Vector status of Aedes species determines geographical risk of autochthonous Zika virus establishment

Mitigating dengue incidence through advanced Aedes larval surveillance and control: A successful experience from Pakistan

Dengue fever is a viral disease caused by one of four dengue stereotypes (Flavivirus: Flaviviridae) that are primarily transmitted by Aedes albopictus (Skuse) and Aedes aegypti (L.). To safeguard public health, it is crucial to conduct surveys that examine the factors favouring the presence of these species. Our study surveyed 42 councils across four towns within the Bhakkar district of Punjab Province, by inspecting man-made or natural habitats containing standing water. First, door-to-door surveillance teams from the district health department were assigned to each council to surveillance Aedes species and dengue cases. Second, data collection through surveillance efforts, and validation procedures were implemented, and the verified data was uploaded onto the Dengue Tracking System by Third Party Validation teams. Third, data were analysed to identify factors influencing dengue fever cases. The findings demonstrated the following: (1) Predominantly, instances were discerned among individuals who had a documented history of having travelled beyond the confines of the province. (2) Containers associated with evaporative air coolers and tyre shops were responsible for approximately 30% of the Aedes developmental sites. (4) Variability in temperature was responsible for approximately 45% of the observed differences in the quantity of recorded Aedes mosquito developmental sites. (5) Implementation of dengue prevention initiatives precipitated a 50% reduction in Aedes-positive containers, alongside a notable 70% decline in reported cases of dengue fever during the period spanning 2019 to 2020, while the majority of reported cases were of external origin. Aedes control measures substantially curtailed mosquito populations and lowered vector-virus interactions. Notably, local dengue transmission was eliminated through advanced and effective Aedes control efforts, emphasising the need for persistent surveillance and eradication of larval habitats in affected regions.

A Habitat Model for Disease Vector Aedes aegypti in the Tampa Bay Area, FloridA

Within the contiguous USA, Florida is unique in having tropical and subtropical climates, a great abundance and diversity of mosquito vectors, and high rates of human travel. These factors contribute to the state being the national ground zero for exotic mosquito-borne diseases, as evidenced by local transmission of viruses spread by Aedes aegypti, including outbreaks of dengue in 2022 and Zika in 2016. Because of limited treatment options, integrated vector management is a key part of mitigating these arboviruses. Practical knowledge of when and where mosquito populations of interest exist is critical for surveillance and control efforts, and habitat predictions at various geographic scales typically rely on ecological niche modeling. However, most of these models, usually created in partnership with academic institutions, demand resources that otherwise may be too time-demanding or difficult for mosquito control programs to replicate and use effectively. Such resources may include intensive computational requirements, high spatiotemporal resolutions of data not regularly available, and/or expert knowledge of statistical analysis. Therefore, our study aims to partner with mosquito control agencies in generating operationally useful mosquito abundance models. Given the increasing threat of mosquito-borne disease transmission in Florida, our analytic approach targets recent Ae. aegypti abundance in the Tampa Bay area. We investigate explanatory variables that: 1) are publicly available, 2) require little to no preprocessing for use, and 3) are known factors associated with Ae. aegypti ecology. Out of our 4 final models, none required more than 5 out of the 36 predictors assessed (13.9%). Similar to previous literature, the strongest predictors were consistently 3- and 4-wk temperature and precipitation lags, followed closely by 1 of 2 environmental predictors: land use/land cover or normalized difference vegetation index. Surprisingly, 3 of our 4 final models included one or more socioeconomic or demographic predictors. In general, larger sample sizes of trap collections and/or citizen science observations should result in greater confidence in model predictions and validation. However, given disparities in trap collections across jurisdictions, individual county models rather than a multicounty conglomerate model would likely yield stronger model fits. Ultimately, we hope that the results of our assessment will enable more accurate and precise mosquito surveillance and control of Ae. aegypti in Florida and beyond.

