Influenza infectious dose

The influenza virus host resistance model has been characterized in mice and rats, and has been widely used to evaluate the potential immunotoxicity of therapeutics. Influenza virus is used as the infectious challenge agent and administered intranasally in a 28-day repeat-dose study. Mice or rats are dosed for 7 days, infected and then dosed for an additional 21 days. Viral clearance is quantified by measuring infectious virus (plaque-forming units) at various times following infection. Dexamethasone may be used as a positive immunomodulatory control. This host resistance assay has been used in Balb/c, C57BL/6, and B6C3F1 mice and Fischer 344 (CDF), Brown Norway, and... 

Methisazone does not interfere with the replication of viral DNA, the synthesis of viral mRNA, or the functioning of early viral mRNA. However, by disorganizing the formation of late proteins, it prevents assembly of complete, infectious virions (Prusoff, 1967). The antiviral spectrum of this drug is wide, in vitro. It inhibits multiplication of all pox-viruses, and other DNA viruses too (e.g. the adenoviruses and varicella), as well as several groups of RNA viruses (e.g. poliomyelitis, common cold, influenza A and B, and some arboviruses). However, in Man, no benefit can be demonstrated in these diseases at any dose that does not cause intense nausea and vomiting (Turner, Bauer and Nimmo-Smith, 1962). 

Previous studies demonstrated the antiviral activity of ascorbate against a broad spectrum of RNA and DNA viruses in vitro (1-4) and in vivo (5, 6). It has been claimed that ascorbate inhibited the activation of a latent human retrovirus (human T-cell leukemia virus 1) induced by 5-iodo-2 -deoxyuridine and JV-methyl-A/ -nitro-A-nitrosoguanidine (7). However, it was not established whether ascorbate exerted a virus-specific effect or interacted directly with the activating substances. In addition, the effects of ascorbate on acute infection by human retroviruses have not been determined. In vivo, oral, and intravenous administration of ascorbate is said to have produced clinical improvements in patients afflicted with influenza, hepatitis, and herpes virus infections, including infectious mononucleosis (5, 6). Clinical improvement was claimed in AIDS patients who voluntarily ingested high doses of ascorbic acid (8). 

The lack of vitamin C effect on incidence of colds in the studies analyzed by Hemila (1994) may be related to the small amount of vitamin tested (Pauling, 1986). Thus, Cathcart has found that the maximum concentration of vitamin C tolerated by persons increases with illness and severity of disease. Based on initial observations made with 9000 patients who had been treated with large doses of vitamin C, Cathcart (1981) reported that while healthy persons can tolerate oral intakes from 4-15 g per day, their bowel-tolerance level—the amount slightly lower than that which produces a laxative effect—increased to values of 30-60 g during a mild cold, 60-100 g during a severe cold, and greater than 100 g during an attack of influenza or flu. In cases of severe viral illnesses such as infectious mononucleosis or pneumonia, the bowel-tolerance doses were found to approach 200 g per day. Cathcart found that vitamin C therapy for the common cold and infectious diseases was most effective when administered at the bowel-tolerance dose. Upon control of... 

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