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The defective step of a temperature-sensitive mutant of western equine encephalitis virus, which synthesize viral RNA but not mature virus at the restrictive temperature, was studied. Cells infected with the mutant virus at the restrictive temperature synthesized the same intracellular viral RNA as that in wild type infection. Cells infected with the mutant at the restrictive temperature formed three proteins (E1, E2 and C) which migrated to positions identical with those of purified virions and a precursor protein of E2 (PE2). The mutant virus was also able to form cytoplasmic nucleocapsids sedimenting at 140S as in the case of wild type infection. On the other hand, cells infected with the mutant could not induce a significant amount of hemadsorbing ability and the ability induced at the permissive temperature disappeared immediately after shifting up to the restrictive temperature. These results suggested that the mutant virus produced a defective envelope protein responsible for hemagglutination at the restrictive temperature. Owing to the incompleteness of the modification of the cell plasma membrane by the envelope proteins, viral nucleocapsids in the mutant infected cells could not bind to the plasma membrane.

The titre of WEE virus produced by organ cultures of brain, muscle and spleen decreased as tissue was taken from older mice. The multiplication of SFV and SFA in muscle organ cultures of mice remained nearly constant, whereas in spleen organ cultures, titers of both viruses decreased with increasing age of mice. There was a striking difference in the rate of decline of the yield of brain organ culture infected with virulent and avirulent SF virus strains. Organ cultures made from the brains of mice over 16 days old were totally resistant to SFA infection, whereas similar cultures from mice up to 42 days of age supported SFV multiplication. These results show that the avirulence of this strain of SF virus is due to age related intrinsic brain insusceptibility.

Cordycepin (3'-deoxyadenosine) inhibited viral RNA synthesis in the replication of western equine encephalitis virus, thereby causing a reduction of virus production. The rate of inhibition of viral RNA synthesis was dependent on drug concentration and the period of treatment with the drug. These results suggest that the virus RNA synthesizing system is sensitive to the drug.

It was found that sera of normal rabbits and guinea pigs all contained nonspecific inhibitors against rabies virus capable of neutralizing the virus in the presence of complement. The nature of the rabbit inhibitors was further analysed in detail. There seemed to exist two different inhibitors, which were tentatively named complement-requiring inhibitors (CRI) I and II. CRI I was present generally in low titers and destroyed by heating at 56° C for 30 minutes, whereas CRI II resisted to the same treatment though its activity was lost after heating at 70°C for 30 minutes. Both the inhibitors were sensitive to treatment with 2-mercaptoethanol. When CRI II was subjected to Sephadex G-200 gel filtration, the activity was recovered in the IgM fraction. These inhibitors exerted little, or if any much lower inactivating effects on Sindbis, herpes, WEE and vaccinia viruses.

Infection of BHK cells with western equine encephalitis (WEE) virus resulted in rapid inhibition of cellular DNA synthesis. The rate of inhibition of DNA synthesis depended on the multiplicity of infection, and was closely related to virus replication. Cellular DNA synthesis was not inhibited in infected BHK cells that had been irradiated with ultraviolet radiation. These results indicated that a functional viral genome was required for the inhibition of DNA synthesis by WEE virus. The sharp decrease in thymidine incorporation into the acid-insoluble fraction was not due to a change in the intracellular pool of the acid-soluble fraction. Sedimentation analysis in alkaline sucrose gradients was used to show that cellular DNA was not degraded during WEE viirus infection. DNA polymerase activity in infected cells was not significantly reduced.

Variations in the metabolism of African green monkey (AGMK) and stable porcine kidney (PS) cells infected with certain arboviruses were investigated. Virus-directed RNA synthesis and RNA polymerase activity were stimulated in actinomycin-treated infected cells. The rate of3H-uridine incorporation into RNA in Western equine encephalitis (WEE) virus-infected AGMK cells reached a maximum at approximately 5 hours after infection. In contrast, the viral RNA synthesis induced by Japanese encephalitis (JE) or dengue virus did not increase appreciably during the first 15 hours, and a maximum was reached from 24 to 30 hours after infection. Cytoplasmic large- and small-particle fractions from cells infected with WEEV or JEV were found to catalyze the incorporation of 4 nucleoside triphosphates into acid-insoluble products. In WEEV-infected AGMK cells, the enzyme activity was associated almost solely with the small-particle fraction, whereas nuclear and large-particle fractions of JEV-infeeted cells still contained 15 to 30% of the total enzyme activity 24 hours after infection. Rapid inhibition of cellular DNA synthesis was observed 4 hours after infection, with each of the three kinds of arbovirus used. Heat-inactivated WEEV was unable to suppress host cell DNA synthesis appreciably, whereas infection by UV-irradiated virus did result in a clear inhibition of DNA synthesis. However, the effect was apparently less marked than that of the active WEE virus.

Three virus strains isolated fromIxodes putus ticks were shown to be related to, though not identical, with Uukuniemi virus by complement-fixation tests. No antigenic relations were detected in the cross-neutralization test performed with the virus isolated and Uukuniemi virus. Two virus strains were isolated in 1969 on Tyuleniy island, Zaliv Terpeniya (Patience Bay) of the Sea of Okhotsk (Sakhalin region), one virus strain in 1970 on the Ariy Kamen' rock situated close to the Pacific coast of Bering island, Commodore islands (Kamchatka region). The isolated agent was named after Zaliv Terpeniya, the place of its primary isolation.

The mechanism of the enhanced replication of Newcastle disease (ND) virus in swine testicle (ST) cells infected with hog cholera (HC) virus (END phenomenon) was studied. Two mechanisms appeared to operate, one being the suppression of interferon production by the coinfecting HC virus and the other a still undefined mechanism not related to interferon. The first mechanism was suggested by the facts that interferon production by ND virus was inhibited by prior infection with HC virus, and that ND virus growth was suppressed by exogenous interferon in both HC infected and uninfected ST cell cultures. The reason for the inhibition of interferon production is unknown; it is neither due to a decreased ND virus adsorption to ST cells nor due to the production of some factor blocking the interferon production. The possibility of an additional mechanism emerged when the effects of 20-methylcholanthrene and actinomycin D were examined. These substances suppressed the interferon induction by ND virus but increased the viral growth only slightly, while in HC infected cells actinomycin D reduced ND virus replication to a marked extent. It thus seems that the second mechanism, which is not related to interferon and which is sensitive to actinomycin D, may be more important than the suppression of interferon production in END phenomenon. Poly I∶C treatment, which could confer on uninfected cells resistance to ND and WEE viruses without inducing detectable amounts of interferon, did not affect the growth of these viruses in HC infected cells. This phenomenon presumably shares a common mechanism with the END phenomenon.

It is now thirty years since the first of the organochlorine insecticides, DDT, was introduced to control insect vectors of human diseases, and twenty-eight years since the development of resistance to DDT was suspected in the housefly, Musca domestica, and the common house mosquito, Culex pipiens. During that period resistance has developed to some insecticide group or other in one hundred and eight species of arthropods of public health importance. Although the past six years have seen only six species added to that list, these recent years have been characterized by some dramatic developments. Not only resistant populations have spread over even wider geographical areas but some species become, in the same area, simultaneously resistant to almost all available insecticides while many other species are only susceptible to compounds that many developing countries cannot afford to purchase for their public health programmes.

Factors Inhibiting the Interference of Western Equine Encephalitis Virus by Rabies Virus in Chick Embryo Tissue Cultures