Vector-Borne Disease Models with Active and Inactive Vectors: A Simple Way to Consider Biting Behavior

Vector-borne diseases are a serious public health problem, mosquitoes being one of the most important vectors. To analyze the dynamics of this type of disease, Ross-Macdonald models are commonly used. In its simplest formulation and the most common in scientific literature, it is assumed that all mosquitoes are biting at a given rate. To improve this general assumption, we developed a vector-borne disease model with active and inactive vectors as a simple way to incorporate the more general characteristics of mosquito feeding behavior into disease dynamics. Our objective is to obtain an estimate of the Ross-Macdonald biting rate from the feeding parameters that reproduce the same dynamics as the model with active and inactive vectors. Two different cases were analyzed: a SIS-SI model and a SIR-SI model with a single epidemic. Different methods to estimate the biting rate in the Ross-Macdonald model were proposed and analyzed. To compare the results of the models, different epidemiological indicators were considered. When the biting rate is estimated considering that both models have the same basic reproduction number, very similar disease dynamics are obtained. This method is a simple way to incorporate the mosquito feeding behavior into the standard Ross-Macdonald model.

A review of models applied to the geographic spread of Zika virus

In recent years, Zika virus (ZIKV) has expanded its geographic range and in 2015–2016 caused a substantial epidemic linked to a surge in developmental and neurological complications in newborns. Mathematical models are powerful tools for assessing ZIKV spread and can reveal important information for preventing future outbreaks. We reviewed the literature and retrieved modelling studies that were developed to understand the spatial epidemiology of ZIKV spread and risk. We classified studies by type, scale, aim and applications and discussed their characteristics, strengths and limitations. We examined the main objectives of these models and evaluated the effectiveness of integrating epidemiological and phylogeographic data, along with socioenvironmental risk factors that are known to contribute to vector–human transmission. We also assessed the promising application of human mobility data as a real-time indicator of ZIKV spread. Lastly, we summarised model validation methods used in studies to ensure accuracy in models and modelled outcomes. Models are helpful for understanding ZIKV spread and their characteristics should be carefully considered when developing future modelling studies to improve arbovirus surveillance.

Zika circulation, congenital syndrome, and current guidelines: making sense of it all for the traveller

PURPOSE OF REVIEW

Zika virus (ZIKV) swept through the Americas and led to recognition of its neurotropism. Zika circulation elsewhere in the world, nonvector transmission including maternal-fetal/sexual/transfusion routes, and additional reports on congenital Zika syndrome (CZS) and Guillain-Barré syndrome (GBS) have been published.

RECENT FINDINGS

In 2018-2019, ZIKV transmission occurred in Cuba, India, and is suspected to appear sporadically in other countries. Maternal-fetal ZIKV transmission appears to occur in about 26% of ZIKV-infected pregnant women. The US ZIKV Pregnancy and Infant Registry identified 6% of live births to have at least one ZIKV-associated birth defect; 9% had at least one neurodevelopmental abnormality; 1% had both. Infectious virus was rarely isolated from semen of ZIKV-infected male patients beyond day 38 after symptom onset. Brazilian blood donations had low ZIKV prevalence in 2015-2016; in the United States, screening donations was cost-effective only in the high mosquito season in Puerto Rico.

SUMMARY

ZIKV transmission continues; many countries with competent mosquitoes are at risk. Transmission can occur without detection where surveillance is poor and laboratory capacity limited. Travelers are important sentinels. Variations exist among ZIKV strains and Aedes mosquitoes that influence competence for transmission. Maternal-fetal transmission results in significant rates of abnormality. Identification of infectious virus in semen clarifies sexual transmission risk, with updated recommendations for preconception planning. ZIKV neurotropism requires further research and long-term follow-up.

Ross-Macdonald models: Which one should we use?

Ross-Macdonald models are the building blocks of most vector-borne disease models. Even for the same disease, different authors use different model formulations, but a study of the dynamical consequences of assuming different hypotheses is missing. In this work we present different formulations of the basic Ross-Macdonald model together with a careful discussion of the assumptions behind each model. The most general model presented is an agent based model for which arbitrary distributions for latency and infectious periods for both, host and vectors, is considered. At population level we also developed a deterministic Volterra integral equations model for which also arbitrary distributions in the waiting times are included. We compare the model solutions using different distributions for the infectious and latency periods using statistics, like the epidemic peak, or epidemic final size, to characterize the epidemic curves. The basic reproduction number (R₀) for each formulation is computed and compared with empirical estimations obtained with the agent based models. The importance of considering realistic distributions for the latent and infectious periods is highlighted and discussed. We also show that seasonality is a key driver of vector-borne disease dynamics shaping the epidemic curve and its duration.

