Poxviridae Orthopoxvirus (image)

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PoxviridaeOrthopoxvirus (image)

• Largest and most complex of all viruses
• Brick shaped
• 250 x 200 x 200 nm in size
• Parapoxviridae are OVOID, 260 x 160 nm
• Virions are complex
• Core
• Lateral bodies
• Outer membrane
• / - envelope
• Core Dumbbell shaped, Contains viral DNA, viral
  proteins
• Lateral bodies unknown nature
• / - Envelope
• Genome is linear and double stranded
• Largest genome of any animal virus
• Encodes all transcription and replication
  enzymes needed for viral genome

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PoxviridaeOrthopoxvirus, Parapoxvirus

• Several poxviruses encode virokines that affect
  the response of the host to infection
• Epidermal growth factor homologue
• Protein that down regulates complement proteins
• Virokines conferring resistance to INF etc.
• Cytoplasmic replication
• Eosinophilic intracytoplasmic inclusions
• All poxviruses share group specific nucleoprotein
  NP antigen that is exposed after being
  digested with alkaline
• Each species in a genus is characterized by
  specific polypeptides
• Cross neutralization and cross- protection occurs
  among members of the same genus none between
  different genera
• Only the Orthopoxviruses produce Hemagglutinin

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PoxviridaeParapoxviridae Pseudopox virus

• Parapoxviridae causes Bovine Papular Stomatitis
  as well as Milkers nodule lesions
• Serologic Assays
• In the assays, a 2-fold serial dilution of
  suspect serum is used
• A constant amount of virus is added to each of
  the dilutions
• The titer is the highest dilution giving the
  desired result
• Antibodies can be detected and/or quantitated
  using any of the assays below
• Hemagglutination- inhibition test see next
  slide
• Complement fixation test
• Immunodiffusion test
• Indirect ELISA test
• Indirect Immunofluorescent test IFA
• Virus neutralization test

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Poxviridae Subfamilies and Genera

• Orthopoxvirus vaccinia
• Parapoxvirus pseudocowpox virus
• Avipoxvirus fowlpox virus
• Capripoxvirus sheeppox virus
• Leporipoxvirus Leooripoxvirus
• Suiposvirus Swinepox virus
• Molluscipoxvirus Myxoma virus
• Yabapoxvirus Yaba monkey tumor virus
• Subfamily Entomopoxvirinae contains viruses of
  insects
• Viral replication cytoplasm

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Poxviridae - Replication

• Occurs in the cytoplasm
• Following the release of the viral core into the
  cytoplasm, the following occur
• Adsorption and penetration via endocytosis for
  non-enveloped viruses
• Fusion with the plasma membrane are used with
  enveloped viruses
• Uncoating 2 step process
• Host cell enzymes partially uncoat the viral
  particle, exposing some viral DNA and polymerase
• Early mRNA are transcribed resulting in several
  polypeptides, including an uncoating protein
  which completes the uncoating of the core.
• DNA replication using enzyme pools

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Poxviridae Replication

• Late mRNA codes for structural proteins and
  proteins to switch off early mRNA activity
• Especially to block uncoating proteins in order
  to protect the progeny virions that are being
  assembled
• Following assembly, mature enveloped virions are
  released by budding or by exocytosis
• Naked virions are released by cell lysis
• Most poxviruses are naked
• Both enveloped and naked are infectious

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Poxviridae Epidemiology, Pathogenesis and
Immunity

• Epidemiology
• Poxviruses are resistant to ambient temperatures
  and can survive for many months or years in dried
  scabs
• Poxviruses are transmitted between animals by
  skin abrasions, aerosol to the URT, mechanical
  transmission by arthropods
• Pathogenesis and Immunity
• Highly epitheliotropic causing cutaneous and
  systemic disease in birds and wild and domestic
  mammals
• Many are host specific, but orthopoxviruses
  infect a wide range of hosts
• After cutaneous introduction or inhalation the
  virus gains access to the systemic circulation
  through the lymphatics.
• Multiplication of the virus at the skin wound
  may lead to direct access to the blood and
  primary viremia.
• Secondary viremia disseminates the virus back to
  the skin and other target organs

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PoxviridaePathogenesis, Immunity

