Submitted by Bored_Survivor t3_zfvx6l in askscience
There seems to be many reports about all kinds of avian flus and diseases targeting other land animals, both domesticated and undomesticated. But you almost never hear about new fish diseases. Why is that so? I found nothing on that on the Internet.
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.
every drop of sea water at the surface has 10 million viruses and 1 million bacteria... Seriously wow
Important note, there are 10 million viruses that are absolutely harmful to sea life. Viruses only exist through the destruction of other cells. However, the vast majority of these viruses target microscopic organisms. So while we as humans never directly see their impacts the ecosystem impacts of viruses are actually massive and very important in how nutrients cycle through the ocean!
Ok, but what does this have to do with the question or are you just soap boxing? Cause that was a strange answer.
Diseases are hugely important in the ocean, you just dont hear about it as much. Just to start off with, viruses are constantly infecting and destroying a significan fraction of planktonic algae. A disease very nearly wiped out sea urchins in the carribbean, another did the same to many starfish on the west coast. Canine distemper outbreaks have big effects on seals and sea lions where they occur. Seagrass wasting disease wiped out north atlantic seagrass ecosystems in the 30's. White spot syndrome had a huge effect on the shrimp industry in the 90s.
Theres a lot going on below the surface
> "Viruses only exist through the destruction of other cells."
Yes, but I would assume they survive significantly longer in ocean water than they would in a dry place on land, right? Thus those 10 million viruses in a seawater drop wouldn't all necessarily have infected an orgamism quite as recently as you would expect from our experience with viruses in the air or on a dry surface.
I think the OP was wondering whether we live more densely on land than in the sea, and maybe if that has an effect. Like, how often does one fish spread an illness to a neighboring fish, versus, how often a sick kid at school touches a door knob and gets the class sick, type of thing?
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Eww. Unrelated but I have a wetsuit, snorkel and mask now up for sale. I'll throw in a beach towel and some flip flops too. Need gone.
Even in freshwater we have things like whirling disease caused by a parasite that seriously impacts trout populations and is very communicable to other fish, some species (rainbow and cutthroat) are dramatically impacted while others are somehow resistant (browns and bulls). It’s actually a pretty big issue out west for trout fisheries after it made it’s way from Europe in the 50’s
It's completely believable which is one of those alarms that makes me want a citation.
Edit: I'll do the homework.
1 - "A teaspoon of seawater typically contains about fifty million viruses." - https://en.wikipedia.org/wiki/Marine_viruses - Suttle, C. (2005). "Viruses in the sea". Nature
2 - "10 million viruses in a drop of seawater" - https://www.futurity.org/millions-of-marine-viruses-ebb-and-flow/
So it's the low-end estimate and probably accurate enough for trivia and Internet gossip.
Aquatic species definitely have their own issues. Even looking at a small subset like aquariums, one sick fish can wipe the entire thing out. Unfortunately, though, any medications we can use in that hobby tend to be broad spectrum, and many of the diseases are also poorly understood. There are a few that if your tank gets it, best nuke the whole thing from orbit, because you’re not getting rid of it easily.
These diseases do exist in the wild as well, obviously- but aquariums are an easily visible example.
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I'd estimate that the vast majority of those viruses are bacteriophages, and pose no threat to multicellular organisms.
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This is selection bias. Just because you don't hear it doesn't mean that it doesn't happen.
We only hear about diseases with land animals because that's the diseases that we do researches on. We do researches on them because they are the animals that are important to us, one way or another.
Diseases on animals that are similar to us affects us directly because of cross species infection. Also, we don't tend to hear or care about animal diseases unless it's economically important. Land animals are farmed at a much greater scale, so we care about them more.
Diseases with sea animals happen aplenty, we just don't know or care enough about them to do the research needed to actually notice them.
Simple as that.
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.
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.
Can I ask a question related to your question? I've heard of a couple of diseases that originated in land animals then moved to humans, but never of diseases that originated in sea creatures then moved to humans. are there such examples or is a transmission not possible because of the different physiology?
Another point is, water teems with life and single cell organisms in water have been around a lot longer than we have, if only one new virus evolved each year, you would still have billions of different types of viruses.
And you didn’t even mention all the different coral diseases affecting our reefs.
And while not a disease how about harmful algae blooms? Like red tide.
I mean, there are about ten times more non-human cells in and on you than human ones. There's no escaping swimming in a sea of microorganisms
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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.
thanks for the detailed answer.
Ah no doubt. It's just one of those believable claims that somehow just needs more, y'know? Nothing personal, I assure you.
In each cubic meter of air, there is between 2 million and 40 million viruses and 1-10 million bacteria. And we breathe about 0.01 cubic meters of air a minute, so it’s not like it’s that much better on land.
Hell, since you’re breathing air through the snorkel, but wearing a wetsuit and mask for the water, you might well get more viruses from air than water while swimming.
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This is reporting bias more than anything. Fish diseases make up the greatest fraction of emerging diseases, not only because global aquaculture and trade is taking off but also because we’re simply learning more.
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The reason is simple, we only support research on things that affect humans, land animals live among humans and thus are more likely to be able to transmit their diseases to humans. Humans don't live with sea creatures, they are less likely than chickens/roosters to affect humans. Money talks in research since the Reagan administration cut most of the basic research in the US. This is why you don't hear about diseases in sea creatures.
Fish do have quite a lot of worms and other parasites, fungal and viral problems, in fact. Some studies suggest marine animals might be more susceptible to diseases due to environmental chances and population densities. Some studies suggest marine animals meet more microbes, while dryness, UV and some other factors reduce half life of terrestrial microbes. However, it is a difficult comparison. Moreover, how do you want to define "disease"? The definition Google gives is "a disorder of structure or function in a human, animal, or plant, especially one that has a known cause and a distinctive group of symptoms, signs, or anatomical changes." I assume pollutants, temperature and so on cause more diseases in the marine environment, at least I hear more of them.
