Several years ago a bacterium, Burkholderia pseudomallei, 'escaped' from a level 3 lab into the environment outside the Tulane Primate Research center. This bacterium is one that has been implicated in biowarfare research. Investigation of the situation suggested that 'sloppy lab procedures' may have been responsible.
It may well be that the research labs are producing the 'nightmares' of virology and microbiology contagion - accidentally or otherwise. There was much research directed at producing a retrovirus to attack gypsy moths that could be transmissible through the air!!! I believe this has been accomplished, and is being used.
The problem with finding microorganisms in certain situations is determining what organisms are causing disease and what organisms are just 'hanging out.' Sometimes this is hard to determine. I did find some old research comments ( several years ago - at a university site) that XMRV was considered pathogenic for humans and appropriate containment should be used. Sorry, can't find original source.
Here is a bit of obscure viral info. There is a lactic dehydrogenase virus described in 1965 by Abner Notkins, National institute of Dental Research. ( Bacteriol Rev 1965 June; 29(2): 143-160) " From these studies, it can be seen that the widespread contamination of tumors, viruses, and animals with LDV adds considerably to the already complex problem of extraneous mouse viruses and of the interpretation of experiments in which LDV is a contaminant." So, the presence of one virus may affect the ability of other viruses to cause disease.
This is a confusing mess. But with our level of technology , you would think the answers could be found. I thought about the AIDS situation. They found the virus, and got a cocktail to save lives. Treated AiDS patients are doing way better than the people on this forum, I think? Way better than me.
But the AIDS story is interesting, and Robert Gallo and others may have had big clues about what virus they were looking for. The River by Edward Hooper details the evidence that chimpanzees were, in fact, used in polio vaccines. ( denied by the vaccine creators) it was the transfer of the undetected chimp immunodeficiency viruses to humans via polio vaccines that gave rise to the AIDS virus.