Chapter 5: Canine Influenza 2 CE Hours
Expiration Date : May 3, 2027 Learning objectives
After completing this course, the learner will be able to: Discuss the background and history of the two canine influenza viruses in the United States, including when each strain was initially observed and each strain’s suspected method of introduction into the canine population.
Give examples of how canine influenza may be spread among a group of dogs in a high-risk environment Compare methods of testing and treatment approaches.
INTRODUCTION
Canine influenza virus has been present in the United States canine population for more than 10 years. The virus was initially noted as a cause of respiratory disease outbreaks among racing greyhounds in 2004, and was noted to cause significant fatalities in greyhound kennels at that time. This initial outbreak was a strain known as H3N8, and that strain of canine influenza has continued to circulate in the United States since 2004. In the spring of 2015, however, a new outbreak of respiratory disease was noted in Chicago and this outbreak was determined to be caused by a different strain of canine influenza. The emergence of the H3N2 strain of canine influenza brought this
disease back to the forefront in the minds of many dog owners, and therefore many veterinarians began receiving frequent questions from clients regarding the threat of the disease and recommended measures to protect pet dogs. This course is designed to provide veterinarians with information on the historical background and epidemiology of canine influenza, as well as practical information related to diagnosis, treatment, and prevention. With this information, veterinarians will be more prepared for canine influenza outbreaks in their community, and also more prepared to educate dog-owning clients and address their concerns.
INFLUENZA VIRUS: GENERAL BACKGROUND
Influenza viruses are members of the family Orthomyxoviridae . These viruses are present in a number of species and can cause varying clinical signs depending on in the individual virus strain and the species infected. Influenza viruses are classified based on a number of characteristics. The first classification of influenza viruses is type, and each virus type is labelled by a letter: A, B, or C. These influenza types differ based on both structural characteristics and epidemiology. Influenza A viruses are the most-commonly discussed influenza viruses. They exist in a wide variety of species and are also the major contributors to human disease, both epidemics and pandemics. Influenza types B and C are found only in humans, and they are typically associated with less significant disease even within the human population. Influenza A viruses are then further divided into subtypes, based on two proteins that are found on the surface of the viral lipid envelope: hemagglutinin (HA) and neuraminidase (NA). The antigenic properties of these two proteins are each labelled Canine influenza A H3N8 Canine influenza A subtype H3N8 was initially noted as a respiratory syndrome in racing greyhounds in 2004. 3 During disease outbreaks, large numbers of affected greyhounds died peracutely, with evidence of significant respiratory pathology and hemorrhage. 4 Between 2003 and 2005, outbreaks of respiratory disease were noted at 20 different greyhound racetracks in eight states. 5 By 2010, canine influenza virus had spread to the pet population and had been identified in 30 states. The virus quickly became enzootic in some communities, most notably Florida, Pennsylvania, New Jersey, New York, and Colorado. 5-7 At the start of the initial 2004 outbreak, there was significant uncertainty regarding the origin of this virus. Even after the respiratory cases were determined to be caused by canine influenza, questions remained as to whether this was a spillover infection of equine H3N8 into greyhounds, or whether equine influenza had established itself in canines and was capable of horizontal transmission. 1 Further examination of banked
by number and these numbers define the influenza subtype. Currently, there are 16 HA subtypes (H1-H16) and 9 NA subtypes (N1-N9) that have been defined. 1 Influenza viruses are relatively host-specific, but are occasionally observed to jump between species. The natural host of influenza A is thought to be migratory birds, where it resides in the gastrointestinal epithelium. Because many strains of influenza virus cause no signs of disease in avian hosts (although highly- pathogenic avian influenza strains can lead to clinical signs), Influenza A viruses are easily spread worldwide and distributed in fecal material by migratory waterfowl. 1 When these viruses pass from their hosts to other species, the cross-species jumps can have important public health implications, such as in the cases of highly pathogenic avian H5N1 viruses (“bird flu”) and swine origin H1N1 virus (“swine flu”) in the human population. 2 In veterinary medicine, however, there have been two recent species jumps that have introduced influenza into our canine population. greyhound sera demonstrated that canine influenza H3N8 had been present in the racing greyhound population as early as 2000, 1 and genetic analysis of the H3N8 strain demonstrated that the virus had derived from a single transfer of equine virus (of the Florida 1 strain) to dogs during 1999-2000. 8 Since this initial outbreak, canine influenza H3N8 has continued to circulate in the United States canine population as a separate lineage, with no evidence of being transferred back to horses. 8,9 Experimental studies have demonstrated that the virus is no longer capable of efficient replication within horses, with naïve horses failing to acquire infections from infected dogs or experimentally-infected horses. 4 Currently, cases of the H3N8 strain are reported sporadically throughout the United States. Outbreaks periodically occur, but these outbreaks typically disappear rapidly. 4 Canine influenza virus H3N8 has not been reported outside of the United States.
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Book Code: VFL1524
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