I could hear it the moment he came through the door.
Pokey, a 9 year-old neutered male domestic shorthair,
was in his carrier, sneezing his head off. “He’s been
doing this for the last two days,” said his owner,
Siobhan Taaffe. “He must have sneezed about fifty times
yesterday.” A few minutes later, in the exam room, it
only took a few moments to figure out Pokey’s problem.
The sneezing, the watery eyes, the snotty nose… this was
your classic upper respiratory infection.
Upper respiratory infections (URIs) are common in pet
cats. Several infectious organisms are responsible for
causing signs of upper respiratory infection, however,
viral URIs are the most prevalent. In the cat, the
majority of upper respiratory infections (80% to 90%) in
cats are attributable to either feline herpes virus,
feline calici (pronounced “kuh-LEE-see”) virus, or both.
Other respiratory pathogens seen in the remaining 10% to
20% include Chlamydophila (formerly called Chlamydia),
Mycoplasma, and Bordatella.
Sneezing and nasal discharge are the main clinical signs
of acute viral URIs. The viruses irritate the nasal
membranes and trigger episodes of sneezing. Episodes of
sneezing tend to be intermittent initially, increasing
in frequency and severity over a 3 to 5 day period. In
the early stages of infection, the nasal discharge tends
to be serous (watery and clear), and is often not even
noticed by the cat owner. As the disease progresses,
nasal discharges may become mucoid (thick and
yellowish), indicating that a secondary bacterial
infection has developed on top of the initial viral
infection. Fever is a common finding.
Other signs associated with URIs in cats may include
epistaxis (bloody nose) due to violent sneezing,
difficulty eating or chewing food (due to oral ulcers
caused by calicivirus), and a discharge from the eyes.
If the eye discharge dries out and becomes pasty, the
eyelids may seal shut. This is more common in kittens.
If the nostrils become occluded with discharge, it may
be unable to breathe through the nose and the cat may
show open-mouth breathing. Because open-mouth breathing
is also associated with severe lung or heart disease, a
cat displaying open-mouth breathing should be treated as
an emergency until a diagnosis of upper respiratory
infection can be verified. The herpes virus causes more
sneezing compared to the calici virus, however, the
calici virus may cause oral ulceration, which can lead
to increased salivation, dehydration, difficulty eating
or chewing, poor appetite, and weight loss. Kittens are
more susceptible to viral URIs, and the disease in
kittens may be severe.
A diagnosis of acute viral URI is based on the history
and clinical signs. Although both feline herpes virus
and calici virus can be isolated from tissue cultures,
it is rarely necessary to isolate the virus for a
definitive diagnosis. Furthermore, it is not usually
important to distinguish between herpes and calici since
the treatment and management strategies are similar for
Routine laboratory tests, such as a complete blood
count, serum chemistry evaluation, and urinalysis are
usually of little diagnostic value in cat with acute
upper respiratory disease. Cats, however, should be
tested for the presence of concurrent feline leukemia
virus (FeLV) or feline immunodeficiency virus (FIV)
infection, since either of these viruses can suppress
the immune system and may be the underlying cause for
the cat’s upper respiratory disease.
Although some veterinarians submit samples of the nasal
discharge for bacterial culture, this is not necessary
and rarely gives useful information, since the organisms
isolated tend to be the normal flora that are typically
found in the nasal cavity.
Treatment for viral URI consists of antibiotics, making
sure the cat stays well-hydrated, and ensuring the cat
meets its daily nutritional needs. An oral antibiotic
such as amoxicillin (Amoxidrops®), or amoxicillin
combined with clavulanic acid (Clavamox®), is an
excellent first choice for cats with URI. Antibiotics,
it should be noted, do not treat the viral infection.
Antibiotics treat the secondary bacterial infection –
the mucoid ocular and nasal discharge – while the cat’s
immune system defeats the virus on its own.
Lysine can help the cat’s immune system keep the herpes
virus in check. Lysine is an amino acid that has been
shown to reduce the severity of the clinical signs of in
humans, and this has been shown to be the case in cats
as well. Lysine is available in vitamin shops and health
food stores, however, the pills are large and hard to
administer to cats. Recently, a palatable lysine paste (Enisyl-F
™) has become available for veterinarians to prescribe
to cats with URIs due to herpes virus. A study in the
American Journal of Veterinary Research, published in
2002, confirmed the effectiveness of lysine in reducing
the clinical signs of herpes virus infection in cats,
compared with placebo.
Cats with fevers often will refuse to eat. Likewise,
cats with nasal discharge may have trouble smelling
their food, causing a decreased interest in eating.
Meeting the nutritional needs of these sick cats may
require force feeding, either by the owner at home, or
by trained veterinary staff during a brief hospital
stay. Liquid diets specifically formulated for cats and
kittens, such as Clinicare®, are recommended, as are
nutritional recovery diets, such as Hill’s a/d or
Eukanuba Maximum-Calorie. These diets are of a
consistency that is ideal for feeding through a syringe
or a feeding tube, and they contain additional calories,
which is appropriate for sick and debilitated animals,
as illness increases a cat’s caloric requirements. Most
cats with URIs will continue to drink water, however,
cats with fevers have increased fluid requirements and
often don’t meet their daily fluid needs. These cats may
need to be given subcutaneous (under the skin) fluids
either at home, by the owner, or by a veterinarian in a
The prognosis for recovery from viral upper respiratory
infections is excellent, with the majority of adult cats
making a full recovery. Kittens usually have a good
prognosis if they receive prompt, thorough medical care.
Occasionally, kittens will succumb to severe infections.
In general, morbidity and mortality rates increase as
the age of the exposed cat decreases.
Compared to the herpes virus, the calici virus causes
milder clinical signs. However, an outbreak involving a
highly virulent vaccine-resistant strain of calici virus
occurred in northern California in 1998, in which 33% to
50% of affected cats died. Since the report of that
outbreak, at least 4 similar outbreaks have been
identified in Pennsylvania, Massachusetts, Tennessee,
and Nevada. Although infection with this virulent calici
virus remains rare, rapid recognition and treatment is
Cats and kittens are routinely vaccinated against herpes
and calici virus, however, feline viral URI is still the
most prevalent infectious disease of cats today. One
reason for this has to do with the persistent nature of
herpes viruses. Once a cat is infected with herpes, a
chronic carrier state is established, and transmission
from an infected carrier cat to a susceptible cat or
kitten is easily accomplished either by direct contact
or by aerosol transmission. It is suspected that about
80% of cats that recover from acute viral URIs will
become chronic carriers, capable of infecting other
susceptible cats and kittens.
Most cats that are vaccinated against the upper
respiratory viruses have already been exposed to the
virus and are already harboring it in their body.
Vaccination induces immunity, but does not prevent
infection. In other words, cats who are properly
vaccinated will usually only show mild clinical signs of
URI if they’re exposed to and infected with herpes or
calici, or if the dormant herpes or calici virus becomes
reactivated in cats previously infected with these
viruses. Cats that are inadequately vaccinated are at
increased risk of significant illness from these
The typical vaccination protocol involves administering
the vaccine to kittens starting at 6 – 8 weeks of age,
and again at 10 – 12 weeks, and once again at 14 – 16
weeks of age. Cats then receive a booster one year
later, and then every three years afterward, as it has
been shown that the vaccine confers immunity for at
least 3 years, and possibly longer in some cats. In lieu
of revaccination, cat owners may elect to have their
cats’ antibody level checked. Cats with protective
levels of antibodies against herpes and calici do not
need to be revaccinated, however, they should have their
antibody level checked yearly, and be revaccinated if
and when their antibody level is deemed too low to be