Enveloped DNA Viruses

As my group member had mentioned about envelope viruses. So let me tell you more about it.
There are two groups of enveloped DNA Viruses. Below are some interesting information about it.

Herpesviridae
Epstein-Barr virus, frequently referred to as EBV, is a member of the herpesvirus family with Linear ds DNA and three origin of replication.One of the most common human viruses. The virus occurs worldwide, and most people become infected with EBV sometime during their lives. In the United States, as many as 95% of adults between 35 and 40 years of age have been infected. Infants become susceptible to EBV as soon as maternal antibody protection (present at birth) disappears. Many children become infected with EBV, and these infections usually cause no symptoms or are indistinguishable from the other mild, brief illnesses of childhood.

The Epstein-Barr virus appears capable of infecting only two major cell types: the outer (epithelial) cells of the salivary gland, and white blood cells known as B lymphocytes (B-cells). Infection with the Epstein-Barr virus develops first in the salivary gland. Large amounts of the virus are released in the saliva, enabling it to spread from one person to another.
Infection of B-cells with the virus causes them to proliferate. This proliferation is controlled by the immune system; if the correct immune response does not develop, individuals are at risk of developing a form of cancer. It is thought to be responsible for a number of diseases in addition to glandular fever (otherwise known as infectious mononucleosis) and Burkitt’s lymphoma.

A late event in a very few carriers of this virus is the emergence of Burkitt's lymphoma and nasopharyngeal carcinoma, two rare cancers
Most individuals exposed to people with infectious mononucleosis have previously been infected with EBV and are not at risk for infectious mononucleosis. In addition, transmission of EBV requires intimate contact with the saliva (found in the mouth) of an infected person. Transmission of this virus through the air or blood does not normally occur. The incubation period, or the time from infection to appearance of symptoms, ranges from 4 to 6 weeks. Persons with infectious mononucleosis may be able to spread the infection to others for a period of weeks. However, no special precautions or isolation procedures are recommended, since the virus is also found frequently in the saliva of healthy people. In fact, many healthy people can carry and spread the virus intermittently for life. These people are usually the primary reservoir for person-to-person transmission. For this reason, transmission of the virus is almost impossible to prevent.

Symptoms of infectious mononucleosis:
Fever, sore throat, and swollen lymph glands. Sometimes, a swollen spleen or liver involvement may develop. Heart problems or involvement of the central nervous system occurs only rarely, and infectious mononucleosis is almost never fatal. There are no known associations between active EBV infection and problems during pregnancy, such as miscarriages or birth defects. Although the symptoms of infectious mononucleosis usually resolve in 1 or 2 months, EBV remains dormant or latent in a few cells in the throat and blood for the rest of the person's life. Periodically, the virus can reactivate and is commonly found in the saliva of infected persons. This reactivation usually occurs without symptoms of illness. EBV also establishes a lifelong dormant infection in some cells of the body's immune system.

Susceptibility
If antibodies to the viral capsid antigen are not detected, the patient is susceptible to EBV infection.

Primary Infection
Primary EBV infection is indicated if IgM antibody to the viral capsid antigen is present and antibody to EBV nuclear antigen, or EBNA, is absent. A rising or high IgG antibody to the viral capsid antigen and negative antibody to EBNA after at least 4 weeks of illness is also strongly suggestive of primary infection. In addition, 80% of patients with active EBV infection produce antibody to early antigen.

Past Infection
If antibodies to both the viral capsid antigen and EBNA are present, then past infection (from 4 to 6 months to years earlier) is indicated. Since 95% of adults have been infected with EBV, most adults will show antibodies to EBV from infection years earlier. High or elevated antibody levels may be present for years and are not diagnostic of recent infection.

Reactivation
In the presence of antibodies to EBNA, an elevation of antibodies to early antigen suggests reactivation. However, when EBV antibody to the early antigen test is present, this result does not automatically indicate that a patient's current medical condition is caused by EBV. A number of healthy people with no symptoms have antibodies to the EBV early antigen for years after their initial EBV infection. Many times reactivation occurs subclinically.

