The spread of influenza; evidence from 1950-1951

Predictors of human-infective RNA virus discovery in the United States, China, and Africa, an ecological study

Background

The variation in the pathogen type as well as the spatial heterogeneity of predictors make the generality of any associations with pathogen discovery debatable. Our previous work confirmed that the association of a group of predictors differed across different types of RNA viruses, yet there have been no previous comparisons of the specific predictors for RNA virus discovery in different regions. The aim of the current study was to close the gap by investigating whether predictors of discovery rates within three regions-the United States, China, and Africa-differ from one another and from those at the global level.

Methods

Based on a comprehensive list of human-infective RNA viruses, we collated published data on first discovery of each species in each region. We used a Poisson boosted regression tree (BRT) model to examine the relationship between virus discovery and 33 predictors representing climate, socio-economics, land use, and biodiversity across each region separately. The discovery probability in three regions in 2010-2019 was mapped using the fitted models and historical predictors.

Results

The numbers of human-infective virus species discovered in the United States, China, and Africa up to 2019 were 95, 80, and 107 respectively, with China lagging behind the other two regions. In each region, discoveries were clustered in hotspots. BRT modelling suggested that in all three regions RNA virus discovery was better predicted by land use and socio-economic variables than climatic variables and biodiversity, although the relative importance of these predictors varied by region. Map of virus discovery probability in 2010-2019 indicated several new hotspots outside historical high-risk areas. Most new virus species since 2010 in each region (6/6 in the United States, 19/19 in China, 12/19 in Africa) were discovered in high-risk areas as predicted by our model.

Conclusions

The drivers of spatiotemporal variation in virus discovery rates vary in different regions of the world. Within regions virus discovery is driven mainly by land-use and socio-economic variables; climate and biodiversity variables are consistently less important predictors than at a global scale. Potential new discovery hotspots in 2010-2019 are identified. Results from the study could guide active surveillance for new human-infective viruses in local high-risk areas.

Funding

FFZ is funded by the Darwin Trust of Edinburgh (https://darwintrust.bio.ed.ac.uk/). MEJW has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No. 874735 (VEO) (https://www.veo-europe.eu/).

Effect of priming with H1N1 influenza viruses of variable antigenic distances on challenge with 2009 pandemic H1N1 virus

Compared to seasonal influenza viruses, the 2009 pandemic H1N1 (pH1N1) virus caused greater morbidity and mortality in children and young adults. People over 60 years of age showed a higher prevalence of cross-reactive pH1N1 antibodies, suggesting that they were previously exposed to an influenza virus or vaccine that was antigenically related to the pH1N1 virus. To define the basis for this cross-reactivity, ferrets were infected with H1N1 viruses of variable antigenic distance that circulated during different decades from the 1930s (Alaska/35), 1940s (Fort Monmouth/47), 1950s (Fort Warren/50), and 1990s (New Caledonia/99) and challenged with 2009 pH1N1 virus 6 weeks later. Ferrets primed with the homologous CA/09 or New Jersey/76 (NJ/76) virus served as a positive control, while the negative control was an influenza B virus that should not cross-protect against influenza A virus infection. Significant protection against challenge virus replication in the respiratory tract was observed in ferrets primed with AK/35, FM/47, and NJ/76; FW/50-primed ferrets showed reduced protection, and NC/99-primed ferrets were not protected. The hemagglutinins (HAs) of AK/35, FM/47, and FW/50 differ in the presence of glycosylation sites. We found that the loss of protective efficacy observed with FW/50 was associated with the presence of a specific glycosylation site. Our results suggest that changes in the HA occurred between 1947 and 1950, such that prior infection could no longer protect against 2009 pH1N1 infection. This provides a mechanistic understanding of the nature of serological cross-protection observed in people over 60 years of age during the 2009 H1N1 pandemic.

INDICATIONS OF HEREDITARY, SPATIAL REARRANGEMENT OF ANTIGEN COMPLEXES, IN THE INFLUENZA VIRUS

During passage in mice which had been vaccinated with the homologous, and with closely related strains of influenza virus, the passage strain developed a lessened susceptibility to the deleterious effects of the "immune" environment, concommittant with which was a developed capacity to evoke antibodies which reacted with earlier strains of virus—a capacity which was inapparent in the parent strain. However, the parent strain exhibited a relatively broad range of surface reactivity which was not apparent in the derived strain. The data are interpreted to mean that the hereditary change resulted from spatial rearrangement and quantitative redistribution of antigens in the virus particle (in which the surface is viewed as being distinct from the inner bulk), and are viewed as enhancing the idea that influenza virus variation (i.e., "mutation") may result from a rearrangement of existing hereditary elements.

