Influenza virus surface charge

In support of this, the HA charge of the globally circulating H3N2 has increased over time since its pandemic. However, the same trend was not seen in H1N1 HA sequences. This is counter-intuitive, since immune escape due to increased avidity due itself to an increase in charge was determined experimentally. Here, we explore whether patterns of local charge of H1N1 HA can explain this discrepancy and thus further associate electrostatic charge with immune escape and viral evolutionary dynamics.

Measures of site-wise functional selection and expected charge computed from deep mutational scan data on an early H1N1 HA yield a striking division of residues into three groups, separated by charge. Although the H1N1 pandemic did not turn out to be as deadly as initially feared, the next pandemic flu virus could emerge at any time, and we must remain vigilant.

Hopefully, the knowledge gained in response to the H5N1 and H1N1 outbreaks, and continued research to more completely understand influenza virus, as well as improvements in vaccine and drug development, will enable us to minimize the effects of future influenza outbreaks. There are three different types of influenza virus — A, B, and C. Type A viruses infect humans and several types of animals, including birds, pigs, and horses. Type B influenza is normally found only in humans, and type C is mostly found in humans, but has also been found in pigs and dogs.

Influenza pandemics are caused by type A viruses, and therefore these are the most feared type of influenza virus; neither types B or C have caused pandemics. Type A influenza is classified into subtypes depending on which versions of two different proteins are present on the surface of the virus. These proteins are called hemagglutinin HA and neuraminidase NA. There are 17 different versions of HA and 10 different versions of NA.

The influenza A subtypes are further classified into strains, and the names of the virus strains include the place where the strain was first found and the year of discovery. Although many different combinations of the HA and NA proteins are possible, viruses with only a few of the possible combinations circulate through the human population at any given time.

Currently, subtypes H1N1 and H3N2 are in general circulation in people. Other combinations circulate in animals, such as the H5N1 virus found in birds. The subtypes that exist within a population change over time. For example, the H2N2 subtype, which infected people between and , is no longer found in humans. Influenza virus has a rounded shape although it can be elongated or irregularly shaped and has a layer of spikes on the outside.

There are two different kinds of spikes, each made of a different protein — one is the hemagglutinin HA protein and the other is the neuraminidase NA protein. The HA protein allows the virus to stick to a cell, so that it can enter into a host cell and start the infection process all viruses need to enter cells in order to make more copies of themselves.

The NA protein is needed for the virus to exit the host cell, so that the new viruses that were made inside the host cell can go on to infect more cells. Inside the layer of spikes, there are eight pieces, or segments, of RNA that contain the genetic information for making new copies of the virus. Each of these segments contains the instructions to make one or more proteins of the virus.

So for example, segment 4 contains the instructions to make the HA protein, and segment 6 contains the instructions to make the NA protein the segments are numbered in size order, with 1 being the largest. When new viruses are made inside the host cell, all eight segments need to be assembled into a new virus particle, so that each virus has the complete set of instructions for making a new virus.

The danger occurs when there are two different subtypes of influenza A inside the same cell, and the segments become mixed to create a new virus. Influenza virus is one of the most changeable viruses known. There are two ways that influenza virus changes — these are called drift and shift. This can result in a slight difference in the HA or NA proteins.

Although the changes may be small, they may be significant enough so that the human immune system will no longer recognize and defend against the altered proteins. This is why you can repeatedly get the flu and why flu vaccines must be administered each year to combat the current circulating strains of the virus.

Shifting, or antigenic shift, is an abrupt, major change in the virus, which produces a new combination of the HA and NA proteins. These new influenza virus subtypes have not been seen in humans or at least not for a very long time , and because they are so different from existing influenza viruses, people have very little protection against them.

When this happens, and the newly created subtype can be transmitted easily from one person to another, a pandemic could occur. Virus shift can take place when a person or animal is infected with two different subtypes of influenza.

Take the case, for example, where there are two different subtypes of influenza circulating at the same time, one in humans and one in ducks. The human subtype is able to infect humans and pigs, but not ducks, while the duck subtype is able to infect ducks and pigs, but not humans.

