23 Jul National Immunization Month: Rabies
RABIES VACCINATION: Misconceptions and the “MUST KNOW” Facts
by Richard B. Ford, DVM, MS
Diplomate ACVIM and (Hon) ACVPM
Professor Emeritus
North Carolina State University
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Of all the companion animal vaccines licensed today for administration to dogs and cats, rabies vaccine is the only one that is actually required by law in most, although not all, States or local jurisdictions throughout the United States. While it is not the veterinarian’s responsibility to assure the individual patient is currently vaccinated, the veterinarian is expected to know the law and comply with State/local management requirements as they pertain to rabies. However, laws/regulations governing rabies and rabies immunization do vary from State to State. Not surprisingly, confusion over vaccination and control requirements has led to misinterpretation of law and inappropriate decisions by practicing veterinarians (sometimes with serious consequences).
The focus of this manuscript, and the presentation it accompanies, is to address the primary responsibilities and requirements a veterinarian accepts when administering rabies vaccine to individual dogs/cats in the United States. Three fundamental issues, and common misconceptions, are presented: the rabies vaccination protocol, the clinical consequences of “exposure” to rabies virus; and rabies virus antibody testing.
The reader is reminded that rabies laws/regulations are determined at the level of the individual State and/or local jurisdictions within that State. There are no national rabies vaccination statutes or regulations. The Compendium of Animal Rabies Control and Prevention (referred to in these proceedings as the Rabies Compendium) offers recommendations for animal rabies prevention and control programs throughout the United States but, alone, is not a regulatory document. Several States and local jurisdictions do incorporate recommendations provided by the Rabies Compendium into State law. However, veterinarians must refer to State/local statutes on rabies when making vaccination and management decisions about individual dogs, cats, or ferrets.
Specific information on individual State rabies laws and regulations is available here. This website, maintained in cooperation with the National Association of State Public Health Veterinarians, Inc., provides contact information and answers to several key questions regarding rabies control and immunization procedures in individual States.
THE RABIES VACCINATION PROTOCOL
There is no debate over the effectiveness of well executed rabies immunization and control programs to reduce the risk of dog-transmitted rabies virus to humans…where control programs are in effect, human rabies virus infections are rare. According to surveillance data from the Centers of Disease Control, human rabies deaths in the US have been declining steadily since the 1970s.
Since 2007, the United States has been free of canine-variant rabies virus…a credit to widespread immunization programs for dogs. Today, human fatalities from rabies virus occurring in the US are typically associated with bat exposure or dog bites acquired outside the US. This represents a significant accomplishment considering that rabies virus, globally, causes at least 60,000 human deaths annually (and probably more)…with dogs being responsible for 99% of those fatalities.
BUT…as the number of dogs imported into the US each year increases(1), the re-introduction of canine rabies is possible. Our “canine-variant rabies virus free” status must be considered fragile. Without question, compliance with State and local rabies vaccination requirements remains a vital part of the veterinarian’s role in public health.
(1) Although precise surveillance data on the number of dogs imported into the US each year is not available, it is estimated based on extrapolated data that over 287,000 dogs were imported into the US during 2006. Of these, approximately 25% were either too young to be vaccinated or lacked proof of valid rabies vaccination.
But compliance with rabies vaccination laws and regulations can be challenging when considering the variation in requirements among individual States. Consider the following:
Which Species?
States laws often stipulate that rabies vaccination is required for dogs, cats, and ferrets. But, species requirements vary among States. Some States only require dogs to be vaccinated. Others stipulate only dogs and cats, not ferrets, must be vaccinated. There are at least 7 States that do not have rabies vaccination laws or regulations in place (although local jurisdictions within a State may). And, in States where rabies laws are in effect, local jurisdictions may impose vaccination requirements that are different from those included in State law. (Generally, local jurisdictions have discretion to impose more stringent rabies laws than those required by the State, but not less stringent). Veterinarians in practice must be aware of local, as well as State, rabies vaccination requirements and control procedures.
