Kenneth
D. Rosenman, M.D.
Michigan State University Extension
Respiratory
hazards that farmers and family members may be exposed to
include various grains that can be contaminated with fungi,
bacteria or microbial toxins; pesticides; solvents; gasoline
and diesel fuels; and irritant gases such as oxides of nitrogen
and ammonia. The specific issue to be discussed in this CMASH
newsletter is occupational asthma.
Occupational
asthma is asthma which occurs after a variable period of symptomless
exposure to a known sensitizing agent. Known sensitizing agents
on the farm include both plant and animal matter. Known allergens
related to farming include:
- Plant
- Grain
dust (all types of grain)
- Animal
- Cow
dander
- Cow
urine
- Egg
yolk proteins
- Fungi
- Grain
mite
- Grain
weevil
- Meal
worm
- Pig
urine
- Pig
dander (Alternaria, Aspergillus, Cladosporium)
- Poultry
mites
- Poultry
dander
- Chemicals
- Antibiotics
used in feed (spiramycin, amprolium)
- Formaldehyde
- Glutaraldehyde
A farmer
works with a large amount of organic matter. Many times this
work is in a confined space such as a swine confinement barn,
silo or chicken coop. Because of limited ventilation in these
structures, the concentration of potential allergens in the
air is markedly increased.
The
typical clinical presentation is that the patient has increasing
symptoms of shortness of breath, wheezing or chest tightness
which eventually causes the farmer to seek medical care. Many
times farmers will have repeated diagnoses of "bronchitis"
before the recurrent nature of the condition suggest asthma.
Farmers may have been exposed their whole life (i.e. many
years) before becoming sensitized.
Four patterns have been recognized in response to exposure
to allergens. There is an immediate response (symptoms occur
10 minutes to an hour after exposure), a late response (symptoms
occur 6-12 hours after exposure), a dual response (patient
has both immediate and late symptoms), and a recurrent nocturnal
response (see Figure 1). Other than the immediate response
pattern it is extremely difficult from the history to see
a clear association between a farm exposure and asthma. Unlike
non-farm work, where the patient is generally exposed to the
allergen only on specified work days, the farmer may be exposed
to the allergen seven days a week. However, an attempt should
be made to see if there is a pattern related to certain work
activity, remembering that the asthma reaction may be delayed
from the time of exposure. As the asthma becomes chronic,
the farmer may now react to many irritants and only a careful
review of the period when the symptoms began may reveal an
association with a particular allergen. Additionally, data
from factory workers with occupational asthma indicates that
the longer patients with work-related asthma are exposed to
the allergen which causes their symptoms the more likely their
symptoms will persist, even when they are removed from exposure.
Farmers
with work related asthma will typically have a positive methacholine
challenge test and an elevated serum IgE. They may or may
not have eosinophilia. Skin tests with the normal battery
of antigens such as pollens, molds, cat and dog dander may
or may not be positive. Since these skin tests are positive
in up to 20% of asymptomatic individuals, they are not helpful
in excluding a specific farm-related allergen. Serum RASTs
are commercially available for a large number of potential
farm-related allergens. Commercially available RASTs for farm
related allergens include:
- Plant
- Grain
dust
- Specific
types of grain (i.e. corn, rye, wheat)
- Animal
- Chicken
feathers
- Cow
dander
- Duck
feathers
- Egg
proteins
- Goat
epithelium
- Goose
feathers
- Horse
hair
- Molds
- Rabbit
hair
- Rabbit
epithelium
- Sheep
epithelium
- Storage
mites
- Swine
epithelium
- Turkey
feathers
The
sensitivity and specificity of the RAST varies by substance.
A positive test only documents exposure, it does not document
that a particular antigen is the causal agent.
There
are other exposures on a farm which can make a farmer wheeze.
These include overexposure to ammonia (used as a fertilizer
or a waste gas in a swine confinement barn), overexposure
to organophosphate pesticides (pharmacological reaction),
and overexposure to oxides of nitrogen (silo-filler's disease
or its late sequalae, bronchiolitis obliterans).
A farmer
may also have non-work related asthma but his/her symptoms
are exacerbated by exposure to non-specific irritants such
as grain dust. This can be recognized by an onset of asthma
which predates farm exposures and/or is clearly caused by
some non-farm allergen.
If possible,
it is important to determine the specific allergen. The most
effective treatment for asthma is to eliminate or minimize
allergen exposure. Improved ventilation, proper respiratory
protection or having another person do a particular task are
all potential ways to intervene. Documentation of a particular
allergen is done by reviewing the potential association between
the patient's symptoms and exposures and following up with
lung function studies. Changes in pre- and post-exposure PFTs,
decreasing methacholine sensitivity with removal from exposure,
and peak flow monitoring are all objective methods of following
up on a patient with suspected occupational asthma. Peak flow
monitoring is the least expensive and most sensitive method.
Detailed
instructions for conducting and evaluating peak flow measurements
used to determine the etiologic allergen in work related asthma
are available from us on request (1-800-446-7805).
At the
minimum, primary treatment is to reduce exposure. Ideally
the patient is able to eliminate the exposure. Given the potential
economic consequences of this removal, some patients elect
to continue working. Steroid and/or cromolyn inhalants to
prevent asthma attacks are typically used in such situations.
How
much occupational asthma occurs among farmers in Michigan
is not known. A study of farmers in Scotland found a 15% prevalence
of occupational asthma or rhinitis. We are interested in how
often occupational asthma in farmers is diagnosed in Michigan
and would appreciate it if you would write Ken Rosemnan, M.D.,
B-338 Clinical Center, Michigan State University, East Lansing,
MI 48824 or call 1-800-446-7805 if you have patients with
this diagnosis.
