VIRUSES & DISEASES

Viral Transmission

Viruses can be transmitted in many different ways:

Respiratory (coughing, sneezing, etc.) Blood, body fluids, salvia Vectors (transmit viruses but are not

infected i.e mosquitoes, ticks, mites, etc.) Direct contact with any membranes (eye)

or openings to the body (mouth, ear, etc.) Fecal – oral (gastrointestinal infections)

Viruses & Plants

Not all viruses infect animals and humans. Some viruses infect plants too! Viruses can cause a huge loss in crop production. One of the first viruses to be discovered was the Tobacco Mosaic Virus (TMV).

TMV is an RNA virus that infects plants, especially tobacco and other members of the family Solanaceae (includes tomatoes).

The infection causes characteristic patterns (discoloration) on the leaves.

The virus can infect the plant by using a vector (a transporter of the virus) such as fungi, mites, insects, nematodes, and bacteria.

Viruses & Bacteria

Viruses that infect bacteria are known as bacteriophage.

One of the most well known bacteriophage is the T4 which infects E.coli. The virus contains double stranded DNA.

Viruses & Animals

An example of a virus that infects animals is the rabies virus, from the family rhabdoviruses.

The rabies virus is a single stranded enveloped RNA virus.

It is most common is raccoons and skunks in SK.

The virus is transmitted through a bite from an infected animal. The virus will be transmitted via the salvia of the infected animal to another uninfected animal. It may also be transmitted via aerosols, such as in bat caves.

The virus first enters the body through the bite. It will then replicate in the muscle or tissue cell at the site of the bite. From here the virus will enter the peripheral nervous system. Eventually the virus infects the eye, salivary glands (hence the typical forming at the mouth), and skin. Lastly the virus infects the brain and spinal cord (causing spasms, loss of coordination, confusion and deliriousness).

The progression of the virus from initial bite to fever, nausea, vomiting, depression, paralysis, coma and death can take 3 months to one year.

West Nile Virus

WNV is enveloped, single stranded RNA From the family flaviviridae The vector of the virus is the culex

mosquitoe. Common host is birds A female mosquitoe acquires the virus from

biting a virus infected host The virus will replicate inside the mosquitoe The virus is further spread when the

mosquitoe bits another host

Usually the virus will cause low grade disease; flu-like symptoms. Only 20% of the population infected with WNV will develop fever, headache, body aches, swollen glands, etc. Only 1% of the infected population will develop encephalitis (infection of the brain) or meningitis (infection of the membranes of the brain).

Horses and crows are highly infected by the virus

Saskatchewan cases of humans with West Nile from 2002-2007 (From Public Health Agency)

2002 2003 2004 2005 2006 2007

Cases in SK

0 937 5 53 19 1285

HIV

HIV is an enveloped RNA virus HIV aka Human Immunodeficiency Virus HIV is transmitted by bodily fluids (blood,

semen and vaginal secretions) HIV primarily infects CD4T cells and

macrophages The disease is incurable and will

eventually lead to AIDS (Acquired Immune Deficiency Syndrome)

People who are at risk: Intravenous drug users Anyone who is highly sexually active Anyone who had an organ/blood

transplant before 1985 Newborns of HIV positive mothers

The earliest symptoms of HIV infection occur while your body begins to form antibodies to the virus between six weeks and three months after infection with the HIV virus

Those who do show early HIV symptoms will develop flu-like symptoms. However, for most people, the first symptoms of HIV will not be apparent. Eventually the immune system deteriorates and will progress to AIDS. Having a compromised immune system makes those who are infected more susceptible to other infections

Hepatitis

Hepatitis has many forms. All generally cause liver damage and can lead to cancer/death.

Hep A – replicates in the liver, shed in the stool; caused by contaminated water, food or dirty hands

Hep B- caused by contaminated blood (sharing needles, body piercings/tattoos, blood transfusions etc.)

Hep C- caused by infected blood (drug use and highly sexually active people).

The liver is important for toxin filtration and bile production.

Hepatitis A and B have vaccines, where Hepatitis C does not. When travelling to third world countries it is often advised to get vaccinated for Hepatitis A and B.

There is also alcohol induced hepatitis, which causes liver damage.

General symptoms include: fever, headache, abdominal pain, fatigue, jaundice. Eventually leading to liver cirrhosis (scar tissue on liver), and possibly death.

Human Papilloma Virus (HPV) Infects the skin and mucous membranes

of humans. It impacts the health of women far more

than it impacts men. Approximately 130 HPV types have been identified.

Some HPV types can cause warts or some types of cancer, while others have no symptoms.

Once an HPV viron invades a cell, an active infection occurs, and the virus can be transmitted. Several months to years may elapse before squamous intraepithelial lesions (SIL) develop and can be clinically detected.

The time from active infection to clinically detectable disease makes it difficult for someone who has become infected to establish which partner was the source of infection.

In 2006 a vaccine to prevent initial HPV infection was released called Gardasil. HPV vaccine is made up of proteins from the outer coat of the virus (HPV). There is no infectious material in this vaccine.

HPV is the most common sexually transmitted infection. Most people will get HPV at some point in their lives but this viral infection usually clears up by itself and causes no signs or symptoms at all.

Type 16 and 18 are the high risk types to cause cervical cancer.

You can’t physically see whether a person has an HPV infection unless the person has genital warts. Many people with HPV don’t have any visible signs but they can still spread the virus.

The Pap test detects cell changes in the cervix (located at the end of the vagina). It doesn’t tell you if you have an STI, including HPV.

Currently there is no cure for HPV

More commonly known as the flu Influenza is an enveloped RNA virus The virus is transmitted via aerosols

such as coughs, sneezes, etc., as well as salvia, nasal secretions, feces, and blood. A person may also become infected by contact with an infected surface.

Initially the virus causes an upper respiratory tract infection. While infected with influenza you are more susceptible to pneumonia. General symptoms include headache, tiredness, fever, chills, and loss of appetite.

The strain H1N1 refers to the glycoproteins which are on the envelope. H refers to the protein hemagglutinin, and the N refers to the protein neuraminidase.

 

Smallpox

Smallpox is one of the largest viruses. It is a DNA virus

Smallpox is an infectious disease unique to humans.

Smallpox enters through inhalation and localizes in small blood vessels of the skin and in the mouth and throat. In the skin, it results in a characteristic rash, and later, raised fluid-filled blisters and high fever.

It replicates in the upper respiratory tract

Was cause of the deaths of one third of children in England in the 18th Century.

Smallpox was the first disease to be controlled by immunization. This disease was eradicated in 1980

This virus was one of the major reasons the Europeans were able to defeat many of the aboriginal population in North America

Herpes Virus

Herpes viruses are double stranded enveloped viruses

Causes lifelong infection Herpes simplex 1 causes cold sores Herpes simples 2 causes oral lesions

(cold sores) and genital lesions Both HSV1 and HSV2 are spread by close

contact

Both establish a latent infection, meaning that the virus will infect and cause symptoms, then go into a period of latency in which there are no symptoms.

Varicella-zoster (chicken pox) VZV is also known as herpesvirus 3 Spread by close contact and respiratory You are contagious before and during the

symptoms Varicella causes the characteristic rash, as well

as a fever Zoster causes shingles, which usually occurs in

the thoracic region. It resembles chicken pox but is generally much more painful