Dengue Virus Exported from Côte d'Ivoire to Japan, June 2017

The role of car tyres in the ecology of Aedes aegypti mosquitoes in Ghana

Aedes aegypti is an important vector of arboviral diseases including dengue and yellow fever. Despite the wide distribution of this mosquito species, there are limited data on the ecology of Ae. aegypti in Ghana. In this study, we report on the oviposition preference and the larval life tables of Ae. aegypti mosquitoes in Accra, Ghana. The oviposition preference of the mosquitoes to three habitat types (car tyres, drums and bowls) was measured by setting up ovitraps. We recorded the presence and abundance of larvae every 3 days. Two-hour-old Ae. aegypti larvae were introduced and raised in three habitat types to undertake larval life tables. The number of surviving larvae at each developmental stage was recorded daily until they emerged as adults. Car tyres showed a higher abundance of Ae. aegypti larvae (52.3%) than drums (32.5%) and bowls (15.1%) (ANOVA, F(2,159) = 18.79, P < 0.001). The mean development time of Ae. aegypti larvae was significantly lower in car tyres (7 ± 1 days) compared to that of bowls (9 ± 0.0 days) and drums (12.6 ± 1.5 days) (P = 0.024). The differences in pupation rates and emergence rates were not significant across the habitat types; however, the highest pupation rate was observed in bowls (0.92 ± 0.17) and the emergence rate was highest in tyres (0.84 ± 0.10). The proportion of first-instar larvae that survived to emergence was significantly higher in car tyres (0.84 ± 0.10) compared to that of bowls (0.72 ± 0.20) and drums (0.62 ± 0.20) (P = 0.009). No mortalities were observed after 9 days in car tyres, 10 days in bowls and 15 days in drums. The results confirm that discarded car tyres were the preferred habitat choice for the oviposition of gravid female Ae. aegypti mosquitoes and provide the best habitat conditions for larval development and survival. These findings are necessary for understanding the ecology of Ae. aegypti to develop appropriate strategies for their control in Ghana.

The Role of Car Tyres in the Ecology of Aedes aegypti Mosquitoes in Ghana

Background

The Aedes aegyptimosquito is an important vector of arboviral diseases including dengue and yellow fever. Despite the wide distribution of the Aedes aegypti mosquito, there is limited data on the ecology of Aedes aegypti mosquitoes in Ghana. In this study, we report on the oviposition preference and the larval life table of Aedes aegypti mosquitoes in Accra, Ghana.

Methods

The oviposition preference of Aedesmosquitoes to three habitat types (tyres, drums and bowls) was measured by setting up ovitraps. Ovitraps were checked for the presence of Aedes larvae every 3 days. The presence and number of larvae were recorded for each habitat type. Two-hour-old Aedes aegypti larvae were introduced into and raised in these three habitat types to undertake larval life tables. The number of surviving larvae at each developmental stage was recorded daily until they emerge as adults.

Results

Car tyres showed a high abundance of Aedeslarvae (52.33%) than drums (32.49%) and bowls (15.18%) (ANOVA, F _ 18.79, df _ 2, 159, P < 0.001). The mean development time of Ae. aegypti larvae was significantly lower in car tyres (7 ± 1 days) compared to that of bowls (9 ± 0.0 days) and drums (12.6 ± 1.5 days) (H (2) = 7.448, P = 0.024). The differences in pupation rates and emergence rates were not significant across the habitat types, however, the highest pupation rate was observed in bowls (0.92) and the emergence rate was highest in tyres (0.84). The proportion of first-instar larvae that survived to adults was significantly higher in tyres with a shorter survival time (0.84; 9 days) compared to that of bowls (0.72; 10 days) and drums (0.62 ± 0.2; 13 days) (H (2) = 2.822, P= 0.009).