Ecology of Neglected Rodent-Borne American Orthohantaviruses

The number of documented American orthohantaviruses has increased significantly over recent decades, but most fundamental research has remained focused on just two of them: Andes virus (ANDV) and Sin Nombre virus (SNV). The majority of American orthohantaviruses are known to cause disease in humans, and most of these pathogenic strains were not described prior to human cases, indicating the importance of understanding all members of the virus clade. In this review, we summarize information on the ecology of under-studied rodent-borne American orthohantaviruses to form general conclusions and highlight important gaps in knowledge. Information regarding the presence and genetic diversity of many orthohantaviruses throughout the distributional range of their hosts is minimal and would significantly benefit from virus isolations to indicate a reservoir role. Additionally, few studies have investigated the mechanisms underlying transmission routes and factors affecting the environmental persistence of orthohantaviruses, limiting our understanding of factors driving prevalence fluctuations. As landscapes continue to change, host ranges and human exposure to orthohantaviruses likely will as well. Research on the ecology of neglected orthohantaviruses is necessary for understanding both current and future threats to human health.

A dynamic neural network model for predicting risk of Zika in real time

BACKGROUND

In 2015, the Zika virus spread from Brazil throughout the Americas, posing an unprecedented challenge to the public health community. During the epidemic, international public health officials lacked reliable predictions of the outbreak's expected geographic scale and prevalence of cases, and were therefore unable to plan and allocate surveillance resources in a timely and effective manner.

METHODS

In this work, we present a dynamic neural network model to predict the geographic spread of outbreaks in real time. The modeling framework is flexible in three main dimensions (i) selection of the chosen risk indicator, i.e., case counts or incidence rate; (ii) risk classification scheme, which defines the high-risk group based on a relative or absolute threshold; and (iii) prediction forecast window (1 up to 12 weeks). The proposed model can be applied dynamically throughout the course of an outbreak to identify the regions expected to be at greatest risk in the future.

RESULTS

The model is applied to the recent Zika epidemic in the Americas at a weekly temporal resolution and country spatial resolution, using epidemiological data, passenger air travel volumes, and vector habitat suitability, socioeconomic, and population data for all affected countries and territories in the Americas. The model performance is quantitatively evaluated based on the predictive accuracy of the model. We show that the model can accurately predict the geographic expansion of Zika in the Americas with the overall average accuracy remaining above 85% even for prediction windows of up to 12 weeks.

CONCLUSIONS

Sensitivity analysis illustrated the model performance to be robust across a range of features. Critically, the model performed consistently well at various stages throughout the course of the outbreak, indicating its potential value at any time during an epidemic. The predictive capability was superior for shorter forecast windows and geographically isolated locations that are predominantly connected via air travel. The highly flexible nature of the proposed modeling framework enables policy makers to develop and plan vector control programs and case surveillance strategies which can be tailored to a range of objectives and resource constraints.

Environmental suitability for Aedes aegypti and Aedes albopictus and the spatial distribution of major arboviral infections in Mexico

Background

This paper discusses a comparative geographic distribution of Aedes aegypti and Aedes albopictus mosquitoes in Mexico, using environmental suitability modeling and reported cases of arboviral infections.

Methods

Using presence-only records, we modeled mosquito niches to show how much they influenced the distribution of Ae. aegypti and Ae. albopictus based on mosquito records collected at the municipality level. Mosquito surveillance data were used to create models regarding the predicted suitability of Ae. albopictus and Ae. aegypti mosquitos in Mexico.

