Random source populations with largely unknown vaccination histories, continuous resident
turnover, and high risk for infectious disease characterize most shelters. Vaccine costs
become a significant management aspect when multiplied by thousands of doses. Therefore,
only those antigens that demonstrate a clear benefit against common and significant shelter
diseases should be utilized.
FPV has re-emerged as a significant cause of mortality in cats in shelters and rescue homes
throughout Europe and the United States. With rare exceptions, all kittens and cats over 4 to 6
weeks of age should be vaccinated regardless of physical condition, pregnancy, or housing
status. Kittens should be vaccinated beginning at 4 weeks of age in the face of an outbreak,
and at 6 weeks of age otherwise. MLV vaccines are advantageous for their faster onset of
action, greater efficacy at overcoming maternal antibody, and greater likelihood of conferring
sufficient immunity. (Greene and Addie, 2005; Greene and Schulz, 2005). Although concerns
have been raised regarding their reversion to virulence, this has never been documented
(Greene and Schulz, 2005). Cats of unknown status should not be housed together.
Vaccination should be repeated every 3 to 4 weeks in kittens, until 16 weeks of age. If adult
cats are ill or otherwise compromised at the time of initial vaccination, another injection when
the cat is in good health (at least two weeks after the initial vaccine) should be considered.
When vaccination is being used to control disease in the face of an outbreak, the more rapid
induction of immunity induced by a MLV preparations is of clinical advantage over killed
vaccines.
Passive immunisation can be used in shelters when available. It is useful at admission if
other diseases are present or in an environment with high infection pressure, as it provides
immediate protection. Efficacy of immunoglobulins to prevent infection, including FPV, has
been proven in experimental studies and in the field some 50 years ago. Efficacy of
immunoglobulins depends on many factors, including the antibody titre against the specific
agent and volume administered, the relative importance of serum antibodies in controlling the
particular infection involved, and the timing of administration of the antibodies compared to
exposure.
Commercial products containing highly concentrated immunoglobulins (multivalent
hyperimmune immunoglobulin preparations) are available in some European countries for
cats (heterologous preparation produced in horses, containing a combination of antibodies
against FPV, FHV-1, and FCV). They are marketed for prophylactic (usually 1 injection of 1
vial/animal subcutaneously) and therapeutic (usually 3 injections of 1 vial/animal
subcutaneously every 24 hours) use. Protection lasts for about 3 weeks. During this period,
active immunization (vaccination) is not recommended because the immunoglobulins will
bind to the vaccinal antigens, tying them up in immune complexes. Although large amounts
of foreign protein are administered, allergic reaction are rare if a cat is treated for the first
time, and treatment is usually not associated with side effects. Repeated treatment (with an
interval of more than 1 week), however, is not recommended because cats can display
anaphylactic reactions to the product produced in horses (Hartmann and Hein, 2002).
Besides commercial products, customised (hyper)immune serum may be administered.
Immune serum is derived from healthy individuals or from groups of animals that have
recovered from a specific disease, whereas hyperimmune serum comes from animals that had
been repeatedly vaccinated against specified infectious agents. If such sera are used, their
antibody content and consequently the duration of protection are unknown. Like all
exogenous proteins, administered antibodies are quickly eliminated from the body.
Feline immune sera can be prepared in veterinary practice, but blood donors must be carefully
screened for insidious infections (e.g. FIV, FeLV, Bartonella infection). Ideally, the blood
type of donor and recipient should match; if cross-matching cannot be performed, only type A
cats should be used as donors. The minimum amount required for protection is unknown, but
the dose recommended for cats is 2 to 4 ml serum per kilogram body weight. Careful attention
must be paid to sterility during collection, storage and administration. Jugular vein puncture is
preferred, and the area over the jugular vein should be shaved and prepared for aseptic
venipuncture. Blood should be collected (at least twice the amount of required serum) into
sterile tubes without additives. Serum can be stored at -20° C in single dose aliquots as IgG is
a very stable molecule and can be kept for up to a year if frozen promptly after collection
(Levy and Crawford, 2000). Usually, sera are given subcutaneously; intraperitoneal injection
is more feasible in kittens. If for an instant effect intravenous administration is required,
plasma (instead of serum) should be used (Greene and Schultz, 2005).
Vaccination schedules used for privately owned cats are appropriate in most breeding
catteries. Queens not up-to-date on vaccinations may receive booster vaccines prior to
breeding to maximize delivery of MDA to kittens (Lawler and Evans 1997). As a
consequence, kittens from such queens may need an extra primary vaccination at 16 to 20
weeks in case of persisting MDAs. As stated before, routine vaccination of pregnant cats
should be avoided.
Lactation is not known to interfere with the immune response. However, administration of
any vaccine may stress the queen and may result in a temporary deterioration of mothering
ability and milk production. Vaccination of lactating queens should therefore be avoided.
Vaccines cannot generate optimum protection in animals with conditions that compromise
immune function. Such conditions include deficient nutrition, genetic immunodeficiencies,
systemic disease, concurrent administration of immunosuppressive drugs, and environmental
stress. Efforts should be made to protect cats from exposure to infectious agents and to correct
these conditions if possible prior to vaccination; if this cannot be assured, vaccination should
be performed nevertheless and repeated after the animal is fully recovered.
Modified live FPV vaccines should be used with caution in severely immunocompromised
individuals, as the failure to control viral replication could potentially lead to clinical signs.
In cats receiving corticosteroids, vaccination should be considered carefully. Depending on dosage and duration of treatment, corticosteroids may cause functional suppression of particularly cell-mediated immune responses, but pertinent studies are lacking. In dogs, corticosteroids do not hamper effective immunization if given for short periods of time at low to moderate doses (Nara et al., 1979). However, the use of corticosteroids at the time of vaccination should generally be avoided.
In cats with chronic illness vaccination may sometimes be necessary. Manufacturers evaluate vaccine safety and efficacy in healthy animals and accordingly label their vaccines for use in healthy animals only. Nonetheless, cats with stable chronic conditions such as chronic renal disease, diabetes mellitus or hyperthyroidism should receive vaccines at the same frequency as healthy cats. In contrast, cats with acute illness, debilitation, or high fever should not be vaccinated, unless there are compelling reasons to do so. In these cases, inactivated preparations should be used.
Retrovirus-infected cats should be kept indoors and isolated, to diminish the likelihood of
infecting other cats and to reduce exposure to other infectious agents. FeLV-infected cats
should be vaccinated against FPV. Although there is no evidence that FeLV-infected cats are
at an increased risk of vaccine-induced disease from residual virulence of MLV vaccines,
non-infectious vaccines are preferred if available. FeLV-infected cats may not be able to
mount adequate immune responses to rabies vaccination and perhaps also to other vaccines.
Therefore, more frequent vaccination should be considered in these cats.
FIV-infected cats are capable of mounting immune responses to administered antigens except
during the terminal phase of infection; also primary immune responses may be delayed or
diminished (Dawson et al., 1991; Reubel et al., 1994; Foley et al. 2003). In one study, cats
experimentally infected with FIV developed vaccine-induced panleukopenia when given
MLV FPV vaccines (Buonavoglia et al., 1993). Immune stimulation of FIV-infected
lymphocytes in vitro promotes virus production, and in vivo, vaccination of chronically
infected cats with a synthetic peptide was associated with a decrease in the CD4+/CD8+ ratio
(Lehmann et al.1992; Reubel et al. 1994). Therefore, a potential trade-off to protection from
secondary disease is the progression of FIV infection due to increased virus production. Thus
only FIV cats at high risk of exposure to infectious agents should be vaccinated, and only
with killed vaccines.