When a pig becomes infected with both the human and duck influenza subtypes at the same time, the segments of both viruses are scrambled or reassorted.

As a result, a human virus particle could assemble that contains the duck HA segment instead of the human HA segment. A new virus subtype has been created. This new subtype could infect humans, but because it has the new duck version of the HA protein, the human immune system would not be able to defend an infected person against the new virus subtype. The virus could continue to change to allow it to spread more easily in its new host, and widespread illness and death could result.

Virus shift can also occur when an avian strain becomes adapted to humans, so that the avian virus is easily transmitted from person to person. In this case, the avian strain jumps directly from birds to humans, without mixing or reassortment of the genetic material of influenza strains from different species.

Influenza epidemics , also known as seasonal flu, occur annually and are the most common emerging infection among humans. These epidemics have major medical impacts, but they are generally not fatal except in certain groups such as the elderly.

Pandemics , on the other hand, happen once every few decades on average. They occur when a new subtype of influenza A arises that has either never circulated in the human population or has not circulated for a very long time so that most people do not have immunity against the virus. The new subtype often causes serious illness and death, even among healthy individuals, and can spread easily through the human population.

The flu, caused by a strain of H1N1, was by far the most deadly. More than , people died in the United States as a result of the Spanish flu, and up to 50 million people may have died worldwide. Nearly half of those of those deaths were among young, otherwise healthy individuals. The pandemic was due to a new H2N2 strain of influenza virus that caused the deaths of two million people, while the pandemic resulted from an H3N2 strain that killed one million people.

One pandemic has occurred so far in the 21st century. This was due to the novel swine-origin H1N1 virus which emerged in The WHO established a six phase pandemic alert system in in response to the potential threat of the H5N1 avian influenza virus. The alert system is based on the geographic spread of the virus, not necessarily the severity of disease caused by the virus. Travel and trade bans may be implemented in some cases, although if the disease is already widespread, these may not be considered effective.

Prior to the emergence of the H1N1 virus, the alert level stood at Phase 3 based on the circulation of the H5N1 virus. On April 27, , after the H1N1 flu virus was recognized to be passing from person to person in Mexico, the alert level was raised to Phase 4. Two days later, on April 29, the WHO again increased the alert level, this time to Phase 5, reflecting the sustained transmission of the novel H1N1 virus in the United States. As H1N1 continued to spread worldwide and infect people in over 70 countries, the WHO raised the alert to Phase 6 — the highest level - on June 11, Over the next few months, H1N1 spread to more than countries and territories worldwide.

Influenza naturally infects wild birds all around the world, although they usually do not become ill. The virus is very contagious, however, and it can become a problem when the virus is transmitted to domesticated birds, such as chickens, ducks, or turkeys, because domesticated poultry can succumb to illness and death from influenza.

Humans generally do not become infected with avian flu. That is why news of humans contracting avian influenza during an outbreak of bird flu in poultry in in Hong Kong was alarming. It indicated that the virus had changed to allow it to directly infect humans.

The virus that caused this particular outbreak is influenza A subtype H5N1. Since , H5N1 infections in birds have spread, initially throughout Asia. Then as birds traveled along their migratory routes, H5N1 dispersed to Russia and Europe, and later to countries in the Middle East and on the African continent. Most human cases of H5N1 influenza have been traced to direct contact with infected poultry, but there have been a few cases of person-to-person transmission, particularly in clusters where multiple family members became infected.

One reason why avian H5N1 is not readily transmissible among people has to do with the hemagglutinin, or HA, protein of the virus that determines which cell type the virus can enter.

As with other viruses, the influenza virus must attach to specific proteins called receptors on the outside of cells in order to gain entry into cells and cause an infection.

Unlike human influenza viruses, which infect cells high in the respiratory tract, the H5N1 HA protein attaches to cells much lower in the respiratory track. The virus is so deep within the respiratory tract that it is not coughed up or sneezed out, and so it does not easily infect other people. If the HA protein of H5N1 were to mutate so that it could infect cells higher in the respiratory tract, then it would more likely be able to pass from person to person.

