A literature review of dispersal pathways of Aedes albopictus across different spatial scales: implications for vector surveillance

New paradigms in the prevention of canine vector-borne diseases

The prevention of canine vector-borne diseases (CVBDs) is pivotal for the health and welfare of dogs as well as for reducing their zoonotic risk to humans. Scientific knowledge gained in recent years contributed to the development of new strategies for the control of these diseases in different social and cultural contexts. Here, we discuss recent advances in the prevention of vector-borne pathogens (VBPs) affecting dogs with a focus on those of zoonotic relevance.

Influence of insular conditions on wing phenotypic variation in two dominant mosquito vectors, Aedes albopictus and Armigeres subalbatus (Diptera: Culicidae), in the border archipelagos of Thailand

Insects geographically separated into island and mainland populations often exhibit phenotypic variations, a phenomenon known as insular conditions. These conditions can lead to rapid evolutionary changes that affect the morphological characteristics of mosquito vectors. Nevertheless, studies that specifically examine phenotype differences between island and mainland mosquito populations have been limited. In this study, wing variation in size and shape was investigated using the geometric morphometric (GM) technique in two dominant mosquito vectors, Aedes albopictus and Armigeres subalbatus, in the Ranong and Trat archipelagos of Thailand. Significant differences in average wing centroid size (CS) were found in 6 out of 15 population pairs for Ae. albopictus (p < 0.05) and in 5 population pairs for Ar. subalbatus (p < 0.05). After removing the allometric effect, canonical variate analyses (CVA) based on wing shape analysis revealed overlap across all populations for both Ae. albopictus and Ar. subalbatus. However, the statistical analysis indicated that Ar. subalbatus exhibited wing shape differences across all populations (p < 0.05), and most Ae. albopictus populations also displayed distinct wing shapes (p < 0.05), except for the populations from Chang Island and the mainland of Ranong, which showed no significant differences (p > 0.05). These findings enhance our understanding of mosquito adaptability in island regions and provide valuable data for the surveillance and monitoring of vector evolution.

Population genetics of Aedes albopictus in the port cities of Hainan Island and Leizhou Peninsula, China

BACKGROUND

Aedes albopictus is an important vector of arboviral diseases, transmitting yellow fever, dengue fever, chikungunya and Zika. Monitoring its population genetic diversity and genetic differentiation has become essential for the control of infectious disease epidemics, especially in the functional areas of ports of entry. Population genetic monitoring of Ae. albopictus in the port area can help in the monitoring of port mosquito invasions and establishing port sanitary and quarantine measures to prevent the introduction and transmission of vector-borne diseases.

METHODS

Seventeen populations of Ae. albopictus were collected from five port cities on Hainan Island and the Leizhou Peninsula, 8 populations were collected from port areas, 4 from urban areas and 5 from rural areas. Nine microsatellite loci and the mitochondrial COI gene were used to study the population genetic diversity, population genetic structure and interpopulation gene flow of Ae. albopictus.

RESULTS

The nine microsatellite loci used were highly polymorphic, with an average PIC value of 0.768. The UPGMA genetic tree, STRUCTURE barplot and PCoA analyses showed that the 17 Ae. albopictus populations could be divided into three genetic groups. All 17 populations showed high haplotype diversity (Hd = 0.8069-0.9678) and formed 133 distinct haplotypes. These haplotypes can be divided into four genetic clades, but they are not associated with the geographical distribution of Ae. albopictus. Fst and Nm showed strong gene flow and little differentiation among populations.

CONCLUSION

Ae. albopictus in port areas are not significantly different from urban and rural populations due to strong gene flow, which prevents differentiation and increases the genetic diversity of the populations. High genetic diversity facilitates mosquito adaptation to complex environmental changes, which is a challenge for vector-borne disease control in port areas.

Entomological risk assessment for transmission of arboviral diseases by Aedes mosquitoes in a domestic and forest site in Accra, Ghana

