Sporothrix schenckii- An Overview

Sporothrix schenckii is a fungus that can cause a chronic infection called sporotrichosis, which affects the skin and sometimes other parts of the body. The fungus is named after Benjamin Schenck, a medical student who first isolated it from a human specimen in 1896.

Sporothrix schenckii is widely distributed in the environment, especially in soil and plant matter such as peat moss, rose bushes, and hay. It can infect humans and animals through skin wounds or inhalation of spores. The infection is more common in people who handle plants or soil, such as gardeners, florists, and forestry workers.

Sporothrix schenckii is a dimorphic fungus, which means it can grow in two different forms depending on the temperature. In the environment and at temperatures below 35°C, it grows as a mold with branching hyphae and conidia (spores). In the body and at temperatures above 35°C, it grows as a yeast with oval or elongated cells that bud.

Sporotrichosis can manifest in different ways depending on the site and extent of infection. The most common form is cutaneous sporotrichosis, which involves the skin and subcutaneous tissues. It usually starts as a small bump that develops into an ulcer and spreads along the lymphatic vessels. Other forms include pulmonary sporotrichosis, which affects the lungs; disseminated sporotrichosis, which affects multiple organs; and osteoarticular sporotrichosis, which affects the bones and joints.

Sporotrichosis can be diagnosed by direct examination, culture, histology, molecular methods, or serology of specimens from infected sites. The treatment of sporotrichosis depends on the type and severity of infection. Antifungal drugs such as itraconazole are usually effective for most cases. Potassium iodide can also be used for cutaneous sporotrichosis. Severe or disseminated infections may require amphotericin B.

Sporotrichosis can be prevented by avoiding contact with contaminated soil or plants, wearing protective clothing and gloves when handling plants or soil, and treating skin wounds promptly. Infected animals should be isolated and treated to prevent zoonotic transmission.

Sporothrix schenckii is a fungus that can be found worldwide in the environment, especially in soil and on plant matter. It can grow as a mold in the environment and as a yeast in host tissues, depending on the temperature.

Some of the plants that can harbor Sporothrix schenckii include barberry shrubs, roses, sphagnum moss, pine bark mulch, and hay. People who work with these plants, such as florists, gardeners, and forestry workers, are at higher risk of getting infected by the fungus through skin injuries.

Sporotrichosis, the infection caused by Sporothrix schenckii, is more common in tropical and subtropical regions, where the climate is warm and humid. However, sporotrichosis can also occur in temperate zones, especially during warm seasons.

Sporothrix schenckii is a dimorphic fungus, meaning that it can exist in two different forms depending on the temperature and the environment. In the soil and on plants, it grows as a mold with branching, septate hyphae that are 1 to 2 μm wide and up to 100 μm long. The hyphae produce small, brown, oval or elongated conidia (asexual spores) that are 3 to 6 μm long and 2 to 3 μm wide. The conidia are arranged in clusters on short stalks called conidiophores that emerge at right angles from the hyphae. The conidia have a distinctive flower-like appearance under the microscope.

When the fungus infects a host, either through a wound in the skin or by inhalation, it transforms into a yeast form that grows at temperatures above 35°C. The yeast cells are round or oval, single-celled, and 2 to 4 μm in diameter. They reproduce by budding, forming chains of cells that can be seen in tissue samples or cultures. The yeast cells are usually white or cream-colored and have a smooth surface.

Figure: Sporothrix schenckii morphology. Left: mold form with conidia and conidiophores. Right: yeast form with budding cells. Image source: .

Sporothrix schenckii can grow on various types of media, depending on the temperature and the nutritional conditions. The fungus exhibits dimorphism, meaning that it can grow as a mold or as a yeast, depending on the environmental factors.

