A review of the recent advances on Lassa fever with special reference to molecular epidemiology and progress in vaccine development

Lassa fever, a viral hemorrhagic fever caused by the Lassa virus (LASV), is endemic in West Africa and is associated with high morbidity and mortality. At least three of the four proposed seven lineages of LASV are found in Nigeria, where the multimammate rat, Mastomys natalensis, serves as the primary reservoir. Endemic countries report approximately 200,000 infections and 5,000 deaths annually, with Nigeria experiencing thousands of infections and hundreds of deaths including healthcare workers. The aim of this review is to provide scientific information for better understanding of the evolutionary biology, molecular epidemiology, pathogenesis, diagnosis, and prevention of Lassa fever in Nigeria and other endemic regions worldwide, which can lead to improved control efforts and reduce morbidity and mortality from recurrent epidemics. To achieve this aim, observational studies such as case series, cross-sectional and cohort studies published between December 2017 and September 2022 were searched for on various online databases including Google Scholar, Africa Journals Online (AJOL), Research Gates, PubMed, PMIC, NCDC, and WHO websites. Although the origin and evolutionary history, and the transmission dynamics of Lassa virus have been revealed through recent. molecular epidemiological studies, the factors that drive the evolution of the virus remain unclear. Genetic changes in the viral genome may have enabled the virus to adapt to humans. Diagnosis of Lassa fever has also advanced from basic serological tests to more sophisticated methods such as quantitative real time polymerase chain reaction (qRT-PCR) and sequencing, which are particularly useful for identifying outbreak strains. Several vaccines, including recombinant vesicular stomatitis virus (rVSV), virus-like particle (VLP), and DNA-based vaccines, have shown promise in animal models and some have progressed to phase 2 clinical trials. Preventing and controlling Lassa fever is critical to safeguard the health and well-being of affected communities. Effective measures such as rodent control, improved sanitation, and early detection and isolation of infected individuals are essential for reducing transmission. Ongoing research into the genetic and ecological factors that drive the evolution of Lassa virus is necessary to reduce the impacts of Lassa fever.

A review of the recent advances on Lassa fever with special reference to molecular epidemiology and progress in vaccine development

Lassa fever, a viral hemorrhagic fever caused by the Lassa virus (LASV), is endemic in West Africa and is associated with high morbidity and mortality. At least three of the four proposed seven lineages of LASV are found in Nigeria, where the multimammate rat, Mastomys natalensis, serves as the primary reservoir. Endemic countries report approximately 200,000 infections and 5,000 deaths annually, with Nigeria experiencing thousands of infections and hundreds of deaths including healthcare workers. The aim of this review is to provide scientific information for better understanding of the evolutionary biology, molecular epidemiology, pathogenesis, diagnosis, and prevention of Lassa fever in Nigeria and other endemic regions worldwide, which can lead to improved control efforts and reduce morbidity and mortality from recurrent epidemics. To achieve this aim, observational studies such as case series, cross-sectional and cohort studies published between December 2017 and September 2022 were searched for on various online databases including Google Scholar, Africa Journals Online (AJOL), Research Gates, PubMed, PMIC, NCDC, and WHO websites. Although the origin and evolutionary history, and the transmission dynamics of Lassa virus have been revealed through recent molecular epidemiological studies, the factors that drive the evolution of the virus remain unclear. Genetic changes in the viral genome may have enabled the virus to adapt to humans. Diagnosis of Lassa fever has also advanced from basic serological tests to more sophisticated methods such as quantitative real time polymerase chain reaction (qRT-PCR) and sequencing, which are particularly useful for identifying outbreak strains. Several vaccines, including recombinant vesicular stomatitis virus (rVSV), virus-like particle (VLP), and DNA-based vaccines, have shown promise in animal models and some have progressed to phase 2 clinical trials. Preventing and controlling Lassa fever is critical to safeguard the health and well-being of affected communities. Effective measures such as rodent control, improved sanitation, and early detection and isolation of infected individuals are essential for reducing transmission. Ongoing research into the genetic and ecological factors that drive the evolution of Lassa virus is necessary to reduce the impacts of Lassa fever

