Vibrio cholerae infection and acquired immunity in an adult rabbit model

We modified the rabbit model for enteric infection by Vibrio cholerae developed by Spira et al. and designated the RITARD (for removable intestinal tie-adult rabbit diarrhea) model (20). Our modification DISC comprises a permanent ligation of the cecum (C) to prevent resorption of the fluid secreted by the small intestine, a temporary ligation of the small intestine (S) to enable the bacteria to colonize, and duodenal inoculation (DI) of the challenge material. The main difference between RITARD and DISC is that in the latter model the challenge material is injected into the duodenum approximately 10 cm distal to the stomach instead of into the jejunum. Four out of 5 V. cholerae strains tested, including 2 serotypes and 2 biotypes, were able to elicit a massive and usually fatal cholera-like diarrhea. The virulence depended strongly on the culturing conditions. One strain, C5, caused fatal diarrhea in a dose of about 1000 organisms, even if the temporary ligation was omitted (DIC model). Other modifications were the DIS and the DI model in which the permanent ligature of the cecum or both ligatures were omitted. Duodenal inoculation of organisms in a dose of 100 X the minimum infective dose (MID) in the DIS or DI model did not cause any disease symptom. However, such inoculations were found to cause protection against subsequent challenges with 100 X MID of homologous and heterologous organisms up to 52 weeks after duodenal inoculation. Subcutaneous injection with classical, whole cell cholera vaccine gave only partial protection of short duration. This model might contribute to the understanding of the pathogenesis of cholera as well as to the improvement of efficacy testing of cholera vaccines.