Why is swine flu (H1N1) now infecting humans?

Many researchers now consider that two main series of events can lead to swine flu (and also avian or bird flu) becoming a major cause for influenza illness in humans.

First, the influenza viruses (types A, B, C) are enveloped RNA viruses with a segmented genome; this means the viral RNA genetic code is not a single strand of RNA but exists as eight different RNA segments in the influenza viruses. A human (or bird) influenza virus can infect a pig respiratory cell at the same time as a swine influenza virus; some of the replicating RNA strands from the human virus can get mistakenly enclosed inside the enveloped swine influenza virus. For example, one cell could contain eight swine flu and eight human flu RNA segments. The total number of RNA types in one cell would be 16; four swine and four human flu RNA segments could be incorporated into one particle, making a viable eight RNA segmented flu virus from the 16 available segment types. Various combinations of RNA segments can result in a new subtype of virus (known as antigenic shift) that may have the ability to preferentially infect humans but still show characteristics unique to the swine influenza virus (see Figure 1). It is even possible to include RNA strands from birds, swine, and human influenza viruses into one virus if a cell becomes infected with all three types of influenza (for example, two bird flu, three swine flu, and three human flu RNA segments to produce a viable eight-segment new type of flu viral genome). Formation of a new viral type is considered to be antigenic shift; small changes in an individual RNA segment in flu viruses are termed antigenic drift and result in minor changes in the virus. However, these can accumulate over time to produce enough minor changes that cumulatively change the virus’ antigenic makeup over time (usually years).

Second, pigs can play a unique role as an intermediary host to new flu types because pig respiratory cells can be infected directly with bird, human, and other mammalian flu viruses. Consequently, pig respiratory cells are able to be infected with many types of flu and can function as a “mixing pot” for flu RNA segments (see Figure 1). Bird flu viruses, which usually infect the gastrointestinal cells of many bird species, are shed in bird feces. Pigs can pick these viruses up from the environment and seem to be the major way that bird flu virus RNA segments enter the mammalian flu virus population.

What is swine flu (novel H1N1 influenza A swine flu)?

Swine flu (swine influenza) is a respiratory disease caused by viruses (influenza viruses) that infect the respiratory tract of pigs and result in nasal secretions, a barking-like cough, decreased appetite, and listless behavior. Swine flu produces most of the same symptoms in pigs as human flu produces in people. Swine flu can last about one to two weeks in pigs that survive. Swine influenza virus was first isolated from pigs in 1930 in the U.S. and has been recognized by pork producers and veterinarians to cause infections in pigs worldwide. In a number of instances, people have developed the swine flu infection when they are closely associated with pigs (for example, farmers, pork processors), and likewise, pig populations have occasionally been infected with the human flu infection. In most instances, the cross-species infections (swine virus to man; human flu virus to pigs) have remained in local areas and have not caused national or worldwide infections in either pigs or humans. Unfortunately, this cross-species situation with influenza viruses has had the potential to change. Investigators think the 2009 swine flu strain, first seen in Mexico, should be termed novel H1N1 flu since it is mainly found infecting people and exhibits two main surface antigens, H1 (hemagglutinin type 1) and N1 (neuraminidase type1). Recent investigations show the eight RNA strands from novel H1N1 flu have one strand derived from human flu strains, two from avian (bird) strains, and five from swine strains.

Herbal soup fights flu A, perhaps useful to guard off swine flu too?

CM NEWS – Swine flu outbreak has scared the world recently, with death toll reaching 100 and counting. While scientists are racing to understand the flu and in full effort to formulate a new vaccine against it, the only things ordinary folks like us can do is to keep ourselves healthy and strong to guard off infection. In traditional Asian medicine, a decoction called Ma Huang Tang (麻黃湯) in Chinese or Mao-to in Japanese.

What’re in Ma Huang Tang?

The main ingredients of Ma Huang Tang are:


In a Japanese study conducted to evaluate the effect of oral Mao-to (麻黃湯) administration in children with type A influenza, the Mao-to powder was more effective in controlling fever due to flu A than administering an antiviral drug commonly used to fight flu A, Oseltamivir, alone.

What is Oseltamivir? Oseltamivir is an antiviral drug that is used in the treatment and prophylaxis of both Influenzavirus A and Influenzavirus B infection. Like zanamivir, oseltamivir is a neuraminidase inhibitor. It acts as a transition-state analogue inhibitor of influenza neuraminidase, preventing progeny virions from emerging from infected cells.

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In the Japanese study, the scientists performed a controlled trial of 60 children, from 5 months through 13 years of age, with fever and influenza-like symptom of up to 48 h duration. Patients assigned into the following 3 groups: oral Mao-to powder 0.06 g/kg body wt. three times daily; Oseltamivir 2 mg/kg body wt. dose twice daily; or both oral Mao-to plus Oseltamivir.

The results indicated that the median duration of fever after treatment was significantly shorter in the Mao-to and Mao-to plus Oseltamivir groups, compared with the Oseltamivir only group. It was thus concluded by the scientists that oral Mao-to administration was effective in the control of fever due to type A influenza infection in children.

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