1951 influenza epidemic, England and Wales, Canada, and the United States

Death rates were substantially higher for England and Canada than for the United States.

Influenza poses a continuing public health threat in epidemic and pandemic seasons. The 1951 influenza epidemic (A/H1N1) caused an unusually high death toll in England; in particular, weekly deaths in Liverpool even surpassed those of the 1918 pandemic. We further quantified the death rate of the 1951 epidemic in 3 countries. In England and Canada, we found that excess death rates from pneumonia and influenza and all causes were substantially higher for the 1951 epidemic than for the 1957 and 1968 pandemics (by >50%). The age-specific pattern of deaths in 1951 was consistent with that of other interpandemic seasons; no age shift to younger age groups, reminiscent of pandemics, occurred in the death rate. In contrast to England and Canada, the 1951 epidemic was not particularly severe in the United States. Why this epidemic was so severe in some areas but not others remains unknown and highlights major gaps in our understanding of interpandemic influenza.

The return of the historic influenza A H1N1 virus and its impact on the population of the United Kingdom

The epidemiology in the United Kingdom of the influenza A H1N1 subtype which returned in 1977 after an absence of 20 years in described for the four winter seasons from 1977/8 to 1980/1. The age distribution of virus isolates and the evidence for antigenic variation is presented. The impact in the susceptible age groups year by year is shown by the change in the population with specific antibody. There was the expected increase of antibody in those under the age of 21 but also evidence for a significant amount of infection or re-infection in the older adult population.

Rapid subtyping of influenza A virus isolates by membrane fluorescence

During the winter of 1977-1978 three influenza A virus serotypes (A/Vic/3/75, A/Texas/1/77 [both H3N2], and A/USSR/90/77 [H1N1]) circulated in Denver, offering us the opportunity to apply fluorescent antibody techniques to the specific identification of these viruses. Surface antigens of infected, unfixed primary monkey kidney cells were stained in suspension by an indirect immunofluorescence technique with anti-H3N2 and anti-H1N1 antisera. In tests of cells infected with known viruses, the members of the H3N2 family could not be distinguished from one another, but were easily distinguished from H1N1 strains. A total of 101 hemadsorption-positive clinical specimens were evaluated over a 6-month period. Forty-five of 48 influenza A H3N2 and 24 of 29 H1N1 specimens confirmed by hemagglutination inhibition were correctly identified by membrane fluorescence of cultured cells, with no misidentifications among influenza strains and with 1 false positive among 24 non-influenza isolates. The average time to identification by this technique was 4 days compared to 7 days by hemagglutination inhibition. Live cell membrane fluorescence is a simple, rapid, and accurate method for identifying and grouping influenza A viruses.

Influenza viruses, 1957-60

During the period 1957-60 large numbers of influenza A viruses were received at the World Influenza Centre from countries throughout the world. With one exception all the strains were antigenically closely related to the A2 viruses isolated early in the Asian influenza epidemic, and strikingly different from the A1 strains of the previous decade. The A2 viruses were very uniform antigenically and in other in vitro characteristics such as insensitivity to the beta-inhibitor of agglutination. However, many of the strains, particularly during the early stages of the epidemic, showed a low avidity for antibody.At the same time as the influenza A viruses showed a large antigenic change the influenza B viruses showed a lesser antigenic change from earlier influenza B viruses. As with influenza A, the new influenza B viruses have replaced earlier B strains.In 1960 one strain of influenza virus A1 was recovered from a soldier in England. Evidence is presented that this could not be explained as a laboratory pick-up and the suggestion is put forward that this patient may have harboured virus in latent form for many years.

The influenza virus flocculation reaction as a method of antigenic typing

The influenza virus serum flocculation previously reported (Belyavin, 1955) opened up a number of lines of investigation. One of obvious importance was extension of the reaction to other viruses belonging to both related and unrelated groups. Indeed, other workers in this laboratory have already achieved the flocculation of poliomyelitis viruses by specific antisera (Smith, Sheffield, Lee & Churcher, 1956) and flocculation of both mumps and Newcastle disease viruses is now reported in this communication. The ease with which the viruses of the mumps-influenza group can be flocculated by homologous rabbit antisera suggested that the technique may be applicable as a method of antigenic analysis. If so, it would have the advantage of being much simpler than the standard haemagglutination inhibition and complement-fixation tests. The exploration of this possibility forms the basis of this paper. A large-scale antigenic survey involving numerous virus strains has not been attempted, greater emphasis being placed on the examination of techniques and their applicability to the end in view. The investigation has also revealed new phenomena peculiar to the direct virus flocculation reaction.

