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