By identifying carriers of the disease at a very early stages of infection, Actiphage enables disease management through the removal of these animals from the herd or prior to movement.
It also supports the introduction of a vaccine which would provide the ultimate protection for herds.
Current test of bTB lacks sensitivity
The primary screening test for tuberculosis in cattle is the Single Intradermal Comparative Tuberculin Test (SICTT) – a tuberculin skin test that detects the presence of a mycobacterial immune response in the animal.
For this test, a veterinarian injects a small amount of Avian and Bovine tuberculin into a fold of skin to see if there is an immunologic reaction. If the animal is infected a localised swelling can be detected three days later.
The test is thought to be only 50-60% effective, takes three days to produce a result, requires at least two visits by a vet and cannot distinguish between infected and vaccinated cattle, thus removing vaccination as a potential control mechanism.
Clinical tests are defined by two measures, specificity and sensitivity. The UK Government estimates the accuracy of the SICTT skin test to be:
- Specificity 99.98% – the ability of the test to correctly reject healthy animals that don’t have bovine tuberculosis.
- Sensitivity 50 -90% – the ability of the test to correctly identify animals that are infected with the disease.
Therefore, for a herd with a hundred cows infected with bTB, the SICCT test could miss up to 50, leaving behind a reservoir of infection.Another issue is that SICCT measures the immune response of the animal, rather than detecting the presence of the mycobacteria and actual infection. Therefore, the skin test may miss cattle that are in the early stages of infection and have not yet developed a strong immune response to it, and also give a false positive to animals that have been vaccinated.
Greater sensitivity with Actiphage
A survey using Actiphage of 41 SICTT-positive UK cattle tested at slaughter found live M.bovis in the blood of all animals with visible lesions (13/13) and in 93% (26/28) of animals with no visible lesions (NVL) following post-mortem examination.
This study confirms that relative to SICCT, Actiphage has a sensitivity of 95% and a specificity of 100%.
Further laboratory verification work is being undertaken to prepare for validation to World Organisation for Animal Health (OIE) guidelines.