Serological studies on infections by respiratory viruses of the inhabitants of Tristan da Cunha

The role of host genetics in susceptibility to influenza: a systematic review

Background

The World Health Organization has identified studies of the role of host genetics on susceptibility to severe influenza as a priority. A systematic review was conducted to summarize the current state of evidence on the role of host genetics in susceptibility to influenza (PROSPERO registration number: CRD42011001380).

Methods and Findings

PubMed, Web of Science, the Cochrane Library, and OpenSIGLE were searched using a pre-defined strategy for all entries up to the date of the search. Two reviewers independently screened the title and abstract of 1,371 unique articles, and 72 full text publications were selected for inclusion. Mouse models clearly demonstrate that host genetics plays a critical role in susceptibility to a range of human and avian influenza viruses. The Mx genes encoding interferon inducible proteins are the best studied but their relevance to susceptibility in humans is unknown. Although the MxA gene should be considered a candidate gene for further study in humans, over 100 other candidate genes have been proposed. There are however no data associating any of these candidate genes to susceptibility in humans, with the only published study in humans being under-powered. One genealogy study presents moderate evidence of a heritable component to the risk of influenza-associated death, and while the marked familial aggregation of H5N1 cases is suggestive of host genetic factors, this remains unproven.

Conclusion

The fundamental question “Is susceptibility to severe influenza in humans heritable?” remains unanswered. Not because of a lack of genotyping or analytic tools, nor because of insufficient severe influenza cases, but because of the absence of a coordinated effort to define and assemble cohorts of cases. The recent pandemic and the ongoing epizootic of H5N1 both represent rapidly closing windows of opportunity to increase understanding of the pathogenesis of severe influenza through multi-national host genetic studies.

Explaining rapid reinfections in multiple-wave influenza outbreaks: Tristan da Cunha 1971 epidemic as a case study

Influenza usually spreads through the human population in multiple-wave outbreaks. Successive reinfection of individuals over a short time interval has been explicitly reported during past pandemics. However, the causes of rapid reinfection and the role of reinfection in driving multiple-wave outbreaks remain poorly understood. To investigate these issues, we focus on a two-wave influenza A/H3N2 epidemic that occurred on the remote island of Tristan da Cunha in 1971. Over 59 days, 273 (96%) of 284 islanders experienced at least one attack and 92 (32%) experienced two attacks. We formulate six mathematical models invoking a variety of antigenic and immunological reinfection mechanisms. Using a maximum-likelihood analysis to confront model predictions with the reported incidence time series, we demonstrate that only two mechanisms can be retained: some hosts with either a delayed or deficient humoral immune response to the primary influenza infection were reinfected by the same strain, thus initiating the second epidemic wave. Both mechanisms are supported by previous empirical studies and may arise from a combination of genetic and ecological causes. We advocate that a better understanding and account of heterogeneity in the human immune response are essential to analysis of multiple-wave influenza outbreaks and pandemic planning.

Aspects of infection in isolated communities

Respiratory viruses are not generally carried by normal subjects and cannot persist in small isolated communities. When infection does occur epidemics are seen and the illness may be more severe than in the outside world. These points are illustrated by reference to studies on the island of Tristan da Cunha and stations of the British Antarctic Survey.

Does previous infection protect against atopic eczema and recurrent wheeze in infancy?

BACKGROUND

Frequent infection in infancy and early childhood has been hypothesized to explain the low prevalence of asthma and other atopic disease among children in developing countries (the so-called 'hygiene hypothesis'), but the low prevalence in Eastern Europe remains unexplained.

OBJECTIVE

To test the hygiene hypothesis in the Republic of Belarus by examining the relationship between gastrointestinal (GI) and respiratory infection and two potentially atopic outcomes in the first 12 months of life: atopic eczema and recurrent wheeze. METHODS; We carried out two case-control studies nested within a large (n=17 046) randomized trial in Belarus, with cases defined as (1) first occurrence of atopic eczema (n=819) and (2) second episode of wheezing (n=112). Incidence density sampling was used to select four matched controls born within 1 month at the same hospital as the case. Exposure was defined as one or more episodes of GI or respiratory infection (examined separately) with onset >7 days before onset of the case's atopic outcome. Analyses controlled for family atopic history, duration of exclusive breastfeeding, sex, birth weight, maternal education, and (for recurrent wheeze) maternal smoking.

