1. Chapter 18

2. How Do Viruses Cause Disease?
Viruses multiply within host cells.
It is during their escape from those cells—either by cell lysis or budding—that the host cells are destroyed.
This cell destruction leads to most of the symptoms of a viral infection, which vary depending on the location of the infection.

3. Viral Infections of the Skin
Chickenpox and shingles
Varicella-zoster virus (a DNA virus which is also known as human herpesvirus 3)
German measles (rubella)
Rubella virus, an RNA virus
Measles (hard measles, rubeola)
Measles (rubeola) virus, an RNA virus
Monkeypox
Monkeypox virus, a DNA virus
Smallpox
Two strains of variola virus (variola minor and variola major), a DNA virus
Warts
At least 70 different types of human papillomaviruses (HPV), DNA viruses

4. Chickenpox

5. Child with Rubella

6. Child with Measles

7. Koplik Spots (an Early Sign of Measles)

8. Viral Infections of the Eyes
Adenoviral conjunctivitis and keratoconjunctivitis—caused by various types of adenoviruses
Herpes simplex and varicella-zoster viruses can also cause keratoconjunctivitis.
Hemorrhagic conjunctivitis—caused by adenoviruses and enteroviruses
People with viral infections (e.g., cold sores) should wash their hands thoroughly before inserting or removing contact lenses or otherwise touching their eyes.

9. Viral Infections of the Upper Respiratory Tract
The common cold (acute viral rhinitis, acute coryza)
Many different viruses cause colds.
Rhinoviruses (more than 100 serotypes) are the major cause in adults.
Other cold-causing viruses include coronaviruses, parainfluenza viruses, respiratory syncytial virus (RSV), influenza viruses, adenoviruses, and enteroviruses.
Transmission occurs via respiratory secretions by way of hands and fomites or direct contact with or inhalation of airborne droplets.

10. Viral Infections of the Lower Respiratory Tract
Acute, febrile, viral respiratory disease
Caused by parainfluenza viruses, respiratory syncytial virus (RSV), adenovirus, rhinoviruses, certain coronaviruses, coxsackieviruses, and echoviruses; transmission occurs via direct oral contact or by droplets.
Avian influenza (bird flu)
Avian influenza virus type A; three prominent subtypes – H5, H7, and H9; bird-to-human transmission occurs via contact with infected poultry or contaminated surfaces.
Hantavirus pulmonary syndrome (HPS)
Caused by at least five different hantaviruses (Sin Nombre, Bayou, Black Creek Canal, New York-1, Monongahela); transmission occurs via inhalation of aerosolized rodent feces, urine, and saliva.

11. Viral Infections of the Lower Respiratory Tract (cont.)
Influenza, flu
Influenza viruses, types A, B, and C; RNA viruses; transmission is via infected humans; pigs and birds also serve as reservoirs
Severe acute respiratory syndrome (SARS)
SARS-associated coronavirus (SARS-CoV) (shown here)
Transmission occurs via infected individuals by respiratory droplets, or by touching the mouth, nose, or eye after touching a contaminated surface or object.

12. Viral Infections of the Oral Region
Cold sores (fever blisters, herpes labialis)
Usually caused by herpes simplex virus type 1 (HSV-1), but can be caused by herpes simplex type 2 (HSV-2)
DNA viruses in the family Herpesviridae
Either HSV-1 or HSV-2 can also infect the genital tract, although genital herpes infections are most often caused by HSV-2.

13. Cold Sore Caused by Herpes Simplex

14. Viral Infections of the GI Tract
Viral gastroenteritis (viral enteritis, viral diarrhea)
The most common viruses infecting children in their first years of life are enteric adenoviruses, astroviruses, caliciviruses, and rotaviruses.
Viruses infecting children and adults include norovirus-like viruses and rotaviruses.
Transmission occurs via infected humans, most often by way of the fecal–oral route; possibly from contaminated water and shellfish.