Conclusion

The results confirm that discarded car tyres were the preferred habitat choice for the oviposition of gravid female Aedes aegypti mosquitoes and provide the best habitat condition for larval development and survival. These findings are necessary for understanding the ecology of Aedes mosquitoes to develop appropriate strategies for their control in Ghana.

Analysis of cross-reactivity among flaviviruses using sera of patients with dengue showed the importance of neutralization tests with paired serum samples for the correct interpretations of serological test results for dengue

Dengue is a febrile illness caused by the dengue virus (DENV) that belongs to the genus Flavivirus in the family Flaviviridae. Cross-reactivity between flaviviruses poses a challenge while interpreting serological test results. In the present study, the cross-reactivity of sera of the patients with dengue, who traveled from Japan to DENV-endemic countries, was analyzed by using an enzyme-linked immunosorbent assay (ELISA) and neutralization test (NT). Sixteen serum samples were collected from patients with dengue and were tested for: i) IgM antibodies against Zika virus (ZIKV), West Nile virus (WNV), Japanese encephalitis virus (JEV), and tick-borne encephalitis virus (TBEV) using IgM ELISA, ii) IgG antibody against TBEV using IgG ELISA, and iii) neutralizing antibody against ZIKV, WNV, TBEV, and JEV. Among the 16 samples tested using ELISA, seven samples were IgM-positive for at least one of the other flaviviruses, and nine samples were IgG-positive for TBEV. Neutralizing antibody titers (NATs) against ZIKV, WNV, and TBEV were one-fourth or lower than those against the causative DENV in all samples. The NATs against JEV were one-fourth or lower than those against the causative DENV in six convalescent-phase serum sample among the seven convalescent-phase serum samples. The NAT against DENV of the residual one convalescent-phase serum was similar to that against JEV and that against JEV of its relevant acute-phase serum sample. These results showed that NTs with paired serum samples are important to correctly interpret the serological test results for DENV.

Spatiotemporal distribution and insecticide resistance status of Aedes aegypti in Ghana

Background

Vector control is the main intervention used to control arboviral diseases transmitted by Aedes mosquitoes because there are no effective vaccines or treatments for most of them. Control of Aedes mosquitoes relies heavily on the use of insecticides, the effectiveness of which may be impacted by resistance. In addition, rational insecticide application requires detailed knowledge of vector distribution, dynamics, resting, and feeding behaviours, which are poorly understood for Aedes mosquitoes in Africa. This study investigated the spatiotemporal distribution and insecticide resistance status of Aedes aegypti across ecological extremes of Ghana.

Methods

Immature mosquitoes were sampled from containers in and around human dwellings at seven study sites in urban, suburban, and rural areas of Ghana. Adult Aedes mosquitoes were sampled indoors and outdoors using Biogents BG-Sentinel 2 mosquito traps, human landing catches, and Prokopack aspiration. Distributions of immature and adult Aedes mosquitoes were determined indoors and outdoors during dry and rainy seasons at all sites. The phenotypic resistance status of Aedes mosquitoes to insecticides was determined using World Health Organization susceptibility bioassays. The host blood meal source was determined by polymerase chain reaction.

Results

A total of 16,711 immature Aedes were sampled, with over 70% found in car tyres. Significantly more breeding containers had Aedes immatures during the rainy season (11,856; 70.95%) compared to the dry season (4855; 29.05%). A total of 1895 adult Aedes mosquitos were collected, including Aedes aegypti (97.8%), Aedes africanus (2.1%) and Aedesluteocephalus (0.1%). Indoor sampling of adult Aedes yielded a total of 381 (20.1%) and outdoor sampling a total of 1514 (79.9%) mosquitoes (z = − 5.427, P = 0.0000) over the entire sampling period. Aedes aegypti populations were resistant to dichlorodiphenyltrichloroethane at all study sites. Vectors showed suspected resistance to bendiocarb (96–97%), permethrin (90–96%) and deltamethrin (91–96%), and were susceptible to the organophosphate for all study sites. Blood meal analysis showed that the Aedes mosquitoes were mostly anthropophilic, with a human blood index of 0.9 (i.e. humans, 90%; human and dog, 5%; dog and cow, 5%).

