Yellow Fever In Africa Research Articles

Seasonal Patterns and Genetic Variability of Aedes Mosquitoes in Some Selected Communities of Maiduguri Metropolitan Council, Borno State, Nigeria

Aedes aegypti and Aedes albopictus mosquitoes spread dengue and yellow fever in Africa and worldwide. Rural-urban drift creates Aedes mosquito breeding sites through uncontrolled urbanization, inadequate urban infrastructure, lack of basic public health delivery, indiscriminate waste disposal, varying socioeconomic activities, and climatic changes. The above have happened in Maiduguri Metropolis since Boko Haram insurgencies began. This study will examine Aedes aegypti's seasonal distribution, abundance, composition, and genetic variability in selected Maiduguri Metropolitan Council and Jere Local Government Council communities. From October 2016 to May 2017, CDC traps and vacuum aspirators collected adult mosquitoes from study sites and stored at – 80 C. These were identified morphologically with taxonomy keys and stereomicroscopes, then molecularly with markers. Aedes mosquito population structure and genetic variability were determined using statistical software and molecular methods on samples. Hot-dry season has the highest relative abundance of this mosquito species in these study sites, while cold-dry season has the lowest. The molecular identification found Aedes aegypti in nine of twelve study locations but not Aedes albopictus. Some mosquitoes from the study locations had mutations due to carrying dengue virus or host population genes, but those without mutations showed a good phylogenetic relationship with Aedes aegypti mosquitoes from other countries, suggesting no genetic variability. The relative abundance of Aedes mosquitoes in Maiduguri Metropolitan Council increases the risk of dengue, zika, yellow fever, and chikungunya virus infections, and this mosquito species' seasonal distributions vary within and across seasons, but no genetic variability was found in the mosquitoes from the different locations used in this study.

Emerging Arboviruses of Public Health Concern in Africa: Priorities for Future Research and Control Strategies

Arboviruses are most prevalent in tropical and subtropical regions, where arthropods are widespread. The World Health Organization (WHO) estimated that the mortality burden of arbovirus diseases, such as yellow fever in Africa, was 84,000–170,000 severe cases and 29,000–60,000 deaths in 2013. These epidemics emphasize the urgent need for integrated control and prevention of arboviral diseases. Challenges in managing and controlling arboviral diseases in Africa are mainly attributed to poor insect vector control, insecticide resistance, and poor sanitation and solid waste management. The removal or reduction of mosquito populations amongst susceptible individuals is identified as the most effective measure to control many vector-borne diseases. Current public health needs call for efficient vector control programs and maintenance of adequate surveillance systems through the availability of trained personnel and rapid diagnostic facilities, providing an interdisciplinary response to control and mitigate the threats of emerging and re-emerging arboviruses. Furthermore, research priorities should focus on understanding the factors responsible for adaptation to other vectors, determinants of infection and transmission, and the development of high efficiency antiviral molecules or candidate vaccines. Here, we explore and review our current understanding of arboviruses of public health importance in Africa, with a focus on emerging arboviruses, their arthropod vectors, and the epidemiology of major arboviruses. Finally, we appraise the role of planetary health in addressing the threat of arboviruses and identify other priority areas of research for effective control.

Malaria transmission in Africa: Its relationship with yellow fever and measles.

Malaria has been strongly linked to the transmission and pathophysiology of some viral diseases. Malaria and vaccine-preventable diseases often co-exist in endemic countries but the implication of their co-existence on their transmission dynamics and control is poorly understood. The study aims to evaluate the relationships between the incidence of malaria and cases of measles and yellow fever in Africa. The malaria incidence, death due to malaria, measles and yellow fever data were sourced from the WHO database. Poisson and zero-inflated time-trend regression were used to model the relationships between malaria and the two vaccine-preventable diseases. P-values <0.05 were considered statistically significant. A significant negative relationship existed between malaria incidence and measles cases (P<0.05), however, malaria showed a positive relationship with yellow fever (P<0.05). The relationships between death due to malaria and measles/yellow fever cases followed similar trends but with a higher level of statistical significance (P<0.001). Malaria varied negatively with measles cases but positively with yellow fever. The relationships observed in this study could be important for the management of malaria and the studied vaccine-preventable diseases. Increase vaccination coverage and/or malaria treatment could modulate the direction of these relationships.

