Slimelung appearance

I loaded up my save game that I was playing earlier today, and approximately 10 million slimelung germs appeared in a cloud of CO2 in my base reducing my duplicants' immume system to zero in a matter of seconds.  There were no germs when I saved and closed my map earlier.  Loading an earlier autosave from about two cycles in advance had the same problem.

Standard Geniuses.sav