Dengue, Zika and chikungunya are Aedes-borne viral diseases that have become great global health concerns in the past years. Several countries in Africa have reported outbreaks of these diseases and despite Ghana sharing borders with some of these countries, such outbreaks are yet to be detected. Viral RNA and antibodies against dengue serotype-2 have recently been reported among individuals in some localities in the regional capital of Ghana. This is an indication of a possible silent transmission ongoing in the population. This study, therefore, investigated the entomological transmission risk of dengue, Zika and chikungunya viruses in a forest and domestic population in the Greater Accra Region, Ghana. All stages of the Aedes mosquito (egg, larvae, pupae and adults) were collected around homes and in the forest area for estimation of risk indices. All eggs were hatched and reared to larvae or adults for morphological identification together with larvae and adults collected from the field. The forest population had higher species richness with 7 Aedes species. The predominant species of Aedes mosquitoes identified from both sites was Aedes aegypti (98%). Aedes albopictus, an important arbovirus vector, was identified only in the peri-domestic population at a prevalence of 1.5%, significantly higher than previously reported. All risk indices were above the WHO threshold except the House Index for the domestic site which was moderate (19.8). The forest population recorded higher Positive Ovitrap (34.2% vs 26.6%) and Container (67.9% vs 36.8%) Indices than the peri-domestic population. Although none of the mosquito pools showed the presence of dengue, chikungunya or Zika viruses, all entomological risk indicators showed that both sites had a high potential arboviral disease transmission risk should any of these viruses be introduced. Continuous surveillance is recommended in these and other sites in the Metropolis to properly map transmission risk areas to inform outbreak preparedness strategies.

Aedes albopictus distribution in Ibagué, Colombia: Potential risk of arboviral outbreaks

Introduction

Aedes albopictus is a vector for arboviruses, such as dengue, Zika, chikungunya, and yellow fever. The first A. albopictus reports on the American continent date back to 1985. It has spread rapidly throughout Colombia since its first report in 1998 due to its ecological and physiological adaptation capability.

Objective

To determine A. albopictus distribution in the 13 communes of Ibagué, Colombia.

Materials and methods

Samples were collected between May and November 2022 in the 13 communes of Ibagué. Vacuum sampling and sweep-netting entomological nets were used in areas with abundant vegetation. The mosquitoes were transported to the Laboratorio de Investigaciones en Parasitología Tropical at the Universidad del Tolima for taxonomic determination.

Results

We identified 708 A. albopictus specimens distributed throughout Ibague’s 13 communes. The highest vector abundance occurred in communes 10, 11, 7, 8, 2, and 9; communes 3, 4, 5, 6, 12, and 13 had a relative abundance of around 3%, while commune 1 had 2% of relative abundance.

Conclusions

Aedes albopictus is distributed throughout all the communes of Ibague. Its dispersion has probably been favored by this region’s environmental and social conditions. We recommend annual monitoring of these vectors populations and molecular characterization of the found arboviruses. Ascertaining this mosquito’s distribution throughout the city will enable focusing entomological control strategies and preventing future arbovirus outbreaks.

A Review of Pathogens Transmitted by the Container-Inhabiting Mosquitoes, Aedes Albopictus, A Global Public Health Threat

Dengue virus (DENV), Chikungunya virus (CHIKV), and Zika virus (ZIKV) are highly pathogenic human arboviruses transmitted by the Aedes (Stegomyia) albopictus (Skuse) (Diptera: Culicidae) or Ae. Albopictus mosquito. These arboviruses are responsible for causing fever, hemorrhagic conditions, and neurological diseases in humans post-bite from an infected Aedes mosquito. Over the past 80 years, the Ae. albopictus has infested every habitable continent, bar Antarctica, thereby escalating the probability of global insect-borne infectious disease outbreaks. This research follows the global transmission pattern of Ae. albopictus and provides a summary of disease prevention and control strategies for mosquito-borne infections, as implemented by the World Health Organization (WHO) and both Asian and European countries. Consequently, this study can aid in the prevention and control of mosquito-borne diseases while acting as a basis for international collaboration on effectively managing arbovirus infection issues in public health.

Invasive hematophagous arthropods and associated diseases in a changing world

Biological invasions have increased significantly with the tremendous growth of international trade and transport. Hematophagous arthropods can be vectors of infectious and potentially lethal pathogens and parasites, thus constituting a growing threat to humans-especially when associated with biological invasions. Today, several major vector-borne diseases, currently described as emerging or re-emerging, are expanding in a world dominated by climate change, land-use change and intensive transportation of humans and goods. In this review, we retrace the historical trajectory of these invasions to better understand their ecological, physiological and genetic drivers and their impacts on ecosystems and human health. We also discuss arthropod management strategies to mitigate future risks by harnessing ecology, public health, economics and social-ethnological considerations. Trade and transport of goods and materials, including vertebrate introductions and worn tires, have historically been important introduction pathways for the most prominent invasive hematophagous arthropods, but sources and pathways are likely to diversify with future globalization. Burgeoning urbanization, climate change and the urban heat island effect are likely to interact to favor invasive hematophagous arthropods and the diseases they can vector. To mitigate future invasions of hematophagous arthropods and novel disease outbreaks, stronger preventative monitoring and transboundary surveillance measures are urgently required. Proactive approaches, such as the use of monitoring and increased engagement in citizen science, would reduce epidemiological and ecological risks and could save millions of lives and billions of dollars spent on arthropod control and disease management. Last, our capacities to manage invasive hematophagous arthropods in a sustainable way for worldwide ecosystems can be improved by promoting interactions among experts of the health sector, stakeholders in environmental issues and policymakers (e.g. the One Health approach) while considering wider social perceptions.

