A NEW TYPE OF VIRUS FROM EPIDEMIC INFLUENZA

Isolation of influenza virus in human lung embryonated fibroblast cells (MRC-5) from clinical samples

Ninety-four pharyngeal swab samples corresponding to 94 patients with suspected influenza virus infection were inoculated in Madin-Darby canine kidney (MDCK) cells, the conventional cell system for the isolation of influenza virus, and in fibroblastic human embryo lung (MRC-5) cells, a cell system less commonly used for this purpose but one frequently used in clinical virology laboratories. Both cell preparations were treated with trypsin. Influenza virus was recovered from 15% of the samples inoculated in MDCK cells and from 18% of those inoculated in MRC-5 cells. The use of MRC-5 cells can simplify the search for respiratory viruses and would assist in the rapid detection of influenza virus during new epidemics.

New aspects of influenza viruses

Influenza virus infections continue to cause substantial morbidity and mortality with a worldwide social and economic impact. The past five years have seen dramatic advances in our understanding of viral replication, evolution, and antigenic variation. Genetic analyses have clarified relationships between human and animal influenza virus strains, demonstrating the potential for the appearance of new pandemic reassortants as hemagglutinin and neuraminidase genes are exchanged in an intermediate host. Clinical trials of candidate live attenuated influenza virus vaccines have shown the cold-adapted reassortants to be a promising alternative to the currently available inactivated virus preparations. Modern molecular techniques have allowed serious consideration of new approaches to the development of antiviral agents and vaccines as the functions of the viral genes and proteins are further elucidated. The development of techniques whereby the genes of influenza viruses can be specifically altered to investigate those functions will undoubtedly accelerate the pace at which our knowledge expands.

Detection and identification of human influenza viruses by the polymerase chain reaction

A series of oligonucleotide primers are described which hybridize to conserved regions of influenza virus cDNA and prime DNA synthesis in Taq polymerase catalyzed amplification reactions (PCR). Primers were designed to hybridize as nested pairs and, following a two-step amplification, produce uniquely sized DNA fragments diagnostic for viral type and subtype. Influenza A and B matrix-protein genes and the influenza C haemagglutinin gene were targets for the type-specific primers. Subtype-specific primers targeted conserved sequences within the three haemagglutinin or two neuraminidase subtypes of different human influenza isolates. The utility of this method was demonstrated using computer search methods and by accurately amplifying DNA from a variety of influenza A, B, and C strains. Type-specific primer sets showed a broad type specificity and amplified DNA from viral strains of unknown sequence. Restriction mapping and DNA sequencing showed that fragments amplified in this manner derived from the input template, confirming the accuracy of the method and demonstrating how PCR can be used to quickly derive sufficient sequence information for analysis of viral relatedness. Subtyping primers were able to distinguish accurately between the three haemagglutinin (H1, H2, H3) and two neuraminidase (N1, N2) alleles of human influenza A isolates. Again DNA was amplified from viruses of unknown sequence confirming that most of these primer sets may prove useful as broad range subtyping reagents. In order to simplify the work associated with analysis of many samples, we have also devised a rapid method for the isolation of viral RNA and synthesis of cDNA. Using this 'mini-prep' technique, it is possible to detect, amplify, and identify picogram quantities of influenza virus in a single day, confirming that PCR provides a useful alternative to existing methods of influenza detection.

[Influenza]

Influenza is the last great uncontrolled plague of mankind. Pandemics and epidemics occur at regular time intervals. The influenza viruses are divided into the types A, B and C and show unique variability of their surface antigens (hemagglutinin and neuraminidase). Influenza viruses of type A show the largest degree of antigenic variation which, in turn, resulted in the definition of a number of subtypes, each comprising many strains. By comparison, influenza viruses of types B and C exhibit much less variation of their surface antigens. As a consequence, no subtypes but many different strains have been recognized. The degree of antigenic variation correlates with the epidemiologic significance of the virus types, type A being the most and type C the least important. Two different kinds of antigenic variation have been recognized: In the case of minor variation of one or both surface antigens, the term "antigenic drift" is employed. Antigenic drift occurs with all three types of virus, it is caused by point mutations which increase the chance of survival of mutants in the diseased host. In addition, influenza A viruses show sudden and complete changes of their surface antigens in regular time intervals, resulting in the appearance of new subtypes. This event is called "antigenic shift". The mechanisms responsible for antigenic shift are poorly understood, only. In addition to the recycling of preceding subtypes, reassortment resulting from double infection of cells with strains of human and animal origin are considered possible explanations. By use of modern DNA recombinant technology, the base sequences of a series of virus genes and, as a consequence, the amino acid sequence of the corresponding antigens have been determined. By means of monoclonal antibodies, the antigenic structure of many influenza antigens has been further elucidated. It can be expected that further research on the molecular basis of antigenic variation could finally result in an understanding of the causal mechanisms. It is an outstanding feature of the epidemiology of influenza A viruses that a family of related strains prevails for a certain period of time and disappears abruptly as a new subtype emerges.(ABSTRACT TRUNCATED AT 400 WORDS)

Severe illness with influenza B

Fifteen patients with recent influenza B infection were admitted to three Dallas hospitals in the first 11 weeks of 1977. The patients' ages ranged from five to 73 years, with a median of 18 years. Most had no significant underlying disease. The spectrum of clinical illness included postinfluenzal bacterial pneumonia (three cases), other severe chest disease (two cases), hyperpyrexia and possible rhabdomyolysis in the elderly (two cases), onset of toxemia of pregnancy, thyroid dysfunction, Stevens-Johnson syndrome, neurologic disorders (two cases), and Reye's syndrome (three cases). Two patients died. Two elderly men with high fever and weakness entered the hospital within three days of illness and two of three patients with Reye's syndrome were admitted four days after the onset of influenza, but the 11 other patients gave a history of seven to 31 days of symptoms before being hospitalized. Morbidity and mortality with influenza B are neither trivial nor restricted to debilitated hosts.

Serological studies with purified neuraminidase antigens of influenza B viruses

Neuraminidase (N) can be extracted from virus particles of influenza B strains by treatment with trypsin, in a form which is free from the viral HA and has specific immunological activity. The N antigen of B/LEE/40 behaves differently from that of 1965-6 strains in gel diffusion and enzyme inhibition tests with animal antisera raised by infection or by artificial immunization with the homologous or heterologous strains. The frequency and titres of NI antibody detected in human sera by B/LEE antigen are different from those found with antigen from B/Eng/13/65. The latter antibody appears to contribute to the effect of serum HI antibody in protecting volunteers exposed to a deliberate intranasal challenge infection of the B/Eng/13/65 strain.

Virus infections and respiratory disease of childhood

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Nasal mucus and influenza viruses. I. The haemagglutinin inhibitor in nasal secretions

A technique is developed by which minimal changes in haemagglutinin inhibitors can be detected.

It is shown that theinhibitor indexof normal human nasal secretions is 33·2 with a standard deviation of ±7·4. This value is independent of the donor, of the absolute amount of mucus collected, of the time of extraction, and of the period of storage.

Minimal amounts of influenza viruses (less than one agglutinating dose) are capable of causing significant alteration in the inhibitor index upon interactionin vitrofor 60 min. at 37° C.