Chronic EBV Infection
Reliable laboratory evidence for continued active EBV infection is very seldom found in patients who have been ill for more than 4 months. When the illness lasts more than 6 months, it should be investigated to see if other causes of chronic illness or CFS are present.

Hepadnaviridae - Hepatitis

• Partial dsDNA
• Endogeneous DNA - dependent DNA polymerase
• Use of overlapping reading frame
• RNA intermediate

The word "hepatitis" means inflammation of the liver. Toxins, certain drugs, some diseases, heavy alcohol use, bacterial and viral infections can all cause hepatitis. Hepatitis is also the name of a family of viral infections that affect the liver; the most common types in the United States are hepatitis A, hepatitis B, and hepatitis C.

Hepatitis A

Is an acute liver disease caused by the hepatitis A virus (HAV), lasting from a few weeks to several months. It does not lead to chronic infection.
Transmission: Ingestion of fecal matter, even in microscopic amounts, from close person-to-person contact or ingestion of contaminated food or drinks.
Vaccination: Hepatitis A vaccination is recommended for all children starting at age 1 year, travelers to certain countries, and others at risk.

Hepatitis B

Is a liver disease caused by the hepatitis B virus (HBV). It ranges in severity from a mild illness, lasting a few weeks (acute), to a serious long-term (chronic) illness that can lead to liver disease or liver cancer.
Transmission: Contact with infectious blood, semen, and other body fluids from having sex with an infected person, sharing contaminated needles to inject drugs, or from an infected mother to her newborn.
Vaccination: Hepatitis B vaccination is recommended for all infants, older children and adolescents who were not vaccinated previously, and adults at risk for HBV infection.

Acute liver infection

• Immediate symptoms
• Loss of appetiet, nausea, vomiting, fever, abdominal pain and jaundice
• About 5% to 10% of acutely infected adults become chronically infected.

Chronic liver infection

• No visual symptoms
• No abnormalities on laboratory testing
• Some will go on to develop cirrhosis and Hepatocellular carcinoma (primary liver cancer)

Hepatitis C

Is a liver disease caused by the hepatitis C virus (HCV). HCV infection sometimes results in an acute illness, but most often becomes a chronic condition that can lead to cirrhosis of the liver and liver cancer.
Transmission: Contact with the blood of an infected person, primarily through sharing contaminated needles to inject drugs.
Vaccination: There is no vaccine for hepatitis C.

Hepatitis D

Is a serious liver disease caused by the hepatitis D virus (HDV) and relies on HBV to replicate. It is uncommon in the United States.
Transmission: Contact with infectious blood, similar to how HBV is spread.
Vaccination: There is no vaccine for hepatitis D.

Hepatitis E

Is a serious liver disease caused by the hepatitis E virus (HEV) that usually results in an acute infection. It does not lead to a chronic infection. While rare in the United States, hepatitis E is common in many parts of the world.
Transmission: Ingestion of fecal matter, even in microscopic amounts; outbreaks are usually associated with contaminated water supply in countries with poor sanitation.
Vaccination: There is currently no FDA-approved vaccine for hepatitis E.

Viral Envelopes. Bad or good?

Have you ever wondered what the viral envelope is meant for? Or whether it is more of a boon or a bane to the functions of viruses? This post is to help solve those mysteries and clear yoiur mind. We all know that these envelopes, that surround the viral capsid, are typically made out of portions from it's host cell membranes such asphospholipods and proteins, and often viral glycoproteins. You could say that viruses are very much like pirates, plundering their resources from their victims for their own benefits. But then again, it is the nature of many organisms, weakening others while strengthening themselves. However, today, I would like to get down to what we really want to know.

For one thing, viral envelopes help viruses to enter the host cells, and the glycoproteins on it's surface help to indentify and bind to specific receptor sites on the cell membranes. Thereafter, the viral envelope fuses with the cell membrane, leaving the capside and viral genome free to enter and infect. This is a pretty effective and logical strategy right?

