Equine influenza


Equine influenza (EI) is an acute, highly contagious, viral disease that can cause rapidly-spreading outbreaks of respiratory disease in susceptible populations of horses.  EI is endemic in Europe (except Iceland) and in North and South America.  In these countries most outbreaks are minor and sporadic, because of the high level of vaccination.  In the past 20 years serious outbreaks have occurred in a number of countries (including Australia in 2007), associated with importations of subclinically infected horses and inadequate post-arrival quarantine procedures.

The primary clinical signs include pyrexia, nasal discharge (initially serous and later mucous or mucopurulent), and a deep, dry, hacking cough.  Most horses recover within a couple of weeks given good care and rest. Rarely, it causes deaths in young foals and debilitated or old horses.  Death in adult horses is usually a consequence of secondary bacterial infection. In the 2007 Australian outbreak, coughing was inconsistently reported.

The features of rapid spread and high morbidity assist the differentiation of EI from other infectious and non-infectious respiratory diseases.  The following diseases should be considered in the differential diagnosis:

  • Bacterial bronchopneumonia / pleuropneumonia
  • Viral bronchopneumonia due to equine herpesvirus 1 and 4, and equine rhinitis A and B viruses
  • Inflammatory airway disease due to exposure to environment irritants and aeroallergens
  • Equine viral arteritis
  • Parasitic infections, including ascarids and lungworms
  • The pulmonary form of African horse sickness
  • Strangles
  • Hendra virus infection

Virus titres are highest during the initial 24-48 hours of fever, which is the best time to sample for detection of the virus. Animals seroconvert about 2-3 weeks after infection.  Serology must be interpreted in the context of vaccination history.

Diagnosis and tests available


The principal diagnostic test for early detection of EI is a real-time PCR which detects all type A influenza viruses.

Serology is useful for retrospective confirmation of infection. In vaccinated horses serology may be complicated by the presence of vaccine-induced antibody, unless vaccines that allow differentiation of infected and vaccinated horses have been used.

Tests available


Sample(s) required

Days of the week test is conducted

Turnaround time1

Equine influenza antibody ELISA

Whole blood (red top tube)

According to demand

Up to 1 week2

Equine influenza HI

Whole blood (red top tube)

According to demand

Up to 1 week

Influenza type A real time PCR


According to demand

Same day to 48 hours3

1 Turnaround times are provided as a guide only. For specific information about your submission please contact Customer Service.
2 Confirmation testing of positives may affect turnaround time.
3 Turnaround time is dependent on urgency.

Specimen requirements

Blood (without anti-coagulant)

  • 10 mL of blood collected into a plain evacuated tube
    • Do not use serum separator tubes.
    • Submit chilled


  • Nasal swabs - Mucosal surface of each nostril, collected separately into viral transport media (PBGS)
    • Submitted chilled.
    • Do not use commercially prepared swabs with plastic sleeves that contain transport medium. Tubes containing PBGS can be ordered via the online media request form. If PBGS is not available, swabs should be placed in 2 mL sterile saline.

Further information