RESULTS

For atopic eczema, prior GI infection occurred in 7.4% of cases vs. 6.0% of controls [adjusted OR=1.27 (0.94-1.72)] and prior respiratory infection in 35.2% vs. 32.6% [adjusted OR=1.14 (95% CI=0.94-1.37)]. For recurrent wheeze, prior GI infection occurred in 9.8% of cases vs. 7.4% of controls [adjusted OR=1.30 (0.60-2.82)].

CONCLUSION

Our results do not support the hypothesis that infection protects against atopic eczema or recurrent wheezing in the first 12 months of life.

Asthma and atopy - the price of affluence?

Irrespective of improved knowledge of many aspects of atopic diseases, the unfavorable trends in their prevalence particularly among children could not have been reversed. A growing body of evidence suggests that something may lack from our societal affluence that has the capacity to provide protection against the development of atopic diseases. Much attention during the last years has been devoted to the hygiene hypothesis. This review outlines the impact of environment and lifestyle, particularly from the perspective of the East-West gradient, on the development of atopic diseases, with a special emphasis on the hygiene hypothesis in its broadest sense.

Prevalence of the antibody to influenza C virus in a northern Luzon Highland Village, Philippines

A total of 101 serum samples were collected from the persons (1 to 85 years of age) living in a Philippine mountain village where the contact with other communities has largely been restricted. These sera were tested for the presence of antibody to influenza C virus with hemagglutination-inhibition and radioimmuno-precipitation tests. The results showed that all the subjects, including the persons who had never been outside the village, contained the antibody to the surface glycoprotein of the virus, and that the age of acquisition of the antibody was significantly lower in this village than in any of the previously studied communities. Thus it appeared that infection with influenza C virus was prevalent even in this small mountain village, presumably with a higher incidence than in the larger, industrialized communities.

Prevalence of antibody against influenza A viruses in the Kren-Akorore, an Indian tribe of Central Brazil, first contacted in 1973

Influenza A antibodies in serum samples obtained in 1980 from two Indian populations in Central Brazil were compared. The Kren-Akorore, who were first contacted in 1973 and two years later transferred to the Xingu Indian Park (PIX), were compared with Indians from other tribes already living in the PIX before 1975. An analysis was made of the prevalence and distribution of antibodies against the influenza A viruses which have circulated in the civilized world since 1918. Antibodies to the early influenza A viruses were absent in both Indian populations, but A/Hong Kong/1/68 (H3N2) virus apparently circulated in the PIX. No antibody to influenza A/Bangkok/1/79 or to A/Brazil/11/78 (H1N1) was found in any of the sera, whereas antibodies to these viruses were commonly found in urban populations in Brazil. The evidence from influenza antibodies agrees with the information that the Kren-Akorore Indians had been living in complete isolation until 1973, when they were first contacted.

Respiratory virus infections in travellers

Respiratory viruses affect travellers, but the main significance of this is probably that it is in this way that the viruses reach new hosts and thus survive as infectious agents.

Lymphocyte reactivity to influenza virus in man

Dermal delayed hypersensitivity and in vitro lymphocyte reactivity, both to purified influenza antigens, have been observed in man. A correlation between these two indices of delayed hypersensitivity was found in subjects without known recent exposure to the virus, but neither correlated with levels of circulating haemagglutination-inhibiting (HAI) antibody. Results suggest that in man immunological sensitization of lymphocytes to influenza virus antigen is long-lived.

Use of single radial immunodiffusion test for serological studies in volunteers inoculated with live attenuated influenza virus

Pre- and post-vaccination serum samples from 278 volunteers, who were given live influenza vaccines, were tested by haemagglutination inhibition (HI) and single radial immunodiffusion tests(SRDT) for antibody to influenza A/Hong Kong/1/68 (H3N2) virus envelope antigens. Those with high antibody titres detected in both tests were less frequently infected, and 85% of the 159 infected showed rises by HI and 70% by SRDT. Similarly, 69 pairs were tested for antibody to Hong Kong (N2) neuraminidase by neuraminidase inhibition test (NI) and by SRD tests. Those with high titres in both tests resisted infection and those who were infected showed a rise in antibody detected both by NI and SRD tests. In general, SRDT was less sensitive than HI and NI in detecting antibody and antibody rises, but in some volunteers it did detect antibody rises which were not detected by conventional tests. Because of its simplicity and speed it appeared to be of use in evaluating such vaccines.

