Previous studies suggested that the most frequent means of transmission of Lassa virus was by either direct or indirect contact with infectious material. Aerosol stability and respiratory infectivity of the Josiah strain of Lassa virus were assessed to determine the effect of environmental factors on aerosol-induced infection. The stability of the virus in aerosol, particularly at low relative humidity (30% RH), plus the ability of the virus to infect guinea pigs and monkeys via the respiratory route emphasize the potential for aerosol transmission of Lassa virus. Biological half-lives at both 24 and 32 degrees C ranged from 10.1 to 54.6 min, and were sufficient for aerosol dispersion of virus to considerable distances in natural situations. Infectivity of Lassa virus in small particle aerosol was demonstrated in outbred guinea pigs and cynomolgus monkeys using dynamic aerosol equipment. Monkeys exposed to inhaled doses to 465 PFU were infected and died. The median infectious dose (ID50) for guinea pigs was 15 PFU, yet a definitive median lethal aerosol dose (LD50) could not be established. Organ tropism of aerosol-induced Lassa virus infections in outbred guinea pigs was similar to that previously reported for inbred guinea pigs infected by subcutaneous inoculation.

Virus population dynamics in the lungs, trachea, and nasopharynx of Swiss-ICR mice were studied after respiratory challenge with mouse-adapted preparations of strain A2/Aichi/2/68 influenza virus. Markedly higher doses of virus were required to produce infection with nasopharyngeal challenge than with bronchoalveolar challenge. In all of the infections, the highest virus concentrations were observed in the lungs. Peak concentrations in the trachea were lower than in the lungs but higher than in the nasopharynx. Decreasing virus levels were observed by 120 h after challenge and were generally below detectable levels by the end of 10 days. A compartmental model of a single mathematical form was developed which provided close fits of the virus concentration measurements regardless of the challenge dose, site of initial deposition, or respiratory tissue considered. The model includes seven compartments with five associated rate parameters. The application of compartmental modeling techniques and expression of the virus population dynamics in mathematical terms is regarded as a new approach to the study of the pathogenesis of infections.

Ribavirin (1-,8--ribofuranosyl-1,2,4-triazole-3-carboxamide) is an effective antiviral agent against type A influenza infection of mice. Therapy was most effective when administered as a small-particle aerosol early in the infection. Treatment was also effective by either the intraperitoneal or aerosol route in mice with histological evidence of pneumonia. Ribavirin increased the percent survival, lowered lung virus titers, and decreased the development of lung pathology when therapy was initiated at 6 h as a small-particle aerosol. There was no evidence of pulmonary toxicity or immunosuppressive effects.Virus diseases of man and animals represent an important group of disease entities. Notwithstanding the influenza pandemic of 1918 to 1919, which was accompanied by great loss of life, influenza, like most virus diseases, is usually self-limiting and not associated with high mortality unless complicated by bacterial pneumonia. In 1957, Horsfall estimated that man suffers with viral diseases for 7 years of a 70-year life span (5). Loosli has stated that influenza is the major incapacitating viral disease not adequately controlled by vaccines (9).Ribavirin has antiviral activity against both ribonucleic and deoxyribonucleic acid viruses (6,13,17). The demonstration that small-particle aerosols containing rimantadine or amantadine-hydrochloride were effective for the treatment of influenza virus-infected mice (15,16) and the reported efficacy of parenterally injected ribavirin against lethal influenza infections in mice (1, 7) suggested that aerosols of ribavirin might be useful for the treatment of influenza. This report describes the therapeutic efficacy of ribavirin given in small-particle aerosols to treat experimental influenza virus infection in mice.MATERIALS AND METHODS Mice. Five-week-old outbred, female mice, Tac:(SW)fBR, were used for all experiments. Upon arrival, mice were housed 15 to a cage in random order. Each group of mice contained a separate subgroup destined for the same treatment, but reserved for serial sacrifice studies in addition to those recorded for survival. Groups contained 55 mice except that continuously treated groups contained 40 mice.Virus. The mouse-adapted variant of the A/Aichi/ 2/68 (H3N2) strain of influenza virus used to infect the mice has been previously described (12, 15).Lung virus titers. Lung samples were homogenized in 4.5 ml of heart infusion broth and assayed in 10-to 12-day-old embryonated eggs (15). Lung titers, expressed as the mean egg infective dose per lung, are the geometric mean of three individual mouse lungs at the indicated times postexposure. When no virus was detected in a lung sample, a value of 1.0 was assigned to calculate the geometric mean titer.Aerosol sampling and dissemination system. The dissemination system used to infect the mice and for intermittent therapy has been previously described (15). The aerosols for continuous therapy were generated by a modified Collison system developed in our laboratory. The particles generated by this system h...

Rimantadine hydrochloride was administered for 4 days in a small-particle (95% < 6.5 μm) aerosol (8.8 mg/kg per day) or intraperitoneally (40 mg/kg per day) to mice previously infected with influenza A/Aichi/2/68 (H 3 N 2 ), mouse adapted. Mean time to death and incidence of survival were significantly increased in all treated groups of mice. The rate of eventual disappearance of virus from lung tissue was also accelerated by therapy. However, maximal mean virus titer per lung, and lung histopathology, did not reveal any difference between control and either group of treated mice. Aerosol therapy initiated at 72 h postinfection was as effective as that initiated at 6 h, even though lung virus titers of these mice had already peaked by 72 h. In contrast, intraperitoneal therapy initiated at 72 h was not effective in all studies.

Ribavirin administered as small-article aerosols had significant therapeutic effect in the treatment of viral respiratory infections induced by influenza virus. The preliminary experiment using ribavirin to treat influenza infection in the squirrel monkey is encouraging. We expect to extend these experiments by initiating therapy at a later time to investigate the potential value of ribavirin in a clinical situation. Several derivatives of ribavirin are effective antiviral compounds. The tri-O-acetyl derivative appears to offer a potential advantage over ribavirin, although this cannot be stated with certainty since the data were obtained from separate experiments. Radiolabeling has been used as a means of measuring tissue concentration and clearance rates of various drugs. It is hoped that the use of labeled ribavirin and the tri-O-acetyl derivative will assist us in determining whether a depot of antiviral drug is created in pulmonary tissues after administration as a small-particle aerosol. These experiments are now in progress.