people associate farming with fresh air and a healthy, robust
environment in which to work and live. However, much of the
air that farmers breathe can be contaminated with particulate
matter or toxic gases that can be lethal. Continued exposure
to some of these contaminants can lead to a Farmers Lung condition.
Farmer's Lung is an allergy related disease usually caused by
breathing in the dust from moldy hay. However, dust from any
moldy crop - straw, corn, silage, grain, or even tobacco - can
also cause Farmer's Lung. Other potential sources of dust particles
include, grain handling, feed handling and processing, and livestock
The disease causes shortness of breath and a feeling of general
illness, either in a sudden attack or as a slow, progressive
disease. When people with Farmer's Lung can avoid breathing
in dust from moldy crops or feed, they seldom have further problems.
On the other hand, lengthy exposure can cause permanent lung
damage, physical disability, or even death.
Usually, people with Farmer's Lung do not associate their health
problem with exposure to moldy hay. Instead, they go to their
doctor complaining of breathing problems. It is important to
recognize the danger of working with moldy crops and to be able
to recognize the signs and symptoms of Farmer's Lung. This enables
people with symptoms to get medical help before it becomes a
Mold spores which are produced by micro organisms which grow
in baled hay, stored grain, or silage with a high moisture content
(30 percent) are main causes of Farmer's Lung. They become active
when temperatures reach 70 degrees Fahrenheit in poorly ventilated
Farmers most often suffer from this disease in winter and early
spring when stored hay or grain is used to feed livestock and
the molds have had time to develop in closed storage areas.
The disease is most common in regions with wet weather at harvest
time. Farmer's Lung is also more common on dairy farms, especially
those not equipped with automated equipment for handling hay
Heavy concentrations of mold spores appear as a dry, white or
gray powder in grain or forage. When the feed is moved, billions
of these microscopic sized particles become airborne and attach
themselves to dust.
These particles pass through the body's natural filtering mechanisms
(nose, hair, and throat mucous) and accumulate in the lungs
where they can cause an allergic type of pneumonia. Repeated
attacks can lead to scarring of lung tissue, which impairs its
function. Such tissue damage is permanent.
Farmers Lung symptoms usually reoccur, and a person can become
sensitized to the mold. This means it usually takes less exposure
for a severe reaction with each succeeding incident.
The symptoms of Farmers Lung are often striking, yet the disease
goes unrecognized by many victims and misdiagnosed by physicians
not familiar with farm health hazards. Victims and doctors alike
often confuse Farmers Lung with asthma attacks, pneumonia, or
flu because the symptoms are similar.
Farmer's Lung is a risk for adults who breathe dust from moldy
hay or other moldy crops. For reasons not completely understood,
children rarely develop Farmer's Lung.
The degree of risk depends on the amount of dust that has collected
in the person's lungs. There is little danger working with loose
hay in an open field. However, the risk increases when farmers
or farm workers are breaking open bales of moldy hay or straw
inside closed barns or cow sheds. A person can inhale an extremely
large amount of dust within a very short time while working
Other people exposed to dust from moldy hay; straw or grain
include grain handlers, stable employees, poultry workers, and
pet shop workers.
The signs and symptoms of Farmer's Lung vary tremendously. At
one extreme, there are the symptoms associated with a sudden
attack; at the other extreme, there are the symptoms associated
with a slow progressive illness.
The allergic response of the afflicted person depends on the
sensitivity of the individual and the amount of moldy dust entering
the lungs. There are three different types of allergic responses:
acute or intense attack, sub-acute or low-level response, and
chronic or long-term response.
Acute Farmer's Lung is easy to notice and occurs in about one
in three cases. It starts as an intense attack about 4 to 8
hours after the person breathes in a large amount of dust from
moldy crops. These are some of the signs and symptoms:
dry irritating cough
sudden general feeling of sickness
rapid heart rate
If the person
avoids further exposure to moldy dust, the signs and symptoms
usually decrease after l2 hours, but they can last up to two
weeks. Serious attacks can last as long as 12 weeks. The symptoms
are sometimes confused with pneumonia.
Sub-acute Farmer's Lung is more common than acute Farmer's Lung
but it is less intense and more difficult to notice. It develops
slowly, responding to continual exposure to small amounts of
moldy dust. The signs and symptoms include:
mild fever and occasional chills
general feeling of sickness
and pains in the muscles and joints
loss of appetite and loss of weight.
are sensitive to dust from moldy crops continue to exhibit these
signs and symptoms as long as they are exposed to the dust.
