Thread by @emmecola

THREAD - What happened at the Huanan #seafood market?

The @WHO report is quite clear on this point: #SARSCoV2 might have jumped from a wild animal sold in this market and maybe other markets in #Wuhan. But what do we know exactly? 1/15

#originsofSARSCoV2

After all this time, the Huanan seafood market still remains the main suspect for a simple reason: most of the early cases had visited at least one market in Wuhan city, and several of them visited the Huanan market. 2/15

According to the report, 10,000 people visited this place every day, making it a perfect setting for an #outbreak. One might argue: what about the cases without market exposure? Good question! 3/15

However, if we plot the early cases according to the onset date, we notice that the cases with market exposure peaked earlier than those without it. In other words, the virus appeared first in the markets and then started spreading outside. 4/15

Interestingly, the first case didn't visit the Huanan market, but another supermarket in the Southern part of the city, more than 20 km away from the Huanan market. Due to the high number of cases, though, Huanan got all the attention. 5/15

Unfortunately, once you enter the market, few things make sense. First of all, only 10 out of 678 stalls sold wild (domesticated) #animals: remember this is a #seafood market, and most products were aquatic or seafood. Not ideal hosts for SARS-CoV-2! 6/15

Second, those 10 vendors didn't even sell live #mammals. According to sale records from December 2019, most animals were frozen/dead. Only #crocodiles were sold alive, while live #snakes and #salamanders were slaughtered before being sold. 7/15

The @WHO team even interviewed two local residents who had been visiting the market for 20-30 years: they never witnessed any live animal being sold. But old photographs and media reports suggest the opposite, so.. Who knows! 8/15

Anyway, Chinese scientists tested several animals or parts of animals in the market area. Some species are now known to be susceptible to SARS2 infection (#rabbits, #cats, #badgers), but unfortunately no sample tested positive. 9/15

They did find some positive samples though: not animal, but #environmental samples (surfaces, sewage, etc). Interestingly, the highest % of positive samples were found in stalls selling #vegetables and #poultry (which can't be infected). 10/15

Ok, but what about the early cases? 30 of them were vendors at the Huanan market, but none of them sold domesticated animals: in fact, the highest % of positive cases were among people selling #vegetables. Weird! 11/15

Also checking the very first cases in the market did not help. This market is a brain teaser! 12/15

Let's recap: no live mammal was officially sold, no vendor selling wildlife products tested positive and only one environmental sample tested positive in their stalls. So where did SARS2 come from? 13/15

Nobody really knows. However, the @WHO experts think there are interesting clues: some of the #wildlife vendors sold animal products coming from farms in Southern China, where SARS-CoV-2 closest relatives were found. 14/15

Scientists hope that sampling more animals among the market suppliers will finally reveal the source of SARS-CoV-2. Easier said than done: more than 80,000 samples from livestock, poultry and wild animals across China have already been tested. All negative! 15/15

Please correct me if I made any mistake! @Peterfoodsafety @MarionKoopmans @TheaKFischer @hung_cenpher