Sporothrix: Introduction, Morphology, Pathogenesis, Complications, Labo

Sporothrix: Introduction, Morphology, Pathogenesis, Complications, Laboratory Diagnosis, Treatment, Prevention and Control

Introduction of Sporothrix schenckii

Sporothrix schenckii is a thermodimorphic fungus widely is widely distributed in soil and in living as well as dead decaying environments. It is a causative agent of sporotrichosis, in both animals and humans. Sporotrichosis is a subacute or chronic infection and a cosmopolitan disease, occurring preferably in tropical and subtropical regions. Infection may also be associated with ulcerative, and suppurative lesions with skin and lymphatic system forming nodular lesions. Sporotrichosis was described for the first time by Benjamin Schenck, who was a medical student at Johns Hopkins Hospital in Baltimore in 1898. After the etiological isolation, Schenck sent the sample to the mycologist Erwin Smith who concluded that the agent was a microorganism of the genus Sporotrichum. The disease was reported for the second time in 1900 by Hektoen and Perkins, who classified the etiological agent as S. schenckii, with the pathogen isolated from the specimen suctioned from the skin lesions of the patient (Hektoen and Perkins 1900). The disease is also known as Rose Gardener’s disease.

Taxonomic Classification of Sporothrix schenckii

(described by Hektoen and Perkins in 1900)

Kingdom: Fungi
Phylum: Ascomycota
Class: Euascomycetes
Order: Ophiostomatales
Family: Ophiostomataceae
Genus: Sporothrix

Species: S. schenckii

Note: New clinically significant species are Sporothrix brasillensis, Sporothrix globosa, and Sporothrix mexicana . A study has proposed Sporothrix schenckii var. luriei to species level (Sporothrix luriei).

Habitat of Sporothrix schenckii

It is commonly found in soil and on living plants such as barberry shrubs and roses or in plant debris such as pine bark mulch and sphagnum moss.
People having professions like florists, gardeners, and forestry workers are prone to infection and infection is common in tropical and subtropical regions.

Morphology of Sporothrix schenckii

S. schenckii is a dimorphous fungus. It has a filamentous form in the basic mycological culture at 25°C, consisting of hyaline, septate hyphae 1 to 2 μm in width. Fungal growth in the colonies is characterized by branched septate hyphae, which produce small distinct asexual spores known as 3-5 μm conidia, which are brown in color. Conidia are produced by conidiophores that arise from the septate hyphae at right angles. The conidiophore, at the ends, is tapered. The conidia formed are lustered on tiny denticles at the apex of the conidiophore forming a flower-like appearance. Conidia are ovoid or elongated, 3-6 x 2-3 μm, hyalin, single-celled and smooth-walled. Large single occurring conidia may also be formed as fungal culture ages. The large conidia are dark, thick, obovate to angular. Budding yeast cells are fusiform on enriched medium approximately 1–3 × 3–10 μm, spherical or oval-shaped, are formed.

Cultural Characteristics of Sporothrix schenckii

Routine mycological agar media, such as malt extract agar and potato dextrose agar, grow slowly at room temperature of 25°C, forming blackish/greyish and shiny colonies, which mature into moist, glabrous, wrinkled, and fuzzy colonies, colored in black. In a rich medium such as the brain heart infusion media (BHI) at 35-37°C, S. schenckii is thermally dimorphic, the growth of which is characterized by multiple budding yeast cells. Colonies are produced in the BHI medium that is glabrous, white-greyish to yellowish in color, yeast cells.

Transmission of Sporothrix schenckii

The inoculation of the fungus into the host is caused by the traumatic implantation of the fungus from contaminated soil, plants, and organic matter with fungus. It’s common in florists, gardeners, miners, and forest workers.
Zoonotic transmission from cats has also been reported in Brazil in a few cases. It has an incubation period of 1-12 weeks.

Pathogenesis of Sporothrix schenckii

Virulence Factors of Sporothrix schenckii are proteinases, melanin, and adherence molecules.

Proteinases: It Produces two extracellular proteinases, proteinase I and II.
Thermotolerance S. schenckii has the ability to grow at temperatures between 35-37°C. At 35°C, it can cause lymphatic sporotrichosis and at 37°C, it can cause disseminated and extracutaneous lesions of sporotrichosis.
Melanin synthesis: Melanin, an insoluble compound that is synthesized by Sporothrix schenckii has been associated with virulence in many fungal groups. Melanin is found on the dematiac conidia of the fungus
Conidial melanization increases the resistance of Sporotrix schenckii to macrophageal phagocytosis, which initiates the first stage of conidia spores infection, the infective fungal particle. Melanin pigmentation plays a key role in causing skin sporotrichosis by increasing the invasiveness of the fungus to the host.

