FIG. 2.

Protection afforded to Dutch-belted dwarf and New Zealand White rabbits by AVP-21D9 (10 mg/kg) administered by s.c. injection at the time of initial challenge with B. anthracis Ames spores by aerosol administration. The Dp for the Dutch-belted dwarf rabbits was calculated to be 1.13 × 10⁷ CFU (100 LD₅₀), while that for New Zealand rabbits was 9.78 × 10⁶ CFU (87 LD₅₀). At 3 or 4 days after initial aerosolization of B. anthracis Ames spores, the survival of both Dutch-belted and New Zealand White rabbits, dosed with AVP-21D9, was significantly different (P < 0.05) from that of untreated control animals by Fisher's exact test. Upon rechallenge 5 weeks later, the Dp for the Dutch-belted dwarf rabbits was calculated to be 1.19 × 10⁷ CFU (106 LD₅₀), while that for New Zealand rabbits was 1.42 × 10⁷ CFU (126 LD₅₀). At 4 days following secondary B. anthracis Ames spore challenge by aerosolization, Dutch-belted, but not New Zealand White, rabbits were still significantly protected (P < 0.05). In this experiment, one of the New Zealand rabbits initially dosed with AVP-21D9 died 7 days after secondary challenge (41 days after initial challenge), and two of the six positive control animals failed to die of inhalation anthrax.