Understanding vaccinosis in dogs and cats

Defined as an adverse reaction to a shot, vaccinosis can affect dogs and cats in various ways, from mild to severe.

Dogs and cats sometimes react negatively to vaccination, just as we humans do. This phenomenon is termed vaccinosis, and reactions can range from mild lethargy or a temporary loss of appetite, to severe conditions such as anaphylactic shock, ataxia, or even death. In this article, we’ll look at vaccinosis in detail, and offer some tips for protecting your own dog or cat from this scary situation.

Reactions may be immediate or delayed

Adverse vaccinal events can be classified as immediate/short-term, or delayed/longer-term.

1. Immediate and short-term

Adverse effects occur immediately or can occur within several days, and manifest as anaphylaxis (allergic shock) or even death, although rapid intervention and therapy are usually successful. Clinical signs can include rapid swelling of the eyelids, lips and face, itching, vomiting, weals and hives, and difficulty breathing. These effects can occur within minutes to hours of vaccination; they can also be biphasic and appear again in several days.

2. Delayed and longer-term

Delayed vaccine reactions can occur anywhere between five to 45 days. Clinical signs associated with these reactions typically include fever, stiffness, sore joints, abdominal tenderness, susceptibility to infections, neurological disorders and encephalitis, collapse with auto-agglutinated red blood cells and icterus (immune-mediated hemolytic anemia, IMHA), or generalized petechiae and ecchymotic hemorrhages (immune-mediated thrombocytopenia, IMTP). Hepatic enzymes may be markedly elevated, and liver or kidney failure may occur by itself or accompany bone marrow suppression.

Diseases associated with vaccinosis

In cats, aggressive tumors (fibrosarcomas) can occasionally arise at the site of vaccination. Additionally, a more recent study from Italy reported similar tumors in dogs at vaccine injection sites. The investigators stated that their “study identified distinct similarities between canine fibrosarcomas from presumed injection sites and feline post-vaccinal fibrosarcomas, suggesting the possibility of the development of post-injection sarcomas not only in cats, but also in dogs.” Other cancers such as leukemia have also been associated with vaccines.
Vaccinating dogs with polyvalent vaccines containing rabies virus or rabies vaccine alone can induce the production of anti-thyroglobulin autoantibodies, which has implications for the subsequent development of canine hypothyroidism.
Post-vaccinal polyneuropathy is a recognized entity occasionally associated with the use of canine distemper and rabies vaccines, although any vaccine could presumably be implicated. These neurological effects can result in various clinical signs including muscular atrophy, inhibition or interruption of neuronal control of tissue and organ function, muscular excitation, uncoordination and weakness, as well as seizures, and unprovoked aggressive behavior.

Vaccine adjuvants and adverse reactions

Killed (inactivated) virus vaccines containing adjuvants, like those for the rabies virus (mercury), can trigger both immediate and delayed adverse vaccine reactions. While immediate hypersensitivity reactions may occur, other acute events tend to manifest 24 to 72 hours later, or up to a week afterwards, and as long as 45 days later in the case of more delayed reactions, as outlined above.

Documented reactions in these cases include behavioral aggression and separation anxiety; destruction and shredding of clothing and bedding; obsessive behavior such as barking, fearfulness, self-mutilation, tail chewing; pica (eating wood, stones, earth, and feces); seizures and epilepsy; fibrosarcomas at the injection site; and autoimmune diseases such as those affecting bone marrow and blood cells, joints, eyes, skin, kidney, liver, bowel, and the central nervous system; muscular weakness or atrophy; and chronic digestive problems.

Rabies vaccines most common culprit

In the US, rabies vaccines are the most common group of biological products identified in adverse event reports received by the United States Department of Agriculture (USDA) Center for Veterinary Biologics (CVB). Currently, 14 rabies vaccines are labeled for use in dogs, but only two do not contain thimerosal (mercury) as a preservative. All rabies vaccines are evaluated for safety prior to licensure, but the trials may not detect all safety concerns for a number of reasons, including an insufficient number of animals for low frequency events, insufficient duration of observation, sensitivities of subpopulations (e.g. breed, reproductive status, and unintended species), or interactions with concomitantly administered products.

“Rabies vaccines are the most common group of biological products identified in adverse event reports received by the CVB,” the organization says. Between April 1, 2004 and March 31, 2007, for example, the CVB states that nearly 10,000 adverse event reports (all animal species) were received by manufacturers of rabies vaccines (and it’s important to note that vaccinal adverse reactions were, and still are, seriously under-reported). Approximately 65% of the manufacturers’ reports involved dogs; during the three-year period covered, the CVB received 246 adverse event reports for dogs in which a rabies vaccine was identified as one of the products administered.

One of the most disturbing aspects of these findings is the failure to consider the potential impact of mercury used as a preservative in all but two licensed canine rabies vaccines, and in some other animal vaccines. Mercury and other metals (aluminum, nickel, chromium, silver and gold) can cause hypersensitivity or autoimmunity, such as autoimmune thyroiditis, multiple sclerosis, neurological disorders, kidney disease, systemic lupus erythematosus, rheumatoid arthritis, myocarditis, and unspecific symptoms such as chronic fatigue and myalgia. Studies also have shown that these toxic metal-induced disorders occur in individuals with a susceptible genotype.

While vaccinosis is a serious problem, it’s not all bad news. There are steps you can take to help minimize the risk of an adverse vaccine reaction in your own dog or cat (see sidebar), while also keeping him safe from the infectious diseases vaccines are designed to protect against.