NOTE: in the US, rabies vaccination of dogs and cats is recommended as core, even in States where vaccination is not required.
Minimum Age: All States that have rabies vaccination laws in place today follow minimum age recommendations outlined by the Rabies Compendium(2) which stipulate 12 weeks of age as the minimum age.
(2 )The latest version of the Compendium of Animal Rabies Prevention and Control (referred to here as the Rabies Compendium) was published in 2016 and is available online (see Additional Reading).
“Must be vaccinated by” Age: many States also stipulate the specific age by which a dog/cat/ferret must be vaccinated against rabies. In contrast to the “Minimum Age” for rabies vaccination, our surveillance of State requirements indicates considerable variation in the age (ranging from 12 weeks of age to 6 months of age) by which a pet shall be vaccinated against rabies. Because this is a State or local statutory requirement, it is important to verify the age requirement in the location(s) where you practice and advise clientele accordingly.
Who can administer a rabies vaccine? Most States clearly stipulate who is qualified to administer rabies vaccine to a dog/cat/ferret. Don’t assume! While a “licensed veterinarian” is usually a correct response, at least one State (eg, Michigan) requires the licensed veterinarian to also be “accredited” when vaccinating a dog (but not a cat).
Furthermore, do not assume that a certified veterinary technician working in your practice is eligible to administer rabies vaccine. Several States specifically do not allow anyone other than a “licensed veterinarian” to administer a dose of rabies vaccine.
“Direct Supervision”: Among States/jurisdictions that do allow someone other than a licensed veterinarian to administer rabies vaccine, the phrase “under the direct supervision of a licensed veterinarian” typically applies. In our review of State rabies laws, this phrase should be interpreted to mean that a licensed veterinarian is physically present in the facility at the time the rabies vaccine is administered.
Overdue for a Booster: the protocol for vaccinating an animal that is overdue for a rabies booster may also be stipulated in State law.
First.… “overdue” is defined as just one day, or longer, beyond the labeled duration of immunity of the last rabies vaccine dose administered (ie, either 1 year or 3 years). Beyond that time, the animal, in law, is no longer “currently vaccinated”. Immunologically speaking, most dogs and cats are expected to enjoy protective immunity for months, or even years, beyond that indicated by the vaccine label. However, in clinical practice, law supersedes immunologic principles when it comes to rabies.
Second… among States that do require rabies vaccination, veterinarians are typically given discretion in administering either a 1-Year or a 3-Year labeled rabies vaccine. A few States, (California, West Virginia, and Mississippi) do not recognize the 1-Year labeled rabies vaccine and, therefore, veterinarians are obligated to administer a 3-Year labeled product. California goes further by stipulating that only a USDA licensed 3-Year labeled rabies vaccine that is approved by the California Dept. of Public Health can be administered to dogs. (There’s no State law mandating vaccination of cats in California.)
Third… States do recognize the recommendation (published in the Rabies Compendium) that a dog/cat/ferret, if “overdue” for re-vaccination, will be considered “immediately currently vaccinated” (ie, immunized) following administration of a booster dose…regardless of the time elapsed since the last dose was administered.
Fourth… most, but not all, States stipulate that, following re-vaccination of the overdue animal, the next booster dose is due based on the label of the vaccine used, ie, either 1 year or 3 years later. However, at least 3 States (eg, California [dogs only], Mississippi, Vermont]) stipulate the next rabies dose must be administered 1 year later, regardless of the product label, and regardless of the length of time the animal is overdue.
