Improving methods for epidemiological control of canine visceral leishmaniasis based on a mathematical model. Impact on the incidence of the canine and human disease.

Clarisa B Palatnik-De-Sousa,Carlile C Lavor,Leopoldina M Batista-De-Melo,Gulnara P Borja-Cabrera,Marcos Palatnik

doi:10.1590/s0001-37652004000300012

Abstract

The mathematical model described by Dye (1996) condemned the epidemiological canine visceral leishmaniasis control campaign, considering it non-efficient. Using this model, we mathematically demonstrate that the control is not efficient, only at low kappa values (rate at which latent and infectious dogs are lost by the destruction program) which match the canine seropositivity observed in the field by the immunofluorescency (IF) blood eluates analysis. With higher k values, corresponding to IF (kappa = 0.07) or ELISA (kappa = 0.25) results in sera samples, the number of infectious dogs declines to a Ro =1 or Ro =0, respectively, interrupting the transmission and the advancement of epidemics. We also experimentally demonstrate that the dog removal, following the results of IF of sera, instead of eluates lead to a 57% (p < 0.005) decrease in canine cases and 87.5% (p < 0.005) in human cases. Our mathematical and experimental results indicate that the control campaign become more efficient by enhancing the sensitivity of the diagnostic assay.

Highlights

Human visceral leishmaniasis or kala-azar is, in the Mediterranean and in the New World, a re-emergent canid zoonoses (Tesh 1995)
In the mathematical model used by Dye (1996), a relatively low value was attributed to the κ parameter, probably based on the low sensitivity of the diagnosis performed by immunofluorescency (IF) in blood eluates, and to the assumption that infected dogs removed by the control program are immediately substituted by susceptible animals (Palatnikde-Sousa 2002)
While very low impact on infectious dog population is seen with κ values ranging from 0 to 0.02 (97.5 to 81.8%) a significant reduction of infectious dogs starts from κ = 0.04 (67%)

Summary

Introduction

Human visceral leishmaniasis or kala-azar is, in the Mediterranean and in the New World, a re-emergent canid zoonoses (Tesh 1995). Etze et al 1997, Furtado Vieira and Coelho 1998), mainly for being too laborious and of doubty efficacy, probably due to the low sensitivity of the diagnostic methods (Machado Braga et al 1998, BorjaCabrera et al 1999, Palatnik-de-Sousa et al 2001) and delay in removal of infectious dogs (Machado Braga et al 1998). Dye (1996), described a mathematical model for the transmission of zoonotic visceral leishmaniasis (ZVL) and concluded that the dog removal would not have impact on the decrease of the canine infectious population. In the mathematical model used by Dye (1996), a relatively low value was attributed to the κ parameter (rate at which latent and infectious dogs are lost and susceptible replaced by the control program), probably based on the low sensitivity of the diagnosis performed by immunofluorescency (IF) in blood eluates, and to the assumption that infected dogs removed by the control program are immediately substituted by susceptible animals (Palatnikde-Sousa 2002)

Methods

Results

Conclusion