Population dynamics of Anopheles nuneztovari in Colombia

An updated checklist of Anopheles (Diptera, Culicidae) of Colombia with new records and distribution data

Several species of Anopheles mosquitoes (Arthropoda, Insecta, Diptera, Culicidae) are important in public health due to their role in malaria transmission. Of the more than 500 Anopheles species worldwide, 47 have been reported in Colombia, but only nine are known to transmit malaria. Taxonomic classification of these mosquitoes is complicated by the existence of species complexes and groups of closely related species that are difficult to distinguish based on morphological characteristics. However, molecular techniques have contributed to resolving taxonomic uncertainties, definition of molecular variants and facilitated the correction of erroneous taxonomic assignments. This study aimed to update the list of Anopheles species reported for Colombia. A species checklist was compiled by reviewing catalogs, publications, databases, and unpublished data. Only formally characterized species were included, along with their geographic range and ecological distribution. The final list includes 44 formally characterized Anopheles species belonging to five subgenera. The Nyssorhynchus subgenus constituted the largest group with 17 species and the widest distribution, occurring in 18 ecoregions. The Anopheles subgenus was the second largest group with 16 species and occurrences in 16 ecoregions. Sixty-six new presence records were added to the checklist. The updated Anopheles checklist, encompassing presence records and ecological distributions, enhances our understanding of Anopheles mosquito biodiversity. Furthermore, it contributes to improved public health by providing a foundation for targeted vector control interventions.

Malaria Vectors and Plasmodium Transmission in Malaria-Endemic Localities of Colombia

Anopheles species composition, abundance, and Plasmodium natural infection are important aspects to assess malaria transmission risk. In this study, these aspects were evaluated in a large number of localities in the most important malaria-endemic regions of Colombia. Mosquitoes were collected from 2012 to 2015 in 55 localities of northwestern and western Colombia. Anopheles species composition, abundance, and Plasmodium infection were estimated. A total of 13,218 Anopheles specimens were evaluated. The highest species richness was detected in the northwest, where the main vectors, An. albimanus (27.8%) and An. nuneztovari (26.7%), were the most abundant species. In the west, An. nuneztovari predominated (51.6%), followed by An. darlingi (29.2%). Six species were infected with Plasmodium, An. darlingi, An. nuneztovari, An. albimanus, An. calderoni, An. triannulatus, and An. braziliensis. Results showed that in these localities the main Colombian vectors are widely spread, which suggests a high malaria risk. Notably, this study is the first to report An. braziliensis from Colombia as being naturally infected with Plasmodium. Infection results for species that are suspected local vectors indicate the importance of conducting further studies to assess their epidemiological importance. This information provides the basis for the application of directed vector control strategies that are species-specific.

Entomological parameters and population structure at a microgeographic scale of the main Colombian malaria vectors Anopheles albimanus and Anopheles nuneztovari

Population subdivision among several neotropical malaria vectors has been widely evaluated; however, few studies have analyzed population variation at a microgeographic scale, wherein local environmental variables may lead to population differentiation. The aim of the present study was to evaluate the genetic and geometric morphometric structure of Anopheles nuneztovari and Anopheles albimanus in endemic localities of northwestern Colombia. Genetic and phenetic structures were evaluated using microsatellites markers and wing geometric morphometrics, respectively. In addition, entomological indices of importance in transmission were calculated. Results showed that the main biting peaks of Anopheles nuneztovari were between 20:00 and 22:00, whereas Anopheles albimanus exhibited more variation in biting times among localities. Infection in An. nuneztovari by Plasmodium spp. (IR: 4.35%) and the annual entomological inoculation rate (30.31), indicated high vector exposure and local transmission risk. We did not detect Plasmodium-infected An. albimanus in this study. In general, low genetic and phenetic subdivision among the populations of both vectors was detected using a combination of phenotypic, genetic and environmental data. The results indicated high regional gene flow, although local environmental characteristics may be influencing the wing conformation differentiation and behavioral variation observed in An. albimanus. Furthermore, the population subdivision detected by microsatellite markers for both species by Bayesian genetic analysis provides a more accurate picture of the current genetic structure in comparison to previous studies. Finally, the biting behavior variation observed for both vectors among localities suggests the need for continuous malaria vector surveys covering the endemic region to implement the most effective integrated local control interventions.

nAnopheles blood meal sources and entomological indicators related to Plasmodium transmission in malaria endemic areas of Colombia

