Lytic Infections by viruses Lysogenic infections by viruses Treating viral infections Viral Epidemics Human Viral Diseases

 Non-living particle made of proteins, nucleic acids, and sometimes lipids  They can reproduce only by infecting living cells  Lytic Infections: virus enters a cell, multiplies, and causes cell to lyse, or burst, sending new viruses out to infect more cells (SARS, common cold, influenza, rabies)  Lysogenic Infections: viral DNA is inserted into host cell DNA and multiplies w/out harming host cell; causes each new cell to be infected with virus (HIV, Herpes, HPV, shingles)

 Viruses are difficult to eliminate b/c their replication pathway requires host cells; drugs are often toxic to the host cell  Also must be grown in live cells and tissues which takes time to do  Methods: vaccinations to provide immunity from infections and antiviral drugs that interfere with viral replication  ** viruses mutate rapidly so antiviral drugs must be used only when necessary  Viruses can become resistant quickly

 Smallpox among Native Americans: , death toll is estimated at 80-90% of the population  Influenza: worldwide, death toll approx. 75 million  HIV/AIDS: 1981-present worldwide, death toll approx. 25 million

 STD’S: HIV/AIDS, herpes  Childhood diseases: measles, mumps, chicken pox  Respiratory diseases: influenza, common cold  Skin diseases: shingles, warts  Digestive tract diseases: gastroenteritis  Nervous system diseases: polio, viral meningitis, rabies  Other diseases: smallpox, hepatitis

 7 APRIL As of 7 April 2013 (16:30 CET), the Chinese health authorities notified WHO of an additional three laboratory-confirmed cases of human infection with influenza A(H7N9) virus.  To date, a total of 21 cases have been laboratory confirmed with influenza A(H7N9) virus in China, including six deaths, 12 severe cases and three mild cases.  The Chinese government is actively investigating this event and has heightened disease surveillance.