The resurgence of yellow fever outbreaks in Nigeria: a 2-year review 2017-2019

Phylodynamic Investigation of Yellow Fever Virus Sheds New Insight on Geographic Dispersal Across Africa

Background

Molecular epidemiology has shown the presence of four genotypes circulating across Africa, a paucity of data exists regarding phylogeography of the African Yellow fever (YF) genotypes. The need to fill this gap with spatiotemporal data from continuous YF outbreaks in Africa conceptualized this study; which aims to investigate the most recent transmission events and directional spread of yellow fever virus (YFV) using updated genomic sequence data.

Methods

Yellow fever sequence data was utilized along with epidemiologic data from outbreaks in Africa, to analyze the case/fatality distribution and genetic diversity. Phylodynamic and phylogeographic were utilized to investigate ancestral history, virus population dynamics, and geographic dispersal of yellow fever across Africa.

Results

There was a sharp increase in laboratory confirmed cases after year 2015, with Nigeria and the Democratic Republic of Congo having the highest numbers of cases. Phylogeny of the YF genotypes followed a previously reported pattern with distinct geographic clustering. Historical dispersal of YFV was discovered to have occurred from West into Central/East Africa, with recent introductions occurring in West Africa.

Conclusions

We have shown the continuous circulation of YF in Africa, with distinct genotype distributions within the west and central African sub-regions. We have also shown the potential contribution of African genotypes, in the historical dispersal of yellow fever. We advocate for expanded and integrated molecular surveillance of YFV and other Arboviruses in Africa.

Evaluation of the sentinel yellow fever surveillance system in Uganda, 2017-2022: strengths and weaknesses

BACKGROUND

Uganda has a sentinel surveillance system in seven high-risk sites to monitor yellow fever (YF) patterns and detect outbreaks. We evaluated the performance of this system from 2017 to 2022.

METHODS

We evaluated selected attributes, including timeliness (lags between different critical time points), external completeness (proportion of expected sentinel sites reporting ≥ 1 suspect case in the system annually), and internal completeness (proportion of reports with the minimum required data elements filled), using secondary data in the YF surveillance database from January 2017-July 2022. We conducted key informant interviews with stakeholders at health facility and national level to assess usefulness, flexibility, simplicity, and acceptability of the surveillance system.

RESULTS

In total, 3,073 suspected and 15 confirmed YF cases were reported. The median time lag from sample collection to laboratory shipment was 37 days (IQR:21-54). External completeness was 76%; internal completeness was 65%. Stakeholders felt that the surveillance system was simple and acceptable, but were uncertain about flexibility. Most (71%) YF cases in previous outbreaks were detected through the sentinel surveillance system; data were used to inform interventions such as intensified YF vaccination.

CONCLUSION

The YF sentinel surveillance system was useful in detecting outbreaks and informing public health action. Delays in case confirmation and incomplete data compromised its overall effectiveness and efficiency.

Perceptions of yellow fever emergency mass vaccinations among vulnerable groups in Uganda: A qualitative study

BACKGROUND

Yellow fever (YF), a mosquito-borne viral hemorrhagic fever, is endemic in Uganda and causes frequent outbreaks. A total of 1.6 million people were vaccinated during emergency mass immunization campaigns in 2011 and 2016. This study explored local perceptions of YF emergency mass immunization among vulnerable groups to inform future vaccination campaigns.

METHODOLOGY

In this qualitative study, we conducted 43 semi-structured interviews, 4 focus group discussions, and 10 expert interviews with 76 participants. Data were collected in six affected districts with emergency mass vaccination. We included vulnerable groups (people ≥ 65 years and pregnant women) who are typically excluded from YF vaccination except during mass immunization. Data analysis was conducted using grounded theory. Inductive coding was utilized, progressing through open, axial, and selective coding.

PRINCIPAL FINDINGS

Participants relied on community sources for information about the YF mass vaccination. Information was disseminated door-to-door, in community spaces, during religious gatherings, and on the radio. However, most respondents had no knowledge of the vaccine, and it was unclear to them whether a booster dose was required. In addition, the simultaneous presidential election during the mass vaccination campaign led to suspicion and resistance to vaccination. The lack of reliable and trustworthy information and the politicization of vaccination campaigns reinforced mistrust of YF vaccines.

