Histopathology Diagnosis of Filamentous Fungi

Fusarium and Neocosmospora: fungal priority pathogens in laboratory diagnosis

Fusarium and Neocosmospora are two fungal genera recently recognized in the list of fungal priority pathogens. They cause a wide range of diseases that affect humans, animals, and plants. In clinical laboratories, there is increasing concern about diagnosis due to limitations in sample collection and morphological identification. Despite the advances in molecular diagnosis, due to the cost, some countries cannot implement these methodologies. However, recent changes in taxonomy and intrinsic resistance to antifungals reveal the necessity of accurate species-level identification. In this review, we discuss the current phenotypic and molecular tools available for diagnosis in clinical laboratory settings and their advantages and disadvantages.

The pathology of canine mammary candidiasis with embolic dissemination in a dog

Candidiasis is a fungal disease caused by Candida albicans or other members of the genus Candida. Descriptions of candidiasis are comparatively reduced in veterinary relative to human medicine, with no cases of mammary candidiasis being identified in pet animals. This report presents the cytological, pathological, and molecular findings of mammary candidiasis with embolic dissemination in a postpartum dog. A 1-year-old, female Shih-tzu dog that had recently given birth was admitted to a veterinary teaching hospital in Southern Brazil after repeated episodes of intermittent mammary disease and a neurological syndrome. The dog was euthanized due to worsened clinical status and poor prognosis despite adequate clinical therapy and was submitted for routine post-mortem evaluation to determine the cause of the neurological manifestations. Cytological analysis of purulent mastitis identified intralesional fungal hyphae. Gross evaluation revealed multiple masses within the kidneys, liver, myocardium, pancreas, and brain. Routine histopathology and histochemistry identified fungal nephritis, hepatitis, myocarditis, pancreatitis, and encephalitis associated with intralesional fungal hyphae, frequently with fungal emboli and vasculitis. Pure cultures of C. albicans were obtained from fragments of the masses observed at the myocardium and kidneys, with the typical germ tube of C. albicans being identified by microscopic evaluation. A PCR assay that targeted the ITS1 and 4 generic regions of fungi, amplified the desired amplicon, and direct sequencing confirmed C. albicans. Immunohistochemical and molecular assays designed to identify common infectious disease pathogens of dogs did not confirm the participation of canine distemper virus, canine parvovirus, or canine adenovirus in the target tissues of this dog. These findings suggest that this dog suffered an initial cutaneous lesion, that probably served as portal of entry to the mammary gland, resulting in mammary candidiasis with subsequent embolic dissemination to multiple organs. This report represent the first description of mammary candidiasis in pet animals and probably one of the few pathological descriptions of mammary candidiasis in domestic animals. In this case, the cause of the fungal infection was probably associated with factors intrinsic to abdominal surgery, pregnancy, and the utilization of antibiotics.

Preliminary Experience in Post-COVID-19 Mycoses: A Pathologist's Perspective

Background Coronavirus disease is caused by the severe acute respiratory syndrome coronavirus-19. Because of co-morbidities and indiscriminate use of steroids and antibiotics, the incidence of opportunistic fungal infections has increased in COVID-affected individuals. Aims and objectives The aim of the study is to analyze the various tissue reaction patterns of COVID-19-associated mucormycosis in the surgical debridement specimens using routine hematoxylin and eosin (H&E) stain and special stains like periodic acid-Schiff (PAS), Grocott-Gomori's methenamine silver (GMS), Masson trichrome (MT) and Prussian blue (PB), and to understand the pathogenesis of COVID-19 sequelae. Materials and methods This retrospective observational study was conducted after the approval from the Institute Human Ethical Committee (IHEC) on 45 tissue samples of COVID-associated mucormycosis using routine H&E and histochemical stains such as PAS, GMS, MT, and PB. Detailed demographic profiles, clinical information, radiological findings, and relevant microbiological data in available cases, like reports on potassium hydroxide (KOH) mount preparation, and fungal culture reports on Saboraud's Dextrose Agar (SDA) medium were collected. The different histomorphological tissue reaction patterns were observed and analyzed. Results All the surgical debridement specimens from post-COVID cases had histomorphology of mucormycosis displaying broad, aseptate, ribbon-like fungal hyphae with right-angle branching (45/45). Six of the 45 cases also reveal thin, narrow septate, acute angle branching hyphae, indicating co-existing Aspergillosis (6/45). The histological tissue reaction patterns observed were categorized as extensive tissue necrosis (100%), vascular proliferation (82%), angioinvasion (58%), giant cell reaction (53%), fibrin thrombi (47%), septic thrombi and angiodestruction (40%), fungal osteomyelitis (33%), necrotizing granulomas (31%). Conclusion This study infers that post-COVID-19 associated mucormycosis, alterations in the local tissue microenvironment are found to have a favorable effect on colonizing fungi and result in destructive tissue reactions such as angioinvasion, angiodestruction, necrosis, necrotizing granulomas, suppurative inflammation, and iron pigment deposition. The spectrum of morphological changes reflects the host's immune status.

Diagnosis from Tissue: Histology and Identification

The diagnosis and initiation of appropriate treatment against invasive fungal infections depend upon accurate identification of pathogens by pathologists and clinical microbiologists. Histopathology is often critical in providing diagnostic insight in patients with suspected fungal infections, and such findings are incorporated into the definitions of proven or probable disease caused by certain pathogens. Such examinations can offer provisional identifications of fungal organisms, which can help guide initial therapy while laboratory results are pending. Common etiologic agents of invasive mycoses may be recognized based on morphologic characteristics observed in tissue and biologic fluids, such as those obtained from bronchoalveolar lavage and bronchial washings. However, care should be taken in the interpretation of these findings, as there may be a false sense of the ability to correctly categorize fungal organisms to the genus or species level by morphologic features alone. Studies have demonstrated discordant results between histopathology and laboratory results due to overlapping morphologic features, morphologic mimics, and sampling errors. Thus, histopathology plays an integral role in providing a differential of potential fungal pathogens but must be combined with results from laboratory studies, including cultures, antigen tests, serology, and molecular assays, in order to improve accuracy in the identification of etiologic agents of fungal infections. Inaccurate identification of the infecting organism can lead to inappropriate antifungal therapy and possibly poor clinical outcomes.