Affects: Cats, Dogs
Ehrlichiosis (; also known as canine rickettsiosis, canine hemorrhagic fever, canine typhus, tracker dog disease, and tropical canine pancytopenia) is a tick-borne disease of dogs usually caused by the rickettsial agent Ehrlichia canis. Ehrlichia canis is the pathogen of animals. Humans can become infected by E. canis and other species after tick exposure. German Shepherd Dogs are thought to be susceptible to a particularly severe form of the disease; other breeds generally have milder clinical signs. Cats can also be infected.
Signs And Symptoms: The acute stage of the disease, occurring most often in the spring and summer, begins one to three weeks after infection and lasts for two to four weeks. Clinical signs include a fever, petechiae, bleeding disorders, vasculitis, lymphadenopathy, discharge from the nose and eyes, and edema of the legs and scrotum. There are no outward signs of the subclinical phase. Clinical signs of the chronic phase include weight loss, pale gums due to anemia, bleeding due to thrombocytopenia, vasculitis, lymphadenopathy, dyspnea, coughing, polyuria, polydipsia, lameness, ophthalmic diseases such as retinal hemorrhage and anterior uveitis, and neurological disease. Dogs that are severely affected can die from this disease.
Although people can get ehrlichiosis, dogs do not transmit the bacteria to humans; rather, ticks pass on the ehrlichia organism. Clinical signs of human ehrlichiosis include fever, headache, eye pain, and gastrointestinal upset. It is quite similar to Rocky Mountain spotted fever, but rash is not seen in patients.
Diagnosis: Diagnosis is achieved most commonly by serologic testing of the blood for the presence of antibodies against the ehrlichia organism. Many veterinarians routinely test for the disease, especially in enzootic areas. During the acute phase of infection, the test can be falsely negative because the body will not have had time to make antibodies to the infection. As such, the test should be repeated. A PCR (polymerase chain reaction) test can be performed during this stage to detect genetic material of the bacteria. The PCR test is more likely to yield a negative result during the subclinical and chronic disease phases. In addition, blood tests may show abnormalities in the numbers of red blood cells, white blood cells, and most commonly platelets, if the disease is present. Uncommonly, a diagnosis can be made by looking under a microscope at a blood smear for the presence of the ehrlichia morulae, which sometimes can be seen as intracytoplasmic inclusion bodies within a white blood cell.
Treatment: Supportive care must be provided to animals that have clinical signs. Subcutaneous or intravenous fluids are given to dehydrated animals, and severely anemic dogs may require a blood transfusion. Treatment for ehrlichiosis involves the use of antibiotics such as tetracycline or doxycycline for a period of three to four weeks; Alternatively minocycline or rifampicin can be used as a second option. Treatment with macrolide antibiotics like clarithromycin and azithromycin is being studied. In addition, steroids may be indicated in severe cases in which the level of platelets is so low that the condition is life-threatening.
Prevention: Tick control is the most effective method of prevention, but tetracycline at a lower dose can be given daily for 200 days during the tick season in endemic regions.
Prognosis: The prognosis for dogs with acute canine monocytic ehrlichiosis is generally good when treatment is started early. In contrast, the prognosis is more guarded in chronic disease, particularly in dogs with pancytopenia or severe bone marrow suppression, which may be associated with a poor response to treatment.