EDIT, with a relevant source for context:
Since 1940, an estimated 50% of zoonotic disease emergence has been associated with agriculture (1–3). This estimate, however, is necessarily conservative because only direct agricultural drivers are considered in the epidemiological literature, i.e., within the farm gat
[…]
The intensification of animal agriculture through confinement and industrialization has directly led to the emergence of viruses including Nipah and H5N1 influenza (“swine flu”) (18) and antibiotic-resistant infectious bacteria including methicillin-resistant Staphylococcus aureus and Escherichia coli (19, 20).
50% is a conservative estimate per the source there
Keep in mind the heavy land use also is a big factor as removes wild creatures habitats
But isn’t that good? Less wild animals means less zoonotic disease emergence, right?
No, it means you have increased wild creatures contact in areas where humans are. It means the creatures themselves will move around more than they normally might looking for somewhere to live
Per the source
So the solution is to kill the animals that come near us. Clearing the land of forest will make it easier to spot the disease bearing animals from a distance allowing us to kill them from further away!
Seriously though, trying to scour around for any random fact to prove meat is bad isn’t an effective tactic. Factory farms that are cruel exists which is a strong point, so coming up with random factoids just invites silly debates about those factoids which only distracts from the stronger points about factory farms. Global Warming from cow farts is a pretty strong point too.
You aren’t going to convince anyone to give up meat with random weak arguments. But you might get people to reduce the amount meat they eat, and choose more ethically produced meat with the more stronger arguments around factory farms. People may not become pure vegan, but if the goal is see fewer animals living in bad conditions, convincing people to reduce meat intake and have preference for meat not coming from factory farms would be a big win, wouldn’t it?
The spread also comes from intensive factory farming. Having billions of creatures in extremely close contact is a major source of the disease spread in animal agriculture
This is not some random fact, it’s been a major point for epidemiologists. For instance, antibiotic resistance is heavily tied to animal agriculture which uses 73% of the entire global antibiotic supply (source)
Ignoring the majority of these things is not sensible to do. Advocating for killing all wild life is not going to be sensible nor even close to pratical politicy
And it doesn’t even solve the spread of disease from farm animals who again directly cause 50% of zoonetic disease spread. The 50% figure was not including land use change. The creatures themselves are shipped around all over and put in those crampt conditions that are ripe for disease