Evidence of transovarial transmission of Chikungunya and Dengue viruses in field-caught mosquitoes in Kenya

Detecting the impacts of humidity, rainfall, temperature, and season on chikungunya, dengue and Zika viruses in Aedes albopictus mosquitoes from selected sites in Cebu city, Philippines

BACKGROUND

Aedes albopictus is the secondary vector for dengue virus (DENV) in the Philippines, and also harbors chikungunya (CHIKV) and Zika (ZIKV) viruses. This study aimed to determine the minimum infection rates (MIRs) of CHIKV, DENV serotypes, and ZIKV in Ae. albopictus collected from selected two-site categories by altitude (highland [H] and lowland [L] sites) in Cebu city, Philippines during the wet (WS) and dry seasons (DS) of 2021-2022, and to explore the relationships between these arboviral MIRs and the local weather.

METHODS

The viral RNA extracts in pooled and reared adult Ae. albopictus collected during the DS and WS from two-site categories were subjected to RT-PCR to amplify and detect gene loci specific for CHIKV, DENV-1 to DENV-4, and ZIKV and analyzed with the weather data.

RESULTS

The range of CHIKV MIRs was higher in the WS (13.61-107.38 infected individuals per 1,000 mosquitoes) than in the DS (13.22-44.12), but was similar between the two-site categories. Rainfall (RF) influenced the CHIKV MIR. The MIR ranges of both DENV-2 (WS: H = 0, L = 0; DS: H = 0-5.92; L = 0-2.6) and DENV-4 (WS: H = 0, L = 0-2.90; DS: H = 2.96-6.13, L = 0-15.63) differed by season but not between the two-site categories. Relative humidity (RH), RF, and temperature did not influence DENVs' MIRs. The MIR range of ZIKV was similar in both seasons (WS: 11.36-40.27; DS: 0-46.15) and two-site categories (H = 0-90.91, L = 0-55.56). RH and temperature influenced ZIKV MIR.

CONCLUSIONS

RF influenced CHIKV MIR in Ae. albopictus, whereas RH and temperature influenced that of ZIKV. Season influenced the MIRs of CHIKV and DENVs but not in ZIKV. Ae. albopictus were co-infected with CHIKV, DENVs, and ZIKV in both highland and lowland sites in Cebu city. Recommendations include all-year-round implementation of the Philippine Department of Health's  4S enhanced strategy and installation of water pipelines in rural highlands for vector and disease control. Our findings are relevant to protect public health in the tropics in this climate change.

Molecular detection of dengue and chikungunya viruses in surveillance of wild-caught Aedes mosquitoes in Punjab, North India

BACKGROUND

Dengue (DENV), Zika (ZIKV) and chikungunya (CHIKV) viruses are transmitted mainly by Aedes mosquitoes and are responsible for a significant global healthcare burden. The current study aimed to detect arboviruses in the Aedes mosquitoes in close proximity of patients during the transmission season.

METHODS

Both immature and adult mosquitoes were collected from in and around the patients' houses. Mosquito pools were homogenized and extracted RNA was subjected to reverse transcription polymerase chain reaction for arboviral detection. Transovarian transmission (TOT) was assessed by screening F0 adults. Mosquito positivity was correlated with the aetiological agents identified in patients.

RESULTS

Of 46 pools, 19 consisted of wild Aedes, with arboviral positivity in 53% (10/19) of pools. Among wild A. aegypti pools, positivity of DENV mono-infection, CHIKV mono-infection and DENV+CHIKV co-infection was noted in four, two and three pools, respectively. One wild pool of Aedes albopictus was positive for DENV-1. Similarly, A. aegypti F0 (adult Aedes developed from immatures) pools showed 59.2% (16/27) positivity for arboviruses. F0 Aedes showed positivity in three, six and seven pools for DENV-2, CHIKV and DENV+CHIKV, respectively, suggestive of TOT. DENV serotypes and CHIKV from 24 patients' serum samples were matched with strains isolated from Aedes and correlation was observed in four instances.

CONCLUSIONS

The study detected DENV and CHIKV from wild-caught Aedes and found evidence of DENV and CHIKV TOT in F0 adults.

