Asfarviridae Asfar swine fever and related viruses

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Asfarviridae Asfar swine fever and related
viruses

• Properties of Asfarviruses
• Large spherical, enveloped virion
• Icosahedral capsid
• Linear genome, ds DNA
• Cytoplasmic replication virions mature by
  budding from plasma membrane
• Acidophilic, intracytoplasmic inclusion bodies
• Thermolabile and sensitive to lipid solvents

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African Swine Fever - ASF

• First reported in 1921 in Kenya
• Acute to chronic disesase
• characterized by high fever
• Cutaneous hyperemia
• Edema
• Hemorrhagic internal organs l.n.
• Abortions
• Can see bloody diarrhea
• Distribution Sub-Saharan Africa
• Europe, Dominican Republic, Haiti, Cuba and
  Brazil
• Endemic in Africa and southern Europe

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African Swine Fever - ASF

• Hosts all breeds of domestic pigs and
  restrictyion endonuclease studies of viral DNA
• European wild boar
• Innapparent infections occur in warthogs, bush
  pigs, and giant forest hogs which act as
  reservoir hosts
• Etiologic Agent Asfivirus
• Five different geotypes have been identified by
  restriction endonuclease studies of viral DNA
• All European and the Americas isolates are within
  one group and the African shows greater variation

• Variations in virulence. Some strains cause
  severe disease with near 100 mortality, others
  cause transient disease or inapparent infections
• Very stable virus
• Can live in soil, blood, bone marrow, or pork at
  room temp for several months
• Can survive for 15 weeks or longer in chilled
  carcasses and up to 5-6 months in processed meat
  products,
• Pepperoni, sausage and salami
• ASF virus can grow in cell cultures, but does not
  replicate easily unless in swine
• Cytopathic effects some do not produce CPE
  syncytia, intracytoplasmic inclusions
• Virus does not hemagglutinate, but infected pig
  buffy coat cells hemadsorb pig RBCs late in
  infection, a virus specific protein appears in
  plasma membrane of infected cells

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African Swine Fever Epidemiology

• Sylvatic cycle
• Maintained in a cycle involving asymptomatic
  infection in wild pigs and argasid tics
• After primary infection, young warthogs develop
  viremia with high titers to infect ticks
• Older warthogs are infected but resistant and do
  not develop viremia
• Ornithororos ticks are biological vectors and
  reservoirs of virus
• Replicates in tick, resulting in transtadial,
  transovarial and sexual transmission
• Infected tics live for several years and can
  transmit disease to swine at each blood meal
• Asfivirus IS THE ONLY ARBOVIRUS AMONG DNA VIRUSES

• Domestic cycle
• Once the virus is introduced into domestic swine,
  infected swine form the most important source of
  virus for susceptible hosts
• Virus is shed in all body secretions e.g. urine,
  feces etc.
• Rapid spread of disease occurs by contact and
  within but from the buildings by aerosols
• Outbreaks result from the bite of an infected
  tick or ingestion of infected uncooked garbage or
  tissues of acutely infected warthogs

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African Swine Fever Pathogenesis

• Asfivirus replicates in several cells of the
  reticuloendotehlial system and causes a severe
  leukopenia
• ASF virus does not infect epithelial cells
• During the viremic phase, the virions multiply in
  RBCs, endothelial cells, and leukocytes MACS
• Gross lesions prominent in the lymphatic and
  vascular system
• Vascular damage e.g. degeneration of vascular
  endothelium, impaired blood coagulation,
  thrombocytopenia and thrombosis, result in edema
  and hemorrhage in many organs and tissues
• Pulmonary edema, engorged spleen, petechiae,
  ecchymotic hemorrhages

• Peracute
• 1-3 day course of high fever, hyperpenea,
  cutaneous hyperemia
• Morbidity and mortality can reach 100
• Acute
• IP 4-10 days
• Hydropericardium, hemorrhages, gall bladder,
  fibrinopurulent bronchopneumonia
• Fever, inappetance, dyspnea, coughing, severe
  leukopenia
• Diarrhea is seldom seen in uncomplicated ASF
• Virus does NOT multiply in intestinal epithelial
  cells
• Pregnant sows usually abort during all stages

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African Swine FeverPathogenesis, Dx, Immunity

• Aborted fetuses are virus free other mechanism
  of death
• Often mummified due to dehydration longer
  than five days old
• Similar to BVD-MD, B. abortus
• Sows that abort often die in 3-6 days
• Mortality 95-100 in primary exposure
• Reduces to 20-40
• Subacute/ chronic infections endemic areas
• Necrotic skin lesions, arthritis, pneumonia,
  growth retardation
• Pathognomonic red lesions

• Diagnosis
• Virus isolation blood, spleen, visceral lymph
  nodes, tonsils
• Hemadsorption and can be demonstrated within a
  few days following inoculation of cell culture
• Antigen detection in tissues
• FAT immunodiffusion using tissue suspension as
  the source of antigen, or
• ELISA
• Immunity humoral immune response does not seem
  to have any substantial protective value because
  sera cannot neutralize virus
• Vaccine attempts unsuccessful

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Asfaviridae Prevention and Control

• Endemic countries management system avoids
  feeding uncooked waste food scraps
• Double fencing to prevent access of ticks and
  warthogs to domestic swine
• ASF- Free countries
• Prohibition of importation of live swine and
  swine products from infected countries
• Monitoring the efficient destruction of all waste
  food scraps from ships and aircraft involved in
  international commerce
• Eradication in case of ASF outbreak