Preventing Asthma in Animal Handlers
DHHS (NIOSH) Publication Number 97-116
NIOSH recommends the following measures to reduce exposures to animal allergens in the workplace and prevent animal-induced asthma and allergies:
- Modify ventilation and filtration systems:
- Increase the ventilation rate and humidity in the animal-housing areas.
- Ventilate animal-housing and -handling areas separately from the rest of the facility.
- Direct airflow away from workers and toward the backs of the animal cages.
- Install ventilated animal cage racks or filter-top animal cages.
- Perform animal manipulations within ventilated hoods or safety cabinets when possible.
- Decrease animal density (number of animals per cubic meter of room volume).
- Avoid wearing street clothes while working with animals. Leave work clothes at the workplace to avoid potential exposure problems for family members.
- Keep cages and animal areas clean. Take particular care to control exposures during cleaning.
- Use absorbent pads for bedding. If these are unavailable, use corncob bedding instead of sawdust bedding.
- Use an animal species or sex that is known to be less allergenic than others.
- Reduce skin contact with animal products such as dander, serum, and urine by using gloves, lab coats, and approved particulate respirators with faceshields.
- Provide training to educate workers about animal allergies and steps for risk reduction.
- Provide health monitoring and appropriate counseling and medical followup for workers who have become sensitized or have developed allergy symptoms.
These recommendations are discussed briefly in the following subsections.
Exposures to airborne allergens are affected by patterns of air flow, air filtration, bedding type, and humidity [Newman-Taylor and Gordon 1993]. Manipulating such environmental factors has successfully reduced or eliminated the risk of animal-induced allergies [Ohman 1978]. For example, patterns of room ventilation can be manipulated to reduce workplace exposures to animal allergens. Recirculated airflow should be avoided unless it is well filtered to remove animal dander and odors [Lincoln et al. 1974; Ohman 1978]. Increasing the ventilation rate and humidity decreases the amount of rat urine protein in laboratory air [Newman-Taylor and Gordon 1993; Hunskaar and Fosse 1993]. Allergen exposures are also reduced by performing animal manipulations within ventilated hoods in safety cabinets, by directing airflow away from the worker and toward the backs of the cages, and by using ventilated animal cage racks or filter-top cages [Lincoln et al. 1974].
To prevent the dispersion of allergens, street clothes should not be worn while working with animals. Potential problems for family members can be minimized by storing and laundering work clothes at the workplace [Ohman 1978; Lincoln et al. 1974].
Animal Maintenance Factors
The following animal maintenance factors influence the worker’s airborne exposures to allergens:
- Animal density (the number of animals per cubic meter of room volume)
- Activity (sweeping and cleaning of cages, which can result in very high exposures)
- Cage design
- Bedding type [Eggleston and Wood 1992; Newman-Taylor and Gordon 1993; Bardana 1992]
The elimination of sawdust bedding and the use of absorbent pads as bedding material have been shown to reduce concentrations of allergens in the air [Gordon et al. 1992]. If absorbent pads are unavailable, corncob bedding is preferable to sawdust bedding [Sakaguchi et al. 1990; Edwards et al. 1983]. Vacuum cleaners or ventilation benches should always be used when cleaning cages to avoid airborne exposure.
Less Allergenic Animals
Some animals appear to produce allergic reactions in workers more frequently than others. For example, male rats are more allergenic than female rats, and rats are more allergenic than rabbits. Using a less allergenic species or sex can help reduce risks [Hunskaar and Fosse 1993; Newman-Taylor and Gordon 1993; Bardana 1992].
Avoiding skin contact with animal products such as animal dander, serum, and urine has no proven benefit, but it may decrease the risk of sensitization. Gloves, lab coats, and approved particulate respirators with faceshields can all decrease skin exposure [Lincoln et al. 1974; Newman-Taylor and Gordon 1993; Bardana 1992].
