ELISA

ELISA

Enzyme-Linked ImmunoSorbent Assay (ELISA) is a biochemical technique used mainly in immunology to detect the presence of an antibody or an antigen in a sample. In simple terms, in ELISA an unknown amount of antigen is affixed to a surface, and then a specific antibody is washed over the surface so that it can bind to the antigen. This antibody is linked to an enzyme, and in the final step a substance is added that the enzyme can convert to some detectable signal. Thus in the case of fluorescence ELISA, when light of the appropriate wavelength is shone upon the sample, any antigen/antibody complexes will fluoresce so that the amount of antigen in the sample can be inferred through the magnitude of the fluorescence.

Types of ELISA

There are 3 types of ELISA. "Indirect", Sandwhich and Competitive ELISA.

"Indirect" ELISA:

The steps of the general, "indirect," ELISA for determining serum antibody concentrations are:

- Apply a sample of known antigen of known concentration to a surface, often the well of a microtiter plate The antigen is fixed to the surface to render it immobile. Simple adsorption of the protein to the plastic surface is usually sufficient.

- A concentrated solution of non-interacting protein, such as bolvine serum albumin(BSA) is added to all plate wells. This step is known as blocking, because the serum proteins block non-specific adsorption of other proteins to the plate.

- The plate wells or other surface are then coated with serum samples of unknown antigen concentration, diluted into the same buffer used for the antigen standards.

- The plate is washed, and a detection antibody specific to the antigen of interest is applied to all plate wells. This antibody will only bind to immobilized antigen on the well surface, not to other serum proteins or the blocking proteins.

- Secondary antibodies, which will bind to any remaining detection antibodies, are added to the wells. These secondary antibodies are conjugated to the substrate-specific enzyme.

- Wash the plate, so that excess unbound enzyme-antibody conjugates are removed.

-Apply a substrate which is converted by the enzyme to elicit a chromogenic or fluorogenic or electrochemical signal.

-View/quantify the result.

The enzyme acts as an amplifier; even if only few enzyme-linked antibodies remain bound, the enzyme molecules will produce many signal molecules. A major disadvantage of the indirect ELISA is that the method of antigen immobilization is non-specific; any proteins in the sample will stick to the microtiter plate well, so small concentrations of analyte in serum must compete with other serum proteins when binding to the well surface.

Sandwhich ELISA:

A less-common variant of this technique, called "sandwich" ELISA, is used to detect sample antigen. The steps are as follows:

- Prepare a surface to which a known quantity of capture antibody is bound.

-Block any non specific binding sites on the surface.

-Apply the antigen-containing sample to the plate.

-Wash the plate, so that unbound antigen is removed.

-Apply primary antibodies that bind specifically to the antigen.

-Apply enzyme-linked secondary antibodies which are specific to the primary antibodies.

-Wash the plate, so that the unbound antibody-enzyme conjugates are removed.

-Apply a chemical which is converted by the enzyme into a color or fluorescent or electrochemical signal.

-Measure the absorbance or fluorescence or electrochemical signal (e.g., current) of the plate wells to determine the presence and quantity of antigen.

The major advantage of a sandwich ELISA is the ability to use impure samples and still selectively bind any antigen that may be present. Without the first layer of "capture" antibody, any proteins in the sample may competitively adsorb to the plate surface, lowering the quantity of antigen immobilized.

Lastly, Competitive ELISA:

A third use of ELISA is through competitive binding. The steps for this ELISA are somewhat different than the first two examples:

-Unlabeled antibody is incubated in the presence of its antigen.

-These bound antibody/antigen complexes are then added to an antigen coated well.

-The plate is washed, so that unbound antibody is removed. (The more antigen in the sample, the less antibody will be able to bind to the antigen in the well, hence "competition.")

-The secondary antibody, specific to the primary antibody is added. This second antibody is coupled to the enzyme.
-A substrate is added, and remaining enzymes elicit a chromogenic or fluorescent signal.

For competitive ELISA, the higher the original antigen concentration, the weaker the eventual signal.

