Table of Contents

 

1. Overview

2. Entry of H1N1 into the Host Cell (for the scientifically minded)

3. Origins and Evolutions of the Virus

4. Swine Flu (H1N1) vs. Sesonal Influenza

5. Precautions

6. Flu Symptoms

7. Sources

 

Overview

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     Swine Flu, the H1N1 virus, has become one of the most common topics in the media today, but don't necessarily believe all the hype. The swine flu was recently raised to a pandemic alert level, but not because of the severity of illness that the virus causes. The alert level was raised because the swine flu has been affecting and spreading to so many people. Although there have been deaths, most people infected with the virus recover with no medical treatment.  This new strain of H1N1 is a greater threat to children 6 months to 25 years of age, and most of the deaths caused by swine flu were in people who had underlying health  problems already.  While fatality rates are not high right now, scientists' main concern is that the virus will mutate and change the surface proteins, causing the virus to be more severe and invade deeper into the lung region, causing greater health risks like pneumonia. With the potential for the virus to mutate increases as the the virus continues to spread, scientists won't know what to do with the new chain of the virus if it mutates. So, just as flu season is beginning to start and your worried about the swine flu, read on to obtain the specific, accurate facts.

 

 

 

HA: Hemagglutinine type 1 (or H1), swine, also in the 1918 influenza. Catches host's cell receptors.

NA: Neuraminidase type 1 (or N1), swine, eurasian, helps start the infection.

PA: avian, north america.

PB1: human, likely from the 1993 H3N2 influenza.

PB2: avian, from north america.

NP: swine, north america.

M: swine, eurasia.

NS: swine, north america.

 

This diagram explains the different genetic components of the H1N1 virus. All of the different gens (bolded) contribute to the overall function and jobs of the virus, and each job/origin of the gene is listed here as well.

 

Photo provided by Wikimedia Commons http://commons.wikimedia.org/wiki/File:2009_H1N1_influenza_virus_genetic-num.svg

 

 

Image of the Virus (Courtesy of CDC)

http://www.cdc.gov/h1n1flu/images/B00526_H1N1_flu_sml.jpg

 

Entry of H1N1 into the Host Cell (for the scientifically minded)

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     Swine Flu, more properly know as H1N1, is a version of the flu virus that has gotten recent attention for being very easy to spread and infecting a large number of the population. H1N1 stands for Hemagglutinin version one and Neuraminidase version one, which are two main enzymes used by the virus to infect cells. Neuraminidase is a type of enzyme that breaks down certain types of molecules called Neuraminic Acids. Neuramic acids are a group of molecules that are present in animal tissue and bacteria. Derivatives of Neuraminic Acids are found in the cell membrane of red blood cells, which is where H1N1 attacks. Neuraminidase allows for new viruses to exit a cell after being created by the parent virus. This "pirating" of one cell at a time is the main way that H1N1 (and the seasonal flu) works. It first latches onto a red blood cell using Hemagglutinin. Hemagglutinin binds to sialic acid receptors found in the glycocalyx on the cell membrane. After undergoing a process called Receptor-Mediated Endocytosis, the PH is lowered, and that prompts the release of the virus' DNA and RNA, which is copied into the cells' nucleus. After the virus releases the DNA and RNA, the cell expresses the genes from the DNA that the virus put in. Finally, the new viruses break free using Neuraminidase, and attack more cells. The virus is airborn, and can be spread by sneezing, coughing, or breathing really close to another person. Also, germs can be spread by touch, by first touching an infected area, then somewhere on the body. The symptoms, according to the CDC, can include "fever, cough, sore throat, runny or stuffy nose, body aches, headache, chills and fatigue."

The image at http://www.time.com/time/interactive/0,31813,1914947,00.html is a great visual description of how H1N1 and the flu work.

