Small red bean (azuki) sheds biologically active substances as a prerequisite step for germination, one of which displays the antiviral activity against the rabies virus infectivity and infections in culture.

When small red beans (azuki bean; Vigna angularis Ohwi et Ohashi) were soaked and warmed in water or saline, the beans began to absorb water to swell and exuded kinds of substances probably as a prerequisite step for seed germination. Such exudate fluids displayed strong antiviral activity against the rabies virus infections in culture. On the other hand, little anti-rabies activity was detected in the aqueous extracts from the red beans when tested soon after the extraction from powdered beans, while low titers of antiviral activity appeared gradually in the extracts during cold storage. In contrast, no antiviral activity was detected in the exudate fluids from non-colored azuki beans (white azuki), implicating that a certain anthocyanin-related substance is involved in the antiviral activity of red beans. Production of antiviral and cytotoxic activities were affected differently depending on the bean-soaking conditions. In addition, the antiviral activity resisted to 10 min-heating in boiling water, while the cytotoxicity was greatly weakened by the heating, suggesting that different substances are involved in the antiviral and cytotoxic activities. Further studies on the antiviral activity of the exudate fluids demonstrated that anti-rabies activity of the bean exudates affected not only the very early phase of infection cycle, but the viral infectivity was also affected similarly, implicating a possible application of azuki bean exudate fluids to post-exposure treatment of rabid dog-bite injuries in combination with vaccination.