A video on the usage of ELISA (:

References:

google

wikipedia

http://www.youtube.com/watch?v=spQ70PZ3mDg&feature=related

Picornaviridae

Poliovirus, in the family picornaviridae

Description and Significance
The name "picornavirus" means " little RNA virus" (pico means "very small" in Greek; pico + RNA virus). Picornaviruses are among the oldest viruses, dating back to 1400 B.C., when a temple record tells of poliovirus infections in ancient Egypt. Picornaviruses are also among the most diverse viruses, with over 200 serotypes causing infections such as Polio, Hepatitis A, and the common cold. Foot-and-Mouth Disease Virus (genus: Apthovirus), which causes infections in livestock, was one of the first viruses to be recognized; it was discovered by Loeffler and Frosch in 1898. (sources: Flynn, Bedard)

Genome Structure
The picornavirus genome consists of a single molecule of linear, postitive(+)-sense, single-strand RNA. It is non-segmented. The complete genome is 7000-8500 nucleotides long. The 5'-terminus of the genome has a long untranslated region 600-1200 bases in length, which is important in translation, virulence, and possibly encapsidation. There is a shorter untranslated region (50-100 bases in length) on the 3'-terminus, which is important in (-)strand-synthesis. The 5'-terminus untranslated region also has a "clover leaf" secondary structure known as the Internal Ribosome Entry Site (IRES), which distinguishes picornaviruses from other RNA viruses; this structure is important in translation and replication. The 5'-terminus is modified by a covalently-attached VPg protein (which takes the place of a cap), while the 3'-terminus is modified by polyadenylation. (sources: ICTVdB, Bedard, Flynn)

Virion Structure of a Picornavirus
Picornavirus virions consist of a non-enveloped, icosahedrally symmetric capsid. The capsid consists of 12 capsomers and has a diameter of 27-30 nm, which makes it one of the smallest of all viruses (thus the name "picornavirus"). The genome is tightly packed into the capsid. The capsid has four unique proteins: VP1, 2, 3, and 4. (sources: ICTVdB, Flynn)
Reproductive Cycle of a Picornavirus in a Host Cell
Using different cellular receptors (depending on the picornavirus), a picornavirus virion attaches to a host cell. Uncoating occurs, and the virus' RNA is released into the cytoplasm of the host cell through a membrane channel. Virus replication occurs entirely in the cytoplasm. The host cell's transcription processes are shut off to a degree that varies with different picornaviruses, while the IRES helps to make sure the virus' transcription is left untouched. Replication occurs. RNA is packaged into preformed capsids. Release of the virus occurs when cell lysis occurs (with the exception of Hepatits A, which is non-lytic and thus creates a more persistent infection). (source: Bedard)

Viral Ecology & Pathology
The mode of transmission, ecology, and pathology of picornaviruses vary greatly between the different genera. Interestingly, the genetics of virulence phenotypes of picornaviruses is poorly understood. According to Tracy et al., "Picornaviruses do not have virulence genes per se, but the design of the capsid and how it interacts with the virus receptor expressed on the host cell surface, specific sequences within the nontranslated regions of the viral genome, as well as coding sequences that result in different protein sequences may all have a part in determining the virulence phenotype."

Herpes Simplex Virus (HSV)

What is Herpes Virus?
Herpes is a virus, named specifically "herpesvirus hominus". Simplex is a sub-category of the herpesvirus family. Herpes Simplex is defined by five categories, types 1, 2, 6, 7, and 8.

Where does it usually infect?
Generally herpes type 1 infects the mouth in humans and type 2 affects the genital area. However, there are recent studies indicating that there are more and more type 1 genital herpes cases are being diagnosed. Type 6 and 7 cause an infection of infancy (i.e. Roseola and Chickenpox) and Type 8 has been associated with Kaposi's sarcoma which is most often seen in HIV related conditions.

Where does the Herpes virus occur?
Herpes simplex virus (HSV) is extremely common in humans. It’s estimated that as many as 80-90% of the entire human population experience oral herpes infections by the age of twelve years old. Some who are infected with oral herpes will have an acute infection that may appear as infected gums and lips which cause high fever. Usually if an infected person has any symptoms, it would be a few only. A substantial portion of the population has recurrent oral herpes infection, showing up as "cold sores" on lips and sides of the mouth. Oral herpes does have a tendency to show up elsewhere on the face thus creating the position for not realizing that the infection actually is “oral herpes.”

Herpes infects the nerve cells of the spinal cord in the pelvic region (as is the case for genital herpes) and of the nerve ganglia in the facial region at the base of the brain (as is the case for oral herpes). Herpes is a DNA-type virus, inserting its DNA directly into the nerve endings of the skin, which then leads along nerve fibers to the nucleus of the nerve cell. Once the viral information is inserted into the cell's nucleus, this blending of viral genetic information with human genetic information is permanent. There is no cure and herpes virus remains in the body forever. The nerve cell then becomes somewhat of a “factory” for making more viral particles which can lead to recurring herpes outbreaks or conditions suitable for active viral shedding.

