Ehrlichiosis (Tick Fever)
The Disease and its Transmission
Ehrlichiosis (also called “tick fever”) is an infectious disease seen across the continental U.S. and occurs with the most frequency in the southern states and desert states. Since systemic signs of this disease are often vague and mild in the early stages, ocular changes may be the first indication to test for Ehrlichiosis. Ocular manifestations include uveitis, retinal disease, and corneal opacities. Early detection, diagnosis, and treatment greatly increase chances for saving vision and even the life of a pet. Rhipicephalus sanguineus, the common brown dog tick, transmits ehrlichiosis to dogs. The disease is spread by a bite from an infected tick; in other words, direct contact between a healthy dog and an infected dog will not spread the disease. Canine ehrlichiosis does not cause disease in humans. Ticks may not always be present when the first signs of disease appear because of the long incubation period of eight to twenty days and the tick’s ability to transmit disease for many months after it becomes infected. Surprisingly, the majority of patients diagnosed do not have a history of tick infestation as it only takes one bite for transmission to occur. Ehrlichiosis may appear at any time during the year, not just tick season, due to the chronic nature of the disease, and because of this tick’s ability to survive indoors throughout the year.
Diagnosis
History and clinical signs may be suggestive of ehrlichiosis while general blood tests may increase suspicion. Ehrlichiosis commonly causes changes in blood screening tests. Once suspected, ehrlichiosis can be diagnosed by sending a blood sample to a laboratory for specific testing. Diagnosis is important for treatment and prevention.
Symptoms
Symptoms of ehrlichiosis are often diverse, vague and can vary during the three different phases of the disease. The first phase, called the acute phase, occurs eight to twenty days following exposure. During this phase, mild signs including fever, nasal discharge, anorexia, lymph node enlargement, and breathing difficulty may occur. Unfortunately, these signs are not specific for ehrlichiosis. After one to two weeks, the pet recovers. The next phase, the subclinical phase, shows no signs and lasts up to four months. During this time, the pet may mount a sufficient immune response to rid itself of the disease. If not, the chronic phase begins. Signs during this phase can be severe and may include depression, weight loss, abdominal tenderness, and bleeding tendencies.
Signs of a poor ability to clot the blood include bleeding from the nose or gums, coughing up blood, or the formation of small bruises. This phase generally continues until a diagnosis can be made and treatment begun.
Treatment
Treatment of ehrlichiosis depends on the severity of the disease at the time of detection. In severe cases, immediate supportive care may include blood transfusions and fluid administration. To treat ocular diseases associated with ehrlichiosis, therapy may include corticosteroids. The ehrlichiosis organism is susceptible to many different antibiotics, but the current antibiotic of choice is doxycycline. This type of antibiotic is works quickly and is effective in most cases. German Shepherds, in particular, are more sensitive to this disease and may require more rigorous and long-term therapy. Once treatment ceases, prevention is important to lower the chances of reinfection. Discuss tick control options with your primary veterinarian.
Prevention
Unfortunately, no effective vaccine exists to prevent ehrlichiosis. However, due to the life cycle of the brown dog tick, other methods of prevention can be employed. Unlike other ticks, which feed on many different kinds of hosts, the brown dog tick feeds only on dogs and survives mainly in areas where dogs live. This facilitates effective tick control. After treatment of ehrlichiosis, no lasting immunity develops. Tick control is often the best method to prevent reinfection; infected ticks may transmit the disease for five months or longer. Therefore, tick control in the environment and on the dog should be maintained on a regular basis.
Prognosis
Tick fever can be a chronic, debilitating, and even fatal disease if not treated. However, successful treatment of ehrlichiosis is common if the disease is detected early. Ocular disease may provide the first clue in the diagnosis of ehrlichiosis. Most ocular diseases associated with ehrlichiosis require aggressive and prompt therapy to prevent permanent damage. Once treatment is finished, prevention by control of the tick population will help to decrease the chance of reinfection so your pet can continue to lead a normal life.
