Post on 06-Jul-2020
Occupational Histoplasmosis Yahya Al-Rayyes
Introduction It is estimated that around 70,000 fungal species inhabit our planet and although few of
them cause disease in humans, opportunistic and pathogenic fungal species thrive in
individuals who are immunocompromised, such as those with HIV/AIDS, transplant
patients and patients undergoing chemotherapy.(1)
Mycotic diseases have a long history. They have been studied and reported prior to the
bacterial, rickettsial, viral and protozoal infections.(2) Occupationally and
environmentally obtained infections due to the inhalation of pathogenic fungi are
becoming more common and identified as an emerging medical problem (2). Among the
most etiologic agents of mycotic diseases is Histoplasma capsulatum which is usually
referred to as the most significant mycotic organism (2).
Histoplasmosis is a fungal infection caused by the germ Histoplasma capsulatum. This
fungus is commonly found in the soil in areas that have accumulated bird or bat
droppings. According to the American Lung Association there is an estimated 50 million
Americans believed to have been infected with Histoplasmosis at some point in their
lives. The Mayo Clinic reports that every year as many as 250,000-500,000 Americans
contract Histplasmosis.
History and Etiology
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Histoplasmosis was first identified and named by Samuel Taylor Darling, a U.S. Army
pathologist who was stationed in the Panama Canal Zone. While performing an autopsy
on an individual whose death was attributed to tuberculosis, Darling found that the
organism which was believed to be tuberculosis was covered in a protective sheath not
associated with the tuberculosis organism. Because of the protective sheath, Darling
named the organism Histoplasma Capsulatum. He published his findings in the Journal
of American Medical Association in 1906. In this article he described this as a tropical
disease similar to tuberculosis. This misconception of Histoplasmosis as a tropical
disease continued until the late 1930’s when the American medical community officially
recognized the disease. In spite of this recognition Histoplasmosis continued to be
misdiagnosed as tuberculosis.
Histoplasmosis can be found throughout the United States, however, the highest number
of people with the disease are located in the central and eastern parts of the country.
Histoplasmosis is endemic to the Ohio and Mississippi River Valleys. In addition to the
United States, Histoplasmosis can be found in many areas of the world including
Australia, South America, Europe, Africa and Asia. Worldwide hundreds of thousands
of people are believed to be infected with Histoplasmosis each year. However, since
Histoplasmosis can be mistakenly be diagnosed as Tuberculosis the full extent of the
disease is still not fully known.
The primary source of Histoplasma capsulatum is soil. The fungus appears to thrive in
soils rich in nitrogen content, especially soil enriched with bird or bat guano. It is
accumulated droppings that pose the greatest risk of containing the fungus. Since birds
do not appear to be infected by Histoplasma capsulatum fresh droppings are not believed
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to pose a health risk. However, birds can transfer the organism by carrying it on the
wings, feet or beaks and infecting soil in other areas.
Unlike birds, bats can become infected with Histoplasma capsulatum and can transmit the
disease through their droppings. Soil contaminated from bats can be potentially infectious
for many years.
The Organisms
Histoplasma capsulatum is a dimorphic fungus, which exist as either a free-living
mycelial (mold) in the soil at a lower growth temperature (optimal 30° C) or as a
parasitic yeast form that inhibit cells such as macrophages within the body of mammalian
hosts(figure1). The mold forms are saprophyte that grows
by absorbing nutrients from dead organic matter
decomposed within the soil and produces infectious spores.
When Histoplasma capsulatum spores become aerosolized
and inhaled by mammals, these spores become induced and
change into a yeast form by the warmer body temperature
of the mammalian respiratory tract.(1,2) Figure 1 (Miravistalabs)
Geographic Distribution
Today reports indicate that geographic distribution of the fungus Histoplasma capsulatum
is not limited to the midwestern United States (Figure2). The fungus is found to be more
prevalent in river valleys between latitudes 45° north and 30° south and can be isolated
from the environment in many areas of the world.(2) This fungus is endemic in some
areas in the United States including Ohio, Indiana, Kentucky, Tennessee, Illinois, and
Missouri. (Figure 3) Although people are more likely to contract Histoplasmosis in an
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endemic area, the infection can be contracted in areas outside of the endemic region as
well (3).