Yellow Fever in Nigeria: A Review of Past, Current, and Future Strides

Since 1985, there has been resurgence of yellow fever in Africa with outbreaks occurring in more than 33 countries. From that time, thousands of cases have occurred in Nigeria which is the most populous country in Africa. Semi-urban and urban centres across the country are densely populated, with numerous sparsely populated rural settings in every State, some of which contain heavy forests. A wide-range of vegetation zones exists which lead to smooth transition of several tropical climates. As a result, there is preponderance of Aedes species in many parts of the country especially during the rainy season when relative humidity is high. Vector control is not applicable to jungle yellow fever, but infection in human population can be prevented by vaccination. Yellow fever deaths were recently reported in Nigeria, causing panic and public outcry. This review highlights the epidemiological trajectory of yellow fever, the past, and the present and future efforts in the country with a view to providing in-depth knowledge of yellow fever activities in order to enhance public health.

The incidence and mortality of yellow fever in Africa: a systematic review and meta-analysis

BackgroundUnderstanding the occurrence of yellow fever epidemics is critical for targeted interventions and control efforts to reduce the burden of disease. We assessed data on the yellow fever incidence and mortality rates in Africa.MethodsWe searched the Cochrane Library, SCOPUS, MEDLINE, CINAHL, PubMed, Embase, Africa-wide and Web of science databases from 1 January 1975 to 30th October 2020. Two authors extracted data from included studies independently and conducted a meta-analysis.ResultsOf 840 studies identified, 12 studies were deemed eligible for inclusion. The incidence of yellow fever per 100,000 population ranged from < 1 case in Nigeria, < 3 cases in Uganda, 13 cases in Democratic Republic of the Congo, 27 cases in Kenya, 40 cases in Ethiopia, 46 cases in Gambia, 1267 cases in Senegal, and 10,350 cases in Ghana. Case fatality rate associated with yellow fever outbreaks ranged from 10% in Ghana to 86% in Nigeria. The mortality rate ranged from 0.1/100,000 in Nigeria to 2200/100,000 in Ghana.ConclusionThe yellow fever incidence rate is quite constant; in contrast, the fatality rates vary widely across African countries over the study period. Standardized demographic health surveys and surveillance as well as accurate diagnostic measures are essential for early recognition, treatment and control.

The global burden of yellow fever.

Yellow fever (YF) is a viral, vector-borne, haemorrhagic fever endemic in tropical regions of Africa and South America. The vaccine for YF is considered safe and effective, but intervention strategies need to be optimised; one of the tools for this is mathematical modelling. We refine and expand an existing modelling framework for Africa to account for transmission in South America. We fit to YF occurrence and serology data. We then estimate the subnational forces of infection for the entire endemic region. Finally, using demographic and vaccination data, we examine the impact of vaccination activities. We estimate that there were 109,000 (95% credible interval [CrI] [67,000-173,000]) severe infections and 51,000 (95% CrI [31,000-82,000]) deaths due to YF in Africa and South America in 2018. We find that mass vaccination activities in Africa reduced deaths by 47% (95% CrI [10%-77%]). This methodology allows us to evaluate the effectiveness of vaccination and illustrates the need for continued vigilance and surveillance of YF.

Assessing the impact of preventive mass vaccination campaigns on yellow fever outbreaks in Africa: A population-level self-controlled case series study.