What herpes is not though it appears to be?
Herpes is not a "skin infection", but rather an infection of nerve cells, by way of the skin. It is not the "skin" that is infected but rather the nerve cell. When the infection becomes active again in the nucleus of the nerve cell, the viral particles flow back out, down the nerve, and out through little blisters that form in the skin. If the quantity of viral particles coming down the nerve cell isn't enough to form a blister, then a number of viral particles can be excreted through the skin without any symptoms at all.


Other facts about HSV
"Genital herpes" and "oral herpes" refer to the location where the herpes infection is found on the individual, not the type of herpes. Most genital herpes is caused by HSV-2, but can be caused by HSV-1 in as many as 30% of new cases. Oral herpes is most often caused by HSV-1, and rarely if ever by HSV-2. Because these locations are often associated with a particular type of herpes (which seem to "take hold" in those particular locations more easily), medical people, websites and literature often equate the location with the herpes type. You might find that people speak of genitally-located herpes infections as HSV-2 and orally-located herpes as HSV-1. However, either virus can occur in either place, and in fact, potentially anywhere on the body depending on the point where infection takes place.
Someone with an HSV-1 lesion on the mouth can transmit the infection to an intimate partner through oro-genital contact with the genitalia of the other (oral sex), causing a recurrent HSV-1 lesion on the genitalia of the partner. Also, other sites of HSV infection can be produced, such as on a finger (often referred to as "herpetic whitlow") or elsewhere.

NOTE: Genital herpes is not always HSV-2 and oral herpes is not always HSV-1.
Genital herpes affects about 20-25% of Americans (that equates to 1 in 5 or even as many as 1 in 4), these numbers likely exceed 50 million Americans. Though most other STDs are seen to be decreasing in their rate of new infections, genital herpes remains one of the fastest growing infectious diseases in the world in absolute numbers of cases. However, Human Papillomavirus (HPV) infections are believed to outnumber herpes infection in both growth rate and likely in absolute numbers.

Generally genital herpes infections are not considered to be extremely contagious. Casual contact on toilet seats, chairs, and similar sorts of common social contact is almost certainly non-contagious, though there is some debate that exists on that issue. Anecdotal case reports of persons acquiring genital herpes through contact in hot tubs have been published though never proven. Obviously such matters would be very difficult to verify. The herpes virus does not survive outside the body for more than about 10 seconds, and although it can survive for slightly longer in warm, damp conditions (i.e. wet towels), it dies very quickly once exposed to the air.


However, genital herpes IS contagious, most oftentimes through direct skin-to-skin contact with an infected area. The method of transmission occurs through an active herpes blister on one person with a challenged or broken area of skin on the other person. For example, a male with an open blister could transmit the virus into the vagina of a female through even the tiniest abrasion in the vaginal mucosa of the female that could occur during intercourse. Similar modes of transmission can occur from female to male, male to male, and even female to female. Oral to oral transmission of either type of virus can also happen much the same way, through infected skin with active viral activity coming in contact with challenged or broken skin.

The virus may be transmitted to the penis, the vagina, the rectum, the mouth, and more rarely, the esophagus, the trachea, and even onto broken areas of skin that may appear anywhere on the body. The New England Journal of Medicine published a photograph of a herpes infection deep down inside the esophagus of a woman in April, 1999. Herpes simplex pneumonias have been reported. And, of course, the Herpes simplex infections of the brain in newborn babies who acquire infection during delivery are well known and may have disastrous consequences. Herpes simplex may also cause wide-spread rashes on the body with redness and swelling in these areas, similar to that of measles.


Once the viral DNA has been transmitted to the receiving person's nerve cells, the infection is permanent.


Viruses are very tiny, far smaller than bacteria and far smaller than the cells of the human body. Viruses are so small that they can even slip through the tiny inter-cellular holes of the "lamb-skin" type of condom which are normally small enough to prevent sperm cells from getting through. Latex-type condoms have been shown to be most protective against viral transmission, considering the condom covers the affected area completely during the sex act. Viral particles from an active lesion can become liquid borne from inside the condom and possibly leak out the base of the condom.

Herpes infections produce a number of different signs and symptoms. Traditional "first episode" herpes, most commonly described in women, are serious illnesses, with high fever, often severe outbreaks, painful urination and even inability to urinate. Hospitalization is sometimes necessary, with catheterization, IV fluids, and intravenous anti-viral medications being required.

