The Impact of Avian Influenza Viruses on Public Health

Aptamers in diagnostics and treatment of viral infections

Aptamers are in vitro selected DNA or RNA molecules that are capable of binding a wide range of nucleic and non-nucleic acid molecules with high affinity and specificity. They have been conducted through the process known as SELEX (Systematic Evolution of Ligands by Exponential Enrichment). It serves to reach specificity and considerable affinity to target molecules, including those of viral origin, both proteins and nucleic acids. Properties of aptamers allow detecting virus infected cells or viruses themselves and make them competitive to monoclonal antibodies. Specific aptamers can be used to interfere in each stage of the viral replication cycle and also inhibit its penetration into cells. Many current studies have reported possible application of aptamers as a treatment or diagnostic tool in viral infections, e.g., HIV (Human Immunodeficiency Virus), HBV (Hepatitis B Virus), HCV (Hepatitis C Virus), SARS (Severe Acute Respiratory Syndrome), H5N1 avian influenza and recently spread Ebola. This review presents current developments of using aptamers in the diagnostics and treatment of viral diseases.

A SPR aptasensor for detection of avian influenza virus H5N1

Rapid and specific detection of avian influenza virus (AIV) is urgently needed due to the concerns over the potential outbreaks of highly pathogenic H5N1 influenza in animals and humans. Aptamers are artificial oligonucleic acids that can bind specific target molecules, and show comparable affinity for target viruses and better thermal stability than monoclonal antibodies. The objective of this research was to use a DNA-aptamer as the specific recognition element in a portable Surface Plasmon Resonance (SPR) biosensor for rapid detection of AIV H5N1 in poultry swab samples. A SPR biosensor was fabricated using selected aptamers that were biotinylated and then immobilized on the sensor gold surface coated with streptavidin via streptavidin-biotin binding. The immobilized aptamers captured AIV H5N1 in a sample solution, which caused an increase in the refraction index (RI). After optimizing the streptavidin and aptamer parameters, the results showed that the RI value was linearly related (R² = 0.99) to the concentration of AIV in the range of 0.128 to 1.28 HAU. Negligible signal (<4% of H5N1) was observed from six non-target AIV subtypes. The AIV H5N1 in poultry swab samples with concentrations of 0.128 to 12.8 HAU could be detected using this aptasensor in 1.5 h.

A single immunization with HA DNA vaccine by electroporation induces early protection against H5N1 avian influenza virus challenge in mice

Background

Developing vaccines for the prevention of human infection by H5N1 influenza viruses is an urgent task. DNA vaccines are a novel alternative to conventional vaccines and should contribute to the prophylaxis of emerging H5N1 virus. In this study, we assessed whether a single immunization with plasmid DNA expressing H5N1 hemagglutinin (HA) could provide early protection against lethal challenge in a mouse model.

Methods

Mice were immunized once with HA DNA at 3, 5, 7 days before a lethal challenge. The survival rate, virus titer in the lungs and change of body weight were assayed to evaluate the protective abilities of the vaccine. To test the humoral immune response induced by HA DNA, serum samples were collected through the eye canthus of mice on various days after immunization and examined for specific antibodies by ELISA and an HI assay. Splenocytes were isolated after the immunization to determine the antigen-specific T-cell response by the ELISPOT assay.

Results

Challenge experiments revealed that a single immunization of H5N1 virus HA DNA is effective in early protection against lethal homologous virus. Immunological analysis showed that an antigen-specific antibody and T-cell response could be elicited in mice shortly after the immunization. The protective abilities were correlated with the amount of injected DNA and the length of time after vaccination.

Conclusion

A single immunization of 100 μg H5 HA DNA vaccine combined with electroporation was able to provide early protection in mice against homologous virus infection.

Up to new tricks - a review of cross-species transmission of influenza A viruses

Influenza is a highly contagious disease that has burdened both humans and animals since ancient times. In humans, the most dramatic consequences of influenza are associated with periodically occurring pandemics. Pandemics require the emergence of an antigenically novel virus to which the majority of the population lacks protective immunity. Historically, influenza A viruses from animals have contributed to the generation of human pandemic viruses and they may do so again in the future. It is, therefore, critical to understand the epidemiological and molecular mechanisms that allow influenza A viruses to cross species barriers. This review summarizes the current knowledge of influenza ecology, and the viral factors that are thought to determine influenza A virus species specificity.

Pathogenic and molecular characterization of the H5N1 avian influenza virus isolated from the first human case in Zhejiang province, China

Since the reemergence of highly pathogenic avian influenza virus H5N1, it caused disease in 20 people with 13 deaths in mainland of China. On February 21, 2006, the first suspected human case in Zhejiang province was reported. Pathogenic analyses, including reverse transcriptase polymerase chain reaction (RT-PCR), real-time RT-PCR, and virus isolation, were carried out to confirm the pathogen from tracheal aspirate specimen. In addition, antibody in serum sample was detected using hemagglutination-inhibition (HI). Results revealed that nucleic acid extracted from the tracheal aspirate specimen was positive for H5N1 avian influenza virus and influenza virus type A. The H5N1 virus strain named A/Zhejiang/16/06 (H5N1) was isolated. The titers of HI antibody for H5N1 avian influenza virus were 1:320 and 1:640, respectively. The sequenced genes were all avian origin. Phylogenetic analyses between the A/Zhejiang/16/06 and other H5N1 influenza viruses were also included.

