The use of the model mouse ICR - Variola virus for evaluation of antiviral drug efficacy

Abstract

Mice of the ICR outbred population were infected intranasally (i/n) with the variola virus (VARV, strain Ind-3a). Clinical signs of the disease did not appear even at the maximum possible dose of the virus 5.2 lg PFU/head (plaque-forming units per head). In this case, 50% infective dose (ID50) of VARV estimated by the presence or absence of the virus in the lungs three days after infection (p.i.) was equal to 2.7 ± 0.4 lg PFU/head. Taking into account the 10% application of the virus in the lungs during the intranasal infection of the mice, it was adequate to 1.7 lg PFU/lungs. This indicates a high infectivity of the VARV for mice comparable to its infectivity for humans. After the i/n infection of mice with the VARV at a dose 30 ID50/head the highest concentration of the virus detected in the lungs (4.9 ± 0.0 lg PFU/ml of homogenate) and in nasal cavity tissues (4.8 ± 0.0 lg PFU/ml) were observed. The pathomorphological changes in the respiratory organs of the mice infected with the VARV appeared at 3-5 days p.i., and the VARV reproduction noted in the epithelial cells and macrophages were noticed. When the preparations ST-246 and NIOCH-14 were administered orally at a dose of 60 ug/g of mouse weight up to one day before infection, after 2 hours, 1 and 2 days p.i., the VARV reproduction in the lungs after 3 days p.i. decreased by an order of magnitude. Thus, outbred ICR mice infected with the VARV can be used as a laboratory model of the smallpox when evaluating the therapeutic and prophylactic efficacy of the antismallpox drugs.