The Possibility of Using the ICR Mouse as an Animal Model to Assess Antimonkeypox Drug Efficacy.

As a result of the conducted experimental studies on intranasal challenge of ICR mice, rabbits and miniature pigs (even in the maximum variant) with the doses of 4.0-5.5 lg PFU of monkeypox virus (MPXV), some clinical signs such as purulent conjunctivitis, blepharitis and ruffled fur were found only in mice. The 50% infective dose (C ID50 ) of MPXV for these animals estimated by the presence of external clinical signs was 4.8 lg PFU, and L ID50 estimated by the virus presence in the lungs of mice 7 days post-infection taking into account its 10% application in the animal respiratory tract was 1.4 lg PFU. When studying the dynamics of MPXV propagation in mice challenged intranasally with 25 L ID50 of MPXV, the maximum pathogen accumulation was revealed in nasal cavity, lungs and brain: 5.7 ± 0.1, 5.5 ± 0.1 and 5.3 ± 0.3 lg PFU/ml, respectively. The pathomorphological examination of these animals revealed the presence and replication of the pathogen in the traditional primary target cells for MPXV (mononuclear phagocyte system cells and respiratory tract epitheliocytes) as well as in some other types of cells (endothelial cells, reticular cells, connective tissue cells). Our use of these animals to assess the antiviral efficacy of some drugs demonstrated the agreement of the results (a significant positive effect of NIOCH-14 and ST-246) with those described in scientific literature, which opens up the prospects of using ICR mice as animal models for monkeypox to develop preventive antismallpox drugs.

Limited potential for mosquito transmission of genetically engineered, live-attenuated western equine encephalitis virus vaccine candidates.

Specific mutations associated with attenuation of Venezuelan equine encephalitis (VEE) virus in rodent models were identified during efforts to develop an improved VEE vaccine. Analogous mutations were produced in full-length cDNA clones of the Cba 87 strain of western equine encephalitis (WEE) virus by site-directed mutagenesis in an attempt to develop an improved WEE vaccine. Isogenic viral strains with these mutations were recovered after transfection of baby hamster kidney cells with infectious RNA. We evaluated two of these strains (WE2102 and WE2130) for their ability to replicate in and be transmitted by Culex tarsalis, the principal natural vector of WEE virus in the United States. Each of the vaccine candidates contained a deletion of the PE2 furin cleavage site and a secondary mutation in the E1 or E2 glycoprotein. Both of these potential candidates replicated in mosquitoes significantly less efficiently than did either wild-type WEE (Cba 87) virus or the parental clone (WE2000). Likewise, after intrathoracic inoculation, mosquitoes transmitted the vaccine candidate strains significantly less efficiently than they transmitted either the wild-type or the parental clone. One-day-old chickens vaccinated with either of the two vaccine candidates did not become viremic when challenged with virulent WEE virus two weeks later. Mutations that result in less efficient replication in or transmission by mosquitoes should enhance vaccine safety and reduce the possibility of accidental introduction of the vaccine strain to unintentional hosts.

Effect of mouse strain and age on detection of mouse parvovirus 1 by use of serologic testing and polymerase chain reaction analysis.

BACKGROUND AND PURPOSE: Detection of mouse parvovirus 1 (MPV) depends on use of serologic and polymerase chain reaction (PCR) assays. These assays were evaluated for their ability to detect virus-specific antibodies or viral DNA in multiple strains and ages of mice inoculated with MPV. METHODS: Twelve-week-old ICR, BALB/c, C3H, C57BL/6, and DBA/2 mice and four- and eight-week-old ICR mice were inoculated with MPV. Serum was harvested four weeks after inoculation and analyzed by use of recombinant non structural protein 1 (rNS1) enzyme-linked immunosorbent assay (ELISA), minute virus of mice (MVM) ELISA, and MPV indirect fluorescent antibody (IFA), MVM IFA, and MPV hemagglutination inhibition (HAI) assays. Select tissues were harvested and analyzed by use of an MPV-specific PCR assay. RESULTS: The number of mice in each group with detectable MPV-specific antibodies or MPV DNA varied with mouse strain, mouse age when inoculated, and viral dose. Seroconversion in mice inoculated at 12 weeks of age was detected almost exclusively by use of the MPV IFA and MPV HAI assays, whereas seroconversion in almost all mice inoculated at 4 and 8 weeks of age was detected by use of all immunoassays except the MVM ELISA. Viral DNA was detected by use of PCR analysis in all strains and ages of mice except DBA/2 mice. CONCLUSIONS: Mouse strain and age have important roles in seroconversion to nonstructural and structural MPV antigens and persistence of viral DNA in mouse tissues. Therefore, diagnostic serologic testing and PCR analysis should be considered within the context of mouse strain and age at the time of MPV exposure, especially when sentinel mice are used for surveillance.

Sendai viruses with altered P, V, and W protein expression.

Wild-type Sendai virus expresses three proteins containing the N-terminal half of the P protein open reading frame due to mRNA editing; a full-length P protein (ca. 70% of the total), a V protein with the N-terminal half fused to a Cys-rich Zn(2+)-binding domain (ca. 25% of the total), and a W protein representing the N-terminal half alone (ca. 5% of the total). To examine the role of these proteins in the virus life cycle, we have prepared recombinant viruses in which the normal V mRNA expresses a W protein (V-stop; 70% P, 30% W), one which cannot edit its P gene mRNA (delta 6A; 100% P), and one which overedits its mRNA like parainfluenza virus type 3 (swap/8;20-40% P, 30% V, 30% W). All these viruses were readily recovered and grew to similar titers in eggs, and except for the P gene products, cell lines individually infected with these viruses accumulated similar amounts of viral macromolecules. The relative competitive advantage of each virus was determined by multiple cycle coinfections of eggs and found to be rSeV-Vstop = rSeV-wt >> rSeV-delta 6A > rSeV-swap/8. On the other hand, rSeV-swap/8 underwent multiple cycles of replication in C57BI/6 mouse lungs and was highly virulent for these animals, whereas rSeV-delta 6A was avirulent in mice and this infection was quickly cleared. Remarkably, rSeV-Vstop appeared to be more virulent for inbred C57BI/6 mice than rSeV-wt, but was partially attenuated in infections of outbred ICR mice. Thus, the expression of either the V or the W proteins is sufficient for multiple cycles of infection and pathogenesis in C57BI/6 mice, whereas W can only partially substitute for V for pathogenesis in ICR mice.

New isolates of pneumonia virus of mice (PVM) from Japanese rat colonies and their characterization.

Two virus strains were isolated from the lungs of athymic rats and mice used as sentinel animals in 2 colonies of laboratory rats in Japan in which antibodies to the pneumonia virus of mice (PVM) had been detected. The new isolates were identified as PVM by the following characteristics: RNA virus, susceptibility to ether treatment, long filamentous viral structure in the cytoplasm of infected cells, and hemagglutinating activity in various erythrocytes, including those of mice and rats. In addition, cross neutralization with the prototype of PVM (No. 15 strain) was observed. This is the first report of the isolation of PVM from laboratory animals in Japan.