24. Diseases of horses caused by EHV-1 and EHV-4 viruses.

Question 1

Occurence?

Answer 1

Equine rhinopneumonitis/epizootic abortion

• *NOTIFIABLE* - HERPES
• originally called influenza same agent causes signs
• Worldwide, frequent - main Eq viral pathogens
• Virus: Alphaherpesvirinae, Varicellovirus
• Equid herpesvirus 1 (EHV-1): respiratory disease, abortion,CNS
• Equid herpesvirus 4 (EHV-4): respiratory adaptation,(abortion)
• EHV 1-4: 74% DNA homology
• VN: cross reaction
• Latency: trigeminal ganglion

Question 2

Epizootiology?

Answer 2

Epizootiology

• Mainly (equids) horse reservoir
• spread by contact, airborne, PO
• respiratory discharges, amniotic fluid, placenta, fetus, introduction of new horse into
• stud/exhibition, tour
• Beginning spread without signs: acute phase (shedding for a few weeks), latent carrier, shedding
• with semen, dispersal in population > abortion storms
• In endemic studs, foals get infected within first year
• maternal immunity protects until 3-6months

Question 3

Pathogenesis?

Answer 3

• Primary multiplication on respiratory mucosa (mainly foals - predisposed for secondary infection
• with Rhodococcus. equi)
• Viremia in lymphatic cells
• Access to fetus: chorion epithel damage, placenta edema, multiplication in fetus (hepatitis)
• ʹ multiples in lung/liver
• abortion, premature birth, weak/fading foals
• Access to CNS: mainly spinal cord endothel damage, neuron degeneration -> paresis, paralysis

Question 4

Clinical signs?

Answer 4

Clinical signs:

• 3-5 days of incubation
• Fever, mild/upper respiratory tract illness, serous nasal discharge, coughing, red mucosal surface
• Adults are asymptomatic
• Weakening factors, bacterial co-infections > pneumonia, sometimes tenosynovitis, laminitis
• Pregnant mare - abortion: after 5th month or pregnancy, 3 weeks - 3 months after infection, sudden
• and without complications
• Weak foals die within a few weeks
• Abortion storms: even 30-40% of pregnant mares
• After recovery regular estrus and fertilization
• CNS: with respiratory signs, sometimes only CNS signs, paresis, paralysis, ataxia, lameness, tail and
• anus paralysis, recovery possible in mild cases, permanent lameness and ataxia can develop

Question 5

Pathology?

Answer 5

Pathology:

• Pneumonia: bacterial coinfection
• Abortion: yellow, edematic CT, peritoneum, mucosal surface hemorrhages, liver and lung edema
• with necrotic foci
• CNS - histopath: hemorrhage, myelitis

Question 6

Diagnosis and differential diagnosis?

Answer 6

Diagnosis:

• Sample collection:nasal, nasopharyngeal swab, aborted fetus lung,liver,spleen,heart,
• kidney,
• WBC storage at 4oC until & during transport to the lab!!
• Direct virus detection
• Virus isolation ʹ EHV-4 more complicated
• Identification ʹ VN test
• Rapid diagnostics: PCR ʹ differentiation of EHV-1 & 4 possible
• IF ʹ from aborted foetus,
• IHC ʹ from aborted foetus & CNS
• Histopathology ʹ intranuclear inclusion bodies
• Serology: Paired sera
• VN, ELISA, IF, CF, antibodies after 7th day
• Convalescent sera: VN titres >1:128
• Quickly decreasing after one month
• In endemic studs usually 1:4 ʹ 1:6 titres
• DIfferential diagnosis:
• respiratory (horse influenza, EHV2, rhino-, adeno-, reovirus)
• abortion (equine arteritis, salmonella abotrus equi, strep equi, leptospira, chlamydia)
• CNS (poisoning, west nile fever, rabies, borna disease)

Question 7

Treatment?

Answer 7

Treatment:

• Respiratory: resting, supportive AB therapy
• CNS: symptomatic
• Prevention of abortion: hyperimmune sera? Acycloguanozin?

Question 8

Prevention?

Answer 8

Prevention:

• Epizootiology, hygienic measures!
• Horse movements on the minimal level
• Early diagnosis
• Isolation, quarantine ʹ one month long after convalescence & vaccinations
• Mares should be kept alone or in small groups
• It is hard to influence an on-going abortion storm!

Question 9

Prevention-Vaccination?

Answer 9

Prevention ʹ vaccination

• Aim: development of uniform & high level immune status in the stuff, at least in the 2nd half of the
• breeding season
• Weak antigen: 1x vaccination: mild elevation of the basic titre (1:4-1:11), 2x vaccinations: 1:16-1:24
• titres, 3x vaccinations: over the 1:45 protective titre, lasts for 3-4monthsÆ
• Thevaccine induced protection is efficient usually againstthe respiratory-derivedvirus!
• the massive amounts of viruses shed during abortion can break through the vaccineprevention
• the vaccine prevents from the signs, but not from the infection!
• Antigenic differences between virulent strains
• Vaccines on the market: mainly inactivated, monovalent, poluvalent (EHV-1 ʹ EHV4, influenza)
• Application
• Foal basic immunization: from 3 months of age 2x, & repeat after 4 months
• Campaign-immunisation of all horses in the stud i.e. in May & in November
• Pregnant mares: in the 5th, 7th & 9th month of pregnancy
• New/returning horse during quarantine, at least 2x

Question 10

Prevention ‘ Continous monitoring?

Answer 10

Prevention ʹ continuous monitoring

• Measures the body temp every morning ʹ first feverÆsample collection
• Nasal swab, repeated in 3-5 days, paired sera
• Rapid diagnosis (PCR)
• Isolation of respiratory positive horses
• Repeated vaccination of all other horses
• Testing the antibody levels