Equine Influenza - Veterinary Medicine PDF

COURSE: EQUINE MEDICINE(VMD VI) Topic: Equine influenza DR. O.O. AKINNIYI University of Ibadan, Department of Veterinary Medicine 1  INTRODUCTION Influenza is currently considered th...

COURSE: EQUINE MEDICINE(VMD VI) Topic: Equine influenza DR. O.O. AKINNIYI University of Ibadan, Department of Veterinary Medicine 1  INTRODUCTION Influenza is currently considered the most economically important respiratory disease of horses in many of the major horse breeding and racing countries in the world. Recognised as a common malady of equids for centuries, influenza is a highly contagious viral infection characterised principally by fever, depression, a mucoid or mucopurulent discharge, coughing, and impairment of performance ability. equine influenza by Dr. O.O Akinniyi 2  SYNONYM Equine flu equine influenza by Dr. O.O Akinniyi 3  AETIOLOGY The virus is an orthomyxovirus of influenza A type. Two structural proteins (haemagglutinin [HA], and neuraminidase [ND]) are the major antigenic determinants and form the basis of categorization into different subtypes. Two major antigenically distinct subtypes exist – A/equine/1 (H7N7) and A/equine/2 (H3N8). The H3N8 influenza viruses are currently the most common sub-types identified in horses worldwide. Antigenic shift (major change in HA and NA antigenic structure – rare) and antigenic drift (minor change in antigenic structure – commoner) can occur, resulting in recurrent epizootics and the need to update commercial vaccines. equine influenza by Dr. O.O Akinniyi 4  EPIDERMIOLOGY Breed, age, and specie Horses of all ages are susceptible, but infection is commonest in young (2–3 years) unvaccinated horses. Equine influenza has a low mortality rate but very high morbidity, which has a major economic effect due to disruption of equestrian activities. Infection may occur in vaccinated horses, although the severity of clinical disease and degree of viral shedding are reduced. It affects all breeds. Disease is more severe in donkeys and mules. Risk factors Areas of high comingling of horses (e.g., racetracks, show grounds, veterinary hospitals). Immunosuppression (e.g., traveling, hospitalization, training, showing) equine influenza by Dr. O.O Akinniyi 5  EPIDERMIOLOGY Zoonotics There is no known zoonosis. Geography and seasonality Not seen in New Zealand and Iceland. The first and only outbreak of EI in Australia occurred in 2007 in Queensland and New South Wales Strict quarantine and massive surveillance measures resulted in the declaration of Australia as free of equine influenza in December 2007. equine influenza by Dr. O.O Akinniyi 6  TRANSMISSION ▪ The respiratory route is the primary mode of transmission for equine influenza. The disease is highly contagious and can spread rapidly among groups of susceptible horses. This is associated with the dispersion of large quantities of infective viruses in aerosolised droplets by the frequent coughing of acutely infected animals. The virus can travel and infect horses over distances of at least 32 m. Indirect transmission of infection through the use of contaminated fomites, e.g., shanks, twitches, head collars, and water buckets, and personnel failing to observe adequate hygienic precautions in handling and/or transporting infected and non- infected animals can also contribute to the spread of the virus. Currently, there is no evidence to indicate the existence of the carrier state in equine influenza. equine influenza by Dr. O.O Akinniyi 7  PATHOPHYSIOLOGY ▪ Aerosolized virus is inhaled and deposits on the mucosa of the upper and lower respiratory tracts. ▪ The virus attaches to the epithelial cells and enters the cell cytoplasm where replication occurs. ▪ The epithelial lining of the entire respiratory tract is affected. ▪ Infected epithelial cells are damaged leading to inflammation, clumping of cilia and focal erosions. ▪ Mucociliary clearance mechanisms are impaired, and secondary bacterial infections are common, which can prolong the recovery period. equine influenza by Dr. O.O Akinniyi 8  CLINICAL SIGNS Loss of appetite, fever, general weakness, poor performance, harsh dry cough, hyperaemia of nasal and conjunctival mucosae, tachycardia, dyspnoea, stiffness in legs due to limb oedema and muscle soreness, enlarged lymph nodes, and serous nasal discharge, which