Although the researchers found that the rats tested negative for the virus, they say it is important to keep an eye on animals for the virus as it smokes, making species previously susceptible to disease.
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Most studies of emerging infectious diseases have focused on animals such as virus reservoirs and how these viruses are transmitted to humans. However, many studies during COVID-19 pandemic disease have reported that the coronavirus 2 of severe respiratory syndrome (SARS-CoV-2) was transmitted from humans to animals.
Domestic dogs and cats were also seen, with which their owners were positive for the virus. Reports also show that farm mink and other zoo animals have contracted the virus from humans.
Animals infected with human-borne SARS-CoV-2 are likely to be dependent on their ecology and genetics. Osbarr The cell activity of the animal allows the virus to enter and bind to receptors in the host cell. In that case, other transmission depends on how long the infected animals shed the virus and how close and frequent the contact is with other animals.
For example, in farmed mink, a highly susceptible species, the transmission was rapid because they were kept indoors in high densities.
Other animals in the country, such as rats, also live in such conditions and often live close to humans. In Europe, Norwegian rats (Rattus norvegicus) thrive in urban areas, often living in urban sewage systems. Due to several reports of detection of SARS-CoV-2 in wastewater, these rats may have been exposed to the virus.
However, previous studies have shown that this rodent species is not susceptible to the Wuhan strain of the virus. However, after passing through several laboratory mice, the virus has improved the ability to introduce this host due to N501Y mutation in the spike protein binding (RBD) domain. This variation has also been observed in the circulating strains of viruses in humans. This indicates that the virus has the ability to infect previously present hosts, including rodents.
Testing sewer rats for SARS-CoV-2
Researchers tested Norwegian rats living in the sewers of Antwerp, Belgium, for SARS-CoV-2 in November and December 2020 after a peak in the cases there. They reported the results of their study in a research paper published on the bioRxiv* preprint server.
The authors captured several rats for the SARS-CoV-2 test. They first tested the rats’ blood serum for antibodies to the virus. They also tested for viral RNA from oral swabs and in feces. Finally, they tested for the virus in the wastewater at the place where the rats were caught.
Of the eight samples of wastewater tested, the team detected SARS-CoV-2 in four samples. The serum of three out of 35 rats was positive for nucleocapsid and IgG antibodies, but the amounts were lower than control rats that were positive for the virus. Further experiments of that sequence for neutralization of negative antibodies showed that the rats had not been exposed to SARS-CoV-2. All swab, cloth, and fecal samples of 39 rats were negative for the virus.
The findings state that the rats examined from the Antwerp sewers were never infected with SARS-CoV-2 despite exposure to the virus in the wastewater.
Monitoring animals for important viruses
There was a difference in the results obtained by fluorescence and neutralization tests. The authors suggest that care should be taken when using samples different from those tested. Although the fluorescence test distinguished between the positive and negative laboratory control rats, it gave false positive values to the wild-type rats. This may be because wild rats are susceptible to many other pathogens, and exhibit higher total fluorescence values from higher antibody binding. Therefore, to test for SARS-CoV-2 in animals, virus-neutralization tests may be preferable.
The authors apparently did not detect the virus in the sewer rats because the experiments were performed before N501Y mutations in human sequences had the upper hand. Emerging variants from the United Kingdom, South Africa and Brazil, are all driven by N501Y, and previously susceptible species such as rodents may be infected.
Rats live close to humans and in high densities, creating ideal conditions for the spread of new epidemics. Therefore, although the results of the current study show that the rats tested negative for the virus, it is necessary to continue to monitor rats and other animals exposed to humans to detect human spread to future animals.
* Important message
bioRxiv publish preliminary scientific reports that are not peer-reviewed and, therefore, should not be seen as final, guiding health-related clinical / behavioral practice, or be treated as information established.