Effect of Eliminating Seropositive Canines on the Transmission of Visceral Leishmaniasis in Brazil

Abstract

In Brazil, where Leishmania chagasi causes endemic American visceral leishmaniasis (AVL), the spread and maintenance of human disease are attributed to canine reservoirs. However, despite measures directed toward the elimination of infected canines, the incidence of human disease continues to increase. To evaluate the role of infected canines in the acquisition of AVL by humans, we undertook a controlled intervention study in three similar, but isolated, valleys of Pancas, Espírito Santo, Brazil. In the two experimental (intervention) valleys, infected dogs were eliminated whereas in the control valley, seropositive canines remained untouched. During the 12-month study period, human seropositivity rates, as measured by dot enzyme-linked immunosorbent assay, increased from 15% to 54% in the intervention valleys and from 14% to 54% in the control valley. The elimination of infected canines in the intervention valleys did not result in a statistically significant difference between the incidences of human serological conversion in the intervention and control valleys at either 6 (20% and 22%, respectively; P = .5961) or 12 months (26% and 27%, respectively; P = .9442). The role of humans as a significant reservoir for AVL is proposed as an explanation for the study results.

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

“…The outcome of the first of these trials was seroconversion of humans, conducted in two rural areas. No difference between the areas of intervention and control (20% vs. 22% and 26% vs. 27% respectively) were verified after periods of 6-months and 1-year 73 . The second study compared the effect of the elimination program with the incidence of pediatric cases in two urban districts and showed that the annual incidence was lower in the intervention areas than in the control areas (5/1,000 vs. 20/1,000), but due to several factors, the authors could not attribute the protective effect to the elimination of dogs 74 .…”

Canine visceral leishmaniasis due to Leishmania (L.) infantum chagasi in Amazonian Brazil: comparison of the parasite density from the skin, lymph node and visceral tissues between symptomatic and asymptomatic, seropositive dogs

“…We must also stress that this poses a rather difficult problem for the governmental programme on the control of AVL 4 , for although the culling of asymptomatic, seropositive dogs have been one of the principal activities in this endeavour, epidemiological studies have failed to show a lasting reduction of the incidence of human and/or canine AVL in Brazil 1,10 . Also of concern is the low efficacy of amastigote detection, principally following the traditional use of Giemsa-stained smears or histological sections from the skin of dogs.…”

“…There is, nevertheless, a growing opinion that this control measure, particularly the destruction of the asymptomatic, serologically positive dogs, has failed to result in any lasting decrease in the incidence of human and/or canine AVL in Brazil 1,10 , thus placing the Brazilian health authorities in a somewhat delicate situation.…”

Visceral leishmaniasis in Brazil: revisiting paradigms of epidemiology and control

“…It has been demonstrated that the culling of seropositive dogs has a limited impact on the reduction of human incidence 5,25,34 . Mathematical models have also shown the limitations of this strategy 16 , which may be less effective than others 26 .…”