Virology

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Virology

• Virus Families and the Diseases they Cause

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Poxviridae

• Largest and most complex of all viruses
• Brick shaped
• Peanut-shaped core containing viral DNA and
  proteins
• Lateral bodies
• /- envelope, but attachment sites are on capsid
  both are infectious
• Linear dsDNA
• Codes for all enzymes for transcription and
  replication of the viral genome
• Orthopoxviruses produce a hemagglutinin clumps
  rbcs in vitro

• Virokines homologue of epidermal growth factor,
  a protein that downregulates complement proteins,
  and resistance to interferon
• Cytoplasmic replication
• Eosinophilic intracytoplasmic inclusions
• All share group specific nucleoprotein (NP)
  antigen cross-reactivity within genus so there
  is cross-neutralization and cross-protection
  between members of the same genus only

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Poxviridae

• Subfamily Chordopoxvirinae vertebrates
• G. Orthopoxvirus Vaccinia virus
• G. Parapoxvirus Pseudocowpox virus
• G. Avipoxvirus Fowlpox virus
• G. Capripoxvirus Sheeppox virus
• G. Leporipoxvirus Leporipox virus
• G. Suipoxvirus Swinepox virus
• G. Molluscipoxvirus Myxoma virus
• G. Yabapoxvirus Yaba monkey tumor virus
• Subfamily Entomopoxvirinae - insects

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Viral Replication

• Cytoplasm, 4-20 hours
• Adsorption (fusion or endocytosis) and release of
  viral core into cytoplasm
• Uncoating is a two step process
• Host cell enzymes partially uncoat exposes some
  genes
• Early mRNA is transcribed, including an
  uncoating protein that completes uncoating of the
  core
• DNA replication
• Late mRNA structural proteins and proteins to
  turn off early mRNA
• Assembly release by budding or exocytosis (most
  not enveloped)

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Epidemiology

• Resistant can survive many months to years in
  dried scabs in enviro
• Breaks in skin main mode of transmission
• Aerosol - minor
• Mechanical transmission biting arthropods -
  minor

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Pathogenesis and Immunity

• Epitheliotropic cutaneous diseases
• Occasionally cause systemic disease
• Primary and secondary viremia virus ends up
  back in skin
• Degenerative changes in the epithelium
  erythematous macule papule vesicle
  umbilicated pustule rupture scab/crust
• Predisposition to secondary bacterial infection
• Cellular hyperplasia from virus encoded epidermal
  growth factor
• Immunity mostly prolonged immunity, except
  parapoxviruses induce weak immune responses

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Diagnosis

• Virus islolation lesion scrapings, vesicular
  fluids and crusts
• Chorioallantoic membrane pock lesions (not for
  parapoxviruses)
• Cell culture
• Electron microscopy
• Histopathology inclusion bodies, epidermal
  hyperplasia

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Genus Orthopox

• Diseases
• Cowpox

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Cowpox

• Only in Europe
• Wide host range cattle, cats, humans, . .
• Rodents are reservoir hosts
• Etiologic agent Orthopox virus
• Transmission through contact with rodents, other
  infected animals (milking)
• IP 3-7 days
• Recovering animals have long lasting immunity

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Clinical Features of Cowpox

• Cows
• Lesions on udder and teats
• Ulcerated pustules with thick red scabs
• Secondary bacterial infection common
• Self-limiting usually heal in 3-4 weeks
• Calves can get ulcers in mouth
• Cats
• Scabs widespread
• Secondary infection can result in pneumonia
• Recovery in 6-8 weeks
• Humans
• Maculopapular lesions on hands and face
• Nausea, fever, lymphadenopathy
• Zoo animals
• Fatal systemic disease

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Genus Parapoxvirus

• Diseases
• Pseudocowpox
• Contagious ecthyma

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Pseudocowpox

• Mimics cowpox, cannot differentiate
• Worldwide
• Chronic infection of dairy herds
• Etiologic agent Bovine parapoxvirus
• Cross-suckling of calves, improper cleaning of
  milking machines, mechanical transmission by
  flies
• Short-lived immunity 4-6 months

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Clinical Features of Pseudocowpox

• Infections mild
• Lesions with dark red ring or horseshoe scabs
  (center of scab falls off) pathognomonic how
  to differentiate cowpox from pseudocowpox
• Majority desquamate by 6 weeks
• Teats, udder, perineum, nursing calves in muzzle
  and mouth
• Humans mild skin ulceration called a milkers
  nodule
• Prevent secondary bacterial infection

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Contagious Ecthyma(scabby mouth, contagious
pustular dermatitis, sore mouth and orf)

• Acute infection of sheep and goats (lambs and
  kids)
• Worldwide
• Etiologic agent Parapoxvirus
• Virus can survive indefinitely in scabs in enviro
• Infection through cutaneous abrasions
• Vesiculopapular eruptions pustules
  yellow-brown scabs desquamation ulceration
• Dermal tissue proliferation
• Susceptible to reinfection, chronic infections

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Clinical Features of Contagious Ecthyma

• Oral lesions (mouth, lips) and on face are
  painful
• Lambs and kids nursing dams with active lesions
  on teats and udder
• Scabs drop off within 1-4 weeks
• Mortality from screwworm fly larvae or bacteria
  (Fusobacterium necrophorum, Pseudomonas
  aeruginosa) invading primary lesion
• Humans maculopapular and nodular lesions
  lasting 4-9 weeks

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Vaccination

• Ewes vaccinated several weeks before lambing
• Non-attenuated virus vaccines derived from
  infected scabs or cell culture
• Grind fresh scabs in saline and centrifuge
  brush supernatant on inside of thigh and under
  tail different portal of entry
• Confers short-term immunity
• Lambs and kids vaccinated at 1 month, 2-3
  months and annually