What is Rocky Mountain Spotted Fever (Rickettsia rickettsii)?
Rocky Mountain spotted fever (RMSF) is a sickness that comes with a fever, caused by a bacteria named Rickettsia rickettsii. This bacteria is most commonly delivered by a tick bite. In North America, RMSF is the most intense and most frequently occurring infection caused by this type of bacteria.
What Causes Rocky Mountain Spotted Fever (Rickettsia rickettsii)?
“Rickettsia rickettsii” is the name of a bacterium that causes the highly dangerous disease called Rocky Mountain spotted fever. The bacterium is of the type “spotted group rickettsiae” and it is the most studied and the deadliest of them all. This bacterium has a specific shape somewhat like a sphere or a rod and it can’t survive outside of a host’s cells.
The way people usually get infected is by a tick bite – ticks are small insects that latch onto the skin and bite to feed on blood. If the tick is carrying the “Rickettsia rickettsii” bacteria and it bites a person, it can pass the bacteria onto the person.
It’s thought that once a tick carrying the bacteria bites a person, the bacteria quickly enters the person’s cells. The bacteria specifically target the cells that line the walls of our blood vessels.
Risk Factors and Frequency for Rocky Mountain Spotted Fever (Rickettsia rickettsii)
R. rickettsia, a type of bacteria, is passed on to humans through the bite of an infected tick. Humans don’t naturally harbour this bacterium, and interestingly, it doesn’t harm the tick that carries it. In the United States, most transmissions happen from bites by the American dog tick, the Rocky Mountain wood tick, or the brown dog tick.
Since these ticks are active in warmer weather, people are more likely to be diagnosed with R. rickettsia infections during the summer, especially if they spend a lot of time outdoors. So, despite its misleading name, these infections commonly occur in the southeastern and south-central parts of the U.S. It’s critical to remember that even if someone can’t recall a tick bite, they should not rule out the possibility of an R. rickettsia infection, particularly if they live in or have visited areas where the bacterium is commonly found.
- R. rickettsia is a bacterium transmitted to humans through an infected tick bite.
- Humans aren’t a natural carrier for this bacterium, and it doesn’t harm the tick.
- Most transmissions in the U.S. come from the bite of the American dog tick, Rocky Mountain wood tick, or brown dog tick.
- Diagnoses are more common in the summer months for people spending time outdoors.
- These infections are typically seen in the southeastern and south-central U.S., not just the Rocky Mountains as the name might suggest.
- Even if someone doesn’t recall a tick bite, they should still consider an R. rickettsia infection if they’re in or have visited a place where this bacterium is commonly found.
Signs and Symptoms of Rocky Mountain Spotted Fever (Rickettsia rickettsii)
Generally, people start to show signs of infection from Rickettsia, a type of bacteria carried by ticks, four to ten days after being bitten. Remember, not everyone realizes they’ve been bitten by a tick, as the tick doesn’t need to be attached for very long to pass on the infection. If someone’s been participating in outdoor activities in areas known to have ticks or where Rickettsia is common, it’s crucial to consider this when they begin showing symptoms. The classic symptoms of Rickettsia infection include a combination of fever, headaches, and a certain kind of rash (either petechial or maculopapular). Other possible symptoms are swelling of the lymph nodes, changes in the central nervous system like confusion or neck stiffness, muscle and joint pain, liver inflammation, vomiting, and unstable heartbeat. The rash usually starts around the wrists and ankles, before developing into petechia (tiny, flat, red or purple spots). It’s particularly important to consider a potential Rickettsia infection if someone begins showing flu-like symptoms during the summer, regardless of whether they recall being bitten by a tick or another insect.
- Signs of infection appear 4-10 days after tick bite
- Common symptoms include fever, headaches, and a petechial or maculopapular rash
- Other symptoms may be swollen lymph nodes, confusion, neck stiffness, muscle and joint pain, liver inflammation, vomiting, and cardiovascular instability
- The rash usually starts around the wrists and ankles before developing into petechia
Testing for Rocky Mountain Spotted Fever (Rickettsia rickettsii)
Rocky Mountain spotted fever is generally identified based on two types of antibody responses: immunoglobulin M (IgM) and IgG to a bacterium called R. rickettsiae. This detection is usually supported by strong clinical suspicion. It is important to note that initial tests may return negative if conducted early in the illness. Therefore, it’s crucial to perform repeat testing after the symptoms have subsided. If there is an increase in Rocky Mountain spotted fever IgG levels when comparing the first and follow-up tests, it usually indicates an infection.
Although it’s possible to grow Rickettsia bacteria in a laboratory for testing, this method is rarely used for diagnosing the disease. This is because the process is complex and carries a risk of exposure to the bacteria, therefore requiring a high level of safety measures. Other methods for diagnosis include, in certain medical centers, molecular tests such as the polymerase chain reaction (PCR), and skin biopsy tests.
A test known as the Weil-Felix agglutination assay, due to its low sensitivity and accuracy, is no longer recommended for the diagnosis of Rocky Mountain spotted fever. Patients with infections related to rickettsial bacteria may also show low platelet count (thrombocytopenia), low sodium levels (hyponatremia), and an increase in the number of white blood cells in the spinal fluid (cerebrospinal fluid pleocytosis).
It’s important to note, however, that white blood cell counts in the blood can vary making it unreliable as a sole indicator for diagnosing a Rickettsial infection. Due to this, and the possibility of early serologic tests returning negative, doctors must be vigilant about considering Rocky Mountain spotted fever in patients displaying flu-like symptoms during warmer months, particularly if they live in or have traveled to areas where the disease is common.
Treatment Options for Rocky Mountain Spotted Fever (Rickettsia rickettsii)
Doxycycline is commonly used to treat Rocky Mountain spotted fever, a disease caused by a tick bite, in both adults and children. Usually, signs of improvement, like a reducing fever, start to show about three days after the start of the treatment. However, recovery from other symptoms may take a bit more time. The duration of the treatment is typically between seven to ten days, or at least three days after the fever subsides.
Without early antibiotic treatment, diseases like Rocky Mountain Spotted Fever can be very serious and even fatal, especially in severe cases where the death rate can reach up to 30%. Therefore, treatment should begin as soon as the disease is suspected and should not be delayed while awaiting results from laboratory tests to confirm the diagnosis. This is highly important for children, as they yield a disadvantage due to their higher risk of becoming severely ill from the disease and the potential complexities of treating children, especially younger than 8, with Doxycycline.
Concerns have been raised about using doxycycline in young children because it can cause tooth staining. However, tooth staining typically results from prolonged use of this medication, and the duration of treatment for Rocky Mountain spotted fever is usually around seven to ten days. Given the risks associated with the disease, concerns about tooth staining should not delay treatment if Rocky Mountain spotted fever is suspected.
What else can Rocky Mountain Spotted Fever (Rickettsia rickettsii) be?
Conditions that may cause similar symptoms include:
- Babesiosis
- Boutonneuse fever
- Dengue
- Drug hypersensitivity
- Disseminated gonococcal infection
- Enteroviruses
- Ehrlichiosis
- Epstein-Barr virus infectious mononucleosis
- Immune complex vasculitis
- Influenza
- Lyme disease
- Leptospirosis
- Luetic exanthem
- Malaria
- Typhus