Improved protection against cholera in adult rabbits with a combined flagellar-toxoid vaccine

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Abstract
Ligated ileal loops of adult rabbits were used to evaluate the prophylactic potential against cholera of a combined vaccine consisting of toxin-free crude flagella (CF) and glutaraldehyde-derived cholera toxoid (TV). The resulting fluid accumulation ratios were compared with those in rabbits immunized with saline (controls) and with CF and TV alone. Data for single vaccines confirmed the superior protection effect of CF over TV. In rabbits vaccinated with CF and TV, maximal fluid accumulation ratios were not obtained with a challenge dose as high as 5 .times. 109 colony-forming units (CFU). Two rabbits similarly immunized failed to produce positive loops with challenges of 6.3 .times. 108 and 5 .times. 109 CFU, respectively. The vibriocidal titer of serum from rabbits immunized with a killed commercial vaccine in addition to those listed above was determined at intervals for 164 days. No vibriocidal activity was detected in serum of control rabbits and of rabbits vaccinated with TV. Serum from animals given CF or commercial vaccine had similar vibriocidal titers even when the test bacteria were nonflagellated. Protection against challenge as evaluated by ileal loops did not correlate with vibriocidal titer.

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