Daily Disease: Influenza and Vaccines

With flu season coming up (depending on where you live) I thought this would be a good review to go over.

Epidemiology
According the Control of Communicable Diseases Manual (<3) it is an "acute viral disease of the respiratory tract characterized by fever, cough (usually dry), headache, myalgia, prostration, coryza, and sore throat." The reservoir is humans and the mode of transmission is through large spread from coughing or sneezing.

Cover your mouth sicko!!

Always cover your mouth when coughing or sneezing, but not with your hands! Use your elbow if you don't have a tissue.

The incubation period is on average two days, which means that from your first exposure to full blown disease takes two days. Influenza can be fatal for the elderly, infants, and those with compromised immune systems and may lead to secondary bacterial infections such as pneumonia.

Molecular
Family Orthomyxoviridae. The virion is enveloped and 80-120 nm in length. The enveloped is taken from the host plasma membrane during the process of budding. The genome is ss RNA negative sense and is in six to eight fragments, each of the segments codes for one or two proteins

The hemagglutinin glycoprotein attaches to host cells sialic acid residues present in the ciliated epithilium, and the loss of these cells is a loss in their function, which is to clear the tracts of debris and bacteria. Viral replication in these cells induces the secretion of interferons and cytokines that causes inflammation.

The HA and NA are the proteins that determine the virions tropism, or what tissues it can infect and is also used in the classification of the virus. An H1N1 and H5N1 differ in the HA protein.
Okay I just notice a discrepancy between the image and my notes, the RNA is negative sense, we'll go with the leading virologist that wrote the section on Orthomyxovirus.

Epidemics and Pandemics
The worst epidemic since the black plague was the 1918 Spanish flu pandemic (meaning it was world wide) that killed 20 million people world wide and unleashed the terror that is Edward Cullen (according to my virology professor).  Other epidemics include the Hong Kong epidemic in 1967, Asian flu in 1956, and the H1N1 flu in 2009. The epidemics appear to be cyclic, occurring every 10 to 50 years.

The epidemics are caused the genomes affinity for genetic variability and rapid evolution. In a process know as antigenic drift the RNA ploymerase that copies the RNA for progeny makes mistakes (there is no proof reading function, unlike DNA polymerase), and the accumulation of mutations causes changes in the HA and NA glycoproteins. This is the main reason why there are new flu vaccines each new flu season. It is a new virus that our immune systems haven't encountered before.

The other process that allows for genetic variability is antigenic shift. Antigenic shift occurs when a cell is infected with multiple types of influenza virions, and the genes are reassorted.

In this picture we can see that the pig is infected with a human  virus and an avian virus. Some of the avian influenza genes are packages with the human influenza genes creating a knew virus that our immune systems have not encountered before.  This was the case with the H1N1 flu last year. And no, you can't get it from eating pork.

Well, hope that made sense (compressing pages and pages of notes is hard) and was interesting if not entertaining. Feel free to ask questions, make requests, etc.

I'm going to eat lunch then post about vaccines and whether or not viruses are alive.
Oh, does anyone know how to get the cute poupee girl gagdet? It's driving me crazy.

My brother just accused me of plagiarism, so here are my sources: CDC, Fundamentals of Molecular Virology, Medical Microbiology sixth edition, and my old papers.