Results

Ae. albopictus had relatively a better predictive performance (area under the curve, AUC = 0.87) to selected bioclimatic variables compared to Ae. aegypti (AUC = 0.81). Ae. aegypti were more suitable for areas with minimum temperature of coldest month (Bio6, permutation importance 28.7%) −6 °C to 21.5 °C, cumulative winter growing degree days (GDD) between 40 and 500, and precipitation of wettest month (Bio13) >8.4 mm. Minimum temperature range of the coldest month (Bio6) was −6.6 °C to 20.5 °C, and average precipitation of the wettest month (Bio13) 8.9 mm ~ 600 mm were more suitable for the existence of Ae. albopictus. However, arboviral infections maps prepared from the 2012–2016 surveillance data showed cases were reported far beyond predicted municipalities.

Conclusions

This study identified the urgent necessity to start surveillance in 925 additional municipalities that reported arbovirus infections but did not report Aedes mosquito.

The use and reporting of airline passenger data for infectious disease modelling: a systematic review

BackgroundA variety of airline passenger data sources are used for modelling the international spread of infectious diseases. Questions exist regarding the suitability and validity of these sources.AimWe conducted a systematic review to identify the sources of airline passenger data used for these purposes and to assess validation of the data and reproducibility of the methodology.MethodsArticles matching our search criteria and describing a model of the international spread of human infectious disease, parameterised with airline passenger data, were identified. Information regarding type and source of airline passenger data used was collated and the studies' reproducibility assessed.ResultsWe identified 136 articles. The majority (n = 96) sourced data primarily used by the airline industry. Governmental data sources were used in 30 studies and data published by individual airports in four studies. Validation of passenger data was conducted in only seven studies. No study was found to be fully reproducible, although eight were partially reproducible.LimitationsBy limiting the articles to international spread, articles focussed on within-country transmission even if they used relevant data sources were excluded. Authors were not contacted to clarify their methods. Searches were limited to articles in PubMed, Web of Science and Scopus.ConclusionWe recommend greater efforts to assess validity and biases of airline passenger data used for modelling studies, particularly when model outputs are to inform national and international public health policies. We also recommend improving reporting standards and more detailed studies on biases in commercial and open-access data to assess their reproducibility.

Aedes albopictus is a competent vector of Zika virus: A meta-analysis

BACKGROUND

Much work has been done in recent years to determine the vector competence of Aedes albopictus (Skuse) for Zika virus (ZIKV). If competent, Ae. albopictus could become an important vector in the spread of ZIKV to areas which until now have been considered safe from the virus. Despite much speculation about Ae. albopictus' competence for ZIKV, there have been, to date, no quantitative syntheses of Ae. albopictus' competence, nor have the potentially confounding differences between studies been addressed.

METHODOLOGY/ PRINCIPLE FINDINGS

This study represents a quantitative meta-analysis of the literature surrounding this topic by examining infection rates (IR) and transmission rates (TR) among sample populations of Ae. albopictus at 7 and 14 days post infection (dpi) across 15 journal articles comprising 23 studies. Our analyses examined potentially confounding variables in the studies contained therein, including: geographic origin of viral strain or mosquito population tested, whether sympatry of the tested viral strain and mosquito population was important, and freshness of blood meal. Our results suggest 1) Ae albopictus is a competent vector for ZIKV and 2) that origin of Ae. albopictus population and origin of viral strain had significant effects on the competence of Ae. albopictus to transmit ZIKV.

CONCLUSIONS/ SIGNIFICANCE

These results indicate a need to further explore the effects of methodology on vector competence studies and to examine in more detail the geographic variation in the competence of Ae. albopictus for ZIKV as well as the underlying causes of said variation. The ability of Ae. albopictus to carry and transmit ZIKV also points to a need to create new vector control strategies in case of a ZIKV outbreak in an area where Ae. albopictus is prominent. Finally, this study represents a potential template for future meta-analyses in the field of vector competence, where this type of study has been under-utilized despite the abundance of relevant studies.

Surveillance for Mosquitoborne Transmission of Zika Virus, New York City, NY, USA, 2016

Sentinel, enhanced passive, and syndromic surveillance in 2016 did not identify any evidence of transmission.