 

Additionally, this animation helpfully depicts the progress of the progress in

http://www.rpc.msoe.edu/cbm/resources/HAAnimation.swf

 

Origins and Evolution of the Virus                                                     

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     The swine flu originated as an influenza virus in pigs. The virus currently infecting humans is a mutated form of the swine influenza virus. Pigs are able to be infected by bird, human, and swine viruses. When many different species' flu viruses infect pigs, the viruses are able to mix together and change, creating a completely new virus. So when a human influenza virus infects a pig, it has the ability to mutate into a new virus that is able to infect pigs AND humans. The H1N1 virus has been mutated and now contains genes from swine (pig) viruses, avian (bird) viruses, and human viruses. Usually, swine flu viruses are sequence specific, meaning they only infect pigs; so the virus rarely infects humans. But, sometimes the virus is able to spread from species to species when the virus is mutated, causing infection of humans in close contact with pigs. The first case of swine flu was reported on a pig farm in Mexico. There was another similar pandemic in 1918, when the swine flu virus mutated and became more severe and more likely to cause illness. Current genetic sequencing has proved that the current virus is the same one as in the 1918 pandemic; it has not changed yet.

 

 

 

This diagram basically describes how the virus has evolved. Bird and human influenza viruses are both able to infect the same host, in this case a pig. Once both the bird and human flu viruses infect the same cell, they are able to mix/combine genes from both strains, and create a new strain of the virus. This new strain that has been created in the pig is then able to be transmitted to humans.

Diagram provided by National Institute of Health  http://www3.niaid.nih.gov/NR/rdonlyres/3D377A8B-747F-480A-832E-02A8ED9D1B3C/0/AntigenicShift_HiRes.jpg

 

 

Swine Flu (H1N1) vs. Seasonal Influenza

 

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      Why are people so worried about the swine flu when so many are affected by seasonal influenza every year? People are much more prepared for seasonal influenza. Since influenza circulates every year (although the virus changes slightly every year), some people have built up some immunity to it, which helps to limit the number of infections. Many people, especially in the United States, get the flu vaccine every year, which also helps to lower the amount of infections. Swine flu, on the other hand, is new. Most people have no, or very little, immunity to it and those who do are mostly the elderly. There is now a swine flu vaccine that has just been approved by the FDA. The difficulty is that there is a limited supply, so not everyone will be able to get vaccinated. It is also important to keep in mind that a lot of the worry and fear surrounding swine flu is due to media hype. 

 

 

As of September 6, 2009, there have been 277,607 reported cases of swine flu and 3,205 reported deaths worldwide (1.15% of those infected, died).  It is important to note that countries are no longer required to test and report individual cases, which means the real number of cases is actually higher (which would also mean that a lower percentage of those infected die). Many cases of swine flu are mild and can go unnoticed and untested.

 

So far, there have been 43,771 reported cases of swine flu and 593 reported deaths from swine flu in the United States. Once again, however, there are many more cases of swine flu than are reported. The CDC made a model that accounted for underestimation to try to determine the true number of cases of the new H1N1 virus in the U.S. According to this model, the CDC estimates that 1 million people in the United States were infected with swine flu. 

 

On average, there are 3-5 million cases of seasonal influenza worldwide that result in severe illness with 250,000 to 500,000 deaths. In the U.S. it is estimated that over 200,000 people are hospitalized from conditions associated with seasonal influenza and an average of 36,171 people in the U.S. die each year from seasonal flu related causes. A study found that people 85 year-olds and older have the highest rates of seasonal influenza associated hospitalization and it is estimated that 90% of influenza-related deaths occur in people 65 or older. 

 

H1N1 appears to be more contagious than seasonal influenza. Contagiousness is measured by the secondary attack rate of the virus. The secondary attack rate reflects the risk of someone being infected with the disease by a close contact who is infected. The secondary attack rate of seasonal influenza ranges from 5% to 15%. Current estimates of the secondary attack rate of H1N1 range from 19% to 33%.

 

Both viruses affect those with underlying conditions. Those with underlying respiratory illnesses are most at risk of having severe symptoms after they have contracted swine flu. This is because swine flu attacks red blood cells, which transport oxygen from your lungs to your heart, where it is then circulated to the rest of the body to be used for cellular respiration. When some of these red blood cells are damaged or destroyed, less oxygen is transported throughout the body. For people who already get a lower supply of oxygen due to a respiratory illness, such as asthma (the constriction of the bronchioles), the damage to the red blood cells and the resulting lack of oxygen transportation is even more damaging. 

