Histoplasmosis is a fungal infection caused by the fungus Histoplasma capsulatum that affects dogs and other animals. The fungus is found in soil that contains large amounts of bird or bat droppings. When soil containing the fungus is disturbed, the fungal spores can become airborne and can then be inhaled by animals. Histoplasmosis primarily affects the lungs but can spread to other organs in the body.
How do dogs get infected with Histoplasmosis?
Dogs become infected with histoplasmosis when they inhale the fungal spores from contaminated soil. This typically happens when:
- Dogs dig in soil containing bird or bat droppings
- Dogs explore areas like chicken coops or caves inhabited by bats
- Dogs are present when contaminated soil or droppings are disturbed through activities like landscaping, construction, demolition, farming, etc.
The fungus grows best in warm, moist environments. Areas along rivers or other sources of water tend to have higher levels of the fungus. Histoplasmosis is more common in the central and eastern United States in states surrounding the Ohio and Mississippi River valleys. Dogs that go hunting, hiking, camping, or swimming in endemic areas have a higher risk of exposure.
What are the symptoms of histoplasmosis in dogs?
The symptoms of histoplasmosis in dogs can vary greatly depending on the severity of infection. Some dogs may only develop very mild symptoms while other dogs develop severe, disseminated infections affecting multiple organs.
Common symptoms of histoplasmosis in dogs include:
- Respiratory symptoms – Dogs infected with histoplasmosis often develop respiratory symptoms including coughing, difficulty breathing, and exercise intolerance. The lungs are often the primary site of infection.
- Fever – Fever is commonly seen with pulmonary histoplasmosis in dogs. Dogs may have a temperature over 103°F (39.4°C).
- Loss of appetite – Infected dogs frequently have reduced appetite and weight loss.
- Fatigue and lethargy – Histoplasmosis often causes dogs to become lethargic and fatigued.
- Swollen lymph nodes – The lymph nodes may become enlarged as the body tries to fight off the infection.
- Gastrointestinal signs – Some dogs develop diarrhea, vomiting, or other GI upset with histoplasmosis.
- Eye inflammation – Dogs may show inflammation of the tissues within the eye (chorioretinitis).
- Bleeding disorders – Disseminated histoplasmosis can cause abnormal bleeding, bruising, and pinpoint red spots on the skin or gums.
- Lameness – Fungal spread to bones and joints may result in lameness or joint pain.
- Heart problems – If the infection spreads to the heart, dogs may show signs of heart failure like cough, difficulty breathing, abdominal enlargement.
- Central nervous system signs – Disseminated histoplasmosis can sometimes infect the brain and lead to seizures, circling, head tilt, or paralysis.
How is histoplasmosis diagnosed in dogs?
Diagnosing histoplasmosis can be challenging due to the variability in symptoms and the difficulty in isolating the fungus. Diagnostic tests used in dogs may include:
- Fungal cultures – Samples like bronchial fluid may be cultured to try to grow Histoplasma capsulatum fungi.
- Biopsies – Lung, lymph node, spleen or other biopsies may reveal histoplasmosis on microscopic examination.
- Blood tests – Blood tests often show high white blood cell counts, anemia, and globulin abnormalities.
- Urine antigen test – A urine test detects antigens of Histoplasma in the urine and is often positive.
- Serology – Blood tests look for antibodies against the histoplasma antigen, rising levels confirm exposure.
- PCR – Polymerase chain reaction can detect Histoplasma DNA in blood or tissues.
- Radiographs and ultrasound – Imaging studies may reveal changes suggestive of histoplasmosis.
In some cases, a definitive diagnosis is made once the dog responds to appropriate antifungal treatment.
What is the treatment for histoplasmosis in dogs?
Histoplasmosis is treated with long-term antifungal medications. The most commonly used antifungal drugs for dogs include:
- Itraconazole
- Fluconazole
- Ketoconazole
Amphotericin B is sometimes used initially in very ill dogs to stabilize them before transitioning to oral antifungal therapy. The antifungal medication may be required for 3 to 12 months depending on the severity of infection and the dog’s immune status. Close monitoring is important to evaluate response to treatment and to watch for any adverse side effects.
What is the prognosis for dogs with histoplasmosis?
The prognosis for histoplasmosis depends on many factors such as:
- The severity of symptoms and infection
- How quickly treatment was started
- Whether the dog has any underlying illnesses
- How well the dog responds to antifungal medication
Mild forms of pulmonary histoplasmosis generally respond well to antifungal treatment and carry a good prognosis. Severe disseminated infections have a poorer prognosis but can sometimes be treated successfully depending on the dog’s overall health status.
