Paracoccidioides brasiliensis: General Characteristics, Pathogenesis, Clin

Paracoccidioides brasiliensis: General Characteristics, Pathogenesis, Clinical Findings, Laboratory Diagnosis, Epidemiology, Prevention and Control

Introduction of Paracoccidioides brasiliensis

Paracoccidioides brasiliensis is a dimorphic fungus that causes Paracoccidioidomycosis, formerly called South American blastomycosis. In parts of Central and South America, this fungus lives. Anybody who lives in or visits areas where it is present can get paracoccidioidomycosis, but it most often affects men who work outdoors in rural areas. Also, the specific habitat of the Paracoccidioides fungus is not precisely known, but it was found in soil near armadillo burrows.

Taxonomic classification of Paracoccidioides brasiliensis

Kingdom: Fungi

Division: Ascomycota

Class: Eurotiomycetes

Order: Onygenales

Family: Ajellomycetaceae

Genus: Paracoccidioides

Species: P. brasiliensis

Morphology of Paracoccidioides brasiliensis

Paracoccidioides brasiliensis is a thermally dimorphic fungus and thus grows in mold form at 25°C and in its yeast form at 37°C.
AT 25°C
Colonies are filamentous, leathery, smooth to wrinkled, woolly, cottony, or glabrous to velvety, with slow development. Within 2 to 3 weeks, the colony matures and its diameter reaches 1 to 2 cm. The front color is cream-white, tan, or brown and the reverse color is brown to brown-yellowish. It produces hyaline, septate hyphae, and aleuriconidia. The hyphae are often sterile and do not sporulate. If present, conidia are oval, unicellular, truncate, and with a broad base and rounded apex. They are located along the hyphae. Arthroconidia and intercalary chlamydospores may also be observed.

AT 37°C
Colonies are yeast-like, white, heaped, wrinkled, or folded. Mold to yeast conversion usually occurs on enriched media, such as brain heart infusion agar, and following 10 to 20 days of incubation. For definitive identification of the fungus, It is fitting to illustrate mold-to-yeast conversion. It develops numerous typical buds that cover the mother yeast cell’s entire surface. A steering wheel resembles this appearance. A narrow neck section connects the daughter cell (bud) to the mother cell. Secondary buds can develop before the bud is detached from the mother cell, forming short chains of yeast cells.

Pathogenesis of Paracoccidioidomycosis

Infection is acquired via the lungs by inhalation of spores from environmental sources. It is most common in humid mountain forests in South and Central America. Males are affected more often than females. It’s possible that female hormones protect women.

Clinical Findings in Paracoccidioidomycosis

Clinical findings depend on the site of involvement as given below.

Pulmonary paracoccidioidomycosis: Most cases have an indolent onset and chronic symptoms such as cough, fever, night sweats, malaise, and weight loss are present in patients. There are characteristic but not diagnostic chest x-rays. It is important to separate the infection from histoplasmosis and tuberculosis.

Mucocutaneous paracoccidioidomycosis: The most typical mucosal sites of infection are the mouth and nose. On the gums, tongue, lips, or palate, painful ulcerated lesions develop and may grow over weeks or months. Palate perforation of nasal septum perforation may occur. Cutaneous lesions around the mouth and nose mostly appear on the face, while widespread lesions may occur in patients with serious infections.

Lymphonodular paracoccidioidomycosis: It is normal for younger patients to have lymphadenitis. The most noticeable manifestation is the cervical and submandibular chains, and lymph nodes may advance to form abscesses with draining sinuses.

Disseminated paracoccidioidomycosis: Paracoccidioides brasiliensis haematogenous spread can lead to widespread disseminated disease, including small or large intestine lesions, hepatic lesions, destruction of the adrenal gland, osteomyelitis, arthritis, endophthalmitis, and meningoencephalitis, or focal cerebral lesions.

Laboratory diagnosis of Paracoccidioides brasiliensis

Specimen: It depends on the site of infection. e.g. in the case of pulmonary paracoccidioidomycosis sputum, pleural fluid, lung biopsy may be taken whereas in mucocutaneous paracoccidioidomycosis cutaneous lesion is preferred.

Direct Examination

Potassium hydroxide (KOH) mount: It shows a large number of yeast cells of P. brasiliensis of about 10–40 µm. Cells usually present as single cells or chains of cells with characteristic multipolar budding.

Culture Characteristics

Paracoccidioides brasiliensis are dimorphic fungi that grow both as molds ( 25°C) and as yeast at 37 ° C. Sabouraud Dextrose Agar (SDA) with yeast extract incubation at 25-30°C for 2 weeks shows mycelial phase.

