Viruses Viruses are infectious particles made only of a strand of DNA or RNA surrounded by a protein coat.

Many people think that viruses fit in one of the Domains. THEY DON’T. Viruses do not eat. Viruses cannot reproduce on their own. Because of this, viruses are not considered to be living, so they are not classified under any of the three domains.

Structure of a virus…

How do viruses work? http://www.brainpop.com/health/diseasesinjuriesandconditions/viruses/

Lytic Infections vs. Lysogenic Infections Lytic infections: an infection pathway in which the host cell bursts, releasing the new viral offspring into the host’s system, where each then infects another cell. Lysogenic infections: a phage combines its DNA into the host cell’s DNA . The virus is passed to daughter cells as the nucleus and cell split during mitosis and cytokinesis. This is how the virus spreads.

Visualization of Lytic vs. Lysogenic Infections http://www.classzone.com/cz/books/bio_09/resources/htmls/animated_biology/unit6/bio_ch18_0550_ab_virus.html

Viruses cause many infectious diseases. Viruses can enter the body through cuts, scrapes, or mucous membranes. Examples of viral infections: common cold influenza SARS (severe acute respiratory syndrome) HIV (a retrovirus)

Vaccines are made from weakened pathogens. Vaccines are substances that stimulate the body’s own immune response against invasion by microbes. They are made from weakened versions of viruses, or parts of the virus, that they are intended to protect against. Viral diseases are difficult to treat once a person is infected. Vaccination is often the only way to protect against the spread of viral disease.

Epidemics Epidemics are rapid outbreaks of infection that affects many people. Famous epidemics: http://www.healthline.com/health-slideshow/10-worst-disease-outbreaks#1