Malaria is an important public health problem, caused by Plasmodium parasites which are transmitted by female Anopheles mosquitoes that bite humans to obtain blood. The aim of this work was to identify the blood feeding sources of Anopheles female mosquitoes and calculate their entomological indices in relation to Plasmodium transmission. Mosquitoes were collected in malaria endemic localities of the Bajo Cauca and Pacific regions of Colombia using human landing catch and barrier screens, from 18:00 - 24:00 hr, in 2018-2021. Animal censuses within a radius of ∼250 meters were carried out at each sampling site. A total of 2,018 Anopheles specimens were collected and the most abundant species were Anopheles (Nys.) darlingi and Anopheles (Nys.) nuneztovari. The highest human biting rate was 77.5 bites per person per night (b/p/n) for An. nuneztovari in Córdoba-Pacific and 17.5 b/p/n for An. darlingi in Villa Grande-Bajo Cauca. Both species were active mainly in indoor unwalled rooms of the houses. Only An. nuneztovari from Córdoba-Pacific was infected with Plasmodium, with an entomological inoculation rate of 91.25 infective bites per year. Detection of blood feeding sources demonstrate that humans were the most common host, however, An. nuneztovari showed a preference for feeding on dogs and An. darlingi on pigs, dogs and Galliformes, rather than humans. These results contribute to entomological surveillance information and provide valuable data that can be used to tailor effective control interventions to minimize human-vector contact in these malaria endemic regions.

Blood feeding habits of mosquitoes: hardly a bite in South America

Mosquito blood feeding plays a key role in epidemiology. Despite its importance and large number of studies worldwide, less attention has been paid in South America. We summarized some general concepts and methodological issues related to the study of mosquito blood feeding habits, and compiled and analyzed all published information regarding the subject in the continent until 2020. Available literature comprised 152 scientific studies, that pursued different approaches: human landing catches (102 studies), baited trap (19), and blood meal analyses of collected specimens (38). Among the latter, 23 used serological and 15 molecular techniques. Species most frequently studied were those incriminated in malaria transmission, whereas relevant vectors such as Aedes aegypti, Ae. albopictus, and Haemagogus janthinomys were surprisingly neglected. Brazil was the leading country both in number of works and species studied. For over 70% of the species and three out of 13 South American countries there is no single information on mosquito blood feeding habits. Data from baited traps included 143 mosquito species, 83.9% of which were attracted to humans, either exclusively (10.5%) or in combination with other vertebrates (73.4%). Host blood identification of field collected specimens provided data on 102 mosquito species, and 60.8% of these fed on humans (55.9% combined with other vertebrates). Only 17 of the 73 species assessed by both methods yielded similar feeding patterns. Finally, supplementary tables are provided in a comprehensive summary of all information available and information gaps are highlighted for future research in the continent.

Effect of land cover and landscape fragmentation on anopheline mosquito abundance and diversity in an important Colombian malaria endemic region

Landscape structure influences the distribution and abundance of anopheline mosquitoes and has an indirect impact on malaria transmission. This work aimed to determine the effect of land cover and landscape fragmentation on anopheline mosquito abundance and diversity in an important Colombian malaria endemic area, the Bajo Cauca region. Diversity indices were calculated for Anopheles mosquitoes collected in various localities of the region. Land cover types were characterized using orthorectified aerial photographs to estimate landscape metrics. The relationship between landscape fragmentation and species diversity was evaluated by regression analysis. The correlation between species abundance and land cover types was determined using canonical correspondence analyses. Results showed a statistically significant tendency for a lower diversity of the Anopheles community in landscapes with higher patch number, patch density and effective mesh size. For most species, there was evidence of a significant relationship between species abundance and land covers modified by anthropic activities which generate forest loss. These results indicate that activities that modify the landscape structure and land cover composition generate changes that affect the spatial distribution and composition of epidemiologically-important Anopheles species, which may impact malaria distribution in a region. This information is useful to guide control interventions that promote unfavorable landscapes for malaria vector propagation.

Spatial fine-resolution model of malaria risk for the Colombian Pacific region

OBJECTIVE

To categorise and map, at high resolution, the risk of malaria incidence in the Pacific region, the main malaria-endemic region of Colombia.

METHODS

The relationship between the environmental variables Normalized Difference Vegetation Index Normalized Difference Water Index, Topographic Wetness Index, precipitation and temperature with the observed Annual Parasitic Index was evaluated using a generalised linear model. An incidence risk map at a resolution of 1 km² was constructed and projected to the entire endemic region. Associations of malaria risk categories with both presence records and co-occurrence of the three main malaria vectors were determined.

