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To date, only one seroepidemiological survey, carried out in Japan, gave a strong indication that dogs may be naturally infected by the influenza C virus, long considered to be exclusively human. In the present work, 134 serum samples were collected during the winter of 1988/89 from dogs aged 6 months to 16 years in northern France. Samples were tested for the presence of antibodies to influenza C virus by both haemagglutination inhibition (HI) and ELISA. Using antibody absorption by staphylococcal protein A, we demonstrated the specificity of the results. In 62% of cases, the results were identical using the two methods. Significant HI activity was found in 32% of the 134 tested sera and titres ranged from 20 to 320. Of the sera tested, 42% were positive by ELISA and titres ranged from 500 to 8,000. The discordant results are discussed. The population tested was divided into five age groups: less than 4 years, 4 to 6 years, 7 to 9 years, 10 to 11 years and greater than 12 years. The distribution of antibodies in the tested canine population, in contrast to that of humans, did not show a significant degree of association with age.

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.

Little is known of the epidemiology of influenza C virus infections in western Europe and of the exact role of this agent in acute viral respiratory infections. Several tests may be used for detecting antibodies against this agent but the significance of their respective results is not clear. A total of 301 samples of serum was collected from persons aged from 4 months to 88 years living in France in 1988. The samples were tested for the presence of antibodies to influenza C virus by haemagglutination-inhibition (HI) tests and ELISA. The specificity of the results was checked by immunoblotting and by antibody absorption with staphylococcal protein A. Significant HI activity was found in 61% of the 301 samples tested, titres ranging from 20-320; 70% were positive by ELISA with titres ranging from 500 to 32,000. The population tested was divided into four age groups: 0-15 years; 16-30 years; 31-50 years and 51-88 years. The highest rates for positive samples were found in the 16-30 year group (76 and 79% by HI tests and ELISA respectively) as well as significant HI and ELISA geometric mean titres. Positive samples were less common in young children (46 and 50% by HI tests and ELISA respectively) and in the oldest group (44 and 54% respectively). The 31-50 years age group formed an intermediate class. The high prevalence of antibody as well as the significant titres indicate intense circulation of influenza C virus, especially among young adults.

The evaluation of the validity of the GROG's indicators is based on the first five years of activity, four of which being epidemic ones. A virological criterion for identifying epidemics is used as the gold standard. For each non-specific indicator, the ratio of epidemic weeks to non-epidemic weeks is outlined. Therefore we can define four epidemic situations in relation with the strains circulating and the non-specific indicators. Influenza A epidemics, which are known as a mortality problem can also be described according to its impact upon morbidity. As a result, it is possible to set up a sensitive and specific surveillance system for early detection of influenza epidemics. This objective is achieved by combining both the weekly collection of virological data as well as the collection of other available indicators either in routine practice or as provided by a network of sentinel practitioners. Such detection can pave the way for an improvement in preventive measures against the harmful effects on health of influenza epidemics.

The prophylactic effectiveness of rimantadine hydrochloride (RH) during an outbreak of influenza A was evaluated in a double-blind study versus placebo (P). After identification of 111 homes with one affected member, 301 household contacts were enrolled and given either RH (151 contacts from 56 households) or a placebo (150 contacts from 55 households). Each treatment was given for ten days. Overall, at least one contact developed influenza in 8 of the 56 RH group households and 19 of the 55 placebo group households (p = 0.013). Numbers of contacts who developed influenza were 8/151 in the RH group and 26/150 in the placebo group. When only the 49 homes where influenza was confirmed by virological studies were considered, these numbers were 4/28 in the RH group and 10/21 in the placebo group (p = 0.011). Adverse effects were seen in 18 of the 151 subjects given RH (11.9 per cent) and 6 of the 150 subjects given the placebo (4 per cent). RH appeared as an effective prophylactic agent in a confirmed influenza A outbreak and was satisfactorily tolerated.

Attempts at virus isolation from cloacal swabs resulted in the recovery of 10 strains of hemagglutinating viruses from a total of 349 ducks, mainly shelducks (Tadorna tadorna) captured in the north of France. Four of these isolates were identified as influenza strains corresponding to the following antigenic composition: Hav6-N2, Hav6-Nav4 and Hav1-N2 (2 strains). Shelduck is known to be a partially migratory species, wintering in western Europe, some of them migrating northward to Scandinavia during the summer. The captures were made between November 1976 and February 1977: one of the birds was caught four times and was found to be negative for virus in November, positive in December (isolation of a strain Hav6-Nav4), negative again in January and February. Blood taken in February did not show the presence of HI antibodies to the homologous virus.