Most people diagnosed with a genital herpes infection don't describe having such severe symptoms; however, they might experience a cluster of small blisters surrounded by a red base on or around the genitalia. Often the blisters have already ruptured, leaving behind a cluster of ulcers which scab over and require as much as one to two weeks to heal. Once the blisters have ruptured, it’s likely that a culture cannot be taken to determine if the blister is in fact herpes related. Thus, it is important to seek medical attention upon first notice of blisters to insure that an accurate culture can be taken and proper diagnosis occurs.

During the blister and ulcer phase, herpes lesions contain enormous amounts of viral particles and should be considered highly contagious to any challenged or broken skin it may come in contact with including but not limited to: the eye, mouth, esophagus, trachea, lungs, anus, urethra, penis and vagina.

In most cases herpes symptoms are subtle and often go undetected. Many have reported slight redness in the skin but without obvious lesions. This area, even without textbook symptoms should be considered contagious. Sometimes the skin will form tiny red bumps that don't blister, called "erythematous papules". Sometimes there are no signs on the skin at all but rather a "prodrome" such as urinary urgency, urinary frequency, and/or aching or tingling in the legs. Tingling has been described best as a sensation similar to a rub burn or mild sunburn. Also, itching, burning, tingling, pain or pressure at a previous or potential outbreak site may occur.

Many people with genital herpes and likely in oral herpes cases produce viral particles even when they have no symptoms whatsoever. These people are likely contagious even when they have no symptoms at all. This term is called "asymptomatic shedding."

In cases of women with genital herpes, herpetic lesions inside the vagina may only produce a vaginal discharge as an external symptom, resembling a yeast infection. It may be difficult without examining the patient to know whether the “yeast infection” is actually what it seems or if it is in fact genital herpes. Some women with both chronic yeast infections and genital herpes infections may find themselves confused as to which problem might be causing the symptoms.

These women should be under the care of a trusted doctor and should not attempt to self-medicate until the symptoms have been clearly explained. Self diagnosing and treatment can only make genital herpes symptoms worse.

Viral shedding can occur from people who have acquired the infection asymptomatically. This means that people can acquire a herpes infection and have no symptoms, and later they can be shedding virus and therefore be contagious. In an article that appeared in the New England Journal of Medicine in 2000, Anna Wald concluded that "seropositivity [testing positive in a blood test] for HSV-2 is associated with viral shedding in the genital tract, even in subjects with no reported history of genital herpes." This means that people can be infected and that only their blood tests might be positive, that they may have no symptoms or few symptoms that are recognized as being caused by herpes, and yet that they may still be shedding virus and may be contagious.

HSV Virus Type
1. Herpes simplex virus type 1 or HSV-1 can cause oral and genital herpes and sometimes infect the hands and other parts of the body. About 80% of HSV-1 cases are oral herpes (cold sores, fever blisters).
2. Herpes simplex virus type 2 usually causes genital herpes but like oral herpes can infect other parts of the body. Both stains of herpes simplex viruses tend to be more virulent in their most common places (oral herpes for HSV-1 and genital herpes for HSV-2)
3. Herpes varicella-zoster virus (also called herpes varicella/chickenpox and herpes zoster/shingles). It mostly affects children (varicella) and people over 60 (shingles)
4. Epstein Barr virus (often abbreviated to EBV)
5. Cytomegalovirus (CMV)
6. Human herpes virus 6 (HHV6)
7. Human herpes virus 7 (HHV7)
8. Human herpes virus 8 (HHV8 or it can be called KSHV)

References

http://www.bmb.leeds.ac.uk/mbiology/ug/ugteach/dental/tutorials/flora/herpes.html
http://www.best-herpes-treatments.com/information-on-herpes-simplex.html

Yellow Fever VIrus

What is yellow fever?

Yellow fever is a serious viral infection, transmitted by mosquitoes in tropical regions. It has both an urban cycle and a jungle cycle that relies on monkeys as carriers ('sylvatic cycle').In mild cases the symptoms are similar to influenza, but serious cases develop a high temperature and may have a series of after effects, such as internal bleeding, kidney failure and meningitis.A classic feature of yellow fever is hepatitis, which is the reason for the yellow colouring of the skin (jaundice) and the name of the disease.Yellow fever can cause sudden epidemics, with a mortality rate of almost 50 per cent. Although a safe, efficient vaccine has been available for the last 60 years, epidemics still occur, constituting a health risk in tropical regions. The disease is covered by the International Quarantine Regulations, which are taken very seriously by authorities everywhere. Therefore, the vaccine has to be administered by a specially authorised doctor. In the UK you can only obtain the yellow fever vaccination from a designated Yellow Fever Clinic.

What causes yellow fever?

