Molecular epidemiology of acute respiratory virus infections

Abstract

Acute respiratory virus infections are very common but can also cause severe disease. In my thesis, I have analysed the molecular epidemiology of acute respiratory virus infections caused by enterovirus D68 and coronaviruses.

In Paper I, we used real-time PCR and Sanger sequencing to analyse the outbreak of enterovirus D68 in Stockholm in 2016. We found that the outbreak was caused by the subclade B3, and we also described three patients with neurological manifestations. The virus sequences were closely related to concurrent sequences from North America.

In Paper II, we developed an assay for whole-genome sequencing of enterovirus D68 a next-generation platform. By using the assay on the samples from the 2016 outbreak, we found that the outbreak was caused by multiple independent introductions of the virus. We also estimated the time to the most common recent ancestor for the subclades B1 and B3 to 2009.

In Paper III, we used the whole-genome sequencing assay in a European multicentre study of enterovirus D68 circulation in the 2018 season. We also included sequences in public repositories. We found that the viruses in 2018 belonged to subclades A2 and B3 and that sequences in subclade B3 originated from the circulation in 2016. We also found that enterovirus D68 had a rapid geographic mixing and that residues on the surface of the virus particle had an elevated substitution rate of amino acids. Hence, we proposed asymptomatic reinfections of adults to explain both rapid geographical dispersal and selective pressure on the surface residues.

In Paper IV, we analysed stored results from routine clinical diagnostics for the four common cold coronaviruses. The data contained the results from September 2009 to April 2020. At the species level, we found a pattern of alternating biennial circulation, and we also found the circulation of Betacoronaviruses to peak earlier than that of Alphacoronaviruses.

In Paper V, we investigated Sweden’s first SARS-CoV-2 pandemic wave in 2020. We analysed stored respiratory samples with real-time PCR for SARS-CoV-2 and found that community transmissions started earlier than previously appreciated. We also se-quenced stored SARS-CoV-2-positive samples. To these sequences, we added infor-mation from contact tracing records and combined them with data from public reposi-tories. Among cases exposed abroad, we mainly found clades 20B and 20A, whereas clade 20C dominated domestic infections. Furthermore, we found the proportion of clade 20C to be correlated with the cumulative number of deaths due to COVID-19. We interpreted this as early undetected introductions of clade 20C having had a significant impact on the further course of the pandemic in Sweden.