 

The graphs and explanations below will help you to take a closer look at swine flu statistics.

 

 

 

The picture above shows that a growing percentage of tested flu cases are H1N1. The numbers below each pie graph (for example 77/110 in Vietnam) show the number of swine flu viruses over the number of tested influenza viruses. The adjacent pie graph provides the same information, but with data from a different week, allowing you to compare the percent of influenza viruses that are swine flu from one week to another. Note that the viruses being tested come from people who present with flu-like symptoms. So, of the total cases of flu world wide, a growing percent is H1N1. This chart is only showing H1N1 is currently the dominant strand of influenza. Just because there is a higher percentage of flu cases that are H1N1 than are seasonal influenza (such as influenza A and B) does not mean that there are necessarily more cases of influenza (either H1N1, A, or B).

 

 

 

Is all the talk about swine flu true or are people just scared? The outbreak in Mexico began in mid-March (approximately during week 11 when referring to the graph above) and reached the United States in mid April (approximately week 14 on the graph above). Soon after (at around the end of April, approximately week 17 on the graph above), there was a sudden jump in visits to the doctor or hospital for influenza-like illness. Although some of the data from this jump may represent a rise in flu cases due to the introduction of swine flu into the population, it is also very likely that the percentage of visits for influenza-like illness increased above the average for the previous two years (shown here in blue and green lines) because of the media coverage and fear surrounding swine flu. Whereas people with a slight fever, a cough, and a runny nose might before put it off as a bad cold or a light case of the flu, now everyone is going to their doctors and to the hospital to get tested for swine flu.

 

You can see on the graph that this year (represented above as the red line), the visits for influenza-like illness dropped off from its sudden peak when swine flu first broke out. As the media coverage of swine flu dropped from the break out in April, so too did the visits to the doctor or hospital for influenza-like illness. Yet as the fall approached with talk of a swine flu vaccine and fears that  the virus would come back stronger during regular flu season (approximately October through April), visits for influenza-like illness shot up again. The more the virus dominates the news, the more afraid people become of catching swine flu and the more likely they are to go to a doctor or hospital with flu-like symptoms that they wouldn't have been too concerned with in earlier years. Because of this, statistics (like the ones represented on the graph above) can often be misinterpreted.

 

A quick glance at the graph would lead you to believe that, even before flu season, there are many more people coming down with the flu because of the swine flu outbreak. The huge jump in percentage of visits for influenza-like illness as the end of the graph (approximately week 35) would also lead you to believe the worst is still to come. It's important to keep in mind that as the media coverage builds, so does the fear of swine flu within the general population. Because of this fear, more people visit the doctor or hospital with influenza or cold-like illnesses that they would not have worried about before. This is the main contributer to the huge jump in percentage of visits for influenza-like illness in weeks 33-35. 

 

 

***EIP: Emerging Infections Program (EIP), a population-based surveillance network 

 

When looking at this graph, it is important to keep in mind the data presented in the graph at the top of this section (the percentages of flu cases that are H1N1). The data in that graph shows that swine flu is currently the dominant strand of influenza. The percentages for the United States in particular also show that swine flu is the dominant strand. Because swine flu is so dominant in the United States, it is fair to assume that a large percent of recent flu cases are H1N1. 

 

The chart directly above this text represents the number of hospitalizations for influenza (by age group) this year. These statistics are of influenza infections severe enough to warrant hospitalization. The gray dotted line represents the national average of influenza hospitalizations (by age group) during flu season (October through April) over that past three years. 