The Eliminate Yellow fever Epidemics (EYE) strategy was launched in 2017 in response to the resurgence of yellow fever in Africa and the Americas. The strategy relies on several vaccination activities, including preventive mass vaccination campaigns (PMVCs). However, to what extent PMVCs are associated with a decreased risk of outbreak has not yet been quantified. We used the self-controlled case series (SCCS) method to assess the association between the occurrence of yellow fever outbreaks and the implementation of PMVCs at the province level in the African endemic region. As all time-invariant confounders are implicitly controlled for in the SCCS method, this method is an alternative to classical cohort or case-control study designs when the risk of residual confounding is high, in particular confounding by indication. The locations and dates of outbreaks were identified from international epidemiological records, and information on PMVCs was provided by coordinators of vaccination activities and international funders. The study sample consisted of provinces that were both affected by an outbreak and targeted for a PMVC between 2005 and 2018. We compared the incidence of outbreaks before and after the implementation of a PMVC. The sensitivity of our estimates to a range of assumptions was explored, and the results of the SCCS method were compared to those obtained through a retrospective cohort study design. We further derived the number of yellow fever outbreaks that have been prevented by PMVCs. The study sample consisted of 33 provinces from 11 African countries. Among these, the first outbreak occurred during the pre-PMVC period in 26 (79%) provinces, and during the post-PMVC period in 7 (21%) provinces. At the province level, the post-PMVC period was associated with an 86% reduction (95% CI 66% to 94%, p < 0.001) in the risk of outbreak as compared to the pre-PMVC period. This negative association between exposure to PMVCs and outbreak was robustly observed across a range of sensitivity analyses, especially when using quantitative estimates of vaccination coverage as an alternative exposure measure, or when varying the observation period. In contrast, the results of the cohort-style analyses were highly sensitive to the choice of covariates included in the model. Based on the SCCS results, we estimated that PMVCs were associated with a 34% (95% CI 22% to 45%) reduction in the number of outbreaks in Africa from 2005 to 2018. A limitation of our study is the fact that it does not account for potential time-varying confounders, such as changing environmental drivers of yellow fever and possibly improved disease surveillance. In this study, we provide new empirical evidence of the high preventive impact of PMVCs on yellow fever outbreaks. This study illustrates that the SCCS method can be advantageously applied at the population level in order to evaluate a public health intervention.

Is the absence or intermittent YF vaccination the major contributor to its persistent outbreaks in eastern Africa?

Despite the availability of a safe and efficacious yellow fever vaccine since 1937, yellow fever remains a public health threat as a re-emerging disease in Africa and South America. We reviewed the trend of reported yellow fever outbreaks in eastern African countries, identified the risk epidemiological factors associated with the outbreaks and assessed the current situation of Yellow Fever vaccination in Africa. Surveillance and case finding for yellow fever in Africa are insufficient primarily due to lack of appropriate diagnostic capabilities, poor health infrastructure resulting in under-recognition, underreporting and underestimation of the disease. Despite these challenges, Ethiopia reported 302,614 cases (30,505 deaths) in 1943–2015, Kenya had 207 cases (38 deaths) in 1992–2016, Sudan experienced 31,750 suspected cases (1855 deaths) from 1940 to 2012 and Uganda had 452 cases (65 deaths) in 1941–2016. Major risk factors associated with past yellow fever outbreaks include climate, human practices and virus genetics. Comparisons between isolates from different outbreaks after 45 years have revealed the genetic stability of the structural proteins of YFV which are the primary targets of the host immune cells. This probably explains why yellow fever 17D vaccine is considered as outstandingly efficacious and safe after being used for 75 years. However, the 14 amino-acid changes among these isolates may have a greater impact on the changing disease epidemiology, virulence and transmission rate. Low population immunity against YF influences outbreak frequency especially in countries where the incorporation of YF vaccination is not combined with mass vaccination campaigns or vaccination is limited to international travellers. Understanding Yellow fever virus epidemiology as determined by its evolution underscores appropriate disease mitigation strategies and immunization policies. Mobilizing scarce resources to enhance population immunity through sufficient vaccination, promoting environmental sanitation/hygienic practices, driving behavioral change and community-based vector control are significant to preventing future epidemics.

