A field study of the survival and dispersal pattern of Lutzomyia longipalpis in an endemic area of visceral leishmaniasis in Brazil

Abstract

Zoonotic Visceral leishmaniasis (ZVL) is a neglected tropical disease that in the Americas is caused by the infection of Leishmania infantum and the domestic dog ( Canis familiaris) is the main parasite reservoir in urban areas. The parasite is mainly transmitted by populations of the sibling species Lutzomyia longipalpis that has been spreading in countries including Brazil, Argentina, Paraguay and more recently Uruguay. Although bionomic parameters such as population survival and the duration of the gonotrophic cycle are critical in evaluating vector capacity, field studies have rarely been applied to sand fly populations. The present study sought to evaluate basic bionomic parameters related to the vectorial capacity of the (S)-9-methylgermacrene-B population of the Lu. longipalpis complex in a visceral leishmaniasis area of Sao Paulo state. The daily survival rate, the duration of the gonotrophic cycle and the dispersal pattern were evaluated through the mark- release-recapture method. A total of 1,547 males and 401 females were marked and released in five experiments carried out between February 2013 and February 2014. The higher recapture rates occurred within 100 meters of the release point and the estimated daily survival rates varied between 0.69 and 0.89 for females and between 0.69 and 0.79 for males. The minimum duration of the gonotrophic cycle observed was five days. The absolute population size, calculated ranged from 900 to 4,857 females and from 2,882 to 9,543 males. Our results demonstrate a high survival rate of this vector population and low dispersal that could be associated with the presence of all necessary conditions for its establishment and maintenance in the peridomiciles of this area. Our findings contribute to the basic data necessary for the understanding of ZVL dynamics and the evaluation of the implementation of prevention and control measures.

Author summary

American Visceral leishmaniasis (VL) is an anthropozoonosis resulting from infection by Leishmania infantum mainly transmitted by the bite of females of the sand fly Lutzomyia longipalpis which feed mainly on domestic dogs. It is a serious tropical disease that in some countries has spread in association with several factors such as human migration, precarious urbanization and vector adaptation to urban areas. In Brazil, although control measures such as the elimination of infected dogs, the application of residual insecticide and environmental management have been applied by the health authorities, however, they have not resulted in any significant reduction in VL incidence. The knowledge of bionomic parameters of vector populations is critical for the understanding of the transmission dynamic of VL and to evaluate prevention and control measures. Therefore, in the present study we applied the mark-release-recapture (MRR) method to evaluate under field conditions some basic bionomic parameters of a population of the Lutzomyia longipalpis complex. Our findings demonstrate a high survival rate of this vector and a low population dispersal. These results suggest that measures applied to dog populations to prevent sand fly bites could contribute to the reduction of the surviving vector population and indirectly to the reduction of the host biting rate. Additionally, the low dispersal suggests that environmental management could contribute to the reduction of vector density. Our data serve as the first estimates of vector survival rates of populations of the sibling species Lu. longipalpis under natural conditions and could be applied in the evaluation of prevention and control measures.