Mammalian Pathogenic Viruses

Viral Diseases

TFC, P.346, Black’s 2nd, p. 266- , Alcamo 323-, Campbell 6th: , Black’s 6th: 264-294, tbl: 270

DISCOVERY:

Chamberland                1884     developed porcelain filter to remove bacteria

Iwanowski                    1892     used filter to try to remove tobacco mosaic disease, “filterable virus”

Beijerinck                     1898    showed could be diluted out, destroyed by heat

Forsh & Loeffler          1898    foot and mouth disease caused by filterable agent

Walter Reed                 1901    yellow fever also filterable disease (in Cuba)

Twort & d’Herrelle       1917     bacteriophage

 

TRAITS: All viruses posses: (p 266)

             capsid             protein coat composed of capsomeres, can contain penetration enzymes

             genome           may be DNA or RNA, double stranded , single stranded, (+ = mRNA) or (-)

 

Spikes:             glycoprotein for attachment, enzymes to assist attachment

             Host range = which species infected

             specificity = which tissue affected, determined by ability to attach, multiply and release

 

three morphologies:               icosahedral (20 faces)              herpes, polio, cytomegaly

(p 267 for sizes and shapes)    helical                                      rabies, TMV

                                                 complex                                   small pox, coronavirus, influenza

 

VARIETY OF VIRUSES, p 270, characterized by comp of genome, enveloped or not, geometry, size

 

VIRAL REPLICATION:

Obligate Intracellular parasites, replicate inside      absorption

                                                                                 Penetration

                                                                                 Synthesis

                                                                                 Maturation

                                                                                 Release

 

Bacteriophage parts (p 279): capsid, genome, tail assembly, tail piece, tail fibers, tail sheath, tailcore

             bacteriophage replication: p 280

             lysogeny: p 283 (lysogen. In mammalian cells, called provirus)

 

enveloped viruses: upon release by budding from host. replication of enveloped virus, p 284

             Enveloped viruses are inactivated by hi temp, hi or lo pH, lipid solv, some disinfectants (Cl, H2O2, phenol)
             Naked viruses            lack an envelope, resist many of the above

EXAMPLES (perhaps not presented during this lecture?)

COMMON COLD: caused in decreasing frequency by : rhinoviruses, paramyxoviruses, enteroviruses, corona viruses, reoviruses, adenoviruses. Can be mixed infection. Portal of Entry: mucous membrane of nose and eyes.

Influenza: H = hemagglutanin, N = neuraminidase

                  Alterations in H and N make virus undetected by immune system until after infection

                  1918: Change to H3N2, killed 20 million world wide. More troops died of flu than combat

Herpes     form provirus, integrated for life into your DNA: Chicken Pox, Herpes simples I and II

HIV          Primarily parenteral POE, through wound or sore. Infects T cells. 

TABLE SUMMARIZING MAJOR CLASSES OF VIRUSES

Cls genome env?, shape example diseases
RNA VIRUSES:
Ia positive
(mRNA)
ssRNA,
smallest rna
naked

polyhedral

Picornavirus

enteroviruses:      repl. 1st in mucous, then GI: polio (70+)

rhinoviruses:       cannot surv in GI tract, 100+, most
common cause of colds.

Hepatoviruses:    hepatitis A (fecal/oral)

Ib positive
(mRNA)
ssRNA
enveloped
polyhedral
Togavirus

rubella                    german measles

many arboviruses  (arthropod borne viruses): EEE, St.
Louis Enceph.,yellow fever, dengue

II negative
ssRNA
Enveloped
helical
Paramyxovirus

measles                  rubeola

mumps                   infection of salivary glands, testes

viral pneumonia     upper resp and bronchitis

  negative

ssRNA

Enveloped

helical

Rhabdovirus some arboviruses, only rabies infects man

newcastle virus in chickens

III negative
ssRNA
enveloped
helical
Orthomyxovirus influenza A, B, C, can agglutinate RBC typed

H: hemagglutinin, N: neuraminidase (H1N1, etc)

IV pos ssRNA envel, Coronavirus helical, 2nd cause, Common Cold, “infectious bronchitis”
V positive
ssRNA
enveloped
helical
Retroviruses requires reverse transcriptase, becomes provirus: leukemia,
Human Immunodeficiency Virus (AIDS)
DNA VIRUSES:
Ia dsDNA
linear
naked
polyhedral
Adenovirus 40+: respiratory

GIitis                     (20% severe diarrhea in children)
sudden onset, short duration

Ib dsDNA
linear
Enveloped
polyhedral,
Herpesvirus 80+, latency characteristic, usually nerves:

simplex 1:             oral,, fever blisters,

simplex 2:             genital,

Varicella zoster: chicken pox, shingles,

cytomegalovirus (leading teratogenic virus)

Epstein-Barr: infectious mononucls.

Ic ds DNA
linear
Enveloped
largest, mst
complex,
Poxvirus brick shaped, cause inclusion bodies

small pox

cowpox = vaccinia

certain warts (molluscum contagiosum)

II dsDNA
circular
naked
polyhedral
Papovavirus papilloma: 25+ in humans: strain 18 connected cerv CA

 polyoma: 2 in humans,

vasculating. Warts (SV-40 : simian virus)

  ssDNA linear, naked
polyhedral
Parvovirus parvo (“small”)