Canine influenza (dog flu) is influenza occurring in canine animals. Canine influenza is caused by varieties of influenzavirus A, such as equine influenza virus H3N8, which was discovered to cause disease in canines in 2004.  Because of the lack of previous exposure to this virus, dogs have no natural immunity to it.  Therefore, the disease is rapidly transmitted between individual dogs. Canine influenza may be endemic in some regional dog populations of the United States.  It is a disease with a high morbidity (incidence of symptoms) but a low incidence of death.

A newer form was identified in Asia during the 2000s and has since caused outbreaks in the US as well. It is a mutation of H3N2 that adapted from its avian influenza origins. Vaccines have been developed for both strains.

The two strains of Type A influenza virus found in canines are A(H3N2) and A(H3N8). Over time, there has been a discovery of sources of transmissions, identification of specific symptoms and the creation of vaccines.

History
The highly contagious equine influenza A virus subtype H3N8 was found to have been the cause of Greyhound race dog fatalities from a respiratory illness at a Florida racetrack in January 2004. The exposure and transfer apparently occurred at horse-racing tracks, where dog racing had also occurred.  This was the first evidence of an influenza A virus causing disease in dogs.  However, serum collected from racing Greyhounds between 1984 and 2004 and tested for canine influenza virus (CIV) in 2007 had positive tests going as far back as 1999.  CIV possibly caused some of the respiratory disease outbreaks at tracks between 1999 and 2003.

H3N8 was also responsible for a major dog-flu outbreak in New York state in all breeds of dogs. From January to May 2005, outbreaks occurred at 20 racetracks in 10 states (Arizona, Arkansas, Colorado, Florida, Iowa, Kansas, Massachusetts, Rhode Island, Texas, and West Virginia).  As of August 2006, dog flu has been confirmed in 22 U.S. states, including pet dogs in Wyoming, California, Connecticut, Delaware, and Hawaii.  Three areas in the United States may now be considered endemic for CIV due to continuous waves of cases: New York, southern Florida, and northern Colorado/southern Wyoming.  No evidence shows the virus can be transferred to people, cats, or other species.

H5N1 (avian influenza) was also shown to cause death in one dog in Thailand, following ingestion of an infected duck.

The H3N2 virus made its first appearance in Canada at the start of 2018, following the importation of two unknowingly infected canines from South Korea. In 2006-2007 canine H3N2 first had reports in South Korea and was thought to be transferred to dogs from avian origins (avian influenza H3N2). It was not until 2015 that the canine H3N2 strain was discovered in the United States after there was an outbreak of dogs having respiratory infections in Chicago. As canine H3N2 influenza began to spread through the United States, in 2016 cats in an Indiana began to show symptoms of the disease as well, it is believed they were infected by coming in to contact with sick dogs.

Following this incidence, reports of the virus possibly spreading, with two other canines reporting alarming symptoms, were made public. By March 5th, 25 cases of infection were reportedly spread, although the number is thought to be closer to approximately 100.

Influenza A viruses are enveloped, negative sense, single-stranded RNA viruses.  Genome analysis has shown that H3N8 was transferred from horses to dogs and then adapted to dogs through point mutations in the genes.  The incubation period is two to five days, and viral shedding may occur for seven to ten days following the onset of symptoms.  It does not induce a persistent carrier state.

In late 2022, together with Bordetella bronchiseptica and other respiratory pathogens, the H3N2 canine flu virus experienced a surge in canine infections. This was partially due to increased human travel and reopened offices following the relaxation of COVID-19 pandemic public health measures, leading to large numbers of dogs being placed together in kennels and doggy day care centers. Changing pet ownership behaviors also led to overcrowded animal shelters, which had been emptied at the height of the pandemic.

Transmissions 
The infection of canine influenza can be transmitted from animal to animal and almost all dogs that come in contact with the virus will contract it. This makes canine influenza most common among dogs but can also be transmitted to cats in a shelter or a household. Canine influenza is an airborne disease, when a dog coughs or sneezes they secrete respiratory droplets that are then inhaled by other animals causing infection. Kennels, dog parks, grooming parlors, and things alike are high risk areas for infections.