Transovarial transmission of mosquito-borne viruses: a systematic review

Background

A number of mosquito-borne viruses (MBVs), such as dengue virus (DENV), zika virus (ZIKV), chikungunya (CHIKV), West Nile virus (WNV), and yellow fever virus (YFV) exert adverse health impacts on the global population. Aedes aegypti and Aedes albopictus are the prime vectors responsible for the transmission of these viruses. The viruses have acquired a number of routes for successful transmission, including horizontal and vertical transmission. Transovarial transmission is a subset/type of vertical transmission adopted by mosquitoes for the transmission of viruses from females to their offspring through eggs/ovaries. It provides a mechanism for these MBVs to persist and maintain their lineage during adverse climatic conditions of extremely hot and cold temperatures, during the dry season, or in the absence of susceptible vertebrate host when horizontal transmission is not possible.

Methods

The publications discussed in this systematic review were searched for using the PubMed, Scopus, and Web of Science databases, and websites such as those of the World Health Organization (WHO) and the European Centre for Disease Prevention and Control, using the search terms "transovarial transmission" and "mosquito-borne viruses" from 16 May 2023 to 20 September 2023.

Results

A total of 2,391 articles were searched, of which 123 were chosen for full text evaluation, and 60 were then included in the study after screening and removing duplicates.

Conclusion

The present systematic review focuses on understanding the above diseases, their pathogenesis, epidemiology and host-parasite interactions. The factors affecting transovarial transmission, potential implications, mosquito antiviral defense mechanism, and the control strategies for these mosquito-borne viral diseases (MBVDs) are also be included in this review.

Identifying Knowledge Gaps through the Systematic Review of Temperature-Driven Variability in the Competence of Aedes aegypti and Ae. albopictus for Chikungunya Virus

Temperature is a well-known effector of several transmission factors of mosquito-borne viruses, including within mosquito dynamics. These dynamics are often characterized by vector competence and the extrinsic incubation period (EIP). Vector competence is the intrinsic ability of a mosquito population to become infected with and transmit a virus, while EIP is the time it takes for the virus to reach the salivary glands and be expectorated following an infectious bloodmeal. Temperatures outside the optimal range act on life traits, decreasing transmission potential, while increasing temperature within the optimal range correlates to increasing vector competence and a decreased EIP. These relatively well-studied effects of other Aedes borne viruses (dengue and Zika) are used to make predictions about transmission efficiency, including the challenges presented by urban heat islands and climate change. However, the knowledge of temperature and chikungunya (CHIKV) dynamics within its two primary vectors-Ae. aegypti and Ae. albopictus-remains less characterized, even though CHIKV remains a virus of public-health importance. Here, we review the literature and summarize the state of the literature on CHIKV and temperature dependence of vector competence and EIP and use these data to demonstrate how the remaining knowledge gap might confound the ability to adequately predict and, thus, prepare for future outbreaks.

Detection of La Crosse Virus In Situ and in Individual Progeny to Assess the Vertical Transmission Potential in Aedes albopictus and Aedes aegypti

La Crosse virus (LACV) is circulating in the midwestern and southeastern states of the United States and can cause human encephalitis. The main vector of the virus is the eastern tree-hole mosquito, Aedes triseriatus. Ae. albopictus has been also described as a natural LACV vector, while Ae. aegypti has been infected with the virus under laboratory conditions. Here, we compare the vertical transmission potential of LACV in Ae. albopictus and Ae. aegypti, with emphasis given to the ovarian infection patterns that the virus generates in both species. Both mosquito species received artificial bloodmeals containing LACV. At defined time points post-infection/bloodmeal, midguts, head tissue, and ovaries were analyzed for the presence of virus. Viral infection patterns in the ovaries were visualized via immunofluorescence confocal microscopy and immunohistopathology assays using an LACV-specific monoclonal antibody. In Ae. aegypti, LACV was confronted with midgut infection and escape barriers, which were much less pronounced in Ae. albopictus, resulting in a significantly higher prevalence of infection in the latter. Following the ingestion of a single virus-containing bloodmeal, no progeny larvae were found to be virus-infected. Regardless, females of both species showed the presence of LACV antigen in their ovariole sheaths. Furthermore, in a single Ae. albopictus female, viral antigen was associated with the nurse cells inside the primary follicles. Following the ingestion of a second non-infectious bloodmeal at 7- or 10-days post-ingestion of an LACV-containing bloodmeal, more progeny larvae of Ae. albopictus than of Ae. aegypti were virus-infected. LACV antigen was detected in the egg chambers and ovariole sheaths of both mosquito species. Traces of viral antigen were also detected in a few oocytes from Ae. albopictus. The low level of vertical transmission and the majority of the ovarian infection patterns suggested the transovum rather than transovarial transmission (TOT) of the virus in both vector species. However, based on the detection of LACV antigen in follicular tissue and oocytes, there was the potential for TOT among several Ae. albopictus females. Thus, TOT is not a general feature of LACV infection in mosquitoes. Instead, the TOT of LACV seems to be dependent on its particular interaction with the reproductive tissues of a female.