RESULTS

A significant correlation was found for the incidence of malaria with precipitation and Normalized Difference Vegetation Index (R²  = 0.98, P < 0.05), whereas there was no significant correlation with the remaining environmental and topographic variables. Moderate- to high-risk areas were located mainly in central Chocó Department along the San Juan and Atrato rivers and in areas west of the Cauca River and Pacific lowlands of the Andes Mountains. There was a statistically significant relationship for the presence of the two main vectors Anopheles darlingi and Anopheles nuneztovari with the high malaria risk category. Furthermore, malaria risk was directly proportional to the number of co-occurring vector species.

CONCLUSIONS

The map obtained provides useful information on the risk of malaria in particular places of the Colombian Pacific region. The data can be used by public entities to optimise the allocation of economic resources for vector control interventions and surveillance.

Potential distribution of main malaria vector species in the endemic Colombian Pacific region

OBJECTIVE

To assess the existing fundamental niche, potential distribution and degree of niche overlap for the three main Colombian malaria vectors Anopheles albimanus, Anopheles darlingi and Anopheles nuneztovari in the major malaria endemic Pacific region.

METHODS

We used models based on presence records and Normalised Difference Vegetation Index (NDVI) data, created using the maximum entropy algorithm.

RESULTS

The three vector species occupied heterogeneous environments, and their NDVI values differed. Anopheles albimanus had the largest niche amplitude and was distributed mainly on coastal areas. Environmentally suitable areas for An. albimanus and An. nuneztovari were the dry forest of inter-Andean Valleys in south-western Colombia, as confirmed for An. albimanus during model validation. There was a slight degree of niche overlap between An. darlingi and An. nuneztovari, and the species co-occurred in humid forests, predominantly in riparian zones of the San Juan and Atrato rivers.

CONCLUSION

The information obtained may be used for the implementation of vector control interventions in selected priority areas to reduce malaria risk in this region while optimising resources.

Relationship between land cover and Anophelinae species abundance, composition and diversity in NW Colombia

Anthropic activities, mainly deforestation, have produced rapid transformation of land cover types in the Urabá region at northwest Colombia. Land cover alterations impact the abundance and composition of the Anophelinae community, affecting malaria transmission dynamics. Therefore, this study used landscape metrics to evaluate the relationship of land cover types with Anophelinae species abundance, composition and diversity in the important malaria endemic Urabá region, in NW Colombia. Orthorectified aerial photographs were used to identify land cover types in four localities of the region. Landscape metrics were obtained and diversity indices were estimated for both, land covers and Anophelinae species collected. The impact of land cover type on the presence and abundance of Anophelinae species was evaluated using a canonical correspondence analysis. Diversity indices showed differences in the Anophelinae community and land covers. The variables with more influence in the Anophelinae community composition were locality, bare soil and the interaction between forest and bare soil covers. The most abundant and dominant species Nyssorhynchus nuneztovari (former Anopheles nuneztovari), related with impacted environments was associated with grass, shrub and bare soil land covers. In conclusion, land covers derived from anthropic activities favored the presence and abundance of the main malaria vectors; but, regardless of differences in landscape, unknown specific factors varying among localities lead to a unique configuration in each site that directly shaped anopheline community composition locally. This information is essential for the development of malaria risk maps and for the design of integrated vector control interventions that include the recognition of the landscape features favoring human-vector contact.

Anopheles species composition and entomological parameters in malaria endemic localities of North West Colombia

Environmental variations associated with alterations derived from human activities affect mosquito abundance and composition. The objective of this study was to evaluate species abundance, composition, biting behavior and human biting rates for Anopheles specimens collected in localities of an important malaria endemic region in NW Colombia. A total of 2041 specimens belonging to nine species were collected in six malaria endemic localities of the Bajo Cauca region. Anopheles braziliensis was the most abundant species (n = 850, 41.7%) and exhibited the highest human biting rate (64.8 b.p.n), followed by the primary vectors Anopheles nuneztovari (n = 614, 30%) and Anopheles darlingi (n = 368, 18%). Biting activity of the main malaria vectors An. nuneztovari and An. darlingi and the opportunistic species An. braziliensis suggests high biting exposure for humans, mainly from 19:00 h to 23:00 h, and therefore, increased malaria risk at these hours. Regarding mosquito species, Puerto Astilla locality in Nechí municipality exhibited the highest α diversity, but in general, diversity in all localities was low. This information provides the bases for the implementation of targeted and effective vector control interventions directed to reduce human vector-contact.

