Histoplasmosis in Dogs: Causes, Symptoms & Treatment Guide

Fungal diseases in dogs fall into two categories: those affecting the skin or mucous membranes, and systemic fungal infections that impact organs such as the liver, brain, and lungs. Histoplasmosis is a systemic fungal infection in dogs caused by the fungus Histoplasma capsulatum. This fungus thrives in environments rich in organic material, particularly soil contaminated by bird or bat droppings. Dogs typically become infected by inhaling or ingesting contaminated soil or droppings.

While the risk of a dog transmitting histoplasmosis to humans is very low, it is crucial to understand the symptoms and treatment options to protect your pet's health and wellbeing.

What Causes Histoplasmosis in Dogs?

The fungal agent Histoplasma capsulatum causes histoplasmosis. Infection occurs when dogs inhale fungal spores or ingest contaminated soil or droppings, especially from birds such as pigeons, poultry, or bats. This fungus prefers warm, moist, and nitrogen-rich environments, making woodland or lakeside areas with high bird or bat activity common sources of infection.

Dogs that explore or hunt in these environments are at greater risk. The fungus colonises the dog's intestines and can spread to other organs, causing systemic illness.

Recognising Symptoms of Histoplasmosis

Early recognition of histoplasmosis symptoms can significantly improve your dog's chances of full recovery. Symptoms generally appear 2-3 weeks after infection and may differ depending on the organs affected. Common signs include:

• Loss of appetite leading to weight loss
• Diarrhoea, sometimes with blood and mucus, causing straining
• Persistent coughing and difficulty breathing
• Lethargy and reluctance to exercise
• Enlarged lymph nodes, liver, or spleen
• Lameness and changes in the eyes or skin appearance
• High fever, sometimes reaching 40°C (104°F)
• Pale gums or yellowish discolouration indicating anaemia or jaundice

Such symptoms may resemble other conditions like lymphoma or respiratory infections, making veterinary assessment vital.

Diagnosing Histoplasmosis in Dogs

A veterinary examination will include a thorough physical check, blood tests including chemical profiles and complete blood count, and urinalysis. However, blood tests alone only detect exposure to the fungus and cannot confirm active infection.

Further diagnostic tools include fungal cultures, cytologic samples, tissue biopsies, chest X-rays if respiratory symptoms exist, and antigen testing. Accurate diagnosis is essential as histoplasmosis symptoms overlap with other diseases.

Treatment of Histoplasmosis

Treatment primarily consists of long-term antifungal medications such as itraconazole, which is the preferred drug. Fluconazole may also be effective for some cases. Early, mild histoplasmosis might be managed with ketoconazole, but resistance can occur. Severe or disseminated infections might require amphotericin B alongside oral antifungals.

Treatment typically lasts 4 to 6 months but often extends beyond 6 months for full clearance. Supportive care like fluid therapy and nutritional support may be necessary, especially if your dog has intestinal absorption issues. In severe cases, hospitalisation and fluid drips help maintain your pet's condition during recovery.

Living with and Caring for a Dog with Histoplasmosis

During treatment, limit your dog's activity to avoid stress and support healing. Vets often recommend cage rest or restricted movement to reduce physical strain. Regular follow-ups are crucial to monitor treatment response and to adjust therapy as needed.

Relapses occur in 10-40% of cases, so ongoing veterinary monitoring including repeated blood tests and clinical exams is necessary even after symptoms resolve. Patience and consistent care are key to helping your dog regain health.

Preventing Histoplasmosis in Dogs

Prevention centres on reducing your dog’s exposure to environments potentially contaminated with Histoplasma capsulatum. Avoid areas with large bird congregations, poultry farms, or known bat roosts, especially disturbed soil laden with droppings.

Avoid letting your dog roam off lead in woodlands or lakesides where exposure risk is high. If your dog shows symptoms such as loss of appetite or diarrhoea, seek veterinary advice promptly.

While it can be difficult to eliminate all risks—given dogs' natural curiosity and willingness to explore—being vigilant can greatly reduce the chance of infection.

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How is Histoplasmosis Treated in Dogs?

Quick Answer: Histoplasmosis is treated with long-term antifungal medications, mainly itraconazole, sometimes fluconazole or ketoconazole. Severe cases may need amphotericin B and supportive care such as fluids and nutrition. Treatment often lasts 4-6 months or longer and requires close veterinary monitoring.

Detailed treatment plans depend on the severity and spread of the disease in your dog. Veterinarians typically prescribe itraconazole at a dose of 10 mg/kg once daily, which inhibits fungal growth effectively. Fluconazole might be preferred for certain cases, while ketoconazole is less commonly used due to resistance concerns. In cases where the infection has spread widely, amphotericin B may be administered intravenously under close supervision. Supportive treatments such as intravenous fluids and nutritional support help manage complications and support recovery.

Continuous monitoring during treatment with blood tests and clinical exams is essential to track the infection's response and to catch any relapses early. Treatment duration is generally a minimum of 4 to 6 months but may be extended depending on the dog’s progress and test results. Responsible pet ownership includes following your vet’s advice closely to improve your dog’s prognosis.

Why Does My Dog Have These Symptoms?

Quick Answer: Symptoms like weight loss, diarrhoea, coughing, difficulty breathing, lethargy, and fever in dogs can be caused by histoplasmosis, a systemic fungal infection acquired from the environment.

Many symptoms seen in histoplasmosis overlap with other common canine illnesses such as bacterial infections, respiratory diseases, or even cancer. The symptoms are due to the fungus spreading in the body, causing inflammation and organ damage. If your dog shows these signs, especially with a history of exposure to bird or bat droppings, veterinary diagnosis is crucial for timely treatment. Do not delay consulting your vet as early intervention improves outcomes for fungal infections including histoplasmosis.

Can Histoplasmosis be Prevented in My Dog?

Quick Answer: Prevention focuses on limiting your dog’s access to environments with soil or droppings contaminated by bird or bat faeces, avoiding high-risk areas like poultry farms, bird roosts and bat caves.

Since the fungus thrives in specific niches, steering your dog away from these high-risk environments helps reduce infection risk. If your dog enjoys off-lead woodland or lakeside walks where birds and bats are common, stay alert to avoid contaminated soil or faeces. Good hygiene and prompt veterinary attention to symptoms are essential parts of responsible dog ownership. While complete prevention may be difficult due to natural exposure risks, awareness and caution can significantly reduce the chance of your dog contracting histoplasmosis.