Rocky mountain spotted fever

Medical quality assurance by Dr. Albrecht Nonnenmacher, MD at June 28, 2016
StartDiseasesRocky mountain spotted fever

Rocky Mountain spotted fever (RSMF) is caused by a human pathogen transmitted by ticks. The disease was first discovered in the Rocky Mountain region of North America, and that is where it got its name. It is a tick-borne disease.

Contents

Definition & Facts 

Howard T. Ricketts first described Rickettsia rickettsii in the early 1900's as afflicting ticks and various rodents. The Rickettsia rickettsii are the intracellular pathogen that causes Rocky Mountain spotted fever by infecting the cells that line the surface of the blood vessels.

Infection with R. rickettsii causes systemic inflammation of the blood vessels. The inflammation of the blood vessels will increase capillary permeability and eventually cause a microhemorrhage, or worse.

This condition manifests externally as skin lesions with the distinctive red or purple spots which are the result of bleeding from broken blood vessels. If the disease is not treated, it can lead to organ damage and eventually death. 

Symptoms & Complaints

Symptoms of RMSF are usually noticed between three to 12 days after the bite from an infected tick or between four to eight days after finding a tick attached to the body. The incubation period of the disease is five days or less.

Infected patients show early symptoms such as headache, nausea or vomiting, shivering, restlessness, photophobia, loss of appetite, abdominal pain, muscle pain, and an onset of fever.

A rash usually appears within two to four days after the start of the fever. The RMSF rash is pink in color and first noticed on the wrists, forearms or ankles before they eventually spread to the legs, soles, palms, arms, and trunk. The presence of the rash on the palms and soles indicate that the disease has advanced.

Some patients have the rash within the first three days of the illness while others may never develop a rash. Children that are less than 15 years old develop rashes more than older patients in the early stages of the disease. Skin pigmentation might make the rash difficult to notice in some patients. Health care personnel should not rule out RMSF due to the absence of rash. Delayed appearance of the rash or lack of rash has led to delay in diagnosis and death of people with RMSF.

Other symptoms associated with RMSF are abdominal pain that feels like acute appendicitis, inflammation of the gallbladder, diarrhea, conjunctival suffusion, peripheral edema, calf pain, acute transient hearing loss, and also the abnormal enlargement of the liver (hepatomegaly) and the spleen (splenomegaly).

In the late stage of RMSF, symptoms may include meningoencephalitis, acute kidney failure, acute respiratory distress syndrome, acute skin necrosis, shock, abnormal heart rhythm, and seizure

Causes

Humans catch RMSF from the bite of the dog tick when it is attached to the body for at least four to six hours or through careless handling of tick secretions or body fluids (such as those that occur when crushing a tick). Ticks can be brought into the household environment by dogs which may eventually become ill with spotted fever.

The R. rickettsii can be transmitted via infected blood transfusion. Infection can occur by receiving blood three days before the onset of symptoms in the donor. Due to routine screening for infections during the blood donation process, transmission from a blood transfusion is rare. RMSF can also be transmitted through an organ transplant.

Diagnosis & Tests

Several clinical methods can be used to diagnose RMSF, but therapeutic interventions for patients with the disease is based on clinical suspicion due to its rapidly progressive nature. (Antibiotic treatment is not delayed while waiting for a laboratory confirmation of RMSF). Blood tests may not show the antibodies in the blood until ten days after the infection has begun.

Diagnosis is based largely on presentation of symptoms and information about when they first appeared. Most of the time, R. rickettsii infection causes rashes on the palms and soles of infected patients, though these rashes may have a delayed appearance or never appear at all in some RMSF cases. Health care personnel may find it difficult to differentiate between a Neisseria meningitidis infection from RMSF because infected patients show a similar type of rash, though the symptoms of meningococcemia progress more rapidly than in RMSF. 

Diagnosis may also be assisted through taking various laboratory tests. Blood tests can show a low platelet count (thrombocytopenia) and elevated liver enzymes which may provide further clues to assist the doctor in diagnosing and rapidly treating the patient.

Treatment & Therapy

Treatment of RMSF is usually started without waiting for laboratory confirmation. The response to treatment of the illness is faster when treatment with antibiotics is started early to prevent severity. Only a few antibiotics like tetracyclines are effective against R. rickettsii. Doxycycline is currently the drug of choice. For patients allergic to tetracycline, other drugs like fluoroquinolones, chloramphenicol, josamycin, or newer macrolides may also be used. There is a risk of severe side effects with chloramphenicol. The availability of some of these drugs varies between countries. Patients are treated for at least three days after the fever subsides and until there is evidence of clinical improvement. Standard duration of treatment is 7 to 14 days.

Prevention & Prophylaxis

Avoidance of tick bites is the major way of preventing RMSF. Using protective shoes and clothing when in tick habitats is crucial as is wearing long-sleeved shirts and tucking trousers into socks. Ticks may be more visible on light-colored apparel.

Use of tick repellents is recommended although their potency tends to not last very long. They should be applied periodically to ensure effectiveness. Clothing worn to areas infested by ticks should be removed and decontaminated promptly.

One should always check and remove ticks whenever one enters a tick-infested environment. It is important to always use tweezers or wear hand gloves to avoid direct contact with fluid from the tick. It is unsafe to crush, squeeze or puncture the tick when removing it.

Tick bites should be disinfected after removing the tick, and one should wash hands with soap and water after handling. Removing ticks from pets to reduce the risk of dogs becoming ill and also to prevent the ticks from entering the home.

Acaricides which kill ticks, biological controls and control of tick habitats can decrease the populations of tick vectors in a community. Dogs can act as sentinels for Rocky Mountain spotted fever in humans. 

Suspected transmission of RMSF from transfusion should be reported as early as possible to the blood product supplier and public health authorities. Timely reporting will help in tracking and quarantine of the infected blood, and also the infected donor and recipients should be notified.

Also, if a donor that recently donated blood develops symptoms of RMSF, the donated blood should be quarantined or recalled by the blood bank. Additionally, screening of organ donors helps to prevent transmission of the bacteria.