- Schwartz
DA, Landas SK, Lassise DL, Burmneister FF, Hunninghake GW
and Merchant JA. Airway Injury in Swine Confinement Workers.
Annals of Internal Medicine 1992; 116:630-635.
Author
Abstract:
Objective:
To determine whether work-related respiratory symptoms are
indicative of underlying lung disease among swine confinement
workers and, if so, to identify whether respiratory changes
were more indicative of airway or of interstitial lung injury.
Design:
Nested case-control study within a population-based longitudinal
study. Setting: University hospital.
Participants:
Study participants were randomly selected from a group of
207 swine confinement workers followed longitudinally. Of
these, 43 workers with respiratory symptoms were identified,
and 31 were randomly selected for inclusion in this study.
Three control groups (swine confinement workers, neighbor
farmers, and blue collar workers) without work-related respiratory
symptoms were frequency-matched by age, sex, and smoking
status to the symptomatic swine confinement workers.
Measurements:
Spirometry and lung volumes, diffusing capacity of carbon
monoxide, chest radiograph, methacholine airway challenge,
and bronchoalveolar lavage were done. An endobronchial biopsy
was done in the last 27 participants evaluated.
Results:
Although spirometric measures of airflow were similar between
the symptomatic swine confinement workers and the three
control groups, swine confinement cases were found to have
significant elevations in residual volume (126.5 ñ 28.2
L) when compared to swine confinement controls (115.4 ñ
38.4 L; P ó 0.05), neighborhood farmer controls (101.1 ñ
29.4 L; P ó 0.005), and blue collar controls (106.4 ñ 30.4
L; P ó 0.05). Swine confinement cases also had an enhanced
airway response t inhaled methacholine and had thickening
of the epithelial basement membrane of the lobar bronchi.
No parenchymal injury was observed in the swine confinement
cases.
Conclusions:
Our findings suggest that swine confinement workers who
have work-related respiratory symptoms are at risk for airway,
but not parenchymal, lung injury, and that spirometry may
not accurately reflect the extent of airway injury.
- Ylonen
J, Mantyjarvi R, Taivainen A, and Virtanen T. IgG and
IgE Antibody Responses to Cow Dander and Urine in Farmers
With Cow-Induced Asthma. Clinical and Experimental Allergy
1992; 22:83-90.
Author
Abstract. Cow-asthmatic farmers' and negative control
subjects' IgG and IgE antibody responses to bovine epithelial
antigen (BEA) and urinary antigen (BUA) were studied by enzyme-linked
immunosorbent assay (ELISA) and Western blotting. The anti-BEA
IgE responses of 10 highly reactive sera were also studied
by crossed radio immunoelectrophoresis (CRIE). The relative
amount of allergens common to both BEA and BUA was measured
by IgE ELISA inhibition and found to be 3%. In immunoblotting
the IgG reactivity of the asthmatic farmers to BEA and BUA
declined along their anti-BEA IgE ELISA titres. Control subjects
had IgG antibodies mainly to high molecular weight components
(50-70 kD) but lacked detectable IgE responses. The IgE reactivity
of the asthmatic farmers was directed to only a few components.
A total of two main allergens were found in cow dander (20
and 22kD) and one in cow urine (2OkD). The 20 kD component
was shown to be the most important allergen in cow antigen
extracts. In CRIE, seven reactive arcs were detected. Arc
1, 2 and 5 were detected by all 10 sera and arc 3 by six and
arc 7 by seven sera.
We are in the process of preparing a report on agricultural
illness and injuries in Michigan.
We will be holding five regional meetings with farmers, farm
representatives and cooperative extension service agents around
the state to discuss the report. We will be developing workplans
from these meetings to reduce the occurrence and morbidity of
agricultural illness and injuries. The meetings will be held
around Saginaw, Kalamazoo, Ingham, Traverse City and Marquette.
If you are interested in attending, please write or call us
at 1-800-446-7805.
- Chaii-Yeung
M, Enarson DA and Kennedy SM. Impact of Grain Dust on
Respiratory Health. American Review of Respiratory Disease
1992; 145:476-487.
- A
good review of the health effects of grain dust from the
acute (asthma, grain fever, harvester's lung disease) to
the chronic (COPD).
- Chan-Yeung
M and Lam S. State of Art: Occupational Asthma. American
Review of Respiratory Disease 1986; 133:686-703.
- Still
the best review of occupational asthma.
Disclaimer
and Reproduction Information: Information in NASD does not
represent NIOSH policy. Information included in NASD appears
by permission of the author and/or copyright holder. More
NASD Review: 04/2002
This
document is Physician's Newsletter, Vol. 2, No. 2, a series
of the Center for Michigan Agricultural Safety and Health,
Michigan State University, East Lansing, Michigan. This newsletter
was made possible in part by a grant from the National Institute
for Occupational Safety and Health, which provided funding
for the Michigan Agricultural Health Promotion System Project.
Publication date: Winter 1993.
Dr.
Kenneth D. Rosenman, M.D., Editor, Howard J. Doss, Agricultural
Safety Specialist, Department of Medicine and Department of
Agricultural Engineering respectively, Michigan State University,
East Lansing, Michigan 48824-1323. Funded by Cooperative Agreement
UO5/CC-4506052-02 and 03. This information is for educational
purposes only.
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