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An upsurge in Lassa fever cases in Nigeria in 2018 does not appear to be related to a single viral strain or increased transmission from human to human, according to a genomic analysis published in The New England Medical Journal. Several institutions collaborated in the preparation of the report, including the African Center of Excellence for Infectious Disease Genomics at Redeemer University in Ede, Nigeria; the Broad Institute of MIT and Harvard in Cambridge, Massachusetts; the Scripps Research Institute in La Jolla, California; and Tulane University in New Orleans, among others. The research was funded in part by the National Institute of Allergy and Infectious Diseases (NIAID), the National Institute for Human Genome Research (NHGRI), and the Human Heredity and Health in Africa program of the NIH Common Fund. all components of the National Institutes of Health. (NIH).
The Nigerian Center for Disease Control (NCDC) reported an unusually large increase in the number of Lassa fever cases in 2018, with 523 laboratory-confirmed cases and 135 deaths from 1 January to 7 October. Lassa fever is endemic in West Africa, where Mastomys natalensis rodents, the main animal reservoir of Lassa virus, are common. The rodent is often found in or around human habitats and people are infected with Lassa virus through direct contact with the urine and stool rodents. People with Lassa fever can also spread the virus to other people through close contact, although experts believe that this is rare. About 15 to 20 percent of people hospitalized with Lassa fever die, but only 1 percent of all Lassa infections result in death, according to US Centers for Disease Control and Prevention.
Public health officials feared that the Lassa fever outbreak in Nigeria in 2018 was due to a previously unknown factor, such as a new strain or a more virulent strain of Lassa virus, according to the authors . This prompted the research team to analyze Lassa virus genomes from patient samples to determine whether genomic data signatures could explain the increase in the number of cases.
The authors analyzed the genomes of Lassa virus in 129 patients from the 2017-2018 epidemic and in 91 patients from the 2015-2017 seasons. They discovered that Lassa genomes from 2018 were derived from a wide range of viruses previously observed in Nigeria rather than from a single dominant strain. This indicates that a single strain of the virus was not causing the increase in the number of cases in 2018. In addition, dating the most recent ancestors of 2018 samples showed limited support for human-to-human transmission. The data set had rather characteristics compatible with many independent zoonotic transmissions (the man being infected by contact with stool from rodents or urine).
The research team communicated its results in real time to the NCDC and local health authorities to support the public health response to the epidemic. The research serves as a model for investigating infectious disease emergencies by combining genomic information with traditional epidemiological data to inform response strategies, the authors note.
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Material provided by NIH / National Institute of Allergy and Infectious Diseases. Note: Content can be changed for style and length.
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