Seasonality in exposure to sand flies in dogs and humans in endemic area for visceral leishmaniasis: an intervention study.
Sand flies, saliva, exposition
Visceral leishmaniasis is a neglected tropical disease caused by the protozoan Leishmania infantum, having the sandfly as vector (Lutzomyia longipalpis) and as main reservoir the domestic dog. The main measure of control of this endemic disease in Brazil is the euthanasia of infected dogs. However, this measure has not been effective due to several factors, including the time lag of realization. The use of collars impregnated with deltamethrin by dogs has been a potential alternative measures of infection control. This strategy appears to decrease the risk of exposure of animals to sandflies, with consequent decrease in dog exposition. This study aimed to determine the vector exposure rates and Leishmania in humans and dogs after adoption of the use of collars impregnated with deltamethrin by resident dogs in an endemic area for visceral leishmaniasis. Dogs from endemic area of Natal, RN, received collars impregnated with deltamethrin, beyond traditional control measures, including euthanasia of dogs that were infected with Leishmania infantum; while dogs controls were subject only to the traditional treatment. Dogs and people of the two areas had collected blood samples, and a collection for humans and two collections for dogs (point of intervention and 6 months). For determination of the vector exposure levels, the investigation of anti-sandfly saliva antibodies was performed by ELISA, with salivary gland homogenate of L. longipalpis and recombinant proteins LJM11/LJM17. It was found that in both areas, dogs showed reduced levels of anti-saliva antibodies after 6 months of the study. For the intervention area, the reductions were 59.58% and 57.85%, for anti-SGH and anti-LJM11/17 respectively. In the control area, the reductions were 57.27% and 62.16%, for anti-SGH and anti-LJM11/17 respectively. In the area of intervention, humans showed lower titers of anti-SGH antibodies (p <0.0001), anti-LJM11 / 17 (p = 0.0002) and anti-Leishmania (p <0.0001) when compared to individuals in the control area. Men and women were equally exposed to the vector, regardless of the study area. The levels of anti-homogenate salivary gland antibodies were strongly correlated with the recombinant protein antibody levels (dogs: r = 0.96; human: r = 0.56). The work demonstrates the need to investigate the effectiveness of new leishmaniasis control measures, taking into account the biological cycle of the parasite, the seasonal aspect of the vector density and specific environmental conditions of each locality.