Introduction
Avian tuberculosis is usually caused by infection with the bacterium Mycobacterium Avium. Less commonly, infection can be caused by Mycobacterium tuberculosis or Mycobacterium Bovis.
There are 4 sub-species of M. Avium.
It is much more common in smaller 'backyard' flocks than in commercial farms, due to (typically) poorer biosecurity and sanitation.
Although nearly all birds can become infected with this disease, most waterfowl are relatively resistant to it, as well as pheasants.
The course of the disease is relatively slow, because the symptoms can last from a few weeks to many months.
Structure of M. Avium
M. Avium can survive in the soil for up to 4 years, and most of its subspecies can survive in temperatures up to 120 fahrenheit (49 celsius). M. Avium is most suited to temperatures between 82 fahrenheit (28 celsius) to 101 fahrenheit (38.5 celsius). It is capable of withstanding somewhat acidic conditions.
They are non-motile, acid-fast (This means that once the bacterium is stained, it cannot be decolorized using acids), rod-shaped and gram-positive (this is when the result of a gram staining test is positive) bacteria. The cell wall is triple-layered.
Transmission
Most commonly, transmission occurs via the oral route, but it is possible for a chicken to become infected by inhaling infectious aerosols.
Once inside the body, M. Avium replicates itself inside macrophages. The bacteria are released into the lumen of the intestines by ulcerative lesions in the intestines, and are then shed in the faeces. This causes environmental contamination, and the cycle begins again.
Above: Simplified diagram showing how M. Avium manifests in the intestinal tract
M. Avium can be transmitted from some mammals (for example, pigs) to chickens, or from wild birds to chickens, and vice versa.
Rodents, such as rats, can also transmit the disease to chicken flocks. Carcasses are a source of infection to chicken flocks, if the chickens ingest it.
It has been found in eggs, but is eliminated after proper boiling of the eggs.
Above: Diagram showing the transmission of Avian tuberculosis
Symptoms
In many cases, symptoms may not be evident -though, they will likely become lethargic shortly before death, and upon post-mortem examination, severe emaciation will become obvious.
If the chicken does show symptoms, they are usually:
In younger birds, lesions found in the body are usually less severe compared to older birds. The disease is also much less common in younger birds than in older ones.
Treatment
M. Avium is resistant to nearly all anti-tuberculosis drugs, so treatment is often ineffective. As a result of this, as well as the high cost, treatment is not usually attempted.
(It has been tried in exotic birds, and treatment can last for up to 18 months)
The recommended 'treatment' is often culling the entire flock, and equipment, housing and bedding materials should either be destroyed or thoroughly disinfected.
There are some treatments, often multiple different drugs administered together, that can be tried.
This link leads to a scientific paper that details some drugs that may be effective in treatment: 7. Therapy in Avian Tuberculosis.
(See the 2nd paragraph of the section)
It is always important to consult a qualified veterinarian when considering treatment options and dosages.
Prevention
Stress dramatically increases the development of the disease, as well as the rate of shedding of M. Avium, so limiting stressors, including overcrowding and environmental stressors such as high ammonia levels, lack of ventilation etc, is extremely important in the prevention of Avian Tuberculosis.
The immune system of the chicken can be improved by feeding high quality feed with the proper nutrition required for the bird. This reduces the risk of infection.
Supplementing your chickens diet with extra nutrients and vitamins, in the correct amounts, can help improve your chickens immune system.
Above: The composition of a 'nutrient boost' for chickens
As always, good sanitation is essential in preventing the disease. This includes regularly removing droppings, and frequently disinfecting and 'deep-cleaning' the birds housing and nest-boxes.
Quarantine any new birds for up to 2 months, monitoring for symptoms of disease, and (if possible) always buy from reputable breeders that practise good biosecurity and sanitation.
Good biosecurity is important: Prevent wild birds from getting access to feeders, waterers, coops and nest-boxes. Humanely control rodent populations as they could potentially infect your flock. If your flock free-ranges, prevent them from accessing areas that have previously had flocks of birds, pigs or any other farm animals, if possible.
Above: Attempting to trap a particularly evasive rodent (The rat trap is in the back)
No vaccine is currently available for safe use in chickens, though one may become available in the future.
Risk to humans
It is extremely important to note that M. Avium can infect humans, especially those that are immunocompromised.
M. Avium poses a high risk to human health, as most commonly used drugs to treat tuberculosis in humans are ineffective in treating it. Therefore, special precautions should be taken when dealing with the disease.
Consult a doctor immediately if you have any concerns.
Useful links
https://www.backyardchickens.com/articles/how-much-room-do-chickens-need.66180/
https://www.backyardchickens.com/ar...-there-and-cut-more-holes-in-your-coop.47774/
https://www.backyardchickens.com/articles/feeding-chickens-an-introductory-guide.67139/
https://www.backyardchickens.com/articles/diy-mice-deterrent-pouches.79542/
Disclaimers
All images/photographs/diagrams in this article are entirely my own. Please do not use them in anything else, without first asking (and gaining) my explicit permission to do so.
I am not a veterinarian, nor am i a doctor, so if you have any concerns or questions on treatment details and dosages etc. please consult a qualified veterinarian or doctor.
Always remember to humanely deal with animals, such as rodents, especially when trapping them.
Also, both diagrams are difficult (not impossible) to see in dark mode, so using light mode is probably better for reading experience!
Thanks for reading!
Avian tuberculosis is usually caused by infection with the bacterium Mycobacterium Avium. Less commonly, infection can be caused by Mycobacterium tuberculosis or Mycobacterium Bovis.
