JUN 28, 2010
Thanks to the veterinary profession’s small animal contingent, the world has some new verbs: To "titer" or "titering," as in the act of submitting a blood sample to determine whether an animal has enough antibodies to ensure immunity against a particular disease.
The idea behind the surge in this verb’s popularity has to do with its use as a vaccine surrogate. So instead of receiving a vaccine against parvovirus this year, Fluffy will have her blood drawn and tested to see if her antibody levels against parvo are high enough for her immune system to overcome an attack of this virus, should she be exposed to it.
With the help of titers, animals need only receive their puppy/kitten vaccines, with the additional booster a year later, and from there on live forever free of the potential tyranny of a bad vaccine reaction. That is, as long as the antibody levels are demonstrably high, year after year.
Simple, right?
Not so fast. Here’s what I had to say about titers a couple of years ago:
"The idea is to lower a pet’s risk of exposure to too many vaccines … but is it really an effective way to measure protection against disease?
The experts seem to be of one mind on this: Titers are useful in legal and regulatory settings (for travel, for example) to determine whether an animal has ever received a vaccine for a disease like rabies. Titers do NOT, however, denote protection against a given disease.
This news may come as a shock to some of the more educated pet owners among you, much as it did to me when I began to pay attention to these experts. After all, I’d been extolling the virtues of titers on [this blog] and in my practice for years. It wasn’t easy to reverse course on my "progressive" titering habits, for which I felt some measure of self-congratulatory satisfaction.
Here’s some history for those of you who might not be privy to the bigger picture on titers:
Vaccines have been problematic for many years due our reliance on their incredible efficacy in reducing the incidence of diseases like rabies, feline leukemia and parvovirus. Veterinarians came to accept yearly vaccination as a no-brainer for its success in this department.
Nonetheless, the emergence of some very shocking vaccine-related illnesses (most notably, deadly vaccine associated sarcomas in cats) helped the profession discover what the human medical profession has always known: It’s better to vaccinate animals as minimally as necessary to protect them from disease.
That’s why task forces and committees were formed across the veterinary profession to determine safe and effective vaccine frequencies for pets. Fast-forward ten years later and most vets are aware of the widely recommended three-year vaccine protocols. But not all small animal vets have jumped on the bandwagon. Many vets fear the loss of income from annual vaccination while others are unconvinced of the efficacy of three year vaccines.
Me? I’m still concerned about safety, which is why I gravitated towards measuring titers in addition to the three-year protocol. Pets who had already been vaccinated twice in their lifetimes were offered the chance to skip the vaccine every third year as long as their titers on key diseases were up to snuff. Sure, it costs a little more than vaccines and requires a blood draw but it’s worth it, right?
Unfortunately, it was brought to my attention that this approach cannot possibly measure the true degree of protection conferred on an animal by vaccination. Even when I used excellent labs (like Cornell’s) to tell me the exact measure of antibodies for a given disease (as opposed to the more subjective and less expensive yes/no tests out there), I wasn’t receiving the true picture of a pet’s immunological status.
That’s because a titer only measures antibodies, not cell-mediated immunity, which is the real-world measure of protection. In fact, as I learned, pets can sometimes come up negative (unprotected) on the titers and still have plenty of perfectly protective, cell-mediated immunity.
Yes, titers can tell me that my patient has likely been vaccinated, especially when it comes to uncommon diseases like rabies (pets are not likely to have natural immunity from having been exposed to another rabid animal). That’s why so many countries require this test before traveling animals may enter. But the inability to say for certain that titers are protective and/or could NOT have come from real disease is what keeps other nations from rescinding their onerous quarantine requirements.
Since determining that titers aren’t exactly what most of us think they are, I’ve been reluctant to cave to owners’ demands that titers totally replace their vaccines. While I can understand the fear of vaccination, animals at risk should still be vaccinated.
How often? I wish I had a crystal ball and could make the decision better than a smart panel of immunologically inclined specialists…but I can’t. That’s why I’m still going with its recommendation to vaccinate every three years—unless my patients are sick, particularly sensitive or geriatric. In these latter cases owners are advised of their pets’ potentially increased risks due to our inability to measure their degree of vaccine protection.
Sure, it’s still every individual pet owner’s decision to make—after all, I’m not the enforcer of municipal vaccination requirements. But I do consider myself the backstop when it comes to advising my clients responsibly.
While titers may make it easier for me to sign off on a rabies certification requirements, I’ll no longer advise a client to consider a pet sufficiently vaccinated just because some lab said his antibody levels suggest that protection is likely. Nope. It simply lulls owners into a false sense of security.
(If it helps any, the American Animal Hospital Association [AAHA], the American Veterinary Medical Association [AVMA] and the American Association of Feline Practitioners [AAFP] are all on board with this view, too.)
Moreover, titering is expensive. If owners and veterinarians are using this information to make clinical decisions on vaccine timing and disease risk, I’d argue that it’s not worth the price. It just doesn’t tell us enough. In these cases titers are more likely a panacea to our fears than a tool worthy of investment. We vets have far better ways to spend your money … I promise."
Since this post, I’ve softened my stance somewhat. While everything I offered above is still true, I am using titers in many cases to help identify serious lapses in vaccine protection (as when we don’t know whether a pet is vaccinated or not) and because cell immunity and antibody immunity have been shown to roughly correlate. But to what extent we don’t know … and there’s the rub.
Vaccines to be safe. Titers to avoid the vaccines. Which is best? The world may never know. Sigh...
Dr. Patty Khuly
Pic of the day: "bloody needle" by Dirty Bunny
