What are Mycobacterium Infections?

Some forms of bacteria in the Mycobacterium genus can cause an illness in birds known as avian tuberculosis. Avian and human tuberculosis are closely related, and although transfers between humans and birds are rare, they can occur. Avian tuberculosis, most often caused by Mycobacterium avium, is somewhat resistant to most of the antibiotic medications that are utilized when humans get tuberculosis, so multiple medications are often required over extended periods of time to eliminate the infection. 

Mycobacterium infections in birds can cause avian tuberculosis, a contagious and often fatal disease that can affect birds of any variety but is most prevalent in chickens and wild birds raised in captivity.

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Symptoms of Mycobacterium Infections in Birds

Birds are notorious for hiding the symptoms of illness as long as they possibly can, so birds that are showing signs of physical distress should be seen by a veterinary professional as soon as possible. Signs of mycobacterium infection may include:

  • Atrophy of sternal muscles
  • Depression
  • Diarrhea
  • Distended abdomen
  • Gradual wasting
  • Increased urination
  • Labored breathing
  • Lameness or difficulty perching
  • Lethargy
  • Loss of appetite
  • Poor feather conditions
  • Weight loss

Types

The genus of bacteria known as Mycobacterium contains bacteria that can cause illness in a great variety of animals, including humans. The most common variety of Mycobacterium to cause illness in birds is Mycobacterium avium; there are several notable subcategories of M. avium that can cause disease; all can lead to avian tuberculosis. Although transmission between humans and birds is rare, avian tuberculosis can also infect humans who are immunocompromised either through age or disease. Tuberculosis in humans is caused by the Mycobacterium tuberculosis, which is also occasionally zoonotic, so humans with tuberculosis should avoid handling birds on a regular basis to avoid infecting them. Other varieties of Mycobacterium that are capable of triggering avian tuberculosis include M. intracellulare, M. bovis, and M. genavense.

Causes of Mycobacterium Infections in Birds

Mycobacterium infections are highly contagious and are shed in large amounts from the infected animal into the environment around it both through organisms thrown up into the air and through the bacterium shed in the feces. Birds may also become infected from contaminated water and food sources. Some forms of mycobacteria infections can be transferred between humans and avians, but the transfer rates are very low. People with diseases that compromise the immune system, the elderly, and the very young are more likely to contract these infections.

Diagnosis of Mycobacterium Infections in Birds

In many cases, birds are capable of hiding this disease until it is late in the course of the disease. This means that avian tuberculosis is often diagnosed posthumously when lesions are found on the liver, spleen, lungs, or kidneys. When you have a bird that is showing symptoms of Mycobacterium infection or that has been exposed to a bird that was diagnosed with avian tuberculosis, the visit to the avian veterinarian will generally start with a complete physical examination. 

The patient will be weighed and measured and then examined from head to toe. The bird will also be checked for the proper functioning of the eyes, ears, and cere, and will have its skeletal system and musculature evaluated. Standard blood tests such as a complete blood count and biochemical profile may indicate that an infection is present, due to an increased level of white blood cells. If infection by Mycobacterium is suspected, there are several tests available that can confirm their presence. These tests may include:

  • Agglutination test
  • Enzyme-linked immunosorbent assay (ELISA) 
  • Microscopic evaluation of infected tissues
  • Polymerase chain reaction (PCR) assay
  • Radiometric culture from tissue or feces

Treatment of Mycobacterium Infections in Birds

Treatment of this disease is challenging in the best of circumstances, and in cases where several birds are infected in a flock of poultry, destruction of the entire flock may be suggested. Mycobacterium are capable of living outside a host for quite some time, so the site where the flock was kept should be avoided for avian or porcine use for at least two years. In those situations where the infection is caught early in the course of the disease, and the animal or animals are able to be quarantined, antibiotic and antituberculosis will be started as soon as possible. 

There are a number of different medications that may be attempted, however, M. avium, in particular, is resistant to many of the drugs used to treat tuberculosis in humans. Your veterinarian will help you to choose the best combination of medications for your particular circumstances and treatment will generally continue for anywhere from six to eighteen months. Quarantine from other birds and susceptible humans should be maintained until the patient is certified free from the bacteria.

Recovery of Mycobacterium Infections in Birds

The prognosis for birds that are showing symptoms due to infection by mycobacterium is guarded at best. For the owners of birds who choose to treat them, not only is the treatment time lengthy, the medications that are required are often expensive. Mycobacterium are often resistant to treatment, so antibiotics and antituberculosis medications are often combined in groups of three or more in order to actually eradicate the disease. If the patient is to recover fully, the owner must adhere strictly to the treatment instructions given by the veterinarian, and ensure that all medications are given daily.