Elsevier

Acta Tropica

Volume 112, Issue 2, November 2009, Pages 101-105
Acta Tropica

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

https://doi.org/10.1016/j.actatropica.2009.07.004Get rights and content

Abstract

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.

Introduction

Canine visceral leishmaniasis (CVL) caused by Leishmania infantum is endemic in most of the Mediterranean regions and its seroprevalence varies from 10% to 37% (Fisa et al., 1999, Mohebali et al., 2005, Sideris et al., 1999). CVL is endemic in the northwestern and southern parts of Iran and its prevalence ranged from 14.2% to 17.4% (Bokaei et al., 1998, Edrissian et al., 1998, Mohebali et al., 2001, Mohebali et al., 2002, Moshfe et al., 2008).

Domestic dogs (Canis familiaris) are the main reservoir hosts for human visceral leishmaniasis (Desjeux, 2004, Moreno and Alvar, 2002, Pinelli et al., 1994).

The clinical manifestations of the disease vary from asymptomatic, self-limiting infections to fatal visceral leishmaniasis. The incubation period of CVL ranges from few months to several years depending on parasite virulence as well as genetic susceptibility of the host (Reiner and Locksley, 1995). Seroepidemiological studies of canine leishmaniasis have revealed a large number of asymptomatic seropositive animals (Portus et al., 1987, Sideris et al., 1999).

Seventy-six years ago, Adler and Theodor (1932) pointed out that sand flies fed on some apparently healthy dogs became infected. Molina et al. (1994) showed that the infectivity of dogs with phlebotomine sand flies was not linked to the symptomatic stage of the disease (Molina et al., 1994). In a recent study, Gomes et al. (2007) highlighted the efficacy of PCR in discriminating the species of Leishmania in infected dogs, particularly in areas where both visceral and cutaneous leishmaniasis were endemic (Gomes et al., 2007, Lachaud et al., 2002).

The golden Syrian hamster (Mesocricetus auratus) is highly susceptible to L. infantum/L. chagasi infections and the infection proceeds to fatal disease possibly due to a fundamental defect in their macrophages (Melby et al., 2001, Mukherjee et al., 2003). The clinical course of the infection and immunopathological mechanisms in the golden hamster is remarkably similar to those in the canine and human, thus it is considered as a good animal model for the study of visceral leishmaniasis (VL) (Melby et al., 2001, Requena et al., 2000).

The aim of this study was to assess the role of asymptomatic dogs compared with symptomatic ones in harboring the L. infantum in their blood and skins. Moreover, the study aimed to evaluate the virulence and infectivity of the isolated parasites from both symptomatic and asymptomatic infected dogs in susceptible animal model.

Section snippets

Dogs and hamsters

This study was conducted from 2007 to 2008 in Meshkin-Shahr district, as an endemic area of canine visceral leishmaniasis in Iran (Mohebali et al., 2006, Moshfe et al., 2008). Subjects of the study were 66 ownership dogs with different breeds and ages. All 66 dogs were clinically examined for any signs of CVL, including lymphadenopathy, dermatitis, hair loss, cachexia and hepatosplenomegaly. Then, the animals were euthanized, using intravenous injection of ketamine hydrochloride (10 mg/kg).

Serum

Results

Based on the clinical signs and serological findings, the 66 dogs were divided into three groups including 13 symptomatic (7 DAT+ at ≥1:320 titers) and 53 asymptomatic (9 DAT+ at ≥1:320 titers) and 44 seronegative at <1:320 titers.

All the symptomatic and asymptomatic dogs (n = 66) had showed anti-Leishmania antibodies titers at ≥1:80, thus, all of the 66 dogs had leishmanial infection but based on the optimal DAT cut-off level of DAT that was calculated and also based on our previous experiences

Discussion

Based on the epidemiological and experimental evidences, infected dogs with signs and symptoms of leishmaniasis are the main reservoir hosts of L. infantum for human and susceptible animals (Ashford, 1994, Dantas-Torres et al., 2006, Desjeux, 2004, Edrissian et al., 1998, Mohebali et al., 2004, Mohebali et al., 2005).

In areas where zoonotic visceral leishmaniasis is endemic, the prevalence of L.infantum infection in dogs is often high where many of them are asymptomatic (Dantas-Torres et al.,

Acknowledgements

Some parts of this study received financial support from the Institute of Public Health Research, Tehran University of Medical Sciences (projects no.: 240/4659 and 130/6/10447).

We thank Dr. B. Sarkari, Dr. H. Hajjaran, Mrs. S. Charehdar and Mrs. M. Bandehpour for helping us in laboratory techniques and Dr. R. Nikzad, Mr. A. Miahipour and Mr. Taghdisi for helping us with sample collecting and the staff of the District Health Centers in Ardabil province and Meshkin-Shahr district, particularly

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