A large number of imported cases of Zika virus infection and the potential for transmission by Aedes albopictus mosquitoes prompted the New York City Department of Health and Mental Hygiene to conduct sentinel, enhanced passive, and syndromic surveillance for locally acquired mosquitoborne Zika virus infections in New York City, NY, USA, during June–October 2016. Suspected case-patients were those >5 years of age without a travel history or sexual exposure who had >3 compatible signs/symptoms (arthralgia, fever, conjunctivitis, or rash). We identified 15 suspected cases and tested urine samples for Zika virus by using real-time reverse transcription PCR; all results were negative. We identified 308 emergency department visits for Zika-like illness, 40,073 visits for fever, and 17 unique spatiotemporal clusters of visits for fever. We identified no evidence of local transmission. Our experience offers possible surveillance tools for jurisdictions concerned about local mosquitoborne Zika virus or other arboviral transmission.

A decision-support framework to optimize border control for global outbreak mitigation

The introduction and spread of emerging infectious diseases is increasing in both prevalence and scale. Whether naturally, accidentally or maliciously introduced, the substantial uncertainty surrounding the emergence of novel viruses, specifically where they may come from and how they will spread, demands robust and quantifiably validated outbreak control policies that can be implemented in real time. This work presents a novel mathematical modeling framework that integrates both outbreak dynamics and outbreak control into a decision support tool for mitigating infectious disease pandemics that spread through passenger air travel. An ensemble of border control strategies that exploit properties of the air traffic network structure and expected outbreak behavior are proposed. A stochastic metapopulation epidemic model is developed to evaluate and rank the control strategies based on their effectiveness in reducing the spread of outbreaks. Sensitivity analyses are conducted to illustrate the robustness of the proposed control strategies across a range of outbreak scenarios, and a case study is presented for the 2009 H1N1 influenza pandemic. This study highlights the importance of strategically allocating outbreak control resources, and the results can be used to identify the most robust border control policy that can be implemented in the early stages of an outbreak.

Zika and the Eye: Pieces of a Puzzle

Zika virus (ZIKV) is an arbovirus mainly transmitted to humans by mosquitoes from Aedes genus. Other ways of transmission include the perinatal and sexual routes, blood transfusion, and laboratory exposure. Although the first human cases were registered in 1952 in African countries, outbreaks were only reported since 2007, when entire Pacific islands were affected. In March 2015, the first cases of ZIKV acute infection were notified in Brazil and, to date, 48 countries and territories in the Americas have confirmed local mosquito-borne transmission of ZIKV. Until 2015, ZIKV infection was thought to only cause asymptomatic or mild exanthematous febrile infections. However, after explosive ZIKV outbreaks in Polynesia and Latin American countries, it was confirmed that ZIKV could also lead to Guillain-Barré syndrome and congenital birth abnormalities. These abnormalities, which can include neurologic, ophthalmologic, audiologic, and skeletal findings, are now considered congenital Zika syndrome (CZS). Brain abnormalities in CZS include cerebral calcifications, malformations of cortical development, ventriculomegaly, lissencephaly, hypoplasia of the cerebellum and brainstem. The ocular findings, which are present in up to 70% of infants with CZS, include iris coloboma, lens subluxation, cataract, congenital glaucoma, and especially posterior segment findings. Loss of retinal pigment epithelium, the presence of a thin choroid, a perivascular choroidal inflammatory infiltrate, and atrophic changes within the optic nerve were seen in histologic analyses of eyes from deceased fetuses. To date, there is no ZIKV licensed vaccines or antiviral therapies are available for treatment. Preventive measures include individual protection from mosquito bites, control of mosquito populations and the use of barriers measures such as condoms during sexual intercourse or sexual abstinence for couples either at risk or after confirmed infection. A literature review based on studies that analyzed ocular findings in mothers and infants with CZS, with or without microcephaly, was conducted and a theoretical pathophysiologic explanation for ZIKV-ocular abnormalities was formulated.

