Histoplasmosis: Causes, risk factors, and treatment
A histoplasmosis infection usually causes mild to moderate symptoms. However, in those who have problems with immunosuppression, such as older people, it can be more severe.
For some people, the infection can lead to long-term complications.
This article explores the causes, risk factors, and available treatments for histoplasmosis.
The Histoplasma capsulatum fungus is responsible for the histoplasmosis infection.
The fungus does not grow in all of the United States (U.S.). Instead, it is located mostly in the Mississippi, Missouri, and Ohio River valleys. People who live in Latin America and Africa also experience the infection.
The fungus thrives in dark damp areas and can be found in the soil. When a person starts digging in the soil, particularly in an enclosed area such as a barn or chicken coop, the fungal spores begin to circulate in the air. When a person breathes in, the fungus enters their lungs where it can cause infections.
Fungal spores can circulate in the air if a person is working in an enclosed space, such as a chicken coop.
People who have occupations that involve working with soil are more at risk of histoplasmosis. These occupations include:
- construction workers
- people working in or exploring caves
The spores from the Histoplasma capsulatum fungus are so small that a person would not be able to see them when working in these environments.
Most of the time a person infected with histoplasmosis will experience no symptoms. They may pass off any symptoms they do have as a common cold, without ever knowing a fungus had caused them.
Histoplasmosis symptoms can resemble those of the flu. Examples include:
According to the Centers for Disease Control and Protection (CDC), these symptoms are most likely to appear 3-17 days after a person initially breathes in the fungus.
Histoplasmosis is not contagious. However, the condition can be long-lasting.
It can take between 2 weeks and several months for the infection to go away. When the condition leads to longer-term effects, it is said to be chronic.
This tends to happen when a person's immune system is suppressed, due to an infection, such as HIV.
Chronic histoplasmosis symptoms include:
- a cough, causing thick, yellow sputum
- a low-grade fever
- night sweats
- shortness of breath
- weight loss
Chronic histoplasmosis can severely affect lung functioning.
Some people can experience a more severe form of histoplasmosis known as disseminated histoplasmosis. This condition is when the infection spreads beyond a person's lungs to other organs of the body.
This can cause severe and potentially deadly illness. The symptoms of disseminated histoplasmosis can include:
- gastrointestinal bleeding
- low blood pressure
- shortness of breath
- swollen spleen and liver
- ulcers in the mouth and lips
- low blood counts
Disseminated histoplasmosis requires hospitalization and antifungal medication.
Sometimes histoplasmosis can travel from the lungs to the eye. The result is a condition known as ocular histoplasmosis syndrome or OHS.
According to the National Eye Institute, OHS is a leading cause of vision loss among people ages 20 to 40 in the U.S.
A person does not usually experience symptoms in the first few days after an OHS infection. However, over time they may have changes in vision, such as wavy lines or blind spots.
A person may be young when they are infected with histoplasmosis. However, they may not experience symptoms associated with the eye infection until decades later.
Exposure to bird or bat droppings increases a person's chance of a histoplasmosis infection.
People experience histoplasmosis when they breathe in fungal spores.
Some of the activities and areas that are linked with histoplasmosis infection include:
- caving, such as spelunking
- cutting and transporting wood from decaying wood piles or dead trees
- engaging in demolishing, remodeling, or working in old buildings
- working in chicken coops, especially when dealing with bird droppings
People working in these types of environments are more likely to experience histoplasmosis.
Exposure to bird and bat droppings brings a particular risk for breathing in the histoplasmosis spores.
Wearing masks and other protective clothing when working in these environments can help.
Also, spraying the soil with water before digging can reduce the likelihood of dust and fungal spores entering the air and infecting people.
There are additional groups, as well, who tend to be more vulnerable to the effects of histoplasmosis and experience a more severe infection. They include people with:
- long-term corticosteroid use, prednisone
- a history of lung diseases, such as emphysema
- a history of organ transplant
- the very old or very young
A doctor will start by taking someone's medical history and asking questions about their symptoms.
If histoplasmosis is suspected, the doctor may ask about a person's occupation and exposure to soil or any recent travel they have done. Other questions include when the symptoms started and what makes them worse or better.
There are several other ways of identifying histoplasmosis, including by testing a person's blood or urine for the presence of the fungus.
If the condition appears severe, a doctor may recommend a bronchoscopy. This involves putting a lighted tube into the lungs, so as to see any inflammation. The procedure can also take a tissue sample to test for fungus.
A doctor can also use imaging scans, such as X-ray imaging or computed tomography scans (CT). These can identify inflammation in the lungs that could indicate the presence of histoplasmosis.
Over-the-counter medications can help alleviate the flu-like symptoms.
When someone has acute histoplasmosis, their symptoms will usually go away with time and supportive treatment, including:
- getting plenty of rest
- drinking lots of fluids
- taking over-the-counter medications for aches
However, if a person's symptoms last longer than 4 weeks, a doctor will often recommend taking anti-fungal medications.
Those with chronic histoplasmosis can take anti-fungal medications. Examples of these include amphotericin or itraconazole.
These medications can help kill the fungus, but can affect a person's kidney and/or liver function, especially amphotericin. A doctor will monitor a person very closely if they take these drugs.
If a person has the HIV virus, they may have to take anti-fungal medications for the rest of their lives.
If a person has disseminated histoplasmosis, they will often require oxygen therapy to support their breathing. They may receive intravenous (IV) antifungal medications to treat their condition as well.
Anyone with ocular histoplasmosis must be treated with a type of laser surgery called photocoagulation. This destroys damaged retinal tissue that prevents the infection from causing further damage to the eyes.
While the laser does not restore vision, it can reduce the risks for further loss of vision.