General Virus Information And Structures Biology Essay

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The T4 Bacteriophage is a virus which infects the E.Coli bacteria. Prior to attachment it appears dormant as an inactive viron until one of its extended legs comes into contact with the ecoli, triggering the baceteriophage into action. These legs are receptors in recognising binding sites on the surface of the host cell. The bacteriophage binds to the surface of the host, punctures the cell with its injection tube, and then injects its own genetic blueprint. ( This manipulates ecoli's biological machinery to create replicas of the T4, they then destroy the host and are relasesd dormant until another ecoli cell is detected.

Mechanism for viral replication

Viruses are naturally inert and do not possess the mechanical components in order for it to reproduce. They are intracellular obligate parasites and therefore a specific host is needed for its survival and replication process. (

In the case of a bacteriophage, once it comes into contact with a specified cell, it will lock itself on the bacteria and inject its DNA. Once it has infected the cell, the virus will exploit the use of its cellular machinery such as the cell's ribosomes and enzymes for viral replication. The viral progeny components are produced by the cellular machinery and the assembly of the viral genome is usually spontaneous as it is a non-enzymatic process. ( After the viruses' have finished their viral replication process by exploiting the host bacteria, it breaks down its cell wall so that the viruses are released.

Host specificity of a virus

Viruses infect only specific types of cells which depend on certain receptors on the host cell. Using a "lock-and-key" analogy, the virus has a specially-shaped "key" that will fit only into a particular "lock"-the receptor.

The host range of viruses is generally divided into three categories: those that infect animals, plants, or bacteria. Plant viruses are transmitted by insects or other organisms that feed on plants. Animal viruses vary from single-celled organisms to complex multicellular organisms such as humans. Animal viruses may infect vertebrate animals, invertebrate animals or some may even infect both.

Virus Host specificity may also be depended on various orders of vertebrates that live in specific environments. Some may only infect ectothermic vertebrates (cold blooded animals) as they can only reproduce at low temperatures. Others are limited to a host range of endothermic animals (warm blooded animals) as they can only reproduce at that temperature rate.

Therefore, most viruses are fairly specific in targeting cells although mutation may increase their host specificity range. Part 2

Historical Perspective

What is the etymology of the term "virus"?

The word virus was Latin word referring to poison and other noxious things, first used in the English language in 1392. Recorded in 1728, the modern etymology term for virus is an "agent that causes infectious disease."

Investigate the meaning of Koch's Postulates and explain why it is sensible to apply these when looking at the cause of a disease.

Koch's postulates were devised in 1890 by German physician and bacteriologist Robert Koch as a benchmark for determining whether a specified bacteria is the cause of a given disease. In a time where much-needed scientific clarity was needed, Koch provided a useful initial set of criteria.

Koch's postulates are as follows:

The bacteria must be present in every case of the disease.

The bacteria must be isolated from the host with the disease and grown in pure culture.

The specific disease must be reproduced when a pure culture of the bacteria is inoculated into a healthy susceptible host.

The bacteria must be recoverable from the experimentally infected host.

However, Koch's postulates have minor technical discrepancies and may not hold if

The particular bacteria (such as the one that causes leprosy) cannot be "grown in pure culture" in the laboratory.

There is no animal model of infection with that particular bacteria.

A harmless bacteria may cause disease if:

It has acquired extra virulence factors making it pathogenic.

It gains access to deep tissues via trauma, surgery, an IV line, etc.

It infects an immunocompromised patient.

Not all people infected by a bacteria may develop disease-subclinical infection is usually more common than clinically obvious infection.

Despite restrictions, Koch's postulates provided a useful benchmark in the cause-and-effect relationship between a bacteria or any other type of microorganism in a time where the field of scientific clarity was needed.

Investigate the work done by Edward Jenner with the cowpox and smallpox viruses. Explain how his work ultimately advanced our understanding of viruses.

Edward Jenner, the father of immunology was an English country doctor who pioneered vaccination.

Jenner lived in a period where smallpox was a widespread and often incurable disease worldwide. However it was his discovery in 1796 of inoculation with cowpox which was an immense medical breakthrough resulting in immunity to smallpox which had saved countless lives.

