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IV. Viral Pathogenesis

Viral Pathogenesis is the capacity of a virus to cause disease in a target host. It is a sophisticated study about the relationship between viral replication, host defence and viral evasion of the host defence.

I’ll just organise this topic into different parts for easier explaining.

1. Sites of Viral Entry into the host.
2. Viral spreading in the host body.
3. Modes of Transmission.
4. Virus-induced injury (cellular).
5. Sites of Viral entry into the host.

I shall now start explaining each and every one of these points…

1. Sites of Viral Entry into the host.

There are various places that a virus can enter and start causing disease to the host.

A. Animal host (E.g. Humans, lions, fishes, etc.)

• Skin
• Cuts, abrasions, etc.
• Conjunctiva (eyelids)
• Urogenital tract
• Respiratory tract
• Alimentary tract

B. Plant host

• Any part of the plant as long as there is direct penetration of the cell wall.

2. Virus spreading in the host body.

i. Systemic infection

• Many organs are infected

ii. Haematogenous spread

• Spread through the bloodstream
• Viremia
• Active / Passive
• Primary / Secondary

iii. Neural spread

3. Modes of Transmission.

• Spread through germ cells
• Consumption of infected tissue
• Respiratory Secretions
• Aerosols during speaking, sneezing, coughing, breathing, singing
• Faeces
• Blood

4. Virus-induced injury (cellular) and effects.

The cells that are infected with viruses will display Cytopathic Effects (CPE).

Some of these effects consist of:

• Altered shape
• Detachment from substrate
• Lysis
• Membrane fusion; syncytium
• Membrane permeability
• Inclusion bodies
• Apoptosis

Other effects shown would be the Formation of Syncytium, shutting off of cell functions and Immunopathological lesions.

a. Formation of Syncytium

Below is a diagram describing Syncytium formation.

b. Shutting off of cell functions

• E.g. poliovirus shuts off cellular function in neurons resulting in cell death and hence paralysis

c. Immunopathological lesions

• Impairment of immune response due to infection of immune cells. (E.g. HIV on CD4⁺ & CD8⁺ T lymphocytes)

• Enhancement of immune response causing haemorrhagic fever. (E.g. Dengue haemorrhagic fever, Hantaan, Ebola, etc.)

Viruses? A deadly weapon of war?

We all know how dangerous viruses can be. They can even cause cell death. However, ever thought about what humans could do with the control of such technology? Sounds dangerous, doesn't it? Imagine terorists being able to bring the world under their control and believes, by threatening citizens with the mastery of perhaps, cowpox? Cowpox is dangerous enough to cause death, especially since vaccination stopped over 30 years ago, and if a strain of virus kept for research was to be stolen.

Although we may not be sure of being able to prevent such theft, we can learn how to play our part in fighting against it.

We should always make sure to vaccine ourselves and our close family. Also, we should take precautions by keeping our body stystems healthy enough to fight against diseases, by keeping a healthy diet and taking medication whenever needed to.

We can all play a part to fight against viruses, artificial or natural. It is simply a matter of whether we want to. How about you?

Emerging Viruses. How to fight this new foe?

At all times, we must all be ever ready and prepared for new rapidly spreading infectious viruses within the human population. But what are these new threats called? We call them, 'emerging viruses'. This has already been explained by my colleague. But what I'm unterested in, is as to how we can fight this new enemy.

It is good to cure this disease after researching about it, but prevention is better than cure. Therefore, we shall learn about the causes of these emrging viruses, which we must take care to avoid, in order to prevent teh enemy from even having an opportunity to strike, or at least hinder the birth of such problems.

Firstly, we know about virus factors, those that we cannot avoid yet. Spontaneous evolution of a new virus entity and generation of a novel strain due to co-infection of different strains in an individual.

The second part consists of what we can prevent, that is, human factors, such as concentration of people with shared lifestyles, breakdown in public health, climate change, and man invading natural habitats such as cutting of forests to increase their land for development and comfort, which may cause zoonoses.

Men are typically selfish. However, we must understand what must be done, and prevent all of these factors from happening as much as possible, as much as we can survive with.

However, although I believe in doing so, there are cases where certain choices are up to you. Imagine if you are a farmer with sick chickens that are infected with avian flu. With your family starving, would you rather kill the chickens as teh government demands, or sell them illegally for bread and butter. Personally, if we were to die of hunger, I would rather send my children to teh government to take care of, and die of hunger on my own with dignity, since I do know that tehy would want it that way, and that it is better than knowing that all were killed due to my selfishness.

Think about this. What would you do?

Virusoids? What are they?

A long time ago, most people believed that infectious diseases were caused by either viruses, bacteria, fungi or parasites. However, the mad cow's disease caused by something else proved this theory wrong.

In this case, I shall be talking about a certain infectious agent known as virusoids that infect plants. Similarly to viroids, they are infectious agents composed exclusively of a single piece of circular single stranded RNA which has some double-stranded areas. It has no capsid or envelope, making it susceptible to certain environment hazards such as heat.

The key is here. Unlike viroids, they do not require assistant virus, as viroids do, such as hepatitis with hepatitis D.

Whether this is better, or if this is not, largely depends on the purpose of the virus. This is what I believe. How about you?

Flaviviridae -II

Next up is Yellow fever. Now, the symptoms first.

