Infectiousness in a Cohort of Brazilian Dogs: Why Culling Fails to Control Visceral Leishmaniasis in Areas of High Transmission

Abstract

The elimination of seropositive dogs in Brazil has been used to control zoonotic visceral leishmaniasis but with little success. To elucidate the reasons for this, the infectiousness of 50 sentinel dogs exposed to natural Leishmania chagasi infection was assessed through time by xenodiagnosis with the sandfly vector, Lutzomyia longipalpis. Eighteen (43%) of 42 infected dogs became infectious after a median of 333 days in the field (105 days after seroconversion). Seven highly infectious dogs (17%) accounted for>80% of sandfly infections. There were positive correlations between infectiousness and anti-Leishmania immunoglobulin G, parasite detection by polymerase chain reaction, and clinical disease (logistic regression, r2=0.08-0.18). The sensitivity of enzyme-linked immunosorbent assay to detect currently infectious dogs was high (96%) but lower in the latent period (<63%), and specificity was low (24%). Mathematical modeling suggests that culling programs fail because of high incidence of infection and infectiousness, the insensitivity of the diagnostic test to detect infectious dogs, and time delays between diagnosis and culling.

Visceral leishmaniasis in Brazil: revisiting paradigms of epidemiology and control

“…Indeed, domestic dogs are the main domestic reservoirs of L. infantum infection in the transmission cycle of zoonotic visceral leishmaniasis (ZVL) 16,20 . But, can other domestic or synanthropic animals play any role as reservoirs of infection?…”

“…There are several points to be considered on the culling of seropositive dogs: the limitation of the immunological screenings to detect anti-Leishmania antibodies, either with indirect immunofluorescence assay 3 or enzyme-linked immunosorbent assay 16 , the opposition of dog owners to the culling of asymptomatic dogs, and the lack of evidence that this method is effective to reduce the incidence rate of VL in all areas where it has been used 14 . It has been demonstrated that the culling of seropositive dogs has a limited impact on the reduction of human incidence 5,25,34 .…”

“…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 .…”

Age structure of owned dogs under compulsory culling in a visceral leishmaniasis endemic area

“…While a large body of literature has addressed the controversy as to whether or not the elimination of positive dogs is associated with a reduction in VL incidence in humans 5,6,7,8,9 , the impact of increased mortality in the structure and composition of canine populations has not been assessed in spite of its potential to influence VL prevalence in dogs and, consequently, in humans 7,10 . Furthermore, the replacement after compulsory culling also affects the structure of the canine population, thus changing the impact of currently used VL control measures.…”

Reproduction of Leishmania (Leishmania ) infantum chagasi in conditioned cell culture growth medium

“…This criterion, however, is considered very controversial, since serology is an indirect method, which may give false-positive results 6 . Further, 60% of serologically positive dogs present spontaneous cure and only 2 to 3% of these dogs actually develop the disease 11 .…”