Assessment of an optimized dog-culling program in the dynamics of canine Leishmania transmission

Abstract

In Brazil, zoonotic visceral leishmaniasis (ZVL) control programs based on the mass elimination of seropositive dogs have failed to reduce the number of leishmaniasis cases. However, these programs have been done under sub-optimal conditions. We studied a cohort of dogs in an urban area in Brazil to determine, whether a dog-culling program optimized with: (i) replacement of a relatively low-sensitivity indirect immune-fluorescent test on blood eluate by a more sensitive enzyme-linked immunosorbent assay on serum blood samples; (ii) shortening of the time interval from serodiagnosis to removal of dogs; (iii) screening a high proportion of the dog population could reduce the incidence of canine Leishmania infection (CLI). The study ran from December 1997 to July 2000, with four follow-up assessments performed at approximately 8-month intervals. All dogs seropositive for anti-Leishmania antibodies were promptly eliminated. A large number of new dogs immigrated to the study area throughout the study period. They comprised 43.8-49.8% of the cohort at each follow-up assessment, and upto 15% of them already had Leishmania infection. Overall, 42 news cases of CLI were identified, for a crude incidence rate of 11.8 cases per 100 dog-years (95% CI 8.6-15.6). In the first, second, third and fourth follow-up assessments the incidence rates were 8.2 (95% CI 3.0-17.9), 12.2 (95% CI 6.3-21.2), 16.4 (95% CI 8.5-28.6) and 13.6 (95% CI 7.1-23.8), respectively. There was no statistically significant change in these rates throughout the study period. Our results suggest that dog-culling programs do not reduce the incidence of CLI, even with an optimized intervention. Possible reasons for this failure include: currently available serologic methods lack sufficient sensitivity and/or specificity to accurately identify all infected dogs warranting removal in order to prevent Leishmania transmission; destroyed dogs are immediately replaced by susceptible puppies, and quite often, by already infected dogs; and other reservoirs may be involved in maintaining canine infection. Further efforts on ZVL control should be directed to developing new strategies or to testing control methods already in place with properly designed trials.

Temporal, spatial and spatiotemporal analysis of the occurrence of visceral leishmaniasis in humans in the City of Birigui, State of São Paulo, from 1999 to 2012

“…Their main questions were regarding the diffi culties observed in most municipalities and were related to the problem of asymptomatic dogs; infections in these animals are generally not detected and contribute to the maintenance of the disease cycle. Furthermore, Moreira Jr et al 24 suggested problems related to the low stability and sensitivity of the assays used to detect the infection in dogs, the long period between diagnosis and canine euthanasia, the resistance of the owners in relation to the euthanasia procedure, and the rapid replacement of the dogs.…”

The Effect of Removing Potentially Infectious Dogs on the Numbers of Canine Leishmania infantum Infections in an Endemic Area with High Transmission Rates

“…15 The results of several intervention studies based on serological screening of dogs and killing of seropositive animals are equivocal. [16][17][18][19][20] In theory, effective control would require a high proportion of infectious dogs to be removed immediately upon detection to achieve a marked reduction in disease transmission. 8,9 Thus, it is postulated that if culling could target infectious (rather than simply infected) dogs, its effectiveness may be increased because the proportion of dogs that have never been infectious in the population may increase.…”

Epidemiologia da leishmaniose visceral no município de Fortaleza, Ceará

“…Entretanto, a correlação entre casos caninos e humanos apresentou-se negativa (r= -0,0388) indicando que a presença de cães infectados não é um fator determinante para o aparecimento da doença em humanos no município de Fortaleza. Além disso, a prática da eutanásia de animais soropositivos não vem diminuindo a prevalência da infecção em humanos (Moreira et al 2004). Este fato corrobora com um estudo de intervenção controlado onde foi sugerido que a eliminação de cães soro reagentes pode afetar a incidência cumulativa de LVC e temporariamente pode também diminuir a incidência de casos da LV em humanos, embora a transmissão continue após a remoção dos cães o que sugere a presença de outros reservatórios (Da Silva et al 2010, Helhazar et al 2013.…”