Experimental inactivated influenza vaccines prepared with strain X 53, derived from A/New Jersey/76 virus were injected to several groups of subjects. Different compositions of vaccine were used and the subjects were selected from different age groups. Antibody responses were measured 15 days after vaccination; it was then possible to evaluate the conversion rates, the percentages of subjects showing a protective level of antibodies and the average level of antibodies. The results show that a very small dose of antigen, probably acting as a booster, gives very good results in the older age group. On the other hand, young adults (below 23) react to a much lower degree to the vaccine. The results are discussed in relation to the age distribution of preexisting antibodies in the experimental groups and in the general population in France.

The aims of influenza surveillance have changed over the years. The early detection of epidemics is essential for practical decisions on vaccine development, strategy of vaccine prophylaxis, chemoprophylaxis or chemotherapy. A new surveillance system is presented which combines the classical specific data related to the isolations, direct detection of virus as well as serological findings, with non-specific indices. The rationale for definition and elaboration of such indices is discussed: selected parameters deal with medical activity of a panel of sentinel doctors (general practitioners and pediatricians), notifications of diagnosed acute respiratory viral infections, measure of emergency doctors activity, absence from work (as seen by physicians, insurance agencies or industrial personnel), selected drug prescription and consumption, hospital admissions. The sentinel physicians also cooperate in taking samples from cases, thereby extending the field of specific surveillance since they have contact with standard cases of the disease and not only hospitalized patients. A weekly comparison of time variations of specific and non-specific indices should permit a reliable evaluation of the epidemic situation and therefore be of great help for practical decisions. The system has operated since 1984, and the initial hypothesis of the sensitivity of some of the indices has already been verified.

The evaluation of morbidity risk is difficult in influenza because of a lack of accurate quantitative information and of a high variability of the virus. The level of specific herd immunity towards epidemic strains is an important factor of prevision. As far as mortality is concerned, there is a net and regular increase of risk up from the age of 45. In addition to elderly, other high risk categories are known such as patients suffering of a number of organic deficiences or chronical conditions, pregnant women and children. The best evaluation of efficacy of vaccines is the study of incidence reduction in a vaccinated group in comparison to unvaccinated controls. Present vaccines are really efficient to reduce the risk of getting the disease, except in the case of an antigenic shift, which means the activity of a new antigenic component. These advantages are to be weighted to the small risk of vaccine reactions, which are not frequent and usually benign. Several vaccination strategies can be used. In France, it has been decided to recommand vaccine to priority groups: people over 65 and deficient patients. This policy is eqlivalent in many western countries (West Europe, USA); it is not efficient in preventing or delaying epidemics.

The collection of data for influenza surveillance is difficult because clinical cases cannot easily be notified by practitioners and because only a few cases are studied by specific biological methods. In different countries, several indices are used such as: morbidity returns, mortality returns, absenteeism returns preferably in combination. In France, the two National Reference Centres in Paris and Lyon coordinate the activities of all diagnostic laboratories where influenza is detected by collecting and redistributing their findings and by identifying the strains they isolate. Furthermore, a collaborative network of physicians and institutions is being organised to provide a complete coverage of the country. I.N.S.E.R.M. and the National Centres have set up during the last two winters a new method of specific surveillance in school children: it combines observation of absenteeism peak in randomly selected classes and etiologic diagnosis by virus isolation. Surveillance of such a group, particularly sensitive to epidemic spread and probably partly responsible for it, was very efficient: early isolations were obtained and the presence of epidemics was detected before overt outbreaks occurred.

Influenza virus demonstrates several levels of antigenic variations, drifts and shifts, which help it to escape to herd immunity pressures. Recent examples show the importance of such variations in the succession and continuity of epidemiological manifestations. During the last few years, simultaneous circulation of several subtypes of influenza A was observed while in the past, one subtype was replacing the other. Thus in 1981, for the only subtype H3N2, A/Texas, A/Bangkok and A/intermediate Texas-Bangkok viruses were isolated in France at the same time in several foci. Furthermore, double infection with different subtypes in the same individual have been documented in man as well as in animals (birds). Related strains have also been isolated simultaneously in the same individual and cloning by plaque analysis makes it possible to evaluate easily this possibility in wild strains. The unexpected frequency of double infections or of variations of virus in feral animals or humans increases the possibility of genetic reassortments and participates for an important part to global variability of the virus.

I.--After showing that bank voles are parasited only by Ixodes ricinus larvae, the authors attempt to found different factors (demographic, biometric, and sexual) who favor individual parasitism. The authors conclude to absent of anti tick immunity for this rodent specie. II.--The search for anti-central european encephalitis antibodies (I.H.A.) are shown that 2 p. cent animals were immuns. Yearly and monthly chronologies of antibodies apparition are shown, factors favoring the growth of specific Central european encephalitis antibodies are discussed. III.--The Central european encephalitis tick viral infection of bank vole is studied according to the number of viral strains isolated from different viscera. The monthly chronology of this infection is shown.