Yellow fever risk assessment in the Central African Republic

Yellow fever still causes high burden in several areas of sub-Saharan Africa and Latin America. There are few well-designed epidemiological studies and limited data about yellow fever in Africa. Staples et al., in a recently published paper in Transactions of the Royal Society of Tropical Medicine & Hygiene, performed a nationwide study in the Central African Republic (CAR) assessing infection risk and the operational impact of preventive measures. The rapid assessment of human, non-human and mosquito data call attention to the potential risk of future yellow fever outbreaks in the CAR and elsewhere. The study reinforces the need for intensified applied and operational research to address problems and human capacity needs in the realm of neglected tropical diseases in the post-2015 agenda.

Yellow Fever in Africa: estimating the burden of disease and impact of mass vaccination from outbreak and serological data.

Yellow fever is a vector-borne disease affecting humans and non-human primates in tropical areas of Africa and South America. While eradication is not feasible due to the wildlife reservoir, large scale vaccination activities in Africa during the 1940s to 1960s reduced yellow fever incidence for several decades. However, after a period of low vaccination coverage, yellow fever has resurged in the continent. Since 2006 there has been substantial funding for large preventive mass vaccination campaigns in the most affected countries in Africa to curb the rising burden of disease and control future outbreaks. Contemporary estimates of the yellow fever disease burden are lacking, and the present study aimed to update the previous estimates on the basis of more recent yellow fever occurrence data and improved estimation methods. Generalised linear regression models were fitted to a dataset of the locations of yellow fever outbreaks within the last 25 years to estimate the probability of outbreak reports across the endemic zone. Environmental variables and indicators for the surveillance quality in the affected countries were used as covariates. By comparing probabilities of outbreak reports estimated in the regression with the force of infection estimated for a limited set of locations for which serological surveys were available, the detection probability per case and the force of infection were estimated across the endemic zone. The yellow fever burden in Africa was estimated for the year 2013 as 130,000 (95% CI 51,000-380,000) cases with fever and jaundice or haemorrhage including 78,000 (95% CI 19,000-180,000) deaths, taking into account the current level of vaccination coverage. The impact of the recent mass vaccination campaigns was assessed by evaluating the difference between the estimates obtained for the current vaccination coverage and for a hypothetical scenario excluding these vaccination campaigns. Vaccination campaigns were estimated to have reduced the number of cases and deaths by 27% (95% CI 22%-31%) across the region, achieving up to an 82% reduction in countries targeted by these campaigns. A limitation of our study is the high level of uncertainty in our estimates arising from the sparseness of data available from both surveillance and serological surveys. With the estimation method presented here, spatial estimates of transmission intensity can be combined with vaccination coverage levels to evaluate the impact of past or proposed vaccination campaigns, thereby helping to allocate resources efficiently for yellow fever control. This method has been used by the Global Alliance for Vaccines and Immunization (GAVI Alliance) to estimate the potential impact of future vaccination campaigns.

Effects of sodium chloride concentrations on larvae and pupae of Aedes aegypti

Aedes aegypti is one of the commonest mosquitoes in the tropics and sub topics, feeding on human blood when exposed and is responsible for the transmission of urban yellow fever in Africa and out side Africa, it transmits dengue fever. Aedes aegypti are basically freshwater mosquito. The effect of different concentrations of saline solution on the survivorship of larvae and pupae of Aedes aegypti is studied to possibly find a control measure that will utilize waste water from our kitchen which contains some form of saline solution. Different grams of NaCl were measured and dissolved in 100 ml of water to get the different concentrations and the different larva were subsequently introduced into these solutions. Increase in salinity, brings about increase in mortality rate as well as increase in length of days for development. While there was no mortality in saline concentration between 0.1 - 1.0 % the length of days for development remains almost the same as in freshwater. But from 1.5%-5.0% saline concentration, mortality recorded was on the increase and rate of development was delayed taking about 4.5 days in pupa as against the normal 2.5 days on the average. However optimal mortality was recorded in the first larval instars having 100% mortality in 1.5% to 5.0%. Where as the pupal stage recorded the highest survivorship rate of 83.3% in all. Finally it was observed that Aedes aegypti even though a freshwater mosquito tolerated some level of salinity and at the same time can be controlled effectively with NaCl solution.

