Leptospirosis

Leptospirosis Now

The re-emerging leptospirosis is not the same disease recognized in the early 1970s.

In the early 1970s, icterohaemorrhagiae and canicola were the most prevalent serovars causing canine leptospirosis. An epidemic of canicola and sporadic cases of icterohaemorrhagiae in dogs led to widespread vaccination and prevalance seemed to be reduced. The re-emerging leptospirosis of today is quite different. By the 1990s, the incidence of pomona and grippotyphosa had increased significantly, coinciding with a general resurgence of leptospirosis, suggesting a change in the epidemiology of this disease.

“There has been an apparent epizootiologic change in canine leptospirosis. The incidence of disease attributed to serovars canicola and icterohaemorrhagiaehas decreased, whereas the number of reports of canine leptospirosis associated with serologic evidence of infection with other serovars, particularly grippotyphosa, pomona... has increased.”

C.A. Brown et al, 1996⁶

“The consensus is that resurging leptospirosis in dogs is the result in most cases of serovar grippotyphosa, acquired from raccoons, and to a lesser extent serovar pomona acquired from skunks, and serovar bratislava acquired from dogs (mostly), horses, pigs and possibly other sources.”

Source: Canine Leptospirosis in Ontario – more cases in 2004, Beverly McEwen, Davor Ojkic, John Prescott, AHL Newsletter, Volume 9, Number 2, p. 15, June 2005

Factors contributing to the re-emergence of leptospirosis

Urban growth in previously rural areas, combined with movement of wildlife reservoirs of Leptospira spp. into urban areas and warmer and wetter climates, has contributed to the re-emergence of leptospirosis in dogs.

"The most likely reason for the high incidence of this disease in dogs… is a large population of species responsible for transmission of grippotyphosa – raccoons, opossums, skunks and, to a lesser extent, small rodents (rats, mice and voles)."

D.M. Levitan, 1998 ⁷

"The re-emergence of leptospirosis may be attributed to changes in the prevalence and pathogenicity of the various serovars, as well as the increased contact between pet dogs and wildlife reservoir species in urban and rural communities."

Vita-Tech, 2004⁸

Host-adapted vs. non-host-adapted serovars

In the wildlife reservoir, Leptospiral organisms reside in the proximal tubules of the kidney and are shed in the urine during the lifetime of the host. The infected hosts are typically not ill or at most mildly ill. The maintenance of this organism without causing disease is termed host adaptation.

When dogs are exposed to leptospires that are not host-adapted to dogs (i.e. serovars other than canicola), they become infected and ill. Thus, raccoons can shed grippotyphosa but apparently be healthy, while dogs exposed to pomona from raccoons can become seriously ill. grippotyphosa and pomona are considered to be the most common serovars infecting dogs today ^4,5,8,9 and can cause serious illness.

To date, researchers have not been able to prove bratislava is a disease of dogs, although bratislava may be a common result of MAT testing. If you are seeing bratislava in your practice area, then exposure to other serovars also is likely. Use the appropriate lepto vaccine protocol to offer protection for the most serovars currently available in a lepto vaccine.

Autumnalis is not thought to be a true infectious serovar for dogs. The most likely reason for this result is the dog was infected with another serovar and autumnalis cross reacted with the infecting serovar, a limitation of the MAT test. Look for the serovar with the next highest titer as the cause, or if possible, perform a convalescent titer two to four weeks after the acute phase titer to further define the infecting serovar.

The re-emerging leptospirosis: a product of climatic change?

Leptospira spp. survive well in temperate, wet conditions. Global climatic change may be contributing to increased survival of this pathogen in the environment.