Nyssorhynchus dunhami: bionomics and natural infection by Plasmodium falciparum and P. vivax in the Peruvian Amazon

BACKGROUND Nyssorhynchus dunhami, a member of the Nuneztovari Complex, has been collected in Brazil, Colombia, and Peru and described as zoophilic. Although to date Ny. dunhami has not been documented to be naturally infected by Plasmodium, it is frequently misidentified as other Oswaldoi subgroup species that are local or regional malaria vectors. OBJECTIVES The current study seeks to verify the morphological identification of Nuneztovari Complex species collected in the peri-Iquitos region of Amazonian Peru, to determine their Plasmodium infection status, and to describe ecological characteristics of their larval habitats. METHODS We collected Ny. nuneztovari s.l. adults in 2011-2012, and Ny. nuneztovari s.l. larvae and adults in 2016-2017. When possible, samples were identified molecularly using cytochrome c oxidase subunit I (COI) barcode sequencing. Adult Ny. nuneztovari s.l. from 2011-2012 were tested for Plasmodium using real-time PCR. Environmental characteristics associated with Ny. nuneztovari s.l. larvae-positive water bodies were evaluated. FINDINGS We collected 590 Ny. nuneztovari s.l. adults and 116 larvae from eight villages in peri-Iquitos. Of these, 191 adults and 111 larvae were identified by COI sequencing; all were Ny. dunhami. Three Ny. dunhami were infected with P. falciparum, and one with P. vivax, all collected from one village on one night. Ny. dunhami larvae were collected from natural and artificial water bodies, and their presence was positively associated with other Anophelinae larvae and amphibians, and negatively associated with people living within 250m. MAIN CONCLUSIONS Of Nuneztovari Complex species, we identified only Ny. dunhami across multiple years in eight peri-Iquitos localities. This study is, to our knowledge, the first report of natural infection of molecularly identified Ny. dunhami with Plasmodium. We advocate the use of molecular identification methods in this region to monitor Ny. dunhami and other putative secondary malaria vectors to more precisely evaluate their importance in malaria transmission.

Insecticide Resistance and Its Intensity in Populations of Malaria Vectors in Colombia

Insecticide resistance in malaria vectors threatens malaria prevention and control efforts. In Colombia the three primary vectors, Anopheles darlingi, An. nuneztovari s.l., and An. albimanus, have reported insecticide resistance to pyrethroids, organophosphates, carbamates, and DDT; however, the insecticide resistance monitoring is not continuous, and the data on the prevalence of resistance is scarce and geographically limited. We describe the resistance levels and intensity of previously detected resistant populations among primary malaria vectors from the most endemic malaria areas in Colombia. The study was carried out in 10 localities of five states in Colombia. Bioassays were carried out following the methodology of CDC Bottle Bioassay using the discriminating concentration and in order to quantify the intensity the specimens were exposed to 2, 5, and 10X discriminating concentrations. Five insecticides were tested: deltamethrin, lambda-cyhalothrin, alpha-cypermethrin, permethrin, and DDT. The results provide evidence of low resistance intensity and resistance highly localized to pyrethroids and DDT in key malaria vectors in Colombia. This may not pose a threat to malaria control yet but frequent monitoring is needed to follow the evolution of insecticide resistance.

Discrimination of Anopheles species of the Arribalzagia Series in Colombia using a multilocus approach

The Arribalzagia Series of the Anopheles Subgenus comprises morphologically similar species or members of species complexes which makes correct species identification difficult. Therefore, the aim of this work was to discriminate the morphospecies of the Arribalzagia Series present in Colombia using a multilocus approach based on ITS2, COI and CAD sequences. Specimens of the Arribalzagia Series collected at 32 localities in nine departments were allocated to seven species. Individual and concatenated Bayesian analyses showed high support for each of the species and reinforced the previous report of the Apicimacula species Complex with distribution in the Pacific Coast and northwestern Colombia. In addition, a new molecular operational taxonomic unit-MOTU was identified, herein denominated near Anopheles peryassui, providing support for the existence of a Peryassui species Complex. Further, the CAD gene, just recently used for Anopheles taxonomy and phylogeny, demonstrated its power in resolving phylogenetic relationships among species of the Arribalzagia Series. The divergence times for these species correspond to the early Pliocene and the Miocene. Considering the epidemiological importance of some species of the Series and their co-occurrence in malaria endemic regions of Colombia, their discrimination constitutes an important step for vector incrimination and control in the country.