Rat Bite

Medically Reviewed By William C. Lloyd III, MD, FACS
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What is a rat bite?

A rat bite is a rodent bite. Rodent bites account for about 3% of animal bites in the United States. Rat bites are the most common type of rodent bite and account for 1% of animal bites. Like other animals, rats bite when they feel startled or threatened. This is true for rats in the wild and for rats people keep as pets. Children are more likely to act in ways that startle animals in general, including rats. This puts them at higher risk of rat bites.

Depending on how the rat bites, it may look like a small puncture wound or it can tear the skin. This can cause bleeding, swelling and pain. Rat bites can also transmit disease. This happens about 10% of the time.

The main concern with a rat bite is an infection called rat-bite fever. It is a bacterial infection that can be fatal without treatment. Signs and symptoms develop anywhere from 3 to 21 days after the bite. Rat-bite fever symptoms include fever, chills, headache, and skin rash. If these symptoms develop after a rat bite, seek immediate medical care.

There are two types of rat-bite fever (RBF):

  • Spirillary RBF is caused by the bacteria Spirillum minus.
  • Streptobacillary RBF is caused by the bacteria Streptobacillus moniliformis.

Other names for rat-bite fever include streptobacillosis, spirillary fever, bogger, and epidemic arthritis erythema.

Immediate rat bite treatment involves thoroughly washing the wound with soap and large amounts of water. If the wound is bleeding, use clean gauze or a clean towel to apply pressure. Use an icepack to help reduce swelling and pain. Contact your doctor to see if you need to make an appointment.

Seek prompt medical care if the bite is bleeding and you can’t get it to stop after 15 minutes. You should also see a doctor if you have a weakened immune system due to medications, cancer, HIV, diabetes, or another medical condition.

Seek immediate medical care if you develop symptoms of rat bite fever or if the wound shows signs of infection. This includes increasing pain, redness, warmth or fever.

What are the symptoms of a rat bite?

Rat bites can be puncture wounds or they can tear the skin, depending on how they bite. Like any animal bite, it can be painful and cause swelling and bleeding. It’s important to monitor the wound for signs of infection, such as warmth, redness, or worsening pain. See a doctor right away if these rat bite symptoms develop.

Common symptoms of rat-bite fever

Rat-bite fever symptoms usually start within 3 to 10 days of the rat bite, but can take as long as 21 days. With streptobacillary RBF, the bite itself usually heals. Common symptoms of streptobacillary RBF include:

  • Headache
  • Joint pain and swelling, which occurs in about half of cases and often affects the knees
  • Red, flat rash with small bumps, which occurs in up to 75% of cases. The rash tends to appear within 2 to 4 days of the fever. It mainly affects the arms, hands, legs and feet. Joint pain and swelling typically follow the rash.

In spirillary RBF, the symptoms usually take three weeks to appear. The fever may come and go, and the rash may be all over the body. Other symptoms include swollen lymph nodes and an ulcer at the wound site with red streaks around it. Joint and muscle involvement is rare.

In both cases, symptoms can resemble other conditions. This can delay diagnosis, so it’s important to communicate information about any potential rat bite.

Rat-bite fever can be life-threatening. Seek immediate medical care (call 911) if you, or someone you are with, have any symptoms of rat-bite fever.

What causes a rat bite?

Animals, including rats, bite when they perceive a threat or something surprises or startles them. Rat bites can transmit several diseases, but rat-bite fever is the main concern. It can be deadly without prompt treatment. To complicate matters, it can be difficult to diagnose.

Rat-bite fever is a bacterial infection that develops in about 10% of rat bites. There are two types of bacteria that cause it:

  • Streptobacillus moniliformis, which is the only reported form in North America, according to the CDC (Centers for Disease Control and Prevention)
  • Spirillum minus, which occurs in Asia

What are the risk factors for a rat bite?

Anyone can get bitten by a rat. The risk is higher if you live in areas with rats, work with rats, or have a pet rat. Children are more at risk than adults because they are more likely to act in ways that startle or threaten the rat.

People with weakened immune systems are at higher risk of complications, including infections, from rat bites. This includes people with cancer, diabetes, HIV, and liver disease. It also applies to people who take medicines to suppress their immune system, pregnant women, and older adults. Children less than 5 years of age have a higher risk of infection as well because their immune systems may not be fully developed.

Reducing your risk of a rat bite

To reduce the risk of a rat bite, it’s important to understand animals. Avoid wild animals and animals you don’t know. Monitor children when they are near animals, including pets. Everyone around animals should follow these rules to avoid startling or threatening situations:

  • Handle animals gently.
  • Leave them alone when they are eating or feeding their young.
  • Never tease an animal.

Always wash your hands after handling a rat or its cage, bedding, urine or droppings. If you are bitten by a rat, washing the wound with soap and large amounts of water may flush germs out of it and reduce your risk of rat-bite fever. Contact your doctor for advice about medical care.

How do doctors diagnose a rat bite?

Diagnosing a rat bite relies on your ability to identify the animal. Diagnosing rat-bite fever can be challenging. In part, this is because the symptoms are nonspecific, meaning they resemble many other systemic illnesses. It is also difficult to culture—or grow—the bacteria that cause rat-bite fever in a lab. These issues can cause a delay in diagnosis unless you communicate about a recent bite, even a suspected or potential rat bite.

What are the treatments for a rat bite?

Rat bite treatment starts with washing the bite with soap and large amounts of water. Apply pressure with a clean towel or gauze to stop any bleeding. Apply antibiotic ointment and cover it with a sterile bandage. Use an ice pack or over-the-counter pain relievers if necessary.

If rat-bite fever develops, it requires prompt treatment with antibiotics. Doctors may start IV (intravenous) antibiotics and then transition treatment to oral antibiotics. The total duration of antibiotic treatment is usually two weeks. It’s important to finish the full course of antibiotics, even if you start to feel better. Stopping antibiotics before treatment is complete increases the risk of developing a resistant infection and complications.

What are the potential complications of a rat bite?

Infection, particularly with rat-bite fever, is the main complication of a rat bite. Most people recover completely from rat-bite fever with proper treatment. Without prompt treatment, rat-bite fever can cause serious complications including:

  • Adrenal gland failure
  • Kidney damage

Left untreated, rat-bite fever is fatal in 10% of cases.

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Medical Reviewer: William C. Lloyd III, MD, FACS
Last Review Date: 2021 Mar 11
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THIS TOOL DOES NOT PROVIDE MEDICAL ADVICE. It is intended for informational purposes only. It is not a substitute for professional medical advice, diagnosis or treatment. Never ignore professional medical advice in seeking treatment because of something you have read on the site. If you think you may have a medical emergency, immediately call your doctor or dial 911.
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