Biobest Laboratories Ltd

Blood Test for Suspect Canine / Feline TB Cases

Diagnosis of Canine / Feline TB is challenging and usually based on suggestive histopathological changes in biopsies, the identification of acid fast bacteria, specialist culture and sometimes PCR. However culture is slow and some samples fail to grow and PCR can have relatively low sensitivity when few mycobacterial organisms are present.

The interferon gamma  test is intended to assist in the diagnosis of suspected canine and feline TB cases. The interferon gamma test can be useful in categorising cats and dogs with suggestive lesions. This in turn can inform decisions as to whether treatment is appropriate and whether it is necessary to report the case to AHVLA (Suspected Bovine TB is a notifiable disease in all mammals). There is also some evidence that the test can be used to monitor treatment, with responses falling in cats in remission. The test has been developed in collaboration with Professor Danielle Gunn-Moore of the University of Edinburgh and with the technical support of colleagues from  AHVLA.

The test method cultures feline peripheral blood mononuclear cells in 5 separate reactions with control materials and TB specific peptides. For this reason it is essential that at least 2ml of heparinised blood is submitted and at no point in the chain of submission is the sample chilled. Following incubation over 72 hours cultures are tested for the production of Interferon Gamma in response to the antigenic stimulation. 

The test will initially be performed on the 1st and 3rd Thursdays of each month at a cost of £200 per sample. Submitting vets and laboratories are requested to phone Biobest in order to discuss testing arrangements, samples should be collected on the Tuesday or Wednesday before the planned test day and sent to Biobest by overnight guaranteed delivery. Biobest can advise further on packaging to reduce the risk on chilling in inclement weather conditions if necessary. 

Summary Test Interpretation table

 

Test Results

Antigen Gamma Interferon Responses

 

 

 

 

Test Interpretation and Clinical Guidance

PPDA

PPDB

ESAT6/CFP10

 

+

 

-

-

Likely exposure to environmental Mycobacteria. Treatment for non-tuberculous mycobacteria can be considered*.

 

+ or -

 

+

-

Less-pathogenic TB complex**, most likely Mycobacterium microti in UK cats. Triple therapy treatment may reasonably be considered*. Some zoonotic implications.

 

+ or -

 

+

+

Pathogenic TB complex**, likely to be Mycobacterium bovis in UK cats or, very rarely, Mycobacterium tuberculosis. Evidence of a notifiable disease with significant zoonotic potential. Under certain circumstances treatment for M. boviscan be considered*.

 

 

* Treatment of feline mycobacteriosis is controversial as differentiation of disease caused by TB complex organisms and non-tuberculous mycobacteria cannot be made on clinical signs alone. Even when the organisms involved has been identified treatment typically involves 2-3 drugs for perhaps 6 months, with all the stress that involves to the cat and the owner, including the cost of the drugs and the monitoring, potential drug toxicity, and the likelihood that when disease is extensive control rather than cure may be all that can be achieved, and long-term therapy may be required. If you have not previously dealt with a case of feline mycobacterial disease, particularly if a member of the TB complex is involved, please contact Professor Danièlle Gunn-Moore (danielle.gunn-moore@ed.ac.uk) to discuss potential zoonotic risks, possible treatment options and likely prognosis. A list of references about feline mycobacterial disease within the UK is available on request.

** TB complex includes Mycobacterium tuberculosis, Mycobacterium bovis and Mycobacterium microti (the vole bacillus).

Please call or email Biobest if you would like to discuss the test or submit samples.

Submission forms can be downloaded here or by using the dropdown menu at the top of the page.