Preliminary Results of a Field Trial to Evaluate the Value of Deltamethrin-Impregnated Collars for the Control of Canine Leishmaniasis in Northeast Brazil
*R.H..C. van den Bos, J.W. Olivera Lima, R. Nonato de Souza, M.J. Teixeira, M. Pompeu, J.R. David
A field trial is in progress in Ceará State, Brazil, to (a) measure the impact of deltamethrin-impregnated dog collars on the transmission of leishmaniasis among dogs; (b) compare collaring dogs with culling seropositive dogs; and (c) develop a protocol to use the collars for the control of canine leishmaniasis and, therefore, reduce the risk of visceral leishmaniasis in the human population.
An area with 2,513 dogs with a leishmanial seroprevalence of around 23% was divided into two similar parts in one of which collars were fitted to all dogs whereas, in the other, seropositive dogs were eliminated. Collars were replaced after six months as, from a previous laboratory trial, it was known that the collars maintained an anti-feeding activity against the Brazilian vector (Lutzomyia longipalpis) for not less than this period. After one year of observation, the incidence of canine leishmaniasis in the area was measured in both the collared and the elimination area. To assess the potentially confounding effects of variables on the association between the intervention (collaring vs. elimination) and the occurrence of seroconversion, a logistic model was fitted adjusting for Sex, Age, Race, Fenced/Not Fenced, Bathing Habit and Fur Length.
After one year of observation, the incidence of canine leishmaniasis in the area where seropositive dogs were eliminated was approximately twice as high as in the area where the dogs were fitted with collars. The crude and adjusted odds ratios were similar and there was no evidence of a confounding effect of the variables investigated. The mortality of dogs in the study area was notably high and death was the most important cause of loss of follow up (64% loss in the first six months). An average of 3.6 collars per dog per year were used and only 10% of the dog population were protected for a full year with the minimum of two collars. The high turnover of dogs and the collar losses emphasize the need for close surveillance.
The preliminary results of this study clearly indicate that, in field conditions in Brazil, deltamethrin-impregnated collars are more effective in preventing the transmission of Leishmania chagasi among dogs than culling seropositive individuals