Antigen detection for systemic mycoses
Antigen testing methods have been used in the diagnosis of cryptococcosis and aspergillosis. A method employing detection
of capsular antigen has been used to find the organism in the body fluids of people. Antigen detection allows for monitoring
the level of infection during treatment as quantitative results are available through the ELISA method. Measurement of antigens
in urine shows cross reactivity with other causes of disseminated mycosis. Further studies in animals are needed.
Soluble capsular polysaccharide antigens are detected in body fluids of dogs or cats with cryptococcosis. This probably is
the most common fungal serologic test used in veterinary practice. Latex-agglutination methods are the most widely used for
this procedure. The test can be performed on serum or CSF and can detect the organism in very low concentrations and with
high specificity. Proteolytic treatment of the serum prior to performing the test improves its accuracy.
Such measurements are used for diagnostic confirmation and as an index of the effectiveness of treatment. The result of the
test is expressed as a titer based on the highest dilution of sera that gives reactivity.
Although the organism can be found as a commensal on mucous membranes, it does not enter the circulation where it can be measured
until it proliferates and a granulomatous response develops in the tissues. Antigen enters the circulation and can be measured
in the blood and CSF of infected animals.
Methods have been developed to detect Aspergillus antigens in body fluids and usually involve detection of the carbohydrate galactomannan. Inaccurate results have been obtained
with the various methods although those with greater sensitivity have been more accurate. Unfortunately, reactions to other
micro-organisms, even those causing urinary infections, have given false-positive test results.
Antigen testing has been used widely in diagnosis of human candidiasis. Several commercially available test systems are being
used. Most systems detect a metabolite, D-arabinitol; however, its increase may be seen under other conditions. As disseminated
infections of Candida have been rarely reported in dogs and cats, there is little information on the use of such procedures.
Molecular detection for systemic mycoses
PCR has been used to a limited degree in various fungal infections of dogs and cats. Generally, this method has been used
to detect organisms isolated by culture. Multiplex PCR has been employed to detect a number of yeasts and filamentous fungi
in clinical specimens. Reference laboratories use these methods to make finite testing on isolates. PCR has been used for
specific identification of filamentous organisms that are often morphologically hard to distinguish in tissue specimens. Molecular
methods must be interpreted in light of the clinical parameters and microscopic lesions in the tissues.
Real-time PCR has been used on peripheral blood to detect disseminated infections with Aspergillus or Candida in people. PCR studies on systemic mycoses such as blastomycosis and histoplasmosis have been limited. It has been used in
situ in a case of canine histoplasmosis to confirm infection. PCR was also used to compare strains found in the soil and in
corresponding human and canine infections.
PCR is used infrequently in the diagnosis of cryptococcosis because antigen detection is so sensitive, specific and widely
available as a test kit. PCR has been used to detect the organism in serum, urine, CSF and tissues of cats. PCR has been used
most to detect disseminated infections in people with aspergillosis and candidiasis. Samples tested include whole blood, urine,
CSF or lavage fluids. Such results have been compared to those measuring serum galactomannan.
Real-time PCR has been used to diagnose disseminated infections in people and to monitor levels of infection following institution
of therapy. There is no information of the use of this procedure for disseminated infection in dogs and cats. PCR has been
used for rapid detection of urinary candidiasis in dogs and greatly shortened the interval for a confirmed determination of
the infecting organism.
PCR has been used only for confirmation of lagenidiosis and pythiosis with testing of tissue specimens; however, there are
no data concerning their use on sera or body fluids.
The cat is the definitive host of this disease caused by Toxoplasma gondii, and so the only difference is that oocysts may be detected in the cat. Otherwise diagnostic tests are aimed at the systemic
manifestations of illness from spread of the infection into various body tissues.