Interesting news

December 30, 2003

Prion proteins may store memories

Study hints at vital job for two-faced proteins.

Mystery proteins called prions, which can flip between two different shapes, might help in laying down memories, according to US researchers. The finding hints at an entirely new set of roles for the proteins.

Prions are unusual in the protein world: when they adopt one of their guises, they can reproduce, converting other identical proteins into copies of themselves. Often such replicating prions are harmful – they clog up the brains of cattle with mad cow disease and patients with variant Creutzfeldt-Jakob disease (vCJD).

Prion

About Prion Diseases Prion diseases or transmissible spongiform encephalopathies (TSEs) are a family of rare progressive neurodegenerative disorders that affect both humans and animals. They are distinguished by long incubation periods, characteristic spongiform changes associated with neuronal loss, and a failure to induce inflammatory response. The causative agent of TSEs is believed to be a prion. A prion is an abnormal, transmissible agent that is able to induce abnormal folding of normal cellular prion proteins in the brain, leading to brain damage and the characteristics signs and symptoms of the disease. Prion diseases are usually rapidly progressive and always fatal.

These diseases

• are transmissible — from host to host of a single species and, sometimes, even from one species to another (such as a laboratory animal)
• destroy brain tissue giving it a spongy appearance

For these reasons, prion diseases are also called transmissible spongiform encephalopathies or TSEs.

Examples

Creutzfeldt-Jakob Disease (CJD)

A number of humans have acquired CJD through accidental exposure to material contaminated with CJD prions.

• Grafts of dura mater taken from patients with inherited CJD have transmitted the disease to more than 100 recipients.
• Corneal transplants have also inadvertently transmitted CJD.
• Instruments used in brain surgery on patients with CJD have transmitted the disease to other patients. Two years after their supposed sterilization, these instruments remained infectious.
• Over 100 people have acquired CJD from injections of human growth hormone or human gonadotropins prepared from pooled pituitary glands that inadvertently included glands taken from humans with CJD.

Now that both hGH and human gonadotropins are available through recombinant DNA technology, such disastrous accidents need never recur.

Variant Creutzfeldt-Jakob Disease (vCJD)

This human disorder appeared some years after the epidemic of BSE (Mad Cow Disease) swept through the cattle herds in Great Britain. Even though the cow and human PRNP genes differ at 30 codons, the sequence of their prions suggests that these patients (155 by 2005) acquired the disease from eating contaminated beef.

All the patients are homozygous for the susceptibility polymorphism of methionine at position 129.

The BSE epidemic has waned, and slaughter techniques that allow cattle nervous tissue in beef for human consumption have been banned since 1989. Now we must wait to see whether more cases of vCJD are going to emerge or whether the danger is over.

http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/P/Prions.html#CPEB

http://www.cdc.gov/ncidod/dvrd/prions/index.htm

http://www.bioedonline.org/news/news.cfm?art=702

Cute origins,scary virus

http://www.primatefreedom.com/images/mangabey.jpg 

Isn’t the monkey cute? It is a Sooty Mangabey. Bet you’re wondering what has it got to do with microbiology.

Well, make a guess? From the title of the post, it must have something to do with a virus.

The virus is the Human Immunodeficiency virus(HIV)! The HIV’s origin was this innocent looking monkey.

During the 20th century, non-human primates in sub-Saharan Africa transferred the virus to humans.

Both HIV-1 and HIV-2 were said to be mutated from the Simian Immunodeficiency Virus (SIV) from the Sooty Mangabey.

The HIV-1 is more virulent, thus it is easily transmitted and is the cause of the worldwide spread of HIV.

HIV-2 is less virulent and is contained in West Africa.

That’s enough about how it all started. Now, let’s understand what it does to our bodies.

The HIV is a lentivirus that can lead to acquired immunodeficiency syndrome (AIDS), a condition in humans in which the immune system begins to fail, leading to life-threatening opportunistic infections. A HIV patient needs different types of medication to suppress the virus to prolong their lives. The information below will allow you to understand why.

HIV attacks specific lymphocytes called T-cells (CD-4), takes them over, and multiplies. This destroys more T-cells, damaging the body’s ability to fight them off.

 

http://kidshealth.org/parent/infections/std/hiv.html

When the levels of T-cells are very low, HIV patients are more susceptible to other infections. This weakened immune deficiency is known as AIDS and would result in severe life-threatening infections, some forms of cancer, and the deterioration of the nervous system.

However, HIV can be controlled by drugs. Firstly, the viral attachment can be blocked by a class of drugs called entry inhibitors. This prevents the HIV from attacking the T-cell which prevents the reproduction of HIV. If HIV is attached, the HIV and T-cell would fuse. Drugs called entry or fusion inhibitors are used to block the fusion.

