Culling Dogs in Scenarios of Imperfect Control: Realistic Impact on the Prevalence of Canine Visceral Leishmaniasis

Abstract

BackgroundVisceral leishmaniasis belongs to the list of neglected tropical diseases and is considered a public health problem worldwide. Spatial correlation between the occurrence of the disease in humans and high rates of canine infection suggests that in the presence of the vector, canine visceral leishmaniasis is the key factor for triggering transmission to humans. Despite the control strategies implemented, such as the sacrifice of infected dogs being put down, the incidence of American visceral leishmaniasis remains high in many Latin American countries.Methodology/Principal FindingsMathematical models were developed to describe the transmission dynamics of canine leishmaniasis and its control by culling. Using these models, imperfect control scenarios were implemented to verify the possible factors which alter the effectiveness of controlling this disease in practice.Conclusions/SignificanceA long-term continuous program targeting both asymptomatic and symptomatic dogs should be effective in controlling canine leishmaniasis in areas of low to moderate transmission (R0 up to 1.4). However, the indiscriminate sacrifice of asymptomatic dogs with positive diagnosis may jeopardize the effectiveness of the control program, if tests with low specificity are used, increasing the chance of generating outrage in the population, and leading to lower adherence to the program. Therefore, culling must be planned accurately and implemented responsibly and never as a mechanical measure in large scale. In areas with higher transmission, culling alone is not an effective control strategy.

Progress in the Mathematical Modelling of Visceral Leishmaniasis

“…The most complex structure for ZVL is given by Costa et al (2013a) in their model which not only accounts for possible infective asymptomatic dogs but also for imperfect screening due to diagnostic tools via the use of extra compartments (see Figure 10). This modelling approach is more sophisticated than its predecessors, with model equations corresponding to this progression allow for delay between diagnosis and culling (discussed in Section 4).…”

“…This modelling approach is more sophisticated than its predecessors, with model equations corresponding to this progression allow for delay between diagnosis and culling (discussed in Section 4). Costa et al (2013a). Here all dogs are born susceptible but only some will develop symptoms after becoming infected and passing through the incubation period.…”

“…Several models of VL (Dye and Wolpert, 1988;Dye, 1988Dye, , 1996Courtenay et al, 2002b;Quinnell et al, 1997;Palatnik-de Sousa et al, 2004;Costa et al, 2013a) utilise this vectorial capacity quasiequilibrium assumption.…”

Age structure of owned dogs under compulsory culling in a visceral leishmaniasis endemic area

“…While a large body of literature has addressed the controversy as to whether or not the elimination of positive dogs is associated with a reduction in VL incidence in humans 5,6,7,8,9 , the impact of increased mortality in the structure and composition of canine populations has not been assessed in spite of its potential to influence VL prevalence in dogs and, consequently, in humans 7,10 . Furthermore, the replacement after compulsory culling also affects the structure of the canine population, thus changing the impact of currently used VL control measures.…”

O controle de leishmaniose visceral no Brasil: transformar é preciso

“…O uso de coleiras impregnadas foi apontado como uma saí-da, mas os desafios operacionais de substituição semestral das coleiras, novamente necessárias pelo curto poder residual dos inseticidas piretroides, tornam-se intransponíveis em situações que exigem cobertura elevada de grande número de cães. Considerando as imperfeições na cobertura da eutanásia canina, a abordagem desenhada por Costa et al 6 indica categoricamente que caso a intervenção sobre a população canina inclua a eutanásia de cães soropositivos o esforço exigiria soluções peculiares, dependendo da força da transmissão na região sob intervenção. Em relação ao possível efeito do manejo ambiental e da educação em saúde para melhorar o impacto das ações de controle em seu conjunto, faltam certamente evidências da sua efetividade, no entanto, as externalidades positivas destas duas intervenções são incontestáveis para o bem-estar das populações expostas ao risco de adquirir LV.…”