The Dog as a Risk Factor in Transmission of Visceral Leishmaniasis: A Review

Visceral leishmaniasis (VL) is a serious public health problem in Brazil and worldwide. Despite the euthanasia of dogs serologically positive, such action has not solved the endemic in Brazil. A risk area for VL involves the presence of the vector, the occurrence of canines and the record of human cases. The factors that have favored the persistence and spread of VL in Brazil are related to the predatory action of man on the environment, to the migratory movements and rural exodus, and a close coexistence of man and animals. Thus considering the epidemiological chain of VL, one fact seems clear: we do not know yet the true extent of the participation of the dog in the infectious cycle of VL. The clinical disease is an important indicator of the extent of the problem in an endemic area. The immunological events are complex and involve resistance and susceptibility to canine visceral leishmaniasis (CVL). One aspect in CVL is that many symptomatic dogs underwent xenodiagnosis not infect the vector. In such cases the pattern recognition receptors CD11b+, TLR2+, and NO present higher values for dogs with results in immunohistochemistry of skin and xenodiagnosis negative (IMH/XENO) than dogs with immunohistochemistry in skin and xenodiagnosis positive (IMH/XENO), suggesting that innate immunity modulates the competence of the dog to infect the vector. The organic response in CVL varies from individual to individual and within the same individual, with a strong evidence of being organ-specific. Only 20% of asymptomatic dogs have parasites in the skin and 15% are able to recover from clinical signs and eliminate the parasites spontaneously. In this review, we analyze the epidemiology of visceral leishmaniasis and clinical, immunological and pathological conditions that can contribute to understanding the role of dogs in transmission of visceral leishmaniasis.