Insulin is made by bacteria now

Testosterone is synthesized from plants that produce similar compounds that we can convert in a lab to create it. Estrogen is done through similar means as well. But bacteria may be used as well to create enzymes needs to syntheize it or make the entire hormone but every manufactuer has their methods and a lot of if it based on cost of the method and the total yield.

But strong knowledge of chemistry means their are multiple ways to get what you want and nature is wonderful resource for bioprospecting and finding tools you need. Again it all depends on price and some methods are more expensive then others. If you have thr funds to invest for the right machinery and tools you can easily make any method work to mass produce enough to make great profits.

Yes its possible. Viruses are an example of something that can silently insert itself into your genetic material and lie dormant and be passed down to your kids before it undergoes its lytic cycle (if it ever does at all) when the right environmental stress factors are present to trigger it. Scientists theorize viruses have helped to drive evolution, may also be a cause for some genetic disorders and cancers.

A lot of the diseases of marine origin ( I mean true marine origin and not just human waste being dumped into the bay) are usually cases of a microorganisn finding its way in the wrong host and encountering a hostile situation and it fights back. Because our immune system and natural flora are only well equipped to deal with the usual threats from land and fresh water pathogens a marine one like Vibrio vulnificus can easily overwhelm our defenses once an infection is established.

Bacteria are more common. Viruses are very host and tissue specific and because we arent around marine mammals all the time it would difficult for a virus to cross over between us if one even could even transmit at all.

Its been almost a decade since I did undergrad research in marine microbiology so I was definitely trying to be conservative with that estimate :P but I am sure the numbers will vary based on polution, salinity, temperature, current flow and so on.

I assumed the author was more concerned with mostly humans and non plankton fauna. Since most marine fauna are so far evolutionary from humans the odds of viruses crossing over to us is extremely low but never zero. But phages, plant viruses, and other viruses that target protists would definitely make up the bulk of viruses in a drop of water.

Marine Microbiology is a neglected field and I would estimate there a lot of bacteria and viruses in a drop of water that dont even have a name yet. I know we found some weird H2S reducing bacteria smelly sand back in undergrad that we sent for sequencing that didnt have a species name yet it was genetically far enough from its closest Desulfovibrio it could be a new species. So who knows what else is out there if you wanted to put the effort into isolating and sequencing every specimen you can.

I am assuming you are talking about diseases sea animals get that we dont or dont easily spread to other sea animals or land animals. One thing to know, every drop of sea water at the surface has 10 million viruses and 1 million bacteria. These number decreases as you get further offshore and dive deeper. Majority of these microscopic organisms are not pathogenic or harmful at all to us or sea life.

Many diseases are very host or tissue specific and require very narrow environmental ranges (temperature, salinity, ect...). The ocean is far more bio diverse than the land so many of the diseases have an already very narrow range of hosts assuning they can overcome their targets immune system.

Sea Turtles can suffer from an HPV virus that targets them is one example of diseases spreading amongst marine animals.

Coral is also plagued by diseases that targets them.

Bringing the topic back to us there are also plenty of Vibrio spp. (V. vulnificus, V. parahaemolyticus, V. Cholerae, V. alginolyticus) which are naturally part of the marine ecosystem but are problematic to us. But majority of Vibrio spp. are not bad to us and do not cause disease in humans.

The ocean is massive so any diseases that do occur are usually very localized and contained and any animals that do get sick are quickly picked off by predators or the corpse is eaten by scavengers which keeps the disease from spreading.

Most of the ocean is unexplored so any "epidemic" that did occur probably went unnoticed by us and nature took care of it.

Yes. There are a lot of leukemias that are T Cell in nature. I am medical technologist with certs in Hematology, Immunology, and Molecular Pathology and currently work in a cancer hospital where I do a lot of T and B cell gene rearrangment tests for cancers of these white blood cells