Trichophyton mentagrophytes
Also known as: Ringworm, Fungal Dermatitis, Trichophyton infection
In short
Dermatophytosis, commonly known as ringworm, is a highly contagious fungal skin infection in guinea pigs. While zoonotic and easily spread to humans, it is highly treatable with veterinary-prescribed antifungals and thorough environmental cleaning.
TL;DR. Dermatophytosis is a highly contagious, zoonotic fungal skin infection in guinea pigs that causes patchy hair loss and crusting, requiring veterinary-prescribed antifungals and rigorous environmental decontamination to cure.
Dermatophytosis in guinea pigs typically begins with hair loss and crusting around the eyes, nose, and ears.
Dermatophytosis, commonly known as ringworm, is a superficial fungal infection of the skin, hair follicles, and occasionally the nails. Despite its common name, ringworm is not caused by a worm or any other parasite. Instead, it is caused by microscopic fungi known as dermatophytes. In guinea pigs, the vast majority of cases are caused by the fungal species Trichophyton mentagrophytes. This organism is highly contagious and poses a significant zoonotic risk, meaning it can easily spread from infected animals to humans and other household pets.
The infection begins when fungal spores (arthrospores) come into contact with compromised skin or hair shafts. The fungus produces specialized enzymes that digest keratin, a structural protein found in the outer layer of the skin, hair, and nails. As the fungus feeds on this keratin, it invades the hair follicles and surrounding tissue, causing the hair shafts to weaken, break, and fall out. This process leads to the classic circular patches of hair loss and scaling associated with the disease.
For guinea pig owners, dermatophytosis is a condition that demands prompt attention. Because the fungal spores are incredibly resilient and easily shed into the environment, an untreated infection can quickly spread through an entire colony of guinea pigs and infect human family members. Managing this disease requires a coordinated approach of targeted veterinary treatment and aggressive environmental sanitation.
The primary cause of dermatophytosis in guinea pigs is direct or indirect exposure to Trichophyton mentagrophytes spores. Direct transmission occurs when an uninfected animal comes into physical contact with an infected guinea pig or an asymptomatic carrier—an animal that harbors the fungus on its skin and hair but shows no clinical signs of illness. Indirect transmission occurs when a guinea pig comes into contact with contaminated objects, such as bedding, cages, grooming brushes, toys, or human clothing.
Several environmental and host factors increase a guinea pig's susceptibility to developing an active infection:
While any guinea pig can contract ringworm under the right conditions, certain companion animal breeds in other species show suspected genetic predispositions to dermatophytosis. These include Persian cats, Yorkshire Terriers, and Jack Russell Terriers. In guinea pigs, however, environmental conditions and exposure play a far more significant role in infection rates than breed genetics.
Clinical signs of dermatophytosis in guinea pigs typically appear first on the face, particularly around the nose, eyes, and ears. From there, the infection can spread to the forelimbs, back, and rest of the body.
"Pruritus, if present, is usually minimal to mild but occasionally may be intense."
Classic lesions of dermatophytosis feature dry, flaky scales, redness, and hairs that break off easily.
Diagnosing dermatophytosis accurately is essential because other common guinea pig skin conditions, such as sarcoptic mange (Trixacarus caviae mites) or bacterial dermatitis, can cause similar symptoms of hair loss and crusting. Your vet will begin with a thorough physical examination and history, followed by specific diagnostic tests.
Because much of the standardized dermatological literature on ringworm focuses on dogs and cats, veterinarians frequently extrapolate diagnostic and treatment protocols from these species to manage guinea pigs safely.
Your vet may perform a Wood's lamp examination, which involves shining a specialized ultraviolet light over the skin lesions in a dark room. However, this test has significant limitations. The ultraviolet light only causes fluorescence when it interacts with specific chemical metabolites produced by certain strains of Microsporum canis (a common ringworm fungus in cats and dogs). As detailed in a prominent veterinary dermatology textbook:
"This unique combination causes tryptophan metabolites produced by some strains of M. canis to fluoresce a bright apple green color. Unfortunately, not all Microsporum strains produce this cell product, making the Wood's lamp useless for other species."
Because guinea pig ringworm is almost exclusively caused by Trichophyton mentagrophytes, which does not fluoresce, a negative Wood's lamp test does not rule out dermatophytosis.
Your vet may pluck several hairs from the active edge of a skin lesion, place them on a glass slide with mineral oil or a clearing agent, and examine them under a microscope. This allows the vet to look for fungal hyphae or spores (ectothrix spores) coating the hair shafts, as well as characteristic
Treatment must be prescribed by a licensed veterinarian based on your pet. Specific drug doses are intentionally not shown here.
Dermatophytosis, commonly known as ringworm, is a highly contagious fungal skin infection in guinea pigs. While zoonotic and easily spread to humans, it is highly treatable with veterinary-prescribed antifungals and thorough environmental cleaning.
Alopecia、Scaling and crusting、Erythema、Papules、Scaling、asymptomatic carrier state、crusts、seborrhea
Fungal Culture on Dermatophyte Test Medium (DTM)、Fungal culture、Cutaneous biopsy、Cytology、Dermatophyte PCR Panel、Direct Microscopic Examination (Trichogram)
Treatment must be prescribed by a licensed veterinarian based on your pet. Specific drug doses are intentionally not shown here.
This article is for general education and is not a substitute for professional veterinary advice. If your pet is unwell, please consult a veterinarian.
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