Leptospirosis is a widespread zoonosis. Different Leptospira serovars are prevalent in many countries and are correlated to disease in dogs, but it is difficult to evaluate their pathogenicity and to describe clinical signs related to specific serovars, due to the multiple cross-reactions seen with the MAT serological screening and to the inability of current molecular diagnostic techniques to identify the Leptospira serovar.
The development of molecular genotyping (MLST, VNTR) allows characterization of strains, but in most cases, these techniques are effective only if performed on isolated strains; isolation is therefore still of primary importance. From January 2013 to June 2016, a total of 876 samples were collected from 352 suspected cases of leptospirosis in dogs : 270 urine samples were analysed by culture and by real time PCR targeting the 16S rrs gene; 214 whole blood samples and 47 organ samples were analysed by PCR; 345 serum samples were tested by MAT.
Sixty-six samples were confirmed by PCR and 78 by serology (titre >400); in 8 cases the isolation of Leptospira strains from urine was achieved. The cultured strains were identified by serotyping and genotyping. The genotyping based on MLST and VNTR profiles identified 6 of the strains as L. interrogans serogroup Icterohaemorrhagiae, 1 as L. kirschneri serogroup Pomona serovar Mozdok, 1 as L. interrogans serogroup Australis. The serotyping identified the same serogroups, with complete concordance. Serology, when available (5 out of 8 times), revealed a positivity with the highest titre against the identified etiological serogroup except in one case. Identification of Icterohaemorrhagiae and Australis confirmed their role in the clinical leptospirosis in dogs; Pomona appeared as a risk for dogs and the absence of a registered Pomona vaccine suggests that leptospirosis should be taken into account in the differential diagnosis of any inflammatory illness, even when dogs are regularly vaccinated.