• At room temperature (25-28°C), Sporothrix schenckii grows as a mold on routine mycological agar media, such as malt extract agar and potato dextrose agar. The growth is slow, taking 5-8 days to form colonies. The colonies are initially blackish or greyish and shiny, but they mature into moist, glabrous, wrinkled and fuzzy colonies that are dark in color . The mold form produces hyaline, septate hyphae that are 1-2 µm wide. The hyphae produce conidiophores that arise at right angles and bear conidia at their tips. The conidia are small (3-5 µm), brown, single-celled and smooth-walled. They are arranged in clusters on tiny projections called denticles, giving a flower-like appearance . Some strains may also produce large, dark, thick-walled conidia that are ovoid or angular. The conidia are the infective particles of the fungus that can enter the host through skin injuries.
• At body temperature (35-37°C), Sporothrix schenckii grows as a yeast on rich media, such as brain heart infusion agar, chocolate agar and blood agar. The growth is faster, taking 2-5 days to form colonies. The colonies are glabrous, white-greyish to yellowish in color and yeast-like . The yeast form produces oval or cigar-shaped cells that are 1-3 x 3-10 µm in size. The cells reproduce by budding, forming multiple daughter cells that remain attached to the mother cell . The yeast form is the invasive form of the fungus that can cause disease in the host tissues.

The cultural characteristics of Sporothrix schenckii may vary depending on the source of isolation. Some strains isolated from nature may have different features, such as producing radulaspores (spindle-shaped spores) or spicules (projections on the hyphae). Therefore, it is important to use multiple methods to identify the fungus accurately.

Sporothrix schenckii is transmitted to humans and animals by traumatic implantation of the fungus from contaminated soil, plants, and organic matter . The fungus can enter the skin through small cuts or scrapes, usually after touching thorny plants such as roses, barberry, or blackberry . It can also be introduced through inhalation of the fungal spores from the environment, although this is rare.

Some occupations and activities are associated with a higher risk of sporotrichosis, such as gardening, forestry, mining, and handling hay bales . People who work with these materials should wear protective gloves and clothing to prevent skin injuries and exposure to the fungus.

Zoonotic transmission of Sporothrix schenckii has also been reported in some cases, especially from cats . Cats can become infected by scratching or biting contaminated plants or soil, or by fighting with other infected cats. They can then transmit the fungus to humans by scratching or biting them. This mode of transmission has been responsible for some outbreaks of sporotrichosis in Brazil and other areas of South America. People who own or handle cats should be aware of the signs and symptoms of sporotrichosis in both themselves and their pets, and seek medical attention if they suspect an infection.

The incubation period of sporotrichosis ranges from one to 12 weeks after exposure to the fungus. The infection usually starts as a small, painless bump on the skin that gradually enlarges and ulcerates. The infection can also spread along the lymphatic vessels, causing nodules and ulcers on other parts of the body. In some cases, the infection can disseminate to other organs such as bones, joints, lungs, or central nervous system . These forms of sporotrichosis are more severe and require prompt diagnosis and treatment.

Sporothrix schenckii is a dimorphic fungus that can cause an infection called sporotrichosis in humans and animals. The infection usually occurs when the fungus enters the body through a break in the skin, such as a cut or a scrape, after contact with contaminated soil, plants, or organic matter . The fungus can also be inhaled into the lungs or spread from animals, especially cats.

The pathogenesis of Sporothrix schenckii involves several factors that enable the fungus to survive and cause disease in the host. Some of these factors are:

• Thermotolerance: Sporothrix schenckii has the ability to grow at temperatures between 35-37°C, which allows it to infect the warm-blooded host . At these temperatures, the fungus transforms from a filamentous form in the environment to a yeast form in the host tissues . The yeast form is more resistant to phagocytosis and can disseminate through the lymphatic system.
• Melanin production: Sporothrix schenckii can synthesize melanin, a dark pigment that protects the fungus from oxidative stress and enhances its virulence . Melanin is found on the conidia (asexual spores) of the fungus, which are the infective particles that enter the host through skin wounds. Melanin also helps the fungus to evade the immune system by inhibiting macrophage activation and cytokine production.
• Adhesins: Sporothrix schenckii has molecules on its surface that can bind to specific receptors on the host cells, such as fibronectin, laminin, and collagen . These adhesins facilitate the attachment and invasion of the fungus to the skin and subcutaneous tissues, as well as its dissemination to other organs.
• Proteases: Sporothrix schenckii produces two extracellular proteases, proteinase I and II, that can degrade various proteins in the host tissues, such as elastin, fibrinogen, and immunoglobulins . These proteases help the fungus to penetrate deeper into the tissues and to evade the immune response by destroying antibodies and complement components.