Skin tests with influenza virus

Skin reactions have been produced in normal subjects by the injection of highly purified influenza A and B viruses. The reactions reached a maximum at 24-48 hr. and the histological pattern was compatible with a delayed hypersensitivity reaction. There was no close relation between skin test results and circulating antibodies. Twenty-seven subjects were challenged intranasally with attenuated influenza A (H3N2): 5 of 14 skin-test-negative subjects were infected, but none of 13 skin-test-positive subjects.

An epidemic of influenza on Tristan da Cunha

Respiratory disease on Tristan da Cunha has been observed since the islanders returned in 1962. An epidemic of unprecedented severity occurred in the winter of 1971 and involved 273 (96%) of 284 islanders, 92 of whom had two attacks.The epidemic was apparently introduced by the Tristania.The illness of both first and second attacks ranged from mild to severe but there were some differences. There were two deaths, both in elderly persons with chronic chest disease and heart failure. Serological evidence suggests that this was due to influenza A2 of the Hong Kong serotype H(3)N(2).

Common colds on Tristan da Cunha

Eight epidemics of respiratory disease have been observed among islanders of Tristan da Cunha. They seem to be initiated by the arrival of ships and transmission seemed to occur as a result of close human contact but could not always be traced. Islanders suffered from less colds than those in less isolated communities.

Antibodies of influenza viruses in military recruits from Argentina, Brazil and Colombia. Their relation to ABO blood group distribution

In a large-scale seroepidemiological study, the prevalence was determined of antibodies to influenza A viruses in the sera of military representative of the inhabited geographical regions of Argentina, Brazil and Colombia. The micro-haemagglutination-inhibition test was used against the Swine, PR/8, FM/1 and Asian antigenic strains. From each of the three recruit populations 500 sera were tested.Positive titres to the FM/1 and Asian strains were found in 72% and 80% respectively of the Colombian sera, in 56% and 69% of the Argentinian sera, and in 49% and 63% of the Brazilian sera. Of these 1500 sera, 5 were positive to the PR/8 strain and 2 to the Swine strain.This study also showed that there were highly significantly greater proportions of positive reactors to the FM/1 and Asian strains among persons of blood groups O and B than among those of blood group A in all three countries.

Antibody against influenza A2 virus neuraminidase in human sera

1. High titres of neuraminidase-inhibiting antibody were detected in convalescent human sera following natural influenza A2 infections.

2. Such antibody was encountered infrequently in acute serum samples. Antibody persisted only 5–6 months after infection in the four individuals from whom serial serum specimens were available.

3. Following immunization with killed influenza virus vaccines (with adjuvant) neuraminidase inhibiting antibody was detected in human sera. The titres were in general lower than those detected in convalescent human sera.

4. The specificity of the neuraminidase-inhibiting antibody in human and animal antisera was studied. Tests with convalescent human sera using purified neuraminidase preparations and with a recombinant virus containing A2 neuraminidase and haemagglutinin distinct from that of human influenza A viruses enabled the conclusion that the antibody detected was specific for influenza A 2 neuraminidase.

We wish to thank Dr D. A. J. Tyrrell of the Clinical Research Centre, Mill Hill, London, for human serum specimens, Dr D. Breeze of Evans Medical Ltd., Liverpool, for sera from an influenza vaccine trial and Dr M. S. Pereira of the Public Health Laboratory, Colindale, London, for serial serum samples from persons who had influenza in 1957. Dr M. S. Pereira carried out the haemagglutination-inhibition tests and complement fixation tests on these sera.

We are grateful to Dr H. G. Pereira and Dr D. A. J. Tyrrell for valuable discussions during the course of this study, and to Professor C. H. Stuart-Harris for his comments on the manuscript.