Yellow fever virus: Increasing imported cases in China

Arboviral vaccines for use in pregnant travelers

Pregnant women traveling abroad can be exposed to a variety of arboviruses, primarily spread by mosquitoes or ticks. Some arboviral infections can be of particular concern for pregnant women or their fetuses. Vaccination is one preventive measure that can reduce the risk for infection. Several arboviral vaccines have been licensed for many years and can be used to prevent infection in travelers, namely Japanese encephalitis, yellow fever, and tick-borne encephalitis vaccines. Recommendations on use of these vaccines in pregnancy vary. Other arboviral vaccines have been licensed but are not indicated for use in pregnant travelers (e.g., dengue vaccines) or are in development (e.g., chikungunya, Zika vaccines). This review describes arboviral vaccines for travelers, focusing on women who are pregnant and those planning travel during pregnancy.

Travel-related infection in Guangzhou, China,2009-2019

BACKGROUND

We analyzed the epidemiological characteristics of travel-related infectious diseases in reported Guangzhou between 2009 and 2019 to provide a scientific basis for prevention and control strategies.

METHOD

The infectious diseases report information system of China was mined for case reports, combined with clinical diagnosis records, and analyzed.

RESULTS

Between 2009 and 2019, 1478 cases of imported infectious diseases were reported in Guangzhou. Dengue fever accounted for 46.14%of cases and malaria accounted for 45.47% of cases. The patients with imported travel-related infection cases were mainly male (75.88%), Chinese (75.57%), and aged 20-45 years (83.01%). Cases increased from May each year, peaked between August and September, and declined rapidly after October. The main source areas of import were Africa and other countries in Asia.

CONCLUSIONS

Dengue fever and malaria are the main travel-related infection in Guangzhou, and are generally brought in by male Chinese workers. Intervention and health education in this population should be strengthened to prevent and control travel-related infection.

Vaccination and Therapeutics: Responding to the Changing Epidemiology of Yellow Fever

At the turn of the nineteenth century, yellow fever (YF) was considered the most dangerous infectious disease with high case fatality. Subsequent, mass vaccination campaigns coupled with widespread elimination of the YF mosquito vector significantly decreased YF cases and reduced outbreaks to the tropical and subtropical forested regions of Africa and South America. However, recent (2016) large outbreaks in Angola, Democratic Republic of Congo (DRC), and South-Eastern Brazil, where previously had been demarcated as low-risk regions, have highlighted the possibility of a rapidly changing epidemiology and the potential re-emergence of yellow fever virus (YFV). Furthermore, the first-ever importation of YFV into Asia has highlighted the potential fear of YFV emerging as a global threat. In this review, we describe the changing epidemiology of YF outbreaks, and highlight the use of public health policies, therapeutics, and vaccination as tools to help eliminate future YFV outbreaks.

Vaccination and Therapeutics: Responding to the Changing Epidemiology of Yellow Fever

Purpose of Review

At the turn of the nineteenth century, yellow fever (YF) was considered the most dangerous infectious disease with high case fatality. Subsequent, mass vaccination campaigns coupled with widespread elimination of the YF mosquito vector significantly decreased YF cases and reduced outbreaks to the tropical and subtropical forested regions of Africa and South America.

Recent Findings

However, recent (2016) large outbreaks in Angola, Democratic Republic of Congo (DRC), and South-Eastern Brazil, where previously had been demarcated as low-risk regions, have highlighted the possibility of a rapidly changing epidemiology and the potential re-emergence of yellow fever virus (YFV). Furthermore, the first-ever importation of YFV into Asia has highlighted the potential fear of YFV emerging as a global threat.

Summary

In this review, we describe the changing epidemiology of YF outbreaks and highlight the use of public health policies, therapeutics, and vaccination as tools to help eliminate future YFV outbreaks.

