Increased prevalence of Dirofilaria immitis antigen in canine samples after heat treatment.
Canine serum samples may contain factors that prevent detection of antigen of Dirofilaria immitis on commercial assays, precluding accurate diagnosis. To determine the degree to which the presence of blocking antibodies or other inhibitors of antigen detection may interfere with our ability to detect circulating antigen in canine samples, archived plasma and serum samples (n=165) collected from dogs in animal shelters were tested for D. immitis antigen before and after heat treatment. Negative samples were also evaluated for their ability to block detection of D. immitis antigen in a sample from a positive dog. All 165 samples were negative prior to heating, but 11/154 (7.1%) became positive after heat treatment, a conversion that was documented and quantified on spectrophotometric plate assays, and 7/165 (4.2%) samples decreased detection of antigen when mixed with a known positive sample, suggesting some blocking ability was present. An additional 103 plasma and serum samples that tested positive prior to heating also were evaluated; the optical density of 14/101 (13.9%) increased by ≥50%, and one sample by as much as 15-fold, after heat treatment. Our results suggest that canine serum and plasma samples from dogs in the southeastern United States can contain inhibitors of D. immitis antigen detection, and that prevalence estimates of heartworm infection based on these assays would benefit from heat treatment of samples prior to testing.
Department of Pathobiology, Center for Veterinary Health Sciences, Oklahoma State University, Stillwater, OK, United States.
Luisa
L
Velasquez
Department of Pathobiology, College of Veterinary Medicine, Auburn University, Auburn, AL, United States.
Byron L
BL
Blagburn
Department of Pathobiology, Center for Veterinary Health Sciences, Oklahoma State University, Stillwater, OK, United States.
Rebecca
R
Duncan-Decoq
Department of Pathobiology, Center for Veterinary Health Sciences, Oklahoma State University, Stillwater, OK, United States.
Eileen M
EM
Johnson
Department of Pathobiology, Center for Veterinary Health Sciences, Oklahoma State University, Stillwater, OK, United States.
Kelly E
KE
Allen
Department of Pathobiology, Center for Veterinary Health Sciences, Oklahoma State University, Stillwater, OK, United States.
James
J
Meinkoth
Department of Pathobiology, Center for Veterinary Health Sciences, Oklahoma State University, Stillwater, OK, United States.
Jeff
J
Gruntmeir
Department of Pathobiology, Center for Veterinary Health Sciences, Oklahoma State University, Stillwater, OK, United States. Electronic address: susan.little@okstate.edu.
Susan E
SE
Little
D000818:Animals; D000947:Antigens, Helminth / Q000097:blood*; D003955:Diagnostic Tests, Routine / Q000592:standards / Q000662:veterinary*; D004183:Dirofilaria immitis / Q000276:immunology / Q000502:physiology; D004184:Dirofilariasis / Q000097:blood*; D004283:Dog Diseases / Q000097:blood*; D004285:Dogs; D006358:Hot Temperature; D015995:Prevalence
D000947:Antigens, Helminth
Antigen test; Dirofilaria immitis; Dog; Heartworm; Prevalence