Epidemiologic aspects of an emerging focus of visceral leishmaniasis in Tbilisi, Georgia

Abstract

Background: Over the last 15 years, visceral leishmaniasis (VL) has emerged as a public health concern in Tbilisi, the capital of Georgia.

Methodology/principal findings: Seroepidemiological surveys were conducted to determine the prevalence and incidence of infection in children and dogs within the main focus of VL, and to identify risk factors associated with human infection. Of 4,250 children investigated, 7.3% were positive by direct agglutination test in a baseline survey; an apparent incidence rate of 6.0% was estimated by one year follow-up. None of the seropositive children progressed to VL during the survey. Increased seropositivity at one year was predicted by presence at baseline of clustered flying insects (OR = 1.49; P = 0.001), perceived satisfactory sanitation (OR = 1.65; P<0.001), stray dogs (OR = 1.33; P = 0.023), and by persistent fever during the 6 months prior to baseline survey (OR = 14.2; P<0.001). Overall, 18.2% (107/588) of domestic and 15.3% (110/718) of stray dogs were seropositive by the rk39 dipstick test. Clinical VL signs were found in 1.3% of domestic and 2.9% of stray, seropositive dogs. Parasites isolated from human and dog samples were identified by PCR and phylogenetic analysis of the Leishmania 70 kDa heat-shock protein (HSP70) gene as Leishmania infantum.

Conclusions/significance: There is an active focus of L. infantum transmission in Tbilisi with a high prevalence of human and canine infections.

Figure 1. Maps showing distribution of human cases of visceral leishmaniasis in Georgia.

Map of Georgia (A) showing the principal active foci of VL in Tbilisi and Shida Kartli region (outlined by —·—). Map of Tbilisi (B) showing distribution of VL cases and location of Krtsanisi, Mtatsminda, and Vake districts surveyed in this study.

Figure 2. Households with all children tested seropositive for Leishmania at the baseline and/or follow-up surveys.

Eighty five households with 2 or more children where all children were DAT positive either in both baseline and follow up surveys, or seroconverted during the follow up period: DAT1− children negative in baseline survey, DAT1+ children positive in baseline survey, DAT2+ children positive in follow-up survey.

Figure 3. Identification of Leishmania species isolated from a human and dogs.

(A) kDNA-PCR performed on DNA extracted from the bone marrow of a sick child and bone marrow cultures of five representative dogs. Lane 1, DNA size marker (100 bp ladder); lane 2, L. major (MHOM/IL/80/Friedlin); lane 3, L. infantum (MHOM/ES/00/UCM-1); lane 4, bone marrow, child, Tbilisi; lanes 5–9, bone marrow, dogs, Tbilisi; lane 10, negative control. (B) Phylogenetic analysis of Leishmania 70 kDa heat-shock protein (HSP70) genes. The sequences are represented by the Leishmania sp., country of origin in parentheses and GenBank nucleotide accession number. Node values indicate branch support.