Week 13

• Canine distemper virus

  Morbilivirus genus

  Highly contagious, acute febrile disease of dogs

  Rare disease in dogs in the developed world

  Can infect canidae, procyonidae, mustelidae, and felidae

  Distinct lineages exist

  America-1 is circulating in raccoons in the USA
• Canine distemper clinical features

  At least 50% of infections are subclinical or mild

  Anorexia, depression, conjunctivitis, leukopenia

  Inflammation of the upper respiratory tract (serous or mucopulent nasal discharge)
• Mild canine distemper

  Inappetence, fever

  Signs of respiratory tract infections - bilateral nasal discharge (serous or mucopurulent), coughing, labored breath
• Severe generalized canine distemper

  Fever followed by systemic spread of virus
• Canine distemper in puppies

  Pneumonia, enteritis, conjunctivitis, rhinitis, tracheitis

  Secondary bacterial infections lead to bronchopneumonia

  Some dogs may developed GI signs (vomiting, watery diarrhea)

  Vesicular and pustular dermatitis - rarely associated with neurological forms; good prognostic sign
• Canine distemper CNS signs

  Some dogs may devloped usually 1-3 weeks from onset of acute signs

  Progressive and indicate poor prognosis

  Seizres, paraperesis or tetraparesis

  Hyperkeratosis on footpads and nose occurs in some dogs with CNS signs due to epitheial cell damage
• Canine distemper transmission

  Virus shed in all secretions and excretions from the 5th day after infection

  Direct contact, droplets, and aerosols

  Virus unstable in environment

  Young dogs are highly susceptible to infection
• Canine distemper pathogenesis

  Virus initially replicated in upper respiratory tract macrophages

  Spread to tonsils and lymph nodes

  Virus infects all cells expression CD150 (signaling lymphocyte activation molecule -SLAM)

  Virus enters blood stream and infects T and B cells leading to primary viremia - immunosuppression

  Infection of epithelial cells in lungs, bladder, and skin
• Canine distemper diagnosis

  Laboratory diagnosis

  Virus isolation - lymphocytes cultured with cell line expressing CD150

  Immunofluorescence test

  rtPCR - conjunctival swabs, urine, epithelial tissue scrapings
• Canine distemper control

  Immunity after infection is lifelong

  Adequate diagnosis, quarantine and sanitation are important for controlling virus spread

  Modified live vaccines available only in canidae - vaccinate puppies only after maternal antibodies have gone down

  Hyperimmune serum administered immediately after exposure to virus may help protect against infection
• Orthomyxoviruses


  Cause diseases referred to as “influenza” hence generally called influenza viruses
• Influenza A virus

  Human and animal viruses
• Thogotovirus genus


  Contains tick borne viruses which infect livestock and humans in Africa, Europe and Asia – not well studied
• Isavirus genus

  Infectious salmon anemia virus
• Orthomyxoviruses

  • Pleomorphic, often spherical, sometimes filamentous
  • Lipid layer with large spikes surrounding 6 or 8 helically symmetrical nucleocapsid segments of different sizes
  • Genome is segmented
• Genome of Orthomyxoviruses

  1. 6-8 segments of linear, negative sense, single stranded RNA
  2. Genome segments have non-translated regulatory sequences at both 5’ and 3’
• Influenza viruses are sensitive to heat (56°C/30 min.), acidic pH and lipid solvents due to the lipid envelope
• Glycoprotein spikes for influenza A and B

  • Homotrimer HA
  • Homotetramer NA
• Influenza C

  • Lacks neuraminidase
  • Has only 1 type of glycoprotein spikes – the hemagglutinin is multifunctional – esterase molecule
• Isavirus has hemagglutinin esterase and F protein
• Structure of the Influenza A viruses

  • Lipid envelope derived from the host cell
  • Envelope harbors hemagglutinin (HA), Neuraminidase (NA), M2 protein
  • M1 – matrix protein lies beneath the lipid layer
  • Virus core contains the ribonucleoprotein (RNP) complex
• Components of the RNP complex


  • Polymerase protein (PB1)
  • PB2 polymerase basic 2
  • PA (polymerase acid)
  • Nucleoprotein (NP)
  • NEP/NS2 (nuclear export protein/non-structural protein 2)
• Genetic shift

  Changes in antigenic setup due to reassortment of gene segments
• Genetic drift

  Changes in antigenic setup due to point mutations (nucleotide substitution, deletion, insertions)
• Nomenclature of influenza viruses

  Based on the type of hemagglutinin and neuraminidase
• Naming of influenza A, B and C viruses

  • Type A, B, C
  • Host (swine, horse, chicken, turkey etc.)
  • Geographical origin
  • Strain number
  • Year of isolation
  • Hemagglutinin and neuraminidase subtype
• Influenza virus transmission

  In aquatic birds - virus shed in feces, fecal-oral transmission is common

  In poultry - ingestion and inhalation

  In mammals - aerosols, droplets, and fomites
• Thogotoviruses are transmitted by ticks and replicate both in the ticks and mammals
• Isavirus may be transmitted in water – gills being the important route
• Equine influenza viruses have been reported worldwide in horses, donkeys and mules
• Equine influenza is the most important viral respiratory disease of horses, reported worldwide in horses, donkeys, and mules
• Pathogenesis of equine influenza

  1. Virus replicates in epithelial cells of upper and lower respiratory tract

  2. Ciliated epithelial lining is destroyed by virus replication

  3. Leads to inflammation and exudate formation (including nasal discharge)

  Other changes include laryngitis, tracheitis, bronchitis (may be accompanied by alveolar edema)

  Secondary infection may lead to bronchopneumonia or chronic respiratory disease
• Clinical features of equine influenza

  • Virus rapidly spreads among susceptible animals
  • Morbidity is high
  • Symptoms visible within 24-48 h after infection
• Animals at risk of equine influenza infection

  • Race horses
  • Breeding stock
  • Show jumpers
  • Horses sent to sales
• Equids are the only source of equine influenza viruses
• Diagnosis of equine influenza

  • Clinical presentation of an acute disease is very characteristic and straight forward
  • Samples - nasal and pharyngeal swabs collected early in infection
  • RT-PCR is a diagnostic test of choice - highly specific
  • Virus isolation for epidemiological characterization
• Methods for virus identification in equine influenza

  • 10 day old chicken embryos can be used to detect virus in allantoic and amniotic fluids of infected chicken embryos using standard hemagglutination test
• Swine influenza viruses

  • First recognized in North Central USA
  • First isolation of A/swine/Iowa/15/30 (H1N1) by Richard Shope
  • Pigs are considered as a “mixing vessel” for influenza viruses because of their ability to become coinfected with both avian and human strains of influenza viruses
  • Pigs possess both human and avian receptors
• 2009 pandemic of swine influenza was a mixture of various North American swine influenza, North American avian influenza virus, human influenza and swine influenza viruses commonly found in Asia and Europe
• Pathogenesis of swine influenza

  1. Highly contagious virus

  2. Transmitted through aerosols

  3. Replication in the upper respiratory tract

  4. Airway plugging, peribronchial and perivascular mononuclear cell infiltration

  5. Bronchopneumonia may develop