Canine vaccines can be divided into essential, core vaccines, and less essential noncore vaccines. The core vaccines are canine distemper, adenovirus-2, and parvovirus. Rabies vaccination is mandatory in many different jurisdictions. Canine ...
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Canine distemper
Canine distemper caused by canine morbillivirus infection remains one of the most significant and lethal viral diseases of dogs. It affects the gastrointestinal and respiratory tract in addition to the nervous system.
There are currently 50 licensed distemper vaccines available in the United States; however, only one of these is directed against canine distemper virus alone. Distemper vaccine is usually combined with those against canine adenovirus 2, canine parvovirus, and canine parainfluenza. These combinations may also contain coronavirus, leptospirosis, and Borrelia vaccines. Three different types of vaccine are available to prevent canine distemper.
Inactivated CDV vaccines generally give inferior protection and are best used in susceptible wildlife species.
Modified live virus vaccines contain attenuated virus strains such as the Snyder Hill and Rockborn strains attenuated by prolonged canine cell culture, or the egg adapted Onderstepoort strain, now adapted to tissue culture. Antigenic differences between these strains are not significant and all are protective when used appropriately. Note that the modified live virus (MLV) distemper vaccines, although safe in domestic dogs, can cause disease in related wildlife such as gray foxes and the black-footed ferret. Indeed, the black-footed ferret, a highly endangered species was nearly wiped out as a result of the inappropriate use of MLV distemper vaccines (
Chapter 20).
A canarypox vectored recombinant vaccine is available in some countries. The genes encoding two immunogenic CDV antigens, the hemagglutinin (HA) and fusion proteins have been inserted into an ALVAC canarypox vector (
Chapter 5). This vaccine is able to overcome some maternal immunity and appears to immunize puppies about four weeks earlier than conventional MLV vaccines. The vectored vaccine has the additional advantage that it is unable to cause postvaccinal distemper encephalitis.
The recombinant and MLV vaccines perform similarly with respect to onset and duration of immunity. Measuring serum antibodies provides a reasonable assessment of protective immunity. Duration of immunity after vaccination is at least five years.
Canine adenovirus 2
CAV-2 is a respiratory pathogen transmitted by the oronasal route. The virus damages bronchial epithelial cells resulting in fever, cough, nasal discharge, and pharyngitis.
Inactivated CAV vaccines are usually administered in combination with CDV and CPV.
The preferred vaccines against canine adenoviruses are modified live products. These MLV also provide immunity against infectious canine hepatitis caused by CAV-1 and against tracheobronchitis caused by CAV-2. Immunity develops about five days postvaccination with the MLV. However, CAV-2 infection or vaccination will not induce the hypersensitivity reaction known as blue-eye caused by CAV-1 (
Fig. 10.5). Both injectable and intranasal forms of CAV-MLV vaccines are available. Because CAV-2 is a contributor to the canine respiratory disease complex, it is commonly used in combination with other respiratory pathogen vaccines such as those against
Bordetella bronchiseptica and canine parainfluenza virus.
The duration of immunity after vaccination is at least nine years. The presence of serum antibodies indicates protection, making serology a useful guide to revaccination.
Canine parvovirus
CPV is one of the major causes of canine acute gastroenteritis. Young puppies two to six months of age are most susceptible, but cases are increasingly recognized in adult dogs. Clinical signs include anorexia, depression, vomiting, and diarrhea that is often hemorrhagic.
The original canine parvovirus (CPV-2) first appeared in the 1970s and was likely a host variant of feline panleukopenia or a related virus. Since then new circulating variants have appeared. For example, CPV-2a and -2b appeared in the 1980s and CPV-2c in 1996. All these variants are antigenically related so that currently available MLV-CPV vaccines are believed to protect against the variants circulating in North America.
The inactivated vaccines are not as effective and are relatively slow to induce protective immunity when compared with the MLV vaccines. As a result, they are not recommended for routine use except possibly in situations such as in an immunosuppressed dog where the use of a live vaccine may be hazardous.
