Diversity patterns, Leishmania DNA detection, and bloodmeal identification of Phlebotominae sand flies in villages in northern Colombia

Abstract

Leishmaniases are neglected tropical diseases exhibiting complex transmission cycles due to the number of parasite species circulating, sand fly species acting as vectors and infected mammals, including humans, which are defined in the New World as accidental hosts. However, current transmission scenarios are changing, and the disease is no longer exclusively related to forested areas but urban transmission foci occur, involving some species of domestic animals as suspected reservoirs. The aim of this study was to determine the transmission cycles in urban environments by evaluating sand fly diversity, detection of Leishmania DNA, and bloodmeal sources through intra and peridomestic collections. The study was carried out in Colombia, in 13 municipalities of Cordoba department, implementing a methodology that could be further used for the evaluation of vector-borne diseases in villages or towns. Our sampling design included 24 houses randomly selected in each of 15 villages distributed in 13 municipalities, which were sampled in two seasons in 2015 and 2016. Sand flies were collected using CDC light traps placed in intra and peridomestic habitats. In addition to the morphological identification, molecular identification through DNA barcodes was also performed. A total of 19,743 sand flies were collected and 13,848 of them (10,268 females and 3,580 males) were used in molecular procedures. Circulation of two known parasite species-Leishmania infantum and Leishmania panamensis was confirmed. Blood source analyses showed that sand flies fed on humans, particularly in the case of the known L. infantum vector, P. evansi; further analyses are advised to evaluate the reservoirs involved in parasite transmission. Our sampling design allowed us to evaluate potential transmission cycles on a department scale, by defining suspected vector species, parasite species present in different municipalities and feeding habits.

Fig 1. Sampling localities in the Cordoba department in Colombia.

a. Córdoba department location in the country. b. Fifteen sampled localities in 13 municipalities of the Cordoba department. Colors correspond to the distribution of Leishmania species, in red Leishmania infantum, in yellow L. panamensis and in black localities with no parasites detected. c. Gridded sampling design with a 25m * 25m resolution built using satellite images to identify houses. On the grid 24 random cells were selected and the houses present inside were sampled in each locality. This grid is an example that corresponds to the Vereda el Vidrial, Cordoba, Colombia.

Fig 2. Sand fly species diversity and community composition in each of the 15 sampled localities in the Cordoba department in Colombia.

Diversity was computed as total number of sand flies captured by locality (grouped from 24 houses, sampled both intra and peridomiciliary). Different colors represent different species of sand flies identified with traditional morphological techniques and confirmed via DNA barcoding.

Fig 3. Cluster dendrogram showing similarity of sand-fly community composition of the sampled towns in Cordoba, Colombia.

The dendrogram is based on a Bray-Curtis distance with towns clustered together having communities more similar to each other than to other towns. For this dendrogram, sandflies from all houses in a single sampled town were grouped irrespective of wether they were sampled intra or peridomicilary.