In Brazil, the population of sheep is approximately 15 million (IBGE, 2004
). Most of the herds are kept together with cattle and horses and thus, a sheep infected with leptospirosis may be a potential disseminator of the disease to other animal species as well as to humans. In this study isolation of L. noguchii
, serogroup Autumnalis from an apparently healthy sheep was obtained. The sequencing of the 16S rRNA gene allowed the classification of this strain as belonging to the L. noguchii
species. This is the first report of isolation of L. noguchii
from sheep. This pathogenic leptospiral species had previously been isolated only from human, armadillo, toad, spiny rat, opossum, nutria, Mustela nivalis
, cattle and Bombina orientalis
(Faine et al., 1999
The existence of sheep carrying L. noguchii
may implicate this animal species as playing an important role in the epidemiology of leptospirosis, acting as a maintenance host for infection of cattle and horses by serogroup Autumnalis. Although L. noguchii
is a pathogenic species, virulence of the Caco strain could not be demonstrated. The bacterium was obtained from an apparently healthy animal, and experimentally inoculated hamster failed to demonstrate signs of leptospirosis. Possible explanations for this fact include: (i
) hamster may not be susceptible to this strain; (ii
) the bacteria may have undergone mutations during in vitro growth, resulting in a non-virulent strain (Haake et al., 1991
). Within L. noguchii
, the only strain that belongs to serogroup Autumnalis is the Fort Bragg strain, a human isolate from USA. Caco strain has not been characterized at serovar level, however it is conceivable that it is different from the serovars described so far.
Serological evidence of leptospiral infection in sheep was found in 20.5% of the animals tested and they reacted against serogroups Autumnalis, Icterohaemorrhagiae, Sejroe, Javanica and Bataviae. A previous study carried out in Brazil by Santa Rosa and Castro (1963)
reported reactions predominantly against the Autumnalis leptospiral antigens. More recently, Favero et al. (2002)
reported a 0.7% (n=284) seropositive rate among sheep, with reactions against Icterohaemorrhagiae, Butembo, Castellonis, and Hebdomadis antigens. In another study, a seropositive rate of 34.2% (n=1,360) was reported, with predominant reactions occurring with Hardjo (30%), Sentot (16.8%), and Autumnalis (6.3%) serogroups (Herrmann et al., 2004
). The etiological significance of these serological findings has not been established.
Considering the economic importance of sheep-raising, the isolation of L. noguchii serogroup Autumnalis strain Caco provides useful information for future epidemiological and serological investigation. Further studies should be carried out to confirm the role of sheep as reservoir of pathogenic leptospires and its implication for public health.