♥ Virology

Thursday, November 20, 2008

3:29 PM

Poxviridae are double stranded DNA viruses with complex capsids and envelope. Poxviridae are the largest and most complex of all viruses. They are the largest of viruses- 300nm in diameter,visible with just a light microscope. Poxviridae infect a wide range of hosts. Many infect mammals like mice, camels, elephants, cattle, and monkey. (Chickenpox is not not cause by poxviridae) All poxviridae produce lesion and result in scars. Lesion progress through a series of stages. The lesion begin as flat, reddened macules, which then become a raised sores called papules. This papules will later be filled with a clear liquid, at this stage it will be called vesicles which then progress to pus-filled pustules, which is known as pocks or pox. Poxvirus pustules then dry up to form a crust, and because these lesions penetrate the dermis of the skin, they result in characteristic scars. Infection of poxviridae occurs primarily through inhalation of viruses in droplets or dried crust. Poxviridae remain stable for hours in air. The main poxvirus disease of human is smallpox-also known as variola.

Smallpox is the first human disease to be globally eradicated in nature. It played an important role in the history of microbiology, immunization and medicine. During the middle ages, 80% of the European poplulation contracted smallpox. It was later spread to Native Americans and resulted as many as 3.5 million people death. Variola exists in two forms or strains. Variola major causes severe disease with mortality rate of 20% or higher, depending on the age and general health of the host; and variola minor causes a less severe disease with mortality rate less than 1%. Both type of variola infect internal organs and produce fever, malaise, delirium and prostration before moving via the bloodstream to the skin where they produce recognizable pox. Both strians also leave severe scars on the skin of survivors, especially on the face.

At this period of time, Vaccination make it appearance. Edward Jenner realise that milkmaids are not infected with smallpox after they are infected with cowpox virus(Vaccinia). He vaccinate cowpox from milkmaids into an 8 years old boy (James Phipps). After the boy recover from cowpox he vaccinate him with smallpox and the boy did not contract smallpox. He carried many other successful test, and he name this idea vaccination from the word vaccinia, latin of cowpox. He was successful cause the antigens from cowpox virus are chemically similar to those of smallpox virus. The exposure of cowpox allowed the immunological memory in our body to be subsequent resistances against smallpox and cowpox virus and successful eradicated.

Signing off

Jiani

Thursday, November 13, 2008

9:58 PM

Be loyal to one. Stay loyal to one. If we don’t then, the predominant AIDS might be more than loyal to us. True enough; AIDS is a deadly disease that kills millions of people each year.

AIDS stand for Acquired Immune Deficiency Syndrome. They are caused by HIV – Human Immunodeficiency Virus which belong to the family RETROVIRUSES.

Retroviruses are RNA viruses and the virion RNA is linear and 7 to 10kb long. The positive sense single stranded RNA genome is packaged into a protein capsid, surrounded by a lipid envelope.

Retrovirus particles also contain the enzyme reverse transcriptase (or RTase), which causes synthesis of a complementary DNA molecule (cDNA) in the host cell using virus RNA as a template. This means that the DNA in the cells contains the virus and the genome does not serve as an mRNA. The virus thereafter replicates as part of the host cell's DNA. mRNA would be then translated into viral proteins that are used to make the virus envelope. New viral particles are assembled and they bud from the plasma membrane, and are released.

This lipid envelope contains polypeptide chains including receptor binding proteins which link to the membrane receptors (complex protein structures) of the host cell, initiating the process of infection. A receptor is often compared to a lock into which a specific key or "ligand" will fit. There are at least two receptors on T-lymphocytes to which the human immunodeficiency virus (HIV) sticks. The primary receptor, called "CD4" is the main molecule responsible for HIV virus to bind. Cells that do not contain “CD4” do not attract HIV.

All retroviruses contain the gag, pol and the env genes.
Gag – Group specific antigen codes for core and structural proteins of the virus.
Pol – Polymerase codes for reverse transcriptase, protease and integrase. They do not contribute to the structure.
Env – Envelope codes for the retroviral coat proteins.

