Ecological niche modelling and predicted geographic distribution of <i>Lutzomyia cruzi</i>, vector of <i>Leishmania infantum</i> in South America

<div><p>In some transmission foci of <i>Leishmania infantum</i> in Brazil, <i>Lutzomyia cruzi</i> could be considered the main vector of this pathogen. In addition, <i>L</i>. <i>cruzi</i> is a permissive vector of <i>L</i>. <i>amazonensis</i>. Its geographical distribution seems to be restricted and limited to <i>Cerrado</i> and Pantanal biomes, which includes some areas in Brazil and Bolivia. Considering that predicting the distribution of the species involved in transmission cycles is an effective approach for assessing human disease risk, this study aims to predict the spatial distribution of <i>L</i>. <i>cruzi</i> using a multiscale ecological niche model based in both climate and habitat variables. Ecological niche modelling was used to identify areas in South America that are environmentally suitable for this particular vector species, but its presence is not recorded. Vector occurrence records were compiled from the literature, museum collections and Brazilian Health Departments. Bioclimatic variables, altitude, and land use and cover were used as predictors in five ecological niche model algorithms: BIOCLIM, generalised linear model (logistic regression), maximum entropy, random forests, and support vector machines. The vector occurs in areas where annual mean temperature values range from 21.76°C to 26.58°C, and annual total precipitation varies from 1005 mm and 2048 mm. Urban areas were most present around capture locations. The potential distribution area of <i>L</i>. <i>cruzi</i> according to the final ecological niche model spans Brazil and Bolivia in patches of suitable habitats inside a larger climatically favourable area. The bigger portion of this suitable area is located at Brazilian States of Mato Grosso do Sul and Mato Grosso. Our findings identified environmentally suitable areas for <i>L</i>. <i>cruzi</i> in regions without its known occurrence, so further field sampling of sand flies is recommended, especially in southern Goiás State, Mato Grosso do Sul (borders with Mato Grosso, São Paulo and Minas Gerais); and in Bolivian departments Santa Cruz and El Beni.</p></div

Summary of model settings.

<p>Summary of model settings.</p

Potential distribution of <i>Lutzomyia cruzi</i> based on ecological niche modelling predictions and known presence records.

<p>Circles represent areas of environmental suitability that need further field studies to assess vector occurrence. Arrows indicate records that were not predicted by the models. Map produced in QGIS.</p

Percentage of land use and cover types observed 500 m around presence records of <i>Lutzomyia cruzi</i> in Brazil (N = 20).

<p>A) urban area; B) open forest; C) dense forest; D) pasture; E) open field; F) other non-forest formations; G) agriculture or pasture; H) non-forest natural areas; I) water bodies; J) unclassified.</p

Compiled occurrence records of <i>Lutzomyia cruzi</i> classified in different spatial precision levels (green: high; yellow: medium; red: low).

<p>The blue line delimits the model calibration area. Map produced in QGIS.</p

Predicted areas of suitable climate (blue) and habitat (green) for <i>Lutzomyia cruzi</i>.

<p>Map produced in QGIS.</p

Minimum, median, mean and maximum values of climatic variables and altitude recorded at capture locations of <i>Lutzomyia cruzi</i>.

<p>Minimum, median, mean and maximum values of climatic variables and altitude recorded at capture locations of <i>Lutzomyia cruzi</i>.</p

Experimental infection and transmission of <i>Leishmania</i> by <i>Lutzomyia cruzi</i> (Diptera: Psychodidae): Aspects of the ecology of parasite-vector interactions

<div><p>Several parameters should be addressed before incriminating a vector for <i>Leishmania</i> transmission. Those may include its ability to become infected by the same <i>Leishmania</i> species found in humans, the degree of attractiveness for reservoirs and humans and capacity to sustain parasite infection under laboratory conditions. This study evaluated the vectorial capacity of <i>Lutzomyia cruzi</i> for <i>Leishmania infantum</i> and gathered information on its ability to harbor <i>L</i>. <i>amazonensis</i>. Laboratory-reared <i>Lu</i>. <i>cruzi</i> were infected experimentally by feeding them on dogs infected naturally with <i>L</i>. <i>infantum</i> and hamsters infected with <i>L</i>. <i>amazonensis</i>. Sand fly attractiveness to dogs and humans was determined using wild caught insects. The expected daily survival of infected <i>Lu</i>. <i>cruzi</i>, the duration of the gonotrophic cycle, and the extrinsic incubation period were also investigated for both parasites. Vector competence was investigated for both <i>Leishmania</i> species. The mean proportion of female sand flies that fed on hosts was 0.40. For <i>L</i>. <i>infantum</i> and <i>L</i>. <i>amazonensis</i>, <i>Lu</i>. <i>cruzi</i> had experimental infection rates of 10.55% and 41.56%, respectively. The extrinsic incubation period was 3 days for both <i>Leishmania</i> species, regardless of the host. Survival expectancy of females infected with <i>L</i>. <i>infantum</i> and <i>L</i>. <i>amazonensis</i> after completing the gonotrophic cycle was 1.32 and 0.43, respectively. There was no association between <i>L</i>. <i>infantum</i> infection and sand fly longevity, but <i>L</i>. <i>amazonensis</i>–infected flies had significantly greater survival probabilities. Furthermore, egg-laying was significantly detrimental to survival. <i>Lu</i>. <i>cruzi</i> was found to be highly attracted to both dogs and humans. After a bloodmeal on experimentally infected hosts, both parasites were able to survive and develop late-stage infections in <i>Lu</i>. <i>cruzi</i>. However, transmission was demonstrated only for <i>L</i>. <i>amazonensis</i>–infected sand flies. In conclusion, <i>Lu</i>. <i>cruzi</i> fulfilled several of the requirements of vectorial capacity for <i>L</i>. <i>infantum</i> transmission. Moreover, it was also permissive to <i>L</i>. <i>amazonensis</i>.</p></div

Estimates obtained for the Cox regression model adjusted by considering the covariates <i>L</i>. <i>infantum</i> infection, egg-laying, and egg-laying time.

<p>Estimates obtained for the Cox regression model adjusted by considering the covariates <i>L</i>. <i>infantum</i> infection, egg-laying, and egg-laying time.</p

Estimates obtained for the Cox regression model adjusted by considering the covariates egg-laying and egg-laying time.

<p>Estimates obtained for the Cox regression model adjusted by considering the covariates egg-laying and egg-laying time.</p