Yellow fever virus belongs to the Flaviviridae family, other members of which cause dengue fever and Japanese encephalitis. The virus is introduced into the bloodstream via the saliva of the mosquito as it bites. The virus can then be transported around the body and reproduce itself in a variety of the body's cells, usually the liver, kidneys and blood vessels. In serious cases, these cells may become damaged themselves.In addition, the cells of the immune system are affected and release large quantities of signalling substances. These substances are the cause of the normal disease symptoms, such as muscular pain and fever, which are also observed in influenza.

How is yellow fever passed on?

The virus is transmitted among humans by a couple of species of mosquito, including Aedes egyptii, which can also transmit dengue fever. It is an unexplained fact that despite the presence of the Aedes mosquito in Asia, yellow fever is limited to Africa and South America. In its original jungle cycle, the mosquito sucks the blood of an infected monkey. The mosquito develops a permanent infection, in which the virus accumulates in its salivary glands. Then the mosquito bites another monkey, which then also becomes infected with the virus. A person travelling through the jungle may also become infected by an infected mosquito. When this person returns to urban areas, a new cycle begins. Urban cycles start when an infected traveller returns from the jungle. A mosquito bites the traveller, who then becomes infected and passes the virus on to other people, and either an epidemic breaks out, or an endemic situation is perpetuated.

Orthomyxoviridae

Influenza virus; a member of the Orthomyxoviridae family

Description and Significance
The orthomyxovirus gets its name from the Greek word 'myxa' that means mucus.
Influenza virus types A and B are both common causes of acute respiratory illnesses. Both virus types may cause epidemics of considerable morbidity and mortality but influenza B infections are often limited to localized outbreaks whereas influenza A viruses are the principal cause of larger epidemics including worldwide pandemics. Influenza occurs in winter epidemics that affect 1-5% of the population in temparate regions. Influenza can be contracted throughout the year in tropical regions and its contribution to overall morbidity and mortality is less well defined. (source: World Health Organization: Immunization, Vaccines and Biologicals)

Genome Structure
The genome of the orthomyxovirus consists of six segments to eight segments of linear, negative-sense, single-stranded RNA. The complete genome is 10000-14600 nucleotides long. Segment 1 is fully sequenced and the complete sequence is 2300-2500 nucleotides long. Although sequenced and of the same length as Segment 1, segment 2 only has an estimate of the sequence so far. Segment 3 is also sequenced, but only estimated, and the complete sequence is 2200-2300 nucleotides long. Segment 4 has been completely sequenced and the complete sequence is 1700-1800 nucleotides long. Segment 5 has been sequenced, but only estimated, and is 300-1900 nucleotides long. Segment 6 has been sequenced, but only estimated, and is 1400-1500 nucleotides long. Segment 7 has been sequenced, but only estimated, and the complete sequence is 800-1100 nucleotides long. The genome has terminally redundant sequences and the sequence is repeated at both ends. The nucleotide sequences at the 3'-terminus are identical. The 5'-terminal sequence has conserved regions and repeats complementary to the 3'-terminus; terminal repeats at the 5'-end are 11-14 nucleotides long. The 3'-terminus has conserved nucleotide sequences; is 11-13 nucleotides long; in the genera of same family. The sequence has conserved regions in all RNA species or some RNA segments. The multipartite genome is encapsidated with each segment in a separate nucleocapsid, and the nucleocapsids are surrounded by one envelope. Each virion contains defective interfering copies.

Virion Structure of an Orthomyxovirus
The virions of an orthomyxovirus consist of an envelope, a matrix protein, a nucleoprotein complex, a nucleocapsid, and a polymerase complex. The virus capsid is enveloped. The virions are spherical to pleomorphic and filamentous forms occur. The virions are 80-120 nm in diameter and 200-300(-3000) nm long. The surface projections are densely dispersed distinctive hemagglitinin-esterase (HEF) spikes, or spaced widely apart hemagglutinin (HA) spikes. Clusters of neuramidase (NA) irregularly inerpose the major glycoprotein in a ratio of HA to NA about 4-5 to 1. There are about 500 spikes evenly dispersed or clustered and are covering the surface comprising hemagglutinin, or neuraminidase, or esterase-esterase. The surface projections are composed of one type of protein or different types of proteins and are 10-14 nm long and 4-6 nm in diameter. The nucleocapsid is elongated with helical symmetry and is segmented with loops at one end. The segments have different sized classes with clear predominate lengths with a length of 50-130 nm (in differnent class sizes) and a width of 9-15 nm.

ref:http://microbewiki.kenyon.edu/index.php/Orthomyxoviridae

About Viral Life Cycle

What is viral replication?
Viral replication is the formation of biological viruses during the infection process in the target host cells. Viruses must first get into the cell before viral replication can occur. For the virus, the purpose of viral replication is to allow production and survival of its kind. By generating abundant copies of its genome and packaging these copies into viruses, the virus is able to continue infecting new hosts. Replication between viruses is greatly varied and depends on the type of genes involved.

