Mycobacterium Avian Complex (MAC)


Health Matters – update August 2012

Since our early report (in 2009) about MAC, little seems to have developed until fairly recently when the internet exploded with ‘information’.

You may recall that 51 Miniatures (mainly American dogs, including 2 in the UK) had been diagnosed with this condition and all (every single one) could be traced back to one American dog. This number now seems to be increasing. You may also recall we had been in contact with Urs Giger who had undertaken some research into the condition and had arranged for a DNA sample of one of the UK affected to be collected by him from the Animal Health Trust.

The condition is usually fatal at a very early age, although one of the UK dogs lived until he was 5 years old. `MAC’ is a type of tuberculosis and is believed to be zoonotic (able to cross species). Very young children, immune-compromised adults and elderly people are thought to be most at risk. However, there has been no case, not one, where the condition has been transmitted by a dog to a human.

The primary clinical sign of MAC infection is lymph node enlargement. The organisms infiltrate the liver and spleen, resulting in liver and spleen enlargement. The more common causes of generalized lymph node enlargement such as lymphoma may result in a misdiagnosis, unless a lymph node biopsy or aspirate is performed with an acid-fast stain to identify cellular changes characteristic of mycobacterial infection. Other clinical signs that may or may not be observed in all cases include lethargy, vomiting, lack of appetite, fever, lameness, blood in the stool, diarrhoea, pale mucous membranes, abdominal distension and eye or nasal discharge.

The American Miniature Schnauzer Club (AMSC) and a group of other breeders throughout the world (including some in the UK) thought that ‘Relative Pedigree Analysis’ (RPA) could work out a likelihood of carrier status. They believed that their ‘experience’ could work out which dogs or bitches were likely to be carriers and which were not. To some of us, especially those closely involved with eye conditions, this always sounded a bit optimistic and complacent.

The AMSC Health Committee has just announced, and requested we publish, the following statement:

“…that Relative Pedigree Analyses like that which we were doing, will no longer be done at Dr Jerold Bell’s direction. Dr Jerold Bell has spoken to Dr. Giger who has confirmed that there has been no definitive conclusion regarding the mode of inheritance for MAC and indeed it is unknown whether it is fully penetrant. Since the Mode of transmission is unknown, Relative Pedigree Analyses is inappropriate according to Dr Bell and therefore we will be suspending pedigree analyses indefinitely until we have more information”.

So our advice must be, as with any situation relating to inherited conditions, breeders should make themselves as fully aware as possible, of the breeding lines they are considering, but especially before using dogs or bitches who may be ‘new’ to the UK. We would expect any caring breeder to be aware of this condition and also know those dogs, believed by both Urs Giger and the AMSC Health Committee, to be primarily implicated in its transmission. We would also urge stud dog owners to be absolutely transparent with any breeder who considers using their dog.

Even with eye conditions, similar care needs to be exercised, as it’s apparent that overseas breeders do not screen litters for Congenital Hereditary Cataract in the same way as we do in the UK and testing for the older-onset condition (HC) seems less rigorous than the UK Eye Scheme.

Dr Urs Giger MS FVH Dipl. ACVIM & ECVIM (Internal Medicine) Dipl. ECVCP (Clinical Pathology) is Charlotte Newton Sheppard Professor of Medicine at School of Veterinary Medicine, University of Pennsylvania

Dr Jerold Bell DVM, Clinical Associate Professor. Department of Clinical Sciences, Cummings School of Veterinary Medicine, Tufts university