Conclusions

Aedes mosquitoes were found at high densities in all ecological zones of Ghana. Resistance of Aedes spp. to pyrethroids and carbamates may limit the efficacy of vector control programmes and thus requires careful monitoring.

Graphical abstract

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.

Epidemiology and Laboratory Diagnostics of Dengue, Yellow Fever, Zika, and Chikungunya Virus Infections in Africa

Arbovirus infections are widespread, and their disease burden has increased in the past decade. In Africa, arbovirus infections and fever with unknown etiology are common. Due to the lack of well-established epidemiologic surveillance systems and accurate differential diagnosis in most African countries, little is known about the prevalence of human arbovirus infections in Africa. The aim of this review is to summarize the available epidemiological data and diagnostic laboratory tools of infections with dengue, yellow fever, Zika, and chikungunya viruses, all transmitted by Aedes mosquitoes. Studies indicate that these arboviral infections are endemic in most of Africa. Surveillance of the incidence and prevalence of the infections would enable medical doctors to improve the diagnostic accuracy in patients with typical symptoms. If possible, arboviral diagnostic tests should be added to the routine healthcare systems. Healthcare providers should be informed about the prevalent arboviral diseases to identify possible cases.

Emerging Mosquito-Borne Viruses Linked to Aedes aegypti and Aedes albopictus: Global Status and Preventive Strategies

Emerging mosquito-borne viruses continue to cause serious health problems and economic burden among billions of people living in and near the tropical belt of the world. The highly invasive mosquito species Aedes aegypti and Aedes albopictus have successively invaded and expanded their presence as key vectors of Chikungunya virus, dengue virus, yellow fever virus, and Zika virus, and that has consecutively led to frequent outbreaks of the corresponding viral diseases. Of note, these two mosquito species have gradually adapted to the changing weather and environmental conditions leading to a shift in the epidemiology of the viral diseases, and facilitated their establishment in new ecozones inhabited by immunologically naive human populations. Many abilities of Ae. aegypti and Ae. albopictus, as vectors of significant arbovirus pathogens, may affect the infection and transmission rates after a bloodmeal, and may influence the vector competence for either virus. We highlight that many collaborating risk factors, for example, the global transportation systems may result in sporadic and more local outbreaks caused by mosquito-borne viruses related to Ae. aegypti and/or Ae. albopictus. Those local outbreaks could in synergy grow and produce larger epidemics with pandemic characters. There is an urgent need for improved surveillance of vector populations, human cases, and reliable prediction models. In summary, we recommend new and innovative strategies for the prevention of these types of infections.

Dengue virus serotype 2 imported case from Côte d'Ivoire to Senegal, 2017

Dengue fever is the most common arboviral infection worldwide. Its epidemiology in Africa is not yet fully understood due to the lack of awareness, the presence of other dengue-like febrile diseases, and insufficient laboratory capabilities. This paper reports on the import of dengue virus serotype 2 case from Côte d'Ivoire to Senegal in West Africa. Phylogenetic analysis based on full-length genome sequence revealed that the isolate clustered with strains of cosmopolitan genotypes from the Burkina Faso outbreak in 2016 and those from the ongoing dengue fever outbreak in Côte d'Ivoire. This suggests a possible spread of strains from the Burkina Faso outbreak to other West African countries including Côte d'Ivoire and Senegal.

