Influenza

Influenza


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Basic Information image



Definition


Influenza virus A-Eq2 (H3N8) is an orthomyxovirus that is an important worldwide respiratory pathogen of horses.



Synonym(s)


Flu



Epidemiology



Species, Age, Sex




• Most common in younger horses (yearlings, ages 2–3 years)


• Rare in foals; however, 11 foals during a recent outbreak in Australia died of severe bronchointerstitial pneumonia as a result of equine influenza infection.



Genetics and Breed Predisposition


Affects all breeds. Disease may be more severe in donkeys and mules.



Risk Factors




• Areas of high comingling of horses (eg, racetracks, show grounds, veterinary hospitals)


• Immunosuppression (eg, traveling, hospitalization, training, showing)



Contagion and Zoonosis




• Eurasian and American lineage strains of equine influenza virus (H3N8) have been isolated.


• There is no known zoonosis.


• Equine influenza A(H3N8) strains were found to be the causative agent of pathogenic respiratory disease outbreaks in dogs in 2004.



Geography and Seasonality




• Not seen in New Zealand and Iceland.


• Australia had been influenza free until an outbreak in 2007. Strict quarantine and massive surveillance measures resulted in declaration of Australia as free of Equine influenza in December 2007.


• Most common in fall and winter.



Clinical Presentation



History, Chief Complaint




• Anorexia


• Fever that may be biphasic (48–96 hours after infection and at 7 days)


• Depression, lethargy, inappetence


• Nasal discharge


• Coughing



Physical Exam Findings




• High fever (≤106° F)


• Mild depression, inappetence


• Distal limb edema


• Serous nasal discharge becoming mucopurulent after 72 to 96 hours


• Slightly enlarged retropharyngeal lymph nodes


• Coughing (dry) that may persist for up to 21 days


• Tachypnea


• Arrhythmia (rare) cause of cardiomyopathy


• Muscle soreness


• Weight loss



Etiology and Pathophysiology




• Highly infectious virus transmission through aerosolized droplets


• Transmission through fomites probably also occurs.


• The virus is inhaled and attaches and multiplies in the respiratory epithelium with a short incubation period of 1 to 3 days.


• The virus causes epithelial cell death and desquamation, with predominant damage in the trachea and bronchial tree, resulting in disruption of mucociliary clearance critical for preventing secondary bacterial infection.


• A high concentration of virus is shed through nasal secretions.


• Fever and virus shedding 48 hours after exposure; shedding for 6 to 7 days


• Subclinical infection with shedding is possible.


• The virus survives on wet surfaces for 72 hours and dry surfaces for 48 hours.

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Jul 24, 2016 | Posted by in SMALL ANIMAL | Comments Off on Influenza

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