La fièvre de Lassa, une fièvre hémorragique virale causée par le virus de Lassa (LASV), est endémique en Afrique de l'Ouest et est associée à une morbidité et une mortalité élevées. Au moins trois des quatre lignées proposées de LASV se trouvent au Nigeria, où le rat multimammaire, Mastomys natalensis, sert de réservoir principal. Les pays endémiques signalent environ 200,000 infections et 5,000 décès par an, le Nigéria connaissant des milliers d'infections et des centaines de décès, y compris des travailleurs de la santé. L'objectif de cette revue est de fournir des informations scientifiques pour une meilleure compréhension de la biologie évolutive, de l'épidémiologie moléculaire, de la pathogenèse, du diagnostic et de la prévention de la fièvre de Lassa au Nigeria et dans d'autres régions endémiques du monde, ce qui peut conduire à des efforts de contrôle améliorés et réduire la morbidité et la mortalité des épidémies récurrentes. Pour atteindre cet objectif, des études observationnelles telles que des séries de cas, des études transversales et de cohorte publiées entre décembre 2017 et septembre 2022 ont été recherchées sur diverses bases de données en ligne, notamment Google Scholar, Africa Journals Online (AJOL), Research Gate, PubMed, PMIC, Sites Web du NCDC et de l'OMS. Bien que l'origine et l'histoire évolutive, ainsi que la dynamique de transmission du virus de Lassa aient été révélées par des études épidémiologiques moléculaires récentes, les facteurs qui déterminent l'évolution du virus restent flous. Des modifications génétiques du génome viral pourraient avoir permis au virus de s'adapter à l'homme. Le diagnostic de la fièvre de Lassa est également passé des tests sérologiques de base à des méthodes plus sophistiquées telles que la réaction quantitative en chaîne par polymérase en temps réel (qRTPCR) et le séquençage, qui sont particulièrement utiles pour identifier les souches épidémiques. Plusieurs vaccins, y compris le virus recombinant de la stomatite vésiculeuse (rVSV), les particules pseudo-virales (VLP) et les vaccins à base d'ADN, se sont révélés prometteurs dans des modèles animaux et certains ont progressé vers des essais cliniques de phase 2. La prévention et le contrôle de la fièvre de Lassa sont essentiels pour préserver la santé et le bien-être des communautés touchées. Des mesures efficaces telles que le contrôle des rongeurs, l'amélioration de l'assainissement et la détection et l'isolement précoces des personnes infectées sont essentielles pour réduire la transmission. Des recherches continues sur les facteurs génétiques et écologiques qui déterminent l'évolution du virus de Lassa sont nécessaires pour réduire les impacts de la fièvre de Lassa.

Clustered lot quality assurance sampling: a pragmatic tool for timely assessment of vaccination coverage.

OBJECTIVES: To evaluate oral poliovirus vaccine (OPV) coverage of the November 2009 round in five Northern Nigeria states with ongoing wild poliovirus transmission using clustered lot quality assurance sampling (CLQAS). METHODS: We selected four local government areas in each pre-selected state and sampled six clusters of 10 children in each Local Government Area, defined as the lot area. We used three decision thresholds to classify OPV coverage: 75-90%, 55-70% and 35-50%. A full lot was completed, but we also assessed in retrospect the potential time-saving benefits of stopping sampling when a lot had been classified. RESULTS: We accepted two local government areas (LGAs) with vaccination coverage above 75%. Of the remaining 18 rejected LGAs, 11 also failed to reach 70% coverage, of which four also failed to reach 50%. The average time taken to complete a lot was 10 h. By stopping sampling when a decision was reached, we could have classified lots in 5.3, 7.7 and 7.3 h on average at the 90%, 70% and 50% coverage targets, respectively. CONCLUSIONS: Clustered lot quality assurance sampling was feasible and useful to estimate OPV coverage in Northern Nigeria. The multi-threshold approach provided useful information on the variation of IPD vaccination coverage. CLQAS is a very timely tool, allowing corrective actions to be directly taken in insufficiently covered areas.