Dog Influenza (Flu)

Introduction

The canine influenza virus ("CIV") is a highly contagious, newly emerging, canine-specific infectious agent which represents an unusual adaptation of the equine influenza virus. In essence, the equine influenza virus mutated, jumped species and now lives, reproduces and spreads quite efficiently among – and so far only among - dogs. Early diagnosis and treatment can dramatically improve the chances of successful recovery and reduce further spread of the disease.

Causes & Prevention

How Canine Influenza Affects Dogs
Unlike disease caused by the human flu virus, canine influenza is not seasonal and can occur in dogs of any age, gender or breed, at any time of the year. There is no natural or vaccine-induced immunity to this recently recognized pathogen. Clinical signs of "dog flu" typically appear suddenly. Most infected dogs have mild symptoms, including a persistent cough that can be moist or dry and usually lasts 2 to 3 weeks despite use of antibiotics and cough suppressants. The cough is accompanied by clear nasal drainage, which often progresses to a thick, greenish discharge. Low-grade fever is common. If the cough is dry and hacking, it may be confused with "kennel cough," a condition caused by the Bordetella bronchiseptica/Parainfluenza virus that in the early stages is virtually indistinguishable from CIV infection.

In severe cases, dogs develop a high-grade fever and pronounced signs of pneumonia. Thankfully, the fatality rate for canine influenza is low.

Causes of Canine Influenza
"Dog flu" is caused by infection with the canine influenza virus. CIV is transmitted by inhalation of airborne respiratory secretions that contain viral particles. It can also be transmitted by direct contact with contaminated objects or surfaces. Reports suggest that the virus can survive in the environment and be infectious for up to 2 days. Given its mode of transmission, CIV tends to infect dogs that are in close contact with other dogs, as in boarding kennels, rescue shelters, humane societies, day-care facilities, dog shows or similar tight-group situations. Almost all exposed dogs become infected, and roughly 80% of infected dogs will develop signs of illness within several days.

Prevention and Control of Canine Influenza
The canine influenza virus seems to be easily killed by common disinfectants, making good hygienic practices the first and best line of prevention. Dogs that have been exposed to sick dogs or that are showing clinical signs of respiratory distress should be isolated from other dogs until those signs resolve. Owners of dogs that are coughing should restrict their own contact with other dogs. The first canine influenza virus vaccine was approved for licensure by the USDA in May of 2009 and is available to help control clinical disease.

Special Notes
If your dog shows signs of coughing, nasal discharge and a moderate fever, contact your veterinarian immediately. Because CIV is so highly contagious, other dogs in the household are at high risk for developing the disease. Until you find out what is causing your dog's symptoms, keep it isolated from other dogs and always wash your hands thoroughly after petting or touching your dog.

Symptoms & Signs

Introduction and Background
In January of 2004, racing greyhounds in Florida experienced an outbreak of a novel, previously undiagnosed viral disease that caused mild to extremely severe respiratory illness, with a 36% case fatality rate in that outbreak. Since then, the Canine Influenza Virus (CIV) has been identified, classified and extensively studied. It is an influenza A H3N8 virus, which is not a human pathogen but rather represents an unusual adaptation of the H3N8 equine influenza virus that has emerged as a new, highly contagious, canine-specific infectious agent. In essence, the equine influenza virus "jumped species" and now lives, reproduces and spreads quite efficiently among dogs.

Canine influenza is not a disease of people. Early diagnosis and treatment can dramatically improve the chances of a successful recovery in affected dogs and can help minimize further spread of the disease.

Symptoms of Canine Influenza
Unlike disease caused by the human flu virus, canine influenza is not seasonal and can occur in dogs of any age and any breed, during any time of the year. CIV is transmitted by airborne respiratory secretions containing viral particles. It can also be transmitted by contact with contaminated objects or surfaces (food and water bowls, kennels or cages, floors, collars, leashes, hands, clothing, shoes, etc.). Reports suggest that the virus can survive and be infectious on surfaces, clothes and hands for up to 48 hours. Given its mode of transmission, CIV tends to cause disease in dogs that are in close contact with many other dogs, such as in boarding kennels, rescue shelters, humane societies, doggy day-care facilities, at dog shows or in similar group situations.

It normally takes 2 to 4 days for clinical signs to develop once a dog has been exposed to and infected by the canine influenza virus (this is called the "incubation period"). Almost all dogs exposed to CIV become "infected" with the virus, and roughly 60-80% of infected dogs ultimately develop clinical disease. Unfortunately, infected dogs are the most contagious to other dogs during the viral incubation period – even though they have not yet shown any clinical signs of illness. Even the 20-40% of infected dogs who never become ill still shed the virus and can infect other dogs.

Signs of canine influenza range from mild to severe and normally appear suddenly. Most infected dogs have mild clinical signs including a persistent cough that can be moist or dry but lasts 2 to 3 weeks despite use of antibiotics and cough suppressants. The cough is usually first accompanied by a clear nasal discharge, which often progresses to a thick, green-ish mucoid discharge in the presence of a secondary bacterial infection. Low-grade fever is often present. If the cough is dry and hacking, it may be confused with "kennel cough," which is a condition caused by the Bordetella bronchiseptica/parainfluenza virus and in the early stages is virtually indistinguishable from CIV infection.

In cases of severe canine influenza, dogs may develop a high-grade fever (104-106 degrees F) and pronounced signs of pneumonia, such as increased respiratory rate, effort and wheezing. They also may become lethargic, depressed and anorexic. The fatality rate for canine influenza is low, and very few dogs infected with CIV will die.

