Abstract
In 2017, Italy experienced a large measles epidemic with 5408 cases and four deaths. As Subnational Reference Laboratory of the Measles and Rubella surveillance NETwork (MoRoNET), the EpiSoMI (Epidemiology and Molecular Surveillance of Infections) Laboratory (University of Milan) set up rapid and active surveillance for the complete characterisation of the Measles virus (Mv) responsible for the large measles outbreak in Milan and surrounding areas (Lombardy, Northern Italy). The aims of this study were to describe the genetic profile of circulating viruses and to track the pathway of measles transmission. Molecular analysis was performed by sequencing the highly variable 450 nucleotides region of the N gene (N-450) of Mv genome. Two-hundred and ninety-nine strains of Mv were analysed. The phylogenetic analysis showed five different variants, two not previously described in the studied area, belonging to D8 and B3 genotypes. Three events of continuous transmission of autochthonous variants (D8-Osaka, D8-London and B3-Milan variants) and two events of continuous transmission of imported variants (B3-Dublin and D8-Hulu Langat) tracked five different transmission pathways. These pathways outlined two epidemic peaks: the first in April and the second in July 2017. The correlation between Mv variant and the epidemiological data may enable us to identify the sources of virus importation and recognise long-lasting virus transmission pathways.
Highlights
The World Health Organization (WHO) planned to eliminate measles by 2015, but due to the numerous measles outbreak in the European Region in the last few years this did not occur [1] and the WHO postponed the target date for the global eradication of measles to 2020 [2, 3]
The Basic Local Alignment Search Tool-nucleotide (BLAST-n) analysis revealed that the sequences belonged to genotypes D8 and B3
A large measles epidemic occurred in Milan in 2017
Summary
The World Health Organization (WHO) planned to eliminate measles by 2015, but due to the numerous measles outbreak in the European Region in the last few years this did not occur [1] and the WHO postponed the target date for the global eradication of measles to 2020 [2, 3]. Measles elimination depends mainly on achieving high vaccination coverage, closing immunity gaps and ensuring high-quality, case-based surveillance [4], which are the main goals of the European Region as outlined in the European Vaccine Action Plan 2015–2020 [5]. The process of verification of elimination will be based on documented evidence of the interruption of endemic measles transmission at national level [5]. Endemic transmission is defined as continuous transmission of an indigenous or imported Measles virus (Mv) for a period of 12 months or more in a defined geographical area. Measles is deemed to be eliminated when no endemic cases have been documented for a period of at least 12 months by a well-performing surveillance system [4]. WHO refers to ‘named’ strains when identical strains are identified due to their prevalence within MeaNS (Measles Nucleotide Surveillance) database [6]
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