Baltimore Classification
Viruses are classed into 7 types of genes, each of which have their own families of viruses, which in turn have differing replication strategies themselves. David Baltimore, a Nobel Prize-winning biologist, devised a system called the Baltimore Classification System to classify different viruses based on their unique replication strategy. There are seven different replication strategies based on this system (Baltimore Class I, II, III, IV, V, VI, VII).

Class I: double-stranded DNA (dsDNA)
- Replication exclusively nuclear; very dependent on host cell factors
- Replication in cytoplasm; viral genome contains all factors for genome replication and transcription
Examples: Herpes virus, pox virus, adenovirus

Class II: single-stranded DNA (ssDNA)
- Replication of genome in nucleus
- dsDNA formed to make new single-stranded daughters
- Extreme parasitism
Example: Parvoviridae

Class III: double-stranded RNA (dsRNA)
- Genome in several fragments
- Replication, transcription, translation regulated separately
- Monocistronic mRNA
- All activity in cytoplasm
Example: Reovirus

Class IV: single-stranded positive RNA [(+)ssRNA]
- Majority of animal and plant viruses
- Group 1 – polycistronic mRNA. Polyprotein formed and cleaved
- Group 2 – complex transcription process. 2 rounds of translation before formation of genomic RNA.
Examples: Hand food mouth disease, hepatitis A virus, hepatitis C virus

Class V: single-stranded negative RNA [(-)ssRNA]
Group 1 –
- Non-segmented genome
- Transcription of –ve RNA by RNA-dependent RNA polymerase to give monocistronic mRNA
- Ambisense organisation
Group 2 –
- Orthomyxoviruses (segmented genome)
- Monocistronic mRNA in nucleus
- Virus transcriptase in nucleocapsid
Example: Influenze virus

Group VI: reverse RNA
- (+)ssRNA with DNA intermediate
- Diploid
- Reverse transcription of viral RNA to dsDNA by viral RT
- Integration of dsDNA into host genome
- Viral RNA not used as mRNA
Example: HIV

Group VII: reverse DNA
- dsDNA with RNA intermediate
- not well understood
- overlapping reading frames
Example: hepatitis B virus

An animation about viral replication..
http://www.liquidjigsaw.com/animation/virus.htm

References:
http://en.wikipedia.org/wiki/Viral_replication
http://www.web-books.com/MoBio/Free/Ch1E2.htm

Varicella Zoster Virus

Varicella-zoster virus (VZV) causes chickenpox which usually mild, but may be severe in infants, adults, and people with impaired immune systems. Almost everyone gets chickenpox before the age of 20.

Chickenpox is highly contagious. The virus spreads from person to person by direct contact, or through the air. There is a high chance (around 90%) of contracting chickenpox if exposed to an infected family member.

The characteristics of chickenpox is having an itchy rash, which then forms blisters that dry and become scabs in 4-5 days. The rash may be the first sign of illness, sometimes coupled with fever and general malaise, which is usually more severe in adults. An infected person may have anywhere from only a few lesions to more than 500 lesions on his or her body during an attack. The averge is 300-400 lesions though.

Adults are more likely to have a more serious case of chickenpox with a higher rate of complications and death.

Chickenpox is contagious 1-2 days before the rash appears and until all blisters have formed scabs. Chickenpox develops within 10-21 days after contact with an infected person.
Varicella vaccine has been available since March 1995 and is approved for use in healthy children 12 months of age or older, and susceptible (i.e., no evidence of having had chickenpox in the past) adolescents and adults.

Varicella vaccine is highly effective in protecting against severe chickenpox. Cases of disease caused by the wild virus, which may occur in a small proportion of vaccinees, are typically very mild, with fewer than 50 skin lesions and no fever.

It is recommended that all children be routinely vaccinated at 12-18 months of age and that all susceptible children receive the vaccine before their 13th birthday. Many states in the USA require vaccination for entry into pre-school or public school beginning in 1999. The vaccine is also approved for susceptible adolescents and adults, especially those with close contact with persons at high risk for serious complications (e.g., health-care workers, family contacts of immunocompromised persons).

A history of chickenpox is considered adequate evidence of immunity.

A blood test is available to test immunity in persons who are uncertain of their history or who have not had chickenpox. Many of these persons will find that they are immune when tested and thus will not need to be vaccinated.

