Vaccine-Associated Sarcoma in Cats

A sarcoma is a cancer of the connective and soft tissues. Sarcomas are not a new form of cancer in cats. But in 1991, veterinarians began to notice a higher than expected number of sarcomas occurring in places where vaccines are commonly injected.

Subsequently, an association between vaccine administration and sarcoma development has been established. FeLV and rabies virus vaccines have more frequently been implicated in sarcoma development than have other vaccines. Both subcutaneous and intramuscular sites have been affected. Injections other than vaccines may also be implicated.

The increased appearance of these sarcomas roughly coincided with the change from using a modified-live rabies virus vaccine to an adjuvanted killed virus vaccine. At about the same time, an aluminum-adjuvanted FeLV vaccine was introduced. Adjuvants are added to vaccines to increase the immune response-especially in vaccines that use killed versions of a virus. Adjuvants in general, and aluminum adjuvants in particular, were therefore thought to be the culprit. However, researchers are no longer certain this is the case. It is believed that these vaccines cause some kind of inflammation at the vaccination site that, in some cases, is associated with sarcoma development, but an exact link has not been proven.

Nonetheless, vaccine manufacturers are developing recombinant vaccines that do not use adjuvant and that cause less inflammation at the vaccination site. Many modified-live virus vaccines are available for other viral diseases and some of them do not contain adjuvant. New vaccination guidelines try to minimize the number of injections given over a cat’s lifetime, as well, and also recommend specific sites on the body for injections to be given.

It’s important to remember that vaccine-associated sarcoma is still a very rare form of cancer. The occurrence rate varies from 1 in 1,000 to 1 in 10,000. The wide range seems to be associated with a genetic predisposition to this problem in certain cats and lines of cats. For instance, some geographic areas show an increased rate.

These cancers may show up months or even years after a vaccination. Although a fair number of cats have a small lump after getting a vaccination, the lump should be gone within a month. If it is not, have the cat examined by a veterinarian.

Because so much is still unknown, the Vaccine-Associated Feline Sarcoma Task Force was formed as a joint effort of the American Association of Feline Practitioners, American Animal Hospital Association, American Veterinary Medical Association, and Veterinary Cancer Society. This group is working to determine the true scope of the problem, the cause, and the most effective treatment for vaccine-associated sarcomas.

Treatment: This is an aggressive cancer that tends to spread in and between muscle layers, making it very difficult to remove all of the cancerous cells surgically. Surgery, with radiation done either before or after the surgery, seems to be the most successful treatment plan, but most of these cancers recur, nonetheless.

Vaccination Schedule: Noncore

Young puppies are highly susceptible to certain infectious diseases and should be vaccinated against them as soon as they are old enough to build immunity. These diseases are distemper, infectious hepatitis, parvovirus, parainfluenza, and rabies. Leptospirosis, giardia, coronavirus, bordetella, bronchiseptica, and Lyme diseasevaccinations are optional, depending on the occurrence of these diseases in your area and your dog’s individual risk factors.

The American Animal Hospital Association (AAHA) has drawn up guidelines categorizing vaccines as core or noncore, and these categories will be indicated for all the vaccines described in this section.

Leptospirosis Bacterin (Noncore)

Leptospira bacterins may protect against two or four of the most common subspecies of bacteria that cause leptospirosis. The two-serovar bacterin may be incorporated into a DHPP shot given at 12 weeks of age and again at 14 to 16 weeks of age. Many veterinarians give the four-serovar bacterin as a separate injection as early as 12 weeks and then two to three weeks later.

Leptospira bacterin has been responsible for 70 percent of post-vaccination DHLPP anaphylactic shock reactions. Toy breeds and puppies younger than 12 weeks old seem to have the highest rate of reactions to this bacterin. In addition, the two-serovar vaccines do not protect against the two species that are currently responsible for the majority of cases. Accordingly, routine vaccination is now considered optional. It is still indicated in areas where the risk of the disease is greater than the risk of the vaccination. Leptospirosis is not contained in all the combination vaccines and can be given separately.

Both Fort Dodge and Pfizer have vaccines that now cover all four of the primary serovars of leptospirosis. These are subunit vaccines, so there is less chance of an allergic reaction to the vaccine. With leptospirosis cases on the rise, this vaccine may be recommended in more areas. Immunity following vaccination averages about four to six months. Therefore, if vaccination is important, it may be advisable to revaccinate every six months. Discuss this with your veterinarian.

Canine Parainfluenza (Noncore)

Parainfluenza is the principal virus implicated in the kennel cough complex. Vaccines will decrease the prevalence and severity of the infection, but will not prevent the disease. Parainfluenza is incorporated into the canine distemper-measles-parainfluenza and DHPP shots. The first dose is given at 8 to 12 weeks of age and the second at 16 weeks. AAHA 2006 guidelines are to give the vaccine at 6 to 8 weeks of age, then every three to four weeks until the dog is 12 to 14 weeks of age, but many veterinarians prefer to wait until a puppy is 7 or 8 weeks of age to start vaccinations. An intranasal vaccine that combines the bordetella vaccine is also available.

The injectable parainfluenza vaccine protects dogs but does not eliminate the virus from nasal secretions. That means dogs can still transmit the infection. The intranasal vaccine protects against both disease and infection, thus eliminating the possibility of transmitting the disease to other dogs.

Annual boosters are recommended by the manufacturer. However, evidence suggests that parainfluenza vaccines do not always protect for the full 12 months, and in many cases should be given twice a year, especially for dogs at increased risk. This recommendation is only for the parainfluenza vaccine-not for the other viruses that are often included in a combination vaccine. This is not a core vaccine, so it should only be given to dogs with lifestyles that increase their risk, such as show dogs and dogs who will be boarded.

Bordetella (Noncore)

Bordetella bronchiseptica vaccines are of some help in controlling kennel cough and other respiratory infections caused by this bacteria. Show dogs, boarded dogs, and dogs living in kennels may benefit from this optional protection.

There are two vaccine types available to prevent bordetella. One is an intranasal vaccine and the other is injectable. The intranasal vaccine, which protects against parainfluenza as well as bordetella, gives the most immediate immunity-although either type of vaccine should ideally be given at least one week before possible exposures.

The injectable bacterin must be given twice. The first injection is given at 8 weeks of age and is repeated two to four weeks later. Puppies born in high-risk areas where bordetella is prevalent can be vaccinated with the intranasal vaccine at 3 weeks of age.

Annual boosters are recommended by the manufacturer. But because of the short duration of immunity, semi-annual boosters may be more appropriate.

Lyme Disease (Noncore)

Lyme disease (also called Borrelia burgdorferi) vaccine is recommended only for dogs in high-risk areas. This includes dogs visiting areas where Lyme disease is prevalent and areas with a high risk of tick exposure.

The killed bacterin version is now out of favor and the subunit vaccine, featuring the OpsA antigen, is recommended if the vaccine is needed. The immunity from this vaccine can be distinguished from a natural exposure. Tick control should be the first line of defense against Lyme disease.