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Differential pathogenesis of Usutu virus isolates in mice.

ABSTRACT: Usutu virus (USUV; Flavivirus), a close phylogenetic and ecological relative of West Nile virus, is a zoonotic virus that can cause neuroinvasive disease in humans. USUV is maintained in an enzootic cycle between Culex mosquitoes and birds. Since the first isolation in 1959 in South Africa, USUV has spread throughout Africa and Europe. Reported human cases have increased over the last few decades, primarily in Europe, with symptoms ranging from mild febrile illness to severe neurological effects. In this study, we investigated whether USUV has become more pathogenic during emergence in Europe. Interferon ?/? receptor knockout (Ifnar1-/-) mice were inoculated with recent USUV isolates from Africa and Europe, as well as the historic 1959 South African strain. The three tested African strains and one European strain from Spain caused 100% mortality in inoculated mice, with similar survival times and histopathology in tissues. Unexpectedly, a European strain from the Netherlands caused only 12% mortality and significantly less histopathology in tissues from mice compared to mice inoculated with the other strains. Viremia was highest in mice inoculated with the recent African strains and lowest in mice inoculated with the Netherlands strain. Based on phylogenetics, the USUV isolates from Spain and the Netherlands were derived from separate introductions into Europe, suggesting that disease outcomes may differ for USUV strains circulating in Europe. These results also suggest that while more human USUV disease cases have been reported in Europe recently, circulating African USUV strains are still a potential major health concern.

SUBMITTER: Kuchinsky SC

PROVIDER: S-EPMC7580916 | biostudies-literature | 2020 Oct

REPOSITORIES: biostudies-literature

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Differential pathogenesis of Usutu virus isolates in mice.

Kuchinsky Sarah C SC Hawks Seth A SA Mossel Eric C EC Coutermarsh-Ott Sheryl S Duggal Nisha K NK

PLoS neglected tropical diseases 20201012 10

Usutu virus (USUV; Flavivirus), a close phylogenetic and ecological relative of West Nile virus, is a zoonotic virus that can cause neuroinvasive disease in humans. USUV is maintained in an enzootic cycle between Culex mosquitoes and birds. Since the first isolation in 1959 in South Africa, USUV has spread throughout Africa and Europe. Reported human cases have increased over the last few decades, primarily in Europe, with symptoms ranging from mild febrile illness to severe neurological effects ...[more]

PMID: 33044987

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Project description:BACKGROUND: Usutu virus (USUV), a flavivirus belonging to the Japanese encephalitis serocomplex, was identified in South Africa in 1959 and reported for the first time in Europe in 2001. To date, full length genome sequences have been available only for the reference strain from South Africa and a single isolate from each of Austria, Hungary, and Italy. METHODS: We sequenced four USUV isolates from Senegal and the Central African Republic (CAR) between 1974 and 2007 and compared the sequence data to USUV strains from Austria, Hungary, Italy, and South Africa using a Bayesian Markov chain Monte Carlo method. We further clarified the taxonomic status of a USUV strain isolated in CAR in 1969 and proposed earlier as a subtype of USUV due to an asymetric serological cross-reactivity with USUV reference strain. RESULTS: A comparison of the four newly obtained USUV sequences with those from SouthAfrica_1959, Vienna_2001, Budapest_2005, and Italy_2009 revealed that they are all 96-99% and 99% similar at the nucleotide and amino acid levels, respectively. The phylogenetic relationships between these sequences indicated that a strain isolated in Senegal in 1993 is most closely related to the USUV strains detected in Europe. Analysis of a strain isolated from a human in CAR in 1981 (CAR_1981) revealed the presence of specific amino acid substitutions and a deletion in the 3' noncoding region. This is the first fully sequenced human USUV isolate.The putative USUV subtype, CAR_1969, was 81% and 94% identical at the nucleotide and amino acid levels, respectively, compared to the other USUV strains. Our phylogenetic analyses support the serological identification of CAR_1969 as a subtype of USUV. CONCLUSIONS: In this study, we investigate the genetic diversity of USUV in Africa and the phylogenetic relationship of isolates from Africa and Europe for the first time. The results suggest a low genetic diversity within USUV, the existence of a distinct USUV subtype strain, and support the hypothesis that USUV was introduced to Europe from Africa. Further sequencing and analysis of USUV isolates from other African countries would contribute to a better understanding of its genetic diversity and geographic distribution.

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Differential pathogenesis of Usutu virus isolates in mice.

Publications

Differential pathogenesis of Usutu virus isolates in mice.

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