— PUBLIC HEALTH
Histoplasmosis:
The Hidden Danger in Bat Guano
Removing bats is only half the job. The guano they leave behind in your attic can also pose a serious health risk long after they’re gone.
Histoplasmosis: The Hidden Danger in Bat Droppings
Most homeowners who discover bats in their attics focus on getting the animals out, but the bigger health concern is what they leave behind. Bat guano that sits undisturbed for months or years can grow a harmful fungus. When cleaning an attic, replacing insulation, or starting a renovation project, you may disturb accumulated droppings, which can release microscopic fungal spores into the air. Once airborne, these spores can be inhaled by anyone nearby, potentially leading to a serious respiratory illness.
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What Is Histoplasmosis?
Histoplasmosis is a lung infection caused by inhaling spores of the fungus Histoplasma capsulatum. It is not a virus, not a bacterium, and not something you catch from another person. You get it by breathing in dust kicked up from contaminated soil or bat droppings.
The fungus lives quietly in the environment until it’s disturbed. Bat guano sitting untouched in a sealed attic isn’t releasing spores into your bedroom. But the second that material is swept, vacuumed, or walked through, it turns into a fine dust that stays in the air, and anyone nearby can inhale it.
Histoplasmosis Symptoms
The mildest cases of histoplasmosis often show no symptoms at all. More severe infections can become life-threatening, especially without prompt treatment. When symptoms do develop, they typically appear 3 to 17 days after breathing in the fungal spores.
- Fever and chills
- Chest pain or discomfort
- Shortness of breath
- Dry or nonproductive cough
- Headache
- Night sweats
- Fatigue and general malaise
- Muscle aches
- Loss of appetite
When to call a doctor
Histoplasmosis is frequently mistaken for pneumonia or bronchitis. If you develop flu-like symptoms within a few weeks of cleaning bat droppings, working in an old attic or barn, or another known exposure, tell your healthcare provider. Seek medical attention if your symptoms worsen, don’t improve after a week, or if you have a weakened immune system.
Where is Histoplasmosis Commonly Found?
Histoplasma thrives in damp, organic-rich soil, and it grows especially well in material loaded with bat guano or bird droppings. The nitrogen content in droppings essentially fertilizes it. In the United States, the fungus is very common in Midwestern states, including Wisconsin.
Attics with Bat Colonies
Years of accumulated guano in a warm, enclosed space with poor ventilation is the most common area of exposure.
Old Barns & Outbuildings
Rural properties often have decades of bat and bird waste in haylofts, rafters, and grain areas.
Chimneys & Soffits
Chimney swifts, starlings, and bats nest in these tight cavities, and droppings pile up directly above living spaces.
Pigeon & Starling Roosts
Ledges, signage, rooftop HVAC units, and warehouse rafters on Milwaukee-area commercial buildings.
Chicken Coops
Backyard flocks are common in Wisconsin, and coop cleanout stirs up exactly the kind of dust that carries spores.
Caves & Demolition Sites
Caving, spelunking, and tearing down or remodeling old structures all disturb long-settled material.
One more detail worth noting: spores can remain viable in guano for years. A colony that moved out three summers ago doesn’t mean the attic is safe. The droppings are still a hazard.
What Are the Health Risks?
Most people who inhale Histoplasma spores never get sick at all, or feel mildly under the weather and recover on their own without ever knowing why. That’s the common outcome.
But the dose matters enormously. A homeowner who spends a weekend shoveling out an attic full of guano without a respirator is inhaling a far heavier load of spores than someone simply passing through a contaminated area. Heavy exposure in a confined space is what turns a minor issue into a real illness. Histoplasmosis shows up in a few different forms:
Form
What it looks like
Acute pulmonary
A flu-like respiratory illness that typically clears within a few weeks to a month.
Chronic pulmonary
A lingering cough, fatigue, weight loss, and fever that drags on for months.
Disseminated
The infection spreads to other organs, making it serious and potentially fatal without treatment.
Ocular (eye)
Scarring in the retina that can affect vision later in life.
Who should be most careful
If you or someone in your home has a weakened immune system from a medical treatment, certain long-term medications, or HIV, stay away from guano cleanup completely. The same goes for babies, adults over 55, and anyone with a long-term lung condition. For these groups, a mask isn’t enough. They should stay out of the building altogether.
Pets can get it too
Dogs and cats can develop histoplasmosis from the same environmental exposure. If your dog has been nosing around the barn or the attic access and develops a persistent cough, weight loss, or lethargy, mention the exposure to your veterinarian.
How Is Histoplasmosis Treated?
Diagnosis typically involves a urine or blood antigen test, sometimes paired with chest imaging, blood work, or a culture. It usually takes a few days to a couple of weeks to receive results. Treatment depends entirely on severity:
Mild Cases
Most healthy people clear the infection on their own within a month with rest and supportive care, often needing no treatment.
Moderate to Severe Cases
Treated with prescription antifungal medication, typically for several weeks to several months.
Severe or Disseminated Cases
Usually begin with an IV antifungal in a hospital setting, followed by a long course of oral antifungals.
How to Protect Yourself from Histoplasmosis
It’s hard to avoid breathing in microscopic fungal spores. But you can take the following steps to reduce your risk of infection.
Don't disturb bat droppings
No sweeping, shop-vac, or dry shoveling. A regular household vacuum will blast spores through its filter and release them into the air you breathe.
Call a professional
Our professional protective equipment, containment methods, and safe disposal protocols keep your household from being exposed to hazardous airborne contaminants.
Use respiratory protection
Cleanup requires at minimum a properly fitted N95, and for heavy accumulations in enclosed spaces, a respirator with HEPA-rated cartridges.
Keep vulnerable people out entirely
Immunocompromised individuals, infants, older adults, and anyone with lung disease shouldn't be in the structure during cleanup — not just out of the attic.
Seal the entry points, permanently
Cleanup without exclusion just resets the clock. Bats find gaps as small as three-eighths of an inch around soffits, ridge vents, chimney flashing, and fascia boards.
Don't wait it out
Every additional season a colony roosts in your attic is more guano, more contamination, and a more expensive remediation later.
Bat Removal & Guano Cleanup in Milwaukee, WI
Finding bat droppings in your attic isn’t a cleanup project; it’s a health and safety issue. That’s why Advanced Wildlife & Pest Control follows a proven process: inspect, protect, exclude, remediate, and permanently seal your home against future bat activity. Contact us today at (262) 242-4390.
Our technicians use professional containment procedures and commercial-grade HEPA filtration equipment that captures 99.97% of microscopic particles down to 0.3 microns, helping prevent contaminated dust from becoming airborne during cleanup. Unlike standard household or shop vacuums, our specialized equipment is designed for safe guano remediation, allowing us to thoroughly restore your attic while protecting your family and ensuring bats don’t return.