Effect of Thiosemicarbazones and Dichlorophenoxy Thiouracil on Multiplication of a Recently Isolated Strain of Variola-Vaccinia Virus in the Brain of the Mouse

Summary The antigenic and biological properties of the Williamsport virus place it in the variola-vaccinia group. It is highly infectious for mice and rabbits. Intracerebral injection in mice is followed by a gradual increase in the concentration of virus in the brain. After reaching a maximal value, the titer decreases. The limiting concentration of virus in the brain is independent of the amount injected. The rate of multiplication varies indirectly with the size of the inoculum. Death usually takes place when the viral content of the brain is greatest but may occur during the next 48 hours. Thiosemicarbazones with antivaccinal activity protect mice against the Williamsport virus following intracerebral injection of the virus. The response is similar whether materials are fed in the diet or administered by the peritoneal route. Isatin and 5-nitro-2-thenaldehyde thiosemicarbazones protected the majority of mice when injected intraperitoneally within a period of 48 hours immediately after the inoculation of virus. Protection of mice against Williamsport virus by treatment with isatin and other thiosemicarbazones is not associated with inhibition of viral proliferation in the brain. Dichlorophenoxy thiouracil may act in part by suppression of viral growth.