Fungal Infections in Livestock: Types and Prevention

Fungal infections are among the most persistent and underestimated health threats on livestock farms. Unlike bacterial or viral diseases, fungi are eukaryotic organisms capable of surviving in diverse environmental conditions – in soil, decaying feed, contaminated bedding, and even on farm equipment – making complete elimination challenging. They can affect cattle, sheep, goats, pigs, poultry, and horses, often starting with subtle symptoms that get overlooked until the infection has already spread. Two diseases in particular – ringworm and aspergillosis – represent the most common and consequential fungal threats to livestock health and farm profitability. Understanding how each one works, how it spreads, and how it can be controlled is essential knowledge for anyone managing an animal operation.

What are fungal infections in livestock? 🔗

Fungal infections in animals, known medically as mycoses, occur when pathogenic fungi invade body tissues. They range from superficial skin conditions to serious internal diseases affecting the lungs and other organs. Superficial mycoses affect the outer skin layers, while systemic mycoses can affect internal organs and prove life-threatening, especially in animals with weakened immune systems. What makes fungal infections particularly difficult to manage on farms is their tendency to thrive in warm, humid housing environments and their ability to spread rapidly through herds before clear clinical signs appear. Young animals with underdeveloped immunity, malnourished animals, and those under physical or environmental stress are consistently the most vulnerable.

Ringworm (dermatophytosis) 🔗

Despite its name, ringworm has nothing to do with worms. It is a highly contagious fungal skin infection caused by dermatophytes – fungi that feed on keratin, the structural protein found in skin, hair, and hooves. In cattle, Trichophyton verrucosum is responsible for more than 90% of cases, though T. mentagrophytes is also occasionally involved. The disease affects cattle, sheep, horses, goats, and pigs, and is seen in farmed animals across the world.

How ringworm affects animals 🔗

The characteristic lesions of ringworm are circular, grey-white, and have a powdery surface with sparse or absent hairs. They can be slightly raised and swollen, particularly at the edges, and severe lesions may become thickened with scales, leaving raw, bleeding skin when removed. In cattle, lesions are most commonly seen around the eyes, ears, and back in calves and young stock. Adult cattle, when affected, tend to develop more widespread lesions on the face, neck, trunk, and tail region. The lesions themselves do not typically cause itching, but infected calves may experience reduced feed intake and weight loss due to discomfort.

How ringworm spreads 🔗

Ringworm spreads both directly and indirectly. Direct contact with clinically infected animals is the primary route of spread. The spores of ringworm fungi can survive in the farm environment for months or even years and may be transmitted via fomites such as brushes, gates, and feed carts, or through asymptomatic carriers. Shared grooming tools, clippers, combs, halters, blankets, fences, and buildings are all capable of carrying infective spores from one animal to another.

Crowded housing conditions during winter months are a well-recognised trigger for outbreaks. Environmental factors play a role – the prevalence of the disease increases in hot, humid climates, and calves kept indoors or with little sunlight exposure have a higher incidence. New infections can also be introduced through bought-in stock that are incubating the disease. The incubation period is typically one to four weeks.

Importantly, ringworm is a zoonotic disease – it can be transmitted from animals to humans. Ringworm spreads easily between people and animals, and human infections typically appear as circular, itchy, red, and exudative lesions on exposed skin such as the arms and neck following close contact with infected cattle. Farm workers, veterinarians, and family members – especially children – are at real risk if precautions are not observed.

Diagnosing and treating ringworm 🔗

Diagnosis is usually made on the basis of the characteristic clinical lesions, but a conclusive identification requires mycological examination – either direct microscopy or fungal culture of plucked hairs and skin scrapings from active lesion sites. Treatment options include topical antifungal agents such as miconazole or clotrimazole, as well as systemic antifungal drugs. Enilconazole is the only licensed topical product in many countries and is effective when applied consistently. Animals often self-cure after being turned out in spring, as ringworm fungi are killed by ultraviolet light.

Treatment typically requires several weeks of application. Vaccination is available in some countries and can be used both prophylactically to reduce clinical signs and therapeutically to shorten recovery time in already-infected animals. Whole-herd vaccination is most effective, as partial vaccination leaves susceptible individuals to maintain infection pressure.