AIDS is transmitted through various ways such as
· Having sex with an infected person
· Sharing a needle (shooting drugs) with someone who is infected
· Blood and blood products
· Child being born when mother is infected
· Drinking the breast milk from an infected mother

Acute stage
Primary infection of HIV may cause flu-like symptoms, fever, skin rash, swollen glands and swollen lymph nodes. These symptoms do not indicate the development of AIDS, and they usually disappear within a few days or weeks.

Asymptomatic stage
People living with HIV may feel and look completely well but their immune systems would nevertheless be damaged. The HIV still replicates within and it will still transmit even if the infected person is healthy.

Symptomatic stage
Over time the immune system becomes severely damaged by HIV. The lymph nodes and tissues become damaged or 'burnt out' because of the years of activity. HIV mutates and becomes more pathogenic, in other words stronger and more varied. It leads to more T helper cell and CD4 T lymphocytes destruction. The body fails to keep up with replacing the T helper cells that are lost. As the immune system deteriorates, the symptoms worsen.
A drug has not been found for AIDS therefore, it is very difficult to treat this disease. Those people who are infected with AIDS should boost their immune system by the intake of vitamins, minerals and anti-oxidants.

lOShiNi

Friday, November 7, 2008

2:26 PM

This week, I am introducing two more viruses from the family Orthomyxoviridae and Picornaviridae.

What’s that with a name so long?

Well, they are actually RNA viruses from the family which cause us Flu and cold respectively.

I shall start explaining from Picornaviridae family.

Picornaviridae are the largest virus family with over 230 serotypes and 9 genera such as Enterovirus, Heptovirus and the Rhinovirus. (If the Rhinovirus sounds familiar, it is actually the virus, WANTED for your common cold!)

The Picornaviridae doesn’t have any envelope and it is a one linear positive RNA virus. With other ends modified, its capsids are mostly empty or uncompleted!
As I go into more of the Rhinovirus; it infects you by infecting the upper respiratory tract as it will not be able to grow as fast in 37 °C and incubates for a short period of around 2 to 3 days before any symptoms for it arise. And once the virus infects our cells and is detected by our antibodies, our locally synthesized IgA would defend itself against the virus. After “defeating” the virus, serum IgG would remain in your blood, which can stay up to your lifetime, to defend itself from any future infection of that virus. However, your body is still at risk of being infected again as there are over 100 rhinoviruses in the world!

As you can see, many of us “usually mistaken cold as flu” as they have similar symptoms! Normally, symptoms such as watery nasal discharge, difficulty breathing through your nose, and sneezing could be seen in patients diagnose with common cold.And Another more accurate diagnose could be done through nasal washings and virus culture as the IgA could be seen and detected from the blood sample.

Talking about flu virus, it is from the virus family Orthomyxoviridae.

Since 430 B.C. there has been report of the influenza epidemic in Athens. But luckily, only 2 types of influenza virus, A and B would cause hectic in humans.
With spikes envelope and single strand negative RNA in 8 segments; Orthomyxoviridae is capable of “changing” its genes every now and then. It also infects the respiratory tract in humans and can be diagnose by the antibodies in blood sample through nasal wash or virus culture in chick embryo. With a longer incubation period of 1 to 4 days, its 8 segments of the genome enable it to actively assort its genes and causing mutation, resulting in new subtypes and new strain.
Antigenic shift normally results in only a small change in the genome, signaling mutation and a new strain which happens most of the time. While an antigenic shift is a major change of the gene, resulting in a new subtype but it happens only once every 10 to 40 years. An example of such antigenic changes is the avian flu which since its outbreak in 1997 have caused 248 deaths in 12 countries as of January 2009 from the WHO

Both virus, Orthomyxoviridae and Picornaviridae can be found abundant in nasal discharge and to combat both common cold and flu, and not to ruin your festive mood (as both common cold and flu are really common during festive seasons!) it is best to washing your hands regularly, practicing healthy habits and preventing inhaling drops of mucus full of rhinovirus from the air when a suspected contagious person coughs or sneezes! As for both of the virus, they have useless effects on vaccines. As cold have over a hundred of types, it is almost impossible to produce so many different vaccines for each of the types because it is considered to have no economic benefits. On the other hand for flu, the antigenic drift and shift that occurs are too fast to occur for vaccines to be produced.

Below, is a video on the avian flu, H5N1 virus, explained by a veterinarian