Abstract

Aspergillosis is well-documented as a cause of morbidity and mortality in captive avian populations worldwide in addition to causing allergy and mycotic disease in humans.¹ When curatorial staff are confronted with cases of aspergillosis, a frequent concern is that there is some source of increased contamination of the exhibit air with Aspergillus species. Our studies of avian exhibits in the United States, Canada, and England over the last 7 yr suggest that this is not usually the case, but that the variation in air handler design in different facilities can be broadly correlated with differing fungal spore loads in the air that could potentially put an antigenic burden on birds and humans in these exhibits. Anecdotal descriptions of aspergillosis cases associated with sudden changes in environmental management exist, but most cases of aspergillosis in zoo exhibits cannot be clearly related to such events.

Air-handling systems for zoo exhibits are typically designed by industrial architects familiar with ASHRAE standards,² which provide air-handling guidelines for institutional spaces such as those constructed for office workers, academic buildings, industrial production areas, hospitals, and smaller medical clinics. When confronted with the unusual requirements of cool-temperature, temperate, or tropical zoo exhibits, the architects try to design systems adequate to the task of assuring reasonable air quality standards for carbon dioxide, humidity, temperature and microorganisms in the air. The lack of national or international standards specifically concerned with the design of zoo exhibit air handlers results in a variety of approaches to providing adequate air quality, including reasonable fungal spore loads. Unfortunately, there are no set standards for acceptable spore loads in indoor air. The standard practice for air sampling compares the spore loads in indoor air with the spore loads in outdoor air, with the suggestion that a larger spore load found in indoor air indicates amplification of fungal populations in indoor spaces due to the active growth of those fungi on interior substrates.

Many zoo workers employ drop-plates for the analysis of fungal populations in indoor air. This method consists of placing open Petri dishes containing an agarized fungal growth medium into exhibit spaces for a period of time, then recovering the dishes and incubating them for another period of time before analyzing the fungi that have fallen out of the air onto the medium, grown, and sporulated so that they can be identified. This method specifically selects against small-spored species such as Aspergillus, the air-borne fungus of chief concern to avian curators. In addition, the information provided is strictly qualitative, and quantitative data are needed to determine whether there is a problem with fungal amplification in the exhibit.

The most widely-accepted tool for providing qualitative and quantitative information about fungal spore loads and identifying fungal populations in indoor air is the Andersen N-6 single-stage viable air sampler. The N-6 allows collection of data in the form of colony-forming- units per cubic meter of air (CFU/m³) as well as the cytologic examination of the colonies in order to key out the fungi collected to genus and species, where desired.

Studies of cool-temperature alcid exhibits over a 3-yr period suggested that the most commonly encountered HEPA-filtered exhibits being designed today reduce fungal spore loads to approximately 100 CFU/m³ of air or less.³ Such a spore load is less than that found in a typical residential dwelling or in outdoor air, so should not pose a significant health risk to the birds on exhibit.

On the other hand, studies of temperate and tropical avian exhibits have revealed a variety of air-handling systems, along with significantly different spore loads.

In conclusion, examination of these different facilities has suggested that HEPA filtration of air for alcid and penguin facilities reduces spore loads sufficiently that bird and keeper health should not be challenged significantly. This type of filtration system is impractical for temperate and tropical exhibits because of the higher spore loads in the exhibit air from the increased biologic material present. On the other hand, preliminary findings from temperate and tropical aviary exhibits show that bag-filtration of exhibit air can reduce spore loads dramatically, and should be considered during initial exhibit design or when refitting the air handling system of an older exhibit. Some of the spore loads recorded in different exhibits are shown in the Table 1.

Table 1. Spore loads recorded in different exhibits.

a. High-efficiency particulate air filters.
b. Non-avian animal species.
NA=not available.

References

1.  Dykstra MJ, M Loomis, K Reininger, D Zombeck, T Faucette. 1997. A comparison of sampling methods for airborne fungal spores during an outbreak of aspergillosis in the forest aviary of the North Carolina Zoological Park. J. Zoo Wildl. Med. 28:454-463.

2.  Anon. 1989. ASHRAE Standard: Ventilation for acceptable indoor air quality. ASHRAE 62-1989. American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. 1791 Tullie Circle, NE, Atlanta GA 30329 USA.

3.  Faucette TG, M Loomis, K Reininger, D Zombeck, H Stout, C Porter, MJ Dykstra. 1999. A three-year study of viable airborne fungi in the North Carolina Zoological Park R.J.R. Nabisco Rocky Coast alcid exhibit. J. Zoo Wildl. Med. 30:44-53.