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Researchers study duration of immunity for rabies vaccines

Public supports work with $400,000 in donations


June 18, 2009
By: Timothy Kirn
For The VIN News Service


A group called the Rabies Challenge Fund has raised more than $400,000 via small, public donations for a study on rabies vaccines and how long the immunity lasts in dogs.

The study, already underway, is being conducted at the University of Wisconsin, which has donated the overhead costs of using its facilities to the project. The purpose is to investigate the duration of rabies-vaccine immunity to see if it might be possible to have dogs go longer than three years between immunizations.

In May, Alabama became the nation's last state to forgo its annual rabies mandate in favor of a three-year schedule, which has become the norm.

The study appears to have struck a chord with those outside the veterinary community, industry and government agencies that usually fund such research. More than 130 breeder groups and kennel clubs have made donations, as have individuals. Two people pledged $10,000 each, although most donors have given less than $250.

Some donors are individuals who contend that their dog was harmed by a rabies vaccine. Rabies Challenge Fund founder Kris L. Christine, of Maine, says she got interested when her six-year-old Labrador Retriever developed a malignant mast-cell tumor at the site of arabies injection.

“There are a lot of people who have had vaccine-damaged animals,” she contends.

Christine says she felt “deceived” and let down by the veterinary medical community before, and after, she began to pursue an inquiry into what had happened to her dog. Veterinarians dismissed her concerns, she says, based on the fact that there is no evidence that adverse events occur regularly after rabies vaccinations. 

Christine “stepped up to the plate” because no one else was, she says.

Her investigations led her to W. Jean Dodds, DVM, a well-known animal welfare advocate and researcher who introduced her to Ronald D. Schultz, DVM, PhD, a longtime vaccine researcher at the University of Wisconsin.

Schultz previously reported that dogs appeared to have rabies antibody titers at levels thought to confer immunity for as long as seven years, and he knew of a 1992 study from French researcher Michel Aubert showing that dogs could survive a rabies challenge five years after vaccination. So, Schultz agreed to design and conduct a study.

Schultz, who has studied vaccine effectiveness since the 1970s and is a member of the American Animal Hospital Association’s (AAHA) Canine Vaccine Task Force, says that giving a dog fewer immunizations would reduce adverse events and might increase immunization rates. He says the data shows that 50 percent of dogs in this country are never vaccinated for rabies or the other three core-vaccine diseases: distemper, parvovirus type 2 and adenovirus type 2, although critics of that statistic argue that it's based on shelter-derived data, which likely does not accurately represent the pet population at large. 

Veterinarians, in general, tend to agree that immunity might last longer than three years, yet their recommendations to triennially vaccinate dogs for rabies are based on information from drug companies, literature and, most importantly, state legal requirements. Craig A. Datz, DVM, a faculty member of the University of Missouri who has an interest in infectious disease, agrees that Schultz's study is a worthwhile endeavor. But, speaking from the perspective of veterinary medicine overall, he says it's not that significant.

While some dogs undoubtedly do get hurt by a rabies vaccine, the number is probably low, Datz contends. 

“Any kind of study that everyday people will support is probably a good thing,” he says. “If it were me, however, it is not where I would want to spend my money.”

Even so, rabies vaccine is the core vaccine most often and strongly associated with adverse events, Schultz says. This may be because the vaccine contains a high amount of killed antigen, or it might be because it is adjuvanted heavily to boost its antigenicity. Those who worry about the vaccine usually mention both features as possibilities.

The most common type of reaction in a dog probably is a localized reaction often characterized as an ischemic vasculitis and some alopecia at the site of infection occurring within one to three months after vaccination, at least according to Richard Ford, DVM, a professor at North Carolina State University and another member of the AAHA Canine Vaccine Task Force. Other times these same lesions can be disseminated to additional locations beyond the injection site. Schultz says rabies inoculation can prime B cells so that the animal has allergic responses or allergies that worsen, although experts like Dr. Melissa Kennedy, a board-certified microbiologist and VIN consultant, stresses that such an occurrence is not a common event. 

Kennedy also warns that "folks shouldn't misinterpret that rabies vaccine contributes to other allergy problems, like flea allergy, as opposed to a hypersensitivity response to a specific antigen contained in the vaccine." 

The evidence supporting the idea that rabies inoculation might induce adverse events in some animals largely comes from two reports. In 2005, George E. Moore, DVM, of Purdue University, reported on the frequency of adverse events occurring within three days of inoculations in data collected from 360 Banfield clinics. With data on 3.4 million vaccine doses given, Moore reported an adverse-event rate of 38 per every 10,000 vaccine doses. The rate associated with rabies vaccine specifically was 25 per 10,000. The adverse event rates were higher for smaller dogs and higher when multiple vaccines were given (J. Am. Vet. Med. Assoc. 2005;227:1102-08).

Last year, the Center for Veterinary Biologics, within the United States Department of Agriculture, reported that rabies vaccines are the most common biologics identified in adverse events reports to the agency. The Center said that between April 2004 and March 2007, it received 246 reports related to canine rabies vaccines, of which 217 were considered likely to have been associated with an administered vaccine. More than 120 million doses of rabies vaccine were distributed in the United States during this time period. Most of the dogs (72 percent) reported to have had adverse reactions received more than one vaccine (J. Am. Vet. Med. 2008;232:1000-03).

The types of adverse events included acute hypersensitivity (59 percent), local reactions (27 percent), systemic reactions (9 percent), autoimmune disorders (3 percent), and others (2 percent).

The Center noted that 14 rabies vaccines are approved for dogs, although it did not identify which vaccines were involved in the adverse-event reports.

The study Schultz is conducting has been designed to meet the Code of Federal Requirements, United States Department of Agriculture, title 9. These are the same regulatory requirements that a vaccine must go through to be approved for use. Although Schultz did not say how many animals or how many of the available rabies vaccines are being used in the trial, the requirements state that there must be at least 25 animals given vaccine and 10 control animals. Those animals — Beagles — are housed, fed and exercised just like the other dogs in the university’s research colony. While Schultz would not be specific about how many vaccines are being tested, he did say it is “more than one.”

At five years and seven years, at least some of the dogs will have to be challenged with rabies virus to test their immunity, and that has caused some fireworks. People for the Ethical Treatment of Animals (PETA) has criticized the study because the dogs that contractrabies after the challenge will have to be euthanized.

The Challenge Fund’s Dodd responded to PETA by saying that there is no equivalent way to test rabies vaccine and that the animals will be killed humanely and promptly should they show any signs of rabies, before there is a chance for suffering.

Microbiologist Kennedy notes that vaccination programs in the United States have led to the eradication of the canine strain of rabies and are "critical" to protecting human and animal health. 

"While dogs can of course still get rabies in the U.S., it is wildlife strains," she says. "In our neighbor (countries) to the south, canine rabies is endemic, and could cross over the border. In addition, both legal and illegal dog movement can bring the strain back. 

"Without rabies vaccines, dog rabies is endemic, leading to many human deaths, often children," she adds. 



VIN News Service commentaries are opinion pieces presenting insights, personal experiences and/or perspectives on topical issues by members of the veterinary community. To submit a commentary for consideration, email news@vin.com.



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