Canine visceral leishmaniasis: Asymptomatic infected dogs as a source of L. infantum infection

Clinically infected dogs have been identified as the main reservoir hosts of visceral leishmaniasis (VL) caused by Leishmania infantum in the Mediterranean region. The objective of this study was to determine the potential of asymptomatic infected dogs compared with symptomatic ones as a source of L. infantum infection to golden hamster.For this purpose, anti-Leishmania antibodies were detected with direct agglutination test (DAT) in 13 symptomatic (7 seropositive = ≥1:320) and 53 asymptomatic (9 seropositive = ≥1:320 and 44 seronegative =  <1:320) ownership dogs. DNA of Leishmania sp. was extracted from skin and peripheral blood tissues of each dog and tested by PCR. Sixty-six Syrian golden hamsters (Mesocricetus auratus) were used for the determination of infectivity and pathogenicity of L. infantum, isolated from the dogs. We used the internal transcribed spacer 2 (ITS 2) rDNA sequence analysis. The results showed that 22 and 11 out of 66 inoculated golden hamsters were positive by PCR and parasitological examinations, respectively. From 22 PCR positive hamsters, 17 were related to asymptomatic dogs and 5 were from symptomatic ones. There was no significant difference between symptomatic and asymptomatic dogs in producing Leishmania infection in the susceptible animal model (P = 0.66). Smears and cultures of 5 dogs from 13 symptomatic dogs (38.5%) and 6 dogs from 53 asymptomatic ones (11.3%) were found to be positive at parasitological examination.All the L. infantum isolates from symptomatic and asymptomatic dogs were similar in sequencing.In conclusion, asymptomatic infected dogs as well as symptomatic ones can harbor L. infantum in their blood and skins which are virulent and infectious for inoculated golden hamster.