Figure 2 (Miravistalabs) Figure 3 (Miravistalabs)
Sex Distribution It is believed that male animals are more prone to contracting the disease Histoplasmosis
than the female of the species; however this may be correlated with certain occupations
and association with endemic areas where soil and the environment is contaminated with
Histoplasma capsulatum. Various Epidemiological studies indicates that males are at a
higher risk of contracting Histoplasmosis in the “ Histo-Hazard” occupations and
avocations.(2)
Incidence Although it is estimated that up to 500,000 persons are infected with Histoplasma
capsulatum annually, the majority of people remain asymptomatic. Symptomatic disease
occurs in only about 1% of those receiving a low inoculum exposure of Histoplasma
capsulatum. The majority of symptomatic patients present with self-limiting syndromes
(4,5) consisting of fever, cough, chest pain, and fatigue which gradually resolve without
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treatment. Some, however, remain symptomatic with fatigue and weakness for months.
Histoplasmosis commonly presents as fever, weight loss, respiratory symptoms (cough,
shortness of breath), lymphadenopathy, hepatosplenomegaly, skin lesions, and even
septic shock in 5% to 10% of patients. Disseminated disease occurs in 20% to 30% of
patients who have AIDS and live in areas where the disease is endemic. The diagnosis is
established by blood and tissue cultures, histopathologic specimens of involved tissues,
or antigen detection in the urine or serum. (4,5)
Histoplasmosis may be asymptomatic or take one of the four clinical forms:
1) Acute benign respiratory - mild respiratory illness with general malaise, fever, chills,
headache, myalgia, chest pains, and nonproductive cough. Small, scattered calcifications
in the lungs, hilar lymph nodes and spleen maybe late findings.
2) Acute disseminated -debilitating fever, GI symptoms, bone marrow
uppression, lymphadenopathy. Most frequent in children and
immunosuppressed; fatal if not treated.
3) Chronic pulmonary - clinically and radiologically resembles chronic
pulmonary tuberculosis with cavitations, usually in middle-aged and
elderly persons with underlying emphysema.
4) Chronic disseminated - low-grade fever, weight loss, weakness, liver and
spleen enlargement, mucosal ulcers, subacute course with slow progression;
fatal if not treated(6)
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Mycology and Route of Entry
The Concise Oxford Dictionary of Current English defines Mycosis as the presence of
parasitic fungi or a disease caused by those fungi. Infection is established after inhalation
of Histoplasma capsulatum microconidia into the lungs. Once inhaled, the microconidia
rapidly convert to the yeast phase within the lung parenchyma. It is thought that the yeast
is phagocytized by macrophages within the lung in an attempt to clear the infection (7).
Those who develop symptoms related to infection are more likely to show various forms
of clinical manifestation within 3 to 14 days of the initial infection.
Unlike Bats and other susceptible mammals which supports the growth of Histoplasma
capsulatum due to their optimum blood temperature, the high blood temperature of birds
and avian species suppress the growth of the fungus in their bodies. It became apparent
that birds roosting habits and their accumulated fecal deposition allow Histoplasma
capsulatum to grow and flourish in the environment. The enrichment of soil with organic
nitrogen is widely recognized fact in which the fungal agent finds it as an optimum
growing condition. On the other hand fecal excrement from bats and dead infected bats
can provide an immediate contamination of the environment, these facts account partially
for the high infection rates among individuals associated with bats guano.(2)
Epidemiology
Although Histoplasma capsulatum has been isolated and identified in many areas of the
world, it is considered to be most endemic in regions of the Ohio and Mississippi river
valleys. The primary source of Histoplasma Capsulatum is soil. Laboratory and field
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studies have documented that Histoplasma Capsulatum requires high relative humidity
and an optimum temperature (30-35°C) to support growth in enriched soil (2). Bird and
bat excrement enhance the growth of H capsulatum in soil by accelerating sporulation. In
areas where birds roost, the fungus is found where the bird excrement is decaying and
mixed with soil. In such areas, infectious particles can exceed 105 particles per gram of
soil(8)
Occupations Every person in an area where the Histoplasmosis fungus is growing and where the
individual can breathe the airborne spores may be at risk on exposure to and possible
infection from Histoplasma capsulatum. Histoplasmosis spores may be carried for miles
by the wind from areas heavily contaminated with the spores towards unsuspecting areas.
In such areas some people might contract the disease while remaining unaware of their
exposure or it’s original source. Although few people will develop the symptomatic form
of the disease due to a moderate level of exposure, others who are exposed to a higher
level of spores or long- term exposure are at greater risk of developing the disease.
