CONDITION
Bartonellosis
Bartonellosis is an infection caused by bacteria of the Bartonella genus, which can affect dogs and cats in different ways. These bacteria are typically transmitted through bites, scratches, or contact with fleas, and they can establish persistent infections that may affect the blood, immune system, heart valves, or other organs. In many cases, infected animals show no signs at all, though some develop fever, lethargy, inflammation in various parts of the body, or less common patterns involving the heart, eyes, or nervous system. Owners often arrive at this page after a positive test result in an animal that appears well, or after episodes of unexplained fever, lameness, or swelling that have been difficult to link to a clear cause. Because the signs can be subtle, intermittent, or absent, and because these bacteria are found in healthy animals as well as unwell ones, the question of what the test means for a particular pet is often central. This page explores what patterns of illness can be associated with Bartonella infection, how the bacteria interact with the body, how infection is detected and interpreted, and what approaches exist when treatment is considered. The aim is to help you understand what may be happening and what conversations may follow.
Why this matters now
Bartonella infection can occur at any age, though younger animals may be more likely to encounter the bacteria through flea exposure or contact with other animals during socialisation. Cats that spend time outdoors, particularly those that hunt or interact with feral populations, tend to have higher exposure rates. In dogs, the pattern is less clear, though working dogs, those in multi-animal households, or animals with a history of tick or flea burden may encounter the bacteria more frequently. There is no strong breed predisposition, though immune function and concurrent illness can influence whether infection leads to signs.
The course of Bartonella infection is highly variable. Many animals carry the bacteria for months or years without ever showing signs, and the infection may resolve spontaneously in some cases. In others, signs may appear weeks to months after exposure, often as intermittent episodes of fever, lameness, or malaise that come and go without obvious pattern. Progression to more persistent or organ-specific illness—such as inflammation of the heart valves, eyes, or nervous system—occurs in a minority of cases and may develop gradually over months, though it can also emerge without preceding signals.
Signals & patterns
Early signals
Intermittent fever without clear cause
The animal may have episodes of raised body temperature that come and go over days or weeks, often without other obvious illness. These fevers may be noticed as warmth to the touch, quieter behaviour, or reduced appetite during the episodes, and they may resolve on their own between episodes.
Shifting lameness or stiffness
Some animals develop lameness that moves from one leg to another, or stiffness that seems to come and go. This can reflect inflammation in joints or bones, and it may be more noticeable after rest or in cooler weather, though the pattern is often unpredictable.
Lethargy or reduced engagement
A general drop in energy or enthusiasm for usual activities may be subtle and gradual. The animal may sleep more, show less interest in play or interaction, or seem slower to respond to familiar routines, though appetite and other functions may remain normal.
Swollen lymph nodes
Lymph nodes under the jaw, in front of the shoulder blades, or behind the knees may become enlarged and firm. This can be felt during handling or grooming and may occur with or without other signs of illness.
Later signals
Heart murmur or exercise intolerance
In some animals, bacteria settle on the heart valves and cause inflammation that interferes with normal blood flow. This may be detected as a new murmur during examination, or the owner may notice reduced stamina, breathlessness, or reluctance to exert themselves as they once did.
Eye redness or vision changes
Inflammation inside the eye or at its surface can cause redness, squinting, discharge, or changes in how the animal navigates familiar spaces. These changes may develop gradually or appear suddenly, and they may affect one or both eyes.
Neurological changes
Less commonly, infection can affect the nervous system, leading to changes in coordination, balance, behaviour, or awareness. These signs may include tremors, head tilt, circling, or altered responsiveness, and they tend to develop over days to weeks.
Click to read about the biological mechanisms
How this is usually investigated
Options & trade-offs
Last reviewed: Invalid Date ·