Vaccination of Wildlife Hybrids: Considerable State-to-State variation exists regarding requirements and recommendations for vaccinating a “hybrid” dog or cat. In law, the intent likely addresses any pet that is known to be a cross between a domestic dog and a non-domestic canid (eg, a wolf) or a cross between a domestic cat and a non-domestic feline (eg, an Ocelot or African Serval). Some States specify that vaccinating a hybrid is illegal. Others either encourage or do not restrict veterinarians from administering rabies vaccine to hybrids…but no State considers rabies vaccination of a wildlife hybrid to be protective. In the event a person is bitten by a vaccinated hybrid dog or cat or if the hybrid animal is exposed to a known or suspect rabid animal, euthanasia ranks high on the list of required actions in such cases. A few States do not address vaccination of hybrid species in law.
The reason behind legal limitations associated with rabies vaccination of hybrid species is actually logical. None of the licensed rabies vaccines available in the US today have ever been tested in hybrid species. Only a few States (eg, California, North Carolina) currently restrict veterinarians from administering rabies vaccine to hybrid dogs/cats.
“EXPOSURE” to RABIES VIRUS
Significant differences exist among States regarding how rabies virus “exposure” is defined, who makes that determination, and what the resulting consequences may be for the client and for the “exposed” pet.
“Exposure”: Uniform wording that defines what is, and what is not, “exposure” is lacking.
Some States seem to have simply extrapolated the definition of “exposure” from that used to define human exposure, ie, “a direct bite or scratch, which results in a break in the skin of the victim, or contact between infectious material (saliva, CNS tissue or fluid) and the eye, inside the nose or mouth, or a pre-existing break in the skin.”
However, such definitions do not take into consideration the myriad of scenarios wherein a pet dog or cat might be exposed to rabies virus (eg, does finding a dead bat in the cat’s litter box constitute “exposure”?)
On the other hand, some States (eg, Connecticut and New Jersey) describe “exposure” in terms of risk categories: wounds from a confirmed rabid animal vs. wounds from a suspect rabid animal vs. wounds of unknown origin vs. exposure by proximity. Clearly stated patient management guidance is provided for each category.
Lack of a clarity in defining “exposure” at the State level is a significant concern for veterinarians, the Public Health community, and pet owners…BECAUSE…the consequences for a dog/cat that is determined to be “exposed to a known or suspect rabid animal” can range from “home observation” to “strict isolation in a designated facility” (at the owner’s expense) to “immediate euthanasia”. Vague definitions of “exposure” could force impractical, expensive enforcement mandates unnecessarily or, on the other hand, could result in failure to appropriately isolate an animal that has, in fact, been exposed to (or infected with) rabies virus.
Determination of “Exposure”: The authority to determine what is, and what is not, “exposure” typically belongs to designated public health officials or animal control officers. The examining veterinarian may be involved or consulted in the process, but the final decision rests with officials who may not be familiar with the circumstances under which the exposure occurred or the extent of injury sustained by the pet during the purported exposure.
Post-Exposure Management: Once a determination is made that a dog or cat has, in fact, been exposed to a known or suspect rabid animal, the next regulatory issue to consider is whether or not the exposed animal is “currently vaccinated”.
- If “currently vaccinated” at the time of exposure, many States allow the animal to remain in the home under the owner’s control for a period of not less than 45 days. In accordance with recommendations outlined in the Rabies Compendium, many States stipulate that the vaccinated animal should receive a booster dose of rabies vaccine “immediately” (State requirements range from 2 to 5 days) following the exposure. If not re-vaccinated within the designated post-exposure period, the observation period may be extended.
- If NOT “currently vaccinated” at the time of exposure, State mandates imposed on the animal can be severe: “immediate euthanasia” is common language in State law.
However, options do apply. Today, several States will consider alternative management protocols if the owner declines to have their overdue/unvaccinated pet euthanized.
Depending on State law, options may include:
- For the unvaccinated dog/cat: The owner of an “exposed” dog/cat that has never been vaccinated against rabies may be offered the option of placing the pet in “strict confinement”, or quarantine, in a designated facility (at the owner’s expense). Today, the duration of the quarantine/confinement period ranges from 4 to 6 months, depending on individual State law.