CONCLUSIONS/SIGNIFICANCE

People in remote areas affected by YF outbreaks rely on community sources of information. We therefore recommend improving health education, communication, and engagement through respected and trusted community members. Vaccination campaigns can never be seen as detached from political systems and power relations.

The Importance of Lassa Fever and Its Disease Management in West Africa

Lassa virus (LASV) is a zoonotic pathogen endemic throughout western Africa and is responsible for a human disease known as Lassa fever (LF). Historically, LASV has been emphasized as one of the greatest public health threats in West Africa, with up to 300,000 cases and 5000 associated deaths per year. This, and the fact that the disease has been reported in travelers, has driven a rapid production of various vaccine candidates. Several of these vaccines are currently in clinical development, despite limitations in understanding the immune response to infection. Alarmingly, the host immune response has been implicated in the induction of sensorineural hearing loss in LF survivors, legitimately raising safety questions about any future vaccines as well as efficacy in preventing potential hearing loss. The objective of this article is to revisit the importance and prevalence of LF in West Africa, with focus on Nigeria, and discuss current therapeutic approaches and ongoing vaccine development. In addition, we aim to emphasize the need for more scientific studies relating to LF-associated hearing loss, and to promote critical discussion about potential risks and benefits of vaccinating the population in endemic regions of West Africa.

Trends in emerging vector-borne viral infections and their outcome in children over two decades

This review utilizes quatitative methods and bibliometric data to analyse the trends of emerging and re-emerging vector-borne diseases, with a focus on their impact on pediatric population. To conduct this analysis, a systematic search of PubMed articles from the past two decades was performed, specifically looking at 26 different vector-borne viruses listed in WHO and CDC list of vector-borne viruses. The review found that diseases like Dengue, Zika, West Nile, and Chikungunya were frequently discussed in the literature. On the other hand, diseases such as Tick-borne encephalitis, Rift Valley fever, Venezuelan equine encephalitis, Sindbis fever, Venezuelan equine encephalitis, Ross River virus, and Eastern equine encephalitis showed an upward trend in publications, indicating potential resurgence. In addition to discussing trends and patterns, the review delves into the clinical manifestations and long-term effects of the top 10 viruses in children. It highlights various factors including deforestation, urbanization, global travel, and immunosuppression that contribute to disease emergence and resurgence. To effectively combat these vector-borne diseases, continuous surveillance is crucial. The review also emphasizes the importance of increased vaccination efforts and targeted research to address the health challenges they pose. IMPACT: This review employs quantitative analysis of publications to elucidate trends in emerging pediatric vector-borne viral diseases over two decades. Dengue, the most prevalent of these diseases, has spread to new regions. New strains of Japanese Encephalitis have caused outbreaks. Resurgence of Tick-borne Encephalitis, West Nile, and Yellow Fever due to vaccine hesitancy has also transpired. Continuous global surveillance, increased vaccination, and research into novel therapeutics are imperative to combat the substantial morbidity and mortality burden these diseases pose for children worldwide.

Behavioral Changes of Some Arboviral Vectors in Zika Forest: A Concern for Emerging and Re-Emerging Diseases in Uganda

Background: The increasing reports on emerging/re-emerging arboviral disease outbreaks or epidemics in Sub-Saharan Africa have been impacted by factors, including the changing climate plus human activities that have resulted in land cover changes. These factors influence the prevalence, incidence, behavior, and distribution of vectors and vector-borne diseases. In this study, we assessed the potential effect of land cover changes on the distribution and oviposition behavior of some arboviral vectors in Zika forest, Uganda, which has decreased by an estimated 7 hectares since 1952 due to an increase in anthropogenic activities in the forest and its periphery. Materials and Methods: Immature mosquitoes were collected using bamboo pots and placed at various levels of a steel tower in the forest and at different intervals from the forest periphery to areas among human dwellings. Collections were conducted for 20 months. Results and Conclusion: Inside the forest, 22,280 mosquitoes were collected belonging to four arboviral vectors: Aedes aegypti, Aedes africanus, Aedes apicoargenteus, and Aedes cumminsii. When compared with similar studies conducted in the forest in 1964, there was a change from a sylvatic to a tendency of peridomestic behavior in A. africanus, which was now collected among human dwellings. There was an unexpected change in the distribution of A. aegypti, which was not only collected outside the forest as in previous reports but also collected in the forest. Conversely, A. cumminsii originally collected in the forest expanded its ranges with collections outside the forest in this study. Aedes simpsoni maintained its distribution range outside the forest among agricultural sites. We suspect that land cover changes were favorable to most of the arboviral vectors hence enhancing their proliferation and habitat range. This potentially increases the transmission of arboviral diseases in the area, hence impacting the epidemiology of emerging/remerging diseases in Uganda.