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There are a lot of superplagues going on in oceans, seas, rivers and other bodies of water at all times, you simply don't hear about them as much. Sometimes you see news of dead fish showing up in droves - every now and then, it's disease.
Fish diseases rarely affect us because we're that different from fish, so the only thing you have to worry about are parasites which use fish as intermediates. (That's why there are strict rules for sushi-grade salmon, for instance.)
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Especially with salt water tanks. Maybe not as much recently with people breeding fish and growing corals in captivity, but it used to be everything came from the ocean so bringing in new diseases were always a threat.
Could an epidemic be the reason for the missing crabs in alaska?
but why do we not feel the weight of those?
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Also, red tides often end with a virus outbreak. The dense population and biological stressors make the algae very susceptible.
You don't feel your own cells too. It's simple you always carry them around so why should you feel them. You don't feel the weight of your t-shirt unless you put it on or off because your body most of the time only feels changes in things.
I mean, more than feeling - why do they not weight on the scale when I get a measurement
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That's quite interesting, the biggest struggle I've had while keeping saltwater fish/tanks is the introduction of pests or undesired organisms. I've found they are carried in anything from live rock to coral itself and even pre-mixed salt water.
I've had considerably fewer problems with disease in my saltwater tanks than freshwater and had attributed it to the salinity of the water being a harsher/more hostile environment for parasites, fungal and bacterial infections to propagate and take hold of another organism.
That said, all my corals and fish are captive bred/grown which would likely contribute to the lower frequence of disease in my anecdotal experience.
They do have weight, NIH estimates 1-3% of body weight https://www.nih.gov/news-events/news-releases/nih-human-microbiome-project-defines-normal-bacterial-makeup-body#:~:text=Because%20of%20their%20small%20size,vital%20role%20in%20human%20health.
Cholera is caused by certain strains of a bacterium that attaches itself to the shells of saltwater/freshwater shellfish! At one point it mutated and gained the ability to latch itself onto our stomach lining in the same way, and voila! Cholera.
If anything, it's quite the opposite: water, especially salt water, is a paradise for viruses. It's estimated that something like a quarter of all cells that die on Earth are bacteria in the ocean killed by phages. I think maybe what you're sensing is actually more about the rate of human contact: maybe we tend to care less about fish diseases because we'd only really get it from eating uncooked fish (or like, drinking water from a fish tank, which I don't advise).
There are also some pretty significant infectious diseases in humans that come from the ocean.
It’s not exactly common, but one of the more disturbing ones I know of off the top of my head is probably Vibrio vulnificans, one of several bacteria known to cause a type of infection that goes by the lovely common name of “flesh-eating disease”, or necrotizing fasciitis to be more technical, which is literally exactly as horrific as it sounds (seriously, I wouldn’t recommend a Google image search). V. vulnificans isn’t nearly as common a cause as culprits like Staphylococcus aureus (especially antibiotic-resistant varieties), and causes a distinct form called “Type II”, but it does uniquely come from exposure to stagnant saline water, which in general isn’t something a lot of people seem to consider as big of a health hazard as they do stagnant freshwater for some reason (maybe due to a mistaken belief that the salt “sterilizes” it or something because it’s a preservative? Who knows), so it’s not always on people’s radar as much when it comes to places you might pick up a horrible disease.
It depends. A salt water tank away from the ocean is very unlikely to find accidental contamination from you, your home, etc that‘s compatible with it.
Cause it would be fresh water species you‘d be introducing through unwashed hands etc.
But: it used to be that virtually anything to do with salt water tanks was wild caught/collected. So any time you bought a new thing for your tank, there was a massive risk of contamination.
While fresh water stuff was usually bred in captivity, with much more focus on keeping the tanks clean. Don‘t want your breeding fish/shrimp etc to just die.
So new fish were likely far removed from the wild, and only carrying the more common parasites of captivity.
Rather than introducing lethal bacteria etc that were freshly picked up from the sea.
Since there‘s also much more salt water breeding now, the risk has kinda gone down.
Plus massive operations can test for viral/bacterial DNA in their tanks and quarantine stuff.
But it you were to just take water from a random pond or a random tide pool, the risk of introducing something bad would be about the same on average.
But any random fresh water bacteria/viruses etc likely wouldn‘t survive the halinity of a salt water tank. So a ‚seperated from sea‘ salt water tank would be harder to accidentally contaminate by using say rain water from your backyard tank.
Just curious as to how a teaspoon of seawater can ' contain' so many viruses. I thought that all viruses need a host to survive? Surely, they're not just floating around in water, right?
Well I'm a layman here, but there's the whole debate if viruses are even alive. I'm sure this generalisation is very wrong, but most viruses are fatty capsules of genetic material at the end of the day. They don't really need a host to survive - just to proliferate.
They float around until they bump into a host. The majority of those viruses probably infect bacteria
but then how can they be 10x as many cells and only weight 1-3‰? our own cells much bigger /heavier? edit:thinking about it, it's probably due to non-cell weight like water, minerals etc?
One of the main reasons you don’t hear so much about ocean diseases compared to land based ones is because not many of the ocean ones can spread to humans. They need aquatic environments to survive, so don’t often spread across land to become an issue for humans. Like most things in life, if it doesn’t effect us, we talk about it less.
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Do you have more information on the parasitic intermediaries found in salmon?
Roundworms (such as anisakid nematodes), flukes and at least one species of tapeworm can all infect humans if you eat salmon raw.
[deleted] t1_izdveii wrote
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