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Dogs which are infected with leishmania parasites serve as major reservoir hosts for zoonotic visceral leishmaniasis. The incidence of zoonotic visceral leishmaniasis is rising in many countries. This may be associated with the continuing drift of people and their pets from rural areas into peri-urban settings, particularly at the fringe of large cities. At the same time, there is evidence of adaptation of sand fly vectors to these urban settings. This has created an alarming situation because, even though domestic and stray dogs may be infected, many remain asymptomatic but are still highly infectious to the sand fly vectors and thus pose a serious threat to human health. Over half of the infected dogs have asymptomatic infections and current assays are not sensitive enough under field conditions to distinguish asymptomatic from symptomatic dogs. There is an urgent need for a specific and sensitive screening tool for use in the field. We have previously demonstrated that promastigote exo-antigen-based ELISAs can be used in the specific diagnosis of human visceral leishmaniasis (HVL). A cocktail of exo-antigens prepared from three species (L. infantum, L. donovani, and L. major) was used to develop and optimize a canine ELISA assay. Serum samples from dogs with a variety of pathological conditions but living in a non-leishmania endemic area were used as negative controls and their reactivity was used to determine a cut-off value for the ELISA. Samples from dogs residing in a leishmania endemic area were tested in parallel using direct agglutination (DAT), immunofluorescence (IFAT), and ELISA. The ELISA results correlated closely (100%) with the clinical symptoms, and were elevated in one asymptomatic dog. This sample was also found to be positive by IFAT. Based on its sensitivity and specificity, the cocktail exo-antigen-based ELISA may prove useful, even at 1:2,000 serum dilutions, for screening dogs in different geographical regions of the world.
Received June 27, 2007. Accepted for publication December 18, 2007.
Acknowledgments: This study was funded internally through Cellabs Pty Ltd. The authors thank the veterinary staff at the Veterinary Teaching Hospital, University of Trás-os-Montes e Alto Douro, Vila Real, Portugal. Thanks are extended to Jeffery Ryan of Walter Reed Army Institute of Medical Research for providing Leishmania-infected dog sera and also to John Jardine of Vet-Path Laboratories, Perth Western Australia for supplying normal dog sera that were used in this study.
* Address correspondence to G-Halli R. Rajasekariah, Cellabs Pty Ltd, 7/27 Dale St, Brookvale NSW, 2100 Australia. E-mail: raj{at}cellabs.com.au
Authors’ addresses: G-Halli R. Rajasekariah, Diane A. Dogcio, and Anthony M. Smithyman, Cellabs Pty Ltd, 7/27 Dale St Brookvale NSW, 2100 Australia, Telephone: +61 2 9905 0133, Fax: +61 2 9905 6426, E-mails: raj{at}cellabs.com.au, diane{at}cellabs.com.au, and smithman{at}cellabs.com.au. Luis Cardoso, Department of Veterinary Sciences, CECAV, University of Trás-os-Montes e Alto Douro, PO Box 1013, 5001-801 Vila Real, Portugal, E-mail: lcardoso{at}utad.pt. Samuel K. Martin, Walter Reed Project, USMRU-K, Kenya Medical Research Institute, Nairobi, Kenya, Telephone: +254 202 2729303, Fax: +1 202 478 5084, E-mail: smartin{at}wrp-nbo.org.
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