Now, the average joe would probably think that besides it's useful role in binding to cell membranes, it would provides some further protection. But! Did you all know that this envelope makes the virus more susceptible to dessication, heat and detergents, amking the viruses easier to sterilize? Yes, in this case, viral envelopes can be more of a bane than a boon, folks. However, ultimately, whether the viral envelope is needed, depends on the goal of the virus. Does it wish to infect cells that badly? Or does it wish to be more protected? Take your time to think about it.

Retroviruses

Lentivirus (HIV)

HIV stands for human immunodeficiency virus. HIV destroys certain white blood cells called CD4+ T cells. These cells are critical to the normal function of the human immune system, which defends the body against illness. When HIV weakens the immune system, a person is more susceptible to developing a variety of cancers and becoming infected with viruses, bacteria and parasites.

• envelope with glycoprotein peplomers


• 2 copies of linear plus sense ssRNA, each 7 to 10kb
  
• 3' polyadenylated tail and 5' cap


• reverse transcriptase (genome doesn't serve as mRNA)

Primary infection

• acute stage
• flu-like symptoms
• fever
• skin rash
• swollen lymph nodes
• rate of replication
• propensity to mutate
• cytopathogenicity
• host resistance (suppresion by CD8 T suppresor cells and presence of cytotoxic T-lymphocytes)
  

Asymptomatic stage

• no apparent disease
• fall in CD4 T lymphocytes (primary target cell)
• fatigue
• depression
• weight loss
• memory disorders

Largest DNA viruses

Orthopoxvirus (Poxvirdae)

The poxviruses are the largest known DNA viruses and are distinguished from other viruses by their ability to replicate entirely in the cytoplasm of infected cells. Poxviruses do not require nuclear factors for replication and, thus, can replicate with little hindrance in enucleated cells. Double-stranded DNA genome and is surrounded by a lipoprotein core membrane. It can remain stable for hours in the air.
Smallpox is caused by the variola virus, a brick-shaped DNA virus in the orthopoxvirus genus. The variola virus is among the largest of all animal viruses and can be seen with a light microscope. The variola virus initially infects the cells in the respiratory tract, then spreads to lymph nodes. The virus enters the bloodstream about 3-4 days after the initial infection.

Eradication of smallpox

The eradication of smallpox occurred with the observation by English physician, Edward Jenner, that milkmaids who developed cowpox, a less serious disease, did not develop the deadly smallpox. In 1796, Jenner took the fluid from a cowpox pustule on a dairymaid's hand and inoculated an 8-year-old boy. Six weeks later, he exposed the boy to smallpox, and the boy did not develop any symptoms. Jenner coined the term "vaccine" from the word "vaca" which means "cow" in Latin. His work was initially criticized, but soon was rapidly accepted and adopted. By 1800 about 100,000 people had been vaccinated worldwide.

Smallest RNA Viruses

Orthomyxoviridae and Picornaviridae

Picornaviridae is the largest virus family (over 230 serotypes)
One linear (+) RNA
5 genera :

• Aphtovirus
  
• Cardiovirus


• Enterovirus


• heptovirus


• Rhinovirus
  

Picornaviridae -Rhinovirus

• upper Respiratory tract infection


• serum IgG persists for years


• over 100 rhinoviruses

Symptoms :

Cold

• watery nasal discharge
  
• congestion
  
• sneezing


• no fever
  

Orthomyxoviridae- Influenza Virus

• Enveloped
• Pleomorphic
• Spikes on envelope
• Groups of HA or NA
• Ratio of HA to NA is 5:1

There are three types of influenza virus, A, B and C. A and B types are known to cause flu like symptoms in humans. Type C is rare in humans and only causes mild symptoms.

