Vector Competence and Vertical Transmission of Zika Virus in Aedes albopictus (Diptera: Culicidae)

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

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

Vector competence evaluation of mosquitoes for Tahyna virus PJ01 strain, a new Orthobunyavirus in China

Introduction

Tahyna virus (TAHV), an arbovirus of the genus Orthobunyavirus, is a cause of human diseases and less studied worldwide. In this study, a new strain of TAHV was isolated from Aedes sp. mosquitoes collected in Panjin city, Liaoning province. However, the competent vector of TAHV in China is still unknown.

Methods

The genome of newly isolated TAHV was sequenced and phylogenetic analysis is performed. Aedes albopictus and Culex pipiens pallens were orally infected with artificial virus blood meals (1:1 of virus suspension and mouse blood), the virus was detected in the midgut, ovary, salivary gland and saliva of the mosquitoes. Then, the transmission and dissemination rates, vertical transmission and horizontal transmission of the virus by the mosquitoes were assessed.

Results

Phylogenetic analysis revealed that the virus shared high similarity with TAHV and was named the TAHV PJ01 strain. After oral infection with virus blood meals, Ae. albopictus showed positive for the virus in all tested tissues with an extrinsic incubation period of 2 days and a fluctuating increasement of transmission and dissemination rates. Whereas no virus was detected in the saliva of Cx. pipiens pallens. Suckling mice bitten by infectious Ae. albopictus developed obvious neurological symptoms, including inactivity, hind-leg paralysis and difficulty turning over, when the virus titer reached 1.70×10⁵ PFU/mL in the brain. Moreover, TAHV was detected in the eggs, larvae and adults of F1 offspring of Ae. albopictus.

Discussion

Ae. albopictus is an efficient vector to transmit TAHV but Cx. pipiens pallens is not. Ae. albopictus is also a reservoir host that transmits the virus vertically, which further increases the risk of outbreaks. This study has important epidemiological implications for the surveillance of pathogenic viruses in China and guiding comprehensive vector control strategies to counteract potential outbreaks in future.

Survival and Replication of Zika Virus in Diapause Eggs of Aedes Albopictus From Beijing, China

Zika virus (ZIKV) has emerged as a globally important arbovirus. The virus is primarily transmitted to humans through the bite of an infective Aedes albopictus in temperate area. Vertical transmission of ZIKV by Ae. albopictus is determined and has been suggested to be a means by which the virus could persist in nature. Ae. albopictus undergoes a well-characterized photoperiodic diapause. Viruses are harbored by overwintering mosquitoes in diapause that contributes to the resurgence of vertebrate diseases in the following spring, yet little is known about the impact of diapause on the regulation of viral replication and survival. The purpose of this study is to determine that Ae. albopictus in Beijing are highly susceptible to ZIKV (92.3%), and viable virus is passed to their organs of progeny via vertical transmission. Moreover, diapause eggs (diapause incidence 97.8%) had significantly lower minimum infection rates and filial infection rates of the first gonotrophic cycle than those of the second gonotrophic cycle in the short-day photoperiod group. Regarding the development of diapause eggs, the minimum infection rates and ZIKV RNA copy number increased significantly, suggesting that virus RNA replication occurred in the diapause eggs. Meanwhile, eggs from the ZIKV-infected mosquitoes had a significantly lower hatching rate compared with uninfected mosquitoes, implying an intriguing interaction between diapause eggs and virus. The findings here suggest that vertical transmission of ZIKV from diapause eggs to progeny may have a critical epidemiological role in the dissemination and maintenance of ZIKV circulating in the vector.

