Transmission, reservoir hosts and control of zoonotic visceral leishmaniasis

Abstract

S U M M A R YZoonotic visceral leishmaniasis (ZVL) caused by Leishmania infantum is an important disease of humans and dogs. Here we review aspects of the transmission and control of ZVL. Whilst there is clear evidence that ZVL is maintained by sandfly transmission, transmission may also occur by non-sandfly routes, such as congenital and sexual transmission. Dogs are the only confirmed primary reservoir of infection. Meta-analysis of dog studies confirms that infectiousness is higher in symptomatic infection ; infectiousness is also higher in European than South American studies. A high prevalence of infection has been reported from an increasing number of domestic and wild mammals ; updated host ranges are provided. The crab-eating fox Cerdocyon thous, opossums Didelphis spp., domestic cat Felis cattus, black rat Rattus rattus and humans can infect sandflies, but confirmation of these hosts as primary or secondary reservoirs requires further xenodiagnosis studies at the population level. Thus the putative sylvatic reservoir(s) of ZVL remains unknown. Review of intervention studies examining the effectiveness of current control methods highlights the lack of randomized controlled trials of both dog culling and residual insecticide spraying. Topical insecticides (deltamethrin-impregnated collars and pour-ons) have been shown to provide a high level of individual protection to treated dogs, but further community-level studies are needed.

Dificuldades na execução das diretrizes do Programa de Vigilância e Controle da Leishmaniose Visceral em grandes municípios brasileiros

“…Em contrário, uma série de outras pesquisas concluiu que não há correlação espacial entre a incidência acumulada de LV humana com a soroprevalência canina, que há ausência de risco significativo de infecção humana na coabitação com cães, que a eutanásia isoladamente não demonstrou vantagem em reduzir a incidência de LV em seres humanos e que existe a possibilidade do envolvimento de outros reservatórios de infecção de L. infantum, tais como pessoas (particularmente crianças desnutridas que podem transmitir para outras crianças), canídeos silvestres e marsupiais 25,26,27,28 .…”

How effective is dog culling in controlling zoonotic visceral leishmaniasis? a critical evaluation of the science, politics and ethics behind this public health policy

“…Another cohort study showed a contradictory association, depending on whether the outcome was measured using skin reaction or serology 61 , while yet another reported no association between the presence of dogs and the development of the disease in people 62 . These fairly ambiguous results suggest that studies that can measure the proportion of the flow of parasites to humans from a canine source have yet to be developed 63 . In order to achieve this, it is essential to conduct specifically designed cohort studies.…”

“…In order to achieve this, it is essential to conduct specifically designed cohort studies. While it is intuitive to believe that dogs are significant reservoirs because they are more competent at infecting sand flies than people 47,[63][64][65][66][67][68] , other parameters that depend on the vectors (vectorial capacity) are much more significant for the basic reproductive number of the disease (e.g., the number of secondary cases emerging from an infectious case) and, therefore, for the incrimination of reservoirs. For example, some observations and mathematical models show that the importance of a reservoir is regulated not only by its competence in infecting vectors, but also by the parameters that measure a) the degree of exposure of vertebrate hosts to vectors and b) the vector daily mortality.…”

Avaliação da infectividade parasitária a Lutzomyia longipalpis por xenodiagnóstico em cães tratados para leishmaniose visceral naturalmente adquirida

“…Porém, a prática da eutanásia de cães tem sido a principal medida empregada, mesmo sendo essa medida considerada eticamente questionável (Passantino et al 2010, Costa 2011. Em áreas onde a eutanásia de cães soropositivos é praticada eventual ou sistematicamente para controle da LV, as taxas de incidência e letalidade da doença vêm aumentando nos últimos anos no Brasil (Quinnell & Courtenay 2009, Barreto et al 2011. Assim, considera-se que nas últimas décadas, milhares de cães foram sacrificados com pouco ou nenhum impacto na expansão da doença (Dantas-Torres 2007, Quinnell & Courtenay 2009, Passantino et al 2010, Costa 2011.…”