Dermatophytosis ("Ringworm"): The Fungal Infection In Cattle 🐄🍄

Dermatophytosis ("Ringworm"): Understanding and Managing The Fungal Infection In Cattle 🐄🍄

Causes of Dermatophytosis

Dermatophytosis, commonly known as "ringworm," is a highly prevalent skin infection that affects dairy calves and occasionally adult cows. The primary pathogen responsible for this condition is Trichophyton verrucosum, although other dermatophytes like Trichophyton mentagrophytes can also be involved. The infection is most commonly observed in calves between the ages of 2 months and the yearling stage. This coincides with the period when young dairy animals are grouped together rather than managed individually. Dermatophytes are hardy organisms that can survive on inanimate objects, bedding, and soil for months, even after the removal of infected cattle. Concentration or grouping of young cattle, especially during winter months, increases the incidence of ringworm in affected herds. Farms with a history of ringworm often experience yearly epidemics in heifers. Conversely, herds that have not encountered clinical ringworm remain free from the problem unless new infected animals are introduced. Interestingly, adult cows may also suffer from severe ringworm infections, particularly during winter months when freshening heifers carrying the infection are introduced into the milking herd. The assumption that adult cows that had ringworm as calves are "immune for life" is challenged by the occurrence of outbreaks in adult cattle, raising questions about the longevity of natural immunity following exposure.

Understanding the Mechanisms of Dermatophyte Infection

Dermatophytes primarily affect the keratinized layers of the skin, releasing toxins and allergens that lead to exudation, crusting, and alopecia. The fungi themselves do not invade the deeper tissues and thrive best when they provoke minimal host inflammatory responses. The lesions typically exhibit an oval or circular shape and often appear in multiple locations. The incubation period ranges from 1 to 4 weeks, with the lesions persisting for 1 to 3 months in most cases. Infection through direct contact is accelerated by mechanical skin irritation caused by contaminated objects. Stanchions, neck straps, halters, milking straps, brushes, curry combs, chutes, and other shared devices can contribute to the spread of the infection among a group of cattle.

Cattle that are chronically ill, unthrifty, poorly nourished, or acutely sick tend to display diffuse or rapidly progressive lesions compared to their healthy herdmates. This suggests the involvement of both cellular and humoral factors that contribute to the worsening of dermatophytosis. Calves persistently infected with Bovine Viral Diarrhea Virus (BVDV) or affected by Bovine Leukocyte Adhesion Deficiency (BLAD) often develop severe ringworm lesions, while their healthy herdmates either remain unaffected or exhibit only mild lesions. Adult cows or heifers with typical ringworm lesions may experience the progression of diffuse lesions when stressed by severe acute infections like pneumonia or peritonitis. The use of exogenous corticosteroids can also exacerbate existing ringworm lesions. Another proposed contributing factor is the lack of sunlight, as animals housed indoors appear to have a higher incidence of ringworm. This theory led some veterinarians to administer vitamins A and D as a treatment. However, the occurrence of ringworm in both calves and adult cows during the summer months diminishes the importance of sunlight in prevention or cure.

Identifying Signs of Dermatophytosis

Ringworm lesions in calves typically manifest as round or oval areas of crusting and alopecia, ranging from 1.0 to 5.0 cm in diameter. Early lesions may appear raised due to serum oozing or secondary bacterial pyoderma beneath the crust. The periocular region, ears, muzzle, neck, and trunk are the most commonly affected areas in calves, although lesions can occur anywhere on the body. Head and neck lesions are particularly prevalent due to contact with contaminated lock-ins, stanchions, or neck straps. Posts or beams used for scratching may provide a source of infection for a group of heifers, leading to lesions on the trunk. The escutcheon, located near the udder, is another area frequently affected by ringworm. While the skin lesions may be painful, they are rarely pruritic (itchy). In adult cattle, ringworm lesions can appear anywhere on the body, but they are more commonly found on the trunk and neck. Facial lesions, which are typical in calves, are less frequent in adult cows. In addition to the oval and circular lesions, larger geographic lesions may occasionally develop in adult cattle. During ringworm outbreaks in adult cattle, individual cows experiencing unrelated systemic illnesses may exhibit a dramatic worsening of their ringworm lesions. Ketotic cattle treated with corticosteroids may also show an aggravation of their ringworm condition. Furthermore, adult cattle may develop lesions on their udder, flank, or hind limbs, increasing the risk of zoonotic transmission as these areas come into contact with milkers. It is not uncommon for milkers or handlers of infected cattle to develop ringworm lesions themselves. Ringworm is the most common example of a zoonotic disease encountered in cattle practice.

