Letter to the Editor
Controlled exposure to Haemophilus parasuis
In regards to the paper published by Oliveira, Pijoan, and Morrison1 in the Journal of Swine Health and Production, May and June, 2004 issue: was there truly sufficient evidence to support improved protection from the controlled exposure method of immunization? After an analysis of means was performed (Wheeler, 1990),2 the average death losses for nonvaccinated controls of Experiments 1 (4.8%) and 2 (7.7%) were detectably different from, and lower than, the average death loss of Experiment 3 (14.3%; P < .05). This causes me to wonder what the effect of the controlled exposure method would have been had its control death loss been as low as the control death losses for pigs vaccinated with the commercial vaccine and the autogenous vaccine.
-- David Baum Milford, Utah
2. Wheeler DJ. Understanding Industrial Experimentation. 2nd ed. Knoxville, Tennessee: SPC Press; 1990.
Controlled exposure to Haemophilus parasuis - Response
The death losses in the control groups during Experiments 1 (commercial vaccine), 2 (autogenous vaccine), and 3 (controlled exposure) were in fact different.1 These experiments were performed at different times, with different groups of pigs, and under different disease challenges. This is certainly a limitation when comparing results over time, and we share Dr Baum's concern about applying results from a certain set of circumstances to a different farm setting. In this case of controlled field exposure, our field experience and published previous research2 lead us to believe that a reduction in death loss by 50% is not unreasonable and may occur even in herds experiencing a lower mortality rate (4%).
-- Simone Oliveira, Carlos Pijoan, Robert Morrison; University of Minnesota, College of Veterinary Medicine, St Paul, Minnesota
2. Oliveira S, Batista L, Torremorell M, Pijoan C. Experimental colonization of piglets and gilts with systemic strains of Haemophilus parasuis and Streptococcus suis to prevent disease. Can J Vet Res. 2001;65:161-167.