• Poxviruses induce lesions by a variety of
  mechanisms
• Degenerative changes in the epithelium
• Lesions start as erytheamatous macules, become
  papular and then vesicular
• Vesicles develop into umbilicated pustules POCK
  LESION
• Pustules rupture and for a crust/scab
• Lesions heal and leave a scar
• Rupture of the pustule can lead to secondary
  bacterial infection
• Proliferative lesions
• Poxviruses replicating in epidermis may result in
  virus induced (encoded epidermal growth factor)
  cellular hyperplasia
• Poxviruses encode proteins which may counteract
  host defenses
• Immunity varies from short lived like in
  parapoxvirus infections to prolonged in others

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PoxviridaeDiagnosis

• Virus isolation
• Scrapings from skin lesions, vesicular lesions
  and crusts
• Chorioallantoic membrane
• Pock lesions not parapoxviruses DO NOT
  replicate in embryonated eggs
• Cell culture
• Poxviruse grow in a variety of cell cultures
• Virus identification
• Negative stain electron microscopy FAT etc.
• Histopathology

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PoxviridaeOrthopoxvirus Vaccinia - Cowpox

• Distribution identified only in Europe
• Hosts cattle, wild and domestic cats, zoo
  animals, elephants, rhinos etc., humans
• Rodents serve as reservoir hosts
• Etiologic agent Orthopoxvirus One serotype
• Transmission infection of cattle and domestic
  cats occurs through intact with rodents. In
  dairy herds, the virus spreads by the process of
  milking
• Clinical features - Disease in cows
• IP 3-7 days. Lesions seen on teats and udder
• Ulcerated pustules give rise to thick red scabs
• Secondary bacterial infection of teat lesions are
  very common
• Uncomplicated teat lesion heal in 3-4 weeks

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Orthopoxvirus DiseasesClinical Features, Immunity

• Disease in cats More severe than in cattle or
  humans
• Scarbs are widespread
• Secondary bacterial infection may result in
  pneumonia VERY COMMOM
• Cats usually recover in 6-8 weeks
• Disease in humans
• Maculopapular leisons on the hands and face
• Nausea, fever, lymphadenopathy
• Immunity
• Recovering animals have long lasting immunity

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PoxviridaeParapoxvirus Diseases

• Range of species - most important are cattle,
  sheep, goats and camels
• Parapoxviruses of domestic animals are zoonotic
• Pseudocowpox
• Common endemic infection in cattle worldwide
• Chronic infection in many dairy herds and beef
  herds
• Etiologic agent Bovine parapoxvirus - one
  serotype
• Clinical features
• Infections are mild morbidity approaches 100
  only 10-15 of cows are affected at one time
• Lesions are dark red ring or horseshoe scabs
• Horseshoe scabs are pathognomonic for the disease
• Lesions affect teats, udder and perineum
• Major lesions desquamate by 6 weeks no scars
• Similar lesions on muzzle and in mouths of
  nursing calves ulcers and vesicles are rare
• Immunity short-lived 4-6 months duration
• Humans mild skin lesion milkers nodule

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PoxviridaeParapoxvirus Contagious Ecthyma

• Worldwide disease resulting in an acute infection
  of all breeds of sheep and goats
• Mostly affecting lambs and kids
• Synonyms scabby mouth, contagious pustular
  dermatitis, sore mouth and orf the human dz.
• Etiologic agent Parapoxvirus one serotype
• Transmission
• Survival in the environment is indefinite in
  scabs
• Infection is through cutaneous abrasions
• Oral lesions in lambs or kids result from nursing
  dams with teat and udder lesions
• Pathogenesis
• Lesions are vesiculopapular eruptions followed by
  pustules with yellow- brown scabs
• Dermal tissue may proliferate resulting in
  verrucose mass under the scabs

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Contagious Ecthyma

• Clinical features
• IP 4-7 days
• High morbidity 90, but low mortality
• Primary lesion develops on skin of the lips and
  extends to the mucosa of the mouth
• Severe cases lesions on genitals, perineum and
  feet lameness can ensue
• Oral and facial lesions are painful and may lead
  to anorexia and weight loss
• Scabs drop off in 1-4 weeks no scars
• Mortality can result when primary lesions are
  invaded with screwworm larvae or Fusobacterium
  necrophorum (gram negative rod - post op wound
  infections, navel ill, soft tissue abscesses,
  metritis, aspiration pneumonia, necrotic lesions
  like FOOT ROT, liver abscesses common)
• Immunity sheep are susceptible to reinfection
  and chronic infections can occur