Accurate Diagnosis of Dermatophytosis

While cultures of hair from the peripheral zone of a lesion on selective media such as dermatophyte test medium, scrapings of lesions for mineral oil or potassium hydroxide preps, or skin biopsies can be used to confirm the diagnosis, clinical signs are typically sufficient for identification. Early lesions may resemble warts or other skin conditions due to their raised appearance, but careful examination can differentiate them from other lesions.

Treatment Approaches for Dermatophytosis

Assessing the efficacy of treatment for ringworm can be challenging due to the self-limiting nature of the infection in most healthy cattle. Controlled studies are necessary to validate the effectiveness of any product against ringworm. Treatment is often sought due to the zoonotic potential of the infection or because an affected heifer or cow needs to participate in a show or sale. Animals with ringworm, like those with warts, are ineligible for admission to shows or sales. This situation often leads to the sudden urgency of treating ringworm, even though the infection may have been present for months.

Before discussing various treatments, it is important to acknowledge the labor-intensive nature of managing hundreds of ringworm lesions in a group of calves, heifers, or cows. The difficulties in catching, restraining, and treating groups of heifers can contribute to treatment failures or a lack of owner interest.

Treatment typically focuses on selected animals that need to be "cured" to ensure their participation in fairs or shows. Owners who are willing to treat their calves should also receive education on disinfection and prevention measures.

Effective Topical Treatments:

1. Lime sulfur (2% to 5% concentration): Applied as a spray or dip daily for 5 days, followed by weekly treatments until the infection is cured.

2. Sodium hypochlorite (0.5% concentration): Applied as a spray or dip daily for 5 days, followed by weekly treatments until the infection is cured.

3. Enilconazole (0.02% concentration): Applied as a spray or dip daily for 5 days, followed by weekly treatments until the infection is cured.

Topical Treatments for Limited Lesions or Selective Treatment:

1. Lime sulfur, sodium hypochlorite, or enilconazole (same concentrations as above): Applied or sprayed topically on affected areas.

2. Thiabendazole paste (3% to 5% concentration): Applied once or twice daily on limited lesions.

3. Miconazole or clotrimazole cream: Applied once or twice daily on limited lesions.

Systemic Treatment:

1. Griseofulvin: Administered orally at a dosage of 20 to 60 mg/kg for 7 or more days. It's important to note that griseofulvin is not approved for use in cattle.

Potentially Efficacious Systemic Treatments:

1. Sodium iodide (20% solution): Administered intravenously (IV) at a dose of 150 cc per 450 kg, repeated in 3 to 4 days.

2. Vitamins A and D: Only indicated if animals have been kept completely out of sunlight. Best results are achieved when animals treated with any of the aforementioned products have their lesions scraped or brushed to remove the infective crusts. Clipping may also be beneficial, but it carries the risk of spreading the infection. Brushes, curry combs, and clippers used on infected animals should be thoroughly cleaned and disinfected. Workers handling the cattle should wear gloves or wash their hands thoroughly after handling the animals using an iodophor or tincture of green soap. Disinfecting premises and fomites offers the best opportunity to prevent future outbreaks. Physical cleansing and pressure spraying, followed by disinfection using lime sulfur or Clorox, can be effective. After disinfection, the premises should be allowed to dry and supplied with new bedding. Only animals without detectable lesions should be reintroduced. Vaccines have been developed in certain parts of the world and have shown efficacy in preventing and managing dermatophytosis.

Managing Dermatophytosis for the Health of Your Cattle 🐄🍄

Understanding the causes, signs, and treatment options for dermatophytosis is essential for effectively managing this fungal infection in cattle. Implementing proper treatment protocols, whether topical or systemic, can aid in the healing process and prevent the spread of the infection to other animals and humans. Additionally, emphasizing good hygiene practices, such as disinfection and prevention measures, is crucial to avoid future outbreaks. Regular veterinary consultations and adherence to vaccination programs can further contribute to the overall health and well-being of your cattle. By staying proactive and prioritizing the management of dermatophytosis, you can ensure a healthy herd and a thriving farming operation.