Fractional Dosing of Yellow Fever Live Attenuated 17D Vaccine: A Perspective

Yellow fever virus (YFV) is a mosquito-borne flavivirus that causes over 109,000 severe infections and over 51,000 deaths annually in endemic areas of sub-Saharan Africa and tropical South America. The virus has a transmission cycle involving mosquitoes and humans or non-human primates (NHPs) as the vertebrate hosts. Although yellow fever (YF) is prevented by a live attenuated vaccine (strain 17D), recent epidemics in Angola, the Democratic Republic of the Congo (DRC), and Brazil put great pressure on vaccine stockpiles. This resulted in the World Health Organization (WHO) and Pan American Health Organization (PAHO) implementing, on an emergency basis only, off-label dose-sparing techniques and policies during 2016-2018 to protect as many people in DRC and Brazil as possible from disease during unexpected large outbreaks of YF. Subsequently non-inferiority studies involving full doses compared to fractional doses indicated promising results, leading some policy-makers and scientists to consider utilizing YF vaccine fractional doses in non-emergency scenarios. Although the additional data on the immunogenicity and safety of fractional doses are promising, there are several questions and considerations that remain regarding the use of fractional doses, including differences in the initial antibody kinetics, differences in the immune response in certain populations, and durability of the immune response to fractional doses compared to full doses. Until the remaining knowledge gaps are addressed, full doses instead of fractional doses should continue to be used unless there are insufficient doses of the vaccine available to control outbreaks of YF.

A Comparison of the Awareness, Attitude, and Uptake of COVID-19, Hepatitis B Virus, and Yellow Fever Vaccines Between Rural and Urban Respondents in Edo State, Nigeria

INTRODUCTION

Despite the target set by WHO, Africa still falls short when it comes to individuals' use of COVID-19 vaccines. There is a similar pattern of low vaccine usage for the hepatitis B virus (HBV) and yellow fever (YF).

AIM AND OBJECTIVE

The objective of our study is to compare the awareness, attitude, and uptake of vaccine-preventable diseases (VPD), COVID-19, HBV, and YF, between a rural and an urban community in Nigeria.

METHODOLOGY

The study was a descriptive cross-sectional study carried out between January 2022 and December 2022 in a rural community, Okada, and an urban community, Benin, in Edo State, Nigeria. A total of 283 rural participants and 483 urban participants were interviewed. SPSS Statistics version 26 (IBM Corp. Released 2019. IBM SPSS Statistics for Windows, Version 26.0. Armonk, NY: IBM Corp.) was used for data collection and analysis. The significant value was set at P<0.05.

RESULTS

A major percentage of both populations, 98.3% urban and 90.1% rural, reported being aware of COVID-19 vaccines (indicated by P<0.001). There was a similar pattern with HBV vaccine awareness. However, awareness of YF vaccines was more common in the rural (63.3%) community than in the urban (55.0%) community. A complete dose uptake of COVID-19 vaccines was reported by 7.7% of the rural and 2.2% of the urban respondents. The major reason for the refusal of vaccine uptake was the fear of possible side effects.

CONCLUSION

The study showed that vaccine uptake for COVID-19, HBV, and YF is low despite seemingly good awareness of these vaccines. The number one reason for any vaccine refusal is the possibility of experiencing side effects.

Mosquito gene targeted RNAi studies for vector control

Vector-borne diseases are serious public health concern. Mosquito is one of the major vectors responsible for the transmission of a number of diseases like malaria, Zika, chikungunya, dengue, West Nile fever, Japanese encephalitis, St. Louis encephalitis, and yellow fever. Various strategies have been used for mosquito control, but the breeding potential of mosquitoes is such tremendous that most of the strategies failed to control the mosquito population. In 2020, outbreaks of dengue, yellow fever, and Japanese encephalitis have occurred worldwide. Continuous insecticide use resulted in strong resistance and disturbed the ecosystem. RNA interference is one of the strategies opted for mosquito control. There are a number of mosquito genes whose inhibition affected mosquito survival and reproduction. Such kind of genes could be used as bioinsecticides for vector control without disturbing the natural ecosystem. Several studies have targeted mosquito genes at different developmental stages by the RNAi mechanism and result in vector control. In the present review, we included RNAi studies conducted for vector control by targeting mosquito genes at different developmental stages using different delivery methods. The review could help the researcher to find out novel genes of mosquitoes for vector control.

