Arboviral bottlenecks and challenges to maintaining diversity and fitness during mosquito transmission.

The term arbovirus denotes viruses that are transmitted by arthropods, such as ticks, mosquitoes, and other biting arthropods. The infection of these vectors produces a certain set of evolutionary pressures on the virus; involving migration from the midgut, where the blood meal containing the virus is processed, to the salivary glands, in order to transmit the virus to the next host. During this process the virus is subject to numerous bottlenecks, stochastic events that significantly reduce the number of viral particles that are able to infect the next stage. This article reviews the latest research on the bottlenecks that occur in arboviruses and the way in which these affect the evolution and fitness of these viruses. In particular we focus on the latest research on three important arboviruses, West Nile virus, Venezuelan equine encephalitis virus and Chikungunya viruses and compare the differing effects of the mosquito bottlenecks on these viruses as well as other evolutionary pressures that affect their evolution and transmission

Silent circulation of arboviruses in Cameroon

Objectives: To investigate the silent circulation and transmission of arthropod-borne viruses (arboviruses) in the Fako Division of Cameroon.Design: This survey was conducted based on clinical observations and laboratory diagnosis; field collections of mosquitoes.Setting: This study was conducted in the Fako Division of South West Cameroon.Subjects: One hundred and two sera were obtained from febrile patients (with negative laboratory findings for malaria and typhoid fever) at clinics in the Fako Division, and diurnal anthropophilic mosquitoes (4,764) collected.Interventions: Virus isolation was attempted from these, and sera were screened for antibodies against 18 African arboviruses by haemagglutination inhibition (HI) and complement fixation (CF) tests.Results: No virus was isolated. Fifty three of 79 (67.1%) sera reacted with one or more viral antigens. Twenty nine sera (36.7%) reacted with members of the genus Alphavirus, with Chikungunya (CHIKV) and O’nyong-nyong (ONNV) viruses as the most frequent (34.2%). Forty six sera (58.2%) reacted with members of the genus Flavivirus: 24 (30.4%)were cross-reactive, but 11.4% reacted monotypically with Zika, 5.1% with yellow fever virus (YFV), 5.1% with dengue virus-2 (DENV-2), 2.5% with DENV-1 and 1.3% with Wesselsbron virus, respectively. The plaque reduction neutralisation test used to specify the agent that elicited the response could not resolve 33.3% of the cross reactions between CHIKV and ONNV. Neutralising antibody titres against ONNV and CHIKV were very high indicating probable re-infection.Conclusion: Our results indicate previously undetected circulation of arboviruses in Cameroon, and suggest that they are important, overlooked public health problems

Plasmodium falciparum (Haemosporodia: Plasmodiidae) and O'nyong-nyong virus development in a transgenic Anopheles gambiae (Diptera: Culicidae) strain

Transgenic Anopheles gambiae Giles (Diptera: Culicidae) mosquitoes have been developed that confer sexual sterility on males that carry a transgene encoding a protein which cuts ribosomal DNA. A relevant risk concern with transgenic mosquitoes is that their capacity to transmit known pathogens could be greater than the unmodified form. In this study, the ability to develop two human pathogens in these transgenic mosquitoes carrying a homing endonuclease which is expressed in the testes was compared with its nontransgenic siblings. Infections were performed with Plasmodium falciparum (Welch) and o'nyong-nyong virus (ONNV) and the results between the transgenic and nontransgenic sibling females were compared. There was no difference observed with ONNV isolate SG650 in intrathoracic infections or the 50% oral infectious dose measured at 14 d postinfection or in mean body titers. Some significant differences were observed for leg titers at the medium and highest doses for those individuals in which virus titer could be detected. No consistent difference was observed between the transgenic and nontransgenic comparator females in their ability to develop P. falciparum NF54 strain parasites. This particular transgene caused no significant effect in the ability of mosquitoes to become infected by these two pathogens in this genetic background. These results are discussed in the context of risk to human health if these transgenic individuals were present in the environment

Genetic Characterization of Venezuelan Equine Encephalitis Virus from Bolivia, Ecuador and Peru: Identification of a New Subtype ID Lineage

Venezuelan equine encephalitis virus (VEEV) has been responsible for hundreds of thousands of human and equine cases of severe disease in the Americas. A passive surveillance study was conducted in Peru, Bolivia and Ecuador to determine the arboviral etiology of febrile illness. Patients with suspected viral-associated, acute, undifferentiated febrile illness of <7 days duration were enrolled in the study and blood samples were obtained from each patient and assayed by virus isolation. Demographic and clinical information from each patient was also obtained at the time of voluntary enrollment. In 2005–2007, cases of Venezuelan equine encephalitis (VEE) were diagnosed for the first time in residents of Bolivia; the patients did not report traveling, suggesting endemic circulation of VEEV in Bolivia. In 2001 and 2003, VEE cases were also identified in Ecuador. Since 1993, VEEV has been continuously isolated from patients in Loreto, Peru, and more recently (2005), in Madre de Dios, Peru. We performed phylogenetic analyses with VEEV from Bolivia, Ecuador and Peru and compared their relationships to strains from other parts of South America. We found that VEEV subtype ID Panama/Peru genotype is the predominant one circulating in Peru. We also demonstrated that VEEV subtype ID strains circulating in Ecuador belong to the Colombia/Venezuela genotype and VEEV from Madre de Dios, Peru and Cochabamba, Bolivia belong to a new ID genotype. In summary, we identified a new major lineage of enzootic VEEV subtype ID, information that could aid in the understanding of the emergence and evolution of VEEV in South America