It has an incubation period of 3-6 days

Headaches, nausea strawberry tongue, flushing of the head and neck, conjunctival injection, just to list a few.

Severe yellow fever is when the patient goes into remission after acute yellow fever

Fever, vomiting, abdominal pain, dehydration, prostration, jaundice, black vomit (coffee-ground diathesis), and bleeding from injection puncture sites. Interestingly, the virusis absent from the blood, which suggests that autoimmunity greatly influences it.

Lastly, the West Nile fever.

It originated in Uganda, discovered way back in 1937, with an epidemic in 2002 in the US. Now let's look at the checklist of symptoms:

Mainly mild to no symptoms

Fever

Headache

Body aches

Skin rash

Swollen lymph glands

Note: these are for the not so severe cases, those are listed below-

Crossing blood-brain barrier- as in it passes through the blood-barrier in the brain, residing there.

Encephalitis

Meningitis

There is no vaccination for this west nile virus and dengue, so please follow this for your sake and your loved ones. 

It's amazing what a tiny insect can do to humans. It's scary, but as long as one takes preventive measures, I'm sure everything will be alright. That's all for now. tune in for more on our blog.

Flaviviridae

This is a family of (+) single-strand RNA viruses that have 3 important structural proteins and a host-derived lipid layer. Below is a simplified diagram on Hepatitis C virus, which belongs to the flaviviridae family.

 Generally, it is  genetic material-containing icosahedron in a lipid-containing envelope. Now, onto the members of this family.

First, let's meet the most important arbovirus (insect-borne) virus today - Dengue.

Dengue- 

It has 4 serotypes, DEN-1, DEN-2, DEN-3 AND DEN-4, based on neutralisation test. DEN-2 has the greatest antigenic and genotypic distance from the others. It is spread by the Aedes aegypti, or Aedes mosquito. 

It causes dengue fever, which has asymptomatic infections. Acute infections has the following symptoms: severe frontal headache, nausea and vomiting. Sever muscle and bone pain are also experiecnced.  

Dengue Haemorrahagic Fever or Dengue Shick Syndrome may also occur. It's symptoms are similar to that of dengue fever, HOWEVER, remission occurs, resulting in the sudden deterioriation of the patient's condition. Severe prostration, hypotension, collapse of the circulatory system, bleeding and shock follows. It can be catergorised into 4 grades. 

Now, onward to pathogenesis. Despite intensive studies conducted, pathogenesis of dengue haemorrhagic fever(DHF), is not really understood, However, there are 2 theories, both of which I will present.

(I)Virulent strain theory

Some strains are more virulent than others, with molecular studies showing variance in sequences among different strains withinserotypes, and early evidence points to DEN-2

(II)Antibody enhancement

This is the main theory, as these cells, the monocytes and marcophages are the main target for the DHF viruses. 

Wow, this was a long post, so I'll be covering on Yellow fever in the next one!! But I realised that something so simple as discarding stagnant water can prevent the breeding of these mosquitos, and eventually, the prevention of such disease. So, get rid of stagnant water, cause Prevention is better that Cure.

Emerging Viruses

First off, what is an emerging virus?? Well, its an known virus, that is thought to infect animals only, but is showing an increasing incidence in humans. Sounds familiar?? If you guessed bird flu or SARS, you're right. 

Now, how does a virus that infects animals only start infecting humans?? There are various factors, which can be lumped into 2 groups: Virus and Human factors.

Virus Factors:
(i) Spontaneous Evolution
Alright, now, viral populations are hetergenous and there IS a limit of variation, but that is a really big number. Furthermore, as there is selection pressure present, this results in high mutation rates, and thus, spontaneous evolution, where a new virus entity is formed.

(ii)Random Assortment, or the generation of a new strain due to the co-infection of different strains in an individual. That was long, so I'll be using Random Assortment instead.

As previously stated, in the life cycle of a virus, the genetic material of the virus undergoes replication and expression. However, when two viruses infect one cell at the same time, or co-infection, the host cell gets mixed up during the assembly stage and a "new" vius is produced and released out of the cell to infect others. Thus RANDOM assortment

Human factors:

(I)Man invading the natural habitat of animals. Truly, this shows why humans, at times, should not destroy Mother Nature. Though other times, we humans, too have no other alternative. Anyway, on with the explanation.

Examples of humans invading the animals' natural habitat would be deforestation, which puts man closer to wild animals. 

(II)Climate change is an important factor, especially with global warming nowadays. 

This increase of global temperature will definitely affect the ecosystem on a whole. Insects, especially, are greatly involved as warmer temperatures have been linked to an increase in reproduction of mosquito, a vector of the virus which causes dengue fever. Hence, increase in temperature = increase in viral vectors = more people infected.

(III)Breakdown in Public Health

Though this might not happen in developed countries, it still happens in less developed countries. Unhygenic surroundings increase the likelihood of incidence. 

(IV)Concentration of people with shared lifestyle

As the concentration of peopple increase, so does the chances of contracting a virus from an infected person. So, when one person is infected, that one person can spread to another 2 people who then infect others, continuously infecting other, increasing incidence.

As seen above, some factors are caused by humanity, others by nature. From this, I realised that the cause of increasing incidence has so many factors, and mostly are results of our own actions.