TB comes in small packages too

Dr. Cindy Bell Diagnostic Pathologist DVM, University of Wisconsin-Madison 2008 Diplomate ACVP
Dr. Cindy Bell
Diagnostic Pathologist
DVM, University of Wisconsin-Madison 2008
Diplomate ACVP

 

TB comes in small packages too

By C. Bell, DVM, DACVP

Strange as it is, one species that the pathologists at WVDL autopsy fairly frequently is the Budgerigar….you know, Budgies….“parakeets”…..those fairly inexpensive but attractive small versions of parrots.  Like parrots, they belong to the family of birds called psittacines.  Many older budgerigars we see have cancer, frequently of the reproductive tract.  In fact, ovarian carcinoma occurs in aged females of many species of birds.  I and others happen to think that it is an underexplored animal model for human ovarian cancer.   But I digress….the most memorable budgerigar autopsy that I have performed was not a cancer case.  While performing this particular autopsy, which is a “gross” post-mortem examination, I saw no tumor, no evidence of disease, not a single clue as to why the bird was sick and died.

This happens to pathologists a lot, but we don’t despair.  “That is why God created a microscope,” says an old pathologist friend, meaning that we perform histopathology, a “microscopic” post-mortem examination.  As I was looking at the glass microscope slides of this little bird’s tissues, I saw something that was not readily recognizable as a particular organ.  There were large cells, and these cells were stuffed full of something….something very small and very hard to see.  I had a hunch.  I ordered a special acid fast slide to be made, which made the little rod bacteria within the cells stand out like hot flamingo-pink confetti.  The cells were stuffed with these “acid fast bacilli” bacteria and the tissue was the sorry remains of this bird’s adrenal gland.

Although not strictly accurate, “acid fast bacilli” is synonymous with bacteria of the genus Mycobacterium.  The most famous is Mycobacterium tuberculosis, the case of Tuberculosis in humans.  There are many other species, some more important than others.  Mycobacterium bovis is the cause of Bovine Tuberculosis, a disease for which we monitor and hope not to see in Wisconsin.  Mycobacterium paratuberculosis causes Johnes Disease in ruminants.  There are other Mycobacterium species and subgroups.  Each tends to have a predilection for a certain group of animal ( birds, rodents, aquatic animals, etc.) yet has the potential to infect a broad range of species, including humans.   Immune-suppressed or immune-compromised humans are most at risk.  As a percentage of our modern population, this group of people is large and continues to grow each year.  Included are people with AIDS, transplant recipients, chemotherapy patients, and people treated for a broad array of immune system disorders.  A final key fact about Mycobacterium is that infections are very difficult to detect and may be impossible to cure.

So, there was my budgie with a Mycobacterium infection, an infection that is not particularly rare in birds, reptiles, aquatic animals, and even some mammals.  Nevertheless, I called the veterinarian who had submitted the bird to WVDL for diagnosis.  After contacting the bird’s owner, the submitting veterinarian and I were again on the phone discussing the implications of the bird having come from a household that included 1. Another bird and, 2. A human family member with a chronic disease condition.  Ultimately, the WVDL sent tissue to the National Veterinary Services Laboratory in Ames, IA.  There, they identified the species of Mycobacterium in the bird.  Fortunately, it was not Mycobacterium tuberculosis or another species known to typically infect humans.  However, the other bird in the household was likely to harbor the infection even if it never got sick, leaving the family with a tough decision regarding the future of the remaining pet bird.