This is so easy, I could skip reading the rules and just explain all of these but I'm not going to do that.

Number 4 is clearly what we call "dental caries". As described in "Caries Ecology Revisited: Microbial Dynamics and the Caries Process" by Takahashi N. and Nyvad B. source the bacteria in mouth and the dental plaque cause the process of tooth surface being deminarilized and thus causing "holes" in teeth. As seen in the picture 4.

If number 4 was bad, then number 6 is worse! It's clearly a pathogen transfer process. The cell number 2 is in pain as the cell which is hosting a disease transfers the dangerous pathogen to it. Not sure what a pathogen is, but I'm assuming it's a super bad gene.

Pathos is the greek word for "suffering". This means it's suffering gene, which is bad.

As described in "Pathogen transfer through environment-host contact: an agent-based queueing theoretic framework." by bunch of people (too many to cite) Source there are host-to-host transferred diseased. I'm assuming this is related to the suffering genes, especially when the header states "Pathogen". And we can see a transfer happening.

Then the final one, number 6. As described on "Viral diseases of marine invertebrates" by P.T. Johnson source there are many known diseases harming... marine introverts.

These contain the group of animals called "Mollusca", which contain also the octopi. In the first image the octopus called "G-Daddy Bobberton" is fighting the virus. The G-Daddy Bobberton seems to be doing OK and it finally defeats the virus. It then hands it over to a biologist who studies viral diseases of marine introvertaberetiums. I'm 100% sure this is how microbiologists get their samples.