There are many research disciplines that make use of animals. And if you work with laboratory research animals, you probably are aware that animal allergies are still one of the most common health hazards faced each day. Although this topic has garnered lots of research attention, allergic reactions, which are a result of immunological and biochemical mechanisms, are not totally understood. And so laboratory animal allergy (LAA) remains a serious occupational hazard. Did you know that approximately one-third of laboratory animal workers have an occupational allergy to animal danders?¹ Or that one-third of that group have symptomatic asthma?^1,2 In fact, about three-quarters of workers with preexisting allergic disease (referred to as the atopic risk group) eventually develop a laboratory animal allergy.² Given these statistics and the potential seriousness, especially if LAA should progress to asthma, we thought it was time to provide some reminders for prevention.

Risk factors and symptoms

Laboratory animal allergy begins with exposure to the allergens; these are usually proteins or glycoproteins. Animal allergens are found in the urine, saliva, dander, and fur of most research species, including rats, mice, cats, dogs, horses, and birds, among others. The exposure route is most often airborne, but skin contact can also produce reactions of a different kind. Most workers who develop LAA do so within one to three years of first exposure.¹ Persons with other allergic conditions such as hay fever are at greater risk of developing LAA, as atopic individuals are 11 times more likely to become sensitized to animal allergens than non-atopics.¹ In addition, atopy may reduce the time for developing LAA and increase the severity should an atopic worker become sensitized. One study found that the median time from first exposure to symptoms of LAA was 2.2 years for atopics, compared to 8.2 years for non-atopics.¹ Other risk factors include the duration of exposure and allergen concentration. Airborne allergen concentrations are directly proportional to the number of animals in the area and depend on the rate of production and the rate of removal. This suggests that ventilation is key in limiting exposures. However, at least one study has shown that although ventilation is effective for lowering concentrations when allergen production is low (i.e., small numbers of animals), it might take up to 127 air changes per hour (ACH) to significantly reduce exposures when allergen production is very high, such as during cage cleaning or in densely populated areas.²

Experience shows that exposure concentrations are definitely related to specific tasks as well. In the study results, cage cleaning ranked at the top, followed by handling and then surgery/euthanasia. Research has shown that airborne allergen concentration increased up to five times and small particles (less than 1 micron average diameter) increased three times in areas where cage cleaning was conducted. Sampling methods are available to measure airborne allergen concentrations as well as particle size. This is very useful information to have, and it is important to keep these facts in mind when developing your prevention program.

Laboratory animal allergy usually begins with nasal symptoms such as sneezing and a runny nose; itchy, watery eyes; and/or rashes. A more serious condition that might affect about 10 percent of workers is occupational asthma; its symptoms are coughing, wheezing, and shortness of breath and lead to chronic symptoms that continue even after exposure is removed.

Of all the animal species used in research, rats are perhaps the most common. The major sources of rat-induced allergen appear to be urine and saliva. Research has shown that handling rat litter can introduce a large amount of allergen, particularly smaller particles that can remain airborne for 15 to 35 minutes.² Mice, which also produce a urinary protein, are another major source of allergen for animal lab workers. Because they are also kept as domestic pets, dogs and cats pose a significant risk of sensitization both in the laboratory and outside the work environment. Cat allergens, produced in saliva and sebaceous glands of the skin, are unique in that they appear to be highly electrostatically charged and therefore tend to stick to surfaces that then act as reservoirs holding and transferring allergens even in the absence of cats. One other major species worth mentioning is birds, exposure to which can cause rhinitis and hypersensitivity pneumonitis, a potentially serious pneumonia-like lung condition.

Preventive measures and allergen control

Laboratory animal allergy is an important occupational health hazard and a difficult problem to solve. The first step is to develop a comprehensive prevention control plan for your facility. The National Institute of Occupational Safety and Health publication, Preventing Asthma in Animal Handlers, provides solid recommendations for your control program.³ Another excellent guidance document is the National Institutes of Health’s Laboratory Animal Allergy Prevention Program.⁴ The recommendations in these publications can be grouped into two main categories: engineering controls that involve facility design and specialized equipment; and administrative controls that include employee screening, work protocols, and personal control measures. We strongly encourage the use of the reference materials in developing your program. A discussion of the highlights will hopefully get you motivated and started in the right direction.

Engineering controls
Engineering controls are perhaps the most important and definitely the most expensive part of a good prevention control program. Facility design and ventilation are two major components. Since we know that aeroallergen loading is equal to allergen production (a function of the number of animals and, to a lesser degree, the species) minus the removal (a function of the ventilation controls), we should strive for the best ventilation systems we can. The ideal is probably a single-pass ventilation system where 100 percent of supply is exhausted, but this is very expensive. If recirculation is necessary, use of high-efficiency particulate air (HEPA) filtration is strongly recommended, which is also expensive both to install and maintain. The next best solution is the use of local exhaust ventilation (LEV), biological safety cabinets, specialty hoods, and back-draft and down-draft workstations. These are designed and set up for the specific tasks and are effective controls.

No matter what type or combination of ventilation you use, a final (as well as routine) check of the system’s test and balance is needed to ensure optimum performance and that appropriate pressure gradients exist for maintaining air flow and isolating the controlled areas.

After ventilation, we turn to state-of-the-art equipment for animal research facilities. Included here are the latest replacements for the old-style open-top cage systems, such as filter-top cages, ventilated cage and rack systems, and individual ventilated cages with or without HEPA filtration. In addition, there are now automated systems for cage emptying/changing, cage washing, and waste handling. As with ventilation, the only downside is the cost.

Administrative controls
The things we do administratively and procedurally, including the implementation of policies, are referred to as administrative controls. One of the most important is a pre-placement screening evaluation of employees for risk factors such as symptoms or history of allergy or asthma or specific allergy to animals (pets or laboratory). Pulmonary function measurement, e.g., spirometry, is also encouraged. And regular health surveillance is recommended by both the NIOSH and the NIH.

Additional administrative controls to consider when developing your LAA prevention program are controlling access and isolating the animal handling areas. Only a minimum number of workers should have authorized entrance, and the transport of animals should be well planned. Be sure to segregate the “clean” tasks from the “dirty” ones. Choice of bedding material is also critical. For example, the NIH recommends using hypoallergenic corncob or recycled wood product and wetting the bedding prior to changing or dumping it to minimize allergen concentrations.⁴

Education and training of employees is a large part of preventing laboratory animal allergy. Every worker must clearly understand the risks and possess awareness of allergy symptoms. Knowledge of prescribed work practices and proper use of equipment and personal protective gear such as gowns, gloves, head and foot coverings, and respirators is essential. The importance of good personal hygiene, e.g., hand washing and prompt reporting of the development of any symptoms, cannot be stressed enough.