Third Street
Veterinary Hospital, PC
McMinnville, Oregon 97128
Office phone: (503) 472-9418
Cryptococcosis
in Cats
Cryptococcosis
a fungal disease caused by the organism Cryptococcus
neoformans. While the first human
case was reported in 1894, this disease was not observed in the cat until
1951. Since that time, we have learned
a great deal about this common fungal disease of the cat.
Contributing Factors
Establishment
of cryptococcosis is thought to depend upon a weakness in one particular branch
of the immune system. A combination of
environmental exposure and a weak immune system provides the right conditions
for successful infection of the cat.
Prevalence
Of
all the systemic (multi-organ) fungal diseases, cryptococcosis is the most
common one infecting cats. There is no
predisposition to a particular sex, age group, or breed of cats.
The
organism thrives in topsoil enriched with feces of birds, especially
pigeons. The birds do not become
infected because of their relatively higher body temperature.
It
is not possible to rid the environment of the fungus. The organism is ubiquitous, meaning that it lives
everywhere. The fungus has a worldwide
distribution.
Clinical Signs
Most
commonly, the fungus affects the nasal passages and sinuses of the cat. Owners often report that the cat has loud,
noisy breathing or has begun to sneeze frequently. Sometimes, a nasal discharge may be present; it can involve one
or both nasal passages. One of the more
classic findings with this fungus is a prominent swelling over the bridge of
the cat’s nose. Less frequently, a mass may be seen protruding from a
nostril.
Lesions
on the skin are also fairly common and develop in about one-third of all
cases. These may appear as multiple
firm nodules or as draining, slimy areas of ulceration. Rarely, the infection is limited to the skin
and no other organs are involved.
For
an occasional cat, the fungus invades the central nervous system. The clinical signs are usually quite
dramatic and include seizures, blindness, disorientation, circling and
incoordination.
Causes/Transmission
The
primary means of infection is believed to occur secondary to inhalation of the
organism; following this, it settles in the upper respiratory tract. This particular fungus is relatively larger
in size than some of the other fungi and this is the reason that the upper
airways are more often involved.
Sometimes, smaller particles of fungus can reach the lower airway (lung)
and a fungal pneumonia develops.
Diagnosis
In
most cases, a conclusive diagnosis of cryptococcosis is achieved with cytology;
occasionally, histopathology is needed.
Cytology, the microscopic study of cells, can be performed in the
veterinarian's office on some of the fluid draining from a skin lesion, or from
a needle aspirate of the nose or a lymph node. Histopathology is the study of cells and tissue
architecture. A tissue sample is
submitted to a veterinary pathologist for microscopic studies. Usually this is type of study is not necessary.
A
serologic (serum) test called the latex agglutination test can be performed to
look for evidence of fungal proteins in the body. This test is also helpful to gauge the cat’s response to therapy. With successful treatment, the level of
fungal proteins is found to decline.
Treatment
Cryptococcosis
is a treatable disease, although not all cats will survive. Fortunately, the newest anti-fungal agents
being used are well-tolerated by most cats and have relatively few side effects
when compared to the drugs used several years ago. These drugs, (itraconazole and fluconazole) are quite
expensive. They are given once or twice
daily for a period of several months.
It is important not to withdraw therapy until you are told to do so
because, despite apparent improvement, some cats will relapse with the
disease.
Prognosis
With
prolonged, aggressive treatment many cats recover completely from this
disease. However, it should be
remembered that many affected cats have an underlying defect in their immune
system. Even though they may initially
improve, they always have a guarded prognosis, especially when the nervous
system is involved.
Transmission to Humans
Studies
on the fungal organism have found that once an animal is infected, the organism
enters a different form or phase; this does not appear to be infectious to
other animals or to humans. However,
common sense would dictate that strict hygiene should be followed in handling
any observed lesions. Thorough hand
washing should follow contact with the cat.
The
infected cat does not need to be segregated from the owner or other household
pets. The true risk of infection to
humans comes from sharing the same environment that infected the pet (i.e.,
soil, etc.). Because the Cryptococcus organism may be harbored
near your home, we would recommend that you advise your family physician of
your pet's diagnosis. Also, if anyone in your family falls into one of the
following categories, we would recommend that you consult with your physician:
1.
Infants or small children
2.
Transplant patients
3.
Chemotherapy patients
4.
HIV/AIDS
5.
Elderly family members
6.
Anyone with a known immunosuppressed state