Virus Intro & Dermotropic Viruses (ch. 17.1)

Herpes simplex I (herpesvirus hominis HVH)

*HERPES SIMPLEX I* recurring viral infection - oral, respiratory secretions, skin and mucous membrane - cold sores/fever blisters

Herpes simplex II

*HERPES SIMPLEX II* venereal genital area

Rubella (*GERMAN MEASLES*)

*aka 3 day measles *more mild than Rubeola *rapid pale pink rash *transmitted by direct contact with nasal or throat secretions *lymph nodes behind ear/neck may swell and cause pain *contagious for 7 days before or after rash onset

Variola (*SMALLPOX*)

*disease eradicated due to vaccination with the Vaccinia virus *primary symptom is sudden appearance of a skin rash* *high fever, chills, headache, myalgias, prostration, nausea and vomiting *after 2 to 4 days fever subsided and rash that first appeared on the face covered entire body* *maculopapular skin lesions matured into vesicles and pustules and dried into sabs that fell off after 3 or 4 weeks* *until 30 years ago was endemic in 31 countries; 10-15 million people developed smallpox yearly & 2 million people died yearly

Edward Jenner

*father of smallpox vaccination* *noticed that people exposed to cowpox did not die from smallpox therefore immunity must be the same *instituted procedure known as "vaccination" *word vaccination is derived b/c of its connection with cowpox; "vacca" is Latin for cow

Coxsackievirus A16 (*FOOT AND MOUTH DISEASE*)

*humans* are only source *common childhood disease but can occur at any age *painful blisters in the mouth, on the gums, and tongue, on palms and fingers of the hand, or on the soles of the feet that usually occur 3 to 5 days after exposure and may last 7 to 10 days *usually goes away without serious complications

Describe the basic structure of a virus.

*infectious agent made up of a core of nucleic acid (DNA or RNA) and a protein coat (capsid)

Rubeola (*MEASLES*)

*most contagious of childhood (almost exclusively) rash diseases but can be contracted at any age* *acute & highly contagious *spread by direct contact through nasal & throat secretions & airborne *90% attack rate after exposure *prodromal period:3 to 5 days (from end of incubation period to appearance of 1st symptoms) *rash may last for up to 14 days after exposure *occurs in 2 stages:* *1.runny nose, cough, and slight fever;eyes may become reddened and sensitive to light as fever rises* *2. begins from days 3 to 7;fever of 103-105F; red blotchy rash that begins on face then spreads over the entire body* *individual is contagious from 5 days prior and 5 days after rash onset

Capsid

*protein coat that surrounds core of virus *composed of *capsomeres*

Virus

*simplest & smallest form of life *not capable of independently creating metabolism on its own *can only reproduce using components of another living cell *OBLIGATE PARASITE*

How are viruses classified?

*type of nucleic acid present in the virion *molecular weight of nucleic acid *whether nucleic acid is single or double stranded *number of genes in the nucleic acid *size and structure *symmetric arrangement of nucleocapsid *presence/absence of envelope *sensitivity to chemical agents *immunology *epidemiology *pathology *name of tissue of preferred growth or elective localization* *according to the diseases that they cause and the pathological effects in humans*

Stages of viral replication

1. *ATTACHMENT*: *Virus recognizes and attaches to specific cost cell *Spikes on envelope attach or proteins on capsule match receptors on host cell 2.*PENETRATION* *Virus taken into cell by endocytosis or viral envelope fuses with host cell membrane and dumps content into host cell 3.*REPLICATION* *Viral genes are copied within minutes and mass produced into viral parts 4.*ASSEMBLY* *Individual viral parts are assembled into a whole virus 5.*RELEASE* *New active viruses are released from host cell

Size range of viruses

25 to 250 nanometers (nanometer is one thousand times smaller than a micrometer)

What is the difference between bacteria and virus reproduction?

*Bacteria*: parent cell splits into 2 daughter cells (*binary fission*) *Virus*: replicates using resources of the host cell to synthesize new virus structure

Give examples of how viruses are named based on their pathologic effects in humans

*DERMOTROPIC* attacks the skin *PNEUMOTROPIC* attacks respiratory system *NEUROTROPIC* attacks nervous system *VISCEROTROPIC* attacks major internal organs (eg. liver) *ADENOTROPIC* attacks glands of the host

Difference between bacteria & virus reproduction

bacteria undergoes binary fission & a virus must use the resources of a host cell to form new structures

Varicella zoster (*CHICKENPOX*)

chickenpox (herpesvirus) is primary infection - highly contagious - one of most readily transmitted diseases - with generalized itchy vesicular rash around hair/clothing areas - 200-500 lesions "successive crops"

Reye's syndrome

complications from taking aspirin or salicylate with early stages of varicella zoster - inflammation of liver & brain

HVH infections

herpesvirus hominis - 85% are subclinical with no noticeable symptoms - carrier for life, reside in sheath of sensory nerves

What is a capsomere of a virus?

individual protein subunits that build capsids

Varicella zoster secondary infection

invasive group A streptococci GAS - can cause acute necrotizing fasciitis or tss

Koplik spots

little white spots that may appear on gums and inside of cheeks

Virions

mature infectious virus organisms capable of causing disease

MMR vaccine

measles, mumps, rubella

What is a nucleocapsid?

nucleic acid + capsid

What provides the genetic code for viral reproduction?

nucleic acid by host cell

envelope

outer non-rigid covering to the capsid

Congenital rubella syndrome CRS

unimmunized pregnancy during 1st trimester - at least 25% infant abnormalities, birth defects

vesicles

water-like blisters from herpes I and II

Coxsackie - animals

Foot & mouth disease - highly contagious to cloven-hoofed animals - mass slaughter to prevent spread - FMD, FAM

Dermotropic diseases

VARIOLA RUBEOLA RUBELLA VARICELLA ZOSTER HERPES SIMPLEX I HERPES SIMPLEX II COXSACKIE

Shingles

Varicella-zoster virus, herpes-zoster - varicella reactivates as adult - vesicles along sensory nerves on dorsal root ganglia - unilateral rash - airborne through respiratory tract or vesicular fluid *very painful*