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Contagious Ecthyma

• Vaccination
• Ewes are vaccinated several weeks before lambing
• Non- attenuated virus vaccines from infected
  scabs or from cell cultured virus
• Vaccine is brushed over scarified areas of skin
  inside of thigh where a localized lesion develops
• Vaccine short term immunity
• Lambs and kids
• Vaccinated at 1 month, revaccinated at 2-3 months
  later, followed by annual revaccination
• Humans Public Health Significance
• Maculopapular lesions and nodular lesions are
  observed 2-4 days following infection
• Lesions last for 4-9 weeks and heal without scars

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Poxviridae Capripoxvirus - Sheeppox

• Diseases include sheeppox, goatpox and lumpy skin
  disease
• Sheeppox is the most important disease of
  domestic animals
• Viruses causing the three diseases may represent
  strains of a single virus. This results in
  cross- infection and cross- protection, however,
  most strains show definite host preferences
• Sheeppox
• Distribution endemic in Africa, Asia and Europe
• Etiologic agent Ovine capripoxvirus. One
  serotype
• Transmission Aerosolization and direct contact
  with saliva, nasal secretions, scabs shed by sick
  animals
• Scabs are infective for up to 6 months

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PoxviridaeSheeppox

• Mechanical transmission by biting arthropods?
• Stomoxys calcitrans stable fly
• Pathogenesis systemic disease
• Inhalation is followed by a leukocyte associated
  viremia
• Leading to a virus localization in skin, and to a
  lesser extent the internal organs
• Severe necrotizing vasculitis developing in
  arterioles and postcapillary venules in the skin
  may be due to immune complex deposition
• TYPE III hypersensitivity virus does not
  multiply in endothelium
• This results in ischemic necrosis of the dermis
  and overlying epidermis

• Clinical features
• IP 4-8 days
• Morbidity up to 80
• Malignant form seen in lambs and susceptible
  nonnative breeds, e.g. merino
• Signs are
• Fever, salivation, lacrimation, hyperpnea, edema
  of the eyelids and serous nasal discharge later
  becoming mucopurulent
• 1-2 days later cutaneous nodules develop
• Can be widely distributed throughout the body
• Nodules scab and persist for 3-4 weeks, leaving a
  permanent depressed scar
• Mortality rate up to 50, Fatality up to 100 in
  lambs
• Benign form more common in adult sheep/resistant
  breeds skin lesion not systemic

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Sheeppox, Goatpox

• Immunity
• Recovered sheep have a solid immunity life long
  
• Prevention and Control
• Notifiable disease in most countries of world
• Goatpox
• Africa, Asia, Europe and U.S.
• Similar to sheeppox
• Lower mortality rate 5
• Strain of goatpox causes more severe dz. In sheep

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PoxviridaeGoatpox and Lumpy Skin Disease

• Infectious, acute to chronic disease of cattle
  characterized by
• multiple skin nodules
• ventral edema
• persistent fever
• lymphadenopathy
• Distribution
• Endemic in certain parts of Africa
• Outbreak in 1989 in Isreal
• Etiologic agent Bovine capripoxvirus one
  serotype
• Hosts cattle and buffalo- African cape buffalo
  is thought to be the reservoir
• Transmission mechanical through biting
  arthropods high concentration in saliva results
  in contact transmission

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Poxviridae Goatpox Lumpy Skin Disease

• Pathogenesis
• After skin inoculation, virus replicates in
  epidermis and dermis
• Infected macrophages migra regional lymph nodes
  for further replication
• Resulting in enlargement of the lymph nodes
• Macrophage associated virema disseminates the
  virus to various tissues skin and endothelium
• Damaged endothelium results in vasculitis,
  thrombosis, marked dermal edema, infarction
• Nodules are circumscribed, round, slightly
  raised, firm and painful and involve the entire
  skin and the mucosa of the GI, RT, genital tract-
  develop inverted conical necrosis the sit fast

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PoxviridaeLumpy skin disease