In order for HIV to reproduce, the RNA from the HIV has to be converted to DNA. Drugs called reverse transcriptase inhibitors block HIV’s reverse transcriptase from using these building blocks. These drugs contain faulty imitations of proteins found in a T-cell’s cytoplasm. The imitation building blocks in NRTIs are inserted into the DNA, preventing the double strand of DNA from becoming fully formed.

The enzyme protease allows the HIV’s material to be separated so they can be reassembled to new HIV. Drugs called such as Kaletra, Crixivan, and Viracept bind to the protease enzyme and prevent it from separating, the HIV subunits.

Enveloped DNA viruses

Enveloped DNA viruses
Virus Family	Virus Group	Disease Produced
Poxvirus	Variola Virus Vaccinia Virus	Smallpox Cowpox
Herpes Virus Family	Herpes Simplex Type 1 (HSV-1) Herpes Simples Type 2 (HSV-2) Varicella-Zoster Virus (VZV) Epstein-Barr Virus (EBV) Herpesvirus- 8 (HV-8)	Cold Sores Genital Herpes Varicella (Chickenpox) and Shingles (Zoster). Infectious Mononucleosis Burkitt Lymphoma and Nasopharyngeal carcinoma. Kaposi Sarcoma
Hepadnavirus	Hepatitis B Virus (HBV)	Hepatitis B

Herpes simplex virus 1

Also called as oral-facial herpesansmission: kissing or sharing drinking utensils

Herpes simplex virus 2

Also called as genital herpes

Transmission: sexual contact

Prevention: Don’t kiss and stop risky behaviours.

http://www.entusa.com/oral_photos.htm

Hepatitis B

Signs and symptoms: malaise, fever, chills, anorexia, abdominal discomfort, jaundice, dark urine, and diarrhoea.

Complete liver regeneration and restored liver function occur in most patients. However, about 10% of patients develop chronic liver disease in the form of cirrhosis (permanent liver scarring and loss of tissue). People with chronic hepatitis B are more likely to develop liver cancer.

Transmissions: sharing of contaminated needles and homosexual contact

Prevention: vaccines and avoid risky behaviours

http://www.herbalprovider.com/imgs/yahoo/fatty-liver-hepatitis.jpg

Poxviridae

Have you ever heard about Poxviridae? It is actually the smallpox virus.

Smallpox is an infectious diesease unique to humans, caused by either of two virus variants, Variola major and Variola minor. The disease is also known by the Latin names Variola or Variola vera, Smallpox can be deadly, so if an outbreak happens, it is vital to stay away from infected people. Get vaccinated if you have been around someone who has smallpox. And if you develop symptoms, seek medical care.

Unique features of Poxviridae

1. It is the largest family of viruses
2. Can just be seen under the light microscope
3. Unique oval-shaped
4. Can remain stable for hours in air  ( 6 to 24 hours, depending on the weather)

What is the symptoms?

The first symptoms of smallpox include a high fever, fatigue, a headache, and a backache. It takes about 12 days for  these symptoms to show. Then after 2 to 3 days of illness, a flat, red rash appears. It usually starts on the face and upper arms, and then it spreads all over your body. Over the next 2 to 3 weeks, the flat, red spots become firm and dome-shaped and fill with pus. Then they scab over. Scabs fall off 3 to 4 weeks after the rash first appears, and they leave pitted scars.

Smallpox virus evenatully can lead to blindess and death.

You may mistake a severe chickenpox rash for a smallpox rash at first. But different viruses cause these illnesses.

Vaccination?

In the past, people realised that milkmaids seldom get infected by smallpox virus. Edward Jenner, a doctor in Berkeley, discovered that immunity to smallpox could be produced by inoculating a person with material from a cowpox lesion. Cowpox is a poxvirus in the same family as variola.  Edward Jenner then vaccinate an 8 yerars old James Phipps with cowpox  then challenged it with small pox.

The procedure was much safer than variolation, and did not involve a risk of smallpox transmission. Vaccination to prevent smallpox was soon practised all over the world.

Bioterrorism Today

No one can be infected by small pox virus anymore as it had been completely removed from the Earth.

However, Smallpox virus is known to exist in labs at the Centers for Disease Control and Prevention (CDC) in the U.S. and at the Institute of Virus Preparations in Siberia, Russia. But it may also be in other labs. Some people worry that terrorists could release the virus and spread smallpox to many people

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Transmission of Influenza A Viruses between Animals and People

Influenza A viruses have infected many different animals. However, certain subtypes of influenza A virus are specific to certain species, except for birds, which are hosts to all known subtypes of influenza A. Subtypes that have caused widespread illness in people either in the past or currently are H3N2, H2N2, H1N1, and H1N2.

Influenza A viruses normally seen in one species sometimes can cross over and cause illness in another species. For example, until 1998, only H1N1 viruses circulated widely in the US pig population. However, in 1998, H3N2 viruses from humans were introduced into the pig population and caused widespread disease among pigs. Most recently, H3N8 viruses from horses have crossed over and caused outbreaks in dogs.

