Occupational Histoplasmosis Yahya Al-Rayyes Introduction › yahoo_site_admin › assets › docs › YAR-0… · Histoplasmosis is endemic to the Ohio and Mississippi River Valleys

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


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


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


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)


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


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.


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


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.


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


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


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


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.


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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Occupational Histoplasmosis Yahya Al-Rayyes Introduction › yahoo_site_admin › assets › docs › YAR-0… · Histoplasmosis is endemic to the Ohio and Mississippi River Valleys