Histoplasmosis in Dogs: Symptoms, Causes, and Treatment

Histoplasmosis is a serious fungal infection that can occur in both pets and people.  

While more common in cats, symptoms of histoplasmosis in dogs are the same and primarily affect the lungs and digestive system.  

This fungus like to live in areas where it is warm and moist and the soil is enriched with bird or bat droppings. 

If you live in an area where histoplasmosis is present, it’s important to know what to look for, when to seek veterinary attention, and how to test for histoplasmosis in dogs 

What Is Histoplasmosis in Dogs?

Histoplasmosis is a fungal infection more commonly seen in cats, but it can also be found in dogs.  

Dogs under 4 years of age are most affected. Predisposed breeds include the Brittany, Pointer, Weimaraner, and other working dogs. 

The fungus that causes histoplasmosis in dogs, Histoplasma capsulatum, can be found anywhere in the world, but it’s especially common in the major river valleys of North and South America. 

The infection is normally contracted after the dog inhales the organisms, often from the droppings of birds or bats.  

Ingesting the fungus by eating bird and bat poop or rotting wood is another method of transmission, although this is theoretical and has not been documented. 

Symptoms of Histoplasmosis in Dogs

Symptoms of histoplasmosis in dogs emerge about two to three weeks after infection and can vary widely depending on which organs the fungus infects. 

First Signs of Histoplasmosis 

Because H. capsulatum typically spreads to the gastrointestinal (GI) tract of dogs, the most common symptoms are gastrointestinal. 

Common symptoms of histoplasmosis in dogs include: 

• Straining to poop 

• Producing diarrhea with small amounts of blood or mucus 

Other symptoms may include: 

• Vomiting 

• Appetite loss 

• Weight loss 

• Lethargy 

• Fever 

Signs of a Severe Histoplasmosis Infection 

As the disease progresses, organ-specific symptoms emerge. Dogs with a heavy fungal infection in their lungs may experience: 

• Coughing 

• Rapid breathing 

• Nasal discharge 

• Jaundice, if the liver is affected 

• Swollen lymph nodes 

Less commonly, the infection spreads to the eyes, bones, and skin, where symptoms can occur including: 

• Blindness 

• Limping 

• Swollen joints 

• Skin lesions, wounds, or oozing nodules 

Causes of Histoplasmosis in Dogs

Histoplasmosis in dogs is caused by H. capsulatum. 

A dog can encounter this fungus when eating fungal spores in bat feces. This is the classic source of the infection, although the fungus can also be transmitted when dogs eat bird droppings and rotting wood, among other sources.  

These spores then infect a dog’s intestines. 

While the GI tract is the most common site of the infection in dogs, other organs can be affected. This includes:  

• Lymph nodes 

• Spleen 

• Liver 

• Eyes 

• Joints 

• Bones 

• Skin 

Dogs can also inhale the spores, which then go into the lungs. This can cause coughing, and even respiratory distress.  

Once inside the lungs, the fungus multiplies. Sometimes the infection remains in the respiratory tract, where it may or may not cause symptoms.

However, the fungus commonly spreads or “disseminates” to other organs. 

How Vets Diagnose Histoplasmosis in Dogs

Because symptoms of histoplasmosis in dogs can be difficult to detect—and because the infection is uncommon in many parts of the United States—diagnosis can be challenging. 

Vets will typically begin with a physical exam, then recommend the following diagnostic testing: 

• Blood work 

• Urinalysis  

• X-ray 

• Ultrasound 

• Biopsies 

• Fine needle aspiration (FNA) 

Treatment for Histoplasmosis in Dogs

Treatment for histoplasmosis in dogs is focused on long-term antifungal medication (such as itraconazole or fluconazole) to destroy the H. capsulatum organisms. 

The goal is to treat until the dog has been symptom-free for at least one month. Many dogs require over six months of antifungal treatment. 

Other medications or therapies may be necessary to manage the symptoms and secondary effects of the disease, like antibiotics for pneumonia or skin infections (such as Clavamox, doxycycline, and/or enrofloxacin and cephalexin). 

Fluids to correct dehydration—or even feeding tubes for dogs that won’t eat—can help keep an affected dog comfortable until the antifungal medications can resolve the infection. 

Recovery and Management of Histoplasmosis in Dogs

Once your dog has a diagnosis of histoplasmosis, your vet will require multiple physical exams to monitor the success of treatment and to look for any new symptoms or problems that may emerge. 

Repeated blood and urine tests can make sure the medications are working and are not damaging your dog’s organs. 

Once your dog has been symptom-free for at least one month after testing negative for H. capsulatum, they should be retested one more time.  

A negative result on this final test before discontinuing medications will ensure the infection has been fully cleared and minimize the risk of relapse. 

Your dog should be tested three to six months later to look for relapse. 

Preventing Histoplasmosis in Dogs

Histoplasmosis in dogs can be prevented by avoiding areas where a pup could be exposed to bird and bat feces.  

If you find yourself in the warm, humid areas where fungal spores are present such as rich soils and river valleys, make sure your dogs is not eating off the ground.  

You should also make sure your dog is not digging or disturbing the ground and not kicking up the fungal spores to be inhaled.