Pasteurella multocida can be dangerous, especially when infection spreads beyond the skin or strikes someone with a weakened immune system. Most infections from animal bites or scratches stay localized and respond well to antibiotics, but when the bacteria reach the bloodstream, the mortality rate is roughly 31%. The level of danger depends heavily on how the infection was acquired, how quickly it’s treated, and the person’s overall health.
How Common the Bacteria Actually Is
Pasteurella multocida lives in the mouths and upper airways of most household pets. Between 70% and 90% of healthy cats carry it in their throats, along with 20% to 50% of dogs. The bacteria don’t make these animals sick. They’re simply part of the normal oral flora, which means any bite, scratch, or even a lick on broken skin can introduce the organism into your body.
Why Cat Bites Are Riskier Than Dog Bites
Cat teeth are narrow, sharp, and designed to puncture. When a cat bites, its teeth push bacteria deep into soft tissue, and the small wound closes up quickly afterward, trapping the bacteria underneath. This creates an ideal environment for infection to take hold in tendons, joints, and bone. Dog bites tend to cause more surface-level tearing, which actually allows better drainage and cleaning.
Because of that deep puncture mechanism, cat bites carry a higher risk of tendon sheath infections, joint infections, and bone infections. Bites to the hands and fingers are particularly concerning because tendons and joints sit close to the skin surface there, giving bacteria a short path to vulnerable structures.
How Quickly Symptoms Appear
Pasteurella infections move fast. Inflammation at the bite or scratch site typically develops within the first 24 hours, often within just a few hours. You’ll usually notice redness, swelling, warmth, and significant pain around the wound. This rapid onset is actually one of the distinguishing features of Pasteurella compared to other wound infections, which often take two or three days to become noticeable.
If the infection stays in the skin and the tissue just beneath it, antibiotics generally clear it without lasting problems. The concern is when treatment is delayed or when the bacteria get a head start in deeper tissue.
When It Becomes Serious
In a small percentage of cases, Pasteurella multocida doesn’t stay local. It can spread through the bloodstream and seed infections in distant organs. The documented complications include:
- Bloodstream infection (sepsis): the bacteria enter the blood and trigger a body-wide inflammatory response that can progress to organ failure
- Heart valve infection: both natural and prosthetic heart valves can be affected
- Meningitis: infection of the membranes surrounding the brain, reported particularly in very young children and older adults after cat licks or bites to the face
- Bone and joint infections: especially following cat bites or in people with joint replacements
- Brain abscess: rare, but documented
When infection reaches the bloodstream, brain, or heart valves, the picture changes dramatically. The mortality rate for Pasteurella bacteremia sits around 31%, and cases involving meningitis or heart valve infection carry a similarly grim prognosis, with roughly 30% of patients not surviving.
You Don’t Always Need a Bite
Bites and scratches are the most common route of infection, but they aren’t the only one. A study of 79 Pasteurella cases identified 34 that occurred without a bite. Open wounds were the most frequent entry point, particularly on the lower legs. Transmission routes included pet licks on broken skin, wound contamination from contact with pet saliva or dander, and even inhalation.
Some of the documented cases were striking in how indirect the exposure was: a foot ulcer infected after stepping in dog drool, a wound contaminated by socks covered in cat hair and dander that led to bloodstream infection, and severe throat swelling after eating food that a dog had partially eaten. These cases are uncommon, but they illustrate that any contact between pet saliva and non-intact skin carries some risk.
Non-bite infections tend to be more dangerous overall. They’re more likely to require intensive care, more likely to occur in people who already have serious health problems, and more likely to be fatal.
Who Faces the Greatest Risk
For a healthy adult who cleans a cat scratch promptly and gets antibiotics early, Pasteurella is usually manageable. The real danger concentrates in people whose immune systems are compromised or whose bodies are already under strain. Specific risk factors for severe or fatal Pasteurella infection include:
- Older age
- Chronic lung disease
- Diabetes
- Liver cirrhosis
- Kidney disease, particularly dialysis dependence
- Immune suppression from medications or conditions like organ transplant, cancer treatment, or HIV
People with multiple overlapping conditions face the highest risk. One documented case involved a man with kidney failure, a failed transplant, diabetes, and heart disease who developed life-threatening bacteremia after multiple cat scratches. The combination of immune suppression and limited organ reserve left his body unable to contain the infection.
If you have a joint replacement, you should also be aware that Pasteurella can infect prosthetic joints, and cat bites near a replaced joint warrant urgent medical attention.
How the Bacteria Cause Damage
Pasteurella multocida has several built-in tools that help it survive in human tissue. A polysaccharide capsule coats the bacterium and shields it from your immune cells. It also produces a toxin and molecules on its surface that trigger intense inflammation, which is why the redness and swelling at a bite site can look alarming within hours. Iron acquisition proteins allow the bacteria to scavenge iron from your tissues, fueling their growth. Together, these features let the organism establish infection quickly and, in some cases, outpace your immune response before treatment begins.
What Treatment Looks Like
The good news is that Pasteurella multocida responds to common antibiotics. For localized wound infections, oral antibiotics typically resolve the problem within days to weeks depending on how deep the infection has reached. The key variable is timing. Starting antibiotics within hours of a bite, before infection has a chance to establish itself in deeper tissue, dramatically improves outcomes.
For deeper infections involving bones, joints, or tendons, treatment lasts longer and may require intravenous antibiotics initially. Surgical drainage or cleaning of the wound is sometimes necessary, particularly for abscesses or infected joint spaces. Bloodstream infections and organ involvement require hospitalization and aggressive treatment, and even with appropriate care, outcomes in these cases are not guaranteed.
Thorough wound cleaning immediately after an animal bite or scratch is the single most important thing you can do before reaching medical care. Flushing the wound with clean water and mild soap helps reduce the bacterial load and buys time. Any bite that punctures the skin, particularly from a cat, warrants professional evaluation rather than a wait-and-see approach.