Impact of Giardia vaccination on asymptomatic Giardia infections in dogs at a research facility

Abstract

Feces were collected from 107 asymptomatic dogs at a research facility in Guelph, Ontario. The prevalence of Giardia infection was 11% (12/107). To assess the effectiveness of Giardia vaccination for treatment of Giardia carriage, 9 additional asymptomatic Giardia antigen-positive dogs were brought into the facility. The Giardia antigen-positive dogs were then randomly allocated to receive either vaccine (n = 10) or a saline placebo (n = 10). Feces were then monitored monthly for 6 mo for Giardia antigen and Giardia cysts. At weeks 4, 8, 12, and 16 following vaccination, there were more Giardia-positive dogs in the vaccinated group (10/10, 9/10, 9/10, 8/10, respectively) compared with the controls (7/10, 7/10, 8/10, 4/10, respectively). At week 20, an equal number of dogs (5/10) were Giardia positive, and at week 24, fewer dogs were positive in the vaccinated group than in the control group (2/10 versus 5/10, respectively). However, there was no significant difference between the 2 groups. Vaccination was, therefore, not an effective treatment for asymptomatic canine Giardia infections in this setting.

Figure 1

Giardia infection status of asymptomatic Giardia-positive dogs^a, administered either vaccine or saline at weeks 0 and 3, and Giardia-negative controls. ^a Giardia positive = Enzyme-linked immunosorbent assay (ELISA) positive and/or zinc sulphate positive.

Figure 2

Giardia infection status of asymptomatic Giardia-positive dogs^a, administered either vaccine or saline at weeks 0 and 3, and Giardia-negative controls. ^a Giardia positive = zinc sulphate flotation positive. Two group 1 dogs and 3 group 2 dogs were enzyme-linked immunosorbent assay (ELISA) positive but zinc sulphate flotation negative at day 0.