An extensive epidemiologic survey was carried out from 1970 to 1974 in order to understand the condition of circulation of tick-borne encephalitis virus between ticks and small mammals in the Alsatian focus, France. The virus has been isolated from Ixodes ricinus adult ticks (30 lots out of 369, representing a total of 5617 ticks), and from Ixodes ricinus nymphs (4 lots out of 251, representing a total of 8587 ticks). The virus has also been isolated from 11 pools of rodent organs (out of 3361 rodents), and HI antibodies were detected in 21 out of 8735 rodent specimens. The virus has never been detected in rodent blood, nor in 10,298 ticks collected engorged from 1505 vertebrate hosts. These results show that Alsatian tick-borne encephalitis focus is stable since the activity of the virus is detected every year, and that the focus is an extended one since the virus is isolated from 5 of 6 study sites, as well as in several control sites.

The effectiveness of polyvalent plasma-derived human immunoglobulins (IVIG) in passive immunotherapy of influenza virus pneumonia was assessed, using the Strain Scotland (A/Scotland/74 (H3N2)) adapted to BALB/c mice by repeated lung passages. Haemagglutinin antibodies in two batches of IVIG at 10 mg/ml had a titre of 1/16. Intravenous injection of 1000-5000 microg of IVIG, 3 h after infection, gave 60-70% protection, whereas intranasal injection of 25-50 microg protected 90% of mice infected with a lethal dose of influenza virus. F(ab')2 fragments were at least as protective as intact IVIG, suggesting that complement or Fcgamma receptor-bearing cells were not required. Topical passive immunotherapy with IVIG or F(ab')2 gave protection up to 8 h after infection, but not at 24 h, suggesting that anti-influenza A antibodies in IVIG, delivered locally, are only effective at early stages of the infectious process. The potential value of topical administration of IVIG or F(ab')2 fragments for influenza A pneumonia prophylaxis was further demonstrated by the protective effects of their intranasal administration 24 h before challenge.

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