Mammalian Pathogenic Viruses

Viral Diseases

TFC, P.346, Black’s 2nd, p. 266- , Alcamo 323-, Campbell 6^th: , Black’s 6^th: 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”)

 

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