Transmission of Equine Influenza Virus during an Outbreak Is Characterized by Frequent Mixed Infections and Loose Transmission Bottlenecks (original) (raw)
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Equine Influenza Virus—A Neglected, Reemergent Disease Threat
Emerging Infectious Diseases, 2019
Equine influenza virus (EIV) is a common, highly contagious equid respiratory disease. Historically, EIV outbreaks have caused high levels of equine illness and economic damage. Outbreaks have occurred worldwide in the past decade. The risk for EIV infection is not limited to equids; dogs, cats, and humans are susceptible. In addition, equids are at risk from infection with avian influenza viruses, which can increase mortality rates. EIV is spread by direct and indirect contact, and recent epizootics also suggest wind-aided aerosol transmission. Increased international transport and commerce in horses, along with difficulties in controlling EIV with vaccination, could lead to emergent EIV strains and potential global spread. We review the history and epidemiology of EIV infections, describe neglected aspects of EIV surveillance, and discuss the potential for novel EIV strains to cause substantial disease burden and subsequent economic distress. E quine influenza is a common, highly contagious respiratory disease of equids with a near-global distribution. Central Asia, Australia, and Japan experienced large equine influenza virus (EIV) outbreaks in 2007 (1,2). Serious outbreaks of EIV have occurred throughout history, causing substantial economic distress worldwide in the 19th and 20th centuries (3). The most common clinical signs of EIV infection in equids are fever, lethargy, anorexia, nasal discharge, and a nonproductive dry cough (4). Mortality rates are generally low during EIV outbreaks; death is most common among foals or equids with preexisting poor health (5). Horses usually recover in 2 weeks with rest, but clinical signs, especially cough, can persist. EIV can result in a secondary bacterial bronchopneumonia, which can be fatal, particularly in young horses (6). Along with loss of life, the rest period required for equine recovery can cause economic hardship in areas where people rely on equids for income, such as for transportation or milk. EIV outbreaks also can disrupt economic drivers, such as the horse racing and show industries. EIV often is overlooked as a disease threat outside of equine communities, despite its known historical commercial importance and current zoonotic potential. Overview of Equine Influenza Viruses EIVs are believed to have originated from avian influenza strains (7,8). Two subtypes, H7N7 and H3N8, historically have infected horses. EIV H7N7 was first recovered from horses in Europe during 1956 (9); it has not been isolated in horses since the 1970s, but serologic evidence suggests subclinical circulation through the 1990s (7,8). EIV H3N8 has 2 lineages, Eurasian and American. The American lineage includes Florida, Kentucky, and South America sublineages (10). The Florida sublineage is further divided into 2 antigenically distinct clades; both have been detected in Asia and Europe, but only clade 1 has been detected in North America. No Eurasian lineage viruses have been isolated since 2007, when it was detected in Switzerland (11). In 2016, all isolated EIV viruses were from the Florida lineage, clade 2 in Europe and clade 1 in the United States (8,10). Historical Impact EIV-like equine respiratory diseases have been recorded since the 13th century (9). Although historical records predate human understanding of viral pathogens, they show EIV-like outbreaks preceded or, less commonly, followed several human influenza outbreaks. Despite the possibility that these illnesses were caused by pathogens other than EIVs (3), a review of records for 1688-1888 identified 56 years with documented outbreaks of influenza-like human or equine diseases in the Western Hemisphere (3). Records included 21 years in which both horses and humans were involved, 25 years with human-only involvement, and 10 years in which only horses were involved (3). Some of the
EVIDENCE OF HUMAN-EQUINE INTERSPECIES INFLUENZA TRANSMISSION
VIRUS Reviews & Research, 2006
High levels of antibodies against the human influenza A(H 1 N 1 ) and A(H 3 N 2 ) strains in horse sera have been reported. The aim of the present study was to survey the human influenza virus strains present in horses using two methodologies, viral isolation and serology.
Zoonoses and public health, 2017
Influenza D virus (IDV) is a newly described influenza type of the Orthomyxoviridae virus family that was first isolated from diseased swine in 2011 and has subsequently been detected in cattle around the world in 2014. In addition, serological evidence for IDV infection in humans has been recently established. Despite all the progress, the full range of susceptible hosts for this novel virus has yet to be determined, but includes swine, bovine, small ruminants and human. This study was designed to determine if equine is a possible host to this newly emerging influenza virus. Three hundred and sixty-four equine serum samples were collected in 2015 from 141 farms within the Midwestern United States. Serum samples were examined using hemagglutination inhibition (HI) assay against two established IDV lineages (D/OK and D/660) and one IDV-related human ICV lineage (C/JHB). Results of this study showed 44 (44 of 364, 12%) samples positive for antibodies against D/OK, 39 (39 of 364, 11%) ...
