Microbial disease etiology and pathogenesis

¶ … disease known as influenza is a respiratory illness and it is caused by flu viruses. Influenza is not to be confused with the common cold. It may originally start out that way, with some cold-like symptoms, but very quickly the person affected by the flu virus will suffer far more serious symptoms. According to the Centers for Disease Control and Prevention (CDC) the following symptoms will be present: fever (and chills); cough; sore throat; runny or stuffy nose; muscle or body aches; headaches; tiredness / fatigue; a possibility of diarrhea and vomiting. The CDC asserts that "not everyone with flu will have a fever" (CDC).

What are the complications associated with influenza? The CDC reports that the average person who is attacked with the influenza virus recover in less than two weeks, but there are serious complications (which is why the government and many healthcare professionals recommend a flu shot at the beginning of the winter season). The influenza virus can lead to pneumonia, bronchitis, and sinus and ear infections -- and in some cases people die from the influenza virus (CDC). In fact during the 1990s there were an estimated 17,000 deaths during the least serious flu season and about 52,000 deaths during the most severe flu season. The flu virus that struck in 2009 (H1N1) took approximately 12,000 lives in the U.S. alone. What worries healthcare professionals is that people who have existing health problems (for example, those with asthma or chronic congestive heart failure) may find the influenza virus will worsen their conditions.

Description of Pathogen

What group does the pathogen belong to? The virus that is the subject of this paper is influenza A virus. Influenza A has subtypes hemagglutinin (H) and the neuraminidase (N). And within the hemagglutinin there are 16 different subtypes and there are 9 different neuraminidase subtypes (CDC).

Influenza viruses (IFVs) are members of the family Orthomyxoviridae; the influenza A virus (IFAV) belongs to the genus Influenzavirus A. Influenza A is the most virulent of the three influenza types. It is the cause of pandemics and flu epidemics, and is known to have an avian host as an intermediate (IH). (http://users.rcn.com).

Any unusual or distinctive features? The influenza A pathogen / virion is a globular particle that is roughly 100 nanometers in diameter. It is sheathed in a lipid bilayer -- that has been derived from the plasma membrane of its host. Inside the lipid bilayer are two membrane proteins that are integral to the process.

The two membrane proteins (also mentioned above) include 500 hemagglutinin (H) and 100 molecules of neuraminidase (N). Within the lipid bilayer some 3,000 molecules of matrix protein will be found along with 8 pieces of RNA. RNA is actually called Ribonucleic acid and it is a chain of nucleotides that are present in the cells of all life. The function of RNA includes having regulatory power over gene expression to assisting with the process of gene copying.

What do the 8 pieces of RNA do? Each of them produces multiple copies of a nucleprotein, several molecules of RNA polymerase (the 3 subunits of polymerase) and each of the 8 molecules also can be broken down into the genes that make up influenza A: the HA gene; the NA gene; the NP gene; the M. gene; the NS gene; and 6-8 genes of influenza A are housed in one RNA molecule (PA, PB1, PB2) for each of the 3 subunits of RNA polymerase. (http://users.rcn.com).

Morphology of the influenza A virus: When contracting the virus from other humans, typically a person who has an acute infection sneezes and the tiny droplets from the sneezed are then inhaled into the pharynx (lower respiratory tract). The spread then has an incubation period of about one to three days. The technical explanation for the morphology of the influenza virion: the virion is usually round but there may be long filament associated with it. The RNA genome (discussed in the section above) is present in eight separate segments of the ribonucleoprotein (RNP) and each of those 8 segments has to be present for replication to take place. The virus is taken into the cell in the lungs by endocytosis. How does it get into the respiratory tract? The droplets enter the nose and pass by the tonsillar lymphoid organs; they are targeting the epithelial cells in the trachea and the bronchial tube and into the lungs to carry the virus into the lungs and hence the bloodstream as well. (University of Cape Town).

Reservoir (Where is the pathogen typically found?)

The influenza A pathogen is most often found in other human beings who have an acute infection of the virus. However, wild birds are the basic (primary) reservoir for every subtype of influenza virus A, according to the Centers for Disease Control and Prevention. Wild birds are also believed to be the primary source of influenza A in every other animal that carries the virus. Some birds are sickened by the virus (which is found in their digestive track) but most birds are not affected by the virus that they carry -- or if they are, it is an asymptomatic infection, usually quite mild and doesn't affect the daily living activities (or flight) of the birds.

That having been said, if the bird is infected with avian influenza A viruses (including the virulent virus strains called H5 and H7), many bird deaths can occur as the virus is transmitted to wild birds, domestic birds like turkeys and chickens as well. In addition to birds, pigs can become infected with and be a carrier of the human-type influenza virus A and the avian type influenza A. When a pig is infected it has symptoms very much like the symptoms humans have. The research shows that pigs can be carriers of avian virus, human virus, and swine influenza viruses -- and they can be infected with all three strains of the influenza virus simultaneously.

When all three of the influenza viruses -- or just two -- are present in a pig, that pig can then become a reservoir for a new virus. The genes of the two viruses, human and avian, for example, can mix and through a chemical process produce a new virus in the pig. That new virus can have most of the genes from the human influenza virus and the hemagglutinin and/or the neuraminidase from the avian virus. And because it is new, it can spread quickly among humans with surface proteins that scientists and healthcare professionals haven't seen before. The type of shift is known as an antigenic shift. It results from a new subtype from which humans have not been inoculated against. When worse comes to worse, an influenza pandemic can occur, if the spreading is quick enough and an antidote is not found in time. (University of Queensland) (CDC).