When the epidemic of smallpox had hit Gloucestershire in 1788, Jenner had realised that many of the milk maids which had experienced cowpox (a much milder version of the disease) had never been affected with the deadly smallpox.

On 14 May 1796, Jenner was given an opportunity when a young milkmaid came to see him as she had caught cowpox sores from handling cows daily. Jenner could now test his theory that the germs from cowpox will act as a vaccine for smallpox.

Extracting liquid from the cowpox sores, Jenner devised an extremely dangerous experiment which could have labelled him a murder. He inoculated a local community member with cowpox. Consequently the results proving his theory, James did not contract smallpox and became immune to the sickness.

Edward Jenner had ultimately revolutionised our understanding of viruses despite many contradictory views from sceptics in his era. He had proved that viruses have the ability to be beneficial in combating illnesses and provide immunity from future contact with similar infections.

Investigate the work of Louis Pasteur and the rabies virus. How did his work contribute to our understanding of viruses?

Louis Pasteur played a significant role in the scientific world for discovering the science of microbiology. Pasteur proved that most infectious diseases are caused by micro-organisms proving the "germ theory" disease. He was the inventor of the process of pasteurisation and also developed vaccines for several diseases including rabies. The discovery of the vaccine for rabies led to the founding of the Pasteur Institute in Paris in 1888. (

Rabies is a highly contagious infection that attacks the central nervous system that is transmitted through the bite of an infected animal or through saliva entering a wound. To find the cause of the disease, Pasteur experimented with the saliva of infected animals and concluded the viruses' lie in the central nervous system of the body. He tested his theory on healthy animals and soon enough the effects of rabies was prevalent. After studying the tissues of infected animals, Pasteur was able to produce an attenuated form of virus which could be used for inoculation. (

Pasteur's first trial on man was on July 6 1885, where he injected his pioneered rabies vaccine. At the end of 10 days of treatment, the man had been cured of Rabies and was once again healthy. His discovery has since saved thousands of infected people.

Even today Pasteur had developed a benchmark from which modifications for rabies are developed today. This has further developed scientific understanding of microbiology and the development of vaccines to combat deadly viruses.

What is the origin of the term "vaccine"?

Latin: vacinnus. It is derived from the word vaca meaning cow.

Originally a preparation used to prevent cow pox and related small pox.

How did Jenner and Pasteur's work lead to the practice of vaccination?

Jenner and Pasteur's work proved to the rest of the sceptical world that the use of virus can be used to combat, reduce and provide immunity to illnesses. Jenner was the founding father of immunology as he was the first noted man to practise inoculation which had saved huge populations of the world since 1796 from dying of smallpox. Pasteur is the founder of microbiology who had proved that microorganisms were the causes of disease where he developed a rabies vaccine in 1885 saving the lives of thousands of people.

How does vaccination provide immunity?

Vaccination is a preparation procedure where an antigen in the form of an injectible solution, digestive liquid or inhalable powder is absorbed into one's system. (

Vaccines may be composed of a variety of different antigens ranging from dead or attenuated (weakened) microorganisms to genetically engineered antigens.

These antigens are modified so that it emulates the effects of a disease to a modified extent so that it stimulates immune system's production of antibodies as an immune response for protection towards harmful microorganisms disease. This further protects the host as it has already been exposed to the antigen. This artificial process of vaccinisation means that the host no longer needs to suffer a bout of the disease to become immune to its effects.

Why are we able to vaccinate against some viruses and not others? Discuss why vaccines to smallpox are possible to prevent the disease (in fact the disease was eradicated by 1980) while diseases such as influenza re-occur?

We are able to vaccinate against some viruses but not others since some of these viruses mutate into new strands of nucleic acid, poison that we have not been exposed to before and therefore we are not immune. For example, influenza is the product of a large pool of hundreds of viruses that are mutating and reassorting.

Even if we have had a flu shot in the past, it is highly likely that in the future a new strand of influenza will develop and we would need another vaccination.

However smallpox was eliminated because its replication rate is relatively slow, which allows the vaccine to prime the immune system. This means that our immune system is already hard at work maintaining defence against the reproduction of the virus and future symptoms from the virus.

As a modern disease, why has HIV (AIDS) been so difficult to treat?

