Phlebotomine sand flies in rural Mayan communities of Southern Mexico: The heterogeneity of the ruralscape increases the entomological risk

In the Yucatan Peninsula, tropical preserved forests harbor a high diversity of phlebotomine sand fly species, potential vectors of Leishmania. As a result, a significant risk of contracting localized cutaneous leishmaniasis (LCL) is associated with entry into these forest ecosystems. However, with the current trajectory of land use in the region, communities now live within modified landscapes which could increase their risk of contact with vectors. In this study, we characterized the sand fly fauna and its relationship with the characteristics of peridomestic habitats in two rural communities in Yucatan characterized by contrasting records of leishmaniasis. Five human dwellings in each community were randomly selected and the peridomestic landscape was characterized (i.e., type and percentage of land use). For the collection of sand flies, CDC traps were deployed in both the intra and peridomicile. Differences in alpha and beta diversity between communities and ecotopes were estimated considering three separate groups, all species together, zoophilic species, and anthropophilic species. In total, 1, 241 sand flies represented by eight species were collected from November 2021-March 2022. Both communities registered the presence of sand flies in the intra and peridomicile, and females were more abundant than males. However, the greatest diversity of species was recorded in the peridomicile of the community with the highest composition of land uses. Our study demonstrates that the transformation of the forest around the communities favors the abundance and richness of sand flies in the peridomestic environment. We discuss the limitations and implications of our findings regarding the potential risk of the emergence of peri‑rural cycles of leishmaniasis in the region.

Biting rhythms and infection rates of anthropophilic sand fly species (Diptera: Phlebotominae) in sites with different land use in southern Mexico

Could tropical forest conversion shape sand fly (Diptera: Phlebotominae) biting rhythms and Leishmania infection rates? Using a Shannon trap, we estimated the bite rate and infection prevalence among anthropophilic sand flies at sites with different land use in southern Mexico. We estimated the expected monthly infection rate of the Leishmania parasite along the gradient and generated information on the biting rhythm of sand flies in a poorly characterized cutaneous leishmaniasis endemic region. We used generalized mixed linear and mixed additives models to evaluate differences in the biting rate, nocturnal activity, and inoculation rate of female sand flies, as well as their relationship with the loss of forest cover and environmental disparities recorded throughout the study area. Our results show that the loss of forest cover influences the biting rhythm of sand fly species and the potential number of infectious bites with Leishmania, but the greatest entomological and potential epidemiological risk continues to be associated with sylvatic areas (amplification events). Despite this, we detected that the effect of forest cover (%) on the entomological exposure seems to be also dependent on the sand fly species, and that, albeit to a lesser extent, Leishmania parasite is circulating in disturbed landscapes through generalist and competent sand fly vector species. We also found that land use change did not affect the nocturnal activity, however we detected that important vector species were active most of the time. Contrary to our expectation, temperature and humidity did not shape the biting rhythm of sand fly species. We discuss the limitations and epidemiological implications of our findings regarding the risk of contracting leishmaniasis in southern Mexico.

Effect of land use change on the phlebotomine sand fly assemblages in an emergent focus of cutaneous leishmaniasis in Yucatan, Mexico

As land use intensifies in tropical forests, it is expected that species assemblages will be modified and that key functions of these ecosystems will be affected. The latter scenario is important from a public health perspective, because the land use change has been linked the outbreaks of vector-borne diseases. In this study, we evaluated the response of Phlebotominae (Diptera: Psychodidae) assemblages and their pattern of co-occurrence in four sites with different land use in an emerging cutaneous leishmaniasis focus in Yucatan, Mexico. Our hypothesis is that the conservation status (as forest cover) will positively influence the structure and composition of sand flies' assemblages. Using three different traps over a period of five months, a sampling effort of 1, 440 night-traps was performed. A total of 7, 897 sand fly specimens belonging to six genera and 10 species were collected. Our hypothesis was partially achieved since sand fly diversity increased as forest cover increased and vice versa, however random patterns of co-occurrence in assemblages were detected among sites. Even though the high abundance of sand flies in the forest fragment suggests an amplification effect, our results show that different vector species directly dominate in each site. We discuss the potential implications of the nestedness of species dominance. We suggest that in this emerging focus and under the land use gradient, Lutzomyia cruciata and Psathyromyia cratifer could play a pivotal role in maintaining the transmission cycles of Leishmania. The apparent generalist or colonialist profile of Lu. cruciata in disturbed areas deserves attention, due to the potential risk of leishmaniasis "domiciliation". This information is essential to understand the eco-epidemiology of leishmaniasis and the factors associated with its emergence in Yucatan, Mexico.