Eliminating yellow fever epidemics in Africa: Vaccine demand forecast and impact modelling

BACKGROUND

To counter the increasing global risk of Yellow fever (YF), the World Health Organisation initiated the Eliminate Yellow fever Epidemics (EYE) strategy. Estimating YF burden, as well as vaccine impact, while accounting for the features of urban YF transmission such as indirect benefits of vaccination, is key to informing this strategy.

METHODS AND FINDINGS

We developed two model variants to estimate YF burden in sub-Saharan Africa, assuming all infections stem from either the sylvatic or the urban cycle of the disease. Both relied on an ecological niche model fitted to the local presence of any YF reported event in 34 African countries. We calibrated under-reporting using independent estimates of transmission intensity provided by 12 serological surveys performed in 11 countries. We calculated local numbers of YF infections, deaths and disability-adjusted life years (DALYs) lost based on estimated transmission intensity while accounting for time-varying vaccination coverage. We estimated vaccine demand and impact of future preventive mass vaccination campaigns (PMVCs) according to various vaccination scenarios. Vaccination activities conducted in Africa between 2005 and 2017 were estimated to prevent from 3.3 (95% CI 1.2-7.7) to 6.1 (95% CI 2.4-13.2) millions of deaths over the lifetime of vaccinees, representing extreme scenarios of none or maximal herd effects, respectively. By prioritizing provinces based on the risk of urban YF transmission in future PMVCs, an average of 37.7 million annual doses for PMVCs over eight years would avert an estimated 9,900,000 (95% CI 7,000,000-13,400,000) infections and 480,000 (180,000-1,140,000) deaths over the lifetime of vaccinees, corresponding to 1.7 (0.7-4.1) deaths averted per 1,000 vaccine doses.

CONCLUSIONS

By estimating YF burden and vaccine impact over a range of spatial and temporal scales, while accounting for the specificity of urban transmission, our model can be used to inform the current EYE strategy.

Multi-epitope based vaccine against yellow fever virus applying immunoinformatics approaches

Yellow fever disease is considered a re-emerging major health issue which has caused recent outbreaks with a high number of deaths. Tropical countries, mainly African and South American, are the most affected by Yellow fever outbreaks. Despite the availability of an attenuated vaccine, its use is limited for some groups such as pregnant and nursing women, immunocompromised and immunosuppressed patients, elderly people >65 years, infants <6 months and patients with biological disorders like thymus disorders. In order to achieve new preventive measures, we applied immunoinformatics approaches to develop a multi-epitope-based subunit vaccine for Yellow fever virus. Different epitopes, related to humoral and cell-mediated immunity, were predicted for complete polyproteins of two Yellow fever strains (Asibi and 17 D vaccine). Those epitopes common for both strains were mapped into a set of 137 sequences of Yellow fever virus, including 77 sequences from a recent outbreak at the state of Minas Gerais, southeast Brazil. Therefore, the present work uses robust bioinformatics approaches for the identification of a multi-epitope vaccine against the Yellow fever virus. Our results indicate that the identified multi-epitope vaccine might stimulate humoral and cellular immune responses and could be a potential vaccine candidate against Yellow fever virus infection. Hence, it should be subjected to further experimental validations. Communicated by Ramaswamy H. Sarma.

Phylogenomic analysis unravels evolution of yellow fever virus within hosts

The yellow fever virus (YFV) recently reemerged in the large outbreaks in Africa and Brazil, and the first imported patients into Asia have recalled the concerns of YFV evolution. Here we show phylogenomics of YFV with serial clinical samples of the 2016 YFV infections. Phylogenetics exhibited that the 2016 strains were close to Angola 1971 strains and only three amino acid changes presented new to other lineages. Deep sequencing of viral genomes discovered 101 intrahost single nucleotide variations (iSNVs) and 234 single nucleotide polymorphisms (SNPs). Analysis of iSNV distribution and mutated allele frequency revealed that the coding regions were under purifying selection. Comparison of the evolutionary rates estimated by iSNV and SNP showed that the intrahost rate was ~2.25 times higher than the epidemic rate, and both rates were higher than the long-term YFV substitution rate, as expected. In addition, the result also hinted that short viremia duration of YFV might further hinder the evolution of YFV.

