Trichophyton verrucosum
| Trichophyton verrucosum | |
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| Chlamydospores of T. verrucosum growing in chains at 37 C | |
| Scientific classification | |
| Kingdom: | Fungi |
| Phylum: | Ascomycota |
| Subphylum: | Pezizomycotina |
| Class: | Eurotiomycetes |
| Order: | Onygenales |
| Family: | Arthrodermataceae |
| Genus: | Trichophyton |
| Species: | T. verrucosum |
| Binomial name | |
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Trichophyton verrucosum E. Bodin (1902) |
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| Synonyms | |
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Trichophyton verrucosum, commonly known as the cattle ringworm fungus, is a dermatophyte largely responsible for fungal skin disease in cattle, but is also a common cause of ringworm in donkeys, dogs, goat, sheep, and horses. It has a worldwide distribution, however human infection is more common in rural areas where contact with animals is more frequent, and can cause severe inflammation of the afflicted region.Trichophyton verrucosum was first described by Emile Bodin in 1902.
Trichophyton verrucosum is very slow-growing compared to other dermatophytes. In culture, it is characterized by being flat, white/cream colour, having an occasional dome, with a glabrous texture, known as the variant album, however other variations are also found: T. verrucosum var. ochraceum has a flat, yellow, glabrous colony; T. verrucosum var. discoides has a gray-white, flat, and tomentose colony; and T. verrucosum var. autotrophicum is rarely seen and is associated with sheep. Under a microscope, macronidia are rare, and have a rat-tail or string bean shape, while micronidia are tear-shaped and have been only observed in laboratories when grown under enriched conditions. It lacks a teleomorph (sexual) stage. At 37 C (the only dermatophyte with an optimum growth temperature this high),chlamydospores become thick-walled and found in long chains. Macronidia are more commonly produced on BCP-milk solids-yeast extract agar, and only on colonies over 7 days old. Under refrigeration, it will die. Regions infected with T. verrucosum will fluoresce under a blacklight in cattle, but not in humans.
Trichophyton verrucosum is thought to have evolved from a soil-dwelling ancestor that migrated to its contemporary cattle host, losing many features that it previously required for survival in soil habitats through genetic drift, such as vitamin prototrophy, urease activity, and the ability to perforate hair. Infection is characterized by 10–50 mm patches of hair loss, desquamation, and formation of thick crusts.Trichophyton verrucosum is endemic in cattle, and almost exclusively the fungus that is isolated from cattle with ringworm, with younger cattle being more prone to infection due to their skin having higher pH, and having weaker immune systems. Infection in cattle peaks in fall and winter due to the overcrowded, cramped facilities of cattle-housing facilities. Transmission can occur directly through contact between sick and healthy animals, and indirectly through fomites (T. verrucosum can be viable for up to 4 years). One study in Italy of 20 farms and 294 cattle found 100% of farms to contain infected cattle, with prevalence within farms ranging between 25-100%. In contrast, T. verrucosum has been eradicated from Eastern Germany due to immunization efforts. Rearing cattle together with ruminants, such as sheep, may increase prevalence of infection due to ruminants being able to roam free, spreading the infection.Trichophyton verrucosum is important economically, as it can spoil milk, meat, and leather quality of cattle.
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