Propagation of influenza virus in immune environments

INFLUENZA VIRUS CAN SURVIVE, AND CAN BE PROPAGATED IN IMMUNOLOGICAL ENVIRONMENTS INDUCED IN MICE BY VACCINATION WITH THE HOMOLOGOUS STRAIN OF VIRUS: survival was associated with the emergence of variants which differed from the parent strain in antigenic characteristics. The data concerning hemagglutinating activity of the variants, on the one hand, and of the antigenicity, on the other, are compatible with the concept that the structure of the influenza virus includes a surface arrangement which is distinct from the inner virus bulk. The points (a) that propagation was accomplished with difficulty whenever the immunological environment was altered, and (b) that once established, passage was continued without difficulty, are interpreted to indicate that the mechanism of variation may involve a rearrangement of the basic hereditary mechanism.

Serological studies during the 1953 epidemic of influenza A in New York state

A number of workers have shown that antibodies to the influenza A viruses which are demonstrable in the sera of normal adults undergo periodic fluctuations in titre related to epidemic occurrence of the disease. The rise in antibodies accompanying infection and demonstrable by neutralization, agglutination-inhibition and complement-fixation tests is used as a method of diagnosis which is admitted to be of greater sensitivity than actual recovery of virus from the throat. Studies of the population during an epidemic have also revealed the existence of subclinical infection with rise in antibodies comparable to that occurring in those suffering clinical illnesses. But surveys of sera from large samples of the population show no general upward shift in antibody levels unless an actual epidemic occurs (Martin, 1940). The studies made by Francis, Magill, Rickard & Beck (1937), Hoyle & Fairbrother (1937), Rickard, Lennette & Horsfall (1940) and Martin (1940) also indicate the relative impermanence of the enhanced antibody levels consequent upon an epidemic. A relatively rapid decrease in antibody is shown both by the neutralization and complement-fixation tests during the 3–6 months after an epidemic and then a slower fall occurs until the next epidemic again causes a rise in titres. There have, however, been relatively few studies on large samples of populations situated in different geographical areas before and during an outbreak.

A method for influenza antibody absorption

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The influenza virus: its morphology, immunology, and kinetics of multiplication

The morphology of influenza virus is described, and the properties of its two components, the elementary body and the soluble substance, differentiated. The relationship between the filamentous and spherical structures observed in the infected allantoic fluid is still obscure, but the filaments are thought to represent either a form of influenza virus or a stage in its multiplication.The antigenic constitution of A and B viruses is discussed and variations in the pattern of individual strains over the past two decades described. The author outlines his speculations on the origin and mechanism of these variations. Other differences in serological behaviour, such as non-specific inhibition and the avidity effect, are discussed.The results of experimental investigation, with various animal hosts, of the kinetics of influenza virus multiplication are reviewed, and the effects of such factors as incubation temperature and concentration of the seed virus considered. The bearing of these studies of enzymatic virus/host-cell interactions on the chemotherapeutic control of influenza is emphasized.

Epidemiology of influenza

The epidemiological pattern of influenza over the past century is outlined; its vagaries are ascribed to the plasticity of the influenza virus. In recent years it has been possible to carry out antigenic studies revealing variations in the strains of virus A, the agent in most major outbreaks. New antigenic variants may have a greater chance to emerge after periods of latency, since the exposed population will have less specific resistance to them. Work on the causation and spread of epidemics is reviewed; the conclusion these studies suggest is that two factors are involved-the existence of a "basic virus", as yet undetectable until activated, and responsible for multicentric outbreaks; and the element of "spread", which under favourable conditions carries the infection to susceptible groups, and results in extensive epidemics.

Strain-specific elements in influenza antigens

Rabbit antisera were prepared against ten antigenically different influenza A strains. These sera were absorbed with one or more heterologous strains and in each case all the heterologous or crossing antibody was removed; the anti-bodies remaining after this treatment were specific for the immunizing strain or group of strains. On the basis of reactions with absorbed sera, the strains fell into seven groups. Absorbed specific antisera of these groups were used to test the HI titer against a large number of influenza A viruses. Most of the strains were inhibited by a single serum, a few were inhibited by none of the sera, and only one strain was inhibited by two antisera. The grouping of strains by this method was less equivocal than classifications based on previous tests. When more fully developed, this technique promises to be of interest and assistance in the study of influenza, especially from the epidemiological and prophylactic standpoints.