Studies on control of visceral leishmaniasis: impact of dog control on canine and human visceral leishmaniasis in Jacobina, Bahia, Brazil.

Abstract

To assess the effect of removing leishmania-infected dogs on the incidence of visceral leishmaniasis, a controlled intervention study was performed in northeast Brazil. The attempted elimination of seropositive dogs resulted in an initial significant decrease in the annual incidence of seroconversion among dogs from 36% to 6% over the first two years. In the following two years, the incidence increased to 11% and 14%, respectively. In a control area in which dogs were surveyed but seropositive dogs were not removed, the cumulative incidence did not vary significantly from year to year, ranging from 16% to 27%. In the intervention area, the prevalence of dog seropositivity decreased from 36% before the intervention to 10% and remained stable. These findings suggest that attempting to remove seropositive dogs is insufficient as a measure for eradicating visceral leishmaniasis in dogs. However, the force of transmission of infection among dogs can be reduced by such programs. Also, when the number of human cases before and after the start of the intervention was calculated, a significant decrease in incidence of disease in the intervention area was observed among children less than 15 years of age (P Ͻ 0.01). The results of this intervention study suggest that the elimination of the majority of seropositive dogs may affect the cumulative incidence of seroconversion in dogs temporarily and may also diminish the incidence of human cases of visceral leishmaniasis.

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.…”

Transmission, reservoir hosts and control of zoonotic visceral leishmaniasis

“…Two published studies have directly investigated the effect of dog culling, but neither was replicated at the community level. In the first study, culling 42-73 % of seropositive dogs annually for 5 years was associated with a reduction in the incidence of human cases, and a variable reduction in canine incidence (Ashford et al 1998). In the second study, culling of all seropositive dogs at 6 month intervals was not associated with reductions in either human or canine incidence (Dietze et al 1997).…”

Hepatic granulomas in canine visceral leishmaniasis and clinical status

“…There is an association between infected dogs and the abundance of Leishmania longipalpis in these states (Deane and Deane, 1962;Cunha et al, 1995;Ashford et al, 1998). Cunha et al (1995) and Ashford et al (1998) found an association between human infection and the presence of infected dogs in or near residences in the State of Bahia. Furthermore, visceral leishmaniasis (VL) appears to be spreading in Brazil and outbreaks have recently been reported in regions where the disease was previously unknown, e.g.…”