Infection with the severe acute respir syndrome coronavirus 2(SARS-CoV-2), which is the causal agent of the ongoing coronavirus virus disease 2019 (COVID-19), can cause a variety of clinical outcomes, from mild to severe infections to death.
The Huanan Seafood Market in Wuhan, China was the source of most early SARS-CoV-2 cases. Here, exotic seafood and animal meats were available for purchase. HSM is believed to have caused the COVID-19 pandemic. However, it is possible that someone introduced SARS-CoV-2 to the market via human-to-human transmission. Early COVID-19 cases were not epidemiologically linked.
Study: Surveillance for SARS-CoV-2 at the Huanan Seafood Market. Image Credit: sleepingpanda / Shutterstock.com
Background
Multiple studies have shown that some of these SARS-CoV-2 negative samples were detected earlier than the first case from Wuhan. These reports suggest that SARS-CoV-2 may have been in circulation elsewhere.
Although bats are believed by many to have been the original source of SARS-CoV-2 in the first place, it is unclear if there was an intermediate host that allowed for the virus to spread between humans or bats. One study indicated that pangolins harboured a receptor binding domain similar to SARS-2. However, limited evidence remains to prove that pangolins were the intermediate host.
Researchers have also previously documented HSM’s animal species between May 2017 – November 2019, and found that neither pangolins nor bats were traded during that period. Further questions remain about whether HSM was the original source for SARS-CoV-2.
About the study
A new study was published on the Research Square*Preprint server describes surveillance of SARS-2 in the HSM. HSM can be divided into two zones: the western zone is for animals and seafood, and the eastern zone is for livestock and meat.
According to the sales record, animals and animal products were sold in ten animal stands during December 2019. Sika deer, avian species such as chickens and ducks as well as snakes and badgers, rabbits and bamboo rats, porcupines and hedgehogs were some of the animals that were sold.
SARS-CoV-2 quickly spread to the market in January 2020. The Chinese Centers for Disease Control and Prevention sent an epidemiological team that collected samples from HSM and environmental samples.
Research findings
The scientists analyzed a total of 1,380 samples from the environment and animals within the market in early 2020 to detect the presence of SARS-CoV-2 through the use of reverse-transcriptase qualitative polymerase chain reaction (RT-qPCR) assay. The nucleic acid test (NAT), revealed that 7.9% were positive for SARS-CoV-2. Researchers also estimated the cycle threshold values (Ct) of real-time polymerase chains reaction (PCR), which ranged between 23.9 and 41.7.
Seventy-three environmental samples were tested positive for SARS CoV-2. Three live viruses were also successfully isolated using these samples, with Ct values lower than 30 in NAT.
High-throughput sequencing using the Miseq platform was used for seven complete SARS/CoV-2 genome sequences. To this end, the viruses isolated from the HSM shared high similarities with human isolate HCoV/Wuhan/IVDC-HB-01. SARS-CoV-2, which was detected in 18 species of animals, was not found in any of these animal samples.
Analyzing the activities of merchants was also done against the NAT results from the environmental samples. The market had 19.8% of its vendors sampled. A majority of SARS CoV-2 positive samples were associated with vendors from the west.
Distribution of positive environmental samples at Huanan Seafood Market. A. The Huanan Seafood Market, which was the site of the first COVID-19 cluster, is divided into western and eastern zones by the Xinhua Rd. Between them. To determine if there was SARS-CoV-2 RNA present, reverse transcription was used. The map of the market was marked with orange the locations of positive samples, while the red labels were for the locations of live viruses. The map also shows the locations of stalls that sold domesticated wildlife products. B. Timeline for environmental and animal samples taken within and around Huanan Fish Market.
Although some vendors sold more than one type, there were no significant differences between vendors, even cold-chain products. This suggests that SARS-CoV-2 may have been present in the HSM, in particular in the western region, and this could have contributed to the widespread spread of the virus within the market. SARS-CoV-2 may have spread due to the inundation of the environment and crowding of buyers.
To identify the origins of the SARS-CoV-2 virus, RNA-sequencing analysis with SARS-CoV-2-positive samples from the environment was conducted. SARS-CoV-2 nucleic acid was found to be significantly correlated with those from infected people when taken from environmental samples. This suggests that SARS-CoV-2 may have been derived from humans in the HSM and not animals.
Conclusions
SARS-CoV-2RNA was detected in HSM’s western zone, confirming that this virus is prevalent in the market. Although live viruses could be isolated from the environment, SARS-CoV-2 RNA was not detected in animal samples.
To prevent the spread of the virus, it is essential to monitor wild animals with a viromic approach.
*Important notice
Research Square publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.