Invasive Aedes mosquitoes in an urban-peri-urban gradient in northern Spain: evidence of the wide distribution of Aedes japonicus

BACKGROUND

The expansion of invasive mosquitoes throughout Europe has increased in recent decades. In northern Spain, Aedes albopictus was detected for the first time in 2014, and Aedes japonicus was detected in the three Basque provinces in 2020. This study aimed to evaluate the distribution of these mosquito species and their association with factors related to urbanization.

METHODS

In 2021, a total of 568 ovitraps were deployed in 113 sampling sites from 45 municipalities with > 10,000 inhabitants. Oviposition substrate sticks were replaced each fortnight and examined for Aedes eggs from June to November. Aedes eggs were counted, and the eggs from a selection of positive oviposition sticks, encompassing at least one stick from each positive ovitrap, were hatched following their life cycle until the adult stage. When egg hatching was not successful, PCR targeting the COI gene and sequencing of amplicons were carried out.

RESULTS

Eggs were detected in 66.4% of the sampling sites and in 32.4% of the ovitraps distributed in the three provinces of the Basque Country. Aedes albopictus and Ae. japonicus were widespread in the studied area, confirming their presence in 23 and 26 municipalities, respectively. Co-occurrence of both species was observed in 11 municipalities. The analysis of the presence of Aedes invasive mosquitoes and the degree of urbanization (urban, suburban, peri-urban) revealed that Ae. albopictus showed a 4.39 times higher probability of being found in suburban areas than in peri-urban areas, whereas Ae. japonicus had a higher probability of being found in peri-urban areas. Moreover, the presence of Ae. albopictus was significantly associated with municipalities with a higher population density (mean = 2983 inh/km²), whereas Ae. japonicus was associated with lower population density (mean = 1590 inh/km²).

CONCLUSIONS

The wide distribution of Ae. albopictus and Ae. japonicus observed confirmed the spread and establishment of these species in northern Spain. A new colonization area of Ae. japonicus in Europe was confirmed. Due to the potential impact of Aedes invasive mosquitoes on public health and according to our results, surveillance programs and control plans should be designed considering different urbanization gradients, types of environments, and population density.

The oral repellent - science fiction or common sense? Insects, vector-borne diseases, failing strategies, and a bold proposition

Over the last decades, unimaginable amounts of money have gone into research and development of vector control measures, repellents, treatment, and vaccines for vector borne diseases. Technological progress and scientific breakthroughs allowed for ever more sophisticated and futuristic strategies. Yet, each year, millions of people still die or suffer from potentially serious consequences of malaria or dengue to more recent infections, such as zika or chikungunya, or of debilitating consequences of neglected tropical diseases. This does not seem value for money. In addition, all current vector control strategies and personal protection methods have shortcomings, some serious, that are either destructive to non-target species or unsatisfactory in their effectiveness. On the other hand, the rapid decline in insect populations and their predators reflects decades-long aggressive and indiscriminate vector control. This major disruption of biodiversity has an impact on human life not anticipated by the well-meaning killing of invertebrates. The objective of this paper is to re-examine current control methods, their effectiveness, their impact on biodiversity, human and animal health, and to call for scientific courage in the pursuit of fresh ideas. This paper brings together topics that are usually presented in isolation, thereby missing important links that offer potential solutions to long-standing problems in global health. First, it serves as a reminder of the importance of insects to human life and discusses the few that play a role in transmitting disease. Next, it examines critically the many currently employed vector control strategies and personal protection methods. Finally, based on new insights into insect chemo-sensation and attractants, this perspective makes a case for revisiting a previously abandoned idea, the oral repellent, and its use via currently successful methods of mass-application. The call is out for focused research to provide a powerful tool for public health, tropical medicine, and travel medicine.

Chikungunya fever

Chikungunya virus is widespread throughout the tropics, where it causes recurrent outbreaks of chikungunya fever. In recent years, outbreaks have afflicted populations in East and Central Africa, South America and Southeast Asia. The virus is transmitted by Aedes aegypti and Aedes albopictus mosquitoes. Chikungunya fever is characterized by severe arthralgia and myalgia that can persist for years and have considerable detrimental effects on health, quality of life and economic productivity. The effects of climate change as well as increased globalization of commerce and travel have led to growth of the habitat of Aedes mosquitoes. As a result, increasing numbers of people will be at risk of chikungunya fever in the coming years. In the absence of specific antiviral treatments and with vaccines still in development, surveillance and vector control are essential to suppress re-emergence and epidemics.

