Location: Duodenum, jejunum, upper small intestine. Tsuchiya (1932) found the optimum location to be 10 to 30 inches posterior to the stomach in puppies on a carbohydrate diet and 25 to 40 inches from the stomach in puppies on a high protein diet.
Geographic Distribution: North America (United States, Canada), South America (Uruguay).
Prevalence: Catcott (1946) found G. canis in 17.7% of 113 dogs in Ohio. Choquette and Gelinas (1950) found it in 9.0% of 155 dogs in Montreal, Canada. Craige (1948) found it in 8.8% of 160 dogs in California. We have seen it a number of times in dogs in Illinois, but have not attempted a survey.
Morphology: The trophozoite is 12 to 17 u long and 7 to 10 u wide. The median bodies are curved bars of the duodenalis type. The cysts measure 9 to 13 by 7 to 9 u.
Pathogenesis: The pathogenicity of G. canis for the dog has still to be incontrovertibly determined. Catcott (1946) noted diarrhea in one-third of his positive dogs. Craige (1948) found Giardia in 17 of 71 dogs with dysentery, but in 13 of them other organisms which he considered pathogenic were also present. Choquette (1950) found Giardia in several cases of dysentery, but some of these were complicated by other conditions. Tsuchiya (1931) reported that diarrheic stools alternated with formed stools in a number of experimentally infected puppies, but was uncertain whether it was due to an existing pathological condition or to the flagellates. According to Tsuchiya (1932), a carbohydrate diet is more favorable for G. canis than a high protein diet.
Diagnosis: Same as for G. lamblia.
Treatment: Quinacrine has been found effective against G. canis. Craige (1949) gave dogs 50 to 100 mg twice daily for 2 or 3 days, repeating if necessary after 3 to 4 days. Choquette (1950) gave large dogs 0.2 g three times the first day and twice a day for 6 more days; he gave small dogs 0.1 g twice the first day and once a day for 6 more days. Chloroquine has also been found effective in man; 0.1 g is given 3 times a day for 5 days.
Prevention and Control: The standard sanitary measures should be used in preventing the transmission of Giardia.