In the absence of maternal antibodies, MLV parvovirus vaccines may be protective within three days. This is probably because of early interferon production rather than antibodies (
Fig. 4.1). These MLV vaccines can replicate in the dog intestine and thus are intermittently shed in the feces of vaccinated dogs. This shedding occurs irrespective of the presence of antibodies. MLV-CPV vaccines should not be used in wildlife as they may be insufficiently attenuated. Inactivated vaccines are safer in other species.
Duration of immunity is thought to be life-long, especially following the use of MLV vaccines.
Rabies
The use of rabies vaccines in the United States is regulated by individual states or other jurisdictions. As a result, requirements may be conflicting and inconsistent. In most, but not all states, vaccination is mandatory. It is essential that practicing veterinarians are fully aware of the appropriate legislation and regulations that govern rabies vaccination.
Although modified live vaccines have been proven safe in dogs, the World Health Organization stopped recommending these vaccines in 2004. As described elsewhere (
Chapter 10), self-inoculation incidents result in an unacceptable risk to humans. No modified live rabies vaccines are currently marketed in the United States.
Inactivated rabies vaccines are commonly used in mass vaccination programs where maintaining the cold chain is less critical and safety is not an issue. These viruses are generally grown to high titer in tissue culture and then inactivated with beta-propiolactone, acetylethylamine, or binary ethyleneimine (
Fig. 3.2). Once inactivated, adjuvants such as aluminum hydroxide, aluminum phosphate, or saponin are added.
Vectored recombinant rabies vaccines express the highly immunogenic rabies glycoprotein G gene. Vectors used include vaccinia, canarypox, and adenoviruses. The vaccinia and adenovirus vectored vaccines may be used in North America and Europe for wildlife vaccination. It is interesting to note that injectable rabies vaccines may be of little use in less developed countries where most cases of canine-induced rabies occur. In these countries there are large numbers of stray dogs and it is not possible to catch and vaccinate them all. In such cases, encouraging results have been obtained by distributing oral recombinant vaccines similar to those used in wildlife (
Chapter 20). Blister packs containing the vaccines may simply be offered to these dogs by hand, enclosed in chicken heads, meatballs or a short segment of boiled beef or pig intestine. The vaccinator can also note that the dog has punctured the vaccine blister and recover used packs. This technique is a viable strategy to supplement parenteral vaccination in otherwise unreachable dog populations.
In many jurisdictions it is a requirement that domestic dogs, cats, and ferrets are to be vaccinated. In general, they are not considered to be vaccinated until 28 days after the initial vaccine dose.
The interval between doses is determined by the manufacturer and indicated on the product label, but legally they are considered unvaccinated one day after the vaccine’s official duration of immunity (one year or three years). In most (but not all) states, only a licensed veterinarian is authorized to administer rabies vaccine.
The definition of exposure to rabies also varies between states. This is determined by the state Department of Health, not by the veterinarian. Most properly vaccinated dogs are immune to rabies. Should such a dog be bitten by a rabid animal, they should be quarantined for 45 days. Unvaccinated animals should be quarantined for four months. They should be vaccinated within 96 hours of exposure on entry into quarantine.
If multiple doses of vaccines are administered to small-breed dogs (<10 kg), this may increase the risk of adverse reactions. Given the importance of the size of the dog, it has been suggested that veterinarians consider delaying administration of noncore vaccines to small dogs until two to four weeks after completion of the core vaccination process.
There is currently no data available to support the practice of reducing vaccine dose or frequency of administration in small dogs. Dose reduction increases the chances that the dog will receive an insufficient dose to confer protective immunity. Likewise, there is no data to suggest that dose reduction will reduce the incidence of adverse events. After all, if the animal is already allergic to a vaccine component, even a reduced dose may trigger a reaction.
Note that vaccination of dogs against rabies has saved millions of humans from a horrible death. This is yet another triumph for the science of immunology.
