Study suggests Huanan seafood wholesale market in China’s Wuhan is “epicentre” of COVID-19 outbreak

wuhanAccording to a research, the WHO advisory panel concluded that the Huanan seafood market in Wuhan, China, had a key role in the spread of the epidemic, and more investigation is required.

The discovery of how the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) developed in 2019 is essential to stopping zoonotic epidemics before they become the next pandemic, according to a group of researchers. Early reports identified the Huanan Seafood Wholesale Market in Wuhan, China, as a possible source of cases, however this conclusion eventually became contentious. According to the findings, the first documented COVID-19 cases from December 2019, including those with no apparent direct ties, were concentrated in this market.

In late 2019, live SARS-CoV-2 susceptible animals were sold at the market, and SARS-CoV-2-positive environmental samples were geographically correlated with vendors selling live mammals. While there is little evidence to characterise upstream events, and the exact conditions remain unknown, our studies demonstrate that SARS-CoV-2 emerged in China via the live animal trade, and that the Huanan market was the epicentre of the COVID-19 epidemic.

The study’s findings were published in the journal Science.

The Chinese government alerted the World Health Organization (WHO) on December 31, 2019, of an epidemic of severe pneumonia of unknown cause in Wuhan, Hubei province, a metropolis of around 11 million people.

27 (66 percent) of the original 41 persons hospitalised with unexplained pneumonia by 2 January 2020 had direct exposure to the Huanan Wholesale Seafood Market (hereafter, “Huanan market”). These initial individuals were found to be infected with a new coronavirus, later termed severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and to be suffering from coronavirus illness 2019. (COVID-19). COVID-19 was initially diagnosed in different hospitals separately between December 18 and December 29, 2019. Because they were based on indications and symptoms before the Huanan market was recognised as a common risk factor, these early reports were devoid of ascertainment bias.

A subsequent systematic review of all cases reported to China’s National Notifiable Disease Reporting System by hospitals in Wuhan as part of the joint WHO-Chinese “WHO-convened global study of origins of SARS-CoV-2: China Part” (hereafter, “WHO mission report”) revealed that this market was responsible for 55 of the 168 earliest known COVID-19 cases. However, the fact that the majority of early cases were related to the Huanan market does not prove that the pandemic began there.

Sustained live animal sales occurred in 2019 at the Huanan and three additional Wuhan markets, including wild and farmed wild-life. Several of these species have been shown to be experimentally sensitive to SARS-related coronaviruses (SARSr-CoVs), including SARS-CoV-1 and SARS-CoV-2.

During the early stages of the COVID-19 pandemic, animals sold at the Huanan market were suspected of being the cause of the unexplained pneumonia cases (data S1), which was consistent with the development of SARS-CoV-1 and other viral zoonoses from 2002 to 2004. This prompted the decision to close and disinfect the Huanan market on January 1, 2020, with environmental samples gathered from vendor stalls as well (data S1).

Early patients resided close and around the Huanan market.

Following a comprehensive review of reported case histories, the WHO mission report for 2021 detected 174 COVID-19 cases in Hubei province in December 2019.

Although we did not have the geographical coordinates of the 164 individuals who resided in Wuhan, we were able to properly derive the latitude and longitude coordinates of 155 cases using maps in the report.

Both early SARS-CoV-2 lineages were regionally connected with the market.

Since the beginning of the COVID-19 pandemic, two SARS-CoV-2 lineages, dubbed A and B, have disseminated globally. Until a recent preprint study, only lineage B sequences were collected at the Huanan market. When compared to the age-matched Wuhan population distribution, the eleven lineage B cases from December 2019 with location information lived closer to the Huanan market than predicted (median 8.30km; p=0.017).

The eleven lineage B instances’ center-point was 1.95km from the Huanan market, which was likewise closer than predicted (p=0.026). The two lineage A examples for which we have location data involve the two earliest known lineage A genomes. In neither occasion was there any mention of the Huanan market. The initial case was discovered before there was any information of a probable link between unexplained pneumonia in Wuhan and the Huanan market, and so could not have been the result of ascertainment bias in favour of people living near the market. The second had spent the five days previous symptom start at a motel near the market.

The first individual lived closer to the Huanan market (2.31km) than predicted (p=0.034) compared to the age-matched Wuhan population distribution. While the actual location of the hotel near the market was not disclosed, at least 20 hotels are within 500 metres (table S1). Under the conservative assumption that the hotel could have been located as far as 2.31km from the Huanan market (as was the residence of the other lineage A case), and assuming that this location is comparable to a residential location given the timing of the stay prior to symptom onset, both of the earliest lineage A cases would be unlikely to be observed this close to the Huanan market (p=0.001 or less).

The fact that both identified lineage A cases had a geographical connection to the market, combined with the detection of lineage A within the market, supports the possibility that during the early epidemic, lineage A was disseminating outward from the Huanan market into the surrounding neighbourhoods, similar to lineage B.

Trading of wild animals at Wuhan marketplaces

In addition to selling fish, poultry, and other goods, the Huanan market was one of four in Wuhan documented to offer a range of live, wild-captured, or farmed animal species in the years and months preceding the COVID-19 outbreak. However, there have been no previous reports of which species, if any, were traded at the Huanan market in the months preceding the pandemic.

We present evidence that many possible intermediate animal hosts of SARS-CoV-2 progenitor viruses, including red foxes (Vulpes vulpes), hog badgers (Arctonyx albogularis), and common raccoon dogs (Nyctereutes procyonoides), were sold live at the Huanan market until at least November 2019. There are no reports of SARS-CoV-2 test findings from these animals at the Huanan market. Despite a typical slowdown in live animal sales during the winter months, we note that raccoon dogs sold for both meat and fur were constantly available for sale throughout the year, including in November 2019 at the Huanan market.

We conducted geographical relative risk analysis to identify prospective market locations with a high density of positive environmental samples. We discovered evidence (p0.05) of a location in the market’s southwest where live animals were sold. Despite the fact that the market’s environmental sampling was incomplete and spatially heterogeneous (data S1 and table S6), our analysis accounts for the empirical environmental sampling distribution, which was biassed toward stalls related to December cases as well as stalls that sold livestock, poultry, and farmed wildlife. Distances to the nearest vendor selling live animals and to the nearest human case were independently predictive of environmental sample positive (p=0.004 and 0.014, respectively for N=6; table S9).

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To test the robustness of our findings to potential sampling biases, we considered three scenarios: I oversampling of live mammal and unknown meat stalls, (ii) over-counting of positive samples, and (iii) excluding the seafood stand near the market’s wildlife area (with five positive samples) from our analysis (table S10). Distance to live animal sellers remained predictive of environmental sample positivity in each case, and the region of increasing positive sample density in the southwest quadrant of the western half of the market remained continuous.

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