Causes, Symptoms, Treatments: A Practical Overview.

By Elizabeth Settles, D.V.M., Veterinary Operations, Pfizer Animal Health

A new global respiratory disease complex has been described in dogs, one that is similar to Shipping Fever in cattle. Part of this disease complex has been around for a long time – Kennel Cough.

We now know that many different organisms and environmental factors can cause Canine Infectious Respiratory Disease (CIRD) ranging in severity from very mild to fatal outcomes. In outbreaks it is important to know what organisms you are dealing with so you can choose appropriate treatments and vaccines for prevention.

CIRD occurs because bacteria and viruses colonize the lining (mucosa) of the nose, larynx, trachea and lower airways, as well as the lungs. When only one bacteria or virus is involved, disease symptoms are mild; but when several infectious agents are present the disease is much worse.

Too much humidity, crowding and extreme temperatures also predispose dogs to infections. Young puppies and very old dogs are particularly susceptible to this disease.

The most common viruses in CIRD are canine parainfluenza, canine adenovirus and canine influenza. The most common bacteria by far are Bordetella bronchiseptica. Other bacteria invade the lungs after Bordetella and these include mycoplasma, Klebsiella sp., Streptococcus equi zooepidemicus and E.Coli.

Canine parainfluenza and canine adenovirus have been known to cause mild respiratory disease for many years. These are agents that are included in Canine influenza is a newer virus first recognized in greyhounds in Florida in 2004. A vaccine has recently become available for influenza. Clinical signs can vary widely with this virus. Most dogs have cough, fever and nasal discharge lasting four to five days that seems worse than "traditional" kennel cough. A few dogs develop hemorrhagic pneumonia and die within a few days.

Many of the fatalities associated with canine influenza also have secondary bacterial invaders like Bordetella and Streptococcus. Bordetella is particularly dangerous because it attaches to and replicates on the cilia of the airways. Cilia are hair-like cell structures that push particles up and away from the lungs; in a Bordetella infection they become paralyzed and some are destroyed.

Bordetella also has all the same weapons other gram negative bacteria have. It can produce exotoxins and endotoxins that can kill the lining cells of the airways and cause fever. Mycoplasma causes pneumonia in the lungs as well as attacking the cilia in the airways. This organism can cause chronic persistent coughs in dogs with chronic bronchitis as well as CIRD. Streptococcus spp. and Pasteurella spp. cause pneumonia and sepsis and are often fatal.

Severe cases of CIRD can occur in puppies from puppy mills, shipped to pet stores or purchased directly from the breeding kennel. They are exposed to stress from travel as well as exposure to other puppies that may be harboring different organisms.

Clinical signs may appear mild at first, with coughing episodes that may be associated with attempts to vomit. In the early stages the puppy or dog appears to be otherwise healthy.

Most dogs will not advance into the more severe form. However, young puppies and older dogs may move quickly into the more severe syndrome. These dogs will have fevers, be lethargic, have difficulty breathing and will refuse to eat. CIRD can appear very similar to canine distemper because of the thick yellow-green discharge that may occur from the nose and eyes.

In mild cases, most dogs respond well to cough medications and antibiotics. In severe cases, dogs may need extensive workups to establish which disease-causing agents are present. In these cases full blood panels should be evaluated to see if the dog or puppy has concurrent kidney or liver problems that are either congenital or related to sepsis.

Chest X-rays should be taken to identify if pneumonia is present and how extensive it is. Transtracheal washes or sampling by bronchoscopy can help to identify the causative agents and to which antibiotics the bacteria may be sensitive.

Dogs may require IV fluids, injectable antibiotics, nutritional support and oxygen therapy. Some cases require a nebulizer to deliver the antibiotics deep into the lungs. Nebulizers can be rented from a pharmacy. A combination of saline and the appropriate antibiotic, based on the culture results, is placed into the chamber and the device is placed over the nose and mouth of the patient. This is usually done two to three times daily for four to seven days.

Even with this extensive treatment the disease may still be fatal.

Prevention is really the best way to contain CIRD in the individual patient as well as in an outbreak. Vaccines are available for the viral components as well as for Bordetella.

The most severe syndromes are usually seen in (a.) dogs with no prior natural exposure to the causative agents or in (b.) unvaccinated dogs. Outbreaks can be difficult to control because Bordetella and Mycoplasma can be shed from a dog that was sick with CIRD for up to three months.

Parainfluenza virus can also circulate in a population of dogs for up to three months. Good husbandry techniques are needed in an outbreak. Ideally, puppies are kept isolated from other puppies until they are vaccinated. Also, they are not shipped at early ages (six to eight weeks) and exposed to extremes in temperature and humidity.

Puppies that show any clinical signs of CIRD should be promptly removed from other puppies and that area and bowls should be cleaned with anti-viral and anti-bacterial agents.