This condition sometimes resembles a "chest cold" that lingers
throughout the winter. Some people lose weight over several
Chronic Farmer's Lung develops after several acute attacks over
a period of years. It afflicts people who have been continually
exposed to large amounts of moldy dust. Sometimes, the illness
lasts several months and is marked by increasing shortness of
breath, an occasional mild fever, and often, a significant loss
in weight and a general lack of energy. The symptoms are accompanied
by permanent lung damage and gradually worsen as exposure to
moldy dust continues.
There is no single, simple test to distinguish between Farmer's
Lung and other types of lung diseases. The most important evidence
for Farmer's Lung is the history of exposure to dust from moldy
hay or other moldy crops and the development of signs and symptoms
4 to 8 hours later. This is why it is so important for a doctor
to know if a patient with shortness of breath has been exposed
to moldy crops.
For people suffering from acute attacks of Farmer's Lung, the
first step in treatment is to avoid further contact with moldy
dust. For serious cases, bed rest is recommended and oxygen
therapy may be needed to relieve shortness of breath.
Certain medications provide relief from an allergic response
during acute attacks and make breathing easier. The long-term
use of these drugs is not advisable since they can hide the
symptoms of Farmer's Lung without preventing lung damage from
re-exposure to moldy dust.
No cure exists for people who become hypersensitive to moldy
dust. Once people become hypersensitive, they remain hypersensitive
for years, perhaps for life.
There is no simple method to prevent conditions that lead to
Farmer's Lung. Steps must be taken to avoid crop spoilage and
production of bacterial or mold spores that cause the allergic
reaction. Workers must also take precautions to avoid breathing
in spores from moldy crops.
The following measures are recommended to prevent the growth
of mold spores or limit the damage they can cause:
with large amounts of dusty material should be properly
ventilation rates to remove particles without high heat
cost. In heated buildings air-to-air heat exchangers may
increase the minimum winter ventilation rate without higher
air circulation. Make sure that the distribution inlets
are managed and operated properly to avoid dead spots.
to mechanical or automated feeding or feed handling systems
can reduce the amount of airborne mold spores or can reduce
hay, grain, or other crops can be dried at harvest. If possible
wet hay should be ensiled. This is the key to stopping mold
mold inhibitors, baling hay, ensiling crops, and harvesting
and storing grains at the recommended moisture content,
limits mold spore growth. It also maximizes the quality
of your feed stuffs.
the facilities clean. Sweep or power wash occasionally to
remove the buildup of dry material on the floor and other
cleaning of barns or stables, dust from moldy crops should
be wetted down before being swept to prevent it from becoming
use a plastic sheet to cap open silos, don't use plant materials.
Hold the edges of the sheet down with heavy weights.
down the top of a silo before uncapping the ensiled material.
This prevents moldy dust from becoming air borne. This should
be done even if the silage was covered with a plastic sheet,
because the top layers still tend to mold.
feed additives. Adding tallow or soybean oil to swine finishing
feed to reduce its dustiness makes good sense.
the work outdoors whenever possible. While this is not usually
practical in the case of feeding operations, be sure to
open bales that you know are moldy outdoors.
dusty work in confined areas. When constructing new farm
buildings or modifying older structures, keep facilities
as open as possible.
you have to work with moldy material, try to keep your distance.
If you have to break open a moldy bale, do so with a fork,
instead of bending over and using your hands.
protection is the last line of defense against Farmers Lung.
The proper type respirator can protect those who have not contacted
the diseases or help prevent the diseases from getting worse.
Approved, properly fitted dust respirators (e.g., masks with
HEPA, High-Efficiency Particulate Air filters) may protect the
lungs from spores of molds or bacteria.
This equipment, however, is seldom viewed as an easy solution.
Professional advice is required for selection of the proper
mask and filter. Individuals must also receive training on the
proper use of the equipment and procedures for maintenance and
To be effective, the respirator should be worn on every occasion
that farm dust is encountered. Make sure the mask is comfortable
and easy to maintain but does not restrict breathing.
The Toxic dust mask, chemical cartridge respirator and powered
air helmet are approved for protection against dust, such as
asbestos and they provide inexpensive protection against mold
spores. More expensive and sophisticated respiratory devices
may be required occasionally.
Commonly available disposable respirators for nuisance dusts
are not effective against the tiny mold spores.
In all cases, however, a key protective measure is to investigate
any procedure that can reduce or completely prevent the growth
of the heat-tolerant bacteria or molds that create the unwanted
The information and
recommendations contained in this publication are believed to
be reliable and representative of contemporary expert opinion
on the subject material. The Farm Safety Association Inc. does
not guarantee absolute accuracy or sufficiency of subject material,
nor can it accept responsibility for health and safety recommendations
that may have been omitted due to particular and exceptional
conditions and circumstances.
Copyright © 2002 Farm Safety Association Inc.
22-340 Woodlawn Road West, Guelph, Ontario (519) 823-5600.
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