Conditions · Emergency medicine and toxicology

Mammalian bites (dog, cat, human) !

Wounds from the teeth of dogs, cats or people. They often get infected and can reach tendons, joints and bone, especially in the hand.

Updated 2026-11-01

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Why it happens

What it is

Wounds caused by the bite of a dog, cat, human or other mammal. Dog bites crush and tear tissue; cat bites are small deep punctures with a high infection rate; human bites, including the 'fight bite' on a knuckle from a punch to the mouth, carry mixed oral bacteria into tendons and joints. Every mammal bite also raises the question of rabies and tetanus prophylaxis.

Who gets it

Dog bites are the most frequent, and children are bitten most, often on the face and neck. In Colombia, aggressions by animals that can transmit rabies are a notifiable public health event with hundreds of thousands of reports a year, nearly all from dogs and cats; each one needs a rabies risk assessment. Cat bites become infected far more often than dog bites. Human fight bites are typical of young men after alcohol and fights.

Causes

Dog bites: crush and laceration injuries
Cat bites and scratches: deep punctures that seal over
Human bites: occlusional bites and clenched-fist injuries over the knuckles
Bites from bats, monkeys, rodents and livestock (rabies risk varies)
Usual bacteria: Pasteurella (cats and dogs), Capnocytophaga (dogs), Eikenella (humans), staphylococci, streptococci and anaerobes

Risk factors

Children (face, head and neck bites)
Bites on the hand, over joints or tendons, or puncture wounds
Delay in seeking care beyond several hours
Diabetes, absent spleen, cirrhosis, immunosuppression or alcohol use disorder
Unvaccinated or unknown animals

Pathophysiology

Teeth inoculate oral and skin bacteria into deep tissues. Narrow punctures close over and trap bacteria, so infection appears within 12 to 24 hours; Pasteurella can cause cellulitis in a few hours. In a clenched-fist injury the skin and extensor tendon are struck with the finger flexed; when the hand opens the wound slides away, sealing bacteria inside the knuckle joint and tendon sheath. Fast-spreading infection can follow the flexor tendon sheaths of the fingers.

Classification

By species: dog, cat, human, other (bat, monkey, rodent)
By wound: abrasion, puncture, laceration, avulsion or crush
By site: high risk (hand, foot, face, over joints, genitals) or lower risk
Rabies exposure category per national guidelines

Symptoms and signs

Puncture wounds, tears or loss of tissue
Pain, redness, swelling and pus developing within hours to a day
Small wound over a knuckle (often hidden by the patient) with pain on moving the finger
Signs of flexor tenosynovitis: finger held flexed, swelling of the whole finger, tenderness along the sheath and pain on passive extension
Fever, swollen lymph nodes and red streaks up the limb

Diagnosis

Clinical: History of the animal, its vaccination status and whether it can be observed, the circumstances (provoked or not) and the time since the bite. Examine the wound through the full range of motion of the hand, checking tendons, nerves and circulation. Any wound over a knuckle is a human bite until proven otherwise.
Tests: Wound cultures only when infected; blood cultures if there are signs of sepsis.
Imaging: X-rays for deep punctures over bones and joints, fight bites (tooth fragments, fractures, air in the joint) and suspected osteomyelitis; ultrasound for abscess.

Differential diagnosis

Cellulitis or abscess from another cause
Boxer's fracture or other hand fracture from a punch
Gout or pseudogout flare in a hand joint
Cat-scratch disease (bartonellosis) with regional lymph nodes weeks later
Self-inflicted or non-accidental injury

Goal of treatment

Clean the wound well, find deep injury, prevent infection, rabies and tetanus, and restore hand function.

Treatment

Acute: Immediate washing with soap and abundant water and high-pressure irrigation; removal of dead tissue. Many facial wounds can be closed after cleaning; puncture wounds, hand wounds and older wounds are usually left open or closed later.
Medical: Prophylactic antibiotics for high-risk wounds (cat bites, hand wounds, punctures, human bites, immunosuppressed patients), with a beta-lactam combined with a beta-lactamase inhibitor as the usual first line. Tetanus vaccine or immunoglobulin as indicated, and rabies post-exposure prophylaxis according to the Ministerio de Salud guideline.
Surgical: Surgical exploration and washout in the operating room for fight bites into the joint, flexor tenosynovitis, abscess or septic arthritis; repair of tendons, nerves and vessels; reconstruction for avulsions.
Follow-up: Wound review within 48 hours; elevation and splinting of the hand; mandatory reporting of the aggression and observation of the dog or cat when possible.
Rehabilitation: Hand therapy after tendon or joint injury; psychological support for children after severe attacks.

Complications

Cellulitis, abscess and lymphangitis
Flexor tenosynovitis, septic arthritis and osteomyelitis of the hand
Sepsis, especially with Capnocytophaga in people without a spleen
Rabies and tetanus if prophylaxis is missed
Disfiguring scars and loss of hand function

Prognosis

Most bites heal well when cleaned early and given prophylaxis when indicated. Delayed care of hand bites, especially fight bites, often leads to joint infection, stiffness and reoperation. Rabies, once symptoms begin, is almost always fatal, which is why prophylaxis matters.

Prevention

Supervise young children with animals and teach them not to disturb animals that are eating or sleeping
Vaccinate dogs and cats against rabies
Responsible pet ownership and control of aggressive dogs
Seek care the same day for any bite that breaks the skin

Test yourself

Think of the answer, then tap the question to see it.

Why are cat bites more likely to become infected than dog bites?

Cat teeth make narrow deep punctures that seal over and trap bacteria such as Pasteurella in tendons, joints or bone.

What injury should be assumed with a small wound over a knuckle after a fist fight?

A human 'fight bite' that may have entered the joint or extensor tendon; it needs exploration, X-ray and antibiotics, often surgical washout.

What are the classic signs of flexor tenosynovitis after a finger bite?

Finger held slightly flexed, uniform swelling of the finger, tenderness along the flexor sheath and severe pain on passive extension (Kanavel signs).

Which antibiotic class is first line for prophylaxis of a high-risk animal bite?

A beta-lactam combined with a beta-lactamase inhibitor, which covers Pasteurella, staphylococci, streptococci and anaerobes.

Besides infection, which two prophylaxes must be assessed after every mammal bite?

Tetanus (vaccine and, if needed, immunoglobulin) and rabies post-exposure prophylaxis according to the national guideline.

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Educational information, not medical advice. For any symptom, see a health professional.

Sources: Animal Bites (MedlinePlus, US National Library of Medicine, 2026); Human bites - self-care (MedlinePlus, US National Library of Medicine, 2026).

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