It was recently brought to our attention that there are rumors circulating online about the existence of two new strains of canine distemper virus. These rumors are untrue. After consulting with two experts, Dr. Ed Dubovi (from Cornell) and Dr. Ron Schultz (from the University of Wisconsin), we provide the following information:

• There is no data to back up claims that the disease is on the rise on a national level, but there have been many outbreaks of distemper covered in the news media.
• Genetic studies of the canine distemper viruses in the U.S. may show strains that were previously undetected here, but it's almost impossible to determine if these strains are newly arrived or just newly detected because of improvements in testing. In addition, minor genetic changes often do not affect the antigenicity of the virus and have no impact on the efficacy of currently available vaccines.
• The currently available distemper vaccines are highly effective and will protect dogs against all currently circulating strains of canine distemper virus.
• The real issue is that there are unvaccinated (or inadequately vaccinated) and unprotected pets at high risk of developing a very deadly, yet preventable, disease.
• Dog owners are strongly urged to consult with their veterinarians regarding vaccination of their dog against distemper and other common diseases, including adenovirus, parvovirus and rabies.
  For more information, please visit the post on our AVMA@Work blog. 
  

EQUINE PIGEON FEVER

There is currently an outbreak in Texas and surrounding states of a condition called Pigeon Fever.  Horses exhibit a pronounced swelling primarily in the pectoral area usually high in the area where a breast collar would cross which looks like the protruding breast of a pigeon, hence the name.  

The swelling is caused by bacteria called Corynebacterium pseudotuberculosis.  This bacterium is found in the soil often associated with very dry dusty conditions such as we have had this year.  Horses contract the bacteria by contaminated soil contacting skin sores or wounds and by insects transmitting the bacteria through bites as with biting insects such as horn flies, horse flies, and biting gnats and even house flies that do not bite but land on lesions and transmit the bacteria to the wounds by contact.  The bacteria are then spread through the lymphatic system and are trapped by lymph nodes which then become infected and abscess weeks to months later.

The pectoral lymph nodes are the most common nodes to be affected, however any lymph node can be affected because the bacteria spreads through the lymphatic vessels which are the sewer system of the body.  The lymphatic vessels carry bacteria to the nearest lymph node which acts as a filter.  The bacteria are trapped there and the immune system attacks the bacteria at the lymph node.  However, in the case of Coryenbacterium, the immune system fails to kill the bacteria and the lymph node cannot kill and contain the bacteria and it abscesses.  Abscesses can form anywhere in the body including the vital organs and the abdomen.  The severity of symptoms and prognosis is related directly to where the abscessation occurs and if the abscess is drained promptly. 

Antibiotics are limited in effectiveness in treating this disease.  Usually, the abscess is deep in the structure and they are not recognized until after the abscess has formed.  The immune system attempts to wall off the bacteria into a protective fibrous capsule.  Blood vessels cannot penetrate to its interior.  Therefore, antibiotics in the blood stream cannot penetrate the abscess capsule to attack the bacteria.  The bacteria continue to proliferate putting more and more pressure which enlarges the capsule.  Usually, superficial abscesses eventually rupture if not lanced because the pressure of the abscess collapses blood vessels of the surrounding tissue until a localized area of skin dies and the abscess ruptures through the skin eliminating the infection.  However, with Coryenbacterium the pus is so thick and the abscess is often so deep under thick inflamed layers of muscle it cannot exert enough localized pressure to the adjacent tissue to allow it to rupture to the outside.  Therefore, the abscess just enlarges until it is lanced or it pressurizes itself between muscle bellies and facial planes to other parts of the body. 

Superficial abscesses' soft areas can be seen and felt and easily lanced after local anesthesia.  However, the more common deep pectoral abscesses can only be located and safely lanced with ultrasound due to the firm and thickened pectoral muscles.  These abscesses are often in close proximity to the jugular veins and carotid arteries as well as large vessels traversing the pectoral muscles. .  In my practice we use a color Doppler ultrasound which identifies these blood vessels and enables us to avoid them during the surgical procedure. After identifying the abscess, a 5 inch long needle is inserted in the abscess which is then used as a guide to direct an incision with a scalpel to lance and drain the abscess.  The draining tract is left to heal as an open wound. 

There is no vaccine available to prevent this disease. Since this bacterium lives in the soil and enters the horse by insects and/or wounds and abrasions, management practices are the best prevention.  Controlling biting flies and houseflies by composting manure and rotting vegetation fly sprays, and fly predators will reduce the risk of infection. Bandaging leg wounds to prevent contamination by dust or houseflies might prevent an occurrence.  Horses that have wounds that cannot be bandaged should be stalled in a bedded stall with fly spray system or frequent fly spray application. Elective surgical procedures that cannot be bandaged are best scheduled during months when flies and dust are not as prevalent.  Horses that have a draining lesion due to Corynebacterium should be confined until drainage stops and the wound closes. The bedding should be disposed of and any tools, halters, and lead ropes should be disinfected.

This disease has become a very prevalent problem in this area recently and will probably persist as long as our drought condition exists.  Historically, horses have immunity for five to seven years after contracting the disease.  There is a vaccine for sheep and goats, but there is no vaccine available yet for horses.  The organism for goats and sheep is a different strain and has not been shown to infect horses. Cattle can be affected and can contaminate horses, but no cattle vaccine is available either.  Hopefully a vaccine will be developed soon.

Charles A. Kerin, D.V.M.