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== Introduction  ==

|linkpage =Viruses

|linktext =VIRUSES

|sublink1=Orthomyxoviridae

|subtext1=INFLUENZA

There are two subtypes of Equine Influenza described in the world today. These are:

*Two subtypes of Equine Influenza have been described:

 

**H7N7 (Equine 1), which was prevalent in the UK between 1963-1977

*H7N7 (Equine 1), which was prevalent in the UK between 1963-1977  

**H3N8 (Equine 2), or the European strains, have been circulating since 1965

*H3N8 (Equine 2), or the European strains, have been circulating since 1965.

 

 

*Aerosol and fomite transmission infects the epithelium of the upper respiratory tract, resulting in cell necrosis

Aerosol and fomite transmission infects the epithelium of the upper respiratory tract, resulting in cell necrosis, which then manifests as [[Bronchiolitis|bronchiolitis]] and serous exudation. There is a 1 - 3 day incubation period, with excretion of the virus in nasal secretions peaking at 3-4 days and finishing by 10 days.

*This manifests a bronchiolitis and serous exudation

 

*1-3 day incubation period

*Excretion of the virus in nasal secretions peaks at 3-4 days and finishes by 10 days

 

*Clinical signs:

 

**Harsh dry cough

== Clinical Signs ==

**Pyrexia (103-106F)

 

There will be a harsh dry cough with pyrexia (39-41^0>C / 103-106F). The horse will appear generally depressed with a loss of appetite and decreased activity. Submandibular lymph nodes will be enlarged on physical examination. Secondary bacterial infection can follow defective muco-ciliary transport, eg ''[[Streptococcus zooepidemicus]]''.

**Loss of appetite

 

**Enlarged submandibular lymph nodes

 

*Secondary bacterial infection can follow defective muco-ciliary transport, eg ''Streptococcus zooepidemicus''

== Diagnosis ==

 

===Diagnosis===

Virus isolation by deep nasal swabs (12 inches) deposited into 10ml of transport medium and transported at 4⁰C. An antigen detection [[ELISA testing|ELISA]] should then be performed. Blood samples for serology should also be taken on day one of the disease (acute phase) and then two weeks later (convalescent stage). A 4-fold increase of haemaglutination inhibition (HI) must be shown to confirm diagnosis.

*Virus isolation: Deep nasal swabs (12 inches) deposited into 10ml of transport medium and transported at 4C

 

*Antigen detection via ELISA: tests for type A nucleoprotein

== Treatment and Control ==

*Serology provides a retrospective diagnosis by '''Haemagglutination Inhibition (HI)''':

 

**Acute and Convalescent (2 weeks post-acute) samples are tested from the same animal

Isolate coughing horses at once to minimize spread and perform thorough disinfection of all shared tack, stables, vehicles, boot and feed buckets. Treat any secondary bacterial infections with suitable antibiotics.

**4-fold increase of HI must be shown to confirm diagnosis

 

===Control===

Control for this disease is by [[Vaccines|vaccination]]. All vaccines include H7 and varieties of the current circulating strains of H3. There are strict rules from the Jockey Club regarding timing of vaccinations: Horses must be certified as completing a vaccination course of 3 injections at least 8 days prior to racing. The course consists of a primary inoculation followed by a second within '''21-92 '''days and a third after a further '''150-215 '''days. Boosters are given annually on or before the anniversary of the third injection to maintain immunity, and in the event a year is missed, the initial course of three injections must be repeated.

*Isolate coughing horses to minimize spread

 

 

**All vaccines include H7 and varieties of the current circulating strains of H3  

 

**UK Jockey Club rules regarding timing:

 

***Horses must be certified as completing a vaccination course of 3 injections at least 10 days prior to racing

***The course consists of a primary inoculation followed by a second within 21-92 days and a third after a further 150-215 days

 

***Boosters are given annually to maintain immunity, and in the event a year is missed the initial course of three jabs must be repeated