Symptoms
About 80% of infected dogs with H3N8 show symptoms, usually mild (the other 20% have subclinical infections), and the fatality rate for Greyhounds in early outbreaks was 5 to 8%, although the overall fatality rate in the general pet and shelter population is probably less than 1%.  Most animals infected with canine influenza will show symptoms such as coughing, runny nose, fever, lethargy, eye discharge, and a reduced appetite lasting anywhere from 2-3 weeks.

Symptoms of the mild form include a cough that lasts for 10 to 30 days and possibly a greenish nasal discharge.  Dogs with the more severe form may have a high fever and pneumonia.  Pneumonia in these dogs is not caused by the influenza virus, but by secondary bacterial infections.  The fatality rate of dogs that develop pneumonia secondary to canine influenza can reach 50% if not given proper treatment.  Necropsies in dogs that die from the disease have revealed severe hemorrhagic pneumonia and evidence of vasculitis.

Diagnosis
The presence of an upper respiratory tract infection in a dog that has been vaccinated for the other major causes of kennel cough increases suspicion of infection with canine influenza, especially in areas where the disease has been documented.  A serum sample from a dog suspected of having canine influenza can be submitted to a laboratory that performs PCR tests for this virus.

Vaccine
In June 2009, the United States Department of Agriculture (USDA) Animal and Plant Health Inspection Service (APHIS) approved the first canine influenza vaccine. This veterinarian provided vaccine help fight the infection and are preventative measures for dogs who are constantly facing exposure of the H3N8 and H3N2 strain.This vaccine must be given twice initially with a two-week break, then annually thereafter.

H3N2 version

A second form of canine influenza was first identified during 2006 in South Korea and southern China. The virus is an H3N2 variant that adapted from its avian influenza origins. An outbreak in the US was first reported in the Chicago area during 2015. Outbreaks were reported in several US states during the spring and summer of 2015 and had been reported in 25 states by late 2015.

As of April 2015, the question of whether vaccination against the earlier strain offered protection had not been resolved. The US Department of Agriculture granted  conditional approval for a canine H3N2-protective vaccine in December 2015.

In March 2016, researchers reported that this strain had infected cats and suggested that it may be transmitted between them.

Human risk 
The H3N2 virus as a stand-alone virus is deemed harmless to humans. According to the Windsor-Essex County Health Unit, it is only when the H3N2 virus strain combines with a human strain of flu, "those strains could combine to create a new virus." The possibility of this is unlikely; however, if an infected dog contracts a human flu, there stands a slight chance.

See also

 Avian influenza
 Equine influenza
 Human flu
 Swine influenza
 Cat flu

References

Further reading
 A New Deadly, Contagious Dog Flu Virus Is Detected in 7 States The New York Times
 States that have identified dogs with CIV
 Canine Influenza from The Pet Health Library
 Canine Influenza from Veterinary Partner
 Canine Influenza Fact Sheet Center for Food Security and Public Health (CFSPH), Iowa State University College of Veterinary Medicine
 AVMA: canine influenza

Influenza
Influenza
Animal viral diseases
개 인플루엔자(canine influenza, dog flu)는 개과동물에서 발생하는 인플루엔자이다. 개 인플루엔자는 말인플루엔자 바이러스인 H3N8 같은 influenza virus A의 변종에 의해 발생하며 개에서 질병을 유발한다는 것을 2004년에 밝혀냈다. 이 바이러스에 노출된적이 없기 때문에 개에서 자연적 면역력은 없다. 따라서 개에서 빠르게 이 질환이 전파되었다. 개 인플루엔자는 미국에서 지역적으로 개가 있는 곳에서 풍토병 양상을 보였다. 이 질환은 높은 이환율을 보이지만, 치사율은 낮다. 2000년대에 아시아에서 새로운 형태가 발견되었고, 이형태가 미국에서 마찬가지로 유행하고 있다.

역사 
매우 전염성높은 말 인플루엔자 A 바이러스(equie influenza A virus)는 2004년 1월 플로리다에서 호흡기질환으로 폐사한 그레이하운드 경주견에서 발견되었다. 개 경주에도 사용되는 경마장 트랙에서 노출 및 전염되었다. 개에서 인플루엔자 A 바이러스가 질환을 유발한다는 첫번째 증거였다. 하지만 1984년과 2004년사이 그레이하운드 경주견에서 채혈한 혈청을 2007년 개 인플루엔자 바이러스(CIV)에 대하여 테스트했을 때 1999년도에도 양성반응이 나타남을 보였다. CIV는 1999년과 2003년사이 경주견 사이에서 호흡기질환의 유행을 유발한 원인이었을 것으로 간주한다.