If your dog shows signs of coughing, nasal discharge and a moderate fever, contact your veterinarian immediately. Because CIV is so highly contagious, other dogs in the household are at high risk for developing the disease. Until you find out what is causing your dog's symptoms, keep your dog isolated from other dogs and always wash your hands thoroughly after petting or touching your dog.

Diagnosis & Tests

Introduction
Canine influenza, sometimes called the "dog flu," is a highly contagious disease caused by a relatively recent adaptation of an equine influenza virus to the canine species. The Canine Influenza Virus (CIV) was identified and classified following an unusual outbreak of respiratory disease in racing greyhounds that occurred in Florida in early 2004. Fortunately, with extensive research directed toward this disease, there now are a number of diagnostic tools available to canine veterinarians.

Diagnosis of Canine Influenza
Once veterinarians realized that a canine influenza outbreak was occurring, there was a rush to isolate the virus in order to find a way to test for - and vaccinate for - the disease. Canine influenza cannot be diagnosed based upon clinical signs alone, because the signs of this disease are virtually identical to those caused by other respiratory pathogens. Technology has progressed to the point where antibodies to CIV can be identified in blood samples after the first week of clinical disease, using what is called a serum hemagglutination inhibition test. While this was a significant improvement over only post-mortem diagnosis, it still required waiting 7 days and prolonged the start of effective treatment.

Newer technology now exists to assist in the diagnosis of influenza in dogs. Called "polymerase chain reaction" technology, or "PCR", it involves identification of viral DNA in samples taken of nasal or pharyngeal (throat) respiratory secretions during the first 4 days of infection, using sterile swabs. Identification of the virus itself during this acute phase of infection is also now possible. While these tests are useful if a dog has been ill for fewer than 4 days, the results are less reliable after that time. Moreover, while positive PCR results mean that the dog probably is infected with CIV, negative PCR results may be falsely negative if the swabs were taken before or after the period of peak viral shedding. The most reliable way to diagnosis canine influenza is paired serologic testing on two blood samples – one collected during the first week of clinical illness, and another taken 2-3 weeks later. Of course, over time other diagnostic tools may be developed for this disease.

If your dog shows signs of influenza, contact your veterinarian immediately. Your veterinarian is in the very best position to determine what is causing your dog's respiratory signs, and how best to treat them.

Treatment Options

Introduction
"Dog flu" is a relatively recent phenomenon. In early 2004, a group of racing greyhounds in Florida came down with cases of mild to severe respiratory disease, with 36% of affected dogs dying. After this outbreak, the Canine Influenza Virus (CIV) was identified, classified and intensively studied. It evolved from and remains strikingly similar to an equine influenza virus, but now is an emerging species-specific pathogen that – at least so far - infects and causes illness only in dogs. Fortunately, the mortality rate associated with canine influenza is very low, and supportive treatments are highly successful. Early diagnosis and treatment can dramatically improve the chances of a successful recovery in affected animals and can also help minimize further spread of the disease.

Canine Influenza - Treatment
Much like viral flu in people, canine influenza cannot be "cured" but instead must simply "run its course." As for most viral diseases, treatment is largely supportive. Initially, affected animals should be isolated or otherwise closely managed for at least 7 to10 days after the onset of clinical signs, to prevent or at least minimize infection of other dogs. In mild cases, dogs should be managed at home rather than hospitalized, not only for comfort and cost considerations but also to prevent contaminating the veterinary hospital environment. Uncomplicated outpatient cases should be managed by enforced rest for at least 2 to 3 weeks. The dogs should be kept in a quiet, calm and familiar environment, and their activity should be restricted to going outside to "potty" only as necessary. They must be kept well-hydrated, with free access to fresh water, and should be fed a nutritious, palatable diet. Broad-spectrum antibiotics may be prescribed for dogs to prevent or control secondary bacterial infections. In mild cases involving a productive cough, cough suppressants normally are not recommended, because coughing is a normal and effective bodily mechanism for eliminating excessive respiratory secretions. Cough suppressants commonly are used for dogs with dry, non-productive coughs.

In more severe cases, where bronchopneumonia or other respiratory infection occurs, it may be appropriate to hospitalize the animal and provide intravenous antibiotic and fluid support. Dogs suffering from pneumonia may need enforced rest for several months and antibiotic therapy for several weeks after radiographic resolution of disease signs.

Some drugs are available and approved to treat viral influenza, but only in people. Use of such drugs in dogs is highly controversial, as their efficacy, side effects and safety in companion animals are unknown at this time.

Canine Influenza – Prevention and Control
The canine influenza virus seems to be easily killed by common disinfectants like ammonium compounds and bleach solutions. Good hygiene should be practiced by all dog owners, and especially by veterinary clinics, boarding and rescue facilities where a number of dogs are regularly in close contact. Dogs showing clinical signs of respiratory disease should be isolated from other dogs until those signs resolve; dogs that have been exposed to sick dogs should also be segregated for several weeks. Owners of dogs that are coughing should restrict their own contact with other dogs and should not pet or participate in activities bringing them in contact with healthy animals.

The first canine influenza virus vaccine was approved for licensure by the USDA in May of 2009. An inactivated whole-virus vaccine developed by Intervet/Schering Plough Animal Health Corporation, it is intended to help control rather than prevent disease caused by CIV infection. While it may not prevent illness in every case, clinical trials have shown this vaccine to be highly effective in reducing the incidence, severity and duration of disease. It also reduces the volume and duration of viral shedding by infected animals, which in turn makes them less contagious to other dogs.