CONDITION
Ehrlichiosis
Ehrlichiosis is an infection caused by bacteria carried by ticks. These bacteria live inside certain white blood cells and can affect how the immune system functions, sometimes leading to problems with blood cells, clotting, or the body's ability to fight other infections. The condition is seen primarily in dogs that have travelled to or live in regions where specific tick species are found, particularly parts of continental Europe, Africa, Asia, and the Americas. Owners may notice signs that develop weeks to months after a tick bite, though the range is broad. These can include lethargy, reduced appetite, fever, unexplained bruising or nosebleeds, swollen lymph nodes, or joint discomfort. In some cases, signs are subtle or intermittent, and the infection may only be discovered during investigations for other concerns. Some dogs develop long-term effects if the infection persists. This page explores the signs that may prompt consideration of ehrlichiosis, what happens inside the body during infection, how the condition is investigated through blood tests and other means, and the approaches used to address it. The focus is on helping owners understand the shape of the condition and the thinking that guides decisions around it.
Why this matters now
Ehrlichiosis can affect dogs of any age, though it is often identified in adults that have travelled to or lived in regions where the brown dog tick or other carrier species are established. Young dogs and certain breeds, particularly German Shepherd Dogs and Doberman Pinschers, may be more susceptible to developing clinical signs after infection. The condition is linked to tick exposure, so risk tends to be higher during warmer months when ticks are active, or following travel to endemic areas in continental Europe, the Mediterranean basin, Africa, parts of Asia, and the Americas.
The infection typically moves through phases, though not every dog shows signs at each stage. An acute phase may appear one to three weeks after the tick bite, with fever, lethargy, and mild bleeding tendencies. This can resolve on its own or progress to a subclinical phase where the dog appears well but the bacteria persist. In some cases, particularly if untreated, a chronic phase develops weeks to months later, with more persistent or severe problems affecting blood cells, the immune system, or multiple organs. The trajectory varies widely between individuals, and some dogs remain in the subclinical phase without further progression.
Signals & patterns
Early signals
Lethargy and reduced activity
The dog may seem less interested in walks, play, or usual routines, often appearing quieter or more reluctant to move. This can develop gradually over days to weeks and may be subtle enough to be attributed to other causes initially.
Reduced appetite or weight loss
A mild drop in interest in food, or a slower pace of eating, may be noticed. Some dogs lose weight over time, particularly if the infection persists or other signs develop.
Intermittent fever
Body temperature may rise and fall, though owners typically notice this as warmth to the touch, shivering, or general discomfort rather than measuring temperature directly. Fever may come and go, making it difficult to detect without observation over several days.
Swollen lymph nodes
Lymph nodes under the jaw, in front of the shoulders, or behind the knees may feel larger or firmer than usual. This reflects the immune system's response to the infection and is sometimes found during routine handling or grooming.
Mild bruising or small bleeds
Small purple or red spots may appear on the gums, belly, or inner ear flaps, or the dog may have brief nosebleeds or blood in the urine. These reflect early effects on platelets or clotting and can be easy to miss.
Later signals
Persistent or worsening bleeding
Nosebleeds, blood in the urine or stool, or larger areas of bruising may become more frequent or pronounced. This signals more significant disruption to platelet numbers or function.
Lameness or joint swelling
Stiffness, reluctance to bear weight, or visible swelling in one or more joints can develop as the infection affects joint linings or causes immune-mediated inflammation. This may shift between legs or persist in one area.
Neurological or eye changes
Some dogs develop signs such as head tilt, loss of balance, seizures, or changes in the appearance of the eyes, including cloudiness or bleeding inside the eye. These patterns suggest more widespread or severe involvement.
Marked pale gums or weakness
Gums may appear white or very pale pink, and the dog may tire quickly, breathe more rapidly, or collapse after mild exertion. This can reflect severe anaemia or low platelet counts affecting oxygen delivery and clotting.
Click to read about the biological mechanisms
How this is usually investigated
Investigation of ehrlichiosis typically begins with a detailed history of recent travel, tick exposure, and the timeline of signs. Physical examination may reveal fever, enlarged lymph nodes, pale gums, or small haemorrhages. Blood tests form the foundation of the diagnostic process, looking both for changes in blood cell counts and for evidence of the infection itself, though no single test provides certainty in every case.
Complete blood count
Serology (antibody testing)
PCR testing
Blood biochemistry and urinalysis
Bone marrow examination
Options & trade-offs
Management of ehrlichiosis usually involves a combination of antimicrobial treatment, supportive care, and monitoring for complications. The approach is shaped by the stage of infection, the severity of signs, and the presence of secondary problems such as anaemia or bleeding. Different dogs tolerate different aspects of treatment differently, and the response can vary widely between individuals.