First record of larval microhabitats of sandflies in Mexico with the description of the fourth instar larva of Brumptomyia hamata

Despite the medical importance of sandflies as vectors (Diptera: Phlebotominae) of Leishmania spp., immature stages of phlebotomine sandflies have never been found in the wild in Mexico. In the present investigation, we sought to identify specific microhabitats associated with the presence of sandfly immature stages. Field work was conducted in 11 localities of the Yucatan Peninsula and we collected soil samples from each site during two periods (November 2007 to April 2008, November 2008). Soil samples were transported to our base camp and were processed using the Berlese's funnels. We processed a total 242 soil samples with an average weight of 362 ± (SD) 317 gr. From these samples, we were able to recover 51 phlebotomine larvae in five different microhabitats and largest number was obtained from mammal burrows (88%) and from tree-buttresses of Brosimium alicastrum (Berg) (6%). We identified larval microhabitat for Brumptomyia hamata (Fairchild & Hertig) and those specimens provided the material to describe for the first time the fourth instar larva. We also include information of a larval microhabitat of Lutzomyia cruciata (Coquillett). In addition, we recorded a total of 4872 arthropods from 15 taxa in all those soil samples in which sandfly larvae were found, being Collembola (76%) and Acari (10%) the most abundant.

Traditional and Geometric Morphometry Analyses of Lutzomyia cruciata (Diptera: Psychodidae: Phlebotominae) Populations of Chiapas, Mexico

The presence of Lutzomyia (Tricholateralis) cruciata (Coquillett 1907) species complex has been suggested by morphological analysis of eggs and genetic studies of females. The present work aimed to compare the diversity in morphology of four populations of Lu. cruciata from the Coast of Chiapas, Mexico, using traditional (TM) and geometric (GM) methods. Several morphological characteristics that were analyzed provided consistency to differentiate at least, three populations of Lu. cruciata. Both methods were effective to detect morphological differences associated with the geographical sites of capture. In both sexes, three and four groups were detected by TM and GM, respectively. These results suggest marked morphological differences in both sexes of Lu. cruciata that make these methods potentially useful to identify the geographical origin of any specimen of this species captured in the study region. Although the results produced by both methods are coincident, geometric morphometrics turned out to be most advantageous with respect to traditional morphometry, since the latter requires more time and effort. The consistency of our results shows that the variability of environmental conditions on the coast of Chiapas determines a high degree of phenotypic plasticity in Lu. cruciata, with the possibility of prezygotic isolation and the formation of species complex.

Inferring distributional shifts of epidemiologically important North and Central American sandflies from Pleistocene to future scenarios

Nine sandfly species (Diptera: Psychodidae) are suspected or proven vectors of Leishmania spp. in the North and Central America region. The ecological niches for these nine species were modelled in three time periods and the overlaps for all time periods of the geographic predictions (G space), and of ecological dimensions using pairwise comparisons of equivalent niches (E space), were calculated. Two Nearctic, six Neotropical and one species in both bioregions occupied a reduced number of distribution areas. The ecological niche projections for most sandfly species other than Lutzomyia shannoni and Lutzomyia ovallesi have not expanded significantly since the Pleistocene. Only three species increase significantly to 2050, whereas all others remain stable. Lutzomyia longipalpis shared a similar ecological niche with more species than any other, although both L. longipalpis and Lutzomyia olmeca olmeca had conserved distributions over time. Climate change, at both regional and local levels, will play a significant role in the temporal and spatial distributions of sandfly species.

