Let me take an example - in our gut and intestines - we have many kilos of bacteria that’s during most circumstances not are pathogenic for us – as long as they stay in our gut. However – if many of them comes out in the body cavities outside the digestive tract – you will be dead rather fast.
I´m sure that if you are unlucky – a marine ich parasite could penetrate your skin and start feeding on your body fluids. but you will not get the disease because you – if you not are in the water for a week or so - will not be reinfected of hundred of new parasites
A bacterium named
Mycobacterium marinum is a bacteria that in fish can form a disease named fish tuberculosis but can also be pathogenic for us. You will often find this bacterium in captive fish, showing no disease and people that handle these systems can sometimes show up symptoms of a disease – but other – working in the same system – will not.
The most common facultative marine bacteria are from different genera’s, mostly
pseudomonas,
Vibrio and myxobacteria. Normally – they are not pathogenic, but circumstances can make them be pathogenic and cause disease. – Vibriosis is a known marine disease. Circumstances can be the amount of bacteria present.
As an example – I have worked with Clarias (a freshwater catfish genera) in recirculated fish farms. This is built on the cleaning capacity of many different bacteria, among them
Flavobacterium spp. However, we notice if the water quality get down (e.g. to many particles) we get outbreak of – probably
- columnaris disease. The way to defeat this was to improve water quality and take away all infected fish we saw.
What I think is very difficult for us to understand is that a beneficial (commensal) microbe can change to be pathogenic (cause a disease) if the connection between host and guest get lost. Sorry for a long quote below – but I think that this is the best explanation I have seen -
from this link
This is true for parasites and virus too and it is basically what
@Paul B have preached for many years and been subjected to much criticism from self-declared pundits. I hope that this excerpt from your own National Center for Biotechnology will give Paul some credits
Very short -
if a microbe will be pathogenic or not (pathogenic = cause disease or dissorder) depends on the interaction between the guest and the host
I think this will answer
@MnFish1 question below too because you will have with microbes of different types as fast as you introduce other living organisms
Sincerely Lasse
.... you're correct if you take those parasites out of a tank - if the fish are exposed again years later - they may have significant problems. However if those fish are never exposed to CI again for example - (somehow) - they will do 'fine'. The problem is that its likely that either by error, failed QT or something else - they may very well be re-exposed.
