The interplay between environmental factors, vector competence and vaccine immunodynamics as possible explanation of the 2019 yellow fever re-emergence in Nigeria

High-Throughput Platform for Detection of Neutralizing Antibodies Using Flavivirus Reporter Replicon Particles

Flavivirus outbreaks require fast and reliable diagnostics that can be easily adapted to newly emerging and re-emerging flaviviruses. Due to the serological cross-reactivity among flavivirus antibodies, neutralization tests (NT) are considered the gold standard for sero-diagnostics. Here, we first established wild-type single-round infectious virus replicon particles (VRPs) by packaging a yellow fever virus (YFV) replicon expressing Gaussia luciferase (Gluc) with YFV structural proteins in trans using a double subgenomic Sindbis virus (SINV) replicon. The latter expressed the YFV envelope proteins prME via the first SINV subgenomic promoter and the capsid protein via a second subgenomic SINV promoter. VRPs were produced upon co-electroporation of replicon and packaging RNA. Introduction of single restriction enzyme sites in the packaging construct flanking the prME sequence easily allowed to exchange the prME moiety resulting in chimeric VRPs that have the surface proteins of other flaviviruses including dengue virus 1-4, Zika virus, West Nile virus, and tick-borne encephalitis virus. Besides comparing the YF-VRP based NT assay to a YF reporter virus NT assay, we analyzed the neutralization efficiencies of different human anti-flavivirus sera or a monoclonal antibody against all established VRPs. The assays were performed in a 96-well high-throughput format setting with Gluc as readout in comparison to classical plaque reduction NTs indicating that the VRP-based NT assays are suitable for high-throughput analyses of neutralizing flavivirus antibodies.

Mosquito control at a tertiary teaching hospital in Nigeria

Background

Mosquitoes are vectors of numerous diseases, including malaria and yellow fever. Mosquito control is therefore a priority in many countries, especially in healthcare settings. Here we investigated the opinions of patients and staff regarding mosquito control at a hospital in Nigeria, and also gathered data on mosquito-control measures in this setting.

Methods

We conducted a cross-sectional questionnaire study of staff and patients and an observational approach to obtain data on mosquito-control measures used at a tertiary teaching hospital in Abakaliki, Nigeria.

Discussion

Both staff (N=517) and patients (N=302) reported experiencing more mosquito bites at the hospital than elsewhere. As well as contributing to discomfort, this exposure may put hospital staff and patients at risk of mosquito-borne infections. Complaints from patients about mosquitoes were reported by over 90% of staff, and over 50% of staff respondents were aware of patient discharge against medical advice due to mosquitoes. The most common control method was killing mosquitoes by hand. We observed a lack of door screens in all wards, window screens were absent or torn, and most beds did not have nets. In the children's wards none of the beds had nets.

Conclusions

Current measures against mosquitoes in this hospital appeared inadequate, and healthcare staff and hospital patients may be at increased risk of mosquito-borne infections. Mosquito control in the hospital requires attention, and the needs for improvement in mosquito control in the healthcare setting more widely should be evaluated and addressed.

The Present and Future of Yellow Fever Vaccines

The disease yellow fever (YF) is prevented by a live-attenuated vaccine, termed 17D, which has been in use since the 1930s. One dose of the vaccine is thought to give lifelong (35+ years) protective immunity, and neutralizing antibodies are the correlate of protection. Despite being a vaccine-preventable disease, YF remains a major public health burden, causing an estimated 109,000 severe infections and 51,000 deaths annually. There are issues of supply and demand for the vaccine, and outbreaks in 2016 and 2018 resulted in fractional dosing of the vaccine to meet demand. The World Health Organization (WHO) has established the “Eliminate Yellow Fever Epidemics” (EYE) initiative to reduce the burden of YF over the next 10 years. As with most vaccines, the WHO has recommendations to assure the quality, safety, and efficacy of the YF vaccine. These require the use of live 17D vaccine only produced in embryonated chicken eggs, and safety evaluated in non-human primates only. Thus, any second-generation vaccines would require modification of WHO recommendations if they were to be used in endemic countries. There are multiple second-generation YF vaccine candidates in various stages of development that must be shown to be non-inferior to the current 17D vaccine in terms of safety and immunogenicity to progress through clinical trials to potential licensing. The historic 17D vaccine continues to shape the global vaccine landscape in its use in the generation of multiple licensed recombinant chimeric live vaccines and vaccine candidates, in which its structural protein genes are replaced with those of other viruses, such as dengue and Japanese encephalitis. There is no doubt that the YF 17D live-attenuated vaccine will continue to play a role in the development of new vaccines for YF, as well as potentially for many other pathogens.