H3N8은 뉴욕주의 모든 품종의 개에서 유행한 개 독감의 원인이다. 2005년 1월부터 5월까지 10개주(아리조나, 아칸소, 콜로라도, 플로리다, 아이오와, 캔사스, 메사추세츠, 로드아일랜드, 텍사스, 웨스트버지니아)의 20개의 경견장에서 유행성을 보였다. 2006년 8월 와이오밍, 캘리포니아, 코네티컷, 델라웨어, 하와이 등 반려견을 포함하여 미국의 22개주에서 확진되었다. 미국의 3개주에서는 지속 발병형태로 CIV가 풍토병양상을 보인다: 뉴욕, 남부플로리다, 북부 콜로라도, 남부 와이오밍. 바이러스가 사람, 고양이, 다른종에 의해 전파된다는 증거는 없다.

1마리 개에서 H5N1 (조류 인플루엔자)에 감염된 오리고기를 섭취한 이후 폐사를 보인적이 태국에서 발생했었다.

바이러스 
인플루엔자 A 바이러스는 외막이 있는 음성극성의 단일가닥 RNA 바이러스이다. 유전자 분석으로 H3N8은 말에서 개로 전이되었고, 유전자의 일부 변이로 인해 개에 적응된 것으로 보인다. 잠복기는 2-5일이며, 바이러스의 증식 배출은 증상이 시작된 이후로 7-10일이다. 지속적 보균형태로 남지는 않는다.

증상 
H3N8에 감염된 80%의 개에서 증상이 나타나며, 일반적으로 가벼운 증상(나머지 20%는 무증상감염)을 보이며, 초기 유행시에는 그레이하운드의 치사율은 5-8%였으나, 일반 반려동물, 동물보호소에서는 1%미만의 치사율을 보였다. 가벼운 증상 형태는 10-30일정도 지속하는 기침과 녹색의 콧물이다. 더 심한 형태의 증상은 고열과 폐렴이다. 폐렴은 인플루엔자 바이러스에 의해 유발되지 않지만, 세균의 이차감염에 의해 발생한다. 이차감염에 의해 폐렴이 발생한 개에서 치사율은 적절한 치료가 없다면 50%에 이른다. 이 질환으로 죽은 개의 부검에서 심한 출혈성 폐렴과 혈관염의 징후가 관찰된다.

진단 
다른 켄넬코프의 주요원인에 대한 예방접종을 한 개에서 상부호흡기 감염이 나타난 경우, 개 인플루엔자 감염의 가능성이 크며, 특히 이 질환이 나타난 적이 있는 지역에서는 더욱 그러하다. 개 인플루엔자 감염이 의심되는 개에서 혈청에서 이 바이러스에 대한 PCR검사를 통해 실험실에서 진단 가능하다.

예방접종 
2009년 6월 미국농무부(USDA)의 동식물 검역소(animaland plant health inspection service: APHIS)에서 최초의 개 인플루엔자 백신을 승인하였다. 이 백신은 2주간격으로 2번, 매년 접종한다.

H3N2 형태 
개 인플루엔자의 2번째 형태가 2006년 대한민국과 중국남부에서 발견되었다. 이 바이러스는 조류 인플루엔자가 원형으로 변이된 H3N2 변종이다. 미국에서의 유행은 2015년 시카고에서 보고되었다. 이 유행은 2015년 봄과 여름 미국 여러주에서 나타났다. 2015 4월부터 인플루엔자 방어를 위해 실시했던 초기 바이러스주를 이용한 백신효과의 여부는 아직 검증되지 않았다.

같이 보기 
 조류 인플루엔자
 Equine influenza
 인플루엔자
 돼지 인플루엔자
 Cat flu

참고 문헌

더 읽을거리 
 A New Deadly, Contagious Dog Flu Virus Is Detected in 7 States The New York Times
 States that have identified dogs with CIV
 Canine Influenza from The Pet Health Library
 Canine Influenza from Veterinary Partner
 Canine Influenza Fact Sheet Center for Food Security and Public Health (CFSPH), Iowa State University College of Veterinary Medicine
 AVMA Backgrounder: canine influenza
 Dr. Cynda Crawford, Clinical Assistant Professor

개 질병
인플루엔자
동물 바이러스성 질병