Fungal Infection (Histoplasmosis) in Dogs

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Last updated on
4 min read

Key takeaways

Histoplasmosis is an infection acquired from soil contaminated with Histoplasma capsulatum fungus, usually originating from bat or bird droppings. 

  • In most cases, dogs exposed to H. capsulatum do not develop symptoms
  • In cases where the immune system is unable to fight effectively, the infecton starts in the lungs and, left untreated, spreads to other organs, potentially becoming fatal
  • Symptoms initially include fever, weight loss, lethargy, and lack of appetite
  • Dogs with symptoms of histoplasmosis require prompt veterinary attention
  • Diagnostic tools include physical examination, bloodwork, fungal culture, and x-rays
  • Treatment involves 4 to 6 months of antifungal medication
  • The side effects of treatment can be severe and the cost is relatively high
  • With treatment, prognosis is generally good unless organ damage occurs
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A closer look: Fungal Infection (Histoplasmosis) in Dogs

Left untreated, histoplasmosis is potentially fatal. In cases that have benefitted from early detection and treatment, the prognosis is good, although treatment takes several months and can be expensive. In cases where the infection has traveled to other systems, or when organ damage has occurred, the prognosis is more guarded. Once infection has occurred, relapse is common. Dogs who have been infected with histoplasmosis are at risk of relapse.

H. capsulatum fungal spores cannot pass from dog to human. However, humans exposed to the original source of the spores are susceptible to infection.

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Risk factors

Histoplasmosis is considered uncommon in dogs. Dogs who are exposed to Histoplasma capsulatum spores usually show no signs of illness.

In some cases, particularly in dogs with poor immune systems, the infection takes hold and starts to spread, causing symptoms. Dogs with symptoms of histoplasmosis require prompt veterinary care. If histoplasmosis is left untreated and spreads throughout the body, it is potentially fatal.

Histoplasmosis is most prevalent in Ohio, Mississippi, and Missouri, but can be found throughout North America.

The severity of histoplasmosis depends on whether the infection has traveled to other systems in the body, which systems are infected, and how severe the infection is.

If left untreated, the infection can overwhelm the body causing death.

Possible causes

The cause of histoplasmosis is the Histoplasma capsulatum fungus. This fungus is common in bird and bat droppings. The droppings contaminate soil, and the fungus releases spores. Dogs inhale the spores, which are deposited into the lungs.

If the immune system responds appropriately, the spores are eliminated before infection can take hold. In cases where the immune system is unable to respond appropriately, an infection develops. If left untreated, the infection travels through the bloodstream to other organs, including the eyes and gastrointestinal tract. In some cases, ingestion of spores can result in infection of the gastrointestinal tract without respiratory infection.

Main symptoms

The main symptoms of histoplasmosis occur from respiratory infection.

Testing and diagnosis

Diagnostic tools include:

  • Physical examination
  • Bloodwork
  • Urinalysis
  • Stool sample
  • X-rays or ultrasounds
  • Fungal culture
  • Cytology (cell study) of swollen lymph nodes

Steps to Recovery

The main treatment for histoplasmosis is antifungal medication. The course of treatment usually lasts between 4 and 6 months. Treatment must be continued 2 months after the symptoms resolve to ensure the infection is gone.

Antifungal medications are expensive and sometimes have severe side effects including:

  • Vomiting
  • Loss of appetite
  • Diarrhea
  • Kidney problems

In cases where the infection affects multiple organs, supportive therapies are often required. These include:

  • IV fluids
  • Antibiotics to prevent opportunistic bacterial infections
  • Oxygen therapy
  • Help with eating, such as a feeding tube

Once the symptoms are gone and the antifungal therapy is complete, check ups and blood tests are required on a monthly basis for several months.


There are no proven preventive measures for histoplasmosis. Avoiding exposure to bat and bird droppings, especially chicken coops, and bird and bat roosts, limits risk.

Is Fungal Infection (Histoplasmosis) in Dogs common?

Histoplasmosis is uncommon in dogs.

Typical Treatment

  • Antifungal medication
  • Supportive care
  • Monitoring


Tamara Gull, DVM, PhD, DACVM, DACVIM (LA), DACVPM - Writing for Merck Veterinary Manual
Kelly Gingerich, DVM / Lynn Guptill, DVM, PhD, DACVIM - Writing for dvm360®
Jacqueline Brister, DVM - Writing for Veterinary Partner

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