Detecting dengue fever in children using online Rasch analysis to develop algorithms for parents: An APP development and usability study

BACKGROUND

Dengue fever (DF) is a significant public health concern in Asia. However, detecting the disease using traditional dichotomous criteria (i.e., absent vs present) can be extremely difficult. Convolutional neural networks (CNNs) and artificial neural networks (ANNs), due to their use of a large number of parameters for modeling, have shown the potential to improve prediction accuracy (ACC). To date, there has been no research conducted to understand item features and responses using online Rasch analysis. To verify the hypothesis that a combination of CNN, ANN, K-nearest-neighbor algorithm (KNN), and logistic regression (LR) can improve the ACC of DF prediction for children, further research is required.

METHODS

We extracted 19 feature variables related to DF symptoms from 177 pediatric patients, of whom 69 were diagnosed with DF. Using the RaschOnline technique for Rasch analysis, we examined 11 variables for their statistical significance in predicting the risk of DF. Based on 2 sets of data, 1 for training (80%) and the other for testing (20%), we calculated the prediction ACC by comparing the areas under the receiver operating characteristic curve (AUCs) between DF + and DF- in both sets. In the training set, we compared 2 scenarios: the combined scheme and individual algorithms.

RESULTS

Our findings indicate that visual displays of DF data are easily interpreted using Rasch analysis; the k-nearest neighbors algorithm has a lower AUC (<0.50); LR has a relatively higher AUC (0.70); all 3 algorithms have an almost equal AUC (=0.68), which is smaller than the individual algorithms of Naive Bayes, LR in raw data, and Naive Bayes in normalized data; and we developed an app to assist parents in detecting DF in children during the dengue season.

CONCLUSION

The development of an LR-based APP for the detection of DF in children has been completed. To help patients, family members, and clinicians differentiate DF from other febrile illnesses at an early stage, an 11-item model is proposed for developing the APP.

Arboviruses and symbiotic viruses cooperatively hijack insect sperm-specific proteins for paternal transmission

Arboviruses and symbiotic viruses can be paternally transmitted by male insects to their offspring for long-term viral persistence in nature, but the mechanism remains largely unknown. Here, we identify the sperm-specific serpin protein HongrES1 of leafhopper Recilia dorsalis as a mediator of paternal transmission of the reovirus Rice gall dwarf virus (RGDV) and a previously undescribed symbiotic virus of the Virgaviridae family, Recilia dorsalis filamentous virus (RdFV). We show that HongrES1 mediates the direct binding of virions to leafhopper sperm surfaces and subsequent paternal transmission via interaction with both viral capsid proteins. Direct interaction of viral capsid proteins mediates simultaneously invasion of two viruses into male reproductive organs. Moreover, arbovirus activates HongrES1 expression to suppress the conversion of prophenoloxidase to active phenoloxidase, potentially producing a mild antiviral melanization defense. Paternal virus transmission scarcely affects offspring fitness. These findings provide insights into how different viruses cooperatively hijack insect sperm-specific proteins for paternal transmission without disturbing sperm functions.

