ABSTRACT
Background: SARS-CoV-2 human-to-animal transmission can lead to the establishment of novel reservoirs and the evolution of new variants with the potential to start new outbreaks in humans. Aim: We tested Norway rats inhabiting the sewer system of Antwerp, Belgium, for the presence of SARS-CoV-2 following a local COVID-19 epidemic peak. In addition, we discuss the use and interpretation of SARS-CoV-2 serological tests on non-human samples. Methods: Between November and December 2020, Norway rat oral swabs, feces and tissues from the sewer system of Antwerp were collected to be tested by RT-qPCR for the presence of SARS-CoV-2. Serum samples were screened for the presence of anti-SARS-CoV-2 IgG antibodies using a Luminex microsphere immunoassay (MIA). Samples considered positive were then checked for neutralizing antibodies using a conventional viral neutralization test (cVNT). Results: The serum of 35 rats was tested by MIA showing 3 potentially positive sera that were later shown to be negative by cVNT. All tissue samples of 39 rats analyzed tested negative for SARS-CoV-2 RNA. Conclusion: This is the first study that evaluates SARS-CoV-2 infection in urban rats. We can conclude that the sample of 39 rats had never been infected with SARS-CoV-2. We show that diagnostic serology tests can give misleading results when applied on non-human samples. SARS-CoV-2 monitoring activities should continue due to the emergence of new variants prone to infect Muridae rodents.
Subject(s)
COVID-19 , Rodent DiseasesABSTRACT
Wastewater-based epidemiology could be applied to track down SARS-CoV-2 outbreaks at high spatio-temporal resolution and could potentially be used as an early-warning for emergence of SARS-CoV-2 circulation in the general population. Epidemiological surveillance of SARS-CoV-2 could play a role in monitoring the spread of the virus in the population and controlling possible outbreaks. However, sensitive sample preparation and detection methods are necessary to detect trace levels of SARS-CoV-2 RNA in influent wastewater (IWW). Unlike predecessors, method development of a SARS-CoV-2 RNA concentration and detection procedure was performed with IWW samples with high viral SARS-CoV-2 loads (in combination with seeding IWW with a surrogate coronavirus). This is of importance since the SARS-CoV-2 genome in IWW might have already been subject to in-sewer degradation into smaller genome fragments or might be present in a different form (e.g. cell debris,...). Centricon Plus-70 (100 kDa) centrifugal filter devices resulted in the lowest and most reproducible Ct-values for SARS-CoV-2 RNA. Lowering pore sizes did not improve our limit of detection and quantification. Real-time polymerase chain reaction (qPCR) was employed for the amplification of the N1, N2, N3 and E_Sarbeco-gene. This is one of the first studies to apply digital polymerase chain reaction (dPCR) for the detection of SARS-CoV-2 RNA in IWW. Interestingly, qPCR results were comparable with dPCR results suggesting that qPCR is a valid method. In this study, dPCR was also used as a proxy to assess the precision of qPCR. In this light, dPCR showed high variability at low concentration levels (100 copies/{micro}L), indicating that variability in bioanalytical assays for SARS-CoV-2 RNA might be substantial. On average, the N2-gene showed high in-sample stability in IWW for 10 days of storage at 4 {degrees}C. Between-sample variability was substantial due to the low native concentrations in IWW. Additionally, the E-gene proved to be less stable compared to the N2-gene and showed higher variability. Freezing the IWW samples resulted in a 10-fold decay of loads of the N2- and E-gene in IWW. Although WBE can already aid in filling some knowledge gaps in the epidemiological surveillance of SARS-CoV-2, future WBE studies should aim to further validate and standardize bioanalytical assays, especially with regards to methodological limitations. HighlightsO_LIDevelopment of an analytical procedure for detection of SARS-CoV-2 RNA in wastewater C_LIO_LIExtraction recovery was evaluated in influent wastewater C_LIO_LIPrecision measured with dPCR used as a proxy for qPCR C_LIO_LIqPCR of the N2 gene fragment showed high in-sample stability of SARS-CoV-2 on average C_LI