 

The national average (of hospitalizations) for the 0-23 month group is the highest, followed by 65+ and 2-4 year olds. This reflects the fact that influenza infections in the very old and very young are more severe than influenza infections in those in the middle age groups, such as someone 18-49. The statistics for this year (represented by the red line), however, show that the 5-17 and 18-49 age groups have already increased above their national averages. Although their national averages are the lowest of all the age groups, the number of hospitalizations in the 5-17 and 18-49 age groups have increased the most when compared to their national average. This means that more people in the 5-17 and 18-49 age groups are coming down with severe cases of influenza this year than the average number of people (in the same age group) over the past three years. The other age groups, however, have not had a greater number of severe cases of influenza than they've had on average over the past three years. This shows that the rate of influenza infections severe enough to warrant hospitalizations is increasing most in the 5-17 and 18-49 age groups. As noted above, a large percent of these influenza infections are from the H1N1 strand. This means that, while the very young and, to a lesser degree, very old (because they have some immunity to swine flu) still have the most cases of hospitalization caused by influenza, the 5-17 and 18-49 age groups have a greater increase in hospitalizations caused by influenza. Since the H1N1 strand is dominant, it appears to be affecting the 5-17 and 18-49 age groups more than the seasonal influenza did (on average) over the past three years. This means that the 5-17 and 18-49 age groups are more vulnerable to swine flu than they are to seasonal flu, although the very young and very old (once again, to a lesser extent) are still the most vulnerable to both swine and seasonal influenza. The very young and very old, however, have not experienced the same increase in vulnerability to swine flu that the 5-17 and 18-49 age groups have.

 

 

The Outbreak in Mexico

Mexico suffered a greater death toll from swine flu than many other countries. The flu's origin in Mexico is a leading contributer to this. People, scientists as well the average person, did not know anything about swine flu (as the virus is a new strand). Symptoms can begin mildly, so anyone infected with it likely continued their daily activities, spreading it to others. Because people didn't realize the severity of the illness, many didn't get anti-viral medication quickly. In fatal cases, people didn't receive anti-virals until a median of 8 days after being infected. Also, because Mexico is a developing country, many didn't have access to medical care. The H1N1 virus affects the lungs. So, some scientists believe the air pollution in Mexico may have contributed to the higher mortality rate. It is important to realize that, because of all these conditions, the mortality rate in Mexico is higher than the mortality rates around the world.

 

Precautions

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       The H1N1 strand of influenza is transmitted in a similar way with the seasonal flu: by the inhalation of respiratory drops infected by the virus. Prevention techniques for swine flu are also similar to prevention techniques taken to avoid contracting the seasonal flu.

This includes:

•             Avoiding contact with those with flu-like symptoms

•             Avoid touching your hands or mouth after touching another person or a potentially contaminated surface.

•             Wash your hands regularly with soap and water or use a hand sanitizer

•             Spend as little time as possible in crowded areas

•             Open windows in your home to increase airflow

     Contrary to popular belief, masks will not protect one against swine flu. If you are ill, a mask will help prevent others from catching the virus from you by means of covering your nose and mouth.

     If one intends on using a mask, be sure to avoid touching a used mask and always dispose of single-use masks. Never reuse them.

 

Flu Symptoms

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     Swine flu symptoms are similar to those of the normal flu, such as sneezing, coughing, sore throat, running/stuffy nose, fevers, headaches, and chills. In children, more severe symptoms include fast/troubled breathing, bluish or grayish skin, and continual vomiting. In adults, severe symptoms include breathing difficulty, confusion, vomiting, dizziness, and chest/abdomen pain. If you are experiencing any of these symptoms seek emergency medical care. If your symptoms appear to improve, but then return worse seek emergency medical care.

 

If you have contracted swine flu get rest and stay home for at least 24 hours. Be sure to drink fluids and avoid contact with others in order to keep them from contracting the virus.

 

Vaccination

The current flu vaccination works by means of introducing a small, killed sample of that particular strand of virus. Within two weeks, the body’s immune system produces antibodies. These antibodies combat the virus and stay in the bloodstream. This produces “immunity” to said virus.

A vaccine to the H1N1 virus strand has just been approved by the FDA. Preliminary reports show that only one dose (15 mug) is necessary to produce immunity as opposed to the two doses originally anticipated. The vaccine should be available Fall 2009. 

 

 

Created by Hanna, Morash, McCormick, Saulnier.

 

 

Sources

 

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