Effect of trapping methods on the estimation of alpha diversity of a phlebotomine sandfly assemblage in southern Mexico

The aims of the study were to (a) investigate the effect of trapping methods on alpha diversity; and (b) enhance the knowledge of the sandfly assemblage in the state of Quintana Roo. Field work was undertaken in a tropical forest of southern Mexico from August 2013 to July 2014. Sampling was conducted monthly during three consecutive nights. For each trapping night, 12 different types of trap were operated from 18.00 to 24.00 hours in four transects. Measures of alpha community diversity were based on the quantification of the number of species (Chao 2, Jackknife 2, Clench's equation, Margalef's index) and the community structure, as well as the dominance (Simpson and Berger-Parker indexes) and evenness (Shannon's entropy index, true diversity of the Jost and Pielou index). With a total sampling effort of 1728 night-traps, 16 101 phlebotomine sandflies were collected; they represented two genera and 13 species. Diversity estimates of 100% (Chao 2 and Clench's equation) and 85% (Jackknife 2) of potential species in the study area were calculated. Shannon traps and CDC light traps indicated the largest number of species, but only Shannon traps showed the greatest abundance. This inventory of sandflies is an important activity to enhance our knowledge of sandfly assemblages and guilds. The ultimate goal of studying alpha diversity in sandflies would be to have a better understanding of the population dynamics and all complex networks of interactions that may, in turn, be associated with the epidemiology of the disease.

Descriptions of the Immature Stages of Lutzomyia (Tricholateralis) cruciata (Coquillett) (Diptera: Psychodidae, Phlebotominae)

The present study presents morphological and chaetotaxic descriptions of the immature stages of Lutzomyia (Tricholateralis) cruciata (Coquillett), a probable vector of leishmaniasis in Mexico. The egg exochorion is consistent with the species already known as Lu. (Tricholaterialis), but different from the Lu. cruciata egg of Chiapas, Mexico. The fourth instar larva of Lu. (Tricholateralis) cruciata possesses a novel antenna, combining morphological characteristics of categories 2 and 3 for neotropical sandflies. Differences between the chaetotaxy of first and fourth instar larvae of Lu. cruciata with those of Lu. (Lutzomyia) and Lu. (Tricholaterlis) are compared and discussed. This is the first time in which the chaetotaxy and morphology of pupa of a species belonging to Lutzomyia (Tricholateralis) sensu Galati have been described, and we recorded for the first time the anterior prothorax setae, which was previously only considered for Old World species.

Assessing the importance of four sandfly species (Diptera: Psychodidae) as vectors of Leishmania mexicana in Campeche, Mexico

Localized cutaneous leishmaniasis represents a public health problem in many areas of Mexico, especially in the Yucatan Peninsula. An understanding of vector ecology and bionomics is of great importance in evaluations of the transmission dynamics of Leishmania parasites. A field study was conducted in the county of Calakmul, state of Campeche, during the period from November 2006 to March 2007. Phlebotomine sandfly vectors were sampled using Centers for Disease Control light traps, baited Disney traps and Shannon traps. A total of 3374 specimens were captured in the two villages of Once de Mayo (93.8%) and Arroyo Negro (6.1%). In Once de Mayo, the most abundant species were Psathyromyia shannoni, Lutzomyia cruciata, Bichromomyia olmeca olmeca and Psychodopygus panamensis (all: Diptera: Psychodidae). The Shannon trap was by far the most efficient method of collection. The infection rate, as determined by Leishmania mexicana-specific polymerase chain reaction, was 0.3% in Once de Mayo and infected sandflies included Psy. panamensis, B. o. olmeca and Psa. shannoni. There were significant differences in human biting rates across sandfly species and month of sampling. Ecological niche modelling analyses showed an overall overlap of 39.1% for the four species in the whole state of Campeche. In addition, the finding of nine vector-reservoir pairs indicates a potential interaction. The roles of the various sandfly vectors in Calakmul are discussed.

Incrimination of four sandfly species previously unrecognized as vectors of Leishmania parasites in Mexico