Equine Veterinary Journal, 2019
Background: Equine influenza is an important cause of respiratory disease of horses worldwide. The equine influenza virus (EIV) undergoes antigenic drift through the accumulation of amino acid substitutions in the viral proteins, which may lead to vaccine breakdown. Objectives: To describe the epidemiological findings and the molecular characteristics of the EIV detected during the multifocal outbreak that occurred in Argentina between March and July 2018 and evidence a vaccine breakdown. Study design: Observational, descriptive study. Methods: Virus was detected in nasopharyngeal swabs using real-time reverse transcriptase PCR (RT-PCR). Nucleotide and deduced amino acid sequences of the haemagglutinin (HA) and neuraminidase (NA) genes were obtained from EIV positive nasopharyngeal swabs, and phylogenetic analysis was undertaken. Amino acid sequences were compared against the current World Organisation for Animal Health (OIE)-recommended Florida clade 1 vaccine strain and strain components of vaccines used in Argentina. Serum samples were tested using haemagglutination inhibition test. Results: Equine influenza virus infection was confirmed using real-time RT-PCR and serological testing. The phylogenetic analysis of the HA and NA genes revealed that all the EIV identified during the outbreak belong to the H3N8 subtype, Florida clade 1. Multiple amino acid changes, some of them at antigenic sites, were observed in the circulating virus when compared with the strains included in the most commonly used vaccine in Argentina. Seventy-six percent of the affected horses had been vaccinated with this vaccine, suggesting the occurrence of vaccine breakdown. Main limitations: The study does not include antigenic characterisation and full genome sequencing of Argentinian strains, that could provide additional information. Conclusions: The occurrence of this multifocal equine influenza outbreak in regularly vaccinated horses is a field evidence of vaccine breakdown, reinforcing the necessity of keeping vaccine strains updated according to OIE recommendations. It also underlines the importance of the implementation of appropriate quarantine measures and restriction of horse movement in the face of disease.
A Review of Evidence that Equine Influenza Viruses Are Zoonotic
Pathogens (Basel, Switzerland), 2016
Among scientists, there exist mixed opinions whether equine influenza viruses infect man. In this report, we summarize a 2016 systematic and comprehensive review of the English, Chinese, and Mongolian scientific literature regarding evidence for equine influenza virus infections in man. Searches of PubMed, Web of Knowledge, ProQuest, CNKI, Chongqing VIP Database, Wanfang Data and MongolMed yielded 2831 articles, of which 16 met the inclusion criteria for this review. Considering these 16 publications, there was considerable experimental and observational evidence that at least H3N8 equine influenza viruses have occasionally infected man. In this review we summarize the most salient scientific reports.
Evolution of equine influenza viruses (H3N8) during a Brazilian outbreak, 2015
Brazilian journal of microbiology : [publication of the Brazilian Society for Microbiology], 2017
Equine influenza is one of the major respiratory infectious diseases in horses. An equine influenza virus outbreak was identified in vaccinated and unvaccinated horses in a veterinary school hospital in São Paulo, SP, Brazil, in September 2015. The twelve equine influenza viruses isolated belonged to Florida Clade 1. The hemagglutinin and neuraminidase amino acid sequences were compared with the recent isolates from North and South America and the World Organisation for Animal Health recommended Florida Clade 1 vaccine strain. The hemagglutinin amino acid sequences had nine substitutions, compared with the vaccine strain. Two of them were in antigenic site A (A138S and G142R), one in antigenic site E (R62K) and another not in antigenic site (K304E). The four substitutions changed the hydrophobicity of hemagglutinin. Three distinct genetic variants were identified during the outbreak. Eleven variants were found in four quasispecies, which suggests the equine influenza virus evolved d...
Influenza and Other Respiratory Viruses, 2015
Background In 2012, equine influenza (EI) virus was confirmed as the cause of outbreaks of respiratory disease in horses throughout South America. In Uruguay and Argentina, hundreds of vaccinated thoroughbred horses in training and racing facilities were clinically affected. Objective To characterise the EI viruses detected during the outbreak in Uruguay and Argentina. Methods Virus was detected in nasopharyngeal swabs by a panreactive influenza type A real-time RT-PCR. The nucleotide sequence of the HA1 gene was determined and analysed phylogenetically using MEGA 5 software. Amino acid sequences alignments were constructed and virus was antigenically characterised with specific ferret antisera. Paired serum samples were tested by haemagglutination inhibition and single radial haemolysis. Results The diagnosis of EIV was confirmed by real-time RT-PCR, virus isolation and serological testing. The phylogenetic analysis of HA1 gene sequences of 18 EI viruses indicated that all of them belong to clade 1 of the Florida sublineage of the American lineage and are closely related to viruses isolated in the United States in 2012. The HA1 of viruses identified in horses in racing facilities in Maroñas, Uruguay, and in Palermo, Argentina, displayed 100% amino acid sequence identity and were identical to that of a virus isolated in Dubai in 2012, from vaccinated endurance horses recently imported from Uruguay. Conclusions The surveillance data reported illustrate the international spread of EI viruses and support the recommendations of the OIE expert surveillance panel to include viruses of the Florida sublineage in vaccines.
Risk factors for disease associated with influenza virus infections during three epidemics in horses
Journal of the American Veterinary Medical Association, 2000
Objective—To identify risk factors associated with respiratory tract disease in horses during 3 epidemics caused by influenza virus infections. Design—Cross-sectional and prospective longitudinal observational studies. Animals—1,163 horses stabled at a Thoroughbred racetrack. Procedure—Investigations were conducted during a 3-year period. An epidemic of respiratory tract disease caused by influenza virus infections was identified in each year. Routine observations and physical examinations were used to classify horses' disease status. Data were analyzed to identify factors associated with development of disease. Results—Results were quite similar among the epidemics. Concentrations of serum antibodies against influenza virus and age were strongly associated with risk of disease; young horses and those with low antibody concentrations had the highest risk of disease. Calculation of population attributable fractions suggested that respiratory tract disease would have been prevente...