The role of wild birds in the spread of influenza viruses.

Eggs deposited by different migrating wild bird species in pond farm areas in Hungary were examined for yolk antibodies to different variants of human A/H3N2 influenza virus. Antibodies to Victoria/75 and Texas/77 occurred in 17.9 and 32.0% of gull eggs, and 5.6 and 16.4% of common tern eggs, respectively, while antibodies to A/H1N1/77 occurred in roughly similar proportions (10.2 and 13.4%) in the eggs of both species. Infection of the gull and tern populations of given areas by human and avian influenza A viruses differed greatly in two consecutive hatching periods. While in 1978 7.6 and 1.1% of the gull and tern eggs, respectively, contained antibodies to the avian subtype Havl, no such antibodies were found in 1977. Subtype A/H3N2/Texas/77 virus was isolated from adult gulls and 1-3 weeks old gull chicks, and subtype H1N1 virus from mallard ducks. Three months before the onset of the Texas/77 epidemic, 95% of SPF chickens, and 71-81% of chickens hatched 3 months after termination of the A/H1N1/77 epidemic, had had HI, VN and SRH antibodies to the Texas/77 strain and A/H1N1/77 strains, respectively.

Susceptibility of birds to type-B influenza virus.

Among Zoo birds and migrating wild birds examined serologically during an outbreak due to influenza B virus, 4.1% were found to have serum antibodies to the agent. Evidence of avian susceptibility to the agent was emerging from reisolations of the virus and primary and secondary HI antibody response of the birds in subsequent infection experiments performed on adult pheasants and mallards, as well as one-day-old domestic ducklings and chicks. The virus persisted in the pheasants for at least three weeks, and adult pheasants, mallards and domestic ducklings were found to transmit it by contact to part of their susceptible mates.

Adaptation of the influenza neuraminidase and neuraminidase-inhibition assays to the microtitrator system.

A micro-method based on Warren's colour reaction has been developed for influenza neuraminidase and neuraminidase-inhibition assays. Extraction with butanol is omitted and the assay is performed in wells of special plexiglass trays, where the reaction mixon and compared to controls in the same tray. The micro-assay, being inexpensive, time-saving and easy to perform even in poorly equipped laboratories, is suitable for large-scale serological screening and identification of the neuraminidase antigen of isolates.

Antigenic analysis of prototype influenza A (H3N2) strains by the antiserum absorption method.

Prototype strains of the influenza A (H3N2) virus can be arranged on a gradient showing the degree of the antigenic drift which the haemagglutinins of the strains have undergone. The demonstration of fine antigenic differences is based on an antiserum absorption test which allows a detailed antigenic analysis of strains. The gradient provides information on variation in strains occurring in different geographical areas and its use may be helpful in differentiating between introduced strains and locally developing variants.

Unusual features of the 1971 influenza epidemic in Hungary and the antigen analysis of the isolates by a serum adsorption test.

In Hungary the 1971 influenza epidemic, unlike earlier influenza A2 epidemics, started unusually early and in 2 foci. Average morbidity (19.3%) was in the usual range but the geographical distribution of the cases was irregular. When 179 isolates were analysed antigenically with monospecific sera prepared by serum adsorption, it was found that they represented 2 clearly distinguishable variants of influenzavirus A (H3N2); 126 strains were closely related to the prototype strain A/Hong Kong/1/68, and 53 strains to the strain A/England/878/69. Adsorbed sera monospecific for closely related variants, like those employed in the present study, are recommended for use in the rapid and accurate identification of influenzavirus isolates.