- For the overdue dog/cat with documentation of prior vaccination: The owner of an “exposed” dog/cat that was overdue for a booster at the time of exposure may be allowed to confine their pet at home for 45 days if they are able to provide documentation of prior rabies vaccination.
- For the overdue dog/cat without documentation of prior vaccination: The owner of an “exposed” dog/cat that was overdue for a booster at the time of exposure, but the owner is unable to provide valid documentation of a prior rabies vaccination, may have 2 options:
- proceed with the protocol outline for an exposed, but unvaccinated, dog/cat (euthanasia or 4 to 6 months quarantine in a designated facility) or,
- Prospective Serological Monitoring(3) (also called PSM), if permitted by State law, may be conducted as a means of establishing serological evidence of prior vaccination if valid documentation is not available. If serological evidence (anamnestic response) can be demonstrated, the length of the required quarantine period could be reduced from 4 or 6 months to 45 days.
(3) The 2016 Rabies Compendium does provide management recommendations for each of the 3 scenarios listed above. However, because these recommendations have not been universally adopted or incorporated into law by all States, the burden still rests with the examining veterinarian to advise the client on required regulatory actions in the even a pet dog/cat is determined to be exposed to a rabid animal.
This gets involved….
Several criteria apply: The exposed animal (…that is overdue and without valid documentation) must have been examined by a veterinarian within 96 hours of the purported exposure. The examining veterinarian does not have discretion to conduct the PSM protocol. Not all States have approved use of PSM. In States that do recognize PSM, the decision to utilize the protocol in an individual dog/cat is ultimately made by the Rabies Control Authority at either the State or local level. If approved, the PSM protocol is very specific and must be strictly adhered to. Test results must be interpreted in conjunction with the laboratory performing the titer and the State or local Rabies Control Authority.
For detailed information on how to perform the PSM protocol, veterinarians should search: “Prospective Serological Monitoring Protocol“
NOTE: depending on the circumstances surrounding the exposure, and whether or not humans may have been injured or bitten by an “exposed” dog/cat, public health officials may have the authority to override an alternative management protocol and force euthanasia and testing.
Animal Bites to Humans
Not uncommonly, confusion exists over the disposition of a dog/cat/ferret that bites a person versus a pet that has a confirmed or suspected exposure to a rabid animal.
Virtually all States follow recommendations outlined in the latest version of the Rabies Compendium, which states that a dog, cat, or ferret that bites a human is to be confined and observed for a minimum period of 10 days…regardless of the animal’s rabies vaccination status.
REASON: rabies virus shedding from infected dogs begins from 1 to 5 days prior to the onset of signs. In cats, virus shedding begins from 1 to 2 days prior to the onset of signs and as late as 3 days after the onset of signs. Therefore animals that remain healthy throughout the 10-day confinement period are considered not to have been shedding rabies virus at the time the bite occurred.
If at any time during the 10-day confinement period a dog or cat develops clinical signs of illness, State Public Health officials may mandate immediate euthanasia and testing. AND…for that reason…a rabies vaccine must NOT be administered at any time after the bite incident through the end of the 10-day confinement period (in case the vaccine were to cause clinical illness or signs that might be interpreted as rabies.)
In the majority of States, hybrid cats and dogs have no status if involved in a bite to a person. Public Health officials characteristically recommend immediate euthanasia and testing, regardless of rabies vaccination status.
RABIES ANTIBODY TESTING
The relationship between rabies vaccination, the antibody response following vaccination, and the meaning of a “POSITIVE” vs. “NEGATIVE” test result for the individual patient is somewhat complex.
Testing Indications: in clinical practice, there are 2 primary indications for rabies virus neutralizing antibody (RVNA) testing of a dog or cat:
- Travel from the US to a rabies-free country or region, and…
- Prospective Serological Monitoring (PSM). In the US, testing for RVNA in animals is limited to a few designated laboratories(4).
