Viruses

Viruses

• Viruses are very simple forms of life.• There is open debate over whether they are

alive at all, since they do not feed, respire or excrete waste.

• Remember MRS GREN• Viruses are extremely efficient at

reproduction, multiplying rapidly in the right conditions.

Virus Structure

• Viruses are extremely tiny, hundreds of times smaller than a bacterium.

• They can only be seen using a powerful electron microscope.

• Viruses come in many shapes:– Rod– Sphere– Threads– More complex forms

TMV – tobacco mosaic virus

Spherical Virus e.g. Influenza

Complex Viruses e.g. T4 and HIV

Virus Structure

• Viruses are made of 2 parts:–A piece of genetic material (DNA or RNA)–A protein case

A Generalised VirusExtensions – for attachment to cells

Protein Coat

Genetic Material

Reproduction

• Viruses use living cells from other organisms such as plants and animals to reproduce.

• The genetic material from the virus enters a living cell and makes copies of the virus.

• See diag.

Viral Diseases

• The organism / cell that the virus infects is called the host.

• Because the host cells are always damaged by viruses, all viruses are pathogenic.

Viral Diseases

• HIV - Human immunodeficiency virus• The common cold - rhinovirus• Measles - Rubeola• German Measles – Rubella virus• Polio - poliovirus• Flu – Influenza virus• Chicken pox - varicella• Mumps – mumps virus

Viral Diseases

• Hepatitis B – Hepatitis B Virus• Herpes – herpes virus• Ebola Hemorrhagic Fever - ebolavirus• Cervical cancer – Human Papilloma Virus• Gastroenteritis – norovirus• Rabies - rabdovirus

Ebola

• one of the most virulent viral diseases known to humankind.

• Ebola virus was first identified in the western equatorial province of Sudan and in a nearby region of Zaire (now Democratic Republic of the Congo) in 1976

• The Ebola virus is transmitted by direct contact with the blood, body fluids and tissues of infected persons.

Ebola

• Transmission of the Ebola virus has also occurred by handling sick or dead infected wild animals (chimpanzees, gorillas, monkeys, forest antelope and fruit.

Ebola

• When a person becomes infected, the virus begins to multiply within the body.

• After four to six days on average, Ebola symptoms can begin.

• The period between infection with the virus and the start of Ebola symptoms is called the incubation period.

• The Ebola incubation period can be as short as 2 days or as long as 21 days.

Common Ebola Symptoms

• Fever • Sore Throat • Weakness • Severe headache • Joint and muscle aches • Diarrhea • Vomiting • Dehydration • Dry, hacking cough • Stomach pain.

Ebola

• A rash, red eyes, hiccups, and internal and external bleeding may be seen in some patients. When the rash develops on dark skin, it is often not recognized until the rash begins to peel.

• In pregnant women, abortion (miscarriage) and heavy vaginal bleeding are common Ebola symptoms.

• Death usually occurs during the second week of Ebola symptoms. Death in Ebola victims is usually from massive blood loss.

HIV/ AIDS

• The first documented cases were in 1981, when homosexual men with symptoms of a disease that now are considered typical of AIDS were first described in Los Angeles and New York.

• The men had an unusual type of lung infection called pneumonia (PCP) and rare skin tumors called Kaposi's sarcomas.

HIV/ AIDS

• The patients were noted to have a severe reduction in a type of cell in the blood that is an important part of the immune system. These cells, often referred to as T cells, help the body fight infections.

• The time from HIV infection to the development of AIDS varies. Rarely, some individuals develop complications of HIV that define AIDS within one year, while others remain completely asymptomatic after as many as 20 years from the time of infection.

HIV/ AIDS• Within weeks of infection, many people will

develop the varied symptoms of primary infection which typically have been described as an "influenza" like illness but can range from minimal fever, aches, and pains to very severe symptoms. The most common symptoms of primary HIV infection are:– fever,– aching muscles and joints,– sore throat, – and swollen glands (lymph nodes) in the neck.

HIV/ AIDS

• Shortly after primary infection, most individuals enter a period of where they have no symptoms at all. During this time, T cells may gradually decline, and with this decline in the immune system, patients may develop the mild symptoms of HIV such as thrush (a fungal infection), fungal infections of the nails, a white brush-like border on the sides of tongue called hairy leukoplakia, chronic rashes, diarrhea, fatigue, and weight loss.

HIV/ AIDS

• This weakening of the immune system means that the patient is prone to secondary infections such as TB, Chronic diarrhea etc.

Viruses

• Viruses are not affected by antibiotics.• Viruses can change their form rapidly, this is

why new diseases caused by viruses have arisen.– HIV in the early 1980s– Ebola in the late 1980s– influenza

Viruses

• Our immune system eventually fights off most diseases caused by viruses.

Culturing Viruses

• Viruses can only be cultured inside living cells.• Fertilised hen’s eggs are a suitable culture

medium.