Cutaneous leishmaniasis (CL) is endemic to the Yucatan Peninsula of Mexico. The main causative agent is the parasite Leishmania mexicana (Biagi) (Kinetoplastida: Trypanosomatidae) and, based on the classic work of Dr Biagi's research team, it has been generally accepted and frequently reported that the only vector of L. mexicana in the region is the sandfly Lutzomyia olmeca olmeca (Vargas & Diáz-Nájera) (Diptera: Psychodidae). Evidence gathered from recent entomological studies conducted mainly in Calakmul, Campeche, however, suggests that other species may also be vectors of L. mexicana. We conducted a field study in two villages in Calakmul, Campeche in the Yucatan Peninsula, where recent cases of CL have been reported, to document the species composition and relative abundances of the sandfly fauna and to identify which species are likely to be the main vectors by assessing the biting rates and parasite infection rates of the suspected vector species. Sandfly catches were conducted from November 2005 to February 2006 in Unión 20 de Junio and Dos Lagunas Sur. Sandflies were captured using Shannon (18.00-22.00 hours), Disney and CDC light traps (18.00-06.00 hours). Biting and infection rates were calculated for the four most abundant species: Lutzomyia cruciata (Coquillett), Lu. o. olmeca, Lutzomyia panamensis (Shannon) and Lutzomyia shannoni (Dyar). In Dos Lagunas Sur, Lu. panamensis and Lu. o. olmeca exhibited the highest biting rates throughout the sampling period. In Unión 20 de Junio, Lu. cruciata and Lu. o. olmeca had the highest biting rates over the same period. Regarding infection rates, we report herein the establishment of a polymerase chain reaction protocol and validation of IR1 and LM17 oligonucleotides to analyse the infection rates of sandflies. Out of 769 females analysed, the overall infection rates were 1.4% in Dos Lagunas Sur and 5.3% in Unión 20 de Junio. In Dos Lagunas Sur we found L. mexicana infections in two sandfly species, Lu. shannoni and Lutzomyia ylephiletor (Fairchild & Hertig), whereas in Unión 20 de Junio we found infections in Lu. shannoni, Lu. cruciata, Lu. o. olmeca and Lu. panamensis. The possible role of these four sandfly species in relation to L. mexicana transmission in Calakmul is discussed.

Relative abundances of sandfly species (Diptera: Phlebotominae) in two villages in the same area of Campeche, in southern Mexico

Leishmania mexicana is the parasite causing most cases of human cutaneous leishmaniasis in southern Mexico, where Lutzomyia olmeca olmeca and Lu. cruciata are the most probable vectors. In the present study, sandflies were collected during one transmission season (November 2001-March 2002) in the village of La Guadalupe and the nearby village of Dos Naciones, in the southern Mexican county of Calakmul. Using Shannon traps, Disney traps and CDC light traps, 5983 sandflies (Brumptomyia and Lutzomyia) were caught. In Dos Naciones the numbers of Lu. panamensis caught in Shannon or CDC traps outnumbered those of the other sandfly species. In La Guadalupe, in contrast, the most abundant species in the collections made with Shannon or CDC traps was Lu. cruciata , followed by Lu. olmeca olmeca and Lu. deleoni. In both locations, the numbers of sandflies attracted to Shannon traps peaked between 18.00 and 22.00 hours. Given the abundance of Lu. olmeca olmeca in the collections made with Shannon and Disney traps (it was the only species caught in the latter), this species is probably the primary vector of Le. mexicana in Calakmul county.

A two years study on vectors of cutaneous Leishmaniasis. Evidence for sylvatic transmission cycle in the state of Campeche, Mexico

Vectors of cutaneous leishmaniasis in the State of Campeche were studied in relation to the transmission cycle of Leishmania (Le.) mexicana. To determine how transmission of leishmaniasis occurs, we collected phlebotomine sand flies for two years. In the first year (October 1990 to November 1991) the collections were made with CDC light traps, Shannon traps and direct captures at natural shelters around the village (< 200 m) of La Libertad. In the second year (February 1993 to January 1994) the catches were performed at 8 km southeast of La Libertad in the forest. Female sand flies were examined for Leishmania. During the first year, 347 sand flies of nine species were collected, most of which were Lutzomyia deleoni (61.3%). When all nine species were considered, more females than males were captured. Low densities of anthropophillic species of sand flies around the village indicated that sylvatic transmission was taking place. For the second year. 1484 sand flies of 16 species were caught. The most common were L. olmeca olmeca (21.7%), L. cruciata (19.2%) and L. ovallesi (14.1%). Similarly, more females were caught than males. Thirty-five females of five species were found infected with flagellates believed to be Leishmania sp. The highest infection rate was found in L. olmeca olmeca (7.1%) followed by L. cruciata (4.5%) and L. ovallesi (1.1%). These data plus other evidence on the epidemiology of human cases and results from reservoir studies are discussed in relation to the sylvatic transmission cycle.