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What is Ratbite Fever: Dangers to Human, Symptoms & Treatments

Fever causes by rat bites

Rat bite fever is a type of acute systemic illness with classic features like fever, rigors, and polyarthralgia. It is caused by the bacteria which is transmitted by rats, rodents or mice to the person who gets a bite or scratch from such infected animal. Moreover, individuals may be liable to this disease by consumption of contaminated water or food which is referred as Haverhill fever.

Alternative Names: Rat bite fever is also known as a Streptobacillary fever, spirillary fever, epidemic arthritic erythema, sodoku or streptobacillosis.

1. Causes of Rat-bite Fever

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As mentioned earlier, these diseases are caused due to bacteria. There are various types of these bacteria and they are Gram-negative facultative anaerobic bacteria. It comprises of Streptobacillus moniliformis, mostly found in North America and is the leading cause of the Streptobacillary fever. In addition to that, Spirillum minus which produces infection that results in spirillary rat-bite fever is found primarily in Africa.

Several people get a rat-bite fever when they come in contact with urine or mucociliary secretions either from the eyes, nose or mouth of an infected animal. Rat bite fever mostly occurs through a bite, but in some cases, it may occur quickly through contact with such secretions. It may occur through consumption of contaminated water or food by rat’s urine or feces. The primary source of infection is a rat. Other animals that may cause this disease include squirrels, gerbils or weasels. Furthermore, pets like cats or dogs can transmit this disease to humans if they are in contact with these infected animals.

2. Signs and Symptoms of Rat-bite Fever

There are several signs and symptoms for both the types of RBF:

Streptobacillary RBF Symptoms:

  • Fever
  • Rigors
  • Nausea
  • Vomiting
  • Headache
  • Muscle & Joint Pain
  • Rashes (EXANTHEM: widespread rash or MACULOPAPULAR RASH: flat one)

Symptoms occur in about 3-10 days after a rodent infects the person, but they may delay for about three weeks. Nevertheless, within this period any bite or scratch usually heals up. Within 2-4 days after the fever begins, a maculopapular rash cover the hands and feet. The identical features of rash are flat, redness along with small bumps may appear reddish or purple. After that, it involves the joints causing them to be red, swollen or painful. Backaches may also occur.

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Spirillary RBF (also referred as Sudoku in Japan) Symptoms:

  • Fever (that may occur repetitively)
  • Growth of an ulcer at the site of bite wound
  • Swelling around the wound
  • Swollen and tender lymph nodes (lymphadenopathy) usually involving groin, underarms and neck areas.
  • Rash
  • Rarely joint pain
  • The symptoms usually occur within 7-21 days of exposure.

The symptoms associated with Haverhill fever (RBF after consumption of contaminated food or water) are different from these which entails severe vomiting and severe throat.

Patient’s Laboratory Values

  • Average white blood cell count= 12,200 per cubic millimeter, predominantly polymorph nuclear cell and band form.
  • Average erythrocyte sedimentation rate = 69 mm per hour.

If these symptoms are left untreated, there is a risk that the patient may undergo serious infections including Endocarditis, Myocarditis, Systemic Vasculitis, Polyarteritis nodosa, Hepatitis, Nephritis, Ammonitis, Pericarditis, Meningitis(inflammation of the meninges), Septic shock or Pneumonia(involving lungs).

An abscess is a collection of pus that may affect any part of the body. Endocarditis is highly associated with this infection and carries a high mortality rate. Before the onset of Endocarditis, most patients were seen to develop the valvular disease, i.e. Rheumatic Heart Disease.

3. Diagnosis and Treatment

  • Diagnose

Rat bite fever diagnosis is made by detecting the bacteria either in blood, skin, joints fluid or lymph nodes.

  • Culture

Diagnosis of rat bite fever caused by Streptobacillus is made by collecting a blood sample or a fluid sample from a joint, which is then cultured to permit their growth. Microscopic Examination allows the identification of Streptobacillus moniliformis bacteria. It appears as a gram-negative, pleomorphic bacilli in chains or clumps with irregular lateral swellings. The growth of the bacteria requires Trypticase soy agar or broth, the growth of the colonies gives a cotton wool appearance. Diagnosis of rat-bite fever caused by Spirillum minus is confirmed by a blood sample or tissue sample from the site of the wound by culture or by direct visualization.

  • Fatty Acid Profiles

Fatty acid profiles are done by gas-liquid chromatography, along with characteristic growth, for identification of S. moniliformis. The key cellular fatty acid that increases is tetradecanoic acid, palmitic acid, octadecanoic acid with linoleic acid, stearic acid and oleic acid. High-resolution polyacrylamide gel electrophoresis along with computer analysis is used to distinguish and identify strains of S. moniliformis.

  • Other Methods

Serologic assays and slide hemagglutination tests were carried out in old times for humans, however, now these tests are unavailable. Although these tests are sufficiently sensitive, yet there is an increasing demand for a rapid and more sensitive test which includes Molecular methods such as PCR. A PCR assay is specifically used for S. moniliformis.

  • Treatment

Penicillin has been proven to be the treatment of choice for rat bite fever.

  • In adults

401,000 to 601,000 IU/day i.e. (250 to 370 mg) of IV penicillin G for about seven days, however, the dose can be increased to about 1.3 million IU/day (730 mg) if you find no response within two days of treatment.

  • In Children

21,000 to 51,000 IU/kg of body weight/day i.e. (13 to 35 mg/kg/day) of IV penicillin G for 7-9 days. Followed by seven days of penicillin V by mouth, 30 to 60 mg/kg/day (maximum, 3 -4g/day) divided into three to four times per day.

  • In Penicillin-allergic Patients

Streptomycin and tetracycline have been effective against Rat bite fever, however, erythromycin is found to be associated with treatment failures. Cephalosporins can be used successfully if no cross allergic reaction is seen with penicillin. Treatment mainly Penicillin for Spirillary Rat-bite fever, while Penicillin, Tetracycline or Doxycycline may be utilized for treating Streptobacillary Rat-bite fever.

Good prognosis is seen for both the types along with the treatment. The streptobacillary form cannot be treated on its own while the spirillary form may get better within a one year period if medications are not prescribed. The streptobacillary form leads to fatal complications if the treatment is not ensured. Before the availability of antibiotics, these infections led to death.

【Read more about Rats】

4. Prevention against Rat-bite Fever

  • Avoid contact with rats.
  • Try to avoid contact with rat dwellings.
  • After a rat bite take antibiotics by mouth to prevent this illness.
  • Avoid contact with animals who have the capability to transmit this disease.

It is a difficult task for people residing in rat-infested buildings to shift from such places. Streptobacillary type of fever can occur quickly after consumption of contaminated milk or dirty water, so it’s advised to drink pasteurized and milk and drink properly boiled water.

This disease is apparently prevented by minimizing the contact with the rodents.

  • Proper washing of face and hands should be done if in contact.
  • Clean the scratches and apply antiseptics.
  • There are no available vaccines in the market for this disease.
  • Best measures for prevention include improving the conditions by minimizing rodents contact.
  • Mostly Animal handlers, sanitation, sewer workers and laboratory handlers are exposed to this disease so they should be advised special precautions.
  • Avoid touching rodents whether alive or dead.
  • Pets should not be permitted to feed on rodents. People residing in areas with sanitation issues and overcrowding are more prone to catch the Rat-bite fever.
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