A Candle in the Dark

A look on science, politics, religion and events

Killing Shambo

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Shambo is/was 6 year old bull, which tested positive in a skin test for exposure to the Bovine Tuberculosis bacteria.

The skin test injects the animal with a small sample of sterile tuberculin (both avian and bovine), and sees if the animal develops an allergic reaction as a result of the interaction of its immune system with the injected tuberculin1 .

If there is no reaction, then the result of the test is a negative, and the animal is spared and thought not to have the bacteria. If there is a reaction, the size of the swelling is analyzed and the animal is classified either as a “reactor”, or an “inconclusive reactor” where it is retested after 60 days.

This test is used worldwide and is an internationally accepted standard, because of the combination of low-cost and decent accuracy. The false positive rate, is around 1 in 10002. That is, when 1000 healthy animals are tested, one of them would be classified as a reactor. However, the positive predictive value3 depends on various factors, the most important being whether other animals in the herd were infected at the time of testing. Shambo tested positive as a reactor, and is therefore scheduled to be executed as a precaution against the spread of the disease.

Open and shut case? Hold on! There’s a slight complication here. The bull also happens to be sacred4!

I mean, people routinely ignore the slaughter of “normal” bulls which test positive, and indeed even the large number of religiously and politically motivated human slaughters which occur on an almost daily basis, but killing a sacred bull? Egads, how dare you cruel, heartless, animal hating, heathen humans kill a poor defenseless sacred bull which even has its own webcam? That totally goes against the beliefs, love, harmony, culture, tradition, respect for animals, blah blah that my religion preaches!!!

In my opinion, faith should may be tolerated as long as it doesn’t interfere with reality.

Yes, there is need for development of vaccines and more accurate testing and detection techniques. However, the rules are clear. If the current test says that the animal is probably infected with the bovine TB virus, you’ve got to kill it, like how you kill all other animals. Tough luck. Why does the magic wand of religion suddenly provide an alternate set of rules?

Notes
[1]- Bovine TB: The tuberculin skin test

[2]- http://www.defra.gov.uk/animalh/tb/pdf/tbinyh.pdf (pdf file)

[3]- This is not the same thing. Consider this example. Let there be an island where people are being tested for a disease X. Now, the equipment which detects the disease isn’t entirely reliable and is accurate 90% of the time (ie, it has a false positive of 10 in 100 healthy people and also detects the disease in 90 of 100 infected people). Now, if the actual rate of occurrence of the disease in the population is 10%, what is the probabilty that if you test positive for the disease you actually have the disease?

To find this, let’s assume that the island has 1000 people, and all the people are tested. From the occurrence rate of the disease, we know that 100 people have the disease. When these 100 people are tested, the equipment will detect 90 of them as true positives and fail to detect the other 10 infected. Further, when the 900 healthy people are tested, the equipment will detect 90 healthy people as false positives. So, the actual probability that you have the disease, even if you test positive, is only 50%!

In Shambo’s case, there are various factors which affect the how accurate the skin test is.

[4]- Whatever that means.

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Written by parseval

July 26, 2007 at 10:48 pm

Posted in animals, death, religion

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