ANTIVIRAL ACTIVITIES OF TRAGACANTHIN POLYSACCHARIDES AN PUNTA-TORO VIRUS-INFECTIONS IN MICE

Tragacanthin polysaccharides from Astragalus brachycentrus (AV208) and Astragalus echidnaeformis (AV212) plants, which are devoid of in vitr o antiviral activity, were evaluated in a mouse model of Punta Toro vi rus (PTV) infection. The PTV (a phlebovirus member of the Bunyaviridae family of viruses) is a model for studying the treatment of Rift Vall ey fever and hantavirus infections. Single intraperitoneal treatments with 12.5-200 mg/kg/day doses of AV212 given 24 h before or 4 and 24 h after virus inoculation protected the majority of mice from mortality . Single treatments with AV208 were ineffective when given 24 h before the virus challenge; however, protection was afforded when treatments were administered at 4 and 24 h following virus inoculation. In a fol low-up study, AV208 treatments of 1.6-50 mg/kg/day given 24 h subseque nt to virus exposure caused reductions in mortality, liver infection s cores, liver and spleen virus titers, and serum transaminases, The pol ysaccharides did not activate lymphocytes or natural killer cells, nor was interferon induced in treated mice. However, mice pretreated with fumed silica (a macrophage poison) and infected with the PTV were not protected by subsequent administration of AV208 or AV212 at 50 mg/kg, providing evidence that activation of peritoneal macrophages by the p olysaccharides affords protection to infected animals. These compounds should be considered for the potential treatment of significant human infections induced by bunyaviruses and hantaviruses.