The pathogenesis of Sporothrix schenckii results in different clinical manifestations depending on the route of infection, the immune status of the host, and the strain of the fungus. The most common form of sporotrichosis is cutaneous or lymphocutaneous, which affects the skin and lymph nodes. Other forms include pulmonary, osteoarticular, disseminated, and extracutaneous sporotrichosis, which affect the lungs, bones, joints, and other organs respectively .

Sporotrichosis is a chronic fungal infection that can affect various parts of the body, depending on the mode of transmission and the immune status of the host. The most common forms of sporotrichosis are:

• Lymphocutaneous sporotrichosis: This is the most frequent manifestation of sporotrichosis, accounting for about 75% of cases. It occurs when the fungus enters the skin through a small cut or scrape, usually after contact with contaminated plant matter or soil. The infection typically affects the hands, arms, legs, or face. The first symptom is a small, painless bump that develops within 1 to 12 weeks after exposure to the fungus. The bump may be red, pink, or purple, and may resemble an insect bite or a boil. The bump gradually enlarges and ulcerates, forming an open sore that may drain pus. The infection can spread along the lymphatic vessels, causing new bumps and sores to appear near the original one. These lesions may also ulcerate and become infected with bacteria. Lymphocutaneous sporotrichosis can last for months or years if left untreated.
• Cutaneous sporotrichosis: This form of sporotrichosis affects only the skin and does not involve the lymphatic system. It can occur when the fungus is introduced into a preexisting wound or skin condition, such as eczema, psoriasis, or dermatitis. Cutaneous sporotrichosis can also result from direct inoculation of the fungus into the skin by a contaminated object, such as a needle or a nail. The symptoms are similar to those of lymphocutaneous sporotrichosis, but the lesions are usually limited to one area of the body and do not spread to other sites. Cutaneous sporotrichosis can also persist for months or years without treatment.
• Fixed cutaneous sporotrichosis: This is a rare form of cutaneous sporotrichosis that occurs when the fungus remains localized in one area of the skin and does not spread to other parts of the body. It usually affects the face, especially the nose, cheeks, or ears. The lesion is usually solitary and may be ulcerated or verrucous (wart-like). It may heal spontaneously or persist indefinitely.
• Pulmonary sporotrichosis: This is an uncommon form of sporotrichosis that affects the lungs. It occurs when the fungus is inhaled into the respiratory tract from the environment or from contaminated materials. It can also occur as a complication of disseminated sporotrichosis (see below). Pulmonary sporotrichosis can cause symptoms such as cough, shortness of breath, chest pain, fever, weight loss, and hemoptysis (coughing up blood). The infection can cause lung damage and complications such as bronchiectasis (abnormal widening of the airways), cavitation (formation of holes in the lung tissue), and empyema (accumulation of pus in the pleural space). Pulmonary sporotrichosis can be fatal if not treated promptly.
• Disseminated sporotrichosis: This is a rare and serious form of sporotrichosis that occurs when the fungus spreads from the primary site of infection to other parts of the body through the bloodstream or lymphatic system. It can affect any organ or tissue, but most commonly involves the bones, joints, central nervous system (CNS), liver, spleen, kidneys, eyes, or mucous membranes. Disseminated sporotrichosis usually affects people with weakened immune systems due to conditions such as HIV/AIDS, diabetes mellitus, alcoholism, cancer, organ transplantation, or corticosteroid therapy. The symptoms of disseminated sporotrichosis depend on the site and extent of involvement. For example, bone and joint infection can cause pain, swelling, deformity, and reduced mobility; CNS infection can cause headache, confusion, seizures, meningitis (inflammation of the membranes covering the brain and spinal cord), or encephalitis (inflammation of the brain); eye infection can cause conjunctivitis (inflammation of the conjunctiva), uveitis (inflammation of the uvea), or endophthalmitis (infection of the inner eye). Disseminated sporotrichosis can be life-threatening if not treated aggressively.

Sporotrichosis is usually diagnosed by taking a small tissue sample (biopsy) of the infected area of the body and sending it to a laboratory for a fungal culture. The laboratory will examine the sample under a microscope and try to grow the fungus on a special medium. The fungus may take several weeks to grow, so the diagnosis may not be confirmed right away.

