[Anopheles cruzii larvae found in bromelias in an urban area on the Brazilian coast]

The influence of anthropogenic habitat fragmentation on the genetic structure and diversity of the malaria vector Anopheles cruzii (Diptera: Culicidae)

Fragmentation of natural environments as a result of human interference has been associated with a decrease in species richness and increase in abundance of a few species that have adapted to these environments. The Brazilian Atlantic Forest, which has been undergoing an intense process of fragmentation and deforestation caused by human-made changes to the environment, is an important hotspot for malaria transmission. The main vector of simian and human malaria in this biome is the mosquito Anopheles cruzii. Anthropogenic processes reduce the availability of natural resources at the tree canopies, An. cruzii primary habitat. As a consequence, An. cruzii moves to the border of the Atlantic Forest nearing urban areas seeking resources, increasing their contact with humans in the process. We hypothesized that different levels of anthropogenic changes to the environment can be an important factor in driving the genetic structure and diversity in An. cruzii populations. Five different hypotheses using a cross-sectional and a longitudinal design were tested to assess genetic structure in sympatric An. cruzii populations and microevolutionary processes driving these populations. Single nucleotide polymorphisms were used to assess microgeographic genetic structure in An. cruzii populations in a low-endemicity area in the city of São Paulo, Brazil. Our results show an overall weak genetic structure among the populations, indicating a high gene flow system. However, our results also pointed to the presence of significant genetic structure between sympatric An. cruzii populations collected at ground and tree-canopy habitats in the urban environment and higher genetic variation in the ground-level population. This indicates that anthropogenic modifications leading to habitat fragmentation and a higher genetic diversity and structure in ground-level populations could be driving the behavior of An. cruzii, ultimately increasing its contact with humans. Understanding how anthropogenic changes in natural areas affect An. cruzii is essential for the development of more effective mosquito control strategies and, on a broader scale, for malaria-elimination efforts in the Brazilian Atlantic Forest.

Neotropical Anopheles (Kerteszia) mosquitoes associated with bromeliad-malaria transmission in a changing world

Kerteszia is a neotropical subgenus of Anopheles composed of 12 species. The species in this subgenus are strongly associated with humid forests rich in epiphytic bromeliads. Forest fragmentation and anthropogenic changes can therefore have a negative impact on the abundance and survival of these mosquito species. Within this subgenus, four species are considered primary vectors of malaria: An. cruzii, An. bellator, An. homunculus and An. neivai. Malaria cases associated with Kerteszia species are often referred to as bromeliad malaria, a type of malaria reported to be endemic in the coastal rainforest of the neotropical region since the end of the nineteenth century. Although the incidence of bromeliad-malaria cases has decreased since the middle of the last century, autochthonous malaria cases continue to be registered every year. The complexity of the epidemiology of bromeliad malaria appears to be increasing as asymptomatic plasmodial infections and transmission of simian Plasmodium to humans have recently been reported. Kerteszia vector species have a great affinity for human beings and can be found in human-modified areas close to forest fragments such as in the Extra-Amazonian region of Brazil, Colombian pacific coast, and the Caribbean coast. Deforestation and forest fragmentation have been occurring continuously in the biomes of the neotropical region, and findings of Kerteszia species in dwellings are frequent in this region. Controlling the species in the Kerteszia subgenus is particularly difficult because they move frequently from natural to rural and peri-urban areas in search of blood sources, posing a challenge for the development of control strategies based on integrated vector management. Furthermore, as it has been shown that some Kerteszia species share similar morphological and genetic characteristics, the existence of a species complex formed by cryptic, sibling species within the Kerteszia group in different areas in the South and Southeast of Brazil cannot be ruled out. The existence of such a complex could represent an obstacle to the control of Kerteszia species and consequently to the elimination of bromeliad-malaria transmission in these regions. Here, we review publications that focus on the biology and ecology of Kerteszia malaria vectors and their association with human-modified areas and bromeliad-malaria transmission.

The dominant Anopheles vectors of human malaria in the Americas: occurrence data, distribution maps and bionomic précis

BACKGROUND

An increasing knowledge of the global risk of malaria shows that the nations of the Americas have the lowest levels of Plasmodium falciparum and P. vivax endemicity worldwide, sustained, in part, by substantive integrated vector control. To help maintain and better target these efforts, knowledge of the contemporary distribution of each of the dominant vector species (DVS) of human malaria is needed, alongside a comprehensive understanding of the ecology and behaviour of each species.

RESULTS

A database of contemporary occurrence data for 41 of the DVS of human malaria was compiled from intensive searches of the formal and informal literature. The results for the nine DVS of the Americas are described in detail here. Nearly 6000 occurrence records were gathered from 25 countries in the region and were complemented by a synthesis of published expert opinion range maps, refined further by a technical advisory group of medical entomologists. A suite of environmental and climate variables of suspected relevance to anopheline ecology were also compiled from open access sources. These three sets of data were then combined to produce predictive species range maps using the Boosted Regression Tree method. The predicted geographic extent for each of the following species (or species complex*) are provided: Anopheles (Nyssorhynchus) albimanus Wiedemann, 1820, An. (Nys.) albitarsis*, An. (Nys.) aquasalis Curry, 1932, An. (Nys.) darlingi Root, 1926, An. (Anopheles) freeborni Aitken, 1939, An. (Nys.) marajoara Galvão & Damasceno, 1942, An. (Nys.) nuneztovari*, An. (Ano.) pseudopunctipennis* and An. (Ano.) quadrimaculatus Say, 1824. A bionomics review summarising ecology and behaviour relevant to the control of each of these species was also compiled.

CONCLUSIONS

The distribution maps and bionomics review should both be considered as a starting point in an ongoing process of (i) describing the distributions of these DVS (since the opportunistic sample of occurrence data assembled can be substantially improved) and (ii) documenting their contemporary bionomics (since intervention and control pressures can act to modify behavioural traits). This is the first in a series of three articles describing the distribution of the 41 global DVS worldwide. The remaining two publications will describe those vectors found in (i) Africa, Europe and the Middle East and (ii) in Asia. All geographic distribution maps are being made available in the public domain according to the open access principles of the Malaria Atlas Project.