There are 4 sub-species of M. Avium.
It is much more common in smaller 'backyard' flocks than in commercial farms, due to (typically) poorer biosecurity and sanitation.
Although nearly all birds can become infected with this disease, most waterfowl are relatively resistant to it, as well as pheasants.
The course of the disease is relatively slow, because the symptoms can last from a few weeks to many months.
Structure of M. Avium
M. Avium can survive in the soil for up to 4 years, and most of its subspecies can survive in temperatures up to 120 fahrenheit (49 celsius). M. Avium is most suited to temperatures between 82 fahrenheit (28 celsius) to 101 fahrenheit (38.5 celsius). It is capable of withstanding somewhat acidic conditions.
They are non-motile, acid-fast (This means that once the bacterium is stained, it cannot be decolorized using acids), rod-shaped and gram-positive (this is when the result of a gram staining test is positive) bacteria. The cell wall is triple-layered.
Transmission
Most commonly, transmission occurs via the oral route, but it is possible for a chicken to become infected by inhaling infectious aerosols.
Once inside the body, M. Avium replicates itself inside macrophages. The bacteria are released into the lumen of the intestines by ulcerative lesions in the intestines, and are then shed in the faeces. This causes environmental contamination, and the cycle begins again.
Above: Simplified diagram showing how M. Avium manifests in the intestinal tract
M. Avium can be transmitted from some mammals (for example, pigs) to chickens, or from wild birds to chickens, and vice versa.
Rodents, such as rats, can also transmit the disease to chicken flocks. Carcasses are a source of infection to chicken flocks, if the chickens ingest it.
It has been found in eggs, but is eliminated after proper boiling of the eggs.
Above: Diagram showing the transmission of Avian tuberculosis
Symptoms
In many cases, symptoms may not be evident -though, they will likely become lethargic shortly before death, and upon post-mortem examination, severe emaciation will become obvious.
If the chicken does show symptoms, they are usually:
- Diarrhoea (usually white in colour)
- Smaller (than normal) comb and wattles
- Pale comb and wattles, that are also thinner and dry
- Sudden death
- In some birds; respiratory signs
- Decreased egg production
- Decreased weight gain
- Soiled feathers
- Lethargy
- Severe weight loss
- Jerky or stilted walking
In younger birds, lesions found in the body are usually less severe compared to older birds. The disease is also much less common in younger birds than in older ones.
Treatment
M. Avium is resistant to nearly all anti-tuberculosis drugs, so treatment is often ineffective. As a result of this, as well as the high cost, treatment is not usually attempted.
(It has been tried in exotic birds, and treatment can last for up to 18 months)
The recommended 'treatment' is often culling the entire flock, and equipment, housing and bedding materials should either be destroyed or thoroughly disinfected.
There are some treatments, often multiple different drugs administered together, that can be tried.
This link leads to a scientific paper that details some drugs that may be effective in treatment: 7. Therapy in Avian Tuberculosis.
(See the 2nd paragraph of the section)
It is always important to consult a qualified veterinarian when considering treatment options and dosages.
Prevention
Stress dramatically increases the development of the disease, as well as the rate of shedding of M. Avium, so limiting stressors, including overcrowding and environmental stressors such as high ammonia levels, lack of ventilation etc, is extremely important in the prevention of Avian Tuberculosis.
The immune system of the chicken can be improved by feeding high quality feed with the proper nutrition required for the bird. This reduces the risk of infection.
Supplementing your chickens diet with extra nutrients and vitamins, in the correct amounts, can help improve your chickens immune system.
Above: The composition of a 'nutrient boost' for chickens
As always, good sanitation is essential in preventing the disease. This includes regularly removing droppings, and frequently disinfecting and 'deep-cleaning' the birds housing and nest-boxes.
Quarantine any new birds for up to 2 months, monitoring for symptoms of disease, and (if possible) always buy from reputable breeders that practise good biosecurity and sanitation.
Good biosecurity is important: Prevent wild birds from getting access to feeders, waterers, coops and nest-boxes. Humanely control rodent populations as they could potentially infect your flock. If your flock free-ranges, prevent them from accessing areas that have previously had flocks of birds, pigs or any other farm animals, if possible.
Above: Attempting to trap a particularly evasive rodent (The rat trap is in the back)
No vaccine is currently available for safe use in chickens, though one may become available in the future.
Risk to humans
It is extremely important to note that M. Avium can infect humans, especially those that are immunocompromised.
M. Avium poses a high risk to human health, as most commonly used drugs to treat tuberculosis in humans are ineffective in treating it. Therefore, special precautions should be taken when dealing with the disease.
Consult a doctor immediately if you have any concerns.
Useful links
https://www.backyardchickens.com/articles/how-much-room-do-chickens-need.66180/
https://www.backyardchickens.com/ar...-there-and-cut-more-holes-in-your-coop.47774/
https://www.backyardchickens.com/articles/feeding-chickens-an-introductory-guide.67139/
https://www.backyardchickens.com/articles/diy-mice-deterrent-pouches.79542/
Disclaimers
All images/photographs/diagrams in this article are entirely my own. Please do not use them in anything else, without first asking (and gaining) my explicit permission to do so.
I am not a veterinarian, nor am i a doctor, so if you have any concerns or questions on treatment details and dosages etc. please consult a qualified veterinarian or doctor.
Always remember to humanely deal with animals, such as rodents, especially when trapping them.
Also, both diagrams are difficult (not impossible) to see in dark mode, so using light mode is probably better for reading experience!
Thanks for reading!