LPCB preparation

LPCB preparation from the plate incubated at 25°C may show hyaline, septate hyphae, and aleuriconidia while from the plate incubated at 37°C shows multiple, narrow base, budding yeast cells ( steering wheels) as shown above images.

Histological Examination

Following stains are useful for identifications of this fungus and they are-

Hematoxylin and Eosin(H &E) stain: It uses to observe neutrophils and pyogranulomatous reactions due to neutrophilic interactions of the granuloma from the host tissues. Hematoxylin stains the nuclei of cells blue to bluish-purple, and eosin stains the cellular elements in the tissues from pink to red as shown above picture.

Gomori’s methenamine silver stain (GMS): It stains the yeast cell wall deep black while the background is green as shown in the image (B).

Periodic acid-Schiff (PAS) Stain: It stains the yeast cells red with a pink background or light green, identified by the type of counterstain that is used. The histological stains may show multiple, narrow base, budding yeast cells ( steering wheels).

Serological Assay: Immunodiffusion tests and complement fixation tests are useful in the diagnosis of 98% of cases.

Molecular Methods: The sensitivity and speed of traditional methods used in diagnostic mycology have a good potential to complement and boost nucleic acid-based assays. In real-time PCR, the reliability of the internal transcribed spacer (ITS) region for molecular detection of P. brasiliensis has also been shown to be a sensitive technique for rapid paracoccidioidomycosis (PCM) diagnosis.

Epidemiology of Paracoccidioidomycosis

The disease is geographically restricted to Central and South America with high incidence in Brazil, Venezuela, and Columbia. Fungus resides in the soil in an environment that has high humidity. Since 1930, over 15,000 cases of paracoccidioidomycosis have been reported. Many more cases, however, are likely to occur because the disorder is underrecognized. In Brazil, about 80% of the cases reported have occurred. Paracoccidioidomycosis in the United States, where it is not a reportable illness, is possibly uncommon. Scientists predict that fewer than 5 percent of paracoccidioidomycosis patients die from the condition.

Treatment of Paracoccidioidomycosis

Antifungal drugs such as itraconazole and amphotericin B can be used to treat paracoccidioidomycosis. Trimethoprim/sulfamethoxazole, which is also known as co-trimoxazole and has several different brand names, including Bactrim, Septra, and Cotrim, is another drug often used to treat paracoccidioidomycosis. Patients usually need about one year of treatment.

Prevention and Control of Paracoccidioidomycosis

Ignore the site where Paracoccidioides lives.
Inform to take the men who work outdoors in rural areas of Central and South America because of being prone to infection.
If involvement is necessary, wear the protective mask.
Most cases of paracoccidioidomycosis have been reported from Brazil, Venezuela, Colombia, and Argentina and therefore inform the travelers who are going there to follow safety guidelines.
To treat paracoccidioidomycosis antifungal drugs are available.

Key Notes on Paracoccidioides brasiliensis

P. brasiliensis needs to be distinguished from Blastomyces dermatitidis when only single buds are observed and multiple buds are not visible. The buds of Blastomyces dermatitidis are wide-based, unlike Paracoccidioides brasiliensis.
Between P. brasiliensis and Loboa loboi, cross-antigenicity has been observed.
Significant characteristics are clinical history, tissue pathology, culture identification with conversion at 37 ° C to the yeast stage.
WARNING: Blastomyces dermatitidis, Coccidioides immitis, Histoplasma capsulatum, and Talaromyces marneffei cultures pose a significant biohazard to laboratory staff and must be treated in a suitable pathogen handling cabinet with severe caution.
Conversion from the mold form to the yeast or spherule form and animal pathogenicity have all been used in previous microscopic morphology; however, culture identification is now preferred to minimize exposure to infectious propagules by either exoantigen test or DNA sequencing.
Mycosis tissue morphology-Blastomycosis: Large broad base unipolar budding yeast cells (8-10 µm). Coccidioidomycosis: Spherules (10-80 µm) with endospores (2-5µm). Histoplasmosis: Small narrow base budding yeast cells (1-5 µm; 5-2um in var. duboisii). Paracoccidioidomycosis: Large narrow base, multi-budding yeast cells (20-60µm). Penicilliosis (Talaromyces marneffei): In this case, there are small, oval to ellipsoidal yeast-like cells (3 µm in diameter). Sporotrichosis (S. schenckii): Small narrow base budding yeast cells (2-5µm).
Direct examination and culture are the gold standards for the diagnosis of paracoccidioidomycosis.

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