Individuals with weakened immune systems might experience more severe illness and
undergo long term consequences, therefore they are advised to take extra precaution and
avoid activities near which maybe contaminated with Histoplasmosis.
Exposure to Histoplasmosis is not limited to people whose activities and jobs are present
near areas contaminated with Histoplasma capsulatum spores, yet every person who lives
or travel through endemic areas is subject to contracting Histoplasmosis.
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People, whose jobs and activities involve contact with soil enriched with bird droppings
and bat guano, are at greater risk of contracting Histoplasmosis. Some occupations and
activities might include:
• Framers
• Gardeners
• Construction workers
• Demolition workers
• Painters
• Chimney cleaners
• Bridge inspectors
• Roofers
• Heating and air conditioning installers or service person
• Restorers of old and abandoned buildings
• Spelunker (Cave explorer)
• Archaeologists
• Geologist in the field and those who work with soil and rock samples
• Microbiology laboratory workers
• Pest control workers
• People who work in wood lots or woodpiles
• Workers in chicken houses
• Workers who work in mining sites inhibited by bats
• Coal miners or People who handle coal
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Preventive Measures
The primary way to prevent exposure to Histoplasmosis is avoidance of areas that are
most likely to be contaminated or the use of precautionary protective measures when
exposure is likely. Prevention relies heavily on avoiding exposure to soil, dust or other
environmental material in potentially contaminated areas.
However, for individuals residing in areas where Histoplasma Capsulatum is endemic it
is practically impossible to avoid exposure. In such cases a more proactive way to
decrease the risk of exposure to Histoplasmosis is to take steps to prevent the growth of
Histoplasma capsulatum in the first place by frequently cleaning areas where bird or bat
droppings accumulate and preventing droppings from composting.
1. Excluding a Colony of Bats or a Flock of Birds from a Building.
In areas where a colony of bats or a flock of birds may roost it is important to take
preventative steps to exclude the intruders from the building. For example, identifying
and sealing all points of entry, using visual deterrents such as balloons, lights and other
devices that may deter roosting, and the use of nontoxic bird repellents.
The disadvantages of these anti-roosting techniques are that most are not permanent.
More permanent repellents include mechanical anti-roosting systems consisting of angled
and porcupine wires made of stainless steel.
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2. Posting Health Warnings
In instances where a colony of bats or a flock of birds is allowed to live in a building or a
stand of trees the accumulation of their manure will create a health risk for individuals
who may come into contact with contaminated material. In such cases it is crucial that
signs should be posted informing the public of the potential health risk. . Posted signs
should provide contact information for local health officials if
there are any questions about the area. In addition to posting signs,
in some cases a fence may need to be built around a property to
prevent unsuspecting or unprotected individuals from entering a
contaminated area.
This picture is in a contaminated area in Kentucky, where the guano of the starlings was 5 to 6 inches thick in places with Histoplasma capsulatum essentially in pure culture.
3. Controlling aerosolized dust when removing bat or bird manure from a
building.
When removing bird or bat manure from a building it is important to utilize work
practices and dust control measures that eliminate or reduce dust generation in order to
decrease the risk of the inhalation of spores that may lead to infection and development
of Histoplasmosis. For example, prior to removing potentially dusty material, carefully
wet the material with a low pressure water spray to reduce the amount of dust aerosolized
during an activity. A surfactant or wetting agent may be added to the water to further
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reduce the amount of aerosolized dust. After the material is wet, it may be collected in a
secure container or heavy duty plastic-bag for disposal Alternate methods of removal
include the use of industrial vacuum cleaners with a high-efficiency filter to bag the
material or the use of truck or trailer mounted vacuum systems for buildings with large
accumulations.
Once the removal of all material that might be contaminated with H.capsulatum is
complete, the area should be cleaned and inspected to ensure that no dust or debris
remains in the area.
4. Disinfecting contaminated material
When bird droppings are left to accumulate for 2 or more years, especially in blackbirds
roosting areas, the soil reaches an optimum state for Histoplasma capsulatum to
overcome the competition from other soil microorganisms. Once established in the soil, it
becomes challenging to eliminate the organism from the soil and disinfection becomes
the alternative. Disinfection has occasionally become the method of choice when removal
of contaminated soil and accumulated bat manure is impractical. While decontamination
using formaldehyde solution have been proven to be the only effective disinfectant, yet
today EPA-registered fungicidal products with content of formaldehyde are not permitted
for use as soil disinfectant.