The first importation of infections into China in 2016 and the following outbreaks in Africa and Brazil of yellow fever virus (YFV) have raised again the concerns of the potential viral spread into new territories. In this study, we aimed to know the evolution dynamics of YFV by using intrahost phylogenomics and to assess the risk of virus epidemics. Through deep sequencing of consecutive samples from 12 patients, we identified hundreds of genomic variations (iSNVs and SNPs), and noticed the nearly linear accumulation of variations within individuals. The estimated evolutionary rate within host is much higher than the epidemic evolutionary rate. In comparison with Dengue virus (DENV) and Zika virus (ZIKV), which share similar host vectors (Aedes spp.), life cycles, mutation rates and replication strategies to YFV, the lower epidemic evolutionary rate of YFV might have been hindered by the shorter viremia duration, which decreased the accumulated variations to get into the transmission cycle.

Travel-related infections in mainland China, 2014-16: an active surveillance study

BACKGROUND

Transmission of infection through international travel is a growing health issue, and the frequency of imported infection is increasing in China. We aimed to quantify the total number of infections imported into mainland China by arriving travellers.

METHODS

We actively surveyed arriving travellers at all 272 international entry-exit ports in mainland China. Suspected cases were detected through fever screening, medical inspection, self-declaration, and reporting by on-board staff. Participants completed a standardised questionnaire with questions about demographics, their travel itinerary (including detailed information about all countries or regions visited), and clinical manifestations. Nasopharyngeal swabs, sputum samples, faecal samples, vomitus, blood, and serum were collected as appropriate for diagnoses. Diagnosis was made by specific laboratory tests according to the national technical guidelines. Infections were classified as respiratory, gastrointestinal, vector-borne, blood-transmitted and sex-transmitted, or mucocutaneous. We divided arriving travellers into two groups: travellers coming from countries other than China, and travellers coming from Hong Kong, Macau, and Taiwan. We integrated surveillance data for 2014-16, calculated incidences of travel-related infections, and compared the frequency of infections among subgroups.

FINDINGS

Between Jan 1, 2014, and Dec 31, 2016, 22 797 cases were identified among 805 993 392 arriving travellers-an overall incidence of 28·3 per million. 45 pathogens were detected in participants: 18 respiratory (19 662 cases), ten gastrointestinal (189 cases), seven vector-borne (831 cases), seven blood-transmitted and sex-transmitted (1531 cases), and three mucocutaneous (584 cases). Both the overall number and incidence of infection were more than five times higher in 2016 than in 2014. Case numbers and incidences also varied substantially by province, autonomous region, and municipality. Overall, 17 643 (77%) infections were detected by fever screening, but 753 (49%) blood-transmitted and sex-transmitted infections were identified through medical inspection. 14 305 (73%) cases of respiratory infection and 96 (51%) of gastrointestinal infections were in tourists. Tuberculosis, hepatitis A virus, vector-borne, and blood-transmitted and sex-transmitted infections were common among Chinese labourers who worked abroad. Dengue and malaria were most commonly diagnosed in travellers arriving from Africa. 12 126 (93%) of the 12 985 cases arriving from Hong Kong, Macau, or Taiwan were respiratory infections. Hand, foot, and mouth disease accounted for 2·90% of infections in travellers from Hong Kong, Macau, or Taiwan and 0·31% of infections in international travellers.

INTERPRETATION

This report is the first to characterise the profile of travel-related infections among arriving travellers in mainland China. Our findings should increase public awareness of the potential risk of imported infections, and help health-care providers to make evidence-based health recommendations to travellers.

FUNDING

The Natural Science Foundation of China.