15. Most Common Types of Viral Hepatitis
Type A hepatitis (HAV infection, infectious hepatitis, epidemic Hepatitis)
Hepatitis A virus (HAV)—a linear ssRNA virus
Fecal–oral transmission
Type B hepatitis (HBV infection, serum hepatitis)
Hepatitis B virus (HBV)—an enveloped, circular dsDNA virus
Sexual transmission or household contact with an infected person; injected drug use; tattooing; needlesticks
Type C hepatitis (HCV infection, non-A non-B hepatitis)
Hepatitis C virus (HCV)—an enveloped, linear ssRNA virus
Primarily parenterally transmitted; rarely sexually
Type D hepatitis (HDV infection, delta hepatitis)
Hepatitis D virus (HDV, delta virus)—an enveloped, circular ssRNA viral satellite; coinfection with HBV is necessary
Exposure to infected blood and body fluids, etc.

16. Most Common Types of Viral Hepatitis
Type E hepatitis
Hepatitis E virus (HEV)—a nonenveloped, ssRNA virus
Fecal–oral transmission; primarily fecally contaminated drinking water; also person-to-person
Type G hepatitis
Hepatitis G virus (HGV)—a linear ssRNA virus
Parenteral transmission

17. Viral STDs Anogenital herpes viral infections (genital herpes)
Usually caused by HSV-2; occasionally by HSV-1
Transmission occurs via infected humans by direct sexual contact; oral-genital, oral-anal, or anal-genital contact when lesions are present.
Genital warts (genital papillomatosis, condyloma acuminatum)
Human papillomaviruses (HPV); DNA viruses
Transmission occurs via infected humans by direct contact, usually sexual.
Genital warts can become malignant.

18. Viral Infections of the Circulatory System
Human immunodeficiency virus (HIV) infection, acquired immunodeficiency syndrome (AIDS)
HIV—two types: HIV-1 (most common) and HIV-2; ssRNA viruses
Transmission occurs via infected humans, by direct sexual contact; contaminated needles/syringes; transfusion of contaminated blood; transplacental transfer from mother to child; transplantation of HIV- infected tissues or organs; needlestick, scalpel, and broken glass injuries.

19. Common Modes of Transmission of HIV

20. Viral Infections of the Circulatory System
Infectious mononucleosis ( “mono,” “kissing disease”)
Caused by Epstein–Barr virus (EBV), which is also known as human herpesvirus 4; a DNA virus in the family Herpesviridae
Transmission occurs via infected humans, person-to-person, direct contact with saliva.
Mumps (infectious parotitis)
Caused by mumps virus—an RNA virus
Transmission occurs via infected humans by droplet spread and direct contact with saliva.

21. Viral Hemorrhagic Diseases (Viral Hemorrhagic Fevers)
Caused by many different viruses, including dengue virus, yellow fever virus, Crimean-Congo hemorrhagic fever virus, Lassa virus, Ebola virus, and Marburg virus
Ebola and Marburg viruses are extremely large filamentous viruses.
Infected humans serve as reservoirs; infected African green monkeys also serve as reservoirs in Marburg infection.
Transmission is person-to-person via direct contact with infected blood, secretions, internal organs, or semen; also needlestick.

22. Viral Infections of the CNS
Poliomyelitis (polio, infantile paralysis)
Caused by polioviruses—RNA viruses
Transmission is person-to-person, primarily via the fecal–oral route; also throat secretions.
Rabies
Caused by rabies virus; a bullet-shaped, enveloped RNA virus
Many reservoirs, including dogs, foxes, coyotes, wolves, jackals, skunks, raccoons, mongooses, bats
Transmission occurs via the bite of a rabid animal which introduces virus- laden saliva; airborne transmission from bats in caves also occurs.
Viral meningitis (aseptic meningitis, abacterial meningitis)
Caused by many different viruses

23. Selected Arthropodborne Viral Encephalitides of the United States
Disease
Reservoirs
Vectors
Eastern equine encephalitis (EEE)
Birds, horses
Aedes, Coquilletidia, Culex, and Culiseta mosquitoes
California encephalitis
Rodents, rabbits
Aedes and Culex mosquitoes
LaCrosse encephalitis
Chipmunks, squirrels
Aedes mosquitoes
St. Louis encephalitis
Birds
Culex mosquitoes
West Nile virus encephalitis
Birds, perhaps horses
Western equine encephalitis (WEE)