Light micrograph of a guinea pig hair infected with the fungus Trichophyton mentagrophytes. Fungal spores (small circles) are visible withing the hair shaft. This fungus species is a common cause of dermatophytoses (skin diseases) in pets and humans, commonly known as ringworm or tinea. Dermatophytosis causes raised, red patches of skin and can cause hair loss. Treatment usually involves topical antifungal medication for around 1-2 weeks.