Vector Competence of a Coastal Population of Aedes aegypti for Dengue 2 and 3 Virus Serotypes in Kenya

Aedes aegypti is the primary vector of dengue, an arboviral disease caused by dengue virus (DENV) that exists as four distinct serotypes (DENV 1-4). While all four DENV serotypes circulate in Kenya, differential distribution of the serotypes in specific regions suggests virus transmission may differ among local vector populations. In this study, we tested the hypothesis that a coastal Ae. aegypti population (Rabai, Kilifi County) varies in its ability to transmit DENV-2 (predominant) and DENV-3 (less dominant) and that transmission is related to Ae. aegypti subspecies—domestic Ae. aegypti aegypti (Aaa) and sylvtic Ae. aegypti formosus (Aaf). We orally exposed F1 females (3-10 days old) to blood meals containing DENV-2 (10 5.30 pfu/ml) or DENV-3 (10 5.13 pfu/ml), tested them individually for infection (body), dissemination (legs), and transmission (saliva) at 7, 14, and 21 days postinfection (DPI), respectively, and compared the rates between the serotypes. We analyzed cytochrome c oxidase I gene (cox-I) sequences among DENV-susceptible and nonsusceptible cohorts. Of 489 mosquitoes tested (DENV-2: 240; DENV-3: 249), we found consistently higher but nonsignificant rates of infection (16% vs. 10%), dissemination (47% (18/38) vs. 35% (9/26)), and transmission (39% (7/18) vs. 11% (1/9)) for DENV-2 than DENV-3. However, DENV-2 exhibited a shorter extrinsic incubation period (EIP) for disseminated infection (7-DPI vs. 14-DPI) and transmission (14-DPI vs. 21-DPI) compared to DENV-3. Two cox-I lineages were recovered in phylogeny, one predominantly clustered with referenced Aaa and a minor lineage grouped with Aaf. Infected mosquitoes and those with disseminated infection were represented in both lineages; those that transmitted the viruses grouped with the Aaa-associated lineage only. We conclude that the coastal Ae. aegypti population is a competent vector for DENV-2 and DENV-3 likely driven by the domestic Aaa that is predominant. The shorter EIP to attain dissemination and transmission for DENV-2 could favour its transmission over DENV-3.

Health education impact on knowledge and management of arboviral diseases in Kenya: Evidence from randomised control trials

Communities' knowledge and management strategies are crucial for mitigating and controlling the threat of existing and emerging diseases. In this study, we conducted randomised control trials (RCT) to examine the impact of health education on households' knowledge and management of three Arboviral Diseases (ADs); Rift Valley fever, Chikungunya fever, and Dengue fever in Kenya. The study was based on a sample of 629 households drawn from the three of Kenya's AD hotspot counties; Baringo, Kwale, and Kilifi. Employing a difference-in-difference method, our findings indicate that health education intervention significantly improved households' understanding of ADs transmission modes, causes, and prevention strategies. However, this intervention did not sufficiently influence households' disease management behaviour. We recommend the implementation of community engagement and outreach initiatives which have the potential to drive behavioural changes at the household level, thus enhancing the management and control of ADs in Kenya.

Evolution and emergence of mosquito-borne viruses of medical importance: towards a routine metagenomic surveillance approach

During the last two decades, the world has witnessed the emergence and re-emergence of arthropod-borne viruses, better known as arboviruses. The close contact between sylvatic, rural and peri-urban vector species and humans has been mainly determined by the environment-modifying human activity. The resulting interactions have led to multiple dead-end host infections and have allowed sylvatic arboviruses to eventually adapt to new vectors and hosts, contributing to the establishment of urban transmission cycles of some viruses with enormous epidemiologic impact. The metagenomic next-generation sequencing (NGS) approach has allowed obtaining unbiased sequence information of millions of DNA and RNA molecules from clinical and environmental samples. Robust bioinformatics tools have enabled the assembly of individual sequence reads into contigs and scaffolds partially or completely representing the genomes of the microorganisms and viruses being present in biological samples of clinical relevance. In this review, we describe the different ecological scenarios for the emergence of viral diseases, the virus adaptation process required for the establishment of a new transmission cycle and the usefulness of NGS and computational methods for the discovery and routine genomic surveillance of mosquito-borne viruses in their ecosystems.

