Commonly called “ringworm,” the public sometimes assumes a parasitic cause, but the veterinary community knows the cause is fungal — an important distinction when diagnosing and managing cases.
Dermatophytosis is one of the more common fungal infections veterinarians encounter, yet it can be deceptively tricky to diagnose and manage. Practitioners can rely on the Texas A&M Veterinary Medical Diagnostic Laboratory, TVMDL, for accurate diagnosis and expert analysis of dermatophytosis.
Recognizing the threat of dermatophytes
Dermatophytes are worth close attention because they can cause persistent skin infections in animals, mimic other dermatologic conditions, and have zoonotic potential, posing a risk to humans in close contact.
Infection can be especially concerning when dealing with shelter animals, households with multiple pets, immunocompromised individuals, and the young or elderly.
Because dermatophytosis is zoonotic, an accurate diagnosis is essential to protect both animal and human health.
Background and clinical signs
In small animals, dermatophytosis is most commonly caused by Microsporum canis, Microsporum gypseum, and Trichophyton mentagrophytes. However, the Trichophyton species tend to appear more often in large animal cases.
Clinically, dermatophytes can present as scaly, crusty lesions, folliculitis, and hair loss. The signs can mimic bacterial infections such as mange, allergic dermatitis, or even immune-mediated conditions like pemphigus. Infection typically occurs through direct contact with an infected animal or by touching contaminated dirt, brushes, carpets, or equipment. Accurate diagnosis of dermatophytosis is the foundation of effective veterinary care.
Considerations from the field
Catherine Campbell, DVM, veterinary diagnostician at the College Station lab, reflects on her clinical experience with ringworm testing.
“When I was in practice, I would keep dermatophytosis at the top of my differential list when presented with a young animal with hair loss and crustiness,” Campbell said. “One of the simple tests I performed at the point of care to support a diagnosis of dermatophytosis was using a Wood’s lamp.”
The blacklight tool can help identify M. canis infections because the fungus sometimes fluoresces a bright apple-green color; however, this diagnostic approach may not always be reliable.
“The best thing to do is to submit a fungal culture,” Campbell said. “With a culture we can identify the actual agent and see that the spores are active. And Wood’s lamps can sometimes present issues with finding false positive lesions.”
As for the DTM, Dermatophyte Test Medium, Campbell ultimately decided against using this method in her office.
“I struggled to train staff in this area,” she said. “And it always seemed like there was overgrowth of saprophytic fungal colonies.”
Sample collection and submission
Proper sample collection is vital for an accurate diagnosis. TVMDL recommends using sterile hemostats to pluck hairs and scabs from the edges of lesions, or broken hairs within the lesion itself. Multiple lesions should be sampled whenever possible.
The collected material can be combined in a single sterile container — a simple red-top tube is sufficient — then padded with protective cushioning and shipped at ambient temperature to the lab. Fresh tissue biopsies should also be submitted in a red-top tube without saline or formalin.
DTM cultures at TVMDL
Once ringworm samples arrive at TVMDL, they are handled by the microbiology team. DTM cultures are inoculated onto specialized agar prepared in-house and observed over 2–3 weeks for fungal growth. If growth occurs, lab staff differentiate dermatophytes from environmental saprophytes by observing colony morphology, hyphal structures, spore formation, and growth characteristics.
Tape mounts and microscopic examination by highly trained staff allow precise identification, and molecular techniques such as 16S rRNA Gene Sequencing are available to confirm results.
Culture vs. PCR
While PCR testing offers the advantage of rapid results, culture provides critical information about whether fungal spores are still viable and capable of causing infection. This distinction becomes especially important when assessing treatment plans and determining whether an animal is truly free of infection before returning to its environment or group housing. Additionally, culture remains a more cost-effective option for many practices.
Choose TVMDL
Fungal cultures can be time-consuming, but they provide significant diagnostic value. To support busy practitioners, TVMDL’s trained staff are equipped to handle the culture process efficiently and accurately.
“It really lifted a heavy load off me as a practitioner,” Campbell said. It was especially helpful to know exactly what I was dealing with.”
Submitting ringworm samples to TVMDL can save time and reduce stress in a busy practice. This top-tier diagnostic service prompts informed treatment decisions quickly and confidently.
Partnering for accuracy and precision
Ringworm remains a common and clinically significant dermatophyte infection across animal species. Accurate identification and interpretation are critical due to its zoonotic potential.
By using TVMDL’s services, veterinarians save time, reduce uncertainty, and provide the best care for their patients.
“It made my life so much easier,” Campbell said. “As a busy practitioner, submitting DTM cultures, TVMDL provided me comfort in knowing that results would be diagnostically accurate.”
For more information about TVMDL services, visit tvmdl.tamu.edu or call the College Station lab at 1.888.646.5623.