As of July , there have been some laboratory-confirmed cases of H5N1 infections in humans, in 16 different countries, and close to deaths. The countries with the overall highest case numbers are Egypt, where almost all cases in have occurred, followed by Indonesia and Vietnam.

H5N1 continues to circulate in poultry, and small and sporadic clusters of human infections are still occurring. However, H5N1 currently does not transmit easily between people, so the risk of a large outbreak is low at this time. Highly pathogenic H5 avian virus infections were first reported in birds in the United States in December Over approximately the next six months, more than findings of infection with H5N2, H5N8, and H5N1 viruses were confirmed, mostly in poultry including backyard and commercial flocks.

More than 40 million birds in 20 states were either infected or exposed. No human infections by these H5 viruses have been reported in the United States, but their presence in birds makes it more likely than human H5 infections could occur in the United States. Individuals having close contact with live infected poultry or surfaces contaminated with the avian influenza viruses are at highest risk of infection in places where the viruses circulate.

There have been no reports of infection occurring from eating properly cooked poultry. In addition to the H5 viral subtypes, other avian influenza strains have occasionally infected humans in recent years. These include the H7N2 strain which infected two individuals in the eastern United States in and , and the H9N2 strain which has caused illness in several people in Asia in and In March of , a new subtype of avian influenza was found to infect humans.

Influenza A H7N9 had previously been detected in birds, but this particular variant had never been seen before in humans or animals. The initial wave of H7N9 infections occurred in the spring of in China, followed by a larger, second wave in the first half of in China and a few neighboring countries. As of February , approximately cases and deaths have been reported to the WHO, mostly in China. People in the majority of cases had exposure to infected poultry or contaminated environments.

The H7N9 virus causes a severe respiratory illness in most infected people, but it currently does not appear to spread easily from person to person. However, in a study using generation of negative and positive ions, influenza virus was inactivated although ozone level was negligible 0.

Our device released a steady-state ozone concentration below the detection limit 0. As infectivity was not lost when virus was nebulized into the air of the room without ionization and only slightly reduced when applied directly on the positively charged collector plate, it is suggested that most reduction of infectivity may be due to increased negative charged levels, presumably resulting in changes in isoelectric point and thus structural changes of the capsid.

As the two viruses investigated are non-enveloped, lipid modification can be ruled out. Previous studies have also shown that the used infectious dose results in a viral growth peak around day 3 p. We examined the immune response at 21 days p. The mode of influenza virus transmission includes direct contact with individuals, exposure to virus-contaminated objects fomites and inhalation of infectious aerosols.

Aerosol released virus from inoculated animals could be detected on the active collector plate by RT-qPCR, albeit at very low gene copy numbers. Using the guinea pig as a host model, Lowen et al. The easy handling, low cost, free of ozone production, robustness, high efficiency and low-voltage 12 volt operation enables large-scale use.

Locations critical for infectious spread, such as airplanes, hospitals, day-care centres, school environments and other public places could thus be monitored and controlled by the collection and analysis of airborne viruses and other pathogens on the collector plate. The device also show potential for transmission prevention, although the potency needs to be further investigated in real-life settings. We conclude that this innovative technology hold great potential to collect and identify viruses in environmental air.

Before the start of aerosol experiments, the room was emptied on particles by the active ionizer and the collector plate was discarded before the experiments begun and replaced with a new collector plate. Humidity and temperature conditions were measured initial to each aerosol experiments.

The ionizing device used in this study was developed on the basis of the ion-flow ionizing technology from LightAir AB, Solna, Sweden www. The ionizer creates electrons, which will render surface molecules of particles in air negatively charged thus attracting them to the positively charged collector plate.

This device generates approximately 35 billion electrons per second www. Viruses captured on the collector plates were analyzed by a RT-qPCR for rotavirus, CaCV and influenza virus, and the results from the active- and inactive ionizers were compared. Scanning- and transmission electron microscopy were used for visualization of collected viruses and latex-particles.