Aspergillosis 🔗

Aspergillosis is a more serious and potentially fatal fungal disease. It is caused by Aspergillus species – primarily Aspergillus fumigatus – which are saprobic filamentous fungi commonly found in soil, decaying vegetation, seeds, grains, and stored hay. Unlike ringworm, which targets skin, aspergillosis is primarily an internal infection. The fungus produces enormous quantities of microscopic airborne spores that, when inhaled, can penetrate deep into the respiratory tract.

How aspergillosis affects different species 🔗

The most common forms include pulmonary infections in poultry and other birds, mycotic abortion in cattle, guttural pouch mycosis and mycotic keratitis in horses, and sinonasal or pulmonary infections in dogs and cats.

In poultry, the disease is often called brooder pneumonia in young chicks. It most frequently affects the lungs and air sacs, producing white to yellow plaques and nodules in the tissue, and can cause high mortality rates in affected flocks. There is no effective treatment in poultry.

In cattle, aspergillosis can present as mastitis, placentitis, diarrhoea, ocular infection, or mycotic pneumonia. Abortion in the second or third trimester of pregnancy has also been described, with foetal lesions such as bronchopneumonia and skin inflammation observed upon examination.

In horses, the primary concern is guttural pouch mycosis. This is characterised by spontaneous nosebleeds, often in a resting horse, nasal discharge, and difficulty swallowing. When the infection spreads to the brain and optic nerve, locomotor disturbances and even blindness can occur. Aspergillosis in horses can be rapidly fatal when the infection fully invades the walls of blood vessels in the guttural pouch.

Transmission and risk factors 🔗

Aspergillosis is a non-contagious disease – it is not spread from animal to animal. It is acquired through individual environmental exposure, specifically by inhaling fungal spores that are ubiquitous in moldy litter, feed, and organic matter. This makes environmental management, rather than isolation, the central pillar of control.

Transmission to dairy calves typically occurs through contaminated feed or bedding, and environmental conditions such as high humidity and poor ventilation facilitate the growth and spread of the fungus. Calves that are immunocompromised or stressed due to transport or weaning are more susceptible to infection. In poultry, moldy bedding, contaminated feed, and inadequate ventilation are the primary risk factors. In horses, factors such as poor ventilation, high humidity, warm temperatures, prolonged antibiotic use, and immunosuppression from other diseases all predispose animals to infection.

Diagnosing and treating aspergillosis 🔗

Diagnosis of aspergillosis requires laboratory confirmation because the Aspergillus fungus is so common in the environment that its mere presence is not sufficient evidence of infection. Diagnosis relies on demonstrating tissue invasion; isolation of the organism alone is insufficient. Fungal cultures, microscopic examination of respiratory secretions, cytological examination, and radiographic imaging are typically used together. In horses, endoscopic examination of the guttural pouches is a primary diagnostic tool.

Azole antifungals are generally the treatments of choice. First-line options include itraconazole, voriconazole, posaconazole, liposomal amphotericin B, and terbinafine. In horses with guttural pouch mycosis, topical antifungal therapy can be administered directly to the lesion via endoscope. A fatal hemorrhagic event can be prevented by occluding the affected arteries using a balloon-tipped catheter or coil embolus. In poultry, individual treatment is generally impractical and ineffective at the commercial scale – the focus must be on removing the source of contamination and improving the environment.

A growing concern in managing aspergillosis is antifungal resistance. Azole fungicide use in agriculture may be contributing to azole-resistant aspergillosis, and antifungal use in the environment and in both human and animal medicine all contribute to antimicrobial resistance. This makes appropriate diagnosis and targeted therapy – rather than empirical treatment – increasingly important.

Prevention strategies for fungal diseases 🔗

Preventing fungal diseases is far more effective and economical than treating established infections, particularly in the case of aspergillosis where treatment outcomes are often uncertain. The following practices apply broadly across species.

Environmental hygiene and housing management 🔗

Identifying and eliminating fungal spore sources, maintaining proper ventilation, controlling litter moisture, and using mold inhibitors in feed are key preventive strategies for aspergillosis. For ringworm, phenolic disinfectants or sodium hypochlorite are recommended for disinfecting buildings and grooming and feeding utensils. Buildings can also be sprayed with a dilute caustic soda solution. Reducing stocking density and maximising natural sunlight exposure – which kills ringworm spores – are additional measures. For poultry, moldy bedding must never be used, and contaminated surfaces should be sprayed or fumigated with enilconazole or other fungicidal disinfectants.

