Serological Diagnosis of Fungal Infections

Abstract

Difficulties are being faced in the diagnosis of invasive fungal diseases due to the lack of sensitivity and specificity of the current diagnostic methods or taking too long time to get a result having clinical importance. Rapid diagnosis is the key point in patient outcomes. Excluding the culture tests, because of its rapid application and no need for invasive sampling, was making the serological tests based on the measurement of response of specific host antibody became attractive. However especially due to immunosuppressive conditions, these tests are not always the indicator of invasive disease in the patients who have no ability to produce specific antibody response. Detection of microbial antigens generally requiring a relatively large microbial burden, limits the assay sensitivity. Nonetheless, several examples of successful antigen detection systems have been developed, and some of these are widely used. To detect circulating Aspergillus galactomannans enyzme immunoassay (Platelia) method utilizing the rat monoclonal antibody EB-A2 is commercially in use. This test is able to detect galactomannan in the level of 0.5-1.0 ng/ml. Furthermore, galactomannan could be detected in the serum at a early stage of invasive aspergillosis before clinical signs and symptoms occured. However, this test has some disavantages like false positive or negative results. (1-3)-β-D-glucan is a characteristic cell-wall component of fungi except for Zygomycetes. A broad range of fungi including Aspergillus, During invasive infections (1-3)-β-D-glucan is released to the blood by some fungi containing Aspergillus, Candida, Fusarium, Trichosporon, Saccharomyces, Acremonium and Pneumocyctis jirovecii. The method used for determination of (1-3)-β-D-glucan concentration depends on activation of glucan by factor G, a horsecrab shoe coagulation factor. There are some commercial test kits available for (1-3)-β-D-glucan both in Europe and USA.Mannan is the major circulating antigen in patients who have invasive candidiasis. There are several serological tests for the detection of antibodies formed against mannan. However, these tests are usually failed in discriminating between colonization and invasive infection. When combination with mannan antigen test was performed, it gave sensivity of 80% and specifity of 93%. In the diagnosis of cryptococcal infections detection of capsular antigen in the both cerebro-spinal fluid or serum, is used. Both latex aglutination and enzymeimmunoassay tests are found to detection of capsular antigen. The diagnosis of fungal infections has moved forward in the past few years and there are many newly developed methods that are likely to provide early detection of fungal infections. However, it seems that best approach is combining both traditional methods like culture or microscopy with serological methods.