title: Experimentally induced clinical Cystoisospora canis coccidiosis in dogs with prior natural patent Cystoisospora ohioensis-like or C. canis infections.
abstract: Diarrhea caused by intestinal coccidia (Cystoisospora species) is a common problem in pet dogs and in dogs in animal shelters. Cystoisospora canis has the largest oocysts of the 4 named species of coccidia infecting dogs. The present study examined an isolate of C. canis obtained from a dog from São Paulo, SP, Brazil. Oocysts sporulated within 2 days at room temperature, and 20 sporulated oocysts were measured at 37.6 by 28.6 μm (range 35-42 by 26-31 μm). Most sporulated oocysts contained 2 sporocysts, each with 4 sporozoites, although a few (<1%) were Caryospora-like and contained 1 sporocyst with 8 sporozoites. Two experiments using a total of 11 female 6-wk-old beagles were conducted to determine the pathogenicity of oral infection with 5 × 10(4) sporulated oocysts of this isolate of C. canis. Five of the 11 dogs had natural infections with Cystoisospora ohioensis-like (n = 4) or C. canis (n = 1) species prior to the predicted patent period of 9-10 days. Ten of the dogs developed diarrhea with occasional blood, and 3 dogs were affected to the extent that clinical treatment for coccidiosis using sulfadimethoxine was recommended. Dog CRU had a natural C. canis infection and did not develop clinical disease after oral infection with C. canis oocysts. This dog had a prepatent period of 9 days and a patent period of 3 days, corresponding to experimental infection with the new isolate of C. canis. It excreted fewer C. canis oocysts than did the other dogs. The 4 dogs with natural C. ohioensis-like infection all developed clinical disease, and 1 required treatment. The prepatent period was 9-10 days, and the patent period was 10-11 days in these dogs. All 6 dogs not naturally infected with Cystoisospora developed clinical disease, and 2 required treatment. The prepatent period was 9-10 days, and the patent period was 8-12 days. The present study confirms that C. canis is a primary pathogen for young dogs. It demonstrates that prior infection with C. canis but not C. ohioensis-like coccidia confers some resistance to clinical disases and a decrease in oocyst production in dogs challenged with C. canis.
authors.affiliation: Center for Molecular Medicine and Infectious Diseases, Department of Biomedical Sciences and Pathobiology, Virginia-Maryland Regional College of Veterinary Medicine, Virginia Tech, 1410 Prices Fork Road, Blacksburg, Virginia 24061-0342;
authors.forename: Alice E
authors.initials: AE
authors.lastname: Houk
authors.forename: Thomas
authors.initials: T
authors.lastname: O'Connor
authors.forename: Hilda F J
authors.initials: HF
authors.lastname: Pena
authors.forename: Solange Maria
authors.initials: SM
authors.lastname: Gennari
authors.forename: Anne M
authors.initials: AM
authors.lastname: Zajac
authors.forename: David S
authors.initials: DS
authors.lastname: Lindsay
mesh_terms: D000818:Animals; D003048:Coccidiosis / Q000469:parasitology / Q000662:veterinary*; D003967:Diarrhea / Q000469:parasitology / Q000662:veterinary*; D004283:Dog Diseases / Q000469:parasitology*; D004285:Dogs; D005243:Feces / Q000469:parasitology; D005260:Female; D033661:Oocysts; D021745:Sarcocystidae / Q000472:pathogenicity*