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Health Issues In Toy Dogs
New Approach to Vaccination of the Canine
by Leanne Bertani, MD 2001
For years, it was believed that annual vaccinations for viral diseases were necessary to keep our beloved companions out of
harm's way. But we have recently come to a turning point in vaccination of the canine. While we are greatful for protection
from diseases such as distemper and parvovirus, there is growing realization that vaccination is not always benign.
In 1996, a study was published suggesting an association between vaccination and autoimmune disease, specifically autoimmune
hemolytic anemia, an often fatal destruction of red blood cells.(1) This was followed by another study that demonstrated that
dogs may develop an autoimmune response after vaccination.(2) In 1998, the American Association of Feline Practitioners
responded to the increasing incidence of vaccine-induced fibrosarcomas in cats by changing the recommendation for feline
distemper vaccination from annually to every three years.
These events, coupled with the knowledge that some vaccinations for viral diseases may protect for seven or more years, have
caused veterinarians and dog breeders alike to begin to ask, "Are we vaccinating too much?"
Duration of Immunity for Common Vaccines
Studies have shown that, once fully immunized, more than 90% of canines retain immunity to Parvovirus-2 and Adenovirus-2 for more
than seven years. (Full immunization may not take place with vaccinations administered prior to 16 weeks, due to interference by
maternal antibodies.) Immunization to Distemper may last up to 15 years, and immunization to Coronavirus probably lasts a
lifetime. Immunization to Rabies and Parainfluenza lasts about 3 years in about 80-85% of dogs. Note that proven duration of
immunity may vary dependent on the type of vaccination used; for instance, modified live parvovirus demonstrated a longer
duration of immunity than killed virus; one strain of distemper tested for a longer duration than another. New recombinant
vaccines may be more efficient and produce a longer-lasting immunity.
Other vaccines, particularly the bacterial ones, are less durable. Some vaccines to Bordetella may last less than a year and
are probably only effective in about 70% of dogs. Sufficient data on Leptospira, Borrelia (Lyme) and Giardia vaccine is not
available to suggest immunization lasting much longer than a year.(4)
Progress in the Veterinary Community
The American Veterinary Medical Association Council on Biologic and Therapeutic Agents published immunization recommendations for
dogs and cats in 1989, suggesting annual revaccination. The companies that produce the vaccines also suggest annual
revaccination. A study published in 1998 found that 27% of vaccinated dogs had a less-than-protective CPV titer, and 21% of dogs
had a less-than-protective CDV titer, and summarized that the current practice of annual revaccination of dogs against CPV and
CDV infection should be maintained. (5) (Critics of that study argue that authors used CDV antibody titers that are inconsistent
with sterilizing immunity and don't take into consideration that those dogs with lower titers will be protected from disease but
not infection.)
With the above in mind, it was understandable that veterinarians were reluctant to buck tradition, as the legal community
generally compares medical practice to the "standard of care".
But the vaccination revolution received a couple big pushes in 2001. The January 2001 issue of The Veterinary Clinics of North
America (Small Animal Practice) featured vaccinations and discussed the need for reconsidering traditional annual vaccinations.
A chapter author, Dr. Ronald Schultz, Professor & Chair at the University of Wisconsin, says that their Veterinary Medical
Teaching Hospital has been on an "every three or more" year vaccination schedule for cats and dogs for over four years.
"The goal for the future should be to vaccinate more animals than are now vaccinated but to vaccinate those animals less
often and only with the products that the animal needs," says Dr. Schultz.
Another advance came in April 2001, when the American Veterinary Medical Association Executive Board approved the Council on
Biological Therapeutics new "Principles of Vaccination." This statement was published in the Journal of the American
Veterinary Medical Association on September 1, 2001. The principles state that "unnecessary stimulation of the immune
system does not result in enhanced disease resistance and may increase the risk of adverse post-vaccination events." It
recommended that veterinarians create "core" and "non-core" vaccination programs (see below for examples),
and that vaccine schedules be tailored to the needs of each specific animal.
High Priority ("Core") Vaccines
The high-priority vaccines are those protecting against diseases that are of greatest risk to the dogs or to public health, and
those that carry a large benefit-risk ratio. Possible vaccines that might be included in many core programs would include:
Minimalist Approach
Like many decisions, the vaccination decision comes down to risk versus benefit. The absolute minimum requirement would be
vaccination with the high priority vaccines at least one time after the age of 4 months, and revaccination with rabies vaccine
according to area law. Using this minimalist approach, a dog living in a rabies-free area may only have one injection in its
entire life. This approach might be useful in families of dogs that are at risk for adverse reactions to vaccines such as
anaphylaxis or autoimmune disease.
