Equine Viral Rhinopneumonitis (EVR)

Equine Viral Rhinopneumonitis (EVR) produces an acute respiratory catarrh, which is inflammation due to excessive discharge or buildup of mucus in the throat and nose.

Etiology

• Equine Viral Rhinopneumonitis (EVR) is a contagious viral disease of horse caused by equine herpes virus (EHV-1 and EHV-4).
• EHV-4 is a major cause of upper respiratory disease than EHV-1.
• EHV-1 causes abortion and myeloencephalopathy sporadically.
• Morbidity rate: 1-90% and mortality rate-0.5-40 %.

Transmission

• Inhalation of infected droplets.
• Ingestion of material contaminated by nasal discharge and aborted foetus.

Pathogenesis

Clinical manifestation

Clinical signs indistinguishable from other respiratory disease.

(1) Respiratory disease

• Incubation period -2-20 days.
• Fever (temp. 39 to 40.5^oc)  conjunctivitis, coughing and mild inflammation of upper respiratory tract, slight enlargement of the lymph node of throat.
• Inapparent infection is common.
• Edema of the limbs and diarrhoea occur rarely.
• Length of illness 2-5 days.
• Nasal discharge and cough may persist for 1-3 weeks.
• EHV-2 or equine cytomegalovirus causes purulent nasal discharge, fever and lymphadenopathy.

(2) Abortion

• Abortion  occur  particularly at 8-10 months of  pregnancy.
• No retention of placenta.

(3) Neonatal viremia and septicaemia

• In utero EHV-1 infection causes abortion or birth of infected foals.
• Some of which normal at birth and become weak and die within 3-7 days

(4) Myeloencephalopathy

• Clinical signs are due to involvement of spinal white matter.
• Ataxia, paresis, stumbling, toe dragging and pivoting circumduction is more severe in  the hind limbs.
• Signs are usually symmetrical.
• Hypotonia of the tail and anus.
• Faecal and urinary incontinence, dribbling of urine may soil the perineum and legs.
• Hemiplegia and paraplegia manifesting as a recumbency and inability to rise.
• Less commonly lingueal or pharyngeal paralysis, head tilt, nystagmus and strabismus.

Necropsy Finding

• Straw yellow colour fluid in the pericardial and peritoneal cavities.
• Focal hepatic necrosis.

Sample collection

• Nasal swab, whole blood (buffy coat) and aborted foetus.

Diagnosis

• Based on clinical signs and lesion.
• Hematology-leukopenia.
• Isolation of virus in cell culture.
• Detection of antigen by PCR.
• Detection of antibodies in serum by ELISA.

Differential diagnosis

• Leptospirosis
• Rabies
• Equine polyneuritis
• Trauma
• Acute spinal cord compression
• Equine degenerative myelopathy
• Neonatal septicaemia

Treatment

• There is no specific treatment.
• Antibiotics should be used to prevent secondary bacterial complications.

Prevention

• Modified live or inactivated vaccine available for EHV-1.
• The combined inactivated vaccine available for  EHV-1 and EHV-4.
• The mares are vaccinated with inactivated vaccine during 5^th, 7^th and 9^th month of gestation. Additional vaccination at breeding and one months before foaling.
• Modified live vaccine to foals at 3-4 months of age, non pregnant mares, two doses administered at 3 months apart and  followed by revaccination every 9 months.

Control

• Enhancing immunity of individual by vaccination.
• Minimising risk of introducing EHV-1 infection to the farm or stable.
• Hygienic maintenance of farm to prevent spread of the disease.
• Isolation of infected horse from stable immediately.