Why Aren't Titers Used in Lieu of Vaccines?

 |  May 12th 2009  |   5 Contributions


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Dr Barchas,

I was reading your post regarding lumps and injection sites. You mentioned using a minimal vaccination schedule for pets that experience these lumps. What is that minimal vaccine schedule? (I live in San Diego).

Also, I recently had my dog's blood titered for parvo, distemper, and rabies. The titers came back greater than 1:5. I didn't have this done through my Vet and he said they are of not much value as they can't guarantee that the dog has immunity. What are your thoughts on titers and whether or not they can used as data to suggest I don't need to vaccinate my pet against the diseases?

Randy
San Diego

A minimal vaccination schedule depends upon a dog's age and lifestyle. In a mature dog, a minimal vaccination schedule would mean avoiding optional injections such as the ones that protect against Bordetella, canine coronavirus, and probably leptospirosis (but talk to your vet about this one first--leptospirosis can spread to humans). Mature dogs generally need vaccines no more often than once every three years. In some cases it may be safe to push vaccines other than rabies (see my previous post) back to once every five years or longer. You will have to find a vet who will take the time to work with you to tailor a vaccine schedule that is appropriate for your dog.

Titers are blood tests that are performed to assess immunity. Titers measure a component of the immune system called antibodies that circulate in the blood. They are reported as a ratio of one to a number. The higher that number, the better. A titer of 1:5 is low. A titer of 1:1,000,000 is very high.

Your vet may have been concerned about using your dog's titers because the titers were low. Or, he may have been concerned by something else: nobody knows how to interpret titers. I am not aware of any studies that show what titer is required to prevent infection with rabies, distemper, or parvovirus. A low titer likely implies susceptibility to disease and a high titer likely implies immunity.

However, we do not know the most crucial piece of information that is necessary for interpreting titers. We do not know the minimum titer measurement that correlates with protection from disease.

There is another factor that complicates the use of titers. Titers measure only half of the immune system. Although it is very useful to know the quantity of antibodies circulating in the bloodstream, antibodies cannot work alone. They depend upon a different portion of the immune system (called cell-mediated immunity) to get the job done. At this time, I am not aware of any way to test cell-mediated immunity.

Consider this analogy. Antibodies are like foot soldiers in the battle against disease. Cell-mediated immunity represents logistics and weaponry. If your dog has a high titer against rabies, that is the equivalent to having a huge army of soldiers ready to battle the disease. But it matters whether the soldiers are armed with high caliber weapons and advanced communications, or whether they are disorganized and can fight only by throwing dirt clods.

Without the ability to measure cell-mediated immunity, one cannot truly know whether a pet is protected against the disease in question.

In general, high titers likely are correlated to strong cell-mediated immunity. I strongly believe that in the future either titers or other tests of immunity will supplant regular vaccinations in pets. I am confident (perhaps optimistic would be a better word) that in the next half decade we will see some major advances in immunology that will lead to decreased animal vaccinations and increased use of immunological assays.

But for now, although titers provide significant information, they do not look set to revolutionize veterinary medicine.

Photo: Jeffrey M. Vinocur

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