Read the section on virus "isolation".
"Virus Isolation
Specimens of enlarged submaxillary glands were removed aseptically" from five Jcl:SD rats (9 to 10 weeks old) showing neck swelling at the second day after onset in an outbreak. The 10 per cent homogenates were prepared separately and clarified by low-speed centrifugation. Each homogenate was inoculated i.e. at approximately 0.02 ml/mouse into groups of ten 2-day-old suckling mice,
which were then housed immediately in a vinyl isolator and observed for 14 days. "
In other words - there was no virus isolation. The experimenters simply took diseased glands from 5 poor rats, homogenised and clarifed these via low-speed centrifuge, and injected into some hapless mice. That is not isolation of the alleged virus.
Similar deceit (whether wilful or ignorant) is undoubtedly the reason for the other "thousands of examples" where a virus is claimed to be isolated, but actually (and scientifically) wasn't.
This is also consistent with the recent freedom of information requests made to various governments for proof of the (isolated) coronavirus, and the typical government responses that the coronavirus has not been able to be isolated (i.e. no such proof exists). The fact is, no virus has ever been isolated (as verified under an electron microscope), and then demonstrated to be the cause of the disease that the virus is said to claim (by introducing it into other healthy subjects).
"Virus Mania: How the Medical Industry Continually Invents Epidemics, Making Billion-Dollar Profits At Our Expense", by journalist Torsten Engelbrecht and doctor of internal medicine Claus Köhnlein, was published in 2007, but is especially valid today. Virus propaganda ignores very basic scientific facts: the existence, the pathogenicity and the deadly effects of so-called viruses have never been proven.