(4) Prospective Serological Monitoring (PSM) may only be performed at: Kansas State University Rabies Laboratory, Atlanta Health Associates, Inc., New York State Dept of Health, Griffin Laboratory (limited to residents of New York State), and the Army Public Health Center, Fort Sam Houston, TX (for military personnel only).
Interpreting Test Results: In the US, a “positive” RVNA test result is not to be interpreted as an index of protective immunity. A “positive” RVNA test (eg, FAVN or RIFITT) result cannot be used in lieu of re-vaccination (booster). A “positive” RVNA test result is only interpreted as evidence of “adequate vaccination”.
Today, States follow the guidance on rabies serology as published in the Rabies Compendium: “Rabies virus antibody titers are indicative of a response to vaccine or infection. Titers do not directly correlate with protection…”
Travel: Animals traveling from the US to a rabies-free country or region may be required to submit rabies antibody test results (Fluorescent Antibody Virus Neutralization test, or FAVN, is required for travel).
An excellent website maintained by the USDA provides details, if available, on importation requirements, including serology, for individuals traveling with pets to most foreign countries/regions of the world: Search: USDA Pet Travel.
A “positive” FAVN test result (≥ 0.5 IU/mL) is interpreted by the importing country/region as proof that the animal demonstrated an adequate antibody response following rabies vaccination and, therefore, is vaccinated. A “positive” test result is not interpreted as “protective immunity”. Animals with a “negative” FAVN test result may be denied entry or subjected to an extended quarantine period by the importing country.
Prospective Serological Monitoring (PSM): Recently highlighted by the National Association of State Public Health Veterinarians, Inc., PSM is a serological testing protocol designed to assess the anamnestic response to a single dose of rabies vaccine in a dog or cat.
The test protocol must be strictly adhered to.
Furthermore, the test is only indicated:
- For dogs/cats determined to be exposed to a known or suspect rabid animal, and…
- when there is reasonable expectation the animal has been previously vaccinated against rabies, and…
- when valid documentation of prior rabies vaccination is not available.
PSM may offer the client an alternative to euthanasia or extended (expensive) quarantine periods. However, PSM is NOT currently recognized in all States. In States/jurisdictions that do allow PSM, testing authority resides with local public health officials or animal control officers and is not necessarily at the discretion of the examining veterinarian.
Updated, detailed instructions addressing the PSM protocol are available here.
CONCLUSION
This manuscript highlights a few of the most important responsibilities accepted by a licensed veterinarian when administering rabies vaccine to dogs, cats, and ferrets. This manuscript also highlights new, key resources available to facilitate rapid access to updated, relevant vaccination and management requirements outlined by individual States.
ADDITIONAL READING
Ford RB, Larson LJ, McClure JD, Schultz RD, and Welborn LV. AAHA Canine Vaccination Guidelines (revised 2017; updated 2018). Available online at: https://www.aaha.org/guidelines/canine_vaccination_guidelines.aspx (accessed November 2018)
Brown CM, Slavinski S, Ettestad P, et al. Compendium of Animal Rabies Prevention and Control, 2016. National Association of State Public Health Veterinarians, Inc. JAVMA March 1, 2016. Vol 248. No 5, pp. 505-517.
Available online at: http://www.nasphv.org/Documents/NASPHVRabiesCompendium.pdf or, search: 2016 Rabies Compendium, accessed November 2018)
Greene CE. Rabies and other Lyssavirus infections. Chapter 20 in CE Greene (ed): Infectious Diseases of the Dog and Cat. 4th Edition (2012). Elsevier-Saunders, Saint Louis, pp. 179-197.
Rabies Surveillance in the US. Centers for Disease Control and Prevention (2017) Available online at: https://www.cdc.gov/rabies/location/usa/surveillance/human_rabies.html (access November 2018)
Ryan W, Pees A, Blanton JD, and Moore SM. Risk factors for inadequate antibody response to primary rabies vaccination in dogs under one year of age. PLoS Neglected Tropical Diseases 11(7):e0005761, July 2017.
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