A review on test methods for insecticidal fabrics and the need for standardisation

Insecticidal fabrics are effective personal protective measures against disease vectors and unlike bed nets, these fabrics can provide protection from day-biting mosquitoes and in outdoor environments. The rapid geographical expansion of day-biting mosquitoes and their role in disease transmission necessitate technological interventions, which can be effectively used during the daytime. There is a renewed interest in insecticidal fabrics mainly due to the recent outbreaks and geographical spread of dengue and chikungunya and with the emerging threat of Zika virus infection. Insecticidal fabrics are useful for protection from night-biting mosquitoes and also in situations were sleeping under a bed net is not possible. They are also effective against other biting arthropods like ticks, mites, tsetse flies, sand flies and body lice. Although long-lasting insecticidal fabrics factory-treated with permethrin are now commercially available for military and civilian use, there are no international guidelines for testing their efficacy. The different methods employed so far for testing bioefficacy, washing and quantification of permethrin are compiled in this review. The future prospects and challenges ahead for long-lasting insecticidal fabrics are discussed in the context of the increased threat from day-biting mosquitoes and the diseases transmitted by them. The review focuses on the need for standardisation of the test methods for ensuring adequate bioefficacy and safety to the user. The differences between long-lasting insecticidal nets and long-lasting insecticidal fabrics are elaborated, and the need for a separate registration and licencing procedure for long-lasting insecticidal fabrics is highlighted. A test procedure for insecticidal fabrics is described, which could be used until internationally accepted guidelines are available.

Sampling considerations for a potential Zika virus urosurvey in New York City

In 2016, imported Zika virus (ZIKV) infections and the presence of a potentially competent mosquito vector (Aedes albopictus) implied that ZIKV transmission in New York City (NYC) was possible. The NYC Department of Health and Mental Hygiene developed contingency plans for a urosurvey to rule out ongoing local transmission as quickly as possible if a locally acquired case of confirmed ZIKV infection was suspected. We identified tools to (1) rapidly estimate the population living in any given 150-m radius (i.e. within the typical flight distance of an Aedes mosquito) and (2) calculate the sample size needed to test and rule out the further local transmission. As we expected near-zero ZIKV prevalence, methods relying on the normal approximation to the binomial distribution were inappropriate. Instead, we assumed a hypergeometric distribution, 10 missed cases at maximum, a urine assay sensitivity of 92.6% and 100% specificity. Three suspected example risk areas were evaluated with estimated population sizes of 479-4,453, corresponding to a minimum of 133-1244 urine samples. This planning exercise improved our capacity for ruling out local transmission of an emerging infection in a dense, urban environment where all residents in a suspected risk area cannot be feasibly sampled.

Threats of Zika virus transmission for Asia and its Hindu-Kush Himalayan region

Asia and its Hindu Kush Himalayan (HKH) region is particularly vulnerable to environmental change, especially climate and land use changes further influenced by rapid population growth, high level of poverty and unsustainable development. Asia has been a hotspot of dengue fever and chikungunya mainly due to its dense human population, unplanned urbanization and poverty. In an urban cycle, dengue virus (DENV) and chikungunya virus (CHIKV) are transmitted by Aedes aegypti and Ae. albopictus mosquitoes which are also competent vectors of Zika virus (ZIKV). Over the last decade, DENV and CHIKV transmissions by Ae. aegypti have extended to the Himalayan countries of Bhutan and Nepal and ZIKV could follow in the footsteps of these viruses in the HKH region. The already established distribution of human-biting Aedes mosquito vectors and a naïve population with lack of immunity against ZIKV places the HKH region at a higher risk of ZIKV. Some of the countries in the HKH region have already reported ZIKV cases. We have documented an increasing threat of ZIKV in Asia and its HKH region because of the high abundance and wide distribution of human-biting mosquito vectors, climate change, poverty, report of indigenous cases in the region, increasing numbers of imported cases and a naïve population with lack of immunity against ZIKV. An outbreak anywhere is potentially a threat everywhere. Therefore, in order to ensure international health security, all efforts to prevent, detect, and respond to ZIKV ought to be intensified now in Asia and its HKH region. To prepare for possible ZIKV outbreaks, Asia and the HKH region can also learn from the success stories and strategies adopted by other regions and countries in preventing ZIKV and associated complications. The future control strategies for DENV, CHIKV and ZIKV should be considered in tandem with the threat to human well-being that is posed by other emerging and re-emerging vector-borne and zoonotic diseases, and by the continuing urgent need to strengthen public primary healthcare systems in the region.