Workers at risk of developing animal-related asthma or allergies should be offered training that reviews the type and timing of typical symptoms, the importance of early detection and intervention, and steps that workers and managers can take to reduce the risk of sensitization.
Medical Monitoring and Surveillance
Ongoing medical monitoring for symptoms of asthma may help protect the health of animal handlers. Medical screening with standardized questionnaires can identify workers with early symptoms of asthma [Venables et al. 1993]. Workers who report symptoms related to their jobs (sneezing, runny nose, chest tightness, wheezing, and episodes of cough or shortness of breath) should be referred for more extensive evaluation and early intervention, as appropriate. Current knowledge suggests that early termination of animal exposure for workers with asthma symptoms can reduce their risk of developing long-term symptoms. Spirometry and blood antibody testing have also been used in medical monitoring for asthma, but their exact roles are not yet defined. NIOSH has developed a surveillance case definition for occupational asthma (see Appendix). This definition may help guide medical evaluations.
Some workers with animal-related asthma and allergies may improve or completely resolve their symptoms, whereas others may have persistent symptoms. Several factors affect this outcome. Individuals are more likely to do poorly if they
- have their symptoms for a long period before the condition is recognized,
- have severe disease at diagnosis (as indicated by lung function and airway responsiveness tests), or
- have a long period of exposure before developing symptoms [Venables and Chan-Yeung 1997; Paggiaro et al. 1994].
Thus delays in recognizing the condition or stopping the exposure may result in more severe and persistent lung disease and disability [Brooks 1992].
Some employers have used preplacement examinations to identify workers at high risk for developing animal-related asthma and allergies. However, no evidence indicates that the use of a particular criterion will predict which workers will become allergic or develop animal-related asthma and allergies [Aoyama et al. 1992; Kibby et al. 1989]. Workers with a history of allergic disease are at increased risk, but this criterion is not useful for screening. For example, in one group of workers using the questionnaire as a screening tool, only 3 of 12 workers with a history of allergy developed animal-induced asthma. The screening criterion would have excluded nine workers who did not develop the problem [Kibby et al. 1989].
The presence of antibodies (IgE) in a worker’s serum also fails to correlate with the presence of symptoms or the development of disease. Pre-employment screening for allergy risk factors is therefore not warranted [Aoyama et al. 1992].
Appropriate Counseling for Affected Workers
Occupational asthma symptoms must be recognized early and affected workers must be removed from exposure to allergens, since prolonged exposure can lead to irreversible disease. However, removal from exposure does not always lead to complete recovery [Venables and Chan-Yeung 1997]. Only about 50% of those with occupational asthma from various causes recover completely after exposures are ended [Brooks 1992].
Some workers may be unwilling to leave their jobs in spite of health problems. A worker who has severe or life-threatening allergic reactions should be strongly advised to change jobs, since no prevention strategy is completely effective [Newman-Taylor and Gordon 1993].
Workers with symptoms who wish to continue working with animals should be advised of the risks. Careful medical monitoring is necessary to assure adequate control of the illness. Strict use of approved particulate respirators (as part of a formal respiratory protection program), prudent work practices, and careful housekeeping may allow a person with mild asthma to continue working [Brooks 1992]. However, the routine use of respirators is not recommended as an allergen control technique [Lincoln et al. 1974]. If extensive medical treatment (for example, the use of steroid tablets) is required, or if repeated asthma attacks occur after all steps have been taken to reduce exposure, the affected worker should leave the offending job.
Surveillance and Disease Reporting
NIOSH encourages the surveillance of occupational asthma by State health departments. To encourage uniform reporting, NIOSH recommends reporting guidelines and an asthma surveillance case definition (see Appendix). These guidelines and the case definition are recommended for public health surveillance of work-related asthma reported by physicians and other health care providers. As of 1998, three State health departments (California, Massachusetts, and Michigan) are funded by NIOSH for asthma surveillance activities.