Rocky Mountain Spotted Fever (RMSF) |

Rocky Mountain Spotted Fever (RMSF)

Rocky Mountain Spotted Fever Definition

Rocky Mountain spotted fever (RMSF) is a bacterial disease that affects blood vessels and is transmitted by tick bites. The infection is caused by the bacterium, Rickettsiae ricketsii. Infection damages the wall of blood vessels thereby making it leaky. Ruptured blood vessels may cause internal bleeding and lead to organ damage. First identified in the mountains, Rocky Mountain spotted fever is equally prevalent in other regions as well. It is characterized by high fever and severe headache with characteristic rash-spots on wrists and ankles.

Rocky Mountain Spotted Fever Incidence

Older people (60 to 70 years) and children less than 10 years of age, are more likely to contract this infection. Although Rocky Mountain spotted fever responds well to treatment, about 20 to 25% cases present life-threatening conditions owing to delayed medical care, misdiagnosis and patient compliance.

Rocky Mountain Spotted Fever Pathophysiology

Spread and incubation period

Infected ticks release the Rickettsiae ricketsii bacteria along with their saliva into blood of host organism. The bacteria are then spread throughout the body through blood and lymph. Depending on the strength of the inoculums (amount of bacteria that is injected into the bloodstream), the incubation period of the bacteria can range from 10 to 12 days but may be as short as 3 days.

Rickettsiae ricketsii infection

The bacteria are able to overcome the immune responses and exploits host cells to thrive. Large amounts of bacteria in the system either directly damages cells or triggers excessive immune responses.

These bacteria invade the cells lining of blood vessels (endothelium). Smooth muscles are also prone to become infected. Damage of blood vessels due to proliferation of bacteria in the endothelial cells, often causes internal bleeding or clot formations. In severe conditions it may led to organ failures or stroke.

Effects of Rocky Mount spotted fever

Tiny blood capillaries are more susceptible to Rickettsiae infections. The damage to the blood vessel coupled with the formation of clots affects the blood flow to various parts of the body. It may not compromise the entire blood supply to an organ but during times of increased activity the oxygen supply is severely hampered. This causes tissue injury and even leads to cell death in some cases.

Rocky Mountain Spotted Fever Causes

The bacterium, Rickettsia ricketsii, is the  cause of Rocky Mountain spotted. Ticks contract these bacteria while feeding on infected animals and humans. These ticks then adhere to the skin and feed off human blood. In order to infect a person, the tick usually needs to be feeding for between 6 to 10 hours. The Rocky Mountain spotted fever bacteria is then passed into the host’s blood through the tick’s saliva in sufficient amounts to cause an infection.

Although Rocky Mountain spotted fever is not contagious, it can be easily spread among humans and animals if there is close contact in an enclosed area and sufficient vectors (ticks) to transmit the bacteria. Another uncommon method of transmission is through a passive infection. Here a person may contract the infection through an open wound or the mouth, nose or eyes when making contact with blood or tissue of the infected ticks.

Risk factors

  • Summer time is a more likely period for infection as the ticks become more active in warm weather.
  • Certain tick infested areas may mean that residents and travelers to the area are at a greater risk.
  • Living or traveling though grassy or marshy areas with inadequate protection against ticks.
  • Males are at a greater risk more likely due the nature of their work and activities.
  • The elderly and children are more likely to suffer from more severe infections.

Rocky Mountain Spotted Fever Symptoms

Non-specific symptoms

Initially the appearance of Rocky Mountain spotted fever does not differ significantly from other bacterial and viral infections. The non-specific symptoms include :

  • High fever
  • Severe headache
  • Generalized aches
  • Nausea and vomiting

Some distinguishing features may be present in children and adults. A high fever with slow breathing rate may be seen in adults while swelling around the eyes may be more prominent in children.

Characteristic symptoms

The more characteristic symptoms of RMSF start appearing within 14 days after inoculation. These symptoms :

  • Very high fever (above 102°F)
  • Frequent and severe headaches
  • Muscle pains
  • Distinct red skin rashes appear initially on the wrists and ankles which may then spread down to palms and soles as the disease progresses. However, some individuals do not develop any rash, which makes the diagnosis of Rocky Mountain spotted fever difficult.

Owing to the delayed presentation of Rocky Mountain spotted fever symptoms, the person usually forgets the incidence of tick-bites.

Picture from Wikimedia Commons

Rocky Mountain Spotted Fever Complications

If the infection is left untreated or is severe it may lead to a range of complications including:

  • Coagulation of blood in the vessels.
  • Gastrointestinal symptoms including abdominal pain, diarrhea or vomiting.
  • Neurological symptoms like confusions, delirium, seizures or coma.
  • Respiratory distress including shortness of breath or difficult breathing.
  • Rarely patients also present with insomnia (difficulty sleeping) or photophobia (sensitivity to light).

Prompt treatment is required as the infection can prove fatal within a few days after the onset of complications.

Rocky Mountain Spotted Fever Diagnosis

The diagnosis of Rocky Mountain spotted fever in the early stages is often missed due to the non-specific symptoms. A medical history indicating travel to endemic areas may raise the suspicion of Rocky Mountain spotted fever. However, many patients often do not report their recent travel or tick bites. Delayed diagnosis is more likely to be associated with severe cases and complications. Some of the factors that may be indicative of Rocky Mountain spotted fever includes :

  • General illness with fever (febrile illness)
  • History of tick-bites
  • Excursions to marshy areas or grasslands
  • Time of disease occurrence – spring or summer

The classical diagnostic symptoms include triad of fever, headache and rashes. Although only a small percentage of patients present with these symptoms in the first few days, almost 70% patients only start showing these symptoms in the second week after contracting the infection. Further testing may be necessary but the diagnosis relies heavily on clinical features and the medical history.

Rocky Mountain Spotted Fever Tests

Blood tests may indicate an infection and show certain biocehmical changes in the body but it often non-specific for Rocky Mountain spotted fever. When the infection is suspected, treatment should be commenced even before confirming the diagnosis. Blood, skin and organ tissue samples can be used to confirm the presence of the bacteria and antibodies against it. However, these tests may false-negative in the early stages of the disease. Sometimes the tick is also tested to confirm the presence of the Rocky Mountain spotted fever bacteria even though there is no clear evidence of the infection in the human host.

Rocky Mountain Spotted Fever Treatment

Antibiotics are necessary to treat the infection. Other medication is used to treat the symptoms and limit the complications associated with Rocky Mountain spotted fever.


Prompt commencement of antibiotics is essential. Treatment should be initiated based on the differential diagnosis.  Common antibiotics used are:

  • Doxycycline are broad spectrum antibiotics and the preferred option for Rocky Mountain spotted fever.
  • Chloramphenicol are generally used during pregnancy as it reportedly has no side effects on unborn child. It is also used by patients allergic to doxycycline.

Other Medication

  • Corticosteroids diminish the inflammatory and immune effects of the infection.
  • Non-steroidal anti-inflammatory drugs (NSAIDS) are used for relieving pain and inflammation.
  • Anti-cholinergic agents are useful for easing the eye symptoms and complications associated with Rocky Mountain spotted fever.

References :

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