Antibody titers are available for the major infectious diseases of dogs and cats, including distemper, parvovirus, panleukopenia, calicivirus, herpesvirus, and rabies. The purpose of running an antibody titer is to verify that the animal has an objective measure of immunity to the disease in question. The titer itself is a blood test, so your vet will draw a blood sample from your pet and send it to a laboratory. The lab determines the greatest dilution at which antibodies to the disease in question can still be found. The laboratory also determines a dilution below which (they suggest) your pet will not have enough antibodies should it encounter the disease.

Now, titer results bear interpretation. It is not realistic to say that if there aren’t enough antibodies, or any measurable antibodies, then there is no immunity. Immunity to disease doesn’t work that way. This is why a titer test should not be used as a screening tool to determine whether your pet needs to be revaccinated.

For example, I have been vaccinated against polio three times in my life, the last time being 27 years ago. Do I have antibodies to polio in my blood right now? I hope not! What a waste of resources for my body to be busy making antibodies against a disease I will likely never encounter. Could I make antibodies to polio if I needed to? Sure, in a fraction of a second. This is why we have whole parts of the immune system devoted to remembering pathogens that we have met previously.

When I do titer tests on dogs for distemper and parvovirus, a very common result is that the dog has a low titer for distemper and a high titer for parvo. Sometimes there is no measurable distemper titer, but almost always that high parvo titer shows up. Why is that?

Parvo is a very stable virus that lasts practically forever in the environment. It is present wherever dogs have been. When dogs are vaccinated against parvo, they shed the virus in their feces for approximately 3 weeks afterwards. Therefore the virus is constantly being renewed in the environment as well. If you take your dog to a public park, parvovirus is there. If the people who lived in your house before you had a dog, parvovirus is there. This means that there is constant exposure and re-exposure to the virus.

Distemper, on the other hand, doesn’t last long outside the dog. Dogs need close contact to transmit distemper. They need to cough on each other and breathe in each other’s faces. Distemper is no longer a common disease outside of the vaccine, so there isn’t the routine exposure like dogs have with parvovirus. I have seen and treated many cases of parvo in my 18-year career as a veterinarian, but only one case of distemper (and that was vaccine-induced).

All this means that your dog might have a low or even not a measurable titer to distemper. Then how do you know whether they are immune? It’s difficult to know. There is also a possibility that the dog did not respond to the vaccine as desired and did not produce antibodies. Will giving another vaccine booster force the dog’s immune system to produce antibodies? Nobody knows.  

So this is the challenge with vaccine titer testing. We love it when test results are clear cut, and yes means yes and no means no. Unfortunately that is not the case with titers.

When I interpret these results, I think that any measurable antibody is a positive result, even if it doesn’t meet the laboratory standard for a “protective titer.” If you can produce one antibody, you can likely produce trillions (or however many it would take to fight off a disease) in nanoseconds. If you have no measurable titer, then the answer is unknown.

As far as I can tell, one antibody titer should be sufficient for the animal’s lifetime. Once you have proven your body’s ability to produce antibodies, you will always be able to. Even quite unhealthy animals and people will respond to vaccination with a positive titer, and this tells me that antibody production is quite easy for the body to do. Therefore, as long as you maintain a basic semblance of health and your immune system doesn’t self-destruct, you should be able to produce antibodies.

Please note that I am discussing viral diseases here, and that this information has no bearing on bacterial diseases, which are a whole other can of worms.

I was vaccinated for rabies in vet school, so likely about 20 years ago. Three or four years later I had my rabies titer checked, and it was high. Nobody ever sends me a postcard telling me to booster my vaccine, and I don’t ever need to check my titer again. It is good for life. And these vaccines likely provide our pets with lifelong immunity as well. For more information, check out the work done by Dr. Ron Schultz and Dr. Jean Dodds, and the Rabies Challenge Fund.