Mapping current and future thermal limits to suitability for malaria transmission by the invasive mosquito Anopheles stephensi

BACKGROUND

Anopheles stephensi is a malaria-transmitting mosquito that has recently expanded from its primary range in Asia and the Middle East, to locations in Africa. This species is a competent vector of both Plasmodium falciparum and Plasmodium vivax malaria. Perhaps most alarming, the characteristics of An. stephensi, such as container breeding and anthropophily, make it particularly adept at exploiting built environments in areas with no prior history of malaria risk.

METHODS

In this paper, global maps of thermal transmission suitability and people at risk (PAR) for malaria transmission by An. stephensi were created, under current and future climate. Temperature-dependent transmission suitability thresholds derived from recently published species-specific thermal curves were used to threshold gridded, monthly mean temperatures under current and future climatic conditions. These temperature driven transmission models were coupled with gridded population data for 2020 and 2050, under climate-matched scenarios for future outcomes, to compare with baseline predictions for 2020 populations.

RESULTS

Using the Global Burden of Disease regions approach revealed that heterogenous regional increases and decreases in risk did not mask the overall pattern of massive increases of PAR for malaria transmission suitability with An. stephensi presence. General patterns of poleward expansion for thermal suitability were seen for both P. falciparum and P. vivax transmission potential.

CONCLUSIONS

Understanding the potential suitability for An. stephensi transmission in a changing climate provides a key tool for planning, given an ongoing invasion and expansion of the vector. Anticipating the potential impact of onward expansion to transmission suitable areas, and the size of population at risk under future climate scenarios, and where they occur, can serve as a large-scale call for attention, planning, and monitoring.

Genetic Diversity of Dengue Vector Aedes albopictus Collected from South Korea, Japan, and Laos

Aedes albopictus is native to Southeast Asia and has emerged as a major vector for vector-borne diseases that are spreading rapidly worldwide. Recent studies have shown that Ae. albopictus populations have different genetic groups dependent on their thermal adaptations; however, studies on Korean populations are limited. In this study, we analyzed the genetic diversity and structure of two mitochondrial genes (COI and ND5) and sixteen microsatellites in mosquitoes inhabiting Korea, Japan, and Laos. The results indicate that the Korean population has low genetic diversity, with an independent cluster distinct from the Laos population. Mixed clusters have also been observed in the Korean population. On the basis of these findings, two hypotheses are proposed. First, certain Korean populations are native. Second, some subpopulations that descended from the metapopulation (East Asian countries) were introduced to Japan before migrating to Korea. Furthermore, we previously demonstrated that Ae. albopictus appears to have been imported to Korea. In conclusion, the dengue-virus-carrying mosquitoes could migrate to Korea from Southeast Asian epidemic regions, where they can survive during the severe winter months. The key findings can be used to establish an integrated pest management strategy based on population genetics for the Korean Ae. albopictus population.

Multiple invasions, Wolbachia and human-aided transport drive the genetic variability of Aedes albopictus in the Iberian Peninsula

The Asian tiger mosquito, Aedes albopictus, is one of the most invasive species in the world. Native to the tropical forests of Southeast Asia, over the past 30 years it has rapidly spread throughout tropical and temperate regions of the world. Its dramatic expansion has resulted in public health concerns as a consequence of its vector competence for at least 16 viruses. Previous studies showed that Ae. albopictus spread has been facilitated by human-mediated transportation, but much remains unknown about how this has affected its genetic attributes. Here we examined the factors that contributed to shaping the current genetic constitution of Ae. albopictus in the Iberian Peninsula, where the species was first found in 2004, by combining population genetics and Bayesian modelling. We found that both mitochondrial and nuclear DNA markers showed a lack of genetic structure and the presence of worldwide dominant haplotypes, suggesting regular introductions from abroad. Mitochondrial DNA showed little genetic diversity compared to nuclear DNA, likely explained by infection with maternally transmitted bacteria of the genus Wolbachia. Multilevel models revealed that greater mosquito fluxes (estimated from commuting patterns and tiger mosquito population distribution) and spatial proximity between sampling sites were associated with lower nuclear genetic distance, suggesting that rapid short- and medium-distance dispersal is facilitated by humans through vehicular traffic. This study highlights the significant role of human transportation in shaping the genetic attributes of Ae. albopictus and promoting regional gene flow, and underscores the need for a territorially integrated surveillance across scales of this disease-carrying mosquito.