Isospora Species in the Dog

Abstract

In a survey of 139 dogs from Illinois, Isospora bigemina was found in 1%, I. rivolta in 18%, I. canis in 16%, and free sporocysts considered to be of I. rivolta in 3%. The sporulated oocysts of I. bigemina measured 10 to 14 by 10 to 12 /L, those of I. rivolta were 20 to 27 by 15 to 24 ,u, those of I. canis were 35 to 42 by 27 to 33 ,u, and the free sporocysts were 15 to 17 by 10 to 11 u. Abnormal, Caryospora-like oocysts of I. rivolta were found in one dog, and of I. canis in another. Accounts of the sporulated oocysts of the species of Isospora in dogs are based on the papers by Wenyon (1923, 1926). However, he thought that dogs and cats had the same species of Isospora. The only species that he actually described from the dog was I. rivolta; he described I. felis and I. bigemina from the cat and believed that they occurred in both animals. Later workers (e.g., Becker, 1934; Lee, 1934; Gassner, 1940; Catcott, 1946; Choquette and Gelinas, 1950; Ehrenford, 1953; Levine, 1961) accepted these three species of Isospora as occurring in dogs. Recently, however, Nemeseri (1959, 1960) showed that the form in the dog previously thought to be I. felis was actually a different species, which he named I. canis. Detailed descriptions of the sporulated oocysts of the species of Isospora in dogs are lacking. The present study was undertaken in order to provide such descriptions and to learn something of the prevalence of each coccidian species in this host. MATERIALS AND METHODS Fresh fecal samples were taken from 139 dogs from Illinois. One hundred were patients submitted to the University of Illinois Small Animal Clinic for treatment or observation (but not for coccidiosis); 15 were stray dogs purchased by the College of Veterinary Medicine for teaching; and 24 were purebred beagle puppies purchased for research. Each fecal specimen was examined for coccidia after flotation with Sheather's sugar solution. The developmental stage of each species was determined. Each fecal sample was then mixed with 2.5% potassium bichromate solution and placed in a thin layer in a petri dish for 1 week at room temperature to permit the coccidian oocysts to sporulate. It was then stored in the refrigerator. The oocysts were again concentrated by flotation Received for publication 27 February 1965. with Sheather's sugar solution and examined with a Leitz Ortholux microscope equipped with apochromatic objectives.