Influenza virus migrations – a lesson from 1961

Influenza A viruses carried by birds

I have been doing quite a lot of digging into virus history recently, and it was interesting to pick up – while checking on who had published what from our University on viruses – a paper from 1966 describing “The isolation and classification of Tern virus: Influenza Virus A/Tern/South Africa/1961″ by WB Becker of the Virus Research Unit here at UCT.  It is interesting because it was isolated from sick migratory Common Terns along the south coast of South Africa, which were infected as part of an “explosive epizootic” which resulted in many deaths.  It became more interesting when it was shown in 1967 to cause few or no symptoms in Swift Terns but was shed in large amounts, to be highly pathogenic in chickens, and was subsequently typed as H5N3.

The discussion of the original paper was not only highly prescient, but may be completely valid today: a significant quote follows.

The isolation of Tern virus raises interesting epidemiological possibilities. The outbreak in chickens in Scotland caused by Chicken/Scot. virus preceded the Tern epizootic by about 17 months and occurred during stormy weather which drove sea-birds a little inland to take shelter. Large numbers ofHerring Gulls (Larus argentatus) were at that time working thef arm at which the out break in chickens occurred in November 1959 (J. E. Wilson, personal communication). The chickens might have contracted the infection from sea-birds, a viewpoint possibly supported by the preceding mass mortality in Kittiwakes (Rissa tridactyla) and Fulmars (Fulmaris glacialis) from February to August 1959 (Joensen, 1959) off the coast of Britain and Scandinavia. Unfortunately the aetiology of the last-mentioned outbreak was not investigated, but it is tempting to think it was caused by the Tern virus which was isolated at Cape Town some 18 months later in 1961, from migrant European Common Terns.

One might postulate: that certain sea-birds suffer latent or sporadic infection with avian influenza; that epizootics may be precipitated in them by conditions of stress, e.g. poor feeding under unfavourable weather conditions such as pre- ceded the Tern epizootic; and that spread to other sea-birds or domestic poultry may occur. [my emphases – Ed]

The 1967 tern infection paper continues this theme:

The outbreak in chickens in Scotland in 1959 (Dr J. E. Wilson, personal communication) and the Tern epizootic in 1961 were caused by influenza A viruses with closely related strain specific antigens which were unrelated to those of any previously known influenza A viruses. Recently strains of influenza A related to the Tern and Scottish viruses were isolated from turkeys in Canada (Dr G.Lang, personal communication). This lends further support to the hypothesis that migrating sea-birds such as the Common Tern may transmit avian influenza A viruses to domestic poultry.

This was followed up more recently (2002) by a paper describing transmission of the tern virus to laughing gulls:

This investigation detailed the clinical disease, gross and histologic lesions, and distribution of viral antigen in juvenile laughing gulls (Larus atricilla) intranasally inoculated with either the A/tern/South Africa/61 (H5N3) (tern/SA) influenza virus or the A/chicken/Hong Kong/220/97 (H5N1) (chicken/HK) influenza virus, which are both highly pathogenic for chickens. Neither morbidity nor mortality was observed in gulls inoculated with either virus within the 14-day investigative period. Gross lesions resultant from infection with either virus were only mild…. Antibodies to influenza viruses …at 14 DPI were detected only in the two tern/SA-inoculated gulls and not in the two chicken/HK-inoculated gulls.

Their conclusions, too, were rather disturbing:

The positive isolation of the tern/SA and chicken/HK viruses from the OP and cloacal swabs suggests that, with adequate exposure, gulls could serve as hosts for these and possibly other HPAI viruses. Isolation of the A/gull/Germany/79 (H7N7) virus during a HPAI outbreak in Eastern Europe provides further evidence to support the potential for pelagic birds to serve as biological vectors for (HP)AI viruses (D. J. Alexander, pers. comm., originally referenced in 29). This is a significant finding in terms of the epidemiology of AI viruses, especially considering the fact that the chicken/HK virus was a zoonosis (26,27). Moreover, pelagic birds have been implicated as the source for other AI viruses that transmitted to and may have caused disease in mammals (8,13).

Everybody is obsessed with H5N1: maybe we should be a little more concerned with what may be raining down from above, as seabirds carry recombinant / reassortant viruses from areas of high H5N1 endemicity around the world.



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