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Investigation of factors predicting disease among zoo birds exposed to avian mycobacteriosis

Carmel L. Witte MS1, Laura L. Hungerford DVM, MPH, PhD2, Rebecca Papendick DVM, DACVP3, Ilse H. Stalis DVM, DACVP4, and Bruce A. Rideout DVM, PhD, DACVP5
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  • 1 Wildlife Disease Laboratories, Zoological Society of San Diego, PO Box 120551, San Diego, CA 92112.
  • | 2 Department of Epidemiology and Preventive Medicine, School of Medicine, University of Maryland, Baltimore, MD 21201.
  • | 3 Wildlife Disease Laboratories, Zoological Society of San Diego, PO Box 120551, San Diego, CA 92112.
  • | 4 Wildlife Disease Laboratories, Zoological Society of San Diego, PO Box 120551, San Diego, CA 92112.
  • | 5 Wildlife Disease Laboratories, Zoological Society of San Diego, PO Box 120551, San Diego, CA 92112.

Abstract

Objective—To characterize infection patterns and identify factors associated with avian mycobacteriosis among zoo birds that were housed with infected enclosure mates.

Design—Matched case-control study.

Animals—79 birds with avian mycobacteriosis (cases) and 316 nondiseased birds (controls) of similar age and taxonomic group that were present in the bird collection of the Zoological Society of San Diego from 1991 through 2005.

Procedures—Inventory and necropsy records from all eligible, exposed birds (n = 2,413) were examined to determine disease incidence and prevalence in the exposed cohort. Cases were matched in a 1:4 ratio to randomly selected controls of similar age and taxonomic grouping. Risk factors for mycobacteriosis (demographic, temporal, enclosure, and exposure characteristics as well as translocation history) were evaluated with univariate and multivariable conditional logistic regression analyses.

Results—Disease prevalence and incidence were estimated at 3.5% and 8 cases/1,000 bird-years at risk, respectively. In the multivariable model, cases were more likely to have been imported into the collection, exposed to mycobacteriosis at a young age, exposed to the same bird species, and exposed in small enclosures than were controls. Odds for disease increased with an increasing amount of time spent with other disease-positive birds.

Conclusions and Clinical Relevance—The low incidence of mycobacteriosis and the risk factors identified suggested that mycobacteria may not be easily transmitted through direct contact with infected enclosure mates. Identification of risk factors for avian mycobacteriosis will help guide future management of this disease in zoo bird populations.

Abstract

Objective—To characterize infection patterns and identify factors associated with avian mycobacteriosis among zoo birds that were housed with infected enclosure mates.

Design—Matched case-control study.

Animals—79 birds with avian mycobacteriosis (cases) and 316 nondiseased birds (controls) of similar age and taxonomic group that were present in the bird collection of the Zoological Society of San Diego from 1991 through 2005.

Procedures—Inventory and necropsy records from all eligible, exposed birds (n = 2,413) were examined to determine disease incidence and prevalence in the exposed cohort. Cases were matched in a 1:4 ratio to randomly selected controls of similar age and taxonomic grouping. Risk factors for mycobacteriosis (demographic, temporal, enclosure, and exposure characteristics as well as translocation history) were evaluated with univariate and multivariable conditional logistic regression analyses.

Results—Disease prevalence and incidence were estimated at 3.5% and 8 cases/1,000 bird-years at risk, respectively. In the multivariable model, cases were more likely to have been imported into the collection, exposed to mycobacteriosis at a young age, exposed to the same bird species, and exposed in small enclosures than were controls. Odds for disease increased with an increasing amount of time spent with other disease-positive birds.

Conclusions and Clinical Relevance—The low incidence of mycobacteriosis and the risk factors identified suggested that mycobacteria may not be easily transmitted through direct contact with infected enclosure mates. Identification of risk factors for avian mycobacteriosis will help guide future management of this disease in zoo bird populations.

Contributor Notes

Supported by the Bud Heller Foundation and the Zoological Society of San Diego.

The authors thank J. Albright, Y. Cates, A. Gorow, L. Keener, and J. P. Montagne for laboratory and technical assistance and D. Heckard, N. Lamberski, M. Mace, D. Orndorff, D. Rimlinger, M. Sutherland-Smith, and P. Witman for assistance with data on bird health and management.

Address correspondence to Ms. Witte (cwitte@sandiegozoo.org).