A new strain of influenza is infecting people in Mexico and the United States and may have killed up to 60 people in Mexico, global health officials said today.
The authorities has analyzed samples of the H1N1 virus from some of the U.S. patients, all of whom have recovered, and said it is a never-before-seen mixture of viruses from swine, birds and humans.
Here are some facts from the U.S. Centers for Disease Control and Prevention about how swine flu spreads in humans:
• Swine flu viruses typically sicken pigs, not humans. Most cases occur when people come in contact with infected pigs or contaminated objects moving from people to pigs.
• Pigs can catch human and avian or bird flu. When flu viruses from different species infect pigs, they can mix inside the pig and new, mixed viruses can emerge.
• Pigs can pass mutated viruses back to humans and they can be passed from human to human. Transmission among humans is thought to occur in the same way as seasonal flu - by touching something with flu viruses and then touching their mouth or nose, and through coughing or sneezing.
• Symptoms of swine flu in people are similar to those of seasonal influenza - sudden fever, coughing, muscle aches and extreme fatigue. This new strain also appears to cause more diarrhea and vomiting than normal flu.
• Vaccines are available to be given to pigs to prevent swine influenza. There is no vaccine to protect humans from swine flu although the CDC is formulating one. The seasonal influenza vaccine may help provide partial protection against swine H3N2, but not swine H1N1 viruses, like the one circulating now.
• People cannot catch swine flu from eating pork or pork products. Cooking pork to an internal temperature of 160 degrees Fahrenheit kills the swine flu virus as it does other bacteria and viruses.
Swine Influenza (swine flu) is a respiratory disease of pigs caused by type A influenza that regularly cause outbreaks of influenza among pigs. Swine flu viruses do not normally infect humans, however, human infections with swine flu do occur, and cases of human-to-human spread of swine flu viruses has been documented.
Swine influenza virus : (referred to as SIV) refers to influenza cases that are caused by Orthomyxoviruses endemic to pig populations. SIV strains isolated to date have been classified either as Influenzavirus C or one of the various subtypes of the genus Influenzavirus A.
Swine flu infects people every year and is found typically in people who have been in contact with pigs, although there have been cases of person-to-person transmission. Symptoms include fever, disorientation, stiffness of the joints, vomiting, and loss of consciousness ending in death. Swine influenza is known to be caused by influenza A subtypes H1N1, H1N2, H3N1, H3N2, and H2N3.
In swine, three influenza A virus subtypes (H1N1, H3N2, and H1N2) are circulating throughout the world. In the United States, the H1N1 subtype was exclusively prevalent among swine populations before 1998; however, since late August 1998, H3N2 subtypes have been isolated from pigs. As of 2004, H3N2 virus isolates in US swine and turkey stocks were triple reassortants, containing genes from human (HA, NA, and PB1), swine (NS, NP, and M), and avian (PB2 and PA) lineages.
Avian influenza virus H3N2 is endemic in pigs in China and has been detected in pigs in Vietnam, increasing fears of the emergence of new variant strains. Health experts[who?] say pigs can carry human influenza viruses, which can combine (i.e. exchange homologous genome sub-units by genetic reassortment) with H5N1, passing genes and mutating into a form which can pass easily among humans. H3N2 evolved from H2N2 by antigenic shift. In August 2004, researchers in China found H5N1 in pigs. Measured resistance to the standard antiviral drugs amantadine and rimantadine in H3N2 in humans has increased to 92% in 2005.
Chairul Nidom, a virologist at Airlangga University's tropical disease center in Surabaya, East Java, conducted an independent research; he tested the blood of 10 apparently healthy pigs housed near poultry farms in West Java where avian flu had broken out, Nature reported. Five of the pig samples contained the H5N1 virus. The Indonesian government has since found similar results in the same region. Additional tests of 150 pigs outside the area were negative.
Swine in Human
The Centers for Disease Control and Prevention (CDC) reports that the symptoms and transmission of the swine flu from human to human is much like seasonal flu, commonly fever, lethargy, lack of appetite and coughing. Some people with swine flu also have reported runny nose, sore throat, nausea, vomiting and diarrhea. It is believed to be spread between humans through coughing or sneezing of infected people and touching something with the virus on it and then touching their own nose or mouth. The swine flu in humans is most contagious during the first five days of the illness although some people, most commonly children, can remain contagious for up to ten days. Diagnosis can be made by sending a specimen, collected during the first five days, to the CDC for analysis.The swine flu is susceptible to four drugs licensed in the United States, amantadine, rimantadine, oseltamivir and zanamivir, however, for the 2009 outbreak it is recommended it be treated with oseltamivir and zanamivir. The vaccine for the human seasonal H1N1 flu does not protect against the swine H1N1 flu, even if the virus strains are the same specific variety, as they are antigenically very different.
1976 U.S. outbreak
On February 5, 1976, an army recruit at Fort Dix said he felt tired and weak. He died the next day and four of his fellow soldiers were later hospitalized. Two weeks after his death, health officials announced that swine flu was the cause of death and that this strain of flu appeared to be closely related to the strain involved in the 1918 flu pandemic. Alarmed public-health officials decided that action must be taken to head off another major pandemic, and they urged President Gerald Ford that every person in the U.S. be vaccinated for the disease. The vaccination program was plagued by delays and public relations problems, but about 24% of the population had been vaccinated by the time the program was canceled.
About 500 cases of Guillain-Barré syndrome, resulting in death from severe pulmonary complications for 25 people, were probably caused by an immunopathological reaction to the 1976 vaccine. Other influenza vaccines have not been linked to Guillain-Barré syndrome, though caution is advised for certain individuals, particularly those with a history of GBS.
