The delays in getting Sydney’s revived tram system up and running have gone on long enough to become the stuff of legend in New South Wales, but the development has thrown up a new problem in addition to the disruption of the seemingly never-ending construction phase: leptospirosis.
Leptospira bacteria can cause disease in humans and dogs which can be fatal. Leptospirosis is zoonotic so can be transferred between humans and dogs, but it is difficult to confirm transmission because the same serovars affect dogs as humans. Only three species of leptospira had been isolated until 1987 when sub-classification identified 19 species and 240-260 pathogenic serovars. Serovars can adapt to their local environment and, to some extent, their identification may vary according to the methodology used. Dogs in Europe are commonly exposed to the Icterohaemorrhagiae serogroups which are transmitted via infected rat urine whereas in Australia, the main vectors were usually other forms of wildlife. It seems that now however, the disruption to the local rat population caused by the building of the tram system in Sydney has enabled the bacterium to spread to the local dog population. The most commonly seen rats in Australia are the Black Rat (Rattus rattus) and the Brown Rat (Rattus norvegicus) . Both were introduced from ships arriving from Europe and Asia. The two native species, the Bush Rat (Rattus fuscipes) and the Water Rat, also known as a rabe or rakali (Hydromys chrysogaster) are unlikely to be seen in urban or suburban areas. People and other animals can become ill when the urine from and infected rat is present in water or soil that is then ingested or enters the body through a cut. It can also be spread though contact with infected blood or tissue.
Wood mice, bank voles, house mice and yellow necked mice can also carry the disease and, in common with rats, do not become ill. Rats living in confined, damp spaces such as sewers are more likely to be infected so it is thought that urban rodents are more likely to spread the disease.
So far, seven dogs have died in Sydney within 48-72 hours of being diagnosed, two of which had played in a park that had been flooded due to construction works.
The World Small Animal Veterinary Association (WSAVA) does not class the leptospirosis vaccine as being core so it is not recommended in all circumstances or geographical locations in spite of the fact that the World Health Organisation (WHO) classify it as the most widespread zoonotic disease in the world. It is not a notifiable disease in the UK. Dogs had therefore not been vaccinated as routine in new South Wales become none had ever been reported as being infected. However, the British Small Animal Veterinary Association (BSAVA) considers that leptospirosis is a core annual vaccine for dogs in the UK because they are at risk of contact with rodents and contaminated water and soil, especially in rural areas. The most common vaccines work against two serovars and there are three and four serovar versions available. Wet and warm conditions increase the chances of survival of the bacteria once they enter soil or water.
There has been some controversy spread in social media about the Lepto 4 vaccine but, although more common than in Lepto 2, adverse reactions are still extremely rare. The incidence of adverse reactions for all L2 vaccine products is 0.015% and for L4 0.069%. That means that fewer than 2 and fewer than 7 suspected adverse reactions were reported for each vaccine respectively in every 10,000 vaccines sold. Some were later found not to be attributable to the Lepto vaccination or could not be classified. Even if reactions are extremely minor (a little swelling at the injection site for a short period, for instance), it will be reported as an adverse reaction. That is not to say that worse reactions do not occur and can sometimes be fatal but, as with all vaccines, the risk of becoming very ill and dying from the disease is also very real and mostly far greater than the chance of an adverse reaction to the vaccine.
The morbidity rate for humans is one in every million in England and Wales and the mortality rate is up to 5%. Many people become infected due to prolonged contact with infected water or soil due to their occupation; the high profile case of the death of Olympic gold medallist Andy Holmes when leptospirosis resulted in multiple organ failure following a fall into a river during a rowing event shows how hazardous rivers can be. This is aggravated in times of flooding but also drought as shrinking areas of water concentrate the number of bacteria present.
Under-diagnosis, often due to differential diagnosis and self-limiting strains in the early stages, and the lack of obligation to report means that estimating the prevalence in the dog population is difficult so there are no available figures to date. Prevention still remains the best option. Dogs living near or with regular contact with water or woodland are most at risk. 14.61% of the 89 vets surveyed in the study mentioned above reported diagnosing leptospiris within the previous 12 months in n=13 dogs, 8 of which died either as a result or via euthanasia. All were under 10 years old. Only one of the dogs in the confirmed cases had been vaccinated but had not received a booster within the recommended 12 month period. Additionally, the practices that reported a lower general level of vaccination also reported higher rates of leptospirosis.
Some owners will vaccinate and then titre test their dogs to assess the level of antibodies still present before deciding whether to undertake booster vaccinations. This is not suitable for leptospirosis because the correlation between antibody levels and protection is poor and the antibodies do not persist for very long. Protection is advised as being valid for twelve months. It is not known whether natural infection results in life-long immunity. Vets will make decisions regarding the most suitable leptospiral vaccination regime by taking into account the knowledge of serovars in circulation locally, the ability of the available vaccines to provide effective coverage against the relevant serogroups, weather, flooding and environmental risks, the lifestyle of the dog, travel plans that may risk exposure to leptospirosis and public health considerations. However, a thesis written in 2014 found that only 60% of dogs attending vets had been given a vaccination. leptospirosis can be misdiagnosed in the early stages and, by the time that signs are unequivocal, mortality rate is likely to be high. Some serovars can be highly contagious. Infected humans can shed bacteria for up to a year after becoming infected and leptospira can cause abortions in cattle, sheep and pigs.
Signs of infection include:
- High fever (which can then drop)
- Gastroenteritis with vomiting and diarrhoea which may include blood
- Jaundice
- Dark urine
- Marked dehydration
- Congestion of the mucous membranes
- Lethargy
- Acute renal failure
- Death.
Bacteria and other organisns are engaged in a constant “arms race” and there is always the risk that a new strain may appear and prove fatal. Even when dogs have been vaccinated, access to potential sources of exposure should be reduced by ensuring that dogs avoid drinking from, wading or swimming in fresh or stagnant water and marshland. Leptospirosis dies when exposed to bright sunlight and in temperatures above 20ºC (68°F), so dogs should definitely be kept away from stagnant water in shady areas. Rodent populations can be controlled by not discarding food or food-related litter or feeding wildlife. your dog may not become ill or die if he is infected but another dog or human might.
Don’t take the risk for yourself or others: vaccinate.