From Guest Author Dr. John Prescott, Professor, Department of Pathobiology, University of Guelph. More information about Leptospira and leptospirosis can be found on our Resources page.
The last decade has witnessed a surge in leptospirosis in dogs throughout much of North America. Ontario and Québec have been part of the surge, which is associated with two serovars of Leptospira, grippotyphosa and pomona.
The reasons for the dramatic increase relate to: 1. The apparent spread of infection in raccoons and to a lesser extent skunks; 2. A changing climate that favours prolonged survival of these bacteria outdoors in the milder fall temperatures; 3. Perhaps to a minor extent increased awareness of the disease by veterinarians. Gillian Alton, a Masters student at the University of Guelph, has shown that the increased infection rate observed in recent years appears to have leveled off, which may be the result of widespread vaccination.
Leptospirosis should be suspected whenever there is kidney or liver inflammation of unknown origin, particularly in the fall of the year. In 2007, there were about 80 positive and 170 suspicious cases in Ontario based on blood tests submitted to the Animal Health Laboratory (AHL), University of Guelph. Since not all such blood tests go through the AHL, it is likely that there would have been about 160 positive and 350 suspicious cases based on this testing throughout Ontario, and an unknown number of cases diagnosed by PCR (a DNA-based test). If one includes cases diagnosed based on clinical signs but without laboratory testing, and about half the suspicious cases as positive cases, then there may be about 400 clinical cases (i.e. cases where the animal actually gets sick) of leptospirosis in dogs occurring annually in Ontario. Clinical leptospirosis in dogs is a serious disease and this number, if the assumptions are correct, represents a high burden of infection.
Arguments for recommending the new 4-way leptospiral vaccines as a “core” vaccine (i.e. all dogs should be vaccinated) in Ontario are:
- The suggested size of the problem;
- The often serious nature of the disease;
- The zoonotic potential of the infection (a small number of human infections acquired from dogs have been recognized in Ontario and Québec in recent years);
- The ongoing widespread presence and sometimes large numbers of raccoons in suburban and urban Ontario;
- The diagnosis of canine leptospirosis throughout the province;
- The diagnosis of the disease in dogs of all types, not just the “male hunting dog” which is sometimes conventionally regarded as “high risk”.
Arguments against recommending the new 4-way vaccines as a “core” vaccine are:
- The sporadic nature of the infection, including the lack of exposure of some dogs to raccoons and other wildlife sources;
- The number of vaccine reactions associated with leptospiral vaccines (this is not a significant problem with at least one of the vaccines);
- The considerable confusion caused by the (almost certainly totally unfounded) suspicion that serovar autumnalis causes canine leptospirosis, but is not in the new vaccines;
- The lack of inclusion of serovar bratislava in the vaccine (although this serovar seems to cause only mild disease in dogs);
- The annual cost of revaccination.
The vaccine manufacturers have the responsibility to provide the supporting data on which a “core vaccine” recommendation should be based, by testing dogs in Ontario for exposure to the different serovars. In the absence of such data, but knowing the possible extent of the problem, veterinarians should always discuss the pros and cons of leptospiral vaccination with dog owners. My opinion is that, barring problems of vaccine reactions and hypersensitivity in individual dogs, annual leptospiral vaccination with a 4-way vaccine should be recommended.