Although it is rare, plague does occur in dogs worldwide, and in the United States, it is most prevalent from May through October in the rural Southwest in semi-arid upland forests and grassland regions that host dense, native rodent populations.
The carriers of the parasitic genus Yersinia pestis bacteria which causes plague are primarily rodents — rats, mice, various species of squirrels, hamsters, prairie dogs, chipmunks, voles, and even rabbits which are lagomorphs, not rodents — and the infected fleas that feed on them.
Plauge is a serious, sometimes acute bacterial disease that is zoonotic or cross-species which means that in addition to dogs, it can be transmitted to cats, goats, pronghorn antelope, camels, llamas, mule deer, and carnivores that feed on infected rodents, non-human primates and humans. It is most commonly transmitted to a dog via a flea bite and infrequently, a rodent bite. It is also transmissible to a dog who bites and/or consumes a carrier rodent or its feces.
Most dogs have a high natural resistance to plague and once infected are asymptomatic and do not exhibit clinical signs of illness. However, they can transmit the disease to humans and plague can be fatal in vulnerable dogs. It's critical to seek veterinary attention immediately after a bite has occurred to save the dog and prevent transmission.
Signs and symptoms of the three forms of plague — bubonic, pneumonic, and septicemic.
Once a dog is infected by coming into contact with a rodent's saliva, tissues, bodily fluids or feces, or is bitten by a flea that fed on a rodent, the Y pestis bacteria travel to the dog's lymph nodes in bubonic plague, the lungs in pneumonic plague, and the blood in septicemic plague, where they rapidly multiply.
Bubonic plague is the most common form of plague. White blood cells are normally produced in the lymph nodes but upon infection by Y pestis, white blood cells multiply at a brisk pace, there an abnormal build-up of fluid, and the nodes begin to swell, sometimes breaking open the skin. Obvious clinical signs of bubonic plague are the following:
- Swollen lymph nodes
- The head and neck area may be visibly swollen.
- Excessive pain from the swelling.
- Lymph nodes may abscess, rupture, and drain.
- Tonsils may be enlarged.
- Loss of appetite
- Visible weight loss
- Discharge from the eyes
- Mouth ulcers
Pneumonic plague infects the lungs which often leads to highly contagious pneumonia.
Septicemic plague infects the blood where the bacteria multiply. Symptoms will mimic bubonic plague with the addition of the systemic infection of the blood.
If your dog is behaving uncharacteristically and you live in a region where plague is endemic, get to a veterinarian quickly. Timing is crucial, and treatment needs to begin before transmission of the Yersinia bacterium can occur. Generally, if plague is suspected, a vet will administer antibiotics pre-diagnosis to inhibit progression of this aggressive disease immediately. The dog will be isolated, and staff will use gloves, surgical masks, eye protection, and hygiene and disinfection protocol to protect them from respiratory droplets, body fluids, and secretions from the dog. Also, you must notify your local public health officials if you suspect your dog may have been infected.
Diagnosis of plague.
Due to the nonspecific nature of many of the plague symptoms of dogs, for example; fever, diarrhea, and depression, your veterinarian may not immediately suspect plague and will need to perform a thorough physical examination and diagnostic evaluation including blood tests and urinalysis before confirmation of a plague diagnosis. A swollen lymphatic system will clearly present as infection and blood tests will ultimately reveal an abnormally high white blood cell level if it's plague. Other bacterial diseases, such as tularemia, a bacterial septicemia, must be ruled out as the testing progresses. If admitted to an emergency clinic, the attending veterinarian needs a complete history of your dog's health, and the nature and extent of any clinical signs you have observed since he was bitten. Once plague is diagnosed, your dog is hospitalized for treatment and isolated during the infectious stage of plague to avoid exposure to other animals and people.
Treatment for the plague.
The incubation period of bubonic plague is from two-to-seven days after being bitten. During early treatment of more severe forms of plague, medications will be injected. If the dog is weak and dehydrated, an intravenous drip will be required to rehydrate him. Flea treatment will also be administered. Dogs that are not treated promptly and effectively have a high incidence of mortality. Once the dog is stable, oral medications may be given. Some of the medications used in the treatment of plague are Streptomycin, Gentamicin, Doxycycline, Tetracycline, and Chloramphenicol. Dogs remain hospitalized until there is no further danger of transmission and they are on the road to recovery from the disease.
Prevention of plague.
If you live in an area where plague occurs, do not allow your dog to roam freely. Keep him on-leash or in an enclosed, safe environment when outdoors to allow for close supervision. Regular flea medication is essential, as is ensuring your dog avoids contact with wild rodents and their burrows which are common in wildlife habitats, garbage, and woodpiles. Dogs who are neutered have less inclination to roam, and therefore to hunt rodents. And finally, flea infestations inside the home should be eliminated by pest control professionals and ongoing, regular flea control helps prevent further infestations.