Testing Flowchart for Cattle, Goats, and Bison for Bovine TB
TESTING CATTLE GOATS,
and BISON for BOVINE TB
The flow chart describes the steps when testing for bovine TB in cattle, goats, and bison. The first test is the Caudal Fold Test, or CFT, in which a small amount of Purified Protein Derivative, or PPD, is injected at the fold of skin under the base of the tail. The test is read 72+/- 6 hours later. If the Caudal Fold Test is negative, no further action is required. If the animal responds, it is classified as a "Suspect" and requires further testing. Most of the animals tested will be negative on the Caudal Fold Test and will not need any further testing, however Johnes and avian TB may also cause a response.
If there is a response, the next test administered will be the Comparative Cervical Test, or CCT. It needs to be done within 10 days of the CFT. If the 10-day window is missed, the animal will be quarantined for a minimum of 60 days until the Comparative Cervical test can be administered. If there is no response, the animal is negative, no further action is required and the quarantine is lifted. If the animal has a response on the Comparative Cervical Test it is classified as either a "Suspect" or "Reactor" depending on the amount of response.
"Reactor" animals are ordered destroyed and must be examined for bovine TB via necropsy, the same as an autopsy in humans.
If the animal responds to the Comparative Cervical Test and the response is in-between negative and reactor it is classified as a "suspect". The producer may opt to have the suspect animal re-tested a second time with the Comparative Cervical Test after 60 days or have it examined for bovine TB via necropsy.
If the animal is negative on the second Comparative Cervical Test, no further action is required and the quarantine is released. If on the second Comparative Cervical Test the animal is again a "suspect" it is automatically reclassified as a "reactor" and ordered destroyed and examined.
If the CCT "suspect" animal is taken directly to the lab and there is no evidence of bovine TB after necropsy and histopathology, no further action is required and the quarantine is released.
Bovine TB cannot be definitely diagnosed without a necropsy and additional special testing (see Bovine TB in Michigan, A Guide for Livestock Producers). In addition to the necropsy, samples are taken for further tests including microbiology, molecular biology and histopathology.
"Reactor" animals require additional special testing to determine that no evidence of bovine TB exists. In addition, finding a "reactor" animal on a farm requires the whole herd to be re-tested a minimum of 60 days after the reactor is removed from the farm. The quarantine is not released until the whole herd tests negative for bovine TB.
If an individual animal in a herd is diagnosed with bovine TB, the entire herd is considered exposed to bovine TB. At this point, producers have two options: complete herd depopulation or a herd plan with an approved test and removal strategy. The decision is made jointly by the producer and appropriate agencies.
The bovine TB eradication project involves a multi-agency team of experts from the Michigan Departments of Agriculture, Natural Resources and Community Health; Michigan State University and the US Department of Agriculture. For additional information you may contact Kevin Kirk, Michigan Department of Agriculture Animal Health Liaison at 241-4339.