brewmaster15
04-05-2002, 09:03 AM
“Disease *Transmission”,
by Al Sabetta, 3/2002
I was recently asked for information on air-born pathogens and discus, so this weeks discussion is not really on a particular disease but on transmission of disease to and among fish.
When considering how a fish could acquire a disease the first thing we need *to do is remember that *fish are vertebrates *just as humans *are and *the modes of disease *transmission *that *would *infect a human *works the same on *fish.
Bacterial and viral pathogens are passed from fish to fish, much the same as they are in humans. *The difference is a human is often infected when they breath in contaminated air, where as a fish is infected when they breath in contaminated water. For a human the point of infection in these kinds of diseases is the respiratory tract. *From there the pathogen can sometimes spread to attack other areas. *For a fish the initial point of infection is the gill surface. This is where the fish is continuously exposed to pathogen in the water because it is where water is passed over the gills and oxygen is obtained. *This is why fish suffering from bacterial diseases attacking the gills, often breath rapidly of not at all from a gill. * Once the defenses of the gill tissue has been compromised the pathogen can attack other areas as well.
Another way a bacterial or viral pathogen can get in, is thru the skin. Consider the recent anthrax scares, where cutaneous infections of anthrax bacteria were found. *In a water environment similar infections can occur where the bacteria is able to get by the fishes immune responses and protective * slime coats. Once this happens the bacterial colony can florish, and possibly attack other areas.
In the two previous examples a person *afflicted in such a fashion, would be removed *from the general population *to allow *for treatment, and prevent the infection of humans in *contact with the ill one. In a fish tank situation the response needs to be the same, for the same reason, hence we have the creation of hospital tanks.
In addition to these kinds of diseases transmissions there is *one *that makes use *of “fomites”. *Fomites are anything that can carry a pathogen from *one host or location *to another. *An example would be an aquarium hobbyist has 2 tanks. One tank *has and outbreak of *columnaris bacteria. The other tank does not. While doing his treatments in the *disease tank the *hobbyist worries about the medicines killing his plants *so he moves them *to the unaffected *tank! *Days latter the infection has spread to that tank , because the plants acted as fomites and carried *the pathogen into the *new tanks. Technically a * drop of water splashed from one tank to another, or a on a persons *hand going from one tank to another *can spread the pathogens and is a fomite.
Luckily, bacteria that thrive in water, usually do not thrive in the air, so the spread of diseases thru the air among * fish tanks is unlikely. That’s is not to say that a virus or bacteria can not survive long enough in the air to get from one tank to another in a 12X12 room. The dreaded “discus plague” is though to be airborn, by the way it spreads sto rapidly among tanks. The problem here is no one knows the diseases incubation time. If its is like a typical human cold, the fish could have the disease for 24 hours or more before showing symptom. Which means it may not have been airborn, but carried on the hand and equipment of diligent hobbyists cleaning multiple tanks.
Typically parasites are spread from tank to tank on contaminated equipment, hobbyist hands, or the introduction of afflicted *fish *(carriers). In many cases the parasites are external *and the fish being in contact with the *water is all that is required for infection. This is the case with gill flukes, lice, anchor worms, mites, and copepods to mention a few. In other case the parasite has to be ingested by its host. This is the case for many worms. *Keep this in mind when your fish are bottom feeders.
There are also some parasites that will get into the fish in any opening they can find and then make there way to the digestive tract or other areas where they will continue their life cycle. *The digestive tract is ideal because it is a site of *rich nutrients, and offers an easy way *to spread, as eggs or adults in the feces.
Hope this is useful to your understanding of disease transmission. If you ever have any questions on it, apply what you know about illness in people and you’ll have a *pretty good idea as to how disease is spread among the fishes.
Hth,
al
by Al Sabetta, 3/2002
I was recently asked for information on air-born pathogens and discus, so this weeks discussion is not really on a particular disease but on transmission of disease to and among fish.
When considering how a fish could acquire a disease the first thing we need *to do is remember that *fish are vertebrates *just as humans *are and *the modes of disease *transmission *that *would *infect a human *works the same on *fish.
Bacterial and viral pathogens are passed from fish to fish, much the same as they are in humans. *The difference is a human is often infected when they breath in contaminated air, where as a fish is infected when they breath in contaminated water. For a human the point of infection in these kinds of diseases is the respiratory tract. *From there the pathogen can sometimes spread to attack other areas. *For a fish the initial point of infection is the gill surface. This is where the fish is continuously exposed to pathogen in the water because it is where water is passed over the gills and oxygen is obtained. *This is why fish suffering from bacterial diseases attacking the gills, often breath rapidly of not at all from a gill. * Once the defenses of the gill tissue has been compromised the pathogen can attack other areas as well.
Another way a bacterial or viral pathogen can get in, is thru the skin. Consider the recent anthrax scares, where cutaneous infections of anthrax bacteria were found. *In a water environment similar infections can occur where the bacteria is able to get by the fishes immune responses and protective * slime coats. Once this happens the bacterial colony can florish, and possibly attack other areas.
In the two previous examples a person *afflicted in such a fashion, would be removed *from the general population *to allow *for treatment, and prevent the infection of humans in *contact with the ill one. In a fish tank situation the response needs to be the same, for the same reason, hence we have the creation of hospital tanks.
In addition to these kinds of diseases transmissions there is *one *that makes use *of “fomites”. *Fomites are anything that can carry a pathogen from *one host or location *to another. *An example would be an aquarium hobbyist has 2 tanks. One tank *has and outbreak of *columnaris bacteria. The other tank does not. While doing his treatments in the *disease tank the *hobbyist worries about the medicines killing his plants *so he moves them *to the unaffected *tank! *Days latter the infection has spread to that tank , because the plants acted as fomites and carried *the pathogen into the *new tanks. Technically a * drop of water splashed from one tank to another, or a on a persons *hand going from one tank to another *can spread the pathogens and is a fomite.
Luckily, bacteria that thrive in water, usually do not thrive in the air, so the spread of diseases thru the air among * fish tanks is unlikely. That’s is not to say that a virus or bacteria can not survive long enough in the air to get from one tank to another in a 12X12 room. The dreaded “discus plague” is though to be airborn, by the way it spreads sto rapidly among tanks. The problem here is no one knows the diseases incubation time. If its is like a typical human cold, the fish could have the disease for 24 hours or more before showing symptom. Which means it may not have been airborn, but carried on the hand and equipment of diligent hobbyists cleaning multiple tanks.
Typically parasites are spread from tank to tank on contaminated equipment, hobbyist hands, or the introduction of afflicted *fish *(carriers). In many cases the parasites are external *and the fish being in contact with the *water is all that is required for infection. This is the case with gill flukes, lice, anchor worms, mites, and copepods to mention a few. In other case the parasite has to be ingested by its host. This is the case for many worms. *Keep this in mind when your fish are bottom feeders.
There are also some parasites that will get into the fish in any opening they can find and then make there way to the digestive tract or other areas where they will continue their life cycle. *The digestive tract is ideal because it is a site of *rich nutrients, and offers an easy way *to spread, as eggs or adults in the feces.
Hope this is useful to your understanding of disease transmission. If you ever have any questions on it, apply what you know about illness in people and you’ll have a *pretty good idea as to how disease is spread among the fishes.
Hth,
al