Introduction 

As more and more people live in crowded towns and cities, it is a fact of life that many of us live near growing rodent populations. An unfortunate side-effect of this is that many rodents can spread diseases, including Rat-Bite Fever.

Rat-Bite Fever or ‘RBF’, is a potentially serious bacterial infection spread through contact with rats or other rodents. RBF is caused when one of two species of bacteria are spread from rodents to humans. This is sometimes through bites and scratches, often when handling rodents, hence the name. However, it can also be spread by touching contaminated surfaces where rodents have been, or consuming food that might be contaminated by rodent urine or droppings.

RBF causes a potentially life-threatening fever if medical attention is not received. Whilst in most cases it can be treated, early recognition of the symptoms of RBF following a bite from or exposure to rodents is crucial. In this article, we will discuss how RBF is spread, how to recognise the symptoms, and how it is treated. By promoting awareness of RBF and effective first-aid for rodent bites, it is possible to improve the odds of successful treatment or avoid it altogether.  

What is Rat-bite-fever (RBF)?

There are two types of RBF, caused by different species of bacteria. Both cause fever, and the symptoms of both types are similar but may appear differently.

Streptobacillary RBF

Streptobacillary RBF is caused by a type of bacteria called Streptobacillus moniliformis. This type of RBF is more common in North America, though cases have occasionally been reported in Europe^.1 

Spirillary RBF

Spirillary RBF is more common in Asia and is caused by a different species called Spirrula minus. It is also known as ‘sodoku’.

The symptoms of Streptobacillary RBF and Spirillary RBF are similar, but there may be some differences.²

How is RBF Transmitted?

While less is known about the bacteria that causes Spirillary RBF compared to Streptobacillary RBF, it is thought that both species are usually found in the upper airways of rodents, particularly rats. Estimates indicate that domesticated rats may carry Streptobacillus anywhere between 10 and 100% of the time. It is even more common in wild rats.

Other rodents that have been shown to carry Streptobacillus include guinea pigs and gerbils.¹

The animal does not need to be sick to spread the disease and it is not always spread by aggressive bites from wild animals. Any contact with rodents can pose a risk of infection. Even when handling pet rodents, sharp claws, and gentle bites may break the skin. As rodents groom by coating their fur with saliva, they can spread the bacteria over their bodies. This can then be spread to humans if they handle rodents whilst they have any existing wounds (e.g. scratches and cuts) or if they then touch mucous membranes (e.g. the eyes, nose, or mouth) where bacteria can easily enter the body.

Another way Streptobacillus can spread is by contamination of food and drink. This can occur when rodent urine or faeces comes into contact with foodstuffs. This type of infection is known as Haverhill fever - the symptoms are similar to other types of RBF, but vomiting and sore throat may be worse.

RBF cannot be spread from person to person.²

Causes and Risk Factors

Those most likely to contract RBF are individuals who have regular contact with rodents, or areas where rodents are abundant (e.g. urban areas or farms), particularly if a rodent infestation is occurring.

Rats have become increasingly popular as pets, and some of the most at-risk individuals are pet owners who have rodents. However, exotic pet owners who handle frozen or live rodents as feed are also exposed.

There is an occupational risk of RBF in professions that may involve exposure to rodents, such as animal testing laboratory workers or pest-control professionals.

As of 2007, Young children account for over 50% of RBF cases in the US and may be more vulnerable to infection as their immune systems are still developing. They are also more likely to not wash their hands after handling pet rodents. Other vulnerable groups include the elderly, and pregnant women. Individuals who have a compromised immune system are also at risk of RBF infection. This includes individuals with HIV/AIDs, or those undergoing immunosuppressive treatments like chemotherapy or steroid treatment.^1,2,3 

RBF Symptoms and Diagnosis

Incubation Period

Streptobacillary RBF does not typically appear immediately after being infected. This period is known as the ‘incubation period’ and symptoms may not appear for anywhere between 3 - 21 days after infection, though normally occur within 7 days.¹ Spirillary RBF may take longer to cause symptoms.² 

Symptoms Onset

The first symptoms to appear are typically fever. This may be followed by a red rash on the hands and feet with raised bumps. This typically appears before joint pain, muscle aches, and headaches. Vomiting and sore throat may occur and are typically worse when Streptobacillary RBF has been contracted by consuming contaminated food or drink (Haverhill fever).

These symptoms are common but may not always occur together. In cases of Spirillary RBF, the fever may come and go. If Spirillary RBD has been spread by a bite, there may be swelling around the wound and the rash might only extend around the wound, or spread across the whole body. Swollen lymph nodes are also associated with Spirilarry RBF.

Complications

It is critical to seek medical attention for these symptoms as Streptobacillary RBF can develop into a more severe illness if untreated, with a mortality rate of 1 in 10.

Uncontrolled infections can lead to painful abscesses forming within the body, leading to potentially life-threatening infections. The bacteria may spread to the bloodstream (septicaemia), nervous system (meningitis), liver (bacterial hepatitis), kidneys (nephritis), heart (carditis), or lungs (pneumonia) if treatment isn’t provided.¹

Medical Diagnosis and Treatment

If RBF is suspected after handling or being exposed to rodents, it is important this is explained to the physician as other infections may cause similar symptoms to RBF. 

It is likely that, except for cases of RBF that are already severe, the physician will take a sample of blood or fluid from any abscess for further laboratory testing and identification to confirm an RBF diagnosis before prescribing antibiotics.

If RBF is confirmed, a course of penicillin will be prescribed. In most cases, this is effective in curing RBF. However, the bacteria that cause RBF can be difficult to grow in the lab and identify, and samples may need to be sent to specialist labs for further testing, potentially delaying diagnosis.^1,2 This is why it is important to seek medical attention as soon as symptoms appear and RBF is suspected.

Preventing RBF

Avoiding exposure to wild rodents

One of the best ways to minimise risk of RBF is to prevent rodents from entering the home or workplace, particularly where food is prepared. Traps may be effective, but it is often easier to avoid attracting rodents in the first place. Proper disposal of edible waste in sealed containers is crucial, as this will draw in rodents and other pests. Rodents are also less likely to move into well-maintained and used buildings.

Recognising the signs of rodent infestation is also important, with gnaw marks or droppings often giving their presence away. Clean all rodent droppings and areas where it is suspected that rodents have been using bleach and gloves. If the infestation is widespread, consider contacting a specialist pest control provider.⁴

Safe handling of rodents

If you own pet rodents, it is still possible to safely handle your animals whilst avoiding RBF. Ensure all enclosures and equipment (water bottles, feeding trays, etc.) are regularly cleaned with pet-safe disinfectant, and wash hands promptly after handling rodents. Young children should be supervised when handling small animals.

Ensure you know how to correctly handle the animal, and avoid holding any rodents that seem distressed or that you are unfamiliar with, as the likelihood of a bite or scratch is greater.

If you are bitten or scratched by a rodent, immediately wash the wound with soapy water. Seek medical advice as soon as any symptoms develop, or if the wound does not heal normally.⁵

Summary

RBF is a potentially dangerous disease spread by both wild and domestic rodents. Those who come into contact with rodents often are at increased risk, but by being aware of how to avoid contracting RBF, performing first-aid on any rodent bites, and seeking medical attention as soon as RBF symptoms are suspected, most cases can be successfully treated. Rodent-proofing your home or workplace and addressing any signs of infestation is often enough to prevent RBF from spreading. Pet owners can ensure they care for their rodent pets safely by being aware of RBF and how it can be spread to humans, properly handling their animals, and following good hygiene practices.