Effective medications (e.g., acyclovir) are available to treat chickenpox in healthy and immunocompromised persons (e.g, those with cancer, human immunodeficiency virus/AIDS; those receiving medications that depress the immune system).

Varicella zoster immune globulin (VZIG), an immune globulin made from plasma of healthy volunteer blood donors with high levels of antibody to VZV, is recommended after exposure for persons at high risk for complications (e.g., immunocompromised persons, pregnant women, premature infants)

Reference:

http://www.uhseast.com/120837.cfm

http://www.medhelp.org/NIHlib/GF-619.html

Retroviridae

Electron micrograph image of Feline Leukemia Virus, a virus in the Retroviridae family.

Higher order taxa
Viruses; Retro-transcribing viruses; Retroviridae

Genera
Orthoretrovirinae (subfamily)
Alpharetrovirus
Betaretrovirus
Deltaretrovirus
Epsilonretrovirus
Gammaretrovirus
Lentivirus
Spumaretrovirinae (subfamily)
Spumaretrovirus

Description and Significance
Retroviruses are viruses that are remarkable for their use of reverse transcription of viral RNA into DNA during replication. Members of this family include Human immunodeficiency virus (the virus that causes AIDS), feline leukemia, and several cancer-causing viruses. Retroviruses were discovered in 1908 by Vilhelm Ellermann and Oluf Bang. The first sixty years of study of retroviruses focused exclusively on animal infection and disease. In the 1960s and 1970s, study focused on the viral replication cycle and pathogenic effects at the cellular level. Current study of retroviruses focuses on the diverse pathogenic effects of these viruses at the cellular and molecular levels. Retroviruses were the first viruses to be modified for gene therapy, and continue to be used in the majority of gene therapy clinical trials.
(sources: Coffin et al., Hu and Pathak)

Genome Structure
The genome of retroviridae is dimeric, unsegmented and contains a single molecule of linear. The genome is -RT and a positive-sense, single-stranded RNA. Minor species of non-genomic nucleic acid are also found in virions. The encapsidated nucleic acid is mainly of genomic origin but virions may also contain nucleic acid of host origin, including host RNA and fragments of host DNA believed to be incidental inclusions. The complete genome of one monomer is 7000-11000 nucleotides long. The 5'-end of the genome has a methylated nucleotide cap with a cap sequence type 1 m7G5ppp5'GmpNp. The 3'-terminus of each monomer has a poly (A) tract and the terminus has a tRNA-like structure. (source: ICTVdB)

Virion Structure of a Retroviridae
The virions of a retroviridae consist of an envelope, a nucleocapsid and a nucleoid. The virus capsid is enveloped. The virions are spherical to pleomorphic and measure 80-100 nm in diameter. The surface projections are small or distinctive glycoprotein spikes that cover the surface evenly. The projections are densely dispersed and 8 nm long. The nucleoid is concentric or eccentric while the core is spherical. (source: ICTVdB)


Reproduction Cycle of a Retroviridae in a Host Cell
Retrovirus virions enter host cells through interaction between a virally-encoded envelope protein and a cellular receptor. Viral RNA is transcribed into a DNA copy by the enzyme reverse transcriptase which is present in the virion. The viral DNA copy is integrated into, and becomes a permanent part of, the host genome. This integrated DNA is referred to as a provirus. The host cell's transcriptional and translational machinery expresses the viral genes. The host RNA polymerase II transcribes the provirus to create new viral RNA, which is then transported out of the nucleus by other cellular processes. A fraction of these new RNAs are spliced to allow expression of some genes, while others are left as full-length RNAs. Viral proteins are synthesized by the host cell's translational machinery. Virions are assembled and bud from the host cell.

This reproduction cycle applies to all of the members of Retroviridae except for spumaviruses. Spumaviruses complete reverse transcription in the virus-producing cells rather than infected target cells, and the infectious virus contains a DNA genome. (source: Hu and Pathak)


Viral Ecology & Pathology
Retroviruses cause a wide variety of malignancies, immunodeficiencies, and neurological disorders affecting a wide variety of species. According to Coffin et al., "Some of these disorders have significant agricultural impact, crippling farm animals during their most productive years, whereas others have a devastating medical and economic impact on humans. Still others, particularly many of the retrovirus-induced malignancies of rodents, were found originally in laboratory settings and provide excellent model systems for probing the biological and molecular mechanisms of carcinogenesis." (source: Coffin et al.)