But the minimalist approach is risky. Knowing that the parvovirus vaccine is over 90% effective is not much comfort if you are
in the small percentage whose dog is unprotected and that dog brings it home to your puppies. Then there is always the worry
that some puppies will be contract disease between the ages of 6-12 weeks, when protection by maternal antibodies begins to
wane. And there are some breeds that don't appear to "immunize easily" (Dobermans, Rottweilers). There is concern
that the initial vaccines may not be effective due to poor handling or other reasons, and that extra vaccines are necessary for
"insurance". There is also concern that without the vaccines to draw pet owners in for annual veterinary visits,
life-threatening conditions may go unnoticed.
Titers
Titer tests (blood tests to attempt to determine the dog's level of immunization) are also becoming more common, but are
inconvenient and expensive in some areas, and remain somewhat controversial.
As yet, there is no consensus on the usefulness of titers. Critics point out that there have been no studies to determine what
levels actually confer protection from disease, or if there is even a correlation between antibody levels and susceptibility to
disease. Some maintain that there is a difference between protection from infection, and protection from disease. Also somewhat
suspect is the lack of standardization for tests determining antibody concentration.
Dr. Richard Ford, of North Carolina State University, states, "The risk lies in the fact that a single serum sample divided
three times and sent to three different laboratories is quite likely to yield three different titers, and quite possibly three
different interpretations. What may be deemed 'protective' by one laboratory could well be labeled 'susceptible' by another.
Furthermore, it is important to note that a vaccinated dog or cat that does not have a significant concentration of antibody
may, in fact, have excellent immunity. A 'negative' antibody titer does not necessarily correlate with susceptibility to
infection. Likewise, the presence of antibody, even at high levels, does not guarantee immunity subsequent to exposure.(6)
At this point, the biggest role of the titer may be merely to convince boarding clinics or show committees that the animal
doesn't require its annual vaccination. It is likely that titer testing will receive greater utilization in the future, but
further studies are obviously needed.
Sample Core Protocols: 1998 Colorado State University Protocol
Some universities have already developed new vaccination programs. One of these is Colorado State University. (7) Their 1998 core
recommendation is a standard three shot series at 8, 12, and 16 weeks of age, including parvovirus, adenovirus 2, parainfluenza,
distemper. A rabies vaccine was recommended after 16 weeks of age. Following the initial puppy immunization series, dogs would
be boostered one year later and then every three years thereafter for the above diseases. Bordetella vaccine was recommended at
least 72 hours prior to possible exposure (dog show, trip to boarding kennel) and could be repeated every two to four months.
The summary is below:
Dr Dodds
Some veterinarians, such as Jean Dodds, DVM, recommend that vaccines be given separately if possible, to minimize the
consequences to the immune system. This is presently difficult, as most vaccines in the United States are only available in
combination (polyvalent) vaccinations – sometimes seven or eight in one injection! But there are a few that are available in
smaller combinations; her recommendations (as of 4/00) for dogs prone to autoimmune disease are below. (8) Dr. Dodds also
recommends that vaccination be avoided during estrus, pregnancy or lactation.
Breeders' Compromise
Because of the fear of puppy mortality from distemper and parvo, many breeders still give annual distemper and parvo vaccinations
to dogs and bitches being bred or shown, but more and more are choosing to discontinue vaccinations for viral diseases at the
time the bitches are retired, with the exception of rabies where required by law.
The Lower-priority (non-core) Vaccines
Again it comes down to risk vs benefit. Killed vaccines are more risky in the short term, ie, more likely to cause immediate
adverse reactions (anaphylaxis/anaphylactic shock) than live vaccines, and bacterial vaccines more risky than viral ones. Those
generalities would denote Leptospira (killed bacterial) as the most likely of the commonly used vaccines to cause anaphylaxis,
followed by Borrelia/Lyme's Disease (killed/recombinant bacterial), and Rabies (killed viral), Corona and Bordetella. Corona is
available as modified live viral, but the killed viral preparation is commonly used. Bordetella bronchiseptica is a bacterial
vaccine, available as modified live and killed; the nasal preparation is thought to have the highest benefit-risk ratio.