Genome of Influenza A & B

• ss (-) RNA in 8 segments
• 3 ploymerase polypeptides with each segment
• 5' and 3' end at all segments highly conserved

The Virus strains are characterised by the nature of the two proteins found on there surface, namely Neuraminidase and Hemagglutinin. Approximately 80 percent of the spikes are hemagglutinin, a trimeric protein that functions in the attachment of the virus to a host cell. The remaining 20 percent or so of the glycoprotein spikes consist of neuraminidase, which is thought to be predominantly involved in facilitating the release of newly produced virus particles from the host cell. The inner of the cell contains the RNA nucleotides which are the genetic code for the virus replication.

• 14 subtypes of HA


• 9 subtypes of NA


• HA 1,2,3 and NA 1 and 2 are found in human.
  

Antigenic Drift and Shift

• Antigenic drift is a mutation in the genetic code of surface antigens (HA/NA) (type A and B)


• Antigenic shift occurs when genes re-assort from different subtypes (only for type A)

Symptoms :

Flu

• fever


• headache


• aches and pains


• fatigue


• exhaustion


• cough

Hierarchy of classification

Hierarchy refers to organization system in which groups are nested in each level. Higher levels are the most general and contain a collection of groups and so on down each level to the most specific. Biological classification is a hierarchy from general groups (such as domains) down to specific groups (genus and species).
Hierarchy of classification
Kingdom
Phylum
• Sub-phylum
• Super-class
Class
• Sub-class
• Super-order
Order
• Sub-order
• Super-family
Family
• Sub-family
Genus
• Sub-genus
Species
• Sub-species

There is a specific hierarchy by which all living things are classified
example of the hierarchy - classification of the house cat:

Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Carnivora
Family: Felidae
Genus: Felis
Species: Felis domesticus

Classification of Humans
Kingdom Animalia :
Usually motile, multi-cellular organisms, without cell walls or
chlorophyll; usually, internal cavity for digestion of nutrients
Phylum Chordata:
Organisms that at one time in their life history have a dorsal
hollow nerve cord, a notochord, and pharyngeal pouches
Class Mammalia:
Warm-blooded vertebrates possessing mammary glands; body
more or less covered with hair; well-developed brain
Order Primates:
Good brain development, opposable thumb and sometimes big
toe; lacking claws, scales, horns, and hoofs
Family Hominidae:
Limb anatomy suitable for upright stance and bipedal locomotion
Genus Homo:
Maximum brain development, especially in regard to particular
portions; hand anatomy suitable to the making of tools
Species Homo sapiens:
Body proportions of modern humans; speech centres of brain
well developed

What is a species: special problems for paleontology
A group of individuals that interbreeds.
A group of individuals that shares a common set of genetic characteristics .

The Virus Taxonomy

Viruses are not like animals or plants, in the sense that viruses do not exhibit the typical signs of life, as stated in the previous post. Virrus Taxonomy focuses on family, genus and species, though not all viruses are assigned order, family and genus. There are 2 systems of virus taxonomy, the Lwolf's Scheme for classification, which makes use of the physical properties of the virus, and Baltimre's System for classification which is based on the viral genome and its relationship to messenger RNA, abbreviated as mRNA.

Baltimore Classification System

The Baltimore classification as previoulsy stated, is based on the viral genome. As shown in the picture, viruses are grouped into 7 groups. 

The first group contains viruses that contain positive sense double stranded DNA, (+) dsDNA. which is then translated to mRNA which then codes the protein. 

Group 2, where positive sense single strand DNA is transcripted to (+/-) dsDNA before it is then translated to mRNA. 

Group 3, dsRNA is translated mRNA.

Group 4 is where (+)RNA is transcripted to (-)RNA before it is then transcripted into mRNA.

Group 5 is where (-)ssRNA is transcripted to mRNA.

Group 6 is where (+)ssRNA is reverse transcripted before it becomes mRNA.

Group 7 is where (+/-)dsDNA becomes a single strand before it undergoes reverse transcription before it finally becomes mRNA.

That's all for this post.