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Histoplasmosis In Dogs

Histoplasmosis In Dogs

Histoplasmosis is an opportunistic, disseminated, non-contagious, granulomatous, fungal infection due to the environmental dimorphic fungus Histoplasma capsulatum. Dr. Samuel Taylor Darling first described Histoplasma in 1906 while he was doing an autopsy.

As of now, three genotypes are identified of Histoplasma, including Histoplasma capsulatum, H. duboisii (Africa), and H. farciminosum (horse pathogen).

The fungal infection of the mammalian hosts can be asymptomatic or it can cause life-threatening systemic disease, which can occur in immunocompromised or healthy hosts, although compromised cellular immunity results in more severe infection. Mammalian host cells are a perfect hunting ground for H. capsulatum yeast cells as they can successfully survive inside intracellular slots in phagocytic cells.

Inhalation of Histoplasma capsulatum fungus (hyphal fragments or microconidia) gives the entry of the fungus into the dog’s body. The fungus evades intracellular and immune-mediated defenses and reaches the alveoli in the respiratory system, where it transforms into a yeast form (this can occur both outside and inside of phagocytes). The favorable niche for reproduction and growth are intracellular spots, which may include the development of a state of latency within granulomas and/or dissemination. The central role in the pathogenesis of histoplasmosis is played by Host phagocytes, as they are the medium for dissemination, initially spreading to the lymph nodes and later on to other organs.

The pathogen’s ability to dodge the intensity of the host immune response and inflammatory responses determine the clinical presentation and severity of symptoms. The disseminated disease predominantly affects the gastrointestinal tract, integument, bone and bone marrow, eyes, liver, and spleen.

Symptoms Of Histoplasmosis

Pulmonary Histoplasmosis:

  • High Fever
  • Labored breathing
  • Raspy cough
  • Harsh lung noises
  • Swollen lymph nodes
  • Endophthalmitis (swelling of the intraocular cavities of the eye).
  • Chorioretinitis (swelling of the uveal tract of the eye - a type of posterior uveitis).
  • Pale mucous membranes and gums.
  • Lethargic
  • Limping

Intestinal Histoplasmosis:

  • Fever
  • Chronic diarrhea
  • Blood in stool
  • Difficulty defecating
  • Loss of appetite / Weight loss
  • Swelling of the liver, spleen, and lymph nodes.
  • Moist sores
  • Ulcerated throat
  • Malaise

Treatment Options For Histoplasmosis

Commonly used Anti-fungal agents are azole antifungals including itraconazole, fluconazole, voriconazole and ketoconazole. They have relatively few side effects and are well-tolerated by most dogs.

Treatment of histoplasmosis requires long-term medications (2 - 6 months in most cases).

Severe cases of histoplasmosis: Amphotericin B - IV antifungal medication or amphotericin B lipid complex.

Ketoconazole (less expensive than the other azole antifungals) or a combination of medications may also be used in certain cases.

Disseminated histoplasmosis: Itraconazole (10 mg/kg/day).

Home Remedies For Histoplasmosis

  • Massage your dog’s coat with Apple Cider Vinegar.
  • Feed your Dog foods that fight Yeast Infections such as treats containing olive leaf, caprylic acid, and Pau D-Arco.
  • Add probiotics containing bacteria-fighting yeast growth to your dog’s meal.

Prevention Of Histoplasmosis

  • Sadly, there is nothing we can do to get rid of this dimorphic fungus from the environment as they are
  • Avoid the Fungal Hotspots are forests, wooded areas, camps, hunting areas, and overgrown bushes. In addition, when your dog's immune system is already compromised, stay away from trips to these high-risk areas.
  • Cut down the access of dogs to construction sites or near bird poops or soil digging areas.

Affected Breeds Of Histoplasmosis

Weimaraner, German Wirehaired Pointer, German Shorthaired Pointer, Spaniel Dog Breeds, Young Male Hunting Breeds. No confirmed breed predisposition.

Additional Facts For Histoplasmosis

  1. Causes:

Vulnerable dogs are those having compromised or suppressed immune systems.

The microscopic spores shed by this dimorphic fungus are found in the droppings of birds, bats, and soil.

They drift in the air and enter the dog’s body when they inhale the spores as they dodge or avoid the dog’s defensive lung mechanisms resulting in infection.

  1. Types:

Pulmonary Histoplasmosis: When your dog breathes in the spores and this starts in the airway; this type of histoplasmosis does not infect any area or spread any further besides the lungs.

Systemic or Disseminated Histoplasmosis: This is typically ingested rather than inhaled; therefore, the fungus enters via the blood and passes through to other organs such as lymph nodes, liver, spleen, and GI tract, etc. This causes more severe generalized or systemic fungal infection.

  1. Morbidity:
  • Endemic region: Outdoor dogs are highly susceptible.
  • Sporting and hunting dogs within close proximity of construction sites, farms, or places of overturned soil are predisposed to the disease.
  • Canine histoplasmosis is not zoonotic or spread to other animals (non-contagious).
  1. Mortality:

Histoplasmosis is a disparaging disease in puppies with lasting complications and/or a high mortality rate. The disseminated infection has a high case fatality rate.

  1. Diagnosis:
  • Skin lesions biopsy
  • Blood / Urine cultures
  • A culture of eye / Nose discharge
  • Specific blood tests to detect fungus.
  • X-rays, Ultrasound, or CT scan.
  1. Prognosis:

The histoplasmosis prognosis is usually good with proper treatment. Mostly, dogs’ treatment will get well within 2 or 3 weeks. Disseminated histoplasmosis prognosis is poor to guarded due to the spread of infection to other organs.

When To See A Vet

Visit the vet clinic immediately, if you notice -

Food Suggestions For Histoplasmosis

Foods to avoid:

  • Sour cream, soft cheese, and Yogurt.
  • Highly processed pet food.
  • Bread, Baked goods, Jams, and jellies.
  • Luncheon meat, Bacon.
  • High fructose corn syrup additives.
  • Starch as an additive or binding agent.

What to feed?

  • Fresh food / Whole, Unprocessed foods.
  • The raw diet, Semi-Homemade Food (commercial homemade diet with a dehydrated formula), or home-cooked meals.
  • Low-carb dog food with Fresh, lean protein.
  • Probiotics and digestive enzymes.
  • Add oregano or basil to their diet.
  • Animal Essentials Detox Blend: (combination of herbs suspended in glycerine). This will help your dog detox.


Although transmission of histoplasmosis from the affected dog is not yet proven, the practice of personal hygiene is always the best method of prevention.

Once treatment is finished, less percentage of affected dogs suffer a relapse. The prognosis for generalized histoplasmosis is affected by the time of diagnosis, severity, and dissemination.

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