Cytologic, histopathologic confirmation remains mainstay of diagnosis - DVM
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Cytologic, histopathologic confirmation remains mainstay of diagnosis


DVM360 MAGAZINE


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.

Toxoplasmosis

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.


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Source: DVM360 MAGAZINE,
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