The organism can deposit in the upper or lower respiratory
tract. However, the organism primarily remains in the upper airways since
the encapsulated organisms are larger than the diameter of the terminal
airways. This leads to a predominance of upper respiratory tract infections
rather than pulmonary disease (Gerds-Grogen et al, 1997).
Mammals with normal immune systems usually clear the cryptococcal
infection prior to its spread. The majority of resistance is provided by
cell-mediated immunity. Infections with C.neoformans may indicate immunosuppression
- damage to the immune system which has left the animal vulnerable to a
wide variety of diseases. Immunosuppression is readily seen in cats infected
with feline leukaemia virus (FeLV) or feline immunodeficiency virus
(FIV). It is this reason that it has been suggested that this cat's
FeLV/FIV status be checked.
The clinical signs of infection include respiratory infections
(seen in >80% of cases), characterised by sneezing, nasal discharge
and respiratory distress (Gerds-Grogan et al, 1997). Although these
signs are presented in this case a definitive diagnosis may require further
testing. The apparent encapsulated organism may be C.neoformans but two
similar organisms Histoplasma capsulatum and Blastomyces dermatitis have
been reported in upper respiratory infections, but are rare.
It would be recommended to use methods of immunohistochemistry to detect
the presence of specific proteins in these cells and to lead to a more accurate
identification of crytococcosis.
A study by Legendre & Toal in 2000 suggested that the
next logical choice for diagnostic testing is latex agglutination, which
detects the crytococcal capsular antigen of all known serotypes found in
serum, urine or CSF. The specificity of this test is highest when the serum
is pre-treated with a protease (pronase). The latex agglutination
test is useful for diagnostic purposes and for the monitoring of treatment
to Cryptococcosis. Further diagnosis involves immunostaining in tissue biopsies,
complement fixation or fungal culture (Raskin et al, 2001).
Infection with Capillaria aerophilia is diagnosed by finding
the adult nematodes or characteristic ova in nasal secretions. One egg was
found in the wash cytology of the cat in this case.
C.aerophilia in cats has a direct cycle, with infected eggs being ingested
with food or water. The pathogenic effects of these lungworms depend on
their location within the respiratory tract, the number of infective larvae
ingested and the animal's immune state.
Clinical signs of lungworm infection range from moderate coughing with slight
increased respiratory rates to severe persistent coughing and respiratory
distress, even failure (Raskin et al, 2001).
References
Gerds-Grogan S & Dayrell-Hart B: Feline Cryptococcosis:
A retrospective evaluation. J Am Anim Hosp Assoc 33:118-122, 1997.
Jacobs GJ, Medleau L, Calvert C & Brown J: Cryptococcal
infection in cats: Factors influencing treatment outcome, and results of
sequential serum antigen titers in 35 cats. J Vet Int Med 11(1):1-4, 1997.
Legendre AM, Toal RL: Diagnosis and treatment of fungal
diseases of the respiratory system.WB Saunders, Philadelphia, 2000, pp 815-819.
Raskin, RE & Mayer, DJ (2001). Atlas of Canine and
Feline Cytology. W.B. Saunders Company. |