Screening for vaccinia virus egress inhibitors: separation of IMV, IEV, and EEV.

Concerns about the possible use of variola virus as a biological weapon as well as the need for therapeutics for the treatment or prevention of naturally acquired poxvirus infections or vaccination complications have led to the search for small molecule inhibitors of poxvirus replication. One unique and attractive target for antiviral development is viral egress. Part of understanding the mechanism of action of viral egress inhibitors involves determining which virion form is being made. This can be accomplished through buoyant density centrifugation.

Topical treatment of cutaneous vaccinia virus infections in immunosuppressed hairless mice with selected antiviral substances.

BACKGROUND: Certain nucleoside, nucleotide and pyrophosphate analogues may be useful for treating severe complications arising as a result of virus dissemination following smallpox (live vaccinia virus) vaccinations, especially in immunocompromised individuals. We used an immunosuppressed hairless mouse model to study the effects of 10 antiviral agents on progressive vaccinia infections. METHODS: Hairless mice were immunosuppressed by treatment with cyclophosphamide (100 mg/kg) every 4 days starting 1 day prior to vaccinia virus (WR strain) infection of wounded skin. Topical treatments with antiviral agents were applied twice a day for 7 days starting 5 days after virus exposure. RESULTS: Topical 1% cidofovir cream treatment was effective in significantly reducing primary lesion severity and decreasing the number of satellite lesions. Topical 1% cyclic HPMPC and 1% phosphonoacetic acid were not quite as active as cidofovir. Ribavirin (5%) treatment reduced lesion severity and diminished the numbers of satellite lesions, but the mice died significantly sooner than placebos. 2-Amino-7-[(1,3,-dihydroxy-2-propoxy)methyl]purine (compound S2242; 1%) moderately reduced primary lesion sizes. Ineffective treatments included 5% arabinosyladenine, 1% arabinosylcytosine, 1% 5-chloro-arabinosylcytosine, 5% arabinosylhypoxanthine 5-monophosphate and 5% viramidine. CONCLUSIONS: Of the compounds tested, topically applied cidofovir was the most effective treatment of cutaneous vaccinia virus infections in immunosuppressed mice. Topical treatment with cidofovir could be considered as an adjunct to intravenous drug therapy for serious infections.

[Evaluation of the vaccinal process in skin-scarification and oral immunization of rabbits with live smallpox vaccines].

On the basis of comparative experimental evaluation of specific features in the course of the vaccinal process after the immunization of laboratory animals with live smallpox vaccines, intended for oral use (in tablets) and for skin scarification was proposed. In experiments on rabbits, made with the use of virological and immunological methods, the counteraction of the elements constituting the vaccinal process was analyzed, the integral evaluation of its course was given, the greater safety of the oral preparation in comparison with the traditional vaccine for immunization by skin-scarification method were established. The conclusion was made that oral immunization was the safest immunization method under modern conditions and promising one for using live vaccines with population immunity being at a low level or absent.

Effects of four antiviral substances on lethal vaccinia virus (IHD strain) respiratory infections in mice.

Intranasal infection of BALB/c mice with the IHD strain of vaccinia virus was found to cause pneumonia, profound weight loss and death. Cidofovir, hexadecyloxypropyl-cidofovir (HDP-CDV), the diacetate ester prodrug of 2-amino-7-[(1,3-dihydroxy-2-propoxy)methyl]purine (HOE961), and ribavirin were used to treat the infections starting 24h after virus exposure. Single intraperitoneal (i.p.) cidofovir treatments of 100 and 30 mg/kg led to 90-100% survival compared with no survivors in the placebo group, whereas a 10 mg/kg dose was ineffective. The 100 mg/kg treatment reduced lung and snout virus titres on day 3 of the infection by 20- and 8-fold, respectively. Mean arterial oxygen saturation levels in these two cidofovir treatment groups were significantly higher than placebo on days 4 through 6 of the infection, indicating an improvement in lung function. Effects of cidofovir on viral pathogenesis were studied on days 1, 3 and 5 of the infection, and demonstrated statistically significant reductions in lung consolidation scores, lung weights, lung virus titre and snout virus titres on days 3 and 5. Cidofovir treatment also reduced virus titres in other tissues and body fluid, including blood, brain, heart, liver, salivary gland and spleen. HDP-CDV was given by oral gavage at 100, 50 and 25mg/kg doses one time only, resulting in 80-100% survival. Lower daily oral doses of 10 and 5mg/kg per day given for 5 days protected only 30% of animals from death. Oral doses (100, 50 and 25 mg/kg per day) of HOE961 for 5 days protected all animals, whereas equivalent oral doses of ribavirin were completely ineffective. The rapidity of recovery from weight loss during the infection was a function of dose of compound administered. These data indicate the utility of parenteral cidofovir, oral HDP-CDV and oral HOE961 in treating severe respiratory infections caused by this virus.

[The comparative study of the safety of a vaccinal process in both oral and epicutaneous immunization against smallpox]. / Sravnitel'noe izuchenie bezopasnosti vaktsinal'nogo protsessa pri oral'noi i nakozhnoi protivoospennoi immunizatsii.

Results of comparative studies of tableted and epicutaneous live smallpox vaccines are presented. In experiments on rabbits by using histological, immunofluorescent, immunological and virological methods, higher safety and efficiency of the tableted vaccine than that of traditional smallpox epicutaneous vaccine were determined. The natural and physiological character of oral immunization was shown. The oral immunization was concluded to be a safe method of inoculation now and perspective for the use of recombinant vaccines based on vaccine virus in the absence of population immunity against smallpox.

Treatment of lethal vaccinia virus respiratory infections in mice with cidofovir.

Intranasal infection of BALB/c mice with the WR strain of vaccinia virus leads to pneumonia, profound weight loss and death. Five days after intranasal inoculation, virus from untreated mice was recovered from 11 organs, tissues and whole blood. The highest titres [>10(8) plaque forming units (pfu)/g] were in lungs and nose/sinus tissue, with about 10(7) pfu/g in spleen and blood. Seven other organs contained 30- to > or = 50-fold lower amounts of virus. Mice infected with the related cowpox virus (for comparative purposes) had the majority of virus located in the respiratory tract. The vaccinia mouse model was used to study the efficacy of cidofovir treatments on the infection. Subcutaneous injections of 30 or 100 mg/kg/day, given on days 1 and 4 after virus challenge, reduced mortality by 60-100%. However, lung virus titres on days 2-5 were reduced no more than 10-fold by these treatments. A moderate improvement in drug efficacy occurred with daily treatments for 5 days. The efficacy of cidofovir also increased as the virus challenge dose decreased, where subcutaneous or intraperitoneal treatment routes showed similar degrees of protection. Although it has been known for many years that the WR strain of vaccinia virus can cause lethal infections by intranasal route, its application to antiviral therapy represents a new model for studying anti-orthopoxvirus agents.