Adherence: Sporotrix schenckii contains adhesives such as integrins and adhesin lectin-like molecules that are capable of detecting glycoproteins on the extracellular matrix of the skin tissues, i.e. fibronectin, laminin, and type II collagen. Fibronectin adhesives are located on the surface of the yeast cells and are attributed to the host by fungal adhesion factors. Laminin receptors are located on the hyphae fungus and the yeasts that have the ability to bind to the extracellular matrix. The presence of these adhesives promotes the adherence of the fungus to the host tissues and enhances the spread of the disease.

Clinical Manifestations of Sporotrichosis

Infection with lymphoma
This is the most common manifestation of S. schenckii. Lesions occur in the hands and arms, lower extremities, trunk, and face. Primary lesions occur within the first few weeks of inoculation. Lesions are small nodules that progress towards ulceration and are a bit painful and unprejudiced.
New nodules spread to the lymphatics and become ulcerated. Lymphangitis can develop, making the lymph nodes swollen and painful.
Cutaneous infections

S. schenckii is a common causative agent for suppurative and granulomatous inflammatory reactions in the dermis and subcutaneous tissues. It is characterized by microabscess and fibrosis, hyperkeratosis, parakeratosis, and pseudoepithelioma hyperplasia.

Fixed Cutaneous Infection

Normally, this is the development of a single lesion on the face. The lesion can be ulcerated or verrucous and it only disappears with antifungal therapy.

Osteoarticular sporotrichosis
It is a rare condition of sporotrichosis, which commonly affects alcoholics.
It is characterized by septic arthritis caused by traumatic inoculation that spreads to the joints. Bursitis and tenosynovitis may occur with carpal tunnel syndrome.
Pulmonary sporotrichosis

It is a subacute to chronic infection and is common in people with chronic obstructive pulmonary disease (COPD). It occurs after conidia are inhaled. It is characterized by fever, fatigue, weight loss, coughing, sputum production, and hemoptysis. Infected individuals often develop chronic cavitary pulmonary histoplasmosis, tuberculosis, or atypical mycobacterial infection.

Clinical classification of sporotrichosis

Skin

Lymphocutaneous
Fixed cutaneous
Multiple inoculations

Mucous membrane

Ocular
Nasal
Others

Systemic

Osteoarticular
Cutaneous disseminated
Pulmonary
Neurological
Other locations/sepsis

Immunoreactive

Erythema nodosum
Erythema multiforme
Sweet’s syndrome
Reactive arthritis

Spontaneous regression

Laboratory Diagnosis of Sporotrichosis

Specimen

It depends on the site of infections and may be tissue biopsy, pus from lesions, sputum, urine, blood, CSF, synovial fluids, etc.

Direct Examination

KOH mount: Presence of yeast cells and an elongated cigar-shaped morphology

Gram stain: Gram-Positive yeast cells

Histological Examination: For this purpose, the following stains may be used-Hematoxylin and eosin stain, Gomori methenamine silver (GMS), and Periodic acid-Schiff (PAS) stain.

Cultural Characteristics
SDA: Sabouraud dextrose agar (SDA) with chloramphenicol and on media with cycloheximide (actidione), growth occurs in 5-7 days at 25°C, forming filamentous hyaline colonies which become dark at the center as the culture ages. Dematiaceous conidia are also observed as shown above image ( few at center)

PDA and CMA: Potato dextrose agar (PDA) and cornmeal agar (CMA)are used to show conidiogenesis.

Dimorphic media: Brain heart infusion agar, chocolate agar, and blood agar are used to show dimorphism at 35 to 37°C. Growth of colonies develops within 5-7 days to form yeast cell colonies which are creamy and yellow, to tan color.

LPCB Preparation

There is the presence of a filamentous state with thin hyphae and denticle microconidia resembling daisy flowers from the culture obtained at 25°C.

Molecular Detection
Detection of PCR amplicons: Oligonucleotide primers for differentiation of S. schenckii from other fungal species.

Serological Test

Antibody detection: Tube agglutination test to detect agglutinin antibodies (high titers)
Antigen detection: Latex Agglutination in which antigen-coated latex particle is used to detect for sporotrichin antigen in the sera of infected patients.

Sporotrichin Skin Test

This skin test is used to detect cell-mediated immune response also called delayed hypersensitivity and it is useful for confirming the present and previous infection by S. schenckii.

Treatment of Sporotrichosis

A saturated solution of potassium iodide is given as oral administration whereas itraconazole is currently the first-choice treatment. For the treatment of systemic infection amphotericin B can be used.

Prevention and Control of Sporotrichosis

Installation of protective clothing such as gloves and long sleeves during high-risk activities, e.g. handling sphagnum moss, wires, rose bushes, hay bales, conifer (pine) seedlings, or other materials that may facilitate exposure to the fungus. Cats with sporotrichosis should be treated correctly and kept isolated in a proper place to prevent zoonotic transmission.

Key Notes on Sporothrix schenckii

S. schenckii var. luriei differs from S. schenckii by producing large, often septate, budding cells and not assimilating creatine and creatinine.
The sporotrichin skin test is used to confirm the diagnosis of bulbar conjunctival sporotrichosis.
The most commonly used dimorphic medium is brain heart infusion (BHI) agar with blood.

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