Vertical Transmission of Sindbis Virus in Culex Mosquitoes

Vertical transmission (VT) is a phenomenon of vector-borne diseases where a pathogen is transferred from an infected arthropod mother to her offspring. For mosquito-borne flavi- and alphaviruses, VT is commonly viewed as rare; however, both field and experimental studies report on vertical transmission efficiency to a notably varying degree. It is likely that this reflects the different experimental methods used to test vertical transmission efficiency as well as differences between virus–vector combinations. There are very few investigations of the VT of an alphavirus in a Culex vector. Sindbis virus (SINV) is an arthritogenic alphavirus that utilizes Culex species as main vectors both in the summer transmission season and for its persistence over the winter period in northern latitudes. In this study, we investigated the vertical transmission of the SINV in Culex vectors, both in the field and in experimental settings. The detection of SINV RNA in field-collected egg rafts and emerging adults shows that vertical transmission takes place in the field. Experimentally infected females gave rise to adult offspring containing SINV RNA at emergence; however, three to four weeks after emergence none of the offspring contained SINV RNA. This study shows that vertical transmission may be connected to SINV’s ability to persist throughout northern winters and also highlights many aspects of viral replication that need further study.

Natural Aedes-Borne Virus Infection Detected in Male Adult Aedes aegypti (Diptera: Culicidae) Collected From Urban Settings in Mérida, Yucatán, México

Aedes-borne viruses (ABVs) such as dengue (DENV), chikungunya (CHIKV), and Zika (ZIKV) contribute significantly to the global burden of infectious diseases, disproportionately affecting disadvantaged populations from tropical and subtropical urban areas. ABVs can be transmitted from female mosquitoes to their progeny by vertical transmission via transovarial and/or trans-egg vertical transmission and contribute to the maintenance of infected-mosquito populations year-round in endemic regions. This study describes the natural infection rate of DENV, CHIKV, and ZIKV in field-caught male Aedes (Sergentomyia) aegypti (Linnaeus) mosquitoes from Mérida, Yucatán, México, as a proxy for the occurrence of vertical virus transmission. We used indoor sequential sampling with Prokopack aspirators to collect all mosquitoes inside houses from ABV hotspots areas. Collections were performed in a DENV and CHIKV post-epidemic phase and during a period of active ZIKV transmission. We individually RT-qPCR tested all indoor collected Ae. aegypti males (1,278) followed by Sanger sequencing analysis for final confirmation. A total of 6.7% male mosquitoes were positive for ABV (CHIKV = 5.7%; DENV = 0.9%; ZIKV = 0.1%) and came from 21.0% (30/143) houses infested with males. Most ABV-positive male mosquitoes were positive for CHIKV (84.8%). The distribution of ABV-positive Ae. aegypti males was aggregated in a few households, with two houses having 11 ABV-positive males each. We found a positive association between ABV-positive males and females per house. These findings suggested the occurrence of vertical arbovirus transmission within the mosquito populations in an ABV-endemic area and, a mechanism contributing to viral maintenance and virus re-emergence among humans in post-epidemic periods.

Decadal Change in Seroprevalence of Chikungunya Virus Infection in Pune City, India

Chikungunya virus (CHIKV) is an arthropod-borne virus capable of causing large outbreaks. We aimed to determine the decadal change in the extent of chikungunya virus infection from 2009 to 2019. We implemented a prospective cross-sectional survey in Pune City using a 30-cluster approach with probability-proportion-to-size (PPS) sampling, with blood samples collected from 1654 participants in early 2019. The study also included an additional 799 blood samples from an earlier serosurvey in late 2009. The samples were tested by an in-house anti-CHIKV IgG ELISA assay. The overall seroprevalence in 2019 was 53.2% (95% CI 50.7−55.6) as against 8.5% (95% CI 6.5−10.4) in 2009. A fivefold increase in seroprevalence was observed in a decade (p < 0.00001). The seroprevalence increased significantly with age; however, it did not differ between genders. Modeling of age-stratified seroprevalence data from 2019 coincided with a recent outbreak in 2016 followed by the low-level circulation. The mean estimated force of infection during the outbreak was 35.8% (95% CI 2.9−41.2), and it was 1.2% after the outbreak. To conclude, the study reports a fivefold increase in the seroprevalence of chikungunya infection over a decade in Pune City. The modeling approach considering intermittent outbreaks with continuous low-level circulation was a better fit and coincided with a recent outbreak reported in 2016. Community engagement and effective vector control measures are needed to avert future chikungunya outbreaks.