2007 Philippine outbreak
On August 20, 2007 Department of Agriculture officers investigated the outbreak of swine flu in Nueva Ecija and Central Luzon, Philippines. The mortality rate is less than 10% for swine flu, if there are no complications like hog cholera. On July 27, 2007, the Philippine National Meat Inspection Service (NMIS) raised a hog cholera "red alert" warning over Metro Manila and 5 regions of Luzon after the disease spread to backyard pig farms in Bulacan and Pampanga, even if these tested negative for the swine flu virus.
2009 swine flu outbreak
In March and April 2009, more than 1,000 cases of swine flu in humans were detected in Mexico, and more than 80 deaths are suspected to have a connection with the virus. The Mexican fatalities are said to be mainly young adults, a hallmark of pandemic flu. Following a series of reports of isolated cases of swine flu, the first announcement of the outbreak in Mexico was documented on April 23, 2009.
The origins of the new Swine Influenza Virus SIV-H1N1 strain remain unknown. One theory is that Asian and European strains traveled to Mexico in migratory birds or in people, then combined with North American strains in Mexican pig factory farms before jumping over to farm workers. The Mexican health agency acknowledged that the original disease vector of the virus may have been flies multiplying in manure lagoons of pig farms near Perote, Veracruz, owned by Granjas Carroll, a subsidiary of Smithfield Foods.
Some of the cases have been confirmed by the World Health Organization to be due to a new genetic strain of H1N1. The new H1N1 strain has been confirmed in 16 of the deaths and 44 others are being tested as of April 24, 2009.
As of April 25, 2009 19:30 EDT there are 11 laboratory confirmed cases in the southwestern United States and in Kansas, and several suspected cases in the New York City metropolitan area.
A variant of H1N1 was responsible for the Spanish flu pandemic that killed some 50 million to 100 million people worldwide from 1918 to 1919.
The seasonal flu tends to kill just a fraction of 1% of those infected. In Mexico, about 71 deaths out of roughly 1,000 cases represents a fatality rate of about 7.1%. The Spanish flu pandemic of 1918, had a fatality rate of about 2.5%.
Statistical projections for this virus pathology based upon the same infection rate as the Spanish flu pandemic and current fatality rate, indicates that as many as 284 million deaths could occur worldwide as a result of the genesis of this new Swine Influenza Virus SIV-H1N1 strain.
At 8 p.m. on Sunday, April 26, the New Zealand Minister of Health confirmed that 22 students returning from a school trip from Mexico had flu-like symptoms (most likely swine flu). 13 of the students with flu-like symptoms were tested and 10 tested positive for Influenza A, their cases strongly suspected to be the swine flu strain. However there is a possibility that the infected are not infected with the swine flu but other forms of the flu. The government has suggested that citizens of New Zealand with flu-like symptoms should see their physician immediately.
There have been five cases of possible swine flu in Canada, according to the Canadian Press. Two are in British Columbia, and three in Nova Scotia. According to the provincial government, four students in Windsor, Nova Scotia have confirmed cases of swine flu.
The new strain appears to be a recombinant between two older strains. Preliminary genetic characterization found that the hemagglutinin (HA) gene was similar to that of swine flu viruses present in U.S. pigs since 1999, but the neuraminidase (NA) and matrix protein (M) genes resembled versions present in European swine flu isolates. Viruses with this genetic makeup had not previously been found to be circulating in humans or pigs, but there is no formal national surveillance system to determine what viruses are circulating in pigs in the U.S.
On April 26, 2009, some schools in the United States announced closures and cancellations related to possibilities that students may have been exposed to swine flu.
According to University of Virginia virologist Frederick Hayden, the most recent flu season was dominated by H1N1 viruses, and people who had received flu shots in the U.S. may have some protection against swine flu.
According to the Centers for Disease Control and Prevention, the seasonal influenza strain H1N1 vaccine is thought to be unlikely to provide protection against the new Swine Influenza Virus SIV-H1N1 strain.
According to the Centers for Disease Control and Prevention, the virus has been detected in multiple areas, indicating that containment is unlikely. This is exacerbated by the incubation and infectious periods of influenza.
Veterinary swine flu vaccine
Swine influenza has become a greater problem in recent decades as the evolution of the virus has resulted in inconsistent responses to traditional vaccines. Standard commercial swine flu vaccines are effective in controlling the infection when the virus strains match enough to have significant cross-protection, and custom (autogenous) vaccines made from the specific viruses isolated are created and used in the more difficult cases.
Present vaccination strategies for SIV control and prevention in swine farms, typically include the use of one of several bivalent SIV vaccines commercially available in the United States. Of the 97 recent H3N2 isolates examined, only 41 isolates had strong serologic cross-reactions with antiserum to three commercial SIV vaccines. Since the protective ability of influenza vaccines depends primarily on the closeness of the match between the vaccine virus and the epidemic virus, the presence of nonreactive H3N2 SIV variants suggests that current commercial vaccines might not effectively protect pigs from infection with a majority of H3N2 viruses.
The current vaccine against the seasonal influenza strain H1N1 is thought unlikely to provide protection. The director of CDC's National Center for Immunization and Respiratory Diseases said that the United States' cases were found to be made up of genetic elements from four different flu viruses—North American swine influenza, North American avian influenza, human influenza A virus subtype H1N1, and swine influenza virus typically found in Asia and Europe. On two cases, a complete genome sequence had been obtained. She said that the virus is resistant to amantadine and rimantadine, but susceptible to oseltamivir (Tamiflu) and zanamivir (Relenza).
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