Vaccination test: Titers

Should I Titer TEST my dog?
If a Titer test will give you peace of mind, or help you make a vaccination decision about a puppy or a dog of unknown vaccine history, elderly dog, or dog with reactions to vaccinations, then it’s worth considering. Talk to your veterinarian to find out which vaccinations your STATE, COUNTY, or municipality will accept in titer form and which are required as vaccination given.

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. (source)

A titer is a measurement... of how much antibody, to a certain virus (or other antigen) is circulating in the blood at that moment in time.

Titers are usually expressed in a ratio, which is, how many times the blood can be diluted before the antibodies can no longer be detected. If a laboratory was able to dilute the blood two times, and then didn't find any more antibodies, that would be expressed as a titer of 1:2. If a laboratory was able to dilute the blood a thousand times, and then didn't find any more antibodies, that would be a titer of 1:1000.

It would be wonderful to be able to say that once a ratio dips below a certain level, it’s time to give another vaccination to boost immunity. But such thinking reflects an incorrect understanding of the immune response. Vaccines don’t inject immunity into a dog. Instead, they STIMULATE the immune system to form two kinds of cells, antibodies that fight the current infection, and memory cells that remain behind after the infection has been eradicated; to pump out more antibodies if the same virus is encountered in the future.

Memory cells persist for 20 years or more, and are not increased when the animal is re-vaccinated or re-exposed to the disease. The detection of antibodies in the bloodstream, (which is what a titer test does), tells us the stimulation process took place and the memory cells are present; but the absence of antibodies does not mean the memory cells are missing or that the dog is not immune. Veterinary immunologist Ian Tizard writes, "You can have a negative titer and if the pet is exposed, memory cells can respond within hours to regenerate enough antibodies for protective immunity." (Tizard, Ian R., Veterinary Immunology: An Introduction, 6th Ed, Saunders 2000)

What Titer Tests Are Good For
If you can’t “top off” your dog’s immunity to viruses with booster shots, and you can’t tell from the titer test if his or her immunity is waning, what could a titer test possibly be good for?

Titer tests are useful to breeders and the owners of young puppies.
Although a series of vaccines is typically given to puppies, this isn’t because a series is needed to produce an immune response. It’s done because some puppies don’t form immunity to the first vaccination, and would be unprotected if the next in the series were not administered. Puppies, like adult dogs, need one vaccine that took effect, what immunologists call a “single immunizing dose.” By checking your puppy’s titers two weeks after the first vaccinations are given, you can determine whether or not immunity formed. This enables you to avoid giving further vaccines that will provide no benefit to the puppy if he or she is already immune, as well as let you know you need to continue to protect your puppy from exposure to these diseases, if it turns out he or she did not form immunity from the first vaccinations.

It takes up to 14 days for the immune system to complete its response to a modified live virus vaccination for canine viruses. This process is called “seroconversion,” and in the vaccination stakes, it’s the brass ring. This means the dog has formed both antibodies and memory cells to those viruses. If you test the dog’s titer two weeks after vaccination, you can tell if he or she formed immunity to the virus.

If, however, the dog did not seroconvert after vaccination, this lets you know that the vaccine didn’t work; that is, it did not provoke the formation of immunity. This is usually because the puppy was too young, and his or her mother’s immunity was still present at a high enough level to prevent successful immunization. (Puppies acquire temporary immunity from their mothers after birth.)

In an adult dog or much older puppy, the reasons that vaccination fails to provoke immunity are usually related to the use of improperly stored, handled, shipped, or administered vaccines. Very rarely, the puppy or dog has a defective immune system and is incapable of seroconverting.

The Exceptions to the Rule
Titer testing is usually done in dogs for the common and deadly canine viruses, parvovirus (CPV) and distemper (CDV). Rabies titer testing is also done, usually for purposes of travel to foreign countries that require it. Some viruses have unusual antibody patterns (such as FIP in cats or HIV in humans), but we do not have vaccines for any diseases of this type in dogs. Also, bacterial antibodies differ from viral antibodies in a number of ways, and bacterial titer testing is typically done in veterinary medicine as a means of diagnosing acute illness, not monitoring vaccine response or ongoing immunity.

Should You Test?
It depends on your circumstances. Nearly all previously vaccinated adult dogs are immune to Parvovirus and Distemper. You cannot make an immune dog “more immune” to a particular strain of virus with additional vaccinations of that strain. (Dr. Schultz, Ronald D.)

Source: Titers and Canine Vaccination Decisions, by Christie Keith.