Histoplasmosis

What causes histoplasmosis

Histoplasma capsulatum lives in soil, especially soil enriched with droppings from birds (starlings, blackbirds, chickens, pigeons) and bats. Disturbing that soil or droppings releases microscopic spores into the air. Breathing them in starts the infection in the lungs.

Activities linked to outbreaks include:

• cleaning chicken coops, barns, attics or old buildings with bird or bat droppings
• demolition, construction and excavation
• clearing roosts, cutting down trees where birds roosted
• exploring caves (hence "cave disease")
• farming, landscaping and pest control

You cannot catch histoplasmosis from another person or directly from a bird or bat. Many people in endemic areas are infected unknowingly at some point in their lives.

Types and symptoms

Most infected people (well over half) have no symptoms. Illness depends on the dose of spores inhaled and the person's immune system.

Acute pulmonary histoplasmosis

The most common illness. Symptoms start 3 to 17 days after exposure:

• fever and chills
• dry cough
• tiredness, often marked
• chest pain or discomfort
• headache and body aches

Most healthy people recover within a few weeks without treatment, although fatigue can linger. A heavy exposure can cause severe pneumonia even in healthy people.

Some people develop reactions such as painful red lumps on the shins (erythema nodosum), joint pain, or inflammation around the heart (pericarditis).

Chronic pulmonary histoplasmosis

A slowly progressive lung infection, usually in older people with emphysema. It causes cough, weight loss, night sweats and cavities in the lungs, and it can look like tuberculosis.

Disseminated histoplasmosis

The fungus spreads from the lungs to the liver, spleen, bone marrow, adrenal glands, skin, mouth, gut or brain. It mainly affects people with weakened immunity:

• advanced HIV/AIDS
• organ or stem cell transplant recipients
• people on TNF-blocker drugs (such as infliximab or adalimumab), high-dose steroids or chemotherapy
• infants and older adults

Symptoms include persistent fever, weight loss, enlarged liver and spleen, mouth ulcers, low blood counts and, without treatment, organ failure. It can also reactivate years after the original infection when immunity falls.

Other forms

• Granulomas and lung nodules: healed infections leave small calcified spots that may be found by chance on scans and mistaken for cancer.
• Mediastinal disease: swollen chest lymph nodes or, rarely, fibrosing mediastinitis, an overgrowth of scar tissue that can compress airways and blood vessels.
• Presumed ocular histoplasmosis syndrome: scarring at the back of the eye that can later threaten central vision.

Diagnosis

Because symptoms resemble flu, pneumonia or tuberculosis, doctors need to suspect histoplasmosis based on where you live or have traveled and what you were doing. Tests include:

• Antigen test of urine or blood: detects fungal proteins. Most sensitive in disseminated and severe acute disease.
• Antibody blood tests: useful 2 to 6 weeks after infection, but can stay positive from past exposure.
• Chest X-ray or CT scan: shows patchy infiltrates, nodules, enlarged lymph nodes or cavities.
• Culture of sputum, blood, bone marrow or tissue, which can take up to several weeks.
• Biopsy with microscope examination of lung, lymph node or other tissue.

Treatment

Treatment follows the Infectious Diseases Society of America guidelines:

Itraconazole interacts with many medicines and needs blood level checks. Pericarditis and joint symptoms are usually treated with anti-inflammatory medicines.

Complications

• severe pneumonia and acute respiratory distress
• adrenal insufficiency from adrenal gland infection
• pericarditis
• fibrosing mediastinitis
• meningitis
• vision loss from eye involvement

Prevention

• Avoid disturbing bird or bat droppings in endemic areas when possible.
• Before cleaning droppings, mist them with water to keep dust down. For large accumulations, professional removal is safer.
• Wear a properly fitted N95 or better respirator, gloves and disposable coveralls when exposure cannot be avoided.
• People with weakened immune systems should avoid caves, chicken coops and demolition sites in endemic regions.
• Some people with advanced HIV in high-risk areas are given preventive itraconazole.

There is no vaccine.

Frequently asked questions

Is histoplasmosis contagious?

No. Histoplasmosis comes only from breathing in spores from the environment, mainly soil or dust containing bird or bat droppings. It does not spread between people, and pets or birds do not pass it on directly. Several people can get sick together because they shared the same exposure.

How long does histoplasmosis last?

In healthy people, acute histoplasmosis usually improves within a few weeks, although tiredness can last a month or more. Moderate cases treated with itraconazole need 6 to 12 weeks of medicine. Chronic and disseminated forms need treatment for a year or longer.

Can histoplasmosis go away on its own?

Yes, in most healthy people. The immune system controls the fungus, and many people never know they were infected. Treatment is needed for severe illness, symptoms lasting more than about a month, chronic lung disease, or anyone with a weakened immune system.

Where is histoplasmosis most common?

In the US it is most common in the Ohio and Mississippi River valleys, covering states such as Ohio, Kentucky, Indiana, Illinois, Missouri, Tennessee and Arkansas, although cases occur well beyond. It is also found in Central and South America, Africa and parts of Asia.

How is histoplasmosis different from blastomycosis and valley fever?

All three are fungal lung infections from soil. Blastomycosis overlaps in geography but more often causes skin lesions. Coccidioidomycosis (valley fever) occurs in the dry Southwest. Histoplasmosis is linked to bird and bat droppings. Specific tests tell them apart.