Titers Part Two: Immunity Without Vaccination?
In my previous blog, I shared the basics of titer testing (click here to read if you missed it). A titer test for distemper and parvovirus is an essential part of my preventative dog health program. Rabies titers are also useful in many cases, but are not yet legally accepted as proof of immunity in many jurisdictions. Hopefully they will be in the future, as laws catch up with science.
Two key terms that are sometimes confused by both owners and veterinarians are immunity and vaccination. Vaccination is the administration of antigenic material (vaccine) to stimulate an individual’s immune system to develop adaptive immunity to a pathogen. Immunity is defined as the ability of an organism to resist a particular infection or toxin by the action of specific antibodies or sensitized white blood cells. Vaccination does not automatically give dog immunity – the dog’s immune system must respond to the vaccine and produce antibodies and memory cells to become immune. But what about the opposite – can a dog be immune without a vaccination?
While you may be thinking of course not, I bet a large percentage of readers are walking examples of immunity without vaccination. Did you get measles mumps as a child? If so, having the disease caused your immune system to develop antibodies so you will not get measles or mumps again. In the dog, having kennel cough can stimulate immunity to the particular strains involved in the particular case. However, because kennel cough can be caused by any number of different bacteria and viruses, a dog does not become completely immune.
Another way a dog can develop immunity without being vaccinated is by low level natural exposure. I experienced this with my own dogs when I was working at a busy animal shelter. My dogs came to work with me, and stayed in my office. My office was between the stray dog holding area and the intake area. Many dogs with kennel cough and other diseases passed in front of my door. My dogs were exposed, but in tiny increments over time (through whatever airborne germs passed under the door as a dog coughed in the hallway). This allowed them to become immune, despite not having been vaccinated against kennel cough.
Along that same line of thinking, I wondered if dogs could develop immunity by exposure to the virus that is shed by a dog that has been recently vaccinated. Today’s distemper parvovirus vaccines (DAP, or DAPP) are what we call infectious or modified live vaccines. The virus in the vaccines has been weakened so it will not cause disease, but it reproduces and spreads in the dog’s body just like the disease causing virus. This is a key reason why it produces such a long-lived response – it’s as close to getting the disease as you can get, which can produce lifelong immunity (like having measles and mumps in humans).
To test this theory, submitted distemper parvovirus titers on my 15 month old puppies, Fame and Flair. They have been vaccinated only against rabies. They attend a doggie daycare that has a variety of dogs, many of which are conventionally and frequently vaccinated. They also come to the veterinary hospital occasionally.
As discussed in my previous blog, as well as widely shared by Dr. Ron Schultz, any measurable titer means that memory cells have been produced. This implies immunity. Most laboratories will have a “minimum” amount of antibodies that they feel assures immunity. For Kansas State’s laboratory, that amount is 1:32 for distemper and 1:80 for parvovirus. (Remember a titer is measured by dilution, so the lower the ratio, the higher the level of antibody present).
Fame and Flair tested at 1:2 and 1:4 for distemper antibody levels. These are low values, but they are measurable, suggesting that memory cells have been produced. The question is, were enough produced by this small response to ensure protection in the face of exposure? Distemper is not a threat in my area at this time – in fact I’ve been blessed to never have seen a case in over 25 years of practice. But it is still often seen in many parts of the country.
Fame and Flair had the same titer response for parvovirus – 1:40. The laboratory minimum for protection is 1:80, or just one more dilution beyond their result. This is much more suggestive of an adequate immune response, including memory cell production. But again, as we have no way to measure them, no one can say for sure if there are enough to be fully protective in the face of exposure. Parvovirus, while less common than in the past, is still seen everywhere. Our current vaccines for parvovirus are extremely effective, and I theorize are shed more by dogs that have been recently vaccinated, leading to my dogs’ exposure and resulting titers.
I am currently consulting with my favorite experts as to what to do with these results, and how best to followup with Fame and Flair. Statistically speaking, with only two dogs, no definitive conclusions can be drawn. I’ll be sharing the thoughts of my experts as well as the future plan in an upcoming blog.
Looking for the link to my current vaccine protocol? Click here.