In aerosol experiments for scanning electron microscopy and infectivity analysis, virus was diluted in Eagles MEM. Virus suspensions in different concentrations were distributed as aerosols in the room by the use of a nebulizer. Ten grid squares were analyzed per specimen and the number of virus particles per unit area was calculated.

Collected samples were added on the surface of a polycarbonate 0. The method has previously been used and reported in studies of cytomegalovirus as well as cerebrospinal fluid 41 , 42 , This real-time PCR uses labeled primers with different fluorophores for each VP6 subgroup and external plasmid standards for semi-quantification Melting temperatures were determined on all samples using the Sequence Detection Software version 1.

Rotavirus stock and samples were diluted in Eagles MEM and subsequently diluted in two-fold dilutions. Determination of viral infectivity was performed as previously described on confluent Green monkey kidney cells MA in well plates To determine the reduction of infectivity, the ratio of viral genome copy numbers versus infectivity was compared between aerosolized virus, virus exposed to active- and inactive collector plates and the viral stock.

We use a guinea pig animal model to investigate whether the ionizing technique could prevent transmission of influenza virus infection, since this model have successfully been used as a model of aerosol transmission studies of influenza virus 31 , All four infected animals were placed into the experimental cage Fig. Air flowed freely between cages, but direct contact between inoculated and exposed animals was prohibited.

Two identical experiments were performed, with an active and inactive ionizer. At 21 days post exposure, serum was collected from the uninfected exposed guinea pigs and the prevalence of antibodies against influenza A virus was determined by ELISA.

Sera taken before exposure to the infected guinea pigs pre-sera , and 21 days days after exposure post-sera were analyzed from each animal. Wells were washed x3 0. Serum samples were diluted and further in two-fold dilutions in dilution buffer PBS containing 0.

Cut off values were calculated as the average value of negative controls OD and 2 times the SD. RNA was extracted from trachea and lung tissue of infected guinea pig.

How to cite this article : Hagbom, M. Ionizing air affects influenza virus infectivity and prevents airborne-transmission. Author Contributions L. National Center for Biotechnology Information , U. Sci Rep. Published online Jun Author information Article notes Copyright and License information Disclaimer. Received Nov 27; Accepted May This work is licensed under a Creative Commons Attribution 4. This article has been cited by other articles in PMC.

Results Visualization and efficiency of aerosol sampling as determined by electron microscopy To develop and validate the ionizing technique for collection and identification of viral pathogens, we used several viruses of clinical importance; calicivirus, rotavirus and influenza virus H3N2, strain Salomon Island as well as latex particles. Open in a separate window. Figure 1. Ionizing air and electrostatic attraction collects aerosol-distributed viruses as determined by RT-qPCR We next determined the capacity of RT-qPCR technology to quantitate the capacity of the ionizer technique to collect and concentrate viruses.

Figure 2. Figure 3. Figure 4. Discussion We describe a simple ionizing device operating at 12 volt that can prevent spread of airborne transmitted viral infections between animals in a controlled setting, whilst simultaneously collecting virus from air for rapid identification. Ionizer technology and device The ionizing device used in this study was developed on the basis of the ion-flow ionizing technology from LightAir AB, Solna, Sweden www.

Scanning electron microscopy SEM Collected samples were added on the surface of a polycarbonate 0. Determination of rotavirus and CaCV infectivity Rotavirus stock and samples were diluted in Eagles MEM and subsequently diluted in two-fold dilutions.

Airborne transmission of influenza virus We use a guinea pig animal model to investigate whether the ionizing technique could prevent transmission of influenza virus infection, since this model have successfully been used as a model of aerosol transmission studies of influenza virus 31 , Extraction of influenza RNA from guniea pig tissue RNA was extracted from trachea and lung tissue of infected guinea pig.

Additional Information How to cite this article : Hagbom, M. Footnotes Author Contributions L. References Lipsitch M. Transmission dynamics and control of severe acute respiratory syndrome. Science , —, Aerosol transmission of influenza A virus: a review of new studies. Dynamics of infectious disease transmission by inhalable respiratory droplets. J R Soc Interface 7 , —, High infectivity and pathogenicity of influenza A virus via aerosol and droplet transmission.