Late or Lack of Vaccination Linked to Importation of Yellow Fever from Angola to China

During March and April 2016, 11 yellow fever cases were identified in China. We report epidemic and viral information for 10 of these patients, 6 of whom had been vaccinated before travel. Phylogenetic analyses suggest these viruses nested within the diversity of strains endemic to Angola, where an outbreak began in 2015.

Landscape of emerging and re-emerging infectious diseases in China: impact of ecology, climate, and behavior

For the past several decades, the infectious disease profile in China has been shifting with rapid developments in social and economic aspects, environment, quality of food, water, housing, and public health infrastructure. Notably, 5 notifiable infectious diseases have been almost eradicated, and the incidence of 18 additional notifiable infectious diseases has been significantly reduced. Unexpectedly, the incidence of over 10 notifiable infectious diseases, including HIV, brucellosis, syphilis, and dengue fever, has been increasing. Nevertheless, frequent infectious disease outbreaks/events have been reported almost every year, and imported infectious diseases have increased since 2015. New pathogens and over 100 new genotypes or serotypes of known pathogens have been identified. Some infectious diseases seem to be exacerbated by various factors, including rapid urbanization, large numbers of migrant workers, changes in climate, ecology, and policies, such as returning farmland to forests. This review summarizes the current experiences and lessons from China in managing emerging and re-emerging infectious diseases, especially the effects of ecology, climate, and behavior, which should have merits in helping other countries to control and prevent infectious diseases.

Persistence of yellow fever virus-specific neutralizing antibodies after vaccination among US travellers

BACKGROUND

Few studies have assessed the duration of humoral immunity following yellow fever (YF) vaccination in a non-endemic population. We evaluated seropositivity among US resident travellers based on time post-vaccination.

METHODS

We identified serum samples from US travellers with YF virus-specific plaque reduction neutralization testing (PRNT) performed at CDC from 1988 to 2016. Analyses were conducted to assess the effect of time since vaccination on neutralizing antibody titer counts.

RESULTS

Among 234 travellers who had neutralizing antibody testing performed on a specimen obtained ≥1 month after vaccination, 13 received multiple YF vaccinations and 221 had one dose of YF vaccine reported. All 13 who received more than one dose of YF vaccine had a positive PRNT regardless of the amount time since most recent vaccination. Among the 221 travellers with one reported dose of YF vaccine, 155 (70%) were vaccinated within 10 years (range 1 month-9 years) and 66 (30%) were vaccinated ≥10 years (range 10-53 years) prior to serum collection. Among the 155 individuals vaccinated, <10 years prior to serum collection, 146 (94%) had a positive PRNT compared with 82% (54/66) of individuals vaccinated ≥10 years prior to serum collection (P = 0.01). Post-vaccination PRNT titers showed a time-dependent decrease. Individuals with immunocompromising conditions were less likely to have a positive PRNT (77%) compared with those who were not immunocompromised (92%; P = 0.04).

CONCLUSION

Although the percentage of vaccinees with a positive PRNT and antibody titers decreased over time, a single dose of YF vaccine provided long-lasting protection in the majority of US travellers. A booster dose could be considered for certain travellers who are planning travel to a high risk area based on immune competence and time since vaccination.

Investigation on Mosquito-Borne Viruses at Lancang River and Nu River Watersheds in Southwestern China