Emerging infections-an increasingly important topic: review by the Emerging Infections Task Force

OBJECTIVES

This paper review trends in emerging infections and the need for increased clinical and laboratory surveillance.

METHODS

Factors that contributed to the emergence of recent outbreaks have been reviewed. Known, major outbreaks over the past two decades were reviewed.

RESULTS

We identified at least four major drivers of emergent infections: (i) increasing density of the human population; (ii) stress from farmland expansion on the environment; (iii) globalization of the food market and manufacturing; (iv) environmental contamination. The factors creating new opportunities for emerging infections include: (i) population growth; (ii) spread in health care facilities; (iii) an ageing population; (iv) international travel; (v) changing and expanding vector habitats.

CONCLUSIONS

Emerging infections are unpredictable. In this review we argue that to discover new trends in infectious diseases, the clinicians have to look for the unusual and unexpected and ensure proper diagnostics and that syndromic surveillance must be supported by highly specialized laboratory services. Mathematical modeling has not been able to predict outbreaks More emphasis on the biology of evolution is needed. EID rarely stands out as unusual, and the continuous pressure on health care budgets forces clinicians and laboratories to prioritize their diagnostic work-up to common and treatable conditions. The European Society for Infectious Diseases and Clinical Microbiology, ESCMID, has established an Emerging Infections Task Force, EITaF, to strengthen the activities of the society on emerging infections and ensure that emerging infections is included in differential diagnostic considerations in everyday clinical practice.

Effects of climate change on the spread of zika virus: a public health threat

Zika is a vector-borne viral disease transmitted to humans primarily by Aedes aegypti mosquitoes. The increased climate instability has contributed to the emergence of infections carried by mosquitoes like dengue, chikungunya and zika. While infection with the zika virus is not new, the recent epidemic of microcephaly in Brazil and other countries in South America resulting from the infection of pregnant women with the zika virus raise a number of serious public health concerns. These include the question of how climate change affects the range of zika vectors, what can we do to shorten the length of mosquito season, how and why the symptoms of zika infection have changed and what can be done to reduce the burden of human disease from this infection? Another important question that needs to be answered is what are the factors that caused the zika virus to leave the non-human primates and/or other mammals and invade the human population?

Climate Change and the Neglected Tropical Diseases

Climate change is expected to impact across every domain of society, including health. The majority of the world's population is susceptible to pathological, infectious disease whose life cycles are sensitive to environmental factors across different physical phases including air, water and soil. Nearly all so-called neglected tropical diseases (NTDs) fall into this category, meaning that future geographic patterns of transmission of dozens of infections are likely to be affected by climate change over the short (seasonal), medium (annual) and long (decadal) term. This review offers an introduction into the terms and processes deployed in modelling climate change and reviews the state of the art in terms of research into how climate change may affect future transmission of NTDs. The 34 infections included in this chapter are drawn from the WHO NTD list and the WHO blueprint list of priority diseases. For the majority of infections, some evidence is available of which environmental factors contribute to the population biology of parasites, vectors and zoonotic hosts. There is a general paucity of published research on the potential effects of decadal climate change, with some exceptions, mainly in vector-borne diseases.

Viral and Antibody Kinetics, and Mosquito Infectivity of an Imported Case of Zika Fever Due to Asian Genotype (American Strain) in Singapore

We report a case of a Singaporean who acquired Zika virus (ZIKV) during a visit to Cuba. The infection was confirmed using molecular and serological methods. This report highlights potential drawbacks of using IgG serology for diagnosis of flavivirus infections in endemic regions. The low viremia detected during the early phase of this case resulted in low mosquito infectivity rates, suggesting the possibility of ZIKV transmission prior to clinical onset. The report also emphasizes the challenges of public health interventions for Zika fever and the importance of sustaining a low vector population to reduce the risk of arbovirus transmission in vulnerable regions.

