Recurrent dissemination of SARS-CoV-2 through the Uruguayan-Brazilian border

Abstract

SummaryBackgroundUruguay is one of the few countries in the Americas that successfully contained the COVID-19 epidemic during the first half of 2020. Nevertheless, the intensive human mobility across the dry border with Brazil is a major challenge for public health authorities. We aimed to investigate the origin of SARS-CoV-2 strains detected in Uruguayan localities bordering Brazil as well as to measure the viral flux across this ∼1,100 km uninterrupted dry frontier.MethodsUsing complete SARS-CoV-2 genomes from the Uruguayan-Brazilian bordering region and phylogeographic analyses, we inferred the virus dissemination frequency between Brazil and Uruguay and characterized local outbreak dynamics during the first months (May-July) of the pandemic.FindingsPhylogenetic analyses revealed multiple introductions of SARS-CoV-2 Brazilian lineages B.1.1.28 and B.1.1.33 into Uruguayan localities at the bordering region. The most probable sources of viral strains introduced to Uruguay were the Southeast Brazilian region and the state of Rio Grande do Sul. Some of the viral strains introduced in Uruguayan border localities between early May and mid-July were able to locally spread and originated the first outbreaks detected outside the metropolitan region. The viral lineages responsible for Uruguayan suburban outbreaks were defined by a set of between four and 11 mutations (synonymous and non-synonymous) respect to the ancestral B.1.1.28 and B.1.1.33 viruses that arose in Brazil, supporting the notion of a rapid genetic differentiation between SARS-CoV-2 subpopulations spreading in South America.InterpretationAlthough Uruguayan borders have remained essentially closed to non-Uruguayan citizens, the inevitable flow of people across the dry border with Brazil allowed the repeated entry of the virus into Uruguay and the subsequent emergence of local outbreaks in Uruguayan border localities. Implementation of coordinated bi-national surveillance systems are crucial to achieve an efficient control of the SARS-CoV-2 spread across this kind of highly permeable borderland regions around the world.Research in contextEvidence before this studySince the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), causative agent of coronavirus disease 19 (COVID-19), was first detected in South America on February 26, 2020, it has rapidly spread through the region, causing nearly 350,000 deaths by December, 2020. In contrast to most American countries, Uruguay avoided an early exponential growth of SARS-CoV-2 cases and during the first six months of the pandemic it registered the lowest incidence of SARS-CoV-2 cases and deaths among South American countries. The intensive cross-border human mobility through the ∼1,100 km uninterrupted dry frontier between Uruguay and Brazil, might poses a major challenge for long-term control of the epidemic in Uruguay. Previous genomic studies conducted in Uruguay have analyzed sequences mostly sampled at the capital city, Montevideo, and detected prevalent SARS-CoV-2 lineages different from those described in Brazil, thus finding no evidence of frequent viral exchanges between these countries.Added value of this studyHere we present the first genomic study of SARS-CoV-2 strains detected in different Uruguayan and Brazilian localities along the bordering region. The samples analyzed include 30% (n = 59) of all laboratory confirmed SARS-CoV-2 cases from Uruguayan departments at the Brazilian border between March and July, 2020, as well as 68 SARS-CoV-2 sequences from individuals diagnosed in the southernmost Brazilian state of Rio Grande do Sul between March and August, 2020. We demonstrate that SARS-CoV-2 viral lineages that widely spread in the Southeastern Brazilian region (B.1.1.28 and B.1.1.33) were also responsible for most viral infections in Rio Grande do Sul and neighboring Uruguayan localities. We further uncover that major outbreaks detected in Uruguayan localities bordering Brazil in May and June, 2020, were originated from two independent introduction events of the Brazilian SARS-CoV-2 lineage B.1.1.33, unlike previous outbreaks in the Uruguayan metropolitan region that were seeded by European SARS-CoV-2 lineages.Implications of all the available evidenceOur findings confirm that although Uruguayan borders have remained essentially closed to non-Uruguayan citizens, dissemination of SARS-CoV-2 across the Uruguayan-Brazilian frontier was not fully suppressed and had the potential to ignite local transmission chains in Uruguay. These findings also highlight the relevance of implementing bi-national public health cooperation workforces combining epidemiologic and genomic data to monitor the viral spread throughout this kind of highly permeable dry frontiers around the world.

Genomic epidemiology of SARS-CoV-2 in Esteio, Rio Grande do Sul, Brazil

“…We speculate a trend towards the perpetuation and diversification of the lineages found in this study (B.1.1.248 and B.1.1.33) inside Brazil. The dissemination of these lineages were also reported in the Uruguayan-Brazilian border, driving viral introductions mainly from Southeast and Southern Brazil (especially RS state) to Uruguay [72]. In this study, we found consistent results, mainly regarding B.1.1.33 diffusion from Southern and Southeast to South-American countries (e. g. Argentina, Chile and Uruguay).…”

Mutation hotspots, geographical and temporal distribution of SARS-CoV-2 lineages in Brazil, February 2020-2021: insights and limitations from uneven sequencing efforts

“…The B.1.1.33 lineage was studied in further details using 190 genomes from 13 Brazilian states, showing its variable abundance in different states (ranging from 2% in Pernambuco to 80% in Rio de Janeiro), and its moderate prevalence in South American countries (5-18%). Surprisingly, this lineage was firstly detected in early-March in other American countries ( e. g ., Argentina, Canada, and USA), and additional analysis suggest that an intermediate lineage (B.1.1.33-like) most probably arose in Europe and was later disseminated to Brazil, where its spread gave origin to lineage B.1.1.33 (Resende et al 2021) and possibly seeded secondary outbreaks in Argentina and Uruguay (Resende et al 2021; Mir et al 2021).…”

Emergence of the novel SARS-CoV-2 lineage VUI-NP13L and massive spread of P.2 in South Brazil

“…4 Southeast Brazil, on 9 March 2020 and then disseminated across the country 16,24,37,38 . This lineage was also associated with outbreaks in Argentina and Uruguay, countries bordering RS 38,39 .…”