A new variant of measles has been identified in Italy, which affects molecular tests for diagnosis, making them less sensitive. This was revealed by a study conducted by the University of Milan, with the Istituto Superiore di Sanità, published in 'Eurosurveillance'.
The five cases
Since January 2024, 5 five cases of measles have been confirmed in the Metropolitan City of Milan and surrounding areas in Lombardy, all classified as genotype D8 and considered sporadic since no clear epidemiological link between them was found. Three of these cases had a recent travel history: the patients had been to Uzbekistan, Thailand and southern Italy. In particular – the researchers explain – two of these cases, i.e. the patients who had traveled to Southern Italy and Thailand, were infected with MeV strains characterized by three mutations previously described by Swiss researchers, coordinated by Francisco José Pérez-Rodríguez, in a study also published in 'Eurosurveillance', in the February 1 issue. This study had attracted the interest of the team from the University of Milan and the Department of Infectious Diseases of the ISS, which then began the hunt for the same mutations. Finding them also in Italy, in a densely populated area, on the border with Switzerland.
The mutation that affects the test
The mutations occurred, explain the Italian researchers, in one particular portion of the nucleoprotein, which is the target of rapid tests commonly used by surveillance laboratories. “This translates – they underline – into a slight loss of sensitivity of the test. None of the other 614 strains (453 D8 and 161 B3) detected by our laboratory between 2017 (beginning of surveillance activities) and 2023 possessed these mutations. Our results now suggest that measles viruses with mutations detected through Swiss molecular surveillance are already circulating in Italy, in line with the results obtained by Pérez-Rodríguez and colleagues, who reported a local case with travel history in Italy”, the researchers point out. “Our communication therefore confirms – they conclude – their discovery, reported promptly to increase awareness of the circulation of a MeV variant which can be detected with reduced sensitivity by many diagnostic tests. And it reports that this variant is spreading. It is important to promptly update the tests – they recommend – to detect all the MeV strains currently circulating”.
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