Evolution, heterogeneity and global dispersal of cosmopolitan genotype of Dengue virus type 2

Dengue virus type 2 (DENV-2) contributes substantially to the dengue burden and dengue-related mortality in the tropics and sub-tropics. DENV-2 includes six genotypes, among which cosmopolitan genotype is the most widespread. The present study investigated the evolution, intra-genotype heterogeneity and dispersal of cosmopolitan genotype to understand unique genetic characteristics that have shaped the molecular epidemiology and distribution of cosmopolitan lineages. The spatial analysis demonstrated a wide geo-distribution of cosmopolitan genotype through an extensive inter-continental network, anchored in Southeast Asia and Indian sub-continent. Intra-genotype analyses using 3367 envelope gene sequences revealed six distinct lineages within the cosmopolitan genotype, namely the Indian sub-continent lineage and five other lineages. Indian sub-continent lineage was the most diverged among six lineages and has almost reached the nucleotide divergence threshold of 6% within E gene to qualify as a separate genotype. Genome wide amino acid signatures and selection pressure analyses further suggested differences in evolutionary characteristics between the Indian sub-continent lineage and other lineages. The present study narrates a comprehensive genomic analysis of cosmopolitan genotype and presents notable genetic characteristics that occurred during its evolution and global expansion. Whether those characteristics conferred a fitness advantage to cosmopolitan genotype in different geographies warrant further investigations.

Establishment and characterization of a cell line from Ghanaian Aedes aegypti (Diptera: Culicidae) focusing on Aedes-borne flavivirus susceptibility

Mosquitoes are generally considered one of the most important vectors of arboviruses, with Aedes aegypti regarded as the most important in transmission of yellow fever and dengue viruses. To investigate why there are differences in the incidence of dengue fever and Zika in different geographical areas and an absence of outbreaks in Ghana in spite of an abundance of A. aegypti mosquitoes, we established a continuous cell line from embryonic cells of A. aegypti collected in Ghana and assessed its susceptibility to dengue, yellow fever, and Zika viruses. The new cell line (designated AeAe-GH98), having an adhesive spindle-shaped web-like morphology, was serially subcultured in both VP-12 and Schneider's medium supplemented with 10% heat-inactivated fetal bovine serum. AeAe-GH98 cells were found to have a population doubling time of 1.3 d during exponential growth. The mosquito colony used to establish the cell line was confirmed to have originated from Africa using microsatellite assay. In terms of susceptibility to Aedes-borne flaviviruses, AeAe-GH98 cells were found to have different degrees of susceptibility to yellow fever, Zika, and dengue virus infection and propagation. While susceptibility of AeAe-GH98 cells to yellow fever and Zika viruses was comparable with that of C6/36 cells, susceptibility to dengue virus was significantly lower. This cell line will serve as a useful tool for determining molecular factors influencing virus-vector susceptibility in vitro.

Dengue Virus Serotype 1 Exported to Japan from Côte d'Ivoire, 2019

Dengue fever outbreaks have been repeatedly reported in Côte d'Ivoire. During the 2019 outbreak, DENV-1 was the predominant strain and phylogenetic analysis of the DENV-1 genome obtained from the present patient who returned to Japan in January 2019 revealed a high homology with the 2013-2014 Southeast Asian strains. In a previous outbreak in 2017, DENV-1 accounted for 5% of the DENV serotypes. The endemic DENV-1 strain in Abidjan in 2019 could be a strain that was imported from Southeast Asia. Dengue virus can spread globally, and imported dengue fever cases could serve as an alert for outbreaks in the exporting country.

Entomological Assessment of the Status and Risk of Mosquito-borne Arboviral Transmission in Ghana

Entomological surveillance is one of the tools used in monitoring and controlling vector-borne diseases. However, the use of entomological surveillance for arboviral infection vector control is often dependent on finding infected individuals. Although this method may suffice in highly endemic areas, it is not as effective in controlling the spread of diseases in low endemic and non-endemic areas. In this study, we examined the efficiency of using entomological markers to assess the status and risk of arbovirus infection in Ghana, which is considered a non-endemic country, by combining mosquito surveillance with virus isolation and detection. This study reports the presence of cryptic species of mosquitoes in Ghana, demonstrating the need to combine morphological identification and molecular techniques in mosquito surveillance. Furthermore, although no medically important viruses were detected, the importance of insect-specific viruses in understanding virus evolution and arbovirus transmission is discussed. This study reports the first mutualistic relationship between dengue virus and the double-stranded RNA Aedes aegypti totivirus. Finally, this study discusses the complexity of the virome of Aedes and Culex mosquitoes and its implication for arbovirus transmission.