References:
Coffin et al. Retroviruses. Cold Spring Harbor Laboratory Press, 1997.
Hu, Wei-Shau and Vinay K. Pathak. "Design of Retroviral Vectors and Helper Cells for Gene Therapy." Pharmacological Reviews 52.4 (2000): 493-511.
ICTVdB - The Universal Virus Database, version 4. http://www.ncbi.nlm.nih.gov/ICTVdb/ICTVdB

Herpsviridae

Herpesviridae is a heterogeneous family of morphologically similar viruses, all of which contain double-stranded DNA and infect humans and a wide variety of other vertebrates.

Infections produce type A inclusion bodies; in many instances, infection may remain latent for many years, even in the presence of specific circulating antibodies. Virions are enveloped, ether sensitive, and vary up to 200 nm in diameter; the nucleocapsids are 100 nm in diameter and of icosahedral symmetry, with 162 capsomeres.

Virus causes viral encephalitis. If passed from mother to baby during childbirth, brain damage may be caused to the baby.

The family is subdivided into three subfamilies:

1. Alphaherpesvirinae

- herpes simplex virus

- varicella-zoster virus,

2. Betaherpesvirinae

- cytomegalovirus

- human herpes type 6

- human herpes type 7

3.Gammaherpesvirinae

- epstein barr virus

- human herpes type 8

Herpesviridae: family of enveloped DNA viruses; occur in man, cold-blooded vertebrates, and invertebrates; some may induce neoplasia; transmission is usually by contact but it can occur by other routes.

Herpes simplex virus -

There's two type of HSV - HSV 1 and HSV 2. The virus can be primary or recurrent. On the infected patient may have cold sores around the mouth for one week or genital herpes for around one to three weeks, sometimes the eyes and gum may be affected too.

HSV 1 is spread by kissing or close proximity. According to the US stats, 100% of the adult population have carriers of HSV 1

HSV 2 is transmitted mainly via sexual contact. According to the US stats, up to 20% of the adult population are infected.

Electron Micrograph of Varicella Zoster

Reference: http://www.ncbi.nlm.nih.gov/ICTVdb/ICTVdB/00.031.htm

Smallpox

What is smallpox

An acute, highly infectious, often fatal disease caused by a poxvirus and characterised by high fever and aches with subsequent wide spread eruption of pimples that blisters, produce pus and forms pockmarks.

The history of smallpox

Smallpox is an acute contagious disease caused by the variola virus, a member of the orthopoxvirus family. It is one of the most devastating diesease known to mankind and throughout the centuries, repeated epidemics swept across the world, decimating populations and changing the course of history.

Smallpox, which had no effective treatment ever developed, killed as many as 30% of those infected. Between 65–80% of survivors were marked with deep pitted scars , most prominent on the face. Blindness was also another result from smallpox.

In the 18th century, smallpox killed every 10th child born in Sweden and France. During the same century, every 7th child born in Russia died from smallpox.

It was Edward Jenner's demonstration in 1798, to protect against smallpox by the inoculation of cowpox, that brought the first hope that the disease could be controlled.

The disease

Smallpox is caused by the variola virus that emerged in human populations thousands of years ago. Variola major is the severe and most common form of smallpox which has an overall fatality rate of about 30%. Variola minor is a less common presentation of smallpox, and a much less severe disease, with death rates of 1% or less.

Transmission

Smallpox can be spread through direct contact with infected bodily fluids or contaminated objects such as bedding or clothing.

Our short summary of the steps to smallpox:
- A layer of red splotches and constant high fever
- Tiny pimples form everywhere
- Pimples develop tiny blistery heads
- The heads grow larger and hurt badly
- The poxes enlarge into boils
- The crusting process begins ( the most fatal process in smallpox)
- The crust falls off
- The patient becomes immune to it after a period of time and may not get it again after that
- Someone else comes in contact with the crust and the cycle starts over again


Conclusion

Will smallpox return?
Maybe. Maybe not.

The USA finds reason to believe that terrorists may have gotten hold on some variola and mass produce it as a biological weapon. There could also be a possible way of making the smallpox virus immune to vaccines. This "Superpox" enhancement has been tested on mousepox and has been proven fatal even to immunized mice.

Some good news though:

• Its existance has been completely eradicted from nature.


• You dont have it.

Not much, but its enough to help people sleep at night. (:

The reality is that smallpox may not be here anymore now. But let us not forget what it did and possibly, what it can do.

In memory of those who died from smallpox.

references:
http://www.who.int/mediacentre/factsheets/smallpox/en/
www. youtube.com
http://www.smallpox.gov/smallpox/aboutdisease.html
www.learnnc.org