• Secondary bacterial infections develop in the
  necrotic cores of the nodules
• Metastatic abscesses in the regional lymph nodes,
  lungs and other organs
• Mortality is due to secondary infection
• Clinical signs
• IP 4-14 days
• Morbidity up to 100, mortality 1-2
• Fever, marked weight loss, hypersalivation oral
  ulcers, nasal discharge
• Lesions can persist for months but usually
  disappear within 4-12 weeks
• Abortion may occur as a result of prolonged fever
• Control Vaccination
• Attenuated Neethling strain prototype virus
  vaccine used
• Goatpox and Sheeppox virus vaccines have also
  been used Heterotypic vaccination

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PoxviridaeSuipoxvirus Swinepox virus

• Suispox is the principal cause of pox lesions in
  swine
• Similar to Vaccinia virus
• Benign disease of young pigs
• Worldwide distribution
• Transmission mechanical by pig louse,
  Hematopinus suis causes skin trauma, carriers
  the virus for weeks or months
• Clinical features IP 3-7 days, Course 1-4 weeks
• Transient low grade fever and anorexia followed
  by the development of papules, vesicles,
  umbilicated pustules
• Pustules crust over and scab by day 7

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PoxviridaeSuipoxvirus Swinepox

• Lesions are found over abdomen and inner aspects
  of thighs primarily. Udder and teat lesions are
  seen in some sows that nurse infected piglets
• Immunity recovered pigs are solidly immune
• Control Eradication of lice from piggery
• There is no commercially available vaccine

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Poxviridae Avipoxvirus Fowlpox virus

• Causes disease in chickens, turkeys, guinea fowl,
  peacocks, pheasants and other avian species.
• Exact relationship between the poxviruses of the
  different avian species is not certain, but it
  has been shown experimentally that the virus
  causing one type of pox can give rise to disease
  in other species and that infection with one may
  stimulate protection against another
• E.g. milk maids

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PoxviridaeAvipoxirus Fowlpox virus

• Distribution worldwide
• Hosts chickens, turkeys, pigeons, pheasants
  etc.
• Etiologic agent Avipoxvirus extremely resistant
  to dessication and can survive in exfoliated
  scabs for prolonged periods
• Inclusions bodies Bollinger Bodies large
  intracytoplasmic inclusions Borrel bodies
  elementary bodies occur inside the Bollinger
  bodies.
• Borrel bodies are minute spherical bodies
  obtained by tryptic digestion of Bollinger bodies
• Transmission occurs through small abrasions in
  the mouth or through injuries to the comb, wattle
  as a result of fighting, pecking or other
  injuries
• Mechanical transmission by mosquitoes, ticks,
  biting flies and lice

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Poxviridae Fowlpox

• Clinical features IP 4-14 days
• Two forms of disease
• Dry form cutaneous form
• small papules on the comb, wattles, and around
  the beak lesions may develop on the legs and
  feet around the cloaca
• Nodules become yellowish and progress to a thick
  scab. Egg production drops markedly. Affected
  birds recover in about 4 weeks
• Wet form diptheritic form
• Involves infection of the mucous membranes of the
  mouth, pharynx, larynx, and sometimes trachea
• Lesions coalesce resulting in a necrotic
  pseudomembrane which may prevent feeding. Death
  results from suffocation by occlusion of the
  larynx.
• Mortality can reach 50

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Poxviridae Ulcerative Dermatosis of Sheep -
unclassified

• Two forms
• Ulcers around the mouth, nose and legs
• Venerally transmitted ulcerations of the prepuce
  and penis or vulva
• World wide
• Synonyms Lip and leg ulceration and venereal
  balanoposthitis and vulvitis
• Etiologic agent Ovine poxvirus
• Transmission Infection results from viral
  contact with damaged skin or by coitus
• Clinical features ulcer with a raw, easily
  bleeding crater - Contains an odorless, creamy
  pus and is covered by a thin brown bloody scab
• Face lesions - upper lip, chin, and nose. Foot
  lesions - between the coronet, carpus and the
  tarsus

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Poxviridae

• Rams
• Lesions partially or completely surround the
  preputial orifice and may become so severe as to
  produce phimosis.
• Rarely, the ulcerative process may extend to the
  glans penis rendering the ram unfit for
  breeding
• Ewes
• Lesions occur as edema, ulceration, and scabbing
  of the lips of the vulva

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