Why Arboviruses Can Be Neglected Tropical Diseases

Why Arboviruses Can Be Neglected Tropical Diseases

US$58 million grant to fight yellow fever in Africa

Efforts to contain the resurgence of yellow fever in 12 West African states have been boosted by a US$58 million grant from the GAVI Alliance to support special immunization campaigns in countries at high risk of yellow fever epidemics. The disease was almost wiped out in the 1960s but many nations

Resurgence of Yellow Fever in Africa Prompts a Counterattack

INFECTIOUS DISEASEExperts tracking the resurgence of yellow fever across Africa worry about one scenario in particular: simultaneous outbreaks in several of the continent's teeming megacities. In response, a major initiative to protect the populations at highest risk was announced at the World Health Assembly last week.

The changing epidemiology of yellow fever and dengue, 1900 to 2003: full circle?

Yellow fever and dengue are old diseases, having caused major epidemics in centuries past. Both were effectively controlled in the mid 1900s, yellow fever in Francophone Africa by vaccination and yellow fever and dengue in the Americas by effective control of the principal urban vector of both viruses, Aedes aegypti. In the last 25 years of the 20th century, however, there was a resurgence of yellow fever in Africa, and of dengue worldwide. The factors responsible for this resurgence are discussed, as are current options for prevention and control.

Fiebre amarilla en Africa: su impacto en salud pública y perspectivas para su control en el siglo XXI

In the last two decades, yellow fever re-emerged with vehemence to constitute a major public health problem in Africa. The disease has brought untold hardship and indescribable misery among different populations in Africa. It is one of Africa's stumbling blocks to economic and social development. Despite landmark achievements made in the understanding of the epidemiology of yellow fever disease and the availability of a safe and efficacious vaccine, yellow fever remains a major public health problem in both Africa and America where the disease affects annually an estimated 200,000 persons causing an estimated 30,000 deaths. Africa contributes more than 90% of global yellow fever morbidity and mortality. Apart from the severity in morbidity and mortality, which are grossly under reported, successive outbreaks of yellow fever and control measures have disrupted existing health care delivery services, overstretched scarce internal resources, fatigued donor assistance and resulted in gross wastage of vaccines. Recent epidemics of yellow fever in Africa have affected predominantly children under the age of fifteen years. Yellow fever disease can be easily controlled. Two examples from Africa suffice to illustrate this point. Between 1939 and 1952, yellow fever virtually disappeared in parts of Africa, where a systematic mass vaccination programme was in place. More recently, following the 1978-1979 yellow fever epidemic in the Gambia, a mass yellow fever vaccination programme was carried out, with a 97% coverage of the population over 6 months of age. Subsequently, yellow fever vaccination was added to the EPI Programme. The Gambia has since then maintained a coverage of over 80%, without a reported case of yellow fever, despite being surrounded by Senegal which experienced yellow fever outbreaks in 1995 and 1996. The resurgence of yellow fever in Africa and failure to control the disease has resulted from a combination of several factors, including: 1) collapse of health care delivery systems; 2) lack of appreciation of the full impact of yellow fever disease on the social and economic development of the affected communities; 3) insufficient political commitment to yellow fever control by governments of endemic countries; 4) poor or inadequate disease surveillance; 5) inappropriate disease control measures, and 6) preventable poverty coupled with misplaced priorities in resource allocation. Yellow fever can be controlled in Africa within the next 10 years, if African governments seize the initiative for yellow fever control by declaring an uncompromising resolve to control the disease, the governments back up their resolve with an unrelenting commitment and unwavering political will through adequate budgetary allocations for yellow fever control activities, and international organisations, such as WHO, UNICEF, GAVI, etc., provide support and technical leadership and guidance to yellow fever at risk countries. Over a ten-year period, of stage-by-stage mass yellow fever vaccination campaigns, integrated with successful routine immunisation, Africa can bring yellow fever under control. Subsequently, for yellow fever to cease being a public health problem, Africa must maintain at least an annual 80% yellow fever vaccine coverage of children under the age of 1 year, and sustain a reliable disease surveillance system with a responsive disease control programme. This can be achieved at an affordable annual expenditure of less than US$1.00 per person per year, with a reordering of priorities.