Surveys of Arboviruses Vectors in Four Cities Stretching Along a Railway Transect of Burkina Faso: Risk Transmission and Insecticide Susceptibility Status of Potential Vectors

Background: A severe outbreak of dengue occurred in Burkina Faso in 2016, with the most cases reported in Ouagadougou, that highlights the necessity to implement vector surveillance system. This study aims to estimate the risk of arboviruses transmission and the insecticide susceptibility status of potential vectors in four sites in Burkina Faso.

Methods: From June to September 2016, house-to-house cross sectional entomological surveys were performed in four cities stretching along a southwest-to-northeast railway transect. The household surveys analyzed the presence of Aedes spp. larvae in containers holding water and the World Health Organization (WHO) larval abundance indices were estimated. WHO tube assays was used to evaluate the insecticide susceptibility within Aedes populations from these localities.

Results: A total of 31,378 mosquitoes' larvae were collected from 1,330 containers holding water. Aedes spp. was the most abundant (95.19%) followed by Culex spp. (4.75%). Aedes aegypti a key vector of arboviruses (ARBOV) in West Africa was the major Aedes species found (98.60%). The relative larval indices, house index, container and Breteau indexes were high, up to 70, 35, and 10, respectively. Aedes aegypti tended to breed mainly in discarded tires and terracotta jars. Except in Banfora the western city, Ae. aegypti populations were resistant to deltamethrin 0.05% in the other localities with low mortality rate under 20% in Ouagadougou whereas they were fully susceptible to malathion 5% whatever the site. Intermediate resistance was observed in the four sites with mortality rates varying between 78 and 94% with bendiocarb 0.1%.

Conclusions: This study provided basic information on entomological indices that can help to monitor the risks of ARBOV epidemics in the main cities along the railway in Burkina Faso. In these cities, all larval indices exceeded the risk level of ARBOV outbreak. Aedes aegypti the main species collected was resistant to deltamethrin 0.05% and bendiocarb 0.1% whereas they were fully susceptible to malathion 5%. The monitoring of insecticide resistance is also important to be integrated to the vector surveillance system in Burkina Faso.

Estimating the actual importation risk of dengue virus infection among Japanese travelers

Background

Frequent international travel facilitates the global spread of dengue fever. Japan has experienced an increasing number of imported case notifications of dengue virus (DENV) infection, mostly arising from Japanese travelers visiting South and Southeast Asian countries. This has led an autochthonous dengue outbreak in 2014 in Japan. The present study aimed to infer the risk of DENV infection among Japanese travelers to Asian countries, thereby obtaining an actual estimate of the number of DENV infections among travelers.

Methodology/Principal findings

For eight destination countries (Indonesia, Philippines, Thailand, India, Malaysia, Vietnam, Sri Lanka, and Singapore), we collected age-dependent seroepidemiological data. We also retrieved the number of imported cases, who were notified to the Japanese government, as well as the total number of travelers to each destination. Using a mathematical model, we estimated the force of infection in each destination country with seroepidemiological data while jointly inferring the reporting coverage of DENV infections among Japanese travelers from datasets of imported cases and travelers. Assuming that travelers had a risk of infection that was identical to that of the local population during travel, the reporting coverage of dengue appeared to range from 0.6% to 4.3%. The risk of infection per journey ranged from 0.02% to 0.44%.

Conclusions/Significance

We found that the actual number of imported cases of DENV infection among Japanese travelers could be more than 20 times the notified number of imported cases. This finding may be attributed to the substantial proportion of asymptomatic and under-ascertained infections.