During 2007 and 2010, an extensive entomological survey was performed to assess the distribution of mosquitoes and mosquito-borne arboviruses at Lancang River and Nu River watersheds in southwestern China. A total of 20,450 mosquitoes consisting 20 species was trapped and submitted 261 pools according to species and location. Culex tritaeniorhynchus and Anopheles sinensis were the most abundant species. Eighty-seven isolates representing 11 virus species in 8 genera were obtained from 6 mosquito species. The new isolates were identified as Getah virus (GETV), Japanese encephalitis virus (JEV), Yunnan Culex-related flavivirus (YNCxFV), Yunnan Aedes-related flavivirus (YNAeFV), Banna virus (BAV), Yunnan orbivirus (YUOV), Banna orbivirus (BAOV), Yunnan totivirus (YNToV), Nam Dinh virus (NDiV), Menghai rhabdovirus (MRV), and Anopheles minimus iridovirus (AMIV). These viruses included confirmed or potential pathogen of human disease, such as JEV, BAV, and NDiV, and several novel or reassortant arboviruses, such as YNAeFV, MRV, AMIV, and BAOV. GETV, JEV, YNCxFV, and NDiV were widely prevalent in the whole basin of the two rivers. The findings contribute to our understanding of the diversity and wide distribution of mosquito-borne arboviruses in the area, and are helpful to explore pathogenic evidence for fevers and viral encephalitis of unknown etiology.

Portuguese expatriates' health in Angola and Mozambique-a cross-sectional study: increasing awareness and need for more surveillance

BACKGROUND

Increasing numbers of expatriates are working in sub-Saharan Africa. There is little published data on the complex population and this survey aimed at understanding expatriate morbidity by accessing self-reported health problems and malaria preventive practices.

METHODS

A cross-sectional web-based survey was conducted targeting Portuguese expatriates in Angola and Mozambique. Logistic regression analysis explored factors associated with self-reported health problems and psychological symptoms in the previous 3 months.

RESULTS

A total sample of 352 adult Portuguese urban civil occupational expatriates was obtained. Median length of expatriation was 3 years. Considering a 3-month timeframe, one in five expatriates reported new health problems and need of medical assistance, 5% were hospitalized and 64% reported general psychological symptoms. Less than 2% of subjects were on malaria chemoprophylaxis. Having chronic health conditions doubled the reporting of new health problems. Increasing length of expatriation was associated with decreasing reporting of general psychological symptoms. Directors and executive managers and expatriates living alone tended to report more general psychological symptoms.

CONCLUSION

Expatriate communities deserve enhanced surveillance for the health issues that affect them. This will improve evidence-based preparation and intervention by public and travel health practitioners.

Yellow fever in the Americas: the growing concern about new epidemics

Yellow fever (YF) is a haemorrhagic viral disease with a high case fatality rate. It is considered a reemerging infectious disease of remarkable importance. During the last outbreaks in Brazil (2016-2017), many cases of YF emerged despite high YF vaccination coverage in some areas. However, there are many areas and populations worldwide where vaccination coverage has been low for years (e.g. Nigeria), which increases the risk of major epidemics in such areas, as would be the case in many of the American territories. Several factors, including the vast border and migratory status of Brazil, the widespread distribution of Aedes mosquitoes and the lack of efficient health policies and surveillance systems, favor this complex epidemiological scenario of reemergence. Therefore, mass vaccination of the population at risk, public health awareness and preparedness are urgently needed in this region. This opinion article describes the current global epidemiological situation of YF, focusing especially on the Americas, as well the risk and vulnerabilities in the region that would be of concern for major expansion to other countries apart from Brazil. Also, imported risk from endemic area outside of Americas (i.e. Africa) are of current concern.

Yellow fever and Hajj: with all eyes on Zika, a familiar flavivirus remains a threat

Hajj is among the world's largest mass gatherings, drawing between 2 and 3.5 million Muslims from 183 nations annually to perform pilgrimage in Mecca, Saudi Arabia. Infectious disease outbreaks can be imported both into the Hajj population and exported internationally by returning pilgrims. The domestic Saudi population can also be at risk of outbreaks traveling amid this mass migration. With yellow fever reported for the first time in China following the infection of expatriate Chinese workers in Angola and a full blown outbreak underway in wider West Africa, the prospect of yellow fever outbreaks in Asia threatens to impact Saudi Arabia, both during and beyond the Hajj season. With global focus trained on Zika, the rising threat of yellow fever cannot be overlooked. Strategies to mitigate risk to Saudi Arabia and the global population are thereby suggested.