Chronic mucocutaneous candidiasis is a chronic refractory disease afflicting the mucous membranes, skin, hair, and nails; it is associated with a variety of underlying T cell defects. These in include Job syndrome, an inherited condition with a variety of abnormalitles including an defect in Th17 T cell responses, which are important in controlling fungal infections (Chapter 5).
Invasive candidiasis implies blood-borne dissemination of organisms to various tissues or organs. Common patterns include (1) renal abscess, (2) myocardial abscess and endocarditis, (3) brain involvement (most commonly meningitis, but parenchymal microabscesses occur), (4) endophthalmitis (virtually any eye structure can be involved), (5) hepatic abscesses, and (6) Candida pneumonia, usually presenting with bilateral nodular infiltrates, resembling Pneumocystis pneumonia (see http://ebooksmedicine.net
Fig. 13.42 Themorphologyoffungalinfections.(A)Candidaorganismhaspseudohyphaeandbuddingyeasts(silverstain).(B)Invasiveaspergillosis(grossappearance)ofthelunginahematopoieticstemcelltransplantrecipient.(C)Gomorimethenamine-silver(GMS)stainshowsseptatehyphaewithacute-anglebranching,consistentwithAspergillus.(D)CryptococcosisofthelunginapatientwithAIDS.Theorganismsaresomewhatvariableinsize.(B,Courtesy of Dr. Dominick Cavuoti,Department of Pathology,University of Texas Southwestern Medical School,Dallas,Texas.) earlier). Patients with acute leukemias who are profoundly neutropenic after chemotherapy are particularly prone to the development of systemic disease. Candida endocarditis is the most common fungal endocarditis, usually occurring in patients with prosthetic heart valves or in intravenous drug abusers.
Cryptococcosis, caused by C. neoformans, almost exclusively manifests as an opportunistic infection in immunocompromised hosts, particularly patients with AIDS or hematolymphoid malignancies.
MORPHOLOGYThefungus,a5-to10-µmyeast,hasathick,gelatinouscapsuleandreproducesbybudding(see
Fig.13.42D ).UnlikeinCandida infections,however,pseudohyphalortruehyphalformsarenotseen.Identificationofthecapsuleisakeydiagnosticclue.InroutineH&Estains,thecapsuleisnotdirectlyvisible,butoftenaclear“halo”representingtheareaoccupiedbythecapsulecanbeseensurroundingtheindividualfungi.Indiainkorperiodicacid–Schiffstainingeffectivelyhighlightsthefungus.Thecapsularpolysaccharideantigenisthesubstrateforthecryptococcallatexagglutinationassay,whichispositiveinmorethan95%ofpatientsinfectedwiththeorganism.
Cryptococcosis usually manifests as pulmonary, central nervous system, or disseminated disease. Cryptococcus is most likely to be acquired by inhalation of aerosolized contaminated soil or bird droppings. The fungus initially localizes in the lungs and then disseminates to other sites, particularly the meninges. Sites of involvement are marked by a variable tissue response, which ranges from florid proliferation of gelatinous organisms with a minimal or absent inflammatory cell infiltrate (in immunodeficient hosts) to a granulomatous reaction (in the more reactive host). In the central nervous system these fungi grow in gelatinous masses within the meninges or expand the perivascular Virchow-Robin spaces, producing so-called “soap-bubble lesions.” http://ebooksmedicine.net
The Opportunistic Molds