Vetiology

There are many types of heart disease that can affect cats. Any type of heart disease can cause heart failure.

Why the Signs of Heart Disease Occur in Cats

In a normal healthy cat, the heart functions as a pump, responsible for moving the blood to various parts of the body. Essentially, as the heart disease progresses, the pump begins to fail.

One of the most common complications of heart failure is fluid build-up within the lungs. This is known as congestive heart failure. It occurs because the heart is no longer able to function as an efficient pump. Occasionally, fluid may build up in the abdomen and in the legs also.

Signs of Congestive Heart Failure in Cats

The signs seen in cats suffering from congestive heart failure include:

• weakness
• lethargy
• decreased appetite
• difficulty breathing
• increased respiratory rate
• increased respiratory effort
• cyanosis (a purple coloration of the gums), if the heart failure is severe enough to cause inadequate levels of oxygen to reach the body
• bloated, fluid-filled abdomen
• swelling of the legs

Unlike in dogs, where coughing is frequently a symptom of heart disease, in feline heart disease coughing is rare. Vomiting or dry heaving is sometimes seen as a symptom of heart disease in cats though.

Feline Thromboembolisms (Blood Clots) and Heart Disease

Another potential sequelae (negative outcome) of heart disease in cats is a condition known as a thromboembolic event. A thromboembolism is a blood clot that forms within one of the chambers of the heart.

In some instances, these blood clots break free and pass out of the heart and into the blood vessels. Eventually, these blood clots become lodged in a blood vessel, causing an obstruction of blood flow in the vessel.

The most common symptom of a thromboembolic event is paralysis in the hind legs. This occurs when the blood clot lodges in the large blood vessel known as the aorta near its end. The aorta normally splits into two arteries that supply the blood flow to the hind legs. When it becomes occluded (plugged), the blood no longer reaches the hind legs. This condition is also sometimes referred to as a saddle thrombus.

The signs seen when a saddle thrombus forms as a result of heart disease in a cat include:

• suddenly beginning to drag the hind legs
• crying in pain
• difficulty breathing, panting, open mouth breathing

Other Signs of Feline Heart Failure

Some cats will develop an arrhythmia (abnormal heart rhythm) as a result of heart disease. This may result in fainting episodes, also known as syncope.

Unfortunately, sudden death is also sometimes seen with feline heart disease.

Canine influenza or dog flu is influenza occurring in canines. Canine influenza is caused by varieties of Influenzavirus A, such as equine influenza virus H3N8, which in 2004 was discovered to cause disease in dogs. Because of the lack of previous exposure to this virus, dogs have no natural immunity to this virus. 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 but a low mortality.

History

The highly contagious equine influenza virus 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 also occurs. 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. It is possible that CIV caused some of the respiratory disease outbreaks at tracks between 1999 and 2003.^[2]

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.)^[3] As of August 2006, dog flu has been confirmed in 22 U.S. states, including pet dogs in Wyoming, California, Connecticut, Delaware, and Hawaii.^[4][5] There is no evidence that the virus can be transferred to people, horses, cats, or other species.^[6] There are three areas in the United States that may now be considered endemic for CIV due to continuous waves of cases: New York, southern Florida, and northern Colorado/southern Wyoming.

H5N1 (avian influenza) was also shown to cause death in one dog in Thailand, following ingestion of an infected duck.^[7]

[edit] The virus

Influenza A viruses are enveloped negative sense single-stranded RNA viruses.^[8] Genome analysis has shown that H3N8 was transferred from horses to dogs and then adapted to dogs through point mutations in the genes.^[9] The incubation period is two to five days and viral shedding may occur for seven to ten days following the onset of symptoms.^[10]carrier state. It does not induce a persistent

[edit] Symptoms

About 80 percent of infected dogs with H3N8 show symptoms, usually mild (the other 20 percent have subclinical infections), and the fatality rate for Greyhounds in early outbreaks was 5 to 8 percent,^[11] although the overall fatality rate in the general pet and shelter population is probably less than 1 percent.^[12] Symptoms of the mild form include a cough that lasts for ten to thirty days and possibly a greenish nasal discharge. Dogs with the more severe form may have a high fever and pneumonia.^[13] 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 percent if not given proper treatment.^[5] Necropsies in dogs that die from the disease reveal severe hemorrhagic pneumonia and evidence of vasculitis.^[14]

[edit] Diagnosis