How long do viruses live in aquariums?

Question

I had a dwarf gourami in my tank for several weeks and it was healthy, as were the rest of my fish, including regular gouramis. I decided to add another dwarf gourami. I purchased another one from the local pet megamart. My quarantine tank had an algae explosion and I hadn't dealt with it, so I stupidly decided to put the new dwarf gourami in the tank.

For a few days everything was fine, but one morning I looked in and saw one of the dwarfs lying on the substrate gasping. There really wasn't anything I could do, as I still hadn't taken care of the quarantine tank. I thought, well, if he dies I can return him and get a new one. Later that day, my other dwarf was dying as well.

My non-dwarf gouramis were doing fine and still are several days later. I thought this could not be a coincidence and started researching online in forums and sites. It would appear that the new dwarf had Dwarf Gourama Indovirus (DGIV) and transmitted it to the other dwarf. It is a dwarf only disease, which makes sense, as my other gouramis are fine. I tested my water and it was acceptable, so that's a plus. I brought the dead dwarfs back to the store and they refunded my money. I looked at the remaining dwarfs in the store and they looked sickly as well. This observation makes me feel fairly confident if was DGIV.

If I were to get more dwarf gouramis (I found a better non-chain store), do I need to wait a specific period before the virus gets inactivated?

I do weekly water changes of 12.5% and I have a small UV filter running.

I definitely prefer answers with sources to back them up.

Answer 1

Viruses can't 'reproduce' in the water in the aquarium, they can only do this within a living cell (i.e. in a fish). However they can be free floating in your aquarium if introduced via an infected fish (which is what appears to have happened here).

As the site you linked said, you should quarantine for at least 6 weeks, due to this virus to make sure any new fish you've got haven't got this virus. (This means the time for the virus to show up can be upto 6 weeks).

As for should your UV lamp be killing the virus? It'd kill any free floating virus which pass through the lamp, as long as the lamp is correctly maintained - this means it's not so old as to be not working effectively anymore.

Finally, an algae bloom, while unsightly, is no reason not to use your quarantine tank. Algae won't harm your fish in anyway, and while ugly, it's a sign of at least semi-healthy tank.

As to why this all happened 'so suddenly' in your tank - I'd suggest that the stress of a new fish being introduced into the tank, and the stress of being introduced to a new tank, was enough to allow the virus to get a foothold on both fish.

Interestingly while finding sources (which are hard to find as most are commercial products claiming all manner of things about purifying your water) I found a study at a university which showed that most viruses became completely inactive after UV treatment, other than e.coli:

Bacteria May Remain Dormant After UV Disinfection

US American - How does UV kill cells