by spiral-shaped bacteria belonging to the genus Leptospira. There are hundreds of different strains, known as "serovars," which are adapted to different maintenance hosts, including rodents, cattle, sheep, pigs, and native wildlife.

Recent research in Australia has shown a shift in the bacterial strains infecting dogs. While Serovar Copenhageni was traditionally considered the primary threat, recent serological studies suggest that Serovar Australis is replacing it as the most common cause of canine leptospirosis in several regions.

The bacteria thrive in warm, moist environments. Once shed into the environment via the urine of an infected host, Leptospira can survive for weeks to months in stagnant water, damp soil, and mud. While dogs are the companion animal most at risk, cats can occasionally be infected, though the disease in felines is rarely reported and typically very mild.

The Australian Landscape: A Shifting Threat

Historically, leptospirosis in Australia was primarily considered an occupational hazard for farmers and abattoir workers, heavily concentrated in the tropical and subtropical regions.

However, the epidemiological map has shifted dramatically over the past decade:

• The Urban Spread: Between 2017 and 2023, significant clusters of canine leptospirosis emerged in Greater Sydney (particularly the Central and Northern beaches), the NSW South Coast, and parts of Victoria and Tasmania; 79 canine cases were acquired in New South Wales alone (and 190 human cases over a similar period), despite the fact that prior to 2017 there had been no published cases of clinical leptospirosis in NSW dogs since 1976. Further cases of canine leptospirosis have been reported in NSW every year since.
• Climate Drivers: Climate change has been implicated in the geographical spread of canine leptospirosis. Research indicates rising temperatures, increased humidity and extended periods of heavy rainfall/flooding create ideal conditions for the Leptospira bacteria to thrive and spread.
• Rodent Populations: Flooding displaces rat and mouse populations, forcing them into closer proximity with residential areas and dog parks. As primary carriers of the bacteria, their urine contaminates local puddles, lakes, and backyards.

Transmission and Clinical Signs

How Dogs Contract the Disease

Dogs are typically exposed to leptospirosis through direct or indirect contact with contaminated environments. The bacteria cannot penetrate intact, healthy skin; instead, they enter the body through:

• Mucous membranes (the lining of the eyes, nose, or mouth) when a dog drinks from or swims in a contaminated puddle, lake, or slow-moving waterway.
• Abrasions or cuts on the skin while walking through contaminated mud or floodwaters.
• Ingestion of tissue from an infected animal or carcass (such as a hunted rat).
• Bite wounds from an infected animal.
• Placental transfer (rarely) from a pregnant female to her puppies.

Symptoms and Progression

Once inside the body, the bacteria rapidly multiply in the bloodstream and spread to vital organs, primarily targeting the kidneys and the liver. The clinical signs of canine leptospirosis vary considerably. Some dogs show only mild, transient illness, while others rapidly develop multisystemic organ failure.

Mortality Rates and Prognosis

Leptospirosis is a life-threatening medical emergency. The prognosis depends heavily on the strain of the bacteria, the dog's immune response, and how quickly aggressive medical intervention is initiated.

The overall fatality rate for infected dogs in Australia is estimated between 40% and 53%. However, during severe localized outbreaks, mortality has spiked to devastating highs of 70% to 88%. Death typically occurs due to severe Acute Kidney Injury (AKI), extensive liver damage, or severe lung disease and bleeding disorders.

There is hope, however. With prompt intensive care, survival rates can exceed 50%. For dogs severely affected by kidney failure, survival rates can climb to over 80% if they receive specialist dialysis (renal replacement therapy).

It is important to note that dogs that survive the acute phase may still face long-term health consequences. A significant percentage of survivors are left with permanent chronic kidney disease requiring lifelong management. This high rate of morbidity and the reliance on intensive treatments underscores why preventative vaccination is so crucial.

Diagnosis and Treatment

Diagnosing leptospirosis quickly is vital but challenging. Vets typically rely on a combination of clinical suspicion, blood work (showing elevated kidney and liver enzymes), and specific specialized testing, such as PCR Testing (detecting bacterial DNA) and the Microscopic Agglutination Test (MAT, which measures the antibody response).

If leptospirosis is suspected, veterinarians will not wait for test results to begin treatment. The standard care involves:

• Antibiotic Therapy: Intravenous antibiotics are used initially to stop the bacteria from multiplying, followed by a long course of oral antibiotics to clear the bacteria from the kidneys and prevent the dog from becoming a chronic carrier.
• Intensive Supportive Care: Dogs require continuous hospitalization with intravenous fluid therapy to support kidney function, anti-nausea medications, and sometimes feeding tubes or blood transfusions.
• Specialist Referral (Dialysis): Given that specialist intervention can push survival rates above 80%, we may recommend referring your dog to a veterinary specialist center. Advanced facilities can provide 24/7 critical care, including dialysis to support the kidneys while they heal from the infection.

Prevention: The Core of Protection

Preventing leptospirosis relies on a two-pronged approach: environmental management and vaccination.

1. Environmental Management

• Limit Exposure: Prevent dogs from drinking from or swimming in high-risk waterways like marshy areas, slow-moving rivers, or stagnant ponds.
• Rodent & Wildlife Control: Keep properties free of food waste to deter rodents, and discourage your dog from hunting rats, mice, or eating carcasses.
• Post-Rain Care: Be particularly vigilant after periods of high rainfall or flooding. Wash your dog with tap water if they walk through floodwaters.

2. Vaccination Strategies

Historically, leptospirosis was not considered a "core" vaccine for all Australian dogs. However, due to recent outbreaks, the 2024 WSAVA guidelines now highly recommend it for dogs in at-risk areas or those with access to stagnant water, livestock, or rodents.

• The Schedule: Dogs require an initial primary course of two vaccines, administered 2 to 4 weeks apart. Note: If traveling to a high-risk area, the final dose must be given at least two weeks prior to travel for optimum protection.
• Annual Boosters: The bacterial leptospirosis vaccine provides shorter-lived immunity than viral vaccines. A strict annual booster is required. If your dog is overdue, the initial two-dose course must be restarted.