Francisella tularensis in Dogs
Tularemia is a zoonotic bacterial disease that is occasionally seen in dogs. It is associated with multiple animal species, including humans, and can be acquired from through contact with infected animals. Also commonly know as rabbit fever for its mode of transmission, even while it can infect several types of animals and be transmitted via any infected animal, as such, the bacteria can also be acquired by ingestion of contaminated water, or through contact with infected soil, where the organism can remain in an infectious state for up to several months.
Infection is often caused by ingestion of an infected mammals' tissue, such as when a dog hunts a small animal, bird or reptile, through water, or by tick, mite, flea or mosquito bite -- all of which can carry and transmit the bacteria. The bacterium may also infect a dog through its skin, or by entering its airways, eyes or gastrointestinal system.
Tularemia is found throughout much of the world, including continental Europe, Japan and China, and in the Soviet Union. In the United States, it is most common in Arkansas and Missouri, though it can be found in most parts of the U.S. It also tends to have higher seasonal incidence, with May through August being a time of increased risk. An increase is also seen during the winter rabbit hunting season, in areas where this is a common practice.
One of the most common vectors of communication of the F. tularensis bacterium is the tick, which includes the American dog tick, the Lone Star tick, and the Rocky Mountain wood tick, along with other types of ticks.
Symptoms and Types
- Sudden onset of fever
- Lack of appetite (anorexia)
- Enlargement of the lymph nodes
- Tender abdomen
- Enlargement of spleen or liver
- White patches or ulcers on the tongue
- Jaundice – may be indicated by yellow eyes
- Bacterial infection (Francisella)
- Contact with an infected source
You will need to give your veterinarian a thorough history of your dog's health and recent activities, including a recent history of boardings, outings, trips, tick bites, and experiences with other animals or with pests.
Your veterinarian will perform a complete physical exam on your dog. Standard laboratory work will include a blood chemical profile, a complete blood count, an electrolyte panel and a urinalysis. If F. tularensis is present, the results of the complete blood count may show a responsive increase in white blood cells (WBCs), but this is not always the case. Tests may also show lower than normal levels of platelets (thrombocytopenia), the cells that help in blood clotting.
The biochemistry profile may reveal abnormally high levels of bilirubin (hyperbilirubinemia) and lower than normal levels of sodium and glucose in the blood. If the blood tests reveal high levels of bilirubin, the orange-yellow pigment found in the bile, this can indicate that liver damage is occurring. This condition is commonly characterized by symptoms of jaundice. The urinalysis may also reveal high levels of bilirubin and blood in the urine.
Your veterinarian may need the assistance of a specialized laboratory service for confirmatory diagnosis. In some cases the diagnosis is not so obvious and samples will need to be taken to be sent for culture testing - controlled growth in a lab environment in order to define the causative organism.
Molecular methods such as polymerase chain reaction (PCR), a method which distinguishes the presence of disease based on its genetic code, are available in reference laboratories. The microbiologist must be informed when tularemia is suspected because F. tularensis requires special media for cultivation, such as buffered charcoal and yeast extract (BCYE). It cannot be isolated in the routine culture media because of the need for sulfhydryl group donors (such as cystein). Serological tests (detection of antibodies in the serum of the patients) are available and widely used. Cross reactivity with brucella can confuse interpretation of the results, and for this reason diagnosis should not rely only on serology.
Early treatment is the mainstay of successful resolution and cure of the symptoms. A high rate of deaths is common in patients that are not treated early. Your veterinarian will prescribe antibiotics to control the infection and its related symptoms. Your dog may need antibiotic therapy for several days for a complete resolution of the symptoms.
Living and Management
The overall prognosis is poor, especially in animals that are not treated early on in the course of the disease.
As previously mentioned, F. tularensis is a zoonotic infection, meaning that it can be passed form one species to another. If your dog is infected with this bacteria you will need to take special precautions to protect yourself from infection. The bacteria most often penetrates the body through damaged skin and mucous membranes, or through inhalation. Humans are most likely to acquire the infection by tick bite, and in some cases, simply through handling an infected animal. Tularemia can also be acquired by inhalation. In some cases, it is known to have occurred during the grooming process with dogs, and hunters are at a higher risk for this disease because of the potential of inhaling the bacteria during the skinning process. Ingesting the infected water, soil, or food that has become contaminated can also cause infection. In some other cases, it has been contracted from inhaling particles from an infected rabbit or other small rodent that was ground up in a lawnmower.
F. tularensis is an intracellular bacterium, meaning that it is able to live parasitically within the host cells. It primarily infects macrophages, a type of white blood cell, thus evading the immune system's response to destroy it. The course of the disease is dependent on the organism's ability to spread to multiple organ systems, including the lungs, liver, spleen, and lymphatic system.