Evidence of Zika virus horizontal and vertical transmission in Aedes albopictus from Spain but not infectious virus in saliva of the progeny

Aedes albopictus mosquitoes have been experimentally demonstrated to be a competent vector for Zika virus (ZIKV) in different countries, but there are still some gaps related to the importance of Ae. albopictus in ZIKV transmission. Recent studies on Spanish Ae. albopictus populations showed controversial results for ZIKV transmission and no studies have been performed yet to detect infectious ZIKV in saliva of progeny of infected female mosquitoes. Herein, the horizontal transmission (HT) and vertical transmission (VT) of ZIKV in field-collected Ae. albopictus mosquitoes from Spain were evaluated for ZIKV strains (African I and Asian lineages) to better estimate the risk of ZIKV transmission by Ae. albopictus. The two field-collected Ae. albopictus populations assayed were infected by all tested ZIKV strains, however differences in terms of vector competence were detected depending on strain-population combination. Moreover, a higher susceptibility to the African I lineage strain than to the Asian lineage strain was observed in both mosquito populations. On the other hand, VT was demonstrated for both ZIKV lineages, detecting the virus in both males and females of the progeny of infected females, although importantly ZIKV dissemination and transmission were not detected in the infected females from the offspring. The results of the present study demonstrate that Spanish Ae. albopictus populations could sustain virus transmission in case of ZIKV introduction, but VT would play a poor role in the ZIKV epidemiology. Overall, our results provide helpful information to health authorities to establish efficient surveillance and vector control programmes for ZIKV.

Susceptibility of Armigeres subalbatus Coquillett (Diptera: Culicidae) to Zika virus through oral and urine infection

Background

Zika virus (ZIKV) disease outbreaks have been occurring in South America since 2015, and has spread to North America. Because birth defects and cases of Guillain Barré have been associated with infection with ZIKV, this has drawn global attention. ZIKV is generally considered an Aedes-transmitted pathogen. The transmission of ZIKV through blood by Aedes mosquito bites has been recognized as the major transmission route. However, it is not clear whether there are other transmission routes that can cause viral infection in mosquitos. The aim of the present study is to describe the susceptibility of Armigeres subalbatus, which often develop in human waste lagoons, to ZIKV, through oral infection in adult mosquitoes and urine infection in larvae.

Methodology/Principal findings

Five-day-old female Ar. subalbatus ingested infectious blood meals containing ZIKV. After 4, 7, and 10 days of ingesting infectious blood meals, ZIKV could be detected in the midguts, salivary glands, ovaries, and collected saliva of mosquitoes. The ZIKV infection rate (IR) on day 10 reached 40% in salivary glands and 13% in saliva, indicating that these mosquitoes were able to transmit ZIKV. In addition, ZIKV infection was also discovered in mosquito ovaries, suggesting the possibility of vertical transmission of virus. Moreover, Ar. subalbatus transmitted ZIKV to infant mice bitten by infectious mosquitoes. In a second experiment, 1^st-instar larvae of Ar. subalbatus were reared in water containing ZIKV and human urine. After pupation, pupae were placed in clean water and transferred to a mosquito cage for emergence. Although ZIKV RNA was detected in all of the larvae tested, ZIKV was not detected in the saliva of any adult Ar. subalbatus. Considering that there are more uncontrollable factors in nature than in the laboratory environment, the possibility that the virus is transmitted to adult mosquitoes via larvae is very small period.

Conclusions/Significance

Adult Ar. subalbatus could be infected with ZIKV and transmit ZIKV through mosquito bites. Therefore, in many rural areas in China and in undeveloped areas of other Asian countries, the management of human waste lagoons in the prevention and control of Zika disease should be considered. Corresponding adjustments and modifications should also be made in prevention and control strategies against ZIKV.

Zika is a serious threat to global health since the outbreak in Brazil in 2015. Zika virus (ZIKV) is generally considered as an Aedes-transmitted pathogen. The transmission of ZIKV by mosquito bite has been recognized as the major transmission route. However, it is possible that some important potential vectors may not yet have been examined. Armigeres subalbatus is one of primary mosquito species in China, which could develop in human waste lagoons. In the study, through oral infection experiments, it was found that Ar. subalbatus could be infected with ZIKV and transmit ZIKV through mosquito bites. Therefore, in many rural areas in China and in undeveloped areas of other Asian countries, it is valid to consider that this mosquito species should be given enough attention in the prevention and control of Zika epidemic.