Page 1479 - Small Animal Internal Medicine, 6th Edition

CHAPTER 93 Prevention of Infectious Diseases 1451

VACCINATION PROTOCOLS of lesser magnitude and shorter duration than infectious
vaccines unless adjuvants are added. Adjuvants improve
VetBooks.ir Vaccines are available for some infectious agents of dogs immune responses in part by stimulating uptake of antigens
VACCINE TYPES
by macrophages that present the antigens to lymphocytes.
and cats and can be administered to prevent infection or
vaccine adverse effects, most newer-generation adjuvants
limit disease depending on the agent. Vaccination can stimu- Although adjuvants have historically been associated with
late humoral, mucosal, or cell-mediated immune responses. induce less inflammation than older adjuvants like those
Humoral immune responses are characterized by the pro- containing aluminum. Subunit vaccines can be superior to
duction of immunoglobulin M (IgM), IgG, IgA, and IgE killed vaccines that use the entire organism because only the
class antibodies, which are produced by B lymphocytes immunogenic parts of the organism are used, which may
and plasma cells after being presented an antigen by mac- decrease the potential for vaccine reactions. However, for
rophages. Binding of antibodies to an infectious agent or some infections, use of only one antigen does not induce
its toxins helps prevent infection or disease by facilitating adequate protection (e.g., feline calicivirus vaccines). Native
agglutination (viruses), improving phagocytosis (opso- DNA vaccines and gene-deleted vaccines are currently being
nization), neutralizing toxins, blocking attachment to cell evaluated for several infectious diseases.
surfaces, initiating the complement cascade, and inducing
antibody-dependent cell-mediated cytotoxicity. Antibody VACCINE SELECTION
responses are most effective in controlling infectious agents Selection of optimal vaccines for use in dogs and cats can be
during extracellular replication or toxin production. Cell- complicated as multiple products for most infectious agents
mediated immune responses are mediated principally by T are available, but efficacy studies that directly compare dif-
lymphocytes. Antigen-specific T lymphocytes either destroy ferent products are often lacking. The veterinarian may need
the infectious agent or mediate destruction of the agent by to choose from infectious and noninfectious options for the
producing cytokines that stimulate other white blood cells, same vaccine antigen. Some vaccine antigens are for intra-
including macrophages, neutrophils, and natural killer cells. nasal or oral administration, and others are for parenteral
Cell-mediated immunity is required for the control of most administration. Not all vaccines for a given infectious disease
cell-associated infections. are comparable in every situation. Long-term duration of
Currently available vaccines are either infectious (attenu- immunity studies and studies evaluating a vaccine’s ability
ated [modified-live] organisms or live virus–vectored recom- to block infection by multiple field strains are not available
binant vaccines) or noninfectious (killed virus, killed bacteria for all individual products. When making decisions about
[bacterins], and subunit vaccines). which products to use or when evaluating a new vaccine, the
Attenuated vaccines replicate in the host to effectively practitioner should request information concerning efficacy,
stimulate an immune response and therefore generally have challenge studies, duration of immunity studies, adverse
low antigen mass and do not require adjuvants. Different reactions, and cross-protection capability. Vaccine issues are
products are administered locally (e.g., modified-live B. commonly debated in veterinary journals and continuing
bronchiseptica intranasal or oral vaccines) or parenterally education meetings; these are excellent sources of current
(e.g., modified-live canine distemper vaccine). In live virus– information. Use of vaccine guidelines from the AAFP
vectored recombinant vaccines, the specific DNA that codes (www.catvets.com; Scherk et al., 2013), the American Animal
for the immunogenic components of the infectious agent Hospital Association (www.aahanet.org), and the World
is inserted into the genome of a nonpathogenic organism Small Animal Veterinary Association (www.wsava.org) can
(vector) that will replicate in the species being vaccinated. help practicing veterinarians made logical vaccination pro-
As the vector replicates in the host, it expresses the immu- tocols for individual pets.
nogenic components of the infectious agent, resulting in the Not all dogs and cats need all available vaccines. Vac-
induction of specific immune responses. Because the virus- cines are not innocuous and should only be given if indi-
vectored vaccine is live and replicates in the host, adjuvants cated. The type of vaccine and route of administration for
and high-antigen mass are not required. Because only DNA the disease in question should also be considered. A benefit,
from the infectious agent is incorporated into the vaccine, risk, and cost assessment should be discussed with the owner
no risk of reverting to the virulent parent strain exists, as of each individual animal before determining the optimal
occasionally occurs with attenuated vaccines. Only vectors vaccination protocol. For example, FeLV only lives outside
that do not induce disease in the animal being vaccinated the host for minutes; it is highly unlikely that an owner
are used. Another advantage to vaccines of this type is would bring the virus into the household. Therefore cats
the potential ability to overcome inactivation by maternal housed indoors are not likely to come in contact with the
antibodies. virus.
Killed virus, killed bacteria (bacterins), and subunit vac- Before administering vaccines, the animal should be eval-
cines are noninfectious and therefore usually require higher uated for factors that may influence the ability to respond to
antigen mass than infectious vaccines to stimulate immune the vaccine or that may affect whether vaccination could be
responses because they do not replicate in the host. Some detrimental. For example, hypothermic animals may have
noninfectious vaccines may stimulate immune responses poor T lymphocyte and macrophage function and may not