**New Advances in the Diagnosis of Canine Visceral Leishmaniasis**

Patrícia Sampaio Tavares Veras, Deborah Bittencourt Mothé Fraga, Manuela da Silva Solcà and Carlos Eduardo Sampaio Guedes

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/57573

**1. Introduction**

Visceral leishmaniasis (VL) is a serious public health problem of great medical and veterinary importance. This disease is endemic in Brazil and in many other countries of Latin America, Asia, Africa and Europe (1). According to recent review (2), approximately 0.2 to 0.4 million cases of VL occur each year and although worldwide distributed, higher prevalence of the disease is concentrated in six countries, including India, Bangladesh, Sudan, South Sudan, Ethiopia and Brazil, that undertake for more than 90% of the cases. The clinical importance of VL resides in the severity of the disease that results in death of unrecognized cases and even for individuals with treatment access, death occurs in 10 to 20% of the cases [2-8].

Most of the VL cases are caused by the *Leishmania* species from *Leishmania donovani* com‐ plex. Parasites from the *Leishmania* genus are diphasic and are transmitted as promastigote form to vertebrate hosts through the bites of female sand flies [9-12]. The genetic similari‐ ties between Old World and New World strains, respectively, of *L. infantum* and *L. infan‐ tum* (syn. *chagasi*) from different regions in Latin America, indicate these parasites belong to the same origin [11, 12].

The notion that dogs are the main urban domestic reservoir for this *Leishmania* in certain part of the globe is supported by the facts including: i) cases of canine visceral leishmaniasis (CVL) have been reported in 50 of the 88 countries where VL is endemic [13], ii) canine cases precede the onset of human cases [14], iii) high rates of prevalence in dogs, and iv) frequency of parasites is high in dog skin [15-18].

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Control strategies include performing accurate and early diagnosis of CVL to identify infected animals [19, 20]. CVL diagnosis is a difficult task since clinical signs of the disease in dogs can be confused with other diseases [19]. In endemic areas, a large percentage of infected animals are asymptomatic or present low number of discrete signs. The role these animals play in parasite transmission is still largely unknown. Several diagnostic strategies have been implemented based on parasitological, serological or molecular methods in association with clinical and epidemiological parameters [21]. Parasite culturing has been considered as gold standard for disease diagnosis [22, 23]. Although offering a high specificity since allows parasite identification, it offers very low sensitivity, besides it is laborious, time-consuming and largely dependent on the expertise of the observer [24, 25].

Serological tests are the most common diagnostic method employed for CVL diagnosis [3]. Several serological methods have been implemented for diagnosis of CVL, including direct agglutination assay (DAT), enzyme linked immunoassay (ELISA) and indirect immunofluor‐ escent antibody test (IFI) [26]. However, most of these classical serological tests present important limitations for CVL diagnosis, including high consumption of time, and lack of sensitivity and specificity, mainly when animals present low antibody titers. This causes underestimation of disease, reflecting in failures in control measures, as well as the mainte‐ nance of infected untreated dogs in endemic areas [27, 28]. New methods based on immuno‐ chromatography have been implemented for serodiagnosis of CVL and have shown excellent results [29]. These techniques offer several advantages since they are rapid tests easily performed even in field areas, and more specific since they use recombinant DNA technology that additionally facilitates reproducibility and large-scale production. These advantages result in better identification of infected dogs. However, the efficacy of immunochromato‐ graphic techniques for CVL diagnosis needs to be improved [30]. In Brazil, a rapid test based in dual path platform (TR DPP®LVC - Biomanguinhos) had been recently implemented as screening test for CVL. This technique seems to be adequate to disease diagnosis in public health system. However, the TR DPP®LVC has shown an excellent performance identifying 98% of symptomatic dogs, it showed less efficacy for diagnosis of asymptomatic dogs (47%) [31]. Since there is evidence that asymptomatic dogs can participate in natural transmission cycle of VL, new strategies should be implemented in order to improve CVL diagnosis [16, 32-34]. For serological diagnosis one strategy can be the development of rapid tests based on impregnation of multi-antigen that would offer more sensitivity, as well specificity.

Finally, it would be important to include more specific confirmatory tests for control strategies that can be advantageous to diagnose inconclusive cases. There is evidence that molecular diagnosis of *Leishmania* spp. provides high levels of sensitivity and specificity when compared to other diagnostic methods [7, 17]. The use of quantitative methods in molecular level allows not only a more accurate detection but also monitoring tissue parasite load in dogs following anti-leishmanial treatment [35-37].
