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Bites and Stings

What to know about rat-bite fever



Rat-bite fever is a bacterial infection that is spread through contact with rats, other rodents, and food and beverages that are infected.

The Centers for Disease Control and Prevention (CDC) announced in May 2020 that several communities had reported increased activity of rodents.

The risk of infection due to a rat bite is approximately 10%, and as a result, children living in poverty have the highest risk of developing rat bite fever (RBF).

RBF may cause serious complications, including damage to bones and inflammation of the heart, brain and spinal cord, without antibiotic treatment. It can be fatal.

We define RBF and address its causes and treatments in this article.

What is RBF?

Image of a rat

RBF is a serious infection caused by the bacteria Streptobacillus moniliformis or Spirillum minus. They spread to humans by bites of rats, contact with urine and feces of rats, and infected food and beverages.

As researchers note in a 2020 study In the United States, more than 2 million animal bites occur annually, and rats are responsible for about 1 percent.”

They continue to report that RBF continues to grow in children under 5 years of age who are living in poor conditions.

The researchers also note that in pet stores and laboratories, people working with rats are at risk, and that the risk of an infection arising from a bite is around 10 percent.

In a 2018 analysis, between 2010 and 2016, researchers found 11 RBF reports on Vancouver Island, Canada. RBF occurred in individuals aged 5-57 years, nine of whom had pet rat bites.

RBF can cause serious complications, and as a result, an estimated 7–13% of individuals who do not receive RBF treatment die, although the incidence is higher in individuals with serious complications.


Two forms of RBF exist. The most prevalent forms in North America is called streptobacillary RBF, as it leads from infection with S. moniliformis.

Spirillary RBF, or sodoku, is the other kind. It is triggered by S. Minus bacteria, and in Asia, this is the primary form.

After one of those types of bacteria enters the body, through an open wound or the mucous membranes of the eyes, nose or mouth, a person develops RBF.

Bacteria that cause RBF are transmitted to individuals by:

  • bites or scratches from infected rodents
  • the saliva, urine, or feces of infected rodents
  • contact with contaminated surfaces
  • contaminated foods or drinks

This disease is relatively uncommon, although reports of RBF occur globally. An individual can, however have a higher risk of RBF if they:

  • handle rats as part of their work
  • live in an infested building or area
  • keep rats or other rodents as pets

RBF does not pass from person to person.


Based on the underlying bacterial infection, the symptoms of RBF differ.

S. Moniliformis has a period of incubation of 3-20 days. The interval between exposure to the bacteria and the appearance of symptoms is the incubation period.

Symptoms of streptobacillary RBF include:

  • a fever that comes and goes for several weeks
  • a rash near a rat bite
  • joint and muscle pain, especially in the lower back
  • chills
  • nausea
  • vomiting
  • a sore throat

Before the symptoms appear, a bite that causes spirillary RBF may start healing. The symptoms can take 1-3 weeks to appear and include the following:

  • a fever and chills
  • muscle and joint pain
  • a headache
  • a sore throat
  • vomiting
  • inflammation and ulceration near the site of the bite
  • a brown or purple rash
  • hard or tender lymph nodes


RBF is treated by doctors with antibiotics. If there are complications, a person takes them for 7–14 days or up to 4 weeks.

RBF can lead to serious complications if a person does not receive treatment, such as:

  • abscesses, or pockets of fluid inside the body
  • inflammation of the liver or kidneys
  • interstitial pneumonia, which causes lung scarring
  • infections of the membranes covering the brain and spinal cord
  • endocarditis, or inflammation of the membrane surrounding the heart
  • bone damage

The mortality rate is 53 percent if RBF causes endocarditis .

The current antibiotic of choice for both forms of RBF is penicillin.

However, in certain individuals, penicillin can cause allergic responses. Around 10 percent of all individuals have penicillin allergies, according to the CDC.

Signs of a penicillin allergy include:

  • hives, which are itchy, raised bumps on the skin
  • swelling of the face, hands, and feet
  • difficulty breathing
  • coughing
  • chest tightness
  • dizziness

People with allergies to penicillin can instead receive either streptomycin or doxycycline.

When to contact a doctor

RBF can cause serious, even life-threatening complications without treatment. If any alarming signs arise after a rat bite, seek urgent medical attention.

A doctor can diagnose S. Moniliformis by the use of a blood or tissue sample for examination. Usually, within 3 days, a person receives the results, although the timing can vary.

To diagnose S. minus, a doctor takes a tissue sample for testing. On a glass slide, the tissue is positioned and treated with a stain. This slide is examined by a laboratory technician and the bacteria can be identified by their scale, shape and color.


RBF is a serious infection caused by the S. moniliformis and S. minus bacteria. Through rat bites and infected food or water, these bacteria move into humans.

Usually, RBF results in nonspecific symptoms such as fever, pain in the joints, and nausea. RBF can lead to serious complications, such as endocarditis or inflammation of the membrane surrounding the heart if left untreated.

RBF is treated by doctors with antibiotics. It is critical that individuals, even if they no longer feel sick, complete the full course of antibiotics. Doing so can help to reduce recurrent infections and resistance to antibiotics.


What happens when you’re bited by a centipede?



Centipede bites are rare in humans but can cause mild to moderate pain when they do happen. Many people may experience severe symptoms or allergic venom reactions from the centipede, but these only occur rarely.

Unless the person experiences a severe allergic reaction, a centipede bite won’t require treatment. Anti-itch and pain relieving drugs can help to soothe the symptoms of a person.