The Leptospirosis vaccine is a controversial one. Leptospirosis is an important disease because it can be transmitted to man and
some other animals, and can cause severe kidney disease. As mentioned above, it is one of the vaccines most likely to cause a
fatal anaphylaxis in puppies, so many breeders just don't give it. Until recently, the vaccine only covered two serovars and
was effective in less than 50-75% of dogs that received the vaccine. But two more serovars have been recently added, and
leptospirosis has become endemic in some areas. Therefore, the decision to include Leptospira will have to be made on the basis
of its presence in the dog's area, as well as the future performance of the two new serovars.
The value of the Canine Coronavirus vaccine is also controversial. Some authors go as far as to say that it is not needed.
Corona is a highly contagious virus, but one that rarely causes death in an adult dog. It may cause protracted diarrhea, though,
and can be fatal to puppies, so the decision on whether or not to vaccinate for Coronavirus probably depends on how much exposure
your dogs have to outside dogs, and also whether or not you raise puppies in your home. Many breeders choose to vaccinate their
adults just one time in hopes that it will decrease the possibility that they will bring the Coronavirus home to their puppies.
Vaccinations for Borrelia/Lyme's Disease and Giardia are generally not necessary for the large population of toy dogs that spend
most of their time on the couch. But some of the sportier toys and those in endemic areas may be vulnerable, so it is best to
consult with your veterinarian and possibly the Public Health Department in making decisions regarding Leptospira, Borrelia,
Corona, and Giardia vaccines.
Bordetella bronchiseptica is a bacteria that causes infection of the trachea and bronchi; the infection is commonly called
"kennel cough", and is kin to the human "whooping cough". The Bordetella bronchiseptica vaccine is often
given when dogs are likely to be exposed to large numbers of other dogs, such as a dog show or boarding kennel. It is available
both as injection and as a nasal inhalant. The inhalant vaccine is thought to be less likely to cause a severe reaction, and
also to have less interference by immunity from colostrum. Immunization to Parainfluenza and CAV-2 is thought to enhance the
protection of the Bordetella vaccine. Unfortunately, the Bordetella vaccine is not one of the more efficient ones, having a short
duration and about a 70% protection rate, but I expect we will have more efficient vaccines in the future.
Considerations for Toy Breeds
It does appear that toy breeds may have more adverse reactions to vaccines, so a less-frequent vaccination schedule may be of
particular benefit to this group. The most frightening response is severe anaphylaxis, most common after killed bacterial
vaccines such as leptospirosis. There are some vets who will not give a leptospirosis vaccine to a dog under ten pounds for this
reason.
The one milliliter dose volume listed on most vaccine labels is recommended because that was the volume tested during the
licensing process. During the efficacy testing, the issue of breed was ignored. Consequently, we really don't have studies to
tell us if the Toy Poodle should get the same volume as the Great Dane. Although a natural inclination would be to halve the
dose for toy breeds, there is little or no scientific data to back up that recommendation.
Human studies, though, advise against decreasing dosage on the basis of size. In a study of premature babies given half of a
DTP vaccination, those babies did not appear to develop an adequate immune response to Pertussis. (9)
A common compromise used by breeders is to halve the dose of the vaccination during the initial puppy series, giving a full
dose after 16 weeks. Leptospirosis is usually omitted until after a year of age, or omitted entirely, unless there is local
concern about the disease. This may change after the performance of the new vaccine is evaluated.
The future
The veterinary community is somewhat hampered by lack of adequate funding for the research needed, but the future should bring
more efficient vaccines. Instead of modified-live virus, we will probably have vaccines available made from recombinant DNA.
We may also see more nasal vaccines, which may be less likely to cause adverse reactions. Hopefully, more work will be done to
correlate antibody titers with immunization to clinical disease. It would also be nice to see some studies done comparing the
prevalence of autoimmune disease between groups of annually-vaccinated dogs, and dogs vaccinated less frequently under the new
proposals. And of course, there will need to be more studies regarding the actual duration of immunity following vaccination.
We can help by encouraging our breed clubs to contribute to funding of veterinary research.
Questions regarding the article may be directed to
The above article is merely an exploration of changing trends in vaccination and should not be misconstrued as advice. Consult
your veterinarian before making changes in your vaccination program.
References:
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