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Incidence of Coccidioides infection among dogs residing in a region in which the organism is endemic

Lisa F. ShubitzDepartment of Veterinary Science and Microbiology, University of Arizona, Tucson, AZ 85721.

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Christine D. ButkiewiczDepartment of Veterinary Science and Microbiology, University of Arizona, Tucson, AZ 85721.

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Sharon M. DialDepartment of Veterinary Science and Microbiology, University of Arizona, Tucson, AZ 85721.

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Christina P. LindanDepartment of Epidemiology and Biostatistics, University of California, San Francisco, CA 94105.

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Abstract

Objective—To determine the incidence of Coccidioides infection among dogs residing in a region in which the organism is endemic (Pima and Maricopa counties, Arizona) and estimate the rate of clinical illness.

Design—Community-based longitudinal and crosssectional studies.

Animals—124 healthy 4- to 6-month-old seronegative puppies (longitudinal study) and 381 4- to 18-monthold dogs with unknown serostatus (cross-sectional study).

Procedure—Dogs in the longitudinal study were tested at 6-month intervals for at least 1 year for anticoccidioidal antibodies. Dogs that became ill were evaluated for coccidioidomycosis. Dogs in the cross-sectional study were tested for anticoccidioidal antibodies once, and clinical abnormalities were recorded.

Results—28 of the 104 (27%) dogs that completed the longitudinal study developed anticoccidioidal antibodies. Thirty-two of the 381 (8%) dogs in the crosssectional study had anticoccidioidal antibodies. Five seropositive dogs in the longitudinal study and 13 seropositive dogs in the cross-sectional study had clinical signs of disease. The remaining seropositive dogs were otherwise healthy and were classified as subclinically infected. Survival analysis indicated that the cumulative probability of infection by 2 years of age was 28%, and the cumulative probability of clinical infection by 2 years of age was 6%. Titers for clinically and subclinically infected dogs overlapped.

Conclusions and Clinical Relevance—Results suggested that young dogs living in the study area had a high likelihood of becoming infected with Coccidioides spp, but few developed clinical illness. Serologic testing alone was insufficient for a diagnosis of clinical disease because of the overlap in titers between clinically and subclinically infected dogs. (J Am Vet Med Assoc 2005;226:1846–1850)

Abstract

Objective—To determine the incidence of Coccidioides infection among dogs residing in a region in which the organism is endemic (Pima and Maricopa counties, Arizona) and estimate the rate of clinical illness.

Design—Community-based longitudinal and crosssectional studies.

Animals—124 healthy 4- to 6-month-old seronegative puppies (longitudinal study) and 381 4- to 18-monthold dogs with unknown serostatus (cross-sectional study).

Procedure—Dogs in the longitudinal study were tested at 6-month intervals for at least 1 year for anticoccidioidal antibodies. Dogs that became ill were evaluated for coccidioidomycosis. Dogs in the cross-sectional study were tested for anticoccidioidal antibodies once, and clinical abnormalities were recorded.

Results—28 of the 104 (27%) dogs that completed the longitudinal study developed anticoccidioidal antibodies. Thirty-two of the 381 (8%) dogs in the crosssectional study had anticoccidioidal antibodies. Five seropositive dogs in the longitudinal study and 13 seropositive dogs in the cross-sectional study had clinical signs of disease. The remaining seropositive dogs were otherwise healthy and were classified as subclinically infected. Survival analysis indicated that the cumulative probability of infection by 2 years of age was 28%, and the cumulative probability of clinical infection by 2 years of age was 6%. Titers for clinically and subclinically infected dogs overlapped.

Conclusions and Clinical Relevance—Results suggested that young dogs living in the study area had a high likelihood of becoming infected with Coccidioides spp, but few developed clinical illness. Serologic testing alone was insufficient for a diagnosis of clinical disease because of the overlap in titers between clinically and subclinically infected dogs. (J Am Vet Med Assoc 2005;226:1846–1850)