Uncovering the Burden of Dengue in Africa: Considerations on Magnitude, Misdiagnosis, and Ancestry

Dengue is a re-emerging neglected disease of major public health importance. This review highlights important considerations for dengue disease in Africa, including epidemiology and underestimation of disease burden in African countries, issues with malaria misdiagnosis and co-infections, and potential evidence of genetic protection from severe dengue disease in populations of African descent. The findings indicate that dengue virus prevalence in African countries and populations may be more widespread than reported data suggests, and that the Aedes mosquito vectors appear to be increasing in dissemination and number. Changes in climate, population, and plastic pollution are expected to worsen the dengue situation in Africa. Dengue misdiagnosis is also a problem in Africa, especially due to the typical non-specific clinical presentation of dengue leading to misdiagnosis as malaria. Finally, research suggests that a protective genetic component against severe dengue exists in African descent populations, but further studies should be conducted to strengthen this association in various populations, taking into consideration socioeconomic factors that may contribute to these findings. The main takeaway is that Africa should not be overlooked when it comes to dengue, and more attention and resources should be devoted to this disease in Africa.

Urban risk factors for human Rift Valley fever virus exposure in Kenya

The Rift Valley fever virus (RVFV) is a zoonotic arbovirus that can also transmit directly to humans from livestock. Previous studies have shown consumption of sick animal products are risk factors for RVFV infection, but it is difficult to disentangle those risk factors from other livestock rearing activities. Urban areas have an increased demand for animal source foods, different vector distributions, and various arboviruses are understood to establish localized urban transmission cycles. Thus far, RVFV is an unevaluated public health risk in urban areas within endemic regions. We tested participants in our ongoing urban cohort study on dengue (DENV) and chikungunya (CHIKV) virus for RVFV exposure and found 1.6% (57/3,560) of individuals in two urban areas of Kenya had anti-RVFV IgG antibodies. 88% (50/57) of RVFV exposed participants also had antibodies to DENV, CHIKV, or both. Although livestock ownership was very low in urban study sites, RVFV exposure was overall significantly associated with seeing goats around the homestead (OR = 2.34 (CI 95%: 1.18-4.69, p = 0.02) and in Kisumu, RVFV exposure was associated with consumption of raw milk (OR = 6.28 (CI 95%: 0.94-25.21, p = 0.02). In addition, lack of piped water and use of small jugs (15-20 liters) for water was associated with a higher risk of RVFV exposure (OR = 5.36 (CI 95%: 1.23-16.44, p = 0.01) and this may contribute to interepidemic vector-borne maintenance of RVFV. We also investigated perception towards human vaccination for RVFV and identified high acceptance (91% (97/105) at our study sites. This study provides baseline evidence to guide future studies investigating the urban potential of RVFV and highlights the unexplored role of animal products in continued spread of RVFV.

Machine learning and deep learning techniques to support clinical diagnosis of arboviral diseases: A systematic review

BACKGROUND

Neglected tropical diseases (NTDs) primarily affect the poorest populations, often living in remote, rural areas, urban slums or conflict zones. Arboviruses are a significant NTD category spread by mosquitoes. Dengue, Chikungunya, and Zika are three arboviruses that affect a large proportion of the population in Latin and South America. The clinical diagnosis of these arboviral diseases is a difficult task due to the concurrent circulation of several arboviruses which present similar symptoms, inaccurate serologic tests resulting from cross-reaction and co-infection with other arboviruses.

OBJECTIVE

The goal of this paper is to present evidence on the state of the art of studies investigating the automatic classification of arboviral diseases to support clinical diagnosis based on Machine Learning (ML) and Deep Learning (DL) models.

METHOD

We carried out a Systematic Literature Review (SLR) in which Google Scholar was searched to identify key papers on the topic. From an initial 963 records (956 from string-based search and seven from a single backward snowballing procedure), only 15 relevant papers were identified.

RESULTS

Results show that current research is focused on the binary classification of Dengue, primarily using tree-based ML algorithms. Only one paper was identified using DL. Five papers presented solutions for multi-class problems, covering Dengue (and its variants) and Chikungunya. No papers were identified that investigated models to differentiate between Dengue, Chikungunya, and Zika.

CONCLUSIONS

The use of an efficient clinical decision support system for arboviral diseases can improve the quality of the entire clinical process, thus increasing the accuracy of the diagnosis and the associated treatment. It should help physicians in their decision-making process and, consequently, improve the use of resources and the patient's quality of life.

