ABSTRACT
Canine leptospirosis, which is caused by infection with pathogenic Leptospira species, occurs worldwide, but information regarding the causative Leptospira serotypes and genotypes and their effects on virulence in dogs remains limited. Monitoring acute leptospirosis in dogs as sentinels can also aid in estimating the risk of human leptospirosis, particularly when the disease is rare, as it currently is in Japan. Among 283 clinically suspected cases of leptospirosis diagnosed from August 2007 to March 2011 in Japan, 83 cases were laboratory diagnosed as leptospirosis by blood culture, a rise in antibody titres in paired sera using a microscopic agglutination test (MAT) and/or DNA detection using flaB-nested PCR. The infected dogs comprised hunting dogs (31 dogs) and companion animals (50 dogs) and two unknown; 63.4 % of the infected dogs were males. The mortality rate was 53.2 %. A rise of at least fourfold in MAT titre was detected in 30 dogs whose paired serum samples were obtained, and the predominant reactive serogroup was Hebdomadis (53.3 %), followed by Australis (16.7 %) and Autumnalis (16.7 %). Leptospira interrogans was isolated from 45 dogs of the following serogroups: Australis (16), Autumnalis (six), Canicola (one), Hebdomadis (21) and Icterohaemorrhagiae (one). All of these serogroups caused lethal infections (57.1-100 %). Genetic heterogeneity was demonstrated in serogroups Australis, Autumnalis and Hebdomadis by multilocus sequence typing (MLST) and/or RFLP analysis based on PFGE. In serogroup Hebdomadis, each genotype determined by MLST had a unique mortality rate in the infected dogs. Although classic canine leptospirosis is associated with serovars Canicola and Icterohaemorrhagiae, serogroup Hebdomadis has become the predominant serogroup causing high mortality in Japan. This study suggests that the virulence of members of serogroup Hebdomadis in dogs may be associated with the genotypes in this serogroup.
