FHV can represent a particular problem in cat shelters. Management to prevent and limit the potential for transfer of infection is as important as vaccination in control. In shelters where the incoming cats are mixed, very high infection rates for FHV are frequently encountered. New cats should be quarantined for the first two weeks and cats should be kept individually – unless known to originate from the same household. The design of the shelter and management used should be aimed at avoiding cross infection of cats. New cats should be vaccinated as soon as possible once they have been assessed as healthy and no contraindications to vaccination have been identified. If there is a particular high risk, i.e. past or recent infection with FHV in the shelter, a modified live vaccine may be preferable as it may provide earlier protection. If acute respiratory infection occurs in a shelter, definitive diagnosis of the agent involved with differentiation of FHV and FCV can be useful in deciding on the appropriate preventative measures that should be adopted.
FHV can be a major problem in breeding catteries. Infection most often appears as an
infection in young kittens prior to weaning. It typically occurs at around 4-8 weeks as
maternally derived immunity (MDI) wanes. The source of infection is frequently the mother
who is a carrier and has shown reactivation of latent infection following the stress of kittening
and lactation.
Infection in such young kittens can be severe and frequently involves all the kittens in the
litter. Mortality can be a consequence and some kittens that recover from acute disease are left
with chronic complications, most notably chronic rhinitis. Vaccination of the queen will not
prevent this problem since it will not prevent the queen from becoming a carrier. However, if
the queen has a good antibody titre, this should ensure that the kittens benefit from good
levels of MDI through the colostrum, providing protection for the first month or so of life.
Booster vaccinations of the queen may therefore be indicated to ensure transfer of strong
levels of MDI; this should ideally take place prior to mating. Vaccination during pregnancy
may be considered if this has been overlooked previously. However, vaccines are not licensed
for use in pregnant cats and in this situation, an inactivated vaccine may be preferable.
Breeding management plays a crucial role in control of FHV in breeding catteries.
Queens should kitten in isolation and the litter should not mix with other cats until they have
been fully vaccinated to avoid the risk of exposure to potential carrier cats. Early vaccination
should be considered for litters from queens that have had infected litters previously or for
which there is concern of infection. The earliest age for which FHV vaccines are licensed for
use is 6 weeks but kittens may become susceptible to infection earlier than this as MDI wanes
and vaccination from around 4 weeks of age may be considered. This is usually repeated
every 2 weeks until the primary vaccination course is given in the normal way.
Early weaning into isolation from around 4 weeks of age is an alternative approach to
protecting kittens from potential exposure of infection from their mother. There are no
reliable tests that will identify which queens are carriers and predict which may potentially
infect their own kittens.
Vaccines may not efficiently stimulate immunity in animals with a substantially compromised immune function. Such situations include the presence of systemic diseases, viral-induced immunodeficiency, nutritional deficiencies, genetic immunodeficiencies, concurrent administration of immunosuppressive drugs and severe, prolonged stress. Such patients should be protected from potential exposure to infectious agents where possible but it may be necessary to consider vaccination to ensure protection. It is generally suggested that an inactivated vaccine is preferable in this situation, based on safety considerations, although there is no evidence to support this recommendation.
It is important that FIV-positive cats that are clinically healthy are protected against FHV.
An effective approach is to confine cats indoors and limit potential for exposure. If this is not
possible, vaccination should be considered. Concerns have been raised that vaccination may
contribute to progression of disease, but this may be outweighed by the benefit of protection
in a potentially immunocompromised cat. It is possible that other infections may contribute to
FIV progression.
In FIV-positive cats with a history of clinical problems that are well controlled and in a
stable medical condition, vaccination should be considered to ensure protection is maintained.
In cats that are sick with FIV-related problems, vaccination is generally contra-indicated as in
any systemically ill cat.
The same considerations apply to FeLV-positive cats as to FIV-positive cats. Vaccination is contra-indicated if there are clinical signs related to the FeLV infection but, if the cat appears to be clinically healthy, vaccination should be considered to maintain protection if prevention of potential exposure to FHV cannot be ensured.
Booster vaccination should be continued in cats with stable chronic medical conditions, such as hyperthyroidism and renal disease. Such cats are often elderly and the consequences of infection can be particularly severe.
In cats receiving corticosteroids, vaccination should be considered carefully. Depending on dosage and duration of treatment, corticosteroids may cause suppression of immune responses. The effect of corticosteroids on vaccine efficacy in cats is not known. However, concurrent use of corticosteroids at the time of vaccination should be avoided if possible.