OUP accepted manuscript

Although metagenomic sequencing has revealed high numbers of viruses in mosquitoes sampled globally, our understanding of how their diversity and abundance varies in time and space as well as by host species and gender remains unclear. To address this, we collected 23,109 mosquitoes over the course of 12 months from a bat-dwelling cave and a nearby village in Yunnan province, China. These samples were organized by mosquito species, mosquito gender, and sampling time for meta-transcriptomic sequencing. A total of 162 eukaryotic virus species were identified, of which 101 were novel, including representatives of seventeen RNA virus multi-family supergroups and four species of DNA virus from the families Parvoviridae, Circoviridae, and Nudiviridae. In addition, two known vector-borne viruses—Japanese encephalitis virus and Banna virus—were found. Analyses of the entire virome revealed strikingly different viral compositions and abundance levels in warmer compared to colder months, a strong host structure at the level of mosquito species, and no substantial differences between those viruses harbored by male and female mosquitoes. At the scale of individual viruses, some were found to be ubiquitous throughout the year and across four mosquito species, while most of the other viruses were season and/or host specific. Collectively, this study reveals the diversity, dynamics, and evolution of the mosquito virome at a single location and sheds new lights on the ecology of these important vector animals.

Genetic characterization of chikungunya virus isolates from Aedes aegypti mosquitoes collected during a recent outbreak in Bangkok, Thailand

Chikungunya virus (CHIKV) is a mosquito-borne emerging pathogen that is transmitted to humans through the bite of female Aedes mosquitoes. CHIKV infection has become a major public health concern worldwide, as it has a significant impact on the healthcare system. Since 2004, the virus has emerged in Africa and subsequently spread to countries located near the Indian Ocean, including India, and to Europe, the Americas, and Asia. In Thailand, a large CHIKV outbreak occurred during 2008-2009 and was caused by a virus originating from the east/central/south African (ECSA) CHIKV genotype. Since then, the ECSA genotype of CHIKV has continued to circulate and has caused sporadic cases in different areas in Thailand. Approximately 20,000 reported cases have been confirmed by the Bureau of Epidemiology, Ministry of Public Health, Thailand, from January 1, 2018 to July 31, 2020. However, the causes of this CHIKV re-emergence remain unclear. To obtain a better understanding of CHIKV circulation during the recent outbreak in Bangkok, Thailand, complete genome analysis of CHIKV isolates from field-caught mosquitoes collected in outbreak areas was performed. A total of 28 Ae. aegypti samples (21 females and 7 males) were collected, and individual mosquitoes were used for CHIKV detection and isolation. Eleven of 28 (39.29%) female and three of 28 (10.71%) male mosquitoes were positive for CHIKV by E1 nested RT-PCR. Four CHIKV isolates were successfully isolated from four female Ae. aegypti mosquitoes. Based on complete genome analysis, several amino acid substitutions were identified in the protein coding region. The E1:K211E and E2:V264A mutations in the background of the E1:226A mutation were observed in all four CHIKV isolates. An important observation was the presence of one amino acid substitution, leading to an E1:K245R change. This mutation was found in all four CHIKV isolates from mosquitoes in this study and in Thai patients described previously. Additionally, phylogenetic analysis indicated that the four CHIKV isolates belonged to the Indian Ocean clade of the ECSA genotype. The results obtained in this study provide detailed information on the molecular characteristics and evolution of currently circulating CHIKV strains in Thailand, which are useful for developing prevention and control strategies.

Rashid MF, Hod R, Dapari R, Hassan MR. A unique double tango: Construct validation and reliability analysis of risk perception, attitude and practice (RPAP) questionnaire on dengue infection

Introduction/background

Dengue fever remains a public health threat despite being preventable. A solution to the constant problem of dengue infection will require active intervention and a paradigm shift. Assessing perceived risk and correlating it with the attitude and practice of the community will help in designing appropriate measures. However, possible instruments for these assessments come with limitations.

Objective

The aim is to develop and validate a new scoring-based questionnaire, using dual statistical approaches to measure risk perception, attitude, and practices (RPAP) related to dengue in the community.