Avian influenza A viruses may be transmitted from animals to humans in two main ways:

· Directly from birds or from avian virus-contaminated environments to people.

· Through an intermediate host, such as a pig.

Influenza A viruses have eight separate gene segments. The segmented genome allows influenza A viruses from different species to mix and create a new influenza A virus if viruses from two different species infect the same person or animal. It is possible that the process of genetic reassortment could occur in a human who is co-infected with avian influenza A virus and a human strain of influenza A virus. The genetic information in these viruses could reassort to create a new virus with a hemagglutinin from the avian virus and other genes from the human virus. Theoretically, influenza A viruses with a hemagglutinin against which humans have little or no immunity that have reassorted with a human influenza virus are more likely to result in sustained human-to-human transmission and pandemic influenza. Therefore, careful evaluation of influenza viruses recovered from humans who are infected with avian influenza is very important to identify reassortment if it occurs.

Although it is unusual for people to get influenza virus infections directly from animals, sporadic human infections and outbreaks caused by certain avian influenza A viruses and pig influenza viruses have been reported. These sporadic human infections and outbreaks, however, rarely result in sustained transmission among humans.

DENGUE VIRUS

The Dengue virus is a member of the virus family Flaviviridae and is transmitted to people through the bite of the mosquitos Aedes aegypti and Aedes albopictus. Dengue virus is now believed to be the most common arthropod-borne disease in the world. Dengue is mainly found in the tropics because the mosquitoes require a warm climate. A major fear of epidemiologists is that the mosquitoes will develop resistance to cooler climates and then be able to infect people in the United States and other temperate climates.

 

 

 

http://www.cdc.gov/ncidod/dvbid/dengue/slideset/set1/images/replication-and-transmission-part1.gif

Replication and Transmission of Dengue Virus

1.	Virus transmitted to human in mosquito saliva
2.	Virus replicates in target organs
3.	Virus infects white blood cells and lymphatic tissues
4.	Virus released and circulates in blood

 

The mosquito remains able to transmit dengue for its entire life. the majority of deaths that result from dengue infection result from Dengue Hemorrhagic Fever (DHF) and Dengue Shock Syndrome (DSS). People who develop DHF have a 5% chance of death but if they go on to develop DSS then the mortality rate can rise as high as 40%.

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Lwoff v.s Baltimore:

Lwoff’s scheme for classification:

Four main characteristics are used:

1. Nature of the nucleic acid: RNA or DNA

2. Symmetry of the capsid

3. Presence or absence of an envelope

4. Dimensions of the virion and capsid

Baltimore’s scheme for classification:

Based on the method of viral mRNA synthesis.

http://expasy.org/viralzone/all_by_protein/254.html

http://www.nlv.ch/Virologytutorials/graphics/classificationtotal.jpg

 

IN SUMMARY:

VIRAL CLASSIFICATION
Nucleic acid	RNA or DNA
	single-stranded or double-stranded
	non-segmented or segmented
	linear or circular
	if genome is single stranded RNA, can it function as mRNA?
	whether genome is diploid (such as in retroviruses)
Virion structure	symmetry (icosahedral, helical, complex)
	enveloped or not enveloped
	number of capsomers

Discovery of Viruses

1892 – Dimitrii Ivanovsky observed that agent of tobacco mosaic disease passes through porcelain filters that retain bacteria

1898 – Marcus Beijerinck makes the same observation; concludes that the pathogen must be a distinctive agent

1898 – Friedrich Loeffler and Paul Frosch (former students of Koch), find that causative agent of foot-and-mouth disease is filterable (the first animal virus)

1901 – Yellow fever virus – Walter Reed (the first human virus)

1903 – Rabies virus (Remlinger, Riffat-Bay)

1908 - Poliovirus (Karl Landsteiner and E. Popper); chicken leukemia virus (Ellerman, Bang)

1911 – Rous sarcoma virus (Peyton Rous)

1915 – Bacteriophages -Frederik Twort, Felix D’Herelle

1931 – Swine influenza virus (Shope)

1933 – Human influenza virus (Smith)

The name virus was coined from the Latin word meaning slimy liquid or poison. It was originally used to described any infectious agent, including the agent of tobacco mosaic disease, tobacco mosaic virus. In the early years of discovery, viruses were referred to as filterable agents. Only later was the term virus restricted to filterable agents that require a living host for propagation.

credit to http://www.virology.ws/

About Microbiology

Have you ever wondered about how small germs are? And what are germs anyway? Are you always being told to wash your hands? Do you know why?

The tiny things you know of as germs are known as bacteria by scientists. They are very small and you can’t see them. Many thousands could fit on a pin head. They are alive, in the same way that you are, or a dog is, or a plant is. The study of these and other small living things or organisms is called Microbiology.