Mutation trend of hemagglutinin of influenza A virus: a review from a computational mutation viewpoint

Since 1999 we have developed two computational mutation approaches to analyze the protein primary structure whose methodology and implications were reviewed in 2002. Our first approach is the calculation of predictable and unpredictable portions of amino-acid pairs in a protein, and the second is the calculation of amino-acid distribution rank in a protein. Both approaches provide quantitative measures to present a protein, which we have used to study a number of proteins with numerous mutations such as p53 proteins. More recently, we focussed our efforts on analyzing the proteins mutating frequently over time such as hemagglutinins of influenza A viruses. In this review we summarise our findings and their implications for hemagglutinin mutations in combination with some newly available data. Our approaches throw light on the true nature of genetic heterogeneity of influenza virus hemagglutinins; that is, the protein variability is highly relevant to its amino-acid construction. Using these approaches, we can monitor new mutations from influenza virus hemagglutinins and may predict their mutations in the future.

Protection against avian influenza H9N2 virus challenge by immunization with hemagglutinin- or neuraminidase-expressing DNA in BALB/c mice

Avian influenza viruses of H9N2 subtype are widely spread in avian species. The viruses have recently been transmitted to mammalian species, including humans, accelerating the efforts to devise protective strategies against them. In this study, an avian influenza H9N2 virus strain (A/Chicken/Jiangsu/7/2002), isolated in Jiangsu Province, China, was used to infect BALB/c mice for adaptation. After five lung-to-lung passages, the virus was stably proliferated in a large quantity in the murine lung and caused the deaths of mice. In addition, we explored the protection induced by H9N2 virus hemagglutinin (HA)- and neuraminidase (NA)-expressing DNAs in BALB/c mice. Female BALB/c mice aged 6-8 weeks were immunized once or twice at a 3-week interval with HA-DNA and NA-DNA by electroporation, respectively, each at a dose of 3, 10 or 30microg. The mice were challenged with a lethal dose (40x LD(50)) of influenza H9N2 virus four weeks after immunization once or one week after immunization twice. The protections of DNA vaccines were evaluated by the serum antibody titers, residual lung virus titers, and survival rates of the mice. The result showed that immunization once with not less than 10microg or twice with 3microg HA-DNA or NA-DNA provided effective protection against homologous avian influenza H9N2 virus.

Isolation and characterization of avian influenza viruses, including highly pathogenic H5N1, from poultry in live bird markets in Hanoi, Vietnam, in 2001

Since 1997, outbreaks of highly pathogenic (HP) H5N1 and circulation of H9N2 viruses among domestic poultry in Asia have posed a threat to public health. To better understand the extent of transmission of avian influenza viruses (AIV) to humans in Asia, we conducted a cross-sectional virologic study in live bird markets (LBM) in Hanoi, Vietnam, in October 2001. Specimens from 189 birds and 18 environmental samples were collected at 10 LBM. Four influenza A viruses of the H4N6 (n = 1), H5N2 (n = 1), and H9N3 (n = 2) subtypes were isolated from healthy ducks for an isolation frequency of over 30% from this species. Two H5N1 viruses were isolated from healthy geese. The hemagglutinin (HA) genes of these H5N1 viruses possessed multiple basic amino acid motifs at the cleavage site, were HP for experimentally infected chickens, and were thus characterized as HP AIV. These HA genes shared high amino acid identities with genes of other H5N1 viruses isolated in Asia during this period, but they were genetically distinct from those of H5N1 viruses isolated from poultry and humans in Vietnam during the early 2004 outbreaks. These viruses were not highly virulent for experimentally infected ducks, mice, or ferrets. These results establish that HP H5N1 viruses with properties similar to viruses isolated in Hong Kong and mainland China circulated in Vietnam as early as 2001, suggest a common source for H5N1 viruses circulating in these Asian countries, and provide a framework to better understand the recent widespread emergence of HP H5N1 viruses in Asia.

Influenza: old and new threats

Influenza remains an important disease in humans and animals. In contrast to measles, smallpox and poliomyelitis, influenza is caused by viruses that undergo continuous antigenic change and that possess an animal reservoir. Thus, new epidemics and pandemics are likely to occur in the future, and eradication of the disease will be difficult to achieve. Although it is not clear whether a new pandemic is imminent, it would be prudent to take into account the lessons we have learned from studying different human and animal influenza viruses. Specifically, reconstruction of the genes of the 1918 pandemic virus and studies on their contribution to virulence will be important steps toward understanding the biological capabilities of this lethal virus. Increasing the availability of new antiviral drugs and developing superior vaccines will provide us with better approaches to control influenza and to have a positive impact on disease load. A concern is that the imposition of new rules for working with infectious influenza viruses under high security and high containment conditions will stifle scientific progress. The complex questions of what makes an influenza virus transmissible from one human to another and from one species to another, as well as how the immune system interacts with the virus, will require the active collaboration and unencumbered work of many scientific groups.

Fate of 130 hemagglutinins from different influenza A viruses

In this study, we use our probabilistic models to analyze 130 hemagglutinins from different influenza A virus in order to gain the insight into their fate. The results provide three lines of evidence regarding the H5, H6, and H9 hemagglutinins: (i) the H5 hemagglutinins are more sensitive to mutations, this is the current state of the H5, H6, and H9 hemagglutinins; (ii) the H5 hemagglutinins had experienced more mutations in the past, this is the history of the H5, H6, and H9 hemagglutinins; and (iii) the H6 hemagglutinins has a bigger potential towards future mutations, this is the future of the H5, H6, and H9 hemagglutinins. Furthermore, this study gives two clues on the mutation tendency that is a degeneration process and the species susceptibility that is the chickens and ducks.