5. Disposing of waste
When removing material from a work site that is suspected to be contaminated with
Histoplasma capsulatum must be disposed of or decontaminated properly. It should not
be relocated to another area where it may continue to pose a health hazard. Prior to the
removal of material that might be contaminated it is necessary to review and follow local
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and state requirements for the removal, transportation and disposal of the material in
question. In addition to following state and local requirements arrangements should also
be made with a landfill operator for the disposal of the quantity of material to be
relocated. Disposal may involve incineration or another decontamination method if the
state or local landfill regulations define material contaminated with Histoplasma
capsulatum to be infectious waste.
6. Wearing Personal protective equipment
It is recommended that workers wear personal protective equipment during the removal
of an accumulation of bird or bat manure from enclosed areas. This protective equipment
should be worn in addition to the use of dust control measures to further reduce the risk
of exposure to Histoplasma capsulatum. This protective equipment should include a
NIOSH-approved respirator and other personal protective equipment.
When choosing a respirator, it is important to consider the circumstances under which the
equipment will be used. Respirators have varying degrees of protection and there have
been reported cases of people developing Histoplasmosis while wearing a respirator or
protective mask
Respirators that should be worn during work activities involving exposure to materials
that may be contaminated with spore-containing dust may range from the low-scale
disposable, filtering facepiece respirator to full-facepiece, powered air-purifying
respirators for jobs involving more exposure to dust.
7. Information for Workers in High Risk Areas
When working in high risk areas it is important that individuals at risk of exposure
receive training regarding the appropriate use of protective gear as well as the proper
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procedures to avoid the potential exposure of innocent bystanders to Histoplasma
capsulatum. In addition to adequate training, workers in areas that might be contaminated
by Histoplasma capsulatum should be informed in writing of the increased risk of
exposure to the fungus. Workers should be informed that individuals with compromised
immune systems are at a greater risk of developing severe and disseminated
Histoplasmosis if they are infected.
Conclusion
Occupational and environmental infections are extremely common and occur throughout
the world. In order to decrease the incidence of outbreaks of occupationally related
fungal infections, such as Histoplasmosis, it is important that individuals working in
fields that are at high risk of exposure take precautions to protect themselves and others
in the surrounding environment. These precautions, which have been discussed in this
paper, are preventative in nature and involve wearing recommended protective gear and
following NIOSH safety guidelines when involved in activities that may result in the
dispersal of spores in a potentially contaminated area. When contamination of an area is
suspected testing should be done to determine if Histoplasma capsulatum spores are
present. If contamination is confirmed posting of signs to warn the public of the presence
of the fungus is necessary and proper clean up and disposal should be conducted
according to NIOSH safety guidelines, if cleanup is deemed feasible.
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References
1. Klein Bruce S. Turning up the Heat on Histoplasma Capsulatum. Science
[serial online]. 2000; 290:1311-1312. Available at: http://www.sciencemag.org/cgi/content/summary/290/5495/1311?rbfvrToken=3214fed01062e81757fdc6ba01bd150d2179a502 . Accessed July 24, 2005.
2. Di Salvo AF. Occupational Mycosis. Philadelphia: Lea & Febiger; 1983. 3. Wheat J. Histoplasmosis Information Guide. 2002:Indianapolis; Indiana 4. Goldman M, Johnson PC, Sarosi GA. Fungal Pneumonias: The Endemic
Mycoses. Clinics in Chest Medicine. 1999; 20(3): 507-519. 5. Wheat LJ. Systemic fungal infections: diagnosis and treatment. Infect Dis Clin
North Am. 1988; (2):841-59. 6. http://chfs.ky.gov/NR/rdonlyres/3BDD5599-ED38-448D-8291-
5EAF94C5BF35/0/Histoplasmosis.pdf 7. Wheat J. Endemic Mycosis In AIDS: a clinical review .Clin Microbiol Rev1995;
8 : 146-59. 8. http://hivinsite.ucsf.edu/InSite?page=kb-05-02-06#S1X 9. Leinhart SW, Schafer M, Singal M, Hajjeh R. Histoplasmosis, Protecting
Workers at Risk. Cincinnati: NIOSH Publication; 2005-109.
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