Methods

The RPAP questionnaire was developed bilingually using the International Society for Pharmacoeconomics and Outcome Research (ISPOR) guidelines. Content analysis was reviewed scrupulously by four expert panels. The initial 35-item scale was tested among 253 Malaysian respondents recruited non-probabilistically via multiple online platforms. Two statistical methods were employed to measure the construct validity: Exploratory Factor Analysis (EFA) as part of the Classical Test Theory (CTT) measurement, while Rasch Measurement Analysis (Rasch) was performed for the Item Response Theory (IRT) measurement. All results were cross-validated with their counterpart to ensure stability. Confirmatory Factor Analysis (CFA) was used to obtain a model fit index.

Results

29 questions were retained after the final analysis. Both EFA and Rasch analysis detect multidimensionality. Nine latent factors were extracted from EFA, while only eight factors remained in the final model following CFA: 1) perceived susceptibility; 2) perceived severity; 3) perceived barrier; 4) perceived benefit; 5) cues to action; 6) self-efficacy; 7) attitude; and 8) practice. All items had adequate factor loadings and showed good internal consistency. The final model after CFA achieved a good fit with an RMSEA value of 0.061, SRMR of 0.068, PNFI of 0.649, and GFI of 0.996.

Conclusion

The RPAP questionnaire contains 29 items and is a reliable and accurate psychometric instrument for measuring the risk perception of dengue fever, attitude, and practice of the community in dengue prevention. The Rasch measurement provides additional rigour to complement the CTT analysis. This RPAP questionnaire is suitable for use in studies related to dengue prevention in the community.

Clinical and epidemiologic characteristics associated with dengue fever in Mombasa, Kenya

OBJECTIVES

Information on dengue in Africa is limited. To estimate the proportion of dengue-positive cases among febrile patients and describe clinical indicators of dengue, we conducted passive health facility-based fever surveillance in Mombasa, Kenya.

METHODS

Non-malarial febrile patients between one and 55 years were enrolled at three health facilities between March 2016 and May 2017. Acute and convalescent blood samples were collected with an interval of 10-21 days. Acute samples were tested with dengue RDT and a selected subset with RT-PCR, and acute/convalescent samples with IgM/IgG ELISA.

RESULTS

Among 482 enrollees, 295 (61.2%) were dengue-positive based on laboratory results. The surveillance covered the beginning of a dengue outbreak in April-May 2017, during which 73.9% of enrollees were dengue-positive. By contrast, during the non-outbreak period, 54.6% were dengue-positive. Dengue case status was positively associated with rash, fatigue, headache, retro-orbital pain, nausea/vomiting, nose bleeding, gum bleeding, loss of appetite, myalgia, and arthralgia. Dengue-positive cases in our study had mostly mild disease, with only two requiring observation, and no DHF.

CONCLUSIONS

The clinical response was generally mild relative to what was observed in SE Asia and the Americas. Given the high level of DENV transmission in Mombasa, more data would be needed to further understand the disease burden and improve case detection for surveillance/monitoring of outbreaks.

Assessing the vertical transmission potential of dengue virus in field-reared Aedes aegypti using patient-derived blood meals in Ho Chi Minh City, Vietnam

BACKGROUND

Dengue viruses (DENV) can be transmitted from an adult female Aedes aegypti mosquito through the germ line to the progeny; however, there is uncertainty if this occurs at a frequency that is epidemiologically significant. We measured vertical transmission of DENV from field-reared Ae. aegypti to their F1 progeny after feeding upon blood from dengue patients. We also examined the transmission potential of F1 females.

METHODS

We examined the frequency of vertical transmission in field-reared mosquitoes, who fed upon blood from acutely viremic dengue patients, and the capacity for vertically infected females to subsequently transmit virus horizontally, in two sets of experiments: (i) compared vertical transmission frequency of field-reared Ae. aegypti and Ae. albopictus, in individual progeny; and (ii) in pooled progeny derived from field- and laboratory-reared Ae. aegypti.

RESULTS

Of 41 DENV-infected and isofemaled females who laid eggs, only a single female (2.43%) transmitted virus to one of the F1 progeny, but this F1 female did not have detectable virus in the saliva when 14 days-old. We complemented this initial study by testing for vertical transmission in another 460 field-reared females and > 900 laboratory-reared counterparts but failed to provide any further evidence of vertical virus transmission.

CONCLUSIONS

In summary, these results using field-reared mosquitoes and viremic blood from dengue cases suggest that vertical transmission is uncommon. Field-based studies that build on these observations are needed to better define the contribution of vertical DENV transmission to dengue epidemiology.