Biosecurity and herd management 🔗

Biosecurity measures significantly reduce ringworm introduction and transmission within herds. All new animals should be quarantined for a minimum of two weeks, and their health status regarding ringworm should be verified before introduction. Shared equipment – brushes, halters, clippers – should be disinfected between uses or kept animal-specific. Implementing a closed herd policy and checking the health status of herds of origin before purchasing animals are effective long-term measures.

Vaccination and nutritional support 🔗

Vaccination against ringworm is available in some countries and can be a useful preventive measure. Where available, a vaccination course of two doses given 10-14 days apart can establish protection within three weeks, with field reports suggesting durable immunity following the recommended course. Nutritional support – including adequate levels of vitamins A, E, and selenium – helps maintain immune competence and skin integrity, making animals more resistant to fungal invasion. Poor nutrition consistently appears as a risk factor in outbreaks of both ringworm and aspergillosis.

Protecting farm workers 🔗

The zoonotic nature of ringworm means that human protection on the farm is not optional. Anyone handling infected animals should wear gloves, wash thoroughly after treatment, and ensure that brushes or equipment used on infected animals are labelled and kept separate from general-use items. The zoonotic implications are serious – once ringworm is confirmed on a farm, all precautions must be taken to prevent spread to farm staff and especially children. Any suspicious circular, itchy skin lesions appearing on handlers following animal contact should be assessed by a medical professional promptly.

Economic impact of fungal diseases on livestock farms 🔗

Fungal infections carry a real economic cost that extends well beyond veterinary bills. For ringworm, the main losses are due to reduced hide value and delays in sending cattle with active lesions to market. Growth rates are also affected during the active stage of infection. Show cattle with visible lesions face entry restrictions, and affected animals may require extended management periods of weeks to months. Aspergillosis, particularly in poultry, can result in mortality across large portions of a flock, with survivors often smaller than normal due to long-term cardiovascular impacts. In cattle, mycotic abortion represents a direct and significant reproductive loss. The cost of remediation – replacing contaminated bedding, disinfecting facilities, and improving ventilation systems – must also be factored into the overall burden of an outbreak. Investing in prevention and early detection consistently offers a better return than reactive treatment.

What do you think? Given that aspergillosis is fundamentally driven by environmental conditions rather than animal-to-animal contact, how confident are you that your current farm housing and ventilation practices would prevent an outbreak? And with ringworm’s zoonotic risk, are the biosecurity protocols on farms in your region strong enough to consistently protect both animals and the people who work with them?

References

1. https://pmc.ncbi.nlm.nih.gov/articles/PMC6251577/
2. https://mycologyst.art/learn-mycology/6-fungal-diseases/6.2-fungal-pathogens-of-humans-and-animals/
3. https://www.msd-animal-health.ie/species/cattle/ringworm/
4. https://www.farmhealthonline.com/disease-management/cattle-diseases/ringworm/
5. https://extension.sdstate.edu/ringworm-dont-let-it-ruin-your-show-season
6. https://pmc.ncbi.nlm.nih.gov/articles/PMC10697087/
7. https://www.cdc.gov/fungal/about/one-health.html
8. https://www.nadis.org.uk/disease-a-z/cattle/calf-management/ringworm/
9. https://www.msdvetmanual.com/infectious-diseases/fungal-infections/aspergillosis-in-animals
10. https://www.merckvetmanual.com/poultry/aspergillosis/aspergillosis-in-poultry
11. https://en.wikivet.net/Aspergillosis
12. https://equimed.com/diseases-and-conditions/reference/aspergillosis
13. https://www.merckvetmanual.com/horse-owners/disorders-affecting-multiple-body-systems-of-horses/fungal-infections-mycoses-in-horses
14. https://www.furrycritter.com/pages/health/farm_animals/aspergillosis.htm
15. https://www.furrycritter.com/pages/health/farm_animals/ringworm.htm
16. https://www.producer.com/livestock/vitamins-solve-ringworm-problem/