Rat Bite Fever

Rat Bite Fever


There is a disease called "Rat Bite Fever". It's very rare. But it can spread easily through a bite or a scratch from a rat. The disease can be quite serious, even fatal, if not treated appropriately.

The increasing popularity of rats as pets may contribute to more cases.

There are a lot of ways to catch Rat Bite Fever (RBF) - even though it is rare. It doesn't have to be a bite. A rat rummages though your garbage and bites you.

A pet rat or a lab rat scratches you. You have rats for a pet snake's food and their droppings get into your food. You eat food from a restaurant contaminated by urine.

The infection occurs worldwide, but there are two different bacteria that cause the infection in different parts of the world:

  • Streptobacillus moniliformis in North America and Europe 
  • Spirillum minue in Asia and Africa

Rat Bite Fever does not spread from person to person.

Rat Bite Fever in North America and Europe

In North America, Streptobacillary RBF is caused by Streptobacillus moniliformis, which is a gram-negative bacteria which is part of the normal bacteria of rats (the normal flora). It is thought many if not most rats - whether domestic pets or wild - carry the bacteria in the US. It is thought 1 in 10 rat bites may transmit the infection.​

Most infections in the US appear to be due to kids handling pet rats. In one study, which looked at 17 cases in San Diego County, California, 94% were due to handling pet rats and it was an infection largely of children (median age was 10 years).

It is thought that 1 in 1000 US homes have a pet rat.

People become sick 3-10 days after being bitten or scratched by a rat (or eating contaminated food). It can take up to 3 weeks to become sick. Usually the bite or scratch has healed and the infection does not at first seem connected to the bite or scratch when someone becomes ill.

About 2-4 days after the fever begins abruptly, someone may develop a rash on the hands and feet (with red with flat areas and small bumps). Some may have painful joints.

In general symptoms include:

  • Fever
  • Shaking Chills
  • Joint Pain
  • Rash
  • Muscle Pain
  • Vomiting
  • Headache
  • Sore Throat

Symptoms may be vague and non-specific. They may be considered to be the flu or gastroenteritis.

However, the disease can become quite serious it can cause: a heart infection (endocarditis or myocarditis), meningitis, lung problems (interstitial pneumonia), liver or spleen inflammation, joint damage, kidney damage, and swelling (hepatosplenomegaly), enlarged lymph nodes. The larger the initial exposure, the more damage the disease may do.

This can be a fatal infection. Without treatment, 1 in 10 die from the infection. In 2015, a 6-month-old baby died from RBF after a bite from a rat raised as food for the family's pet snake. A 10-year-old boy died in San Diego in 2013 after a scratch from his rat. His doctor, seeing an otherwise healthy kid, had thought he simply had gastroenteritis.

Fortunately, the infection is fairly rare. The disease is not well tracked, but in the US, there are cases reported each year. There are fewer cases in Europe (the UK sees 2 cases reported a year).

Because the infection is difficult to diagnose, it is often not diagnosed. The bacteria responds to empiric antibiotics that doctors may choose without knowing what the bug is - and so many get better without even knowing they were infected.​

Rat Bite Fever in Asia and Africa

The other type of Rat Bite Fever is Spirillary RBF which is caused by Spirillum minus. It is usually seen in Asia. It is also called sodoku in Japan. The disease is often spread through food or water contaminated by rats (urine or droppings).

Unlike the other RBF, Spirillary RBF involves the wound if there is one.

What the disease is like:

  • Fever (may come and go)
  • Ulcer and swelling near wound (if there is one)
  • Slow healing wound (if there is one)
  • Swollen lymph nodes
  • Rash (red or purple flat patches)
  • Gastroenteritis

Symptoms usually begin 1-3 weeks after exposure.

This disease is treated by penicillin. It can be treated correctly without laboratory diagnosis.​

Is it serious?

Yes, maybe 1 in 10 will die without treatment. It can cause serious heart and brain infections.

How is treated?

Fortunately, the bacteria respond to penicillin (and potentially other antibiotics like doxycyline). These antibiotics may be given empirically even without a definitive diagnosis. 

How is it diagnosed?

Diagnosis is often delayed. The initial symptoms are very non-specific and resemble mild illnesses. With the US form (Streptobacillary RBF), the wound has usually healed and someone may not even mention it to their health care providers. The bacteria are difficult to diagnose in a laboratory. PCR detection may be required.

Treatment is often empiric, given before a definitive diagnosis, through the laboratory, is made.

How is it transmitted?

  • Bites
  • Scratches
  • Food contaminated by rat droppings or urine

Is it always through bites and scratches?

Haverhill fever describes the infection when it occurs from eating food contaminated by rat dropping and urine. It can have more sore throat and abdominal symptoms. It may be harder to diagnose as exposure is often unknown. It can come from raw milk. It was named after an outbreak in Haverhill, Massachusetts where it was spread through milk.

How is it prevented?

Avoid rats that aren't your pets. Rat infestation is a real risk. Ensure living and eating areas are rat-free.

It's best to handle rats with gloves. Wash hands frequently. Avoid bites.

Wash any wounds with soap and water. Seek medical attention for bites and be sure to mention the bite to a health care provider.​

Anything else spread by rats?

Oh yes, indeed. Rats are to blame for a number of infections. Some through bites, some through their droppings and urine. Some diseases are spread by inhalation, some by contact, some by ingestion. Some of these are:

  • Hantavirus Pulmonary Syndrome  
  • Hemorrhagic Fever with Renal Syndrome  
  • Lassa
  • Omsk Hemorrhagic Fever 
  • Plague 
  • Rat-Bite Fever  
  • Salmonellosis  
  • South American Arenaviruses (Argentine hemorrhagic fever, Bolivian hemorrhagic fever, Sabiá-associated hemorrhagic fever, Venezuelan hemorrhagic fever)

Can my pets get sick?

Maybe. Rats carry the bacteria without being sick. There have been studies that have found the bacteria in a variety of pet animals - gerbils, ferrets, cats, dogs, but it is unclear how significant this is and whether this is only colonization.

Guinea pigs and mice may show signs of the infection. It can make monkeys​ ill

There is also a possibility that the infection can be spread by contact with pets that have contact with rats. There was transmission where the only contact was with a dog or cat - that may have had rat exposure.

It would be a good idea to keep this in mind when having pet rats at home.

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