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Herpes viruses are some of the more difficult viruses to combat as they quite contentedly go latent for long periods of time. They often produce an initial respiratory response but go subclinical until the animal becomes immunosuppressed. Protection against herpes is challenging, as immunity relies on stimulating a CD8+ T-cell response, which is difficult to provoke by conventional vaccination.


  • Double stranded DNA that becomes a closed circle in the host nucleus
  • Remains unintegrated while latent

Virulence and Pathogenesis

  • Three types of genes involved in replication:
    • Immediate early genes (IE genes): strong promoter of the expression of adjacent viral genes
    • Early genes: stimulate viral DN replication; potential cause of lymphoproliferation and tumors in the absence of cell lysis
    • Late genes: encode viral structural proteins
      • Cause large intranuclear inclusion bodies typical of herpes viruses as capsid proteins are assembled
      • Envelope buds through nuclear membrane, containing spike glycoproteins (gA to gE)
      • Masses of virus then either lyse or fuse cells, causing ulceration, etc.
  • Initial replication in respiratory tract
  • Spread determines pathogenicity:
    • Cell-associated spread means that virus is spread by cell fusion
    • Can target crucial tissues: brain, placenta, etc
  • All become latent and reactivate under stress
  • Reactivation is associated with the presence of thymidine kinadse (tk) gene (which is deleted in GE vaccines)
    • Accelerates DNA synthesis


  • Some herpes and pox viruses express non-structural proteins known as virokines
  • Virokines appear to help the virus evade the Th-1 response by altering the inflammatory response

Virus by Species

Virus Abbreviation Clinical signs
Equine Herpesvirus 1 EHV1 Respiratory disease, abortion, paresis
Equine Herpesvirus 2 EHV2 Avirulent
Equine Herpesvirus 3 EHV3 Pustular lesions on genitalia
Equine Herpesvirus 4 EHV4 Mild respiratory disease
Bovine Herpesvirus 1

Infectious Bovine Rhinotracheitis Virus

Infectious Pustular Vulvovaginitis Virus




IBRV: Upper respiratory disease, abortion

IPVV: Irritant pustular lesions on genitalia

Bovine Mammilitis Virus BHV2 (BHMV) Erosive lesions on teat and udder, Zoonotic
Malignant Catarrhal Fever Virus MCFV Infection of eye and upper respiratory
Suid Herpesvirus 1 (Pseudorabies) PSV Respiratory disease, abortion (CNS in piglets, pruritis in cattle)
Suid Herpesvirus 2 (Porcine Cytomegalovirus) PCMV Subclinical, atrophic rhinitis
Canine Herpesvirus 1 CHV1 Fading puppies, repro failure
Feline Herpesvirus 1 FHV1 Rhinitis, bronchitis
Channel Catfish virus Death with hemorrhage
Koi herpes Death with gill necrosis
Herpesvirus cyprini Carp pox, also in goldfish
Elephant endotheiliotropic herpes virus African elephant: mild, skin papillomas

Indian elephant: FATAL with hemorrhage

Gallid Herpesvirus 1 MDV Lymphoproliferative, invades CNS, visceral tumors
Gallid Herpesvirus 2 HVT Avirulent, protective
Gallid Herpesvirus 3 (Infectious Laryngo-tracheitis) AHV1 (ILT) Tracheitis and bronchitis
Duck Plague Virus Endothelial and enteric lesions
Pigeon Herpesvirus Respiratory disease
Mareks Disease MDV Paralysis, encephalitis
Psittacid and Raptor Herpes Death with yellow diarrhoea and coma
Herpesvirus B (Monkeys) Potential zoonosis; oral ulcers in Asiatic monkeys, fatal encephalitis in man


Liver herpesvirus infections:

Look for the intranuclear inclusions in surrounding surviving hepatocytes

Herpesviridae Learning Resources
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