''Sporothrix brasiliensis'' is a

fungus A fungus (: fungi , , , or ; or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and mold (fungus), molds, as well as the more familiar mushrooms. These organisms are classified as one ...

that is commonly found in soil. It is an emerging fungal pathogen that is causing disease in humans and cats mainly in

Brazil Brazil, officially the Federative Republic of Brazil, is the largest country in South America. It is the world's List of countries and dependencies by area, fifth-largest country by area and the List of countries and dependencies by population ...

and other countries in

South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a considerably smaller portion in the Northern Hemisphere. It can also be described as the southern Subregion#Americas, subregion o ...

. Similar to other species in ''Sporothrix'' genus, this fungus causes the disease

sporotrichosis Sporotrichosis, also known as rose handler's disease, is a fungal infection that may be localised to skin, lungs, bone and joint, or become systemic. It presents with firm painless nodules that later ulcerate. Following initial exposure to '' Sp ...

. However, it has been observed that more severe disease results from infection by ''Sporothrix brasiliensis'' compared to other species. The fungus is a thermally

dimorphic fungus A dimorphic fungus is a fungus that can exist in the form of both mold and yeast. As this is usually brought about by a change in temperature, this fungus type is also described as a thermally dimorphic fungus. An example is '' Talaromyces ma ...

as it is found in the mycelium phase at room temperature and as yeast in the warmer temperatures of host bodies.

Morphology

The two morphologies displayed by ''Sporothrix brasiliensis'' are a hyphal form which occurs in the environment and a yeast form which occurs at higher temperatures (36 - 37 °C) such as within the bodies of

mammals A mammal () is a vertebrate animal of the class Mammalia (). Mammals are characterised by the presence of milk-producing mammary glands for feeding their young, a broad neocortex region of the brain, fur or hair, and three middle e ...

Hyphal Phase

The hyphal form of ''S.brasiliensis'' occurs at room temperature. Melaninization level of the hyphal form can vary from light (albino) to dark (pigmented) phenotypes. Sympodial conidia are obovoid shaped with a glassy (hyaline) appearance while sessile conidia are dark colored and globose.

Yeast Phase

The yeast form of ''S.brasiliensis'' occurs at higher temperatures. Micro-morphologically the yeast takes the shape of an elongated cigar.

Habitat and Ecology

''S.brasiliensis'' is commonly found in the soil and is saprophytic in its mycelium phase. The main vector of the pathogen is thought to be cats which spread the fungus through bites and scratches as well as lesions found on the bodies of cats. It is believed that the origin of the pathogen comes from the ingestion of rats by cats where it zoonotically spread to humans.

Epidemiology

''Sporothrix brasiliensis'' was first described in the Southeastern region of

and sporotrichosis caused by the fungus was endemic to the region prior to 1990. However disease has quickly spread to other parts of

and neighboring countries in South America with reported cases in

Argentina Argentina, officially the Argentine Republic, is a country in the southern half of South America. It covers an area of , making it the List of South American countries by area, second-largest country in South America after Brazil, the fourt ...

Paraguay Paraguay, officially the Republic of Paraguay, is a landlocked country in South America. It is bordered by Argentina to the Argentina–Paraguay border, south and southwest, Brazil to the Brazil–Paraguay border, east and northeast, and Boli ...

Bolivia Bolivia, officially the Plurinational State of Bolivia, is a landlocked country located in central South America. The country features diverse geography, including vast Amazonian plains, tropical lowlands, mountains, the Gran Chaco Province, w ...

, Columbia and

Panama Panama, officially the Republic of Panama, is a country in Latin America at the southern end of Central America, bordering South America. It is bordered by Costa Rica to the west, Colombia to the southeast, the Caribbean Sea to the north, and ...

. A review in 2015 reported that of 5,814 cases of sporotrichosis in Brazil, 88% of cases were caused by ''S.brasiliensis.'' The fungus has been isolated from intestinal and feline fecal samples which suggest that feces from infected cats may contaminate soil and contribute to the spread of the disease.

Sporotrichosis

Sporotrichosis Sporotrichosis, also known as rose handler's disease, is a fungal infection that may be localised to skin, lungs, bone and joint, or become systemic. It presents with firm painless nodules that later ulcerate. Following initial exposure to '' Sp ...

is traditionally associated with subcutaneous exposure of '' Sporothrix'' propagules typically through minor injury while coming in contact with plants, soil, or organic matter. However zoonotic transmission through cats mainly through scratching, biting, or coming in contact with skin lesions has been the main mode of transmission for ''S.brasiliensis,'' constituting the current epidemic in South America. While cutaneous infection is most common, pulmonary sporotrichosis from inhaling conidia, and disseminated sporotrichosis can also occur, primarily in individuals who are immunocompromised. It is believed that ''S.brasiliensis'' is more virulent than other species that cause sporotrichosis like '' S.schenckii'' and results in larger, longer lasting lesion with a higher degree of local and systemic inflammation as demonstrated on mice. A report in May 2020 reported a fatal case of pulmonary sporotrichosis caused by ''S.brasiliensis'' in a patient with no history of skin trauma or immunocompromise further supporting the notion of increased fungal virulence in ''S.brasiliensis'' relative to ''S.schenckii.''

Treatment

Sporotrichosis caused by ''S.brasiliensis'' is difficult to treat due to resistance to main antifungal therapies. Current treatment recommendations for both felines and humans mainly include the antifungal drug

itraconazole Itraconazole, sometimes abbreviated ITZ, is an antifungal medication used to treat a number of fungal infections. This includes aspergillosis, blastomycosis, coccidioidomycosis, histoplasmosis, and paracoccidioidomycosis. It may be given ...

. Alternative therapies include the use of

terbinafine Terbinafine, sold under the brand name Lamisil among others, is an antifungal medication used to treat pityriasis versicolor, onychomycosis, fungal nail infections, and ringworm including jock itch and athlete's foot. It is either oral adminis ...

and

potassium iodine Potassium iodide is a chemical compound, medication, and dietary supplement. It is a medication used for treating hyperthyroidism, in radiation emergencies, and for protecting the thyroid gland when certain types of radiopharmaceuticals are u ...

for cutaneous infection, and

amphotericin B Amphotericin B is an antifungal medication used for serious fungal infections and leishmaniasis. The fungal infections it is used to treat include mucormycosis, aspergillosis, blastomycosis, candidiasis, coccidioidomycosis, and cryptococ ...

for severe pulmonary and disseminated forms of infection.

Issues with Treatment

While itraconazole has shown moderate effectiveness against ''S.brasiliensis, s''trains of the fungus that display resistance against the drug have been documented. In addition, the treatment of felines is particularly difficult as care requires prolonged intervals of time daily and many cats fail to respond well to therapies. As such abandonment of treatments is frequent and typically occurs with the observed healing of skin lesions. Due to this the recurrence of disease can typically occur with higher severity while increasing the chances of antifungal resistance strain development. Failure to complete treatment regimens also contributes to the continued spread of the disease to other cats and humans.

References

{{Taxonbar, from=Q10676463 Fungi described in 2007 Ophiostomatales Fungi of South America Fungus species