Yellow-fever vaccine stocks low

With current stocks scarce, the WHO has appealed to the international community to stockpile yellow-fever vaccine. Vaccine stocks were used up in a recent successful vaccination campaign that immunized an estimated 2.6 million people in Cote d'Ivoire in less than two weeks, in an attempt to curb the first urban outbreak of yellow fever in Africa in a decade. Yellow fever is responsible for an estimated 200 000 cases of illness and 30 000 deaths each year. Currently, there are, at most, 1 million remaining doses of vaccine available worldwide for the coming month. ‘If there were another urban outbreak, we would need to do a similar campaign and there would not be enough vaccine right now’, warned Michael Zaffran, of the WHO's Department of Vaccines and Biologicals. Only two vaccine manufacturers supply the international market, but a third has recently received WHO official quality approval – which should alleviate the situation somewhat. Ideally, routine immunization against yellow fever, with catch-up campaigns, should be offered by all countries at risk. However, only a minority of countries at risk has invested in routine vaccination against the disease. Immunization Focus (2001) http:\\www.VaccineAlliance.org AL

Impact of Yellow Fever on The Developing World

Yellow fever (YF) has remained a disease of public health importance since it was first described in the fifteenth century. At different periods in human history, YF has caused untold hardship and indescribable misery among populations in the Americas, Europe, and Africa. It brought economic disaster in its wake, constituting a stumbling block to development. Yellow fever is an arboviral infection with three epidemiological transmission cycles between monkeys, mosquitoes, and humans. It is an acute infectious disease characterized by sudden onset, with two phases of development separated by a short period of remission. The clinical spectrum of YF varies from a very mild, nonspecific, febrile illness to a fulminating, sometimes fatal disease with pathognomonic features. In severe cases, jaundice and bleeding diathesis with hepatorenal involvement are common. The fatality rate of severe YF is 50% or higher. Despite landmark achievements in the understanding of the epidemiology of YF and the availability of a safe, efficacious vaccine, YF remains a major public health problem in both Africa and South America, where annually the disease affects an estimated 200,000 persons, causing an estimated 30,000 deaths. Since the 1980s epidemics of YF in Africa have affected predominantly children under the age of 15 years. The failure to control YF arises from a misapplication of public health strategies and insufficient political commitment by governments in YF endemic areas, especially in Africa, to control the disease.

Discovery of the yellow fever virus

The re-emergence of yellow fever in Africa and South America during the past decade tempers previous optimism that this disease could be eliminated as a public health problem during the twentieth century. Fortunately yellow fever is well understood by virtue of discoveries made between 1930 and 1932. These were proof of the mosquito transmission hypothesis; urban control by eradicating Aedes aegypti; development of a nonhuman primate model leading to isolation of the virus; development of a mouse model leading to a vaccine; and recognition that mosquitoes other than A. aegypti could serve as vectors. The least well known of these stories may be the development of an animal model reported in 1928 by Adrian Stokes Johannes H. Bauer and N. Paul Hudson from the Rockefeller Foundation’s West African Yellow Fever Commission in Nigeria. Stokes contracted the disease during the experiments and dying asked that studies be performed on himself--studies that established the viral etiology beyond reasonable doubt. His co-authors honored him with first authorship on the sentinel paper portions of which are reproduced here. (excerpt)

Prevention and Control of Yellow Fever in Africa

Prevention and Control of Yellow Fever in Africa