The wide variety of pathogenic Leptospira serovars and the weak protection offered by the available
vaccines encourage the search for protective immunogens against
leptospirosis. We found that the
secretin GspD of the
type II secretion system (T2S) of Leptospira interrogans serovar Canicola was highly conserved amongst pathogenic serovars and was expressed in vivo during
infection, as shown by immunohistochemistry. Convalescent sera of hamsters, dogs, and cows showed the presence of
IgG antibodies, recognizing a recombinant version of this
protein expressed in Escherichia coli (rGspDLC) in Western blot assays. In a pilot vaccination study, a group of eight hamsters was immunized on days zero and 14 with 50 µg of rGspDLC mixed with Freund's incomplete adjuvant (FIA). On day 28 of the study, 1,000 LD50 (Lethal Dose 50%) of a virulent strain of Leptospira interrogans serovar Canicola (LOCaS46) were inoculated by an intraoral submucosal route (IOSM). Seventy-five percent protection against disease (p = 0.017573, Fisher's exact test) and 50% protection against
infection were observed in this group of vaccinated hamsters. In contrast, 85% of non-vaccinated hamsters died six to nine days after the challenge. These results suggest the potential usefulness of the T2S
secretin GspD of Leptospira as a protective
recombinant vaccine against
leptospirosis.