With aggressive antifungal therapy and supportive care, many dogs with histoplasmosis can achieve a complete recovery. However, relapse is possible if antifungal medication is discontinued too soon before the body has cleared the infection. Regular follow-up testing helps determine if and when medication can be stopped.
How can histoplasmosis be prevented in dogs?
Since infection occurs through inhalation of contaminated soil, some ways to help prevent dogs from developing histoplasmosis include:
- Avoid areas with heavy contamination from bird/bat droppings
- Prevent dogs from digging or rolling in suspect soil
- Keep dogs away from areas during construction, demolition, or landscaping projects
- Use caution when exposing dogs to wooded areas, caves, or hollow trees where bats roost
- Pick up and dispose of bird and bat droppings promptly
- Use soil fungicides in contaminated areas
Unfortunately, complete avoidance of Histoplasma fungus exposure can be difficult as the organism is so widespread in certain areas. Dogs diagnosed with histoplasmosis that live in highly endemic regions may need to be on chronic antifungal medication during seasons where exposure risk is highest.
What are some key points about histoplasmosis in dogs?
- Histoplasmosis is an infection caused by inhalation of Histoplasma fungal spores from contaminated soil.
- Common symptoms include cough, fever, breathing problems, lethargy, weight loss, and swollen lymph nodes.
- Diagnosis involves a combination of radiographs, blood tests, biopsies, cultures, and antigen testing.
- Treatment is with long term antifungal medication like itraconazole, fluconazole, or ketoconazole.
- With treatment, prognosis is good except in severe disseminated cases.
- Prevention involves avoiding exposure to areas contaminated with bird/bat droppings.
Frequently Asked Questions
What are the most common symptoms of histoplasmosis in dogs?
The most common symptoms of histoplasmosis in dogs are respiratory symptoms like coughing and difficulty breathing, fever, lethargy, reduced appetite, and swollen lymph nodes. However, symptoms can vary depending on the organs infected.
How do dogs get infected with histoplasmosis?
Dogs become infected by inhaling fungal spores when exposed to soil contaminated with droppings from birds or bats infected with Histoplasma capsulatum fungus. Disturbing contaminated soil can release infectious spores into the air.
What dog breeds are most at risk for histoplasmosis?
There is no evidence that certain dog breeds are more susceptible to histoplasmosis. However, dogs that spend more time engaged in outdoor activities like hunting, digging, or exploring areas contaminated with bird/bat droppings may be at higher risk.
Is histoplasmosis in dogs fatal if left untreated?
Histoplasmosis can potentially be fatal in dogs if left untreated. However, the severity of illness can range widely in dogs. Mild forms may resolve spontaneously, while severe disseminated infection involving multiple organs is often fatal without treatment.
How long do dogs need to be treated for histoplasmosis?
Dogs with histoplasmosis typically need to be on antifungal medication for 3 to 12 months. The duration depends on the severity of infection and how well the dog responds to treatment. Lifelong treatment may be needed in certain cases.
Can histoplasmosis in dogs be cured?
Many dogs with histoplasmosis can be successfully cured with prompt diagnosis and appropriate antifungal treatment. However, in some dogs the infection may recur after treatment is stopped, requiring additional medication. Lifelong treatment is sometimes needed in certain cases.
Can histoplasmosis spread between dogs or to humans?
Histoplasmosis cannot spread directly from an infected dog to another dog or to people. Transmission requires inhalation of new spores from a contaminated environment. However, inhaling spores stirred up from an infected dog’s feces is theoretically possible.
Where is histoplasmosis most common in dogs in the United States?
In the United States, histoplasmosis is most prevalent in the Ohio and Mississippi River Valleys, as well as some southeastern and mid-Atlantic states. Areas around caves, bird roosts, chicken coops, and hollow trees have higher levels of fungus.
How can I prevent my dog from getting histoplasmosis?
The main prevention is avoiding areas contaminated with droppings from birds or bats infected with the Histoplasma fungus. Pick up droppings promptly, use protective gear when working in contaminated areas, and consider antifungal soil treatment. But complete avoidance is difficult.
Conclusion
Histoplasmosis is a serious fungal disease in dogs that requires prompt veterinary care. However, with early diagnosis and appropriate long-term antifungal treatment, many dogs can make a full recovery. Preventing exposure to contaminated droppings can reduce a dog’s risk. Dog owners in endemic areas should be aware of the symptoms of histoplasmosis and seek veterinary assessment for appropriate testing and treatment if signs develop.