Doxycycline treatment
Doxycycline, a tetracycline antibiotic, is used to target the bacteria inside infected cells. Treatment is typically given for four weeks, though longer courses may be considered in chronic cases. The medication is usually given orally, once or twice daily.
Trade-offs: Doxycycline can cause nausea or vomiting in some dogs, particularly if given without food, and it may stain developing teeth in very young animals. Response is often gradual, with clinical improvement appearing over days to weeks, and blood test abnormalities may take longer to resolve.
Supportive care for anaemia and bleeding
Dogs with severe anaemia or very low platelet counts may require additional support, which can include transfusions of red blood cells or plasma, fluid therapy, and careful monitoring of clotting function. Activity may be restricted to reduce the risk of injury in dogs with significant bleeding tendencies.
Trade-offs: Transfusions carry risks including immune reactions and the potential for transmission of other infections, and they address the immediate problem rather than the underlying cause. Not all dogs with low cell counts require transfusion, and the decision depends on clinical signs as much as laboratory numbers.
Immunosuppressive therapy
In cases where the immune system appears to be attacking the body's own blood cells, medications such as corticosteroids or other immunosuppressive drugs may be used alongside doxycycline. The aim is to reduce the rate of cell destruction while the antibiotic addresses the infection.
Trade-offs: Immunosuppressive drugs can increase susceptibility to other infections and may cause side effects including increased thirst, appetite, and urination. Their use requires careful balancing, as suppressing the immune response too much may interfere with clearing the bacteria.
Monitoring and follow-up testing
Blood tests are typically repeated during and after treatment to assess response, looking for improvement in cell counts and resolution of other abnormalities. Some dogs require prolonged monitoring, particularly if the infection was chronic or if complications developed.
Trade-offs: Repeated blood tests add to the cost and require regular handling, which some dogs find stressful. The timeline for normalisation is variable, and persistent low-grade changes do not always indicate treatment failure or the need for additional intervention.
Common misconceptions
"If a dog has been treated for ehrlichiosis, it cannot become infected again."
Treatment clears the active infection, but it does not confer immunity. Dogs remain susceptible to reinfection if exposed to infected ticks again, and protective antibodies do not prevent new bacteria from establishing themselves in white blood cells.
"A positive antibody test means the dog is currently infected and needs treatment."
Antibodies can persist for months or years after an infection has been successfully treated or has resolved on its own. A positive result indicates exposure at some point, but additional tests such as PCR or assessment of clinical signs and blood cell counts are needed to determine whether active infection is present.
"Removing a tick within a few hours always prevents ehrlichiosis."
While prompt tick removal reduces the risk of transmission for some tick-borne infections, the exact timeframe required for Ehrlichia transmission is not firmly established and may be shorter than for other pathogens. Removal as soon as a tick is noticed is sensible, but it does not guarantee that transmission has not occurred.
Related conditions
Anaplasmosis
Anaplasmosis is another tick-borne bacterial infection that can produce clinical signs very similar to ehrlichiosis—including fever, lethargy, and effects on blood cells—and the two conditions may occur together in dogs exposed to ticks carrying multiple pathogens. Distinguishing between them often requires specific blood tests, as their presentations and geographic distributions can overlap.
Babesiosis
Babesiosis is a tick-borne parasitic infection that destroys red blood cells and can present with overlapping signs such as fever, weakness, and abnormal bleeding, making it part of the differential diagnosis when ehrlichiosis is considered. Co-infection with both organisms can occur in the same animal, and both may contribute to anaemia and clotting disturbances.
Lyme Nephritis
Lyme nephritis arises from immune-mediated kidney inflammation following tick-borne Borrelia infection, and dogs with a history of tick exposure may carry multiple tick-borne pathogens concurrently, including Ehrlichia species. Both conditions illustrate how the immune response to persistent tick-borne bacteria can lead to organ-specific complications beyond the initial infection.
Immune-Mediated Polyarthritis
Immune-mediated polyarthritis can occasionally develop in dogs with ehrlichiosis, as the immune response to the intracellular bacteria may trigger inflammation in multiple joints. Joint discomfort in a dog with fever and a history of tick exposure may prompt investigation for both conditions.
Feline Immunodeficiency Virus (FIV)
Feline immunodeficiency virus causes progressive immune suppression in cats, which can make them more vulnerable to secondary infections and alter the course of other immune challenges. While ehrlichiosis is seen primarily in dogs, the concept of persistent infection affecting immune cell function and predisposing to complications is shared between the two conditions.
Understanding how ehrlichiosis fits into the broader landscape of tick-borne infections may be useful, as dogs exposed to one pathogen may have encountered others. The Immune & Inflammatory Health pillar explores related conditions and the ways in which infections and immune responses interact. For dogs that have travelled or live in endemic areas, patterns of tick activity and the practical aspects of tick prevention can be part of ongoing conversations.