The symptoms usually resolve within a couple of hours or days, and the probability of any long-term effects is small.

We address the possible symptoms and treatments of a centipede bite in this article, as well as the outlook for a person who receives one. Centipede bites are also compared with millipede bites.


Effects of a bite

While people use the word “bite,” in fact a centipede does not use its mouthparts to harm the skin. If a centipede feels threatened, it will pierce his prey’s skin with the pincer-like tips of the legs closest to the eyes, called forcipules.

The bite looks like two red marks on the skin which, due to the location of the centipede forcipules, form a V-shape.

People rarely experience serious symptoms from a bite of a centipede.

Some possible effects of a bite of one centipede include:

  • localized pain
  • swelling and redness
  • bleeding
  • itchiness or burning
  • numbness, tingling, and tenderness
  • hardening of the skin
  • throbbing
  • red streaks on the skin
  • localized infection
  • tissue death
  • swelling of the lymph nodes

In extremely rare cases, there have been reports of more severe symptoms, such as:

  • lack of oxygen to the heart muscle
  • heart attack
  • blood in the urine
  • hemoglobin in the urine
  • rhabdomyolysis, which is the break down of damaged skeletal muscle tissue
  • excessive bleeding
  • skin infections

Anaphylactic shock

Some people may get an allergic reaction to a bite of one hundredfold. Researchers in Thailand described a situation where a 23-year-old man suffered anaphylactic shock— a severe allergic reaction— after bitting him by a centipede.

An allergic reaction may occur within minutes of a bite being taken. Some signs of a severe response include:

  • facial swelling
  • generalized hives and rash on the skin
  • chest discomfort
  • loss of consciousness or responsiveness
  • severely low blood pressure, called hypotension

Centipede venom

When a person bites a hundredfold they inject venom into the skin. The venom production occurs in a gland in the forcipule. Centipedes inject venom into their prey for defense and defence. Sometimes, a human might feel the centipede threatened.

Researchers have isolated more than 500 components of centipede venom but only a few of these have been identified.

Some of the components include hormones, such as serotonin and histamine, which occur naturally in the brain. Researchers note that usually, these substances do not cause neurological effects in humans.

Neurological symptoms (rare)

Some people can rarely report the following neurological symptoms from a bite of one centipede:

  • headaches
  • anxiety
  • dizziness
  • the feeling of losing consciousness

After a centipede bite, a few people reported euphoric feelings, psychological effects and memory disturbances.

Scientists will continue studying centipede bites to establish how the various components of centipede venom affect humans.


Persons may be frightened when a centipede bites them, both because of the bite pain and the multi-legged creature’s presence. Nonetheless, a person will not need to seek medical attention in most situations, because a bite of centipede is rarely serious.

If a person is seeing a doctor, the doctor may suggest that treatments be used to soothe the pain, itchiness and skin swelling. The symptoms, nonetheless, tend to resolve themselves within a few hours, or at most a few days.

Many people may need a pain reliever, like acetaminophen, or an anti-inflammatory, like ibuprofen, for example. Cortisone cream and antihistamines can also help reduce allergy symptoms.

If a person has a severe allergic reaction to a bite of one centipede, such as an anaphylactic shock, they need immediate medical attention. Physicians treat anaphylactic shock with:

  • epinephrine
  • intravenous fluids
  • intravenous antihistamine

If someone experiences anaphylactic shock, auto-injectors with epinephrine, such as an EpiPen, can reduce the symptoms and prevent death. However, as centipede bites are uncommon, a person may not know they’re allergic to centipede venom until a bite is given. As a result, they may not have an auto-injector for the epinephrine.


Persons with centipede bites in the affected area can experience local reactions, but the symptoms typically resolve within a few hours to a few days.

In some cases, underlying conditions will affect a person’s outlook with a bite of centipede. People with diabetes, for example, may experience more severe skin reactions and infections following a bite of one hundred per cent.

In cases of anaphylactic shock, if a person receives timely treatment, clinical signs will likely improve without long-term consequences. Doctors may prescribe an auto-injector with epinephrine and recommend avoiding centipedes.

Millipede bites

Millipedes protect themselves by secreting a toxic fluid on the side in their body from glands. The liquid is having a corrosive effect on the skin, and people in the affected area can feel burning and redness. Doctors can prescribe antibiotics and topical pain relievers if necessary.

Immediately after exposure to the millipede toxin washing the area with soap and water may help reduce symptoms.

Sometimes the toxic liquid can cause a change of local skin colour. The affected area may turn brown or black, and this change in color can last for months.


People who are getting the toxic liquid in their eyes from a millipede can experience more severe effects. Ulcers may grow on the cornea, or may infect the eye. If this occurs, people should meet with an ophthalmologist for treatment. Treatment may include following:

  • eye irrigation
  • fluorescein staining
  • topical antibiotics
  • cycloplegic drugs


Centipedes rarely bite humans, but this is generally because they feel threatened when they do.

After a centipede bite, most people will experience only short-term pain, skin irritation and redness. Many people may however be resistant to the venom that is injected into the skin by the centipede.

Unless the person experiences a severe allergic reaction, a centipede bite usually requires no medical attention.

Pain relievers and anti-itch medications may be helpful in easing a centipede bite’s pain. The bite’s symptoms usually go away within a few hours to a few days.

Usually, centipede bites don’t have long lasting results.

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