may turn yellowish due to secondary bacterial infection and abortion, are all clinical signs of EI. There is a high morbidity rate in EI while the mortality rate is low, and death usually occurs due to pneumonia as a sequela. In rare cases, myocarditis and chronic obstructive pulmonary disease are seen, especially when horses return to training too soon. Encephalitis in horses and rapid fatal pneumonia in foals and donkeys have also been recorded, but their pathogenesis is not clear. equine influenza by Dr. O.O Akinniyi 9  CLINICAL SIGNS The incubation period usually depends on the immune status of the animals (varying from 1 to 5 days under experimental settings) and can be very short, up to 24 h in naïve horses. High fever (up to 106°F [41.1°C]) with depression, anorexia, and weakness Serous nasal discharge that may become mucopurulent due to secondary bacterial infection Submandibular or retropharyngeal lymphadenopathy (slight) Cough (dry, harsh, and nonproductive) equine influenza by Dr. O.O Akinniyi 10  DIAGNOSIS ▪ Clinical signs: ▪ A presumptive diagnosis may be made on the basis of the clinical signs and rapid spread of disease, especially in unvaccinated horses; however, vaccinated horses may show few if any clinical signs, and laboratory analysis is required for diagnosis. ▪ Haematology: Anaemia, leucopenia and lymphopenia are seen early in the course of the infection (1–5 days). Neutrophilia often occurs later as secondary bacterial infections arise. Plasma fibrinogen and plasma viscosity may be elevated. ▪ Virus isolation from nasopharyngeal swabs: ▪ Samples should be collected within 24–48 hours after clinical onset. Swabs should be submitted in viral isolation transport media (not bacterial transport media). If no viral transport media is available, place swabs in a red-topped tube with a few sterile saline drops. Ship on ice. ▪ Serology ▪ Real-time PCR (RT-PCR) from nasopharyngeal swabs equine influenza by Dr. O.O Akinniyi 11  TREATMENT Rest with minimal stress is the most important component of therapy. Nursing care Damaged respiratory epithelium takes a minimum of 3 weeks to regenerate. Antibiotic (penicillin or trimethoprim/sulphonamide) treatment is necessary only if there is significant secondary bacterial infection. If bronchopneumonia is suspected, antibiotic selection should be based on culture of transtracheal aspirate. Antipyretics (nonsteroidal anti-inflammatory drugs [NSAIDs]) for high fever or significant myalgia Hydration and fluids if needed. Immunostimulants, such as mycobacterial cell wall extracts, are reported to be beneficial. Bronchodilators and mucolytics may be helpful in some cases. Antiviral medication has not been evaluated in horses, but there have been some suggestions that amantadine at 10 mg/kg IV q8h or 5 mg/kg q4h (avoid in renal patients because central nervous system effects have been reported) or rimantadine at 30 mg/kg PO q12h may reduce the severity and duration of infection in horses. equine influenza by Dr. O.O Akinniyi 12  CONTROL OF OUTBREAK ▪ Isolate infected horses as soon as possible (as soon as a temperature rise is identified). ▪ Provide adequate ventilation and minimal dust conditions. ▪ Avoid all contact between healthy and sick horses. ▪ Cease exercise/training to minimize stress. ▪ Maintain separate feeding, cleaning and grooming equipment, and personnel for sick horses. ▪ Vaccinate healthy horses in face of the outbreak. equine influenza by Dr. O.O Akinniyi 13  PREVENTION 1) Vaccination: ▪ Recommendations for equine vaccination are available from a variety of sources. ▪ Administer 1 dose (1 ml), by intramuscular injection, preferably in the neck region, according to the following programme: ▪ Primary vaccination: First injection from 5 to 6 months of age, second injection 4 to 6 weeks later. ▪ Revaccination: 5 months after primary vaccination ▪ Booster vaccination: Annually. ▪ In case of increased infection risk, unvaccinated mare, or insufficient colostrum intake, an initial vaccination can be given at 4 months of age followed by the full vaccination programme (primary vaccination at 5 to 6 months of age and 4 to 6 weeks later followed by revaccination). 2) Isolate new arrivals for 3 weeks. 3) Maintain adequate ventilation rates for all stabled horses, especially in barns. equine influenza by Dr. O.O Akinniyi 14