Absence of transmission of vYF next generation Yellow Fever vaccine in mosquitoes

One of the most effective vaccines against an arbovirus is the YFV-17D live-attenuated vaccine developed in 1937 against Yellow Fever (YF). This vaccine replicates poorly in mosquitoes and consequently, is not transmitted by vectors. Vaccine shortages, mainly due to constrained productions based on pathogen-free embryonated eggs, led Sanofi to move towards alternative methods based on a state-of-the-art process using continuous cell line cultures in bioreactor. vYF-247 is a next-generation live-attenuated vaccine candidate based on 17D adapted to grow in serum-free Vero cells. For the development of a new vaccine, WHO recommends to document infectivity and replication in mosquitoes. Here we infected Aedes aegypti and Aedes albopictus mosquitoes with vYF-247 vaccine compared first to the YF-17D-204 reference Sanofi vaccines (Stamaril and YF-VAX) and a clinical human isolate S-79, provided in a blood meal at a titer of 6.5 Log ffu/mL and secondly, to the clinical isolate only at an increased titer of 7.5 Log ffu/mL. At different days post-infection, virus replication, dissemination and transmission were evaluated by quantifying viral particles in mosquito abdomen, head and thorax or saliva, respectively. Although comparison of vYF-247 to reference vaccines could not be completed to yield significant results, we showed that vYF-247 was not transmitted by both Aedes species, either laboratory strains or field-collected populations, compared to clinical strain S-79 at the highest inoculation dose. Combined with the undetectable to low level viremia detected in vaccinees, transmission of the vYF-247 vaccine by mosquitoes is highly unlikely.

Ecology of Aedes vittatus (Diptera: Culicidae) in rock pools across agroecosystem in Northern Savanna, Nigeria

BACKGROUND & OBJECTIVES

This study focuses on modulating dexterity of some ecological variables of Aedes vittatus classically breeding in rocky habitats. The study provides a useful insight into ecological variables that underpin or hinder profuse breeding of Ae. vittatus in rock pools and its probable role in disease transmission.

METHODS

HANNA HI98129 pH/EC/TDS/TEMP meter was used in situ while standard protocols were used to determine other hydro-chemical variables. Aedes vittatus larvae were obtained with soup ladle and modified ladle dippers. D-frame net was used to capture macroinvertebrates while plankton net was used to obtain samples of microalgae. Tadpoles and water turtles were collected with fine mesh invertebrate net. Macrophytes were uprooted and identified at the Herbarium Unit, Department of Botany, Ahmadu Bello University, Zaria. The influence of physicochemical variables was correlated with distribution of Ae. vittatus using Principal Component Analysis. Regression and ANOVA were used to test for association between predictor variables and mosquito abundance and for the difference amongst inselbergs.

RESULTS

Linear larval density of Ae. vittatus in rock pools which tapered across Guinea savanna were obtained from twenty-one sites with average density of 139.6 in Sudan savanna. Guinea savanna had an average larval density of 75.5 with lower subsets of moving average densities compared to Sudan savanna. One hundred and sixty-one aquatic insects belonging to four insect orders cohabited rock pools with Ae. vittatus. Toads and frogs' tadpoles were of Bufonidae and Pyxicephalidae families while water turtles belong to Emydidae. pH, TDS (ppm), EC (μs/cm) and alkalinity (mg/l) differed significantly (p<0.05) with the abundance of Ae. vittatus in rock pools. Temperature, depth, water hardness and total suspended solid had direct influence on the distribution of Ae. vittatus in rock pools across sites. Significant positive correlation exists between aquatic insects and abundance of Ae. vittatus. Hydroperiod length, concentration of nitrate and pH were determinants that leverage profuse breeding of Ae. vittatus and survival of rock pool biota.

INTERPRETATION & CONCLUSION

Results revealed that the bearing influence of rock pool variables is inevitable for breeding of Ae. vittatus. A well defined measure of efficacy incorporating indigenous communities for sustained vector control on inselbergs will go a long way in decimating population of Ae. vittatus and limit the risk of spread of yellow fever hitherto areas not thriving.