HIV is very difficult to treat because it is a retrovius. This means that after the illness infects the cell, the RNA genome is changed into DNA and integrated into the host cell's DNA. This viral DNA is then read and turned into proteins which reproduce to develop more HIV virions to infect other cells. However, after this process, the virus may remain dormant. HIV is a latent virus, a virus that is not actively reproducing or killing cells, but remains invisible to the immune system and many trailed drugs. The current theory is that HIV cannot be cured since drugs only kill viruses that are actively replicating, they don't search out latent viruses that are hidden in the cell's genome.

Professor Ian Fraser, the 2006 Australian of the Year (and parent of Grammar old boy) has pioneered a vaccination for the human papilloma virus (HPV).

Outline the symptoms caused by this virus

There are about 100 known strains of HPV, 30 of these are considered to be sexually transmitted diseases since the only way a person can be infected with one of these strains is through vaginal, anal or oral sex. (

HPV Symptoms

HPV often remains in one's body dormant and therefore affected people may not be aware of it as there are no symptoms. However, even if no symptoms are felt, the person is still very contagious and infectious to a partner.

Symptoms for Genital Warts

One strain of HPV may result in genital warts which may appear in a time period anytime from a few weeks to several months after contraction of the virus. Genital warts often appear to look like little cauliflower florets that are usually white or flesh-coloured, may either lay flat or be raised, appear by themselves or in clusters, and can be found in or around the vagina or anus or on the vulva or penis. may also interfere with normal bodily functions, such as urinating and bowel movements, making these actions painful and uncomfortable.

HPV and Cervical Cancer

Cervical cancer is the second most common and dangerous type of cancer that affects women. HPV has proved to be the leading cause of cervical cancer however since HPV may be dormant, there may be no symptoms.

However some other signs to watch out for when it comes to cervical cancer include:

Abnormal vaginal bleeding (particularly after sex)

Pain in the lower back

Pain while urinating

Pain during sex

Traditional methods of treatment (prior to development of the vaccine)

Traditionally, the HPV virus cannot be treated however the absence of symptoms means the body is clearing the HPV infection on its own.

HPV Treatments for Tissue Changes

If the HPV infection has caused abnormal cell changes that could lead to cervical cancer, there are four main treatment options:

Watch and wait. Sometimes the cell changes -- called cervical dysplasia, precancerous cell changes, or cervical intraepithelial neoplasia -- will heal on their own.

Cryotherapy. This involves freezing the abnormal cells with liquid nitrogen.

Conization. This procedure, also known as a cone biopsy, removes the abnormal areas.

LEEP or Loop Electrosurgical Excision Procedure. The abnormal cells are removed with a painless electrical current.

The goal is to remove all the abnormal cells and thus remove most or all of the cells with HPV.

Wart-removal treatments

Cryotherapy, the freezing off of the wart with liquid nitrogen

Trichloracetic acid, a chemical applied to the surface of the wart

Surgical removal, cutting the cells out with a scalpel

Electrocautery, burning off warts using an electric current

Laser vaporization or excision of the warts

The way in which the vaccine will be used

The vaccine Gardasil has been utilised as a preventative measure for all women who are at risk at catching HPV whether healthy or sick. Worldwide there have been 54 million doses distributed as it's an important drug saving the lives of many women.

The impact this new vaccine will have on society

The impact of this new vaccine will influence greater awareness in society about the effects of HPV and how it may lead to the deadly virus of cervical cancer. Therefore all women are encouraged to take the vaccine as a preventative measure towards HPV, cervical cancer and its symptoms.

Part 3

Investigation of One Specific Virus


Describe your selected disease; include:


There are currently 4 subtypes of the Ebola virus three of which have had reported incidences of human infection. These are Ebola-Zaire (isolated in 1976), Ebola-Sudan (also isolated in 1976), and Ebola-Ivory Coast (isolated in 1994). The fourth species, called Ebola-Reston, causes disease in primates.

As of 2006, four species of Ebola virus have been identified, based on differences in their genetic sequences and in the immune reaction they elicit in infected individuals. Three of the species cause disease in humans.

