IMBECU   20882
INSTITUTO DE MEDICINA Y BIOLOGIA EXPERIMENTAL DE CUYO
Unidad Ejecutora - UE
capítulos de libros
Título:
Equine influenza
Autor/es:
ANN CULLINANE; ARMANDO DAMIANI; DEBRA ELTON
Libro:
Manual of Diagnostic Tests and Vaccines for Terrestrial Animals 2017
Editorial:
OIE
Referencias:
Año: 2018; p. 1 - 16
Resumen:
Equine influenza is an acute respiratory infection of horses, donkeys, mules and zebras caused by two distinct subtypes (H7N7, formerly equi-1, and H3N8, formerly equi-2) of influenza A virus within the genus Influenzavirus A of the family Orthomyxoviridae. Viruses of the H7N7 subtype have not been isolated since the late 1970s. Equine influenza viruses of both subtypes are considered to be of avian ancestry and highly pathogenic avian H5N1 has been associated with an outbreak of respiratory disease in donkeys in Egypt. In fully susceptible equidae, clinical signs include pyrexia and a harsh dry cough followed by a mucopurulent nasal discharge. In partially immune vaccinated animals, one or more of these signs may be absent. Vaccinated infected horses can still shed the virus and serve as a source of virus to their cohorts. Characteristically, influenza spreads rapidly in a susceptible population. The disease is endemic in many countries with substantial equine populations. In recent years, infection has been introduced into Australia and re-introduced into South Africa and Japan; to date New Zealand and Iceland are reported to be free of equine influenza virus.While normally confined to equidae, equine H3N8 influenza has crossed the species barrier to dogs. Extensive infection of dogs has been reported in North America where it normally produces mild fever and coughing but can cause fatal pneumonia. While equine influenza has not been shown to cause disease in humans, serological evidence of infection has been described primarily in individuals with an occupational exposure to the virus. During 2004?2006 influenza surveillance in central China (People?s Rep. of) two equine H3N8 influenza viruses were also isolated from pigs.Identification of the agent: Embryonated hens? eggs and/or cell cultures can be used for virus isolation from nasopharyngeal swabs or nasal and tracheal washes. Isolates should always be sent immediately to an OIE Reference Laboratory. Infection may also be demonstrated by detection of viral nucleic acid or antigen in respiratory secretions using the reverse-transcription polymerase chain reaction (RT-PCR) or an antigen-capture enzyme-linked immunosorbent assay (ELISA), respectively.Serological tests: Diagnosis of influenza virus infections is usually only accomplished by tests on paired sera; the first sample should be taken as soon as possible after the onset of clinical signs and the second approximately 2 weeks later. Antibody levels are determined by haemagglutination inhibition (HI) or single radial haemolysis (SRH).Requirements for vaccines: Spread of infection and severity of disease may be reduced by the use of potent inactivated equine influenza vaccines containing epidemiologically relevant virus strains. Inactivated equine influenza vaccines contain whole viruses or their subunits. The vaccine viruses are propagated in embryonated hens? eggs or tissue culture, concentrated, and purified before inactivation with agents such as formalin or beta-propiolactone. Inactivated vaccines provide protection by inducing humoral antibody to the haemagglutinin protein. Responses are generally short-lived and multiple doses are required to maintain protective levels of antibody. An adjuvant is usually required to stimulate durable protective levels of antibody. Live attenuated virus and viral vectored vaccines have been licensed in some countries.Vaccine breakdown has been attributed to inadequate vaccine potency, inappropriate vaccination schedules, and outdated vaccine viruses that are compromised as a result of antigenic drift. An in-vitro potency test (single radial diffusion) can be used for in-process testing of the antigenic content of inactivated products before addition of an adjuvant. In process testing of live and vectored vaccines relies on titration of infectious virus. International surveillance programmes monitor antigenic drift among equine influenza viruses and each year the Expert Surveillance Panel (ESP) for Equine Influenza makes recommendations for suitable vaccine strains. Following a change in recommendations, vaccines should be updated as quickly as possible to ensure optimal protection. This is particularly important for highly mobile horse populations and for any horse travelling internationally.