Depending on the type and location of the infection, different specimens may be collected for diagnosis. For example, pus from skin lesions, sputum from lungs, urine from kidneys, blood from bloodstream, and cerebrospinal fluid from brain and spinal cord may be used .

Some blood tests can help diagnose severe or disseminated sporotrichosis, but they are usually not reliable for skin infections. These tests include tube agglutination test and latex agglutination test, which detect antibodies against the fungus in the blood serum. Another test is sporotrichin skin test, which measures delayed hypersensitivity reaction to an antigen derived from the fungus. This test can indicate past or present infection, but it may not be available in some areas.

The diagnosis of sporotrichosis may be challenging because the symptoms are often non-specific and similar to other infections or conditions. The differential diagnosis for sporotrichosis depends on the form and site of the infection. For example, cutaneous sporotrichosis may be confused with bacterial or mycobacterial infections, leishmaniasis, tularemia, or lymphoma. Pulmonary sporotrichosis may mimic tuberculosis, histoplasmosis, or lung cancer. Osteoarticular sporotrichosis may resemble rheumatoid arthritis, gout, or osteomyelitis. Therefore, a high index of clinical suspicion and appropriate laboratory tests are required for accurate diagnosis of sporotrichosis.

The treatment of sporotrichosis depends on the type and severity of the infection. The most common treatment for cutaneous (skin) sporotrichosis is itraconazole, an oral antifungal agent that is taken for 3 to 6 months. Supersaturated potassium iodide (SSKI) is another treatment option for cutaneous sporotrichosis, which is given three times per day for three to six months until all the lesions have gone away. However, SSKI can cause side effects such as nausea, vomiting, rash, and thyroid problems. Therefore, itraconazole is preferred over SSKI for most patients.

For severe or disseminated sporotrichosis, such as pulmonary (lung), osteoarticular (bone and joint), or central nervous system infection, intravenous (IV) amphotericin B is the preferred treatment. Amphotericin B is a potent antifungal drug that can kill the fungus rapidly, but it can also cause serious side effects such as kidney damage, fever, chills, and low blood pressure. Therefore, patients who receive IV amphotericin B need to be monitored closely in a hospital setting. According to the CDC, patients may need to take itraconazole for up to one year after their IV treatments are complete to ensure that the fungus is completely eliminated from their body.

Some patients with pulmonary sporotrichosis may also need surgery to remove infected lung tissue or cavities. Surgery may also be needed for patients with osteoarticular sporotrichosis who have severe joint damage or deformity.

The treatment of sporotrichosis may vary depending on the patient`s age, health status, and response to therapy. Therefore, it is important to consult a healthcare provider who can prescribe the appropriate treatment regimen and monitor the patient`s progress and potential complications. Early diagnosis and treatment of sporotrichosis can prevent serious complications and improve the patient`s prognosis.

Sporotrichosis is a fungal infection that can be prevented by avoiding contact with the spores of Sporothrix schenckii, which are found in soil and plant matter. The following measures can help reduce the risk of sporotrichosis :

• Wear protective clothing such as gloves, long sleeves, and boots when handling or working with materials that may contain the fungus, such as rose bushes, sphagnum moss, hay bales, pine seedlings, or soil.
• Cover any cuts or wounds on the skin with bandages or dressings to prevent the entry of the fungus.
• Wash the skin thoroughly with soap and water after exposure to potentially contaminated materials.
• Seek medical attention promptly if you develop any signs or symptoms of sporotrichosis, such as a painless bump or ulcer on the skin, fever, cough, or joint pain.
• Follow the prescribed treatment regimen for sporotrichosis, which usually involves oral antifungal medication such as itraconazole for several weeks or months. Do not stop taking the medication without consulting your doctor.
• Avoid contact with animals that may have sporotrichosis, especially cats. If you have a cat with sporotrichosis, keep it isolated and treat it with appropriate antifungal medication under veterinary supervision.

Sporotrichosis is a rare but potentially serious infection that can affect various parts of the body. By taking preventive measures and seeking early diagnosis and treatment, you can avoid complications and improve your chances of recovery.

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