Genetic and Anatomic Determinants of Enzootic Venezuelan Equine Encephalitis Virus Infection of Culex (Melanoconion) taeniopus

Venezuelan equine encephalitis (VEE) is a re-emerging, mosquito-borne viral disease with the potential to cause fatal encephalitis in both humans and equids. Recently, detection of endemic VEE caused by enzootic strains has escalated in Mexico, Peru, Bolivia, Colombia and Ecuador, emphasizing the importance of understanding the enzootic transmission cycle of the etiologic agent, VEE virus (VEEV). The majority of work examining the viral determinants of vector infection has been performed in the epizootic mosquito vector, Aedes (Ochlerotatus) taeniorhynchus. Based on the fundamental differences between the epizootic and enzootic cycles, we hypothesized that the virus-vector interaction of the enzootic cycle is fundamentally different from that of the epizootic model. We therefore examined the determinants for VEEV IE infection in the enzootic vector, Culex (Melanoconion) taeniopus, and determined the number and susceptibility of midgut epithelial cells initially infected and their distribution compared to the epizootic virus-vector interaction. Using chimeric viruses, we demonstrated that the determinants of infection for the enzootic vector are different than those observed for the epizootic vector. Similarly, we showed that, unlike A. taeniorhynchus infection with subtype IC VEEV, C. taeniopus does not have a limited subpopulation of midgut cells susceptible to subtype IE VEEV. These findings support the hypothesis that the enzootic VEEV relationship with C. taeniopus differs from the epizootic virus-vector interaction in that the determinants appear to be found in both the nonstructural and structural regions, and initial midgut infection is not limited to a small population of susceptible cells

A novel live-attenuated vaccine candidate for mayaro Fever.

Mayaro virus (MAYV) is an emerging, mosquito-borne alphavirus that causes a dengue-like illness in many regions of South America, and which has the potential to urbanize. Because no specific treatment or vaccine is available for MAYV infection, we capitalized on an IRES-based approach to develop a live-attenuated MAYV vaccine candidate. Testing in infant, immunocompetent as well as interferon receptor-deficient mice demonstrated a high degree of attenuation, strong induction of neutralizing antibodies, and efficacy against lethal challenge. This vaccine strain was also unable to infect mosquito cells, a major safety feature for a live vaccine derived from a mosquito-borne virus. Further preclinical development of this vaccine candidate is warranted to protect against this important emerging disease

Phenoloxidase activity acts as a mosquito innate immune response against infection with semliki forest virus

Several components of the mosquito immune system including the RNA interference (RNAi), JAK/STAT, Toll and IMD pathways have previously been implicated in controlling arbovirus infections. In contrast, the role of the phenoloxidase (PO) cascade in mosquito antiviral immunity is unknown. Here we show that conditioned medium from the Aedes albopictus-derived U4.4 cell line contains a functional PO cascade, which is activated by the bacterium Escherichia coli and the arbovirus Semliki Forest virus (SFV) (Togaviridae; Alphavirus). Production of recombinant SFV expressing the PO cascade inhibitor Egf1.0 blocked PO activity in U4.4 cell- conditioned medium, which resulted in enhanced spread of SFV. Infection of adult female Aedes aegypti by feeding mosquitoes a bloodmeal containing Egf1.0-expressing SFV increased virus replication and mosquito mortality. Collectively, these results suggest the PO cascade of mosquitoes plays an important role in immune defence against arboviruses

Transformative learning as pedagogy for the health professions : a scoping review

Context Transformative learning (TL) has been described as learning that challenges established perspectives, leading to new ways of being in the world. As a learning theory it has resonated with educators globally, including those in the health professions. Described as a complex metatheory, TL has evolved over time, eliciting divergent interpretations of the construct. This scoping review provides a comprehensive synthesis of how TL is currently represented in the health professions education literature, including how it influences curricular activities, to inform its future application in the field. Methods Arksey and O'Malley's six‐step framework was adopted to review the period from 2006 to May 2018. A total of 10 bibliographic databases were searched, generating 1532 potential studies. After several rounds of review, first of abstracts and then of full texts, 99 studies were mapped by two independent reviewers onto the internally developed data extraction sheet. Descriptive information about included studies was aggregated. Discursive data were subjected to content analysis. Results A mix of conceptual and empirical research papers, which used a range of qualitative methodologies, were included. Studies from the USA, the UK and Australia were most prevalent. Insights relating to how opportunities for TL were created, how it manifests and influences behaviour, as well as how it is experienced, demonstrated much congruency. Conceptions of TL were seen to be clustered around the work of key theorists. Conclusions The training of health professionals often takes place in unfamiliar settings where students are encouraged to be active participants in providing care. This increases the opportunity for exposure to learning experiences that are potentially transformative, allowing for a pedagogy of uncertainty that acknowledges the complexity of the world we live in and questions what we believe we know about it. TL provides educators in the health professions with a theoretical lens through which they can view such student learning