You’ve probably heard in the news about Geronimo the alpaca, whose owner has recently lost a three year battle against an order to euthanase him due to positive tuberculosis tests. So we asked farm vet Cassandra Longhi-Browne to look behind the headlines…
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The problems with tests
Not every test is perfect; there isn’t a single laboratory test that can achieve 100% certainty of a true positive or true negative; even the best ones can only achieve as high as 99.9% in either sensitivity or specificity, but not both. When you choose the most appropriate test to use to diagnose a specific disease, usually you need to make a compromise between the possibility of never getting a healthy animal wrong, plus a few false negatives (therefore letting go of truly infected animals), or finding all the infected animals plus a few false positives (therefore condemning animals that don’t have that disease).
This is a very hard and complex decision to make, one that usually sits in the hands of your vet. They can then weigh the pros and cons of each test. In certain cases though, when a zoonotic disease such as bovine tuberculosis (bTB) or one with high potential to become one (avian flu) is involved, the decisions about tests need to be taken by a higher authority, in order to protect not only the national herd/flock/etc, but also human public health.
Bovine TB
In the specific case of bTB, there used to be a time not that long ago when thousands of people died every year from it (and no doubt countless cattle and other animals, but nobody was keeping tally at the time). We did not have camelids in the UK back then – probably for the best, as they are highly susceptible to this disease and very good at transmitting it without showing many symptoms.
Geronimo the alpaca has reached national fame because of the contestations over his positive test results. As sad as it is, we need to try and look at the bigger picture. When it comes to zoonotic diseases in livestock, the national policy is very clear – if they show a positive result using the approved tests, they must be slaughtered. The positive test result does not tell you 100% if they are infected – it gives you a very high chance that they are; but public health cannot really take the risks. The risks are that the disease is really there, hiding, biding its time, slowly infecting not only other animals but people too.
Camelids and the law
Despite a bit of a grey area, camelids are considered livestock, not pets. Their keepers need to take this into consideration when they decide to adopt some. They are still relatively new to the UK and the diseases that are present here. As a result, owners need to be aware of the zoonotic risk, not just how cute they are. Approved tests are validated for use; they may not be perfect, but if they were picked it’s because there wasn’t a better alternative. They are also regularly reviewed on the basis of new scientific evidence. Lobbying for better tests is always a good idea. But do take into consideration that science takes time to develop. In the meantime, we cannot risk animals kicking around when they have a track record of positive results to the currently used tests.
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