Inferring the risk factors behind the geographical spread and transmission of Zika in the Americas

BACKGROUND

An unprecedented Zika virus epidemic occurred in the Americas during 2015-2016. The size of the epidemic in conjunction with newly recognized health risks associated with the virus attracted significant attention across the research community. Our study complements several recent studies which have mapped epidemiological elements of Zika, by introducing a newly proposed methodology to simultaneously estimate the contribution of various risk factors for geographic spread resulting in local transmission and to compute the risk of spread (or re-introductions) between each pair of regions. The focus of our analysis is on the Americas, where the set of regions includes all countries, overseas territories, and the states of the US.

METHODOLOGY/PRINCIPAL FINDINGS

We present a novel application of the Generalized Inverse Infection Model (GIIM). The GIIM model uses real observations from the outbreak and seeks to estimate the risk factors driving transmission. The observations are derived from the dates of reported local transmission of Zika virus in each region, the network structure is defined by the passenger air travel movements between all pairs of regions, and the risk factors considered include regional socioeconomic factors, vector habitat suitability, travel volumes, and epidemiological data. The GIIM relies on a multi-agent based optimization method to estimate the parameters, and utilizes a data driven stochastic-dynamic epidemic model for evaluation. As expected, we found that mosquito abundance, incidence rate at the origin region, and human population density are risk factors for Zika virus transmission and spread. Surprisingly, air passenger volume was less impactful, and the most significant factor was (a negative relationship with) the regional gross domestic product (GDP) per capita.

CONCLUSIONS/SIGNIFICANCE

Our model generates country level exportation and importation risk profiles over the course of the epidemic and provides quantitative estimates for the likelihood of introduced Zika virus resulting in local transmission, between all origin-destination travel pairs in the Americas. Our findings indicate that local vector control, rather than travel restrictions, will be more effective at reducing the risks of Zika virus transmission and establishment. Moreover, the inverse relationship between Zika virus transmission and GDP suggests that Zika cases are more likely to occur in regions where people cannot afford to protect themselves from mosquitoes. The modeling framework is not specific for Zika virus, and could easily be employed for other vector-borne pathogens with sufficient epidemiological and entomological data.

Mosquitoes as Arbovirus Vectors: From Species Identification to Vector Competence

Mosquitoes and other arthropods transmit a large number of medically important pathogens, in particular viruses. These arthropod-borne viruses (arboviruses) include a wide variety of RNA viruses belonging to the Flaviviridae family (West Nile virus (WNV), Usutu virus (USUV), Dengue virus (DENV), Japanese encephalitis virus (JEV), Zika virus (ZIKV)), the Togaviridae family (Chikungunya virus (CHIKV)), and Bunyavirales order (Rift Valley fever virus (RVFV)) (please refer also to Table 9.1). Arboviral transmission to humans and livestock constitutes a major threat to public health and economy as illustrated by the emergence of ZIKV in the Americas, RVFV outbreaks in Africa, and the worldwide outbreaks of DENV. To answer the question if those viral pathogens also pose a risk to Europe, we need to first answer the key questions (summarized in Fig. 9.1):

Who could contribute to such an outbreak? Information about mosquito species resident or imported, potential hosts and viruses able to infect vectors and hosts in Germany is needed.

Where would competent mosquito species meet favorable conditions for transmission? Information on the minimum requirements for efficient replication of the virus in a given vector species and subsequent transmission is needed.

How do viruses and vectors interact to facilitate transmission? Information on the vector immunity, vector physiology, vector genetics, and vector microbiomes is needed.

Culex quinquefasciatus mosquitoes do not support replication of Zika virus

The rapid spread of Zika virus (ZIKV) in the Americas raised many questions about the role of Culex quinquefasciatus mosquitoes in transmission, in addition to the key role played by the vector Aedes aegypti. Here we analysed the competence of Cx. quinquefasciatus (with or without Wolbachia endosymbionts) for a ZIKV isolate. We also examined the induction of RNA interference pathways after viral challenge and the production of small virus-derived RNAs. We did not observe any infection nor such small virus-derived RNAs, regardless of the presence or absence of Wolbachia. Thus, Cx. quinquefasciatus does not support ZIKV replication and Wolbachia is not involved in producing this phenotype. In short, these mosquitoes are very unlikely to play a role in transmission of ZIKV.