The appearance of the Ebola virus only dates back to 1976. The explosive onset of the illness and the under-developed and remote nature of the African region of the virus's appearance has complicated the definitive determinations of the origin and natural habitat of Ebola. The source of the Ebola virus is still unknown. However, given that filovirus, which produce similar effects, establish a latent infection in African monkeys, macaques, and chimpanzees, scientists consider the possibility that the Ebola virus likewise normally resides in an animal that lives in Africa.

distribution (range),


Ebola Symptoms: An Overview

Ebola symptoms begin to develop within an incubation period which can vary from as short as 2 days to a period of 3 weeks. Out of the 4 variations of the Ebola virus, the Zaire virus and the Sudan virus are the most common. Symptoms of these viruses include

abdominal pain (60-80%)

fever (90%-100%),

headache (40%-90%),

bloody vomit (10%-40%)

Maculopapular rash (5%-20%)

Malaise (75%-85%)

Joint and Muscle pain (40%-80%)

Inflammation of the pharynx (20%-40%)

Blood fails to clot (71%-78%)

Chest pain (SEBOV only 83%)

CNS involvement (rare)

Dry and sore throat (63%)

Hemorrhagic diathesis (71%-78%)

Hiccups (15%)

Non-bloody diarrhea (81%)

Vomiting (59%)

Purpura, petechia, sclerotic arterioles, and low blood-pressure are characteristic as the disease progresses.

 Data from:

Death occurs in 50-90% of all Ebola patients in which many die from massive blood loss within the second week of developing the symptoms.


Historical incidences of the disease.

The first historical incident of Ebola arose in 1976 in Sudan and Zaire where the first epidemic occurred in Sudan, (Ebola-Sudan) infecting 284 people with a mortality rate of 53%

Several months later, the second outbreak of the Ebola virus occurred from Zaire (Ebola-Zaire) where it had the highest mortality rate of all the Ebola virus (88%), infecting 318 people.

In 1989, Ebola Reston infected monkeys imported to Reston, Virginia, from Mindanao in the Philippines. However few people had contracted the disease and never developed life-threatening symptoms.

Ebola Cote d'Ivoire was discovered in 1994 whilst a female ethologist performed a necropsy on a dead chimpanzee from the Tai Forest, Cote d'Ivoire, accidentally infected herself during the necropsy.

Discuss the biology of your selected virus including


Currrently there are 4 known strains of Ebola including the Ebola Zaire, Ebola Cote d'Ivoire, and Ebola Reston which are all members of the filovirus family. "Filoviruses (Ebola) are helical, non-segmented, negative, single-stranded RNA viruses, polymorphic, noninfectious, and have variable lengths."

"Infectious Ebola virions are usually 920 nm in length, 80 nm in diameter, and have a membrane stolen from the host cell by budding. The virus encodes for a nucleoprotein, a glycoprotein, 7 polypeptides, a polymerase, and 4 other undesignated proteins. These proteins are made from polyadenylated mRNA transcribed in the host cell from the virus RNA."


Method of transmission


Fruit bats -

Pigs -

Mutation from primate hosts to other animals

Methods of control

Discuss the issues arising from your selected disease on:

The individual

Immediate contacts

The Ebola virus currently preys on primates and human species and due to the vast population of mankind; we are at risk of developing and passing on the infection if we are not equipped with efficient sanitation and hygiene. Many previous outbreaks were due to victims in contacts of those of the infected. This is one of the reasons why the Ebola virus is currently an infection within the borders of Africa. However if a mutation were to occur to make the virus airborne, we would all be under threat as currently Ebola is limited to its spread.


If there were to be an Ebola outbreak, society must act with preventative measures to reduce the outbreak of the infectious Ebola virus. However, currently the virus can only be spread through contact with one's infected bodily fluids so hygiene will play a major factor in infection rates .


Summarise the disease you have investigated.

What are the future problems associated with this disease?

It is possible in the future for the Ebola virus to develop new strands as it mutates to infect a greater range of species from the current humans and primates. It may also develop an airborne trait to increase progression and spread of its devastation.

Based on your research what possible future scenario do you envisage could arise from this disease?

Due to the devastating effects of Ebola on its victims, an outbreak of such an epidemic will cause widespread devastation to mankind. The development of an airborne trait mutation will wreak infections within society as it wills the evolution and progression of the virus. With no current vaccine or cure for this deadly disease, it means that if mankind loses the race between to the mutation and spread of Ebola, it is very likely that a large population of the world will be wiped out if not all.