Mycobacterium Avium Complex (MAC) In Dogs

Mycobacterium avium complex is a hereditary flaw caused by a gene mutation that can be found in certain breed lines of the Miniature Schnauzer dog breed, which makes dogs with the flaw at risk of catching or developing a serious form of mycobacterial infection that other dogs are usually able to fight off successfully.

Mycobacterium avium infection is the result of this hereditary health problem, and this is a type of disease that runs a similar course to tuberculosis, and which is very serious and usually causes the death of the affected dog while they are still young.

The condition was first recognised in the miniature Schnauzer breed in America several years ago, but has now been identified in certain breed lines of miniature Schnauzers in this country too.

The Kennel Club, in conjunction with various miniature Schnauzer breed clubs in the UK, have now formally approved a DNA health testing scheme to permit breeders to find out their dogs’ status prior to making a mating match, in order to make an informed decision about breeding healthy dogs.

In this article, we will look at Mycobacterium avium complex health testing for dogs, and how the Mycobacterium avium infection that this disorder causes affects dogs. Read on to learn more.

Mycobacterium avium complex and Mycobacterium avium infection

Understanding how it is possible to perform a DNA test for a health condition that is ultimately caused by an infection is the first step to understanding the condition, and its impact on and risk for dogs. Mycobacterium avium infection itself is an illness that develops from exposure to Mycobacterium-a type of bacteria-which leads to symptoms and effects of the tuberculosis type.

However, this bacteria is highly unlikely to make most dogs ill, even if they are exposed to the bacteria (which is very common in the environment), because their bodies defend against it. But dogs that have Mycobacterium avium complex suffer from a genetic mutation or hereditary flaw that affects their ability to defend against the bacteria, in turn causing them to develop the infection. Mycobacterium is widely found in the environment, and so exposure cannot realistically be avoided.

What sort of dogs are at risk of the condition?

Mycobacterium avium complex is a hereditary disorder or gene fault that has been found within some dogs of the miniature Schnauzer breed, and which affects both sexes equally. The condition usually presents in dogs aged anywhere between ten months and three years of age, although the condition generally becomes apparent whilst the dog in question is still reasonably young.

Sadly, the infection usually proves fatal in affected dogs at a young age.

Implications for other species-including humans

Most readers will have picked up on the references within this guide to the fact that Mycobacterium avium infection is a type of tuberculosis-which is of course an illness that humans can catch as well.

Research and studies into Mycobacterium avium indicates that the condition has all the markers of being zoonotic-which means a condition that can jump species and be passed from certain species of animals to other types of animals, including humans.

This theoretically poses a potential risk for people with compromised immune systems such as elderly and people and those with immune disorders, however, at the time of writing there have been no recorded cases of Mycobacterium avium infections being passed from a dog to a person.

The symptoms of Mycobacterium avium infection in dogs

Dogs that inherit Mycobacterium avium complex generally show signs of infection between the ages of ten months and three years of age.

Enlarged lymph nodes is the first warning sign, and the bacteria goes on to infect the spleen and liver, causing both organs to become enlarged too. Owners at home may see early symptoms such as a high temperature, pale mucous membranes, loss of appetite, frequent vomiting, and exercise intolerance. Some dogs will also suffer from diarrhoea, bloody stools and potentially, a discharge from the eyes and nose.

Most dogs with the condition will feel generally unwell, and may be reluctant to play and exercise.

In order to diagnose the condition, generally a fine needle aspirate or biopsy of the lymph nodes is performed to identify the changes that the infection causes at a cellular level.

How is the disorder transmitted?

Mycobacterium avium complex is hereditary, but the exact form of heredity is unknown; current research indicates that the disorder is likely to be passed from dog to dog by means of autosomal recessive heredity, meaning that some dogs may be carriers of the condition whilst being unaffected themselves.

However, this is by no means a given at this stage-there is also a possibility that the condition is passed on by means of polygenic heredity, which means that more than one gene is involved in the transmission of the condition, making it harder to identify and pinpoint the risk factors or combination of gene mutations required to cause the condition.

DNA testing for Mycobacterium avium complex

In order to identify whether or not any given miniature Schnauzer may be a carrier of Mycobacterium avium complex, a DNA test can be performed to return the dog’s status. This result will identify whether the dog is clear, a carrier, or affected.

It does not indicate whether or not the dog has Mycobacterium avium infection-this is the disease that the Mycobacterium avium complex gene fault causes, and not the genetic fault itself.

The Kennel Club now holds a database of DNA testing results for registered pedigree miniature Schnauzers, and breeders are advised to test their own dogs and submit their results for inclusion.

Potential buyers of miniature Schnauzer puppies are advised to ask breeders about test results for their own dogs, and choose a breeder that takes part in health screening and can show proof of the results.