Controlling Exposure to Lab Animal Allergies

Allergies: An Overview

The concern of lab animal allergies as an occupational illness has been well-reported in trade organization publications, scientific journal articles, and governmental agency reports. Studies show that 20 to 30 percent of lab animal workers experience some form of allergic response. When this percentage is multiplied by the large numbers of individuals employed in this sector, the scope of this issue becomes clear. For many of the affected population, the health effects are mild and transient and include skin and eye irritation and rhinitis. In a small percentage of this population, the severity of illness can progress to more severe reactions.

Prevention of lab animal allergies and other allergies is a difficult task. In order for a lab animal allergy prevention program to be successful, a broad cross section of safety and health program elements must be established and maintained. Programs must include a combination of engineering controls, administrative controls, and personal protective equipment.

Use of engineering controls such as specially designed vivariums and ventilated caging are at the heart of most programs. Development and use of animal transfer stations have further reduced exposure during animal transfer. These controls will continue to expand in use and effectiveness. However, there is no current equipment that can completely eliminate worker exposure. Administrative controls such as post-offer/pre-hire medical examinations, regular physicals and medical testing are critical to allergy prevention. Incident reporting and prompt medical treatment are also essential elements. Industrial hygiene programs can also enhance allergy prevention, but only if the efforts are properly focused and recommendations are fully implemented. Other required elements include proper worker training, standard operating procedures, facility and equipment maintenance, vivarium and equipment sanitization, and consistent use of personal protective equipment.

Mouse urine protein (Mus m 1, MUP) is a well-known occupational allergen. In order to assess the rack system capture efficiency of this allergen, six in-cage and four room air samples were collected over the course of the study. All MUP samples were 16 hours in duration. These sampling conditions are far more severe than actual worker exposure patterns around properly operating Micro-Vent units.

Airborne levels of ammonia, a contaminant generated during the decomposition of urine, and carbon dioxide generated during mouse respiration were also measured in both occupied caging and in the animal room using colorimetric dositubes. As would be expected, airborne levels of ammonia increased over the study timeline. Carbon dioxide levels remained fairly steady over the entire test period.

More than 3,000 measurements of temperature and humidity levels inside occupied caging were collected during the 12-day test using calibrated data-logging meters. Mean temperature and relative humidity remained well within the ranges published in the “Guide for Care and Use of Laboratory Animals” during the entire test.

Materials and Methods

The micro environmental (in the animal caging) and the macro environmental (in the animal room) conditions were maintained during the entire assessment timeline. One dedicated vivarium room was used for this project. This room was used to house the animals and to conduct all husbandry and animal handling work. The room pressure was positive to the service corridor. The facility was equipped with a properly designed and balanced interstitial blower system and the rack was connected to this system. The exhaust rate in the vivarium room was at the high end of the cage manufacturer suggested range.

During the course of the study, room temperature ranged from 70 degrees Fahrenheit to 72 degrees Fahrenheit; room humidity ranged from 27 percent RH to 53 percent RH. The room was placed on a diurnal cycle of 12 hours light and 12 hours dark. The room was a standard vivarium room in a research suite. The racks were equipped with an automatic watering system.

Room ventilation rates were maintained at 12 to 15 air changes per hour. Room supply air was 100 percent single pass fresh air. The static pressure of this room was maintained positive to service corridors. This room and the research pod are brand new and had never been used to house animals. Baseline airborne testing for Mus m 1 protein confirmed that airborne mouse urine protein levels were below detectable limits.

A total of 448 males and 112 female mice were used. The males were no older than 21 days at shipment. Females were no older than 35 days at shipment. After quarantine in a special area of the facility, the animals were moved to the research suite and allowed to reach the target weight of 25 to 30 grams.

The animals were housed in a 140-cage MicroVent IVC Rack. The rack was operated at manufacturer recommended setting of 60 air changes per hour in each cage and in the positive pressure mode. The details of the rack used and operating parameters were fully documented including verification of cage flows.

All MUP samples were collected using TSI SidePak High Volume Air Sampling Pumps drawing air at approximately two liters per minute through SKC PTFE filters into SKC Sure Seal two-piece, closed-face cassettes. The pumps were programmed to run uninterrupted for 960 minutes. After sampling, the cassettes were placed in frozen storage until analysis.

Ammonia measurements were collected using Gastec ammonia color dosimeter tubes. Carbon dioxide measurements also were collected using Gastec carbon dioxide color dosimeter tubes. Both sets of dosimeter tubes provide acceptable accuracy for sampling durations up to 10 hours and more accurately reflect “average” conditions in the occupied caging compared to colorimetric short-term grab samples.

The dosimeter tubes for both ammonia and carbon dioxide sampling were placed into pre-drilled ports in the tops of six sampling cages. One sample as placed in the room in close proximity to the air supply register. The tubes remained in place for at least seven hours. After sampling the reading on the tube was converted to an average airborne level by dividing the observed concentration by the number of sampling hours.

Temperature and humidity levels were recorded using Omega Engineering OMCP MicroRHTEMP data-logging sensors. The sensor heads were placed into pre-drilled ports in the tops of six cages. The meters remained in place during the entire 12-day study period. The data from the meters was downloaded at the end of the test. Room temperature and humidity were obtained from facility room check data.

Results/Conclusion

At all measurement intervals, capture efficiencies of the 140 cage Micro-Vent IVC system exceeded 99.8 percent. As would be expected, airborne levels of ammonia increased over the study timeline. In-cage mean ammonia levels for males ranged from none detected on Day 1 and 2.33 ppm on Day 12. Mean ammonia levels for females ranged from none detected on Day 1 through 0.64 ppm on Day 12. Carbon dioxide levels remained fairly steady over the entire test period. The maximum average measured level was 2032 ppm (Males – Day 1).

Both ammonia and carbon dioxide levels were well below levels considered harmful to vivarium staff and the population of mice in the rack. The results also showed that both temperature and humidity were well controlled during the test. Ultimately, in-cage temperature and humidity depend heavily on the quality of temperature and humidity control in the vivarium room.

The determination of capture efficiency presented in this report was performed in the most conservative fashion. Field blanks were prepared at the same time as the room and cage samples. These samples were handled in the same way as the test samples with the exception that no air was drawn through them. These blanks are used validate that the test media was not contaminated during manufacturing, the cassette loading process, or subsequent handling. Some test methods and equipment manufacturers use a measurement of exhaust plenum levels of MUP. While this approach may result in higher “reported” capture efficiencies, the results are prone to significant experimental error because sampling is not performed at rates that are isokinetic with the exhaust stream and because deposited particulate can dislodge and become re-entrained in the air stream.

These results clearly demonstrate that the Allentown Inc. MicroVent rack system is highly effective at controlling and capturing airborne mouse allergen. The results also confirm that the system performs equally well in controlling ammonia and carbon dioxide levels and maintaining proper in-cage temperature and humidity levels.

Reprinted with Permission
?2007 Safety Synergy LLC

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Fig. 3

In-cage Sampling Locations

The inlet poets of the PTFE filers were attached to airtight connections in the tops of six IVC sampling cages to collect the mouse urine protein. Colorimetric dosimeter tubes were placed into pre-drilled ports on the tops of six sampling cages to measure ammonia and carbon dioxide.