Rickettsial illness are all zoonotic infections that are characterized by fever, severe headaches, and rashes. There are many different species within this genera which differ on the progression of the rash, the geographical distribution, the animal reservoir, and arthropod vector. So focusing in on those differences will help you in diagnosis of the exact causative agent.
Rickettsia spp. bacteria are Gram-negative bacilli that are obligate aerobes and obligate intracellular organisms that require host coenzyme A and NAD+
The first one we’ll talk about is Rickettsia rickettsii which is the causative agent of Rocky Mountain Spotted Fever (RMSF). RMSF is the most common rickettsial illness in the US, and is typically found east of the Mississippi River (which honestly makes it a bit of a misnomer). This organism typically resides in rodents or dogs and is transmitted to humans through the bite of a wood tick from the Dermacentor spp. Once it’s transmitted it will cause a fever, chills, headache, myalgias, thrombocytopenia, hyponatremia, and high serum transaminase levels. The rash for RMSF starts on the wrists and ankles, and progresses onto the trunk and eventually becomes a petechial rash that involves the palms of the hands and soles of the feet. If untreated, RMSF has a mortality rate of 20%.
The next organism we’ll talk about is Rickettsia prowazekii, which is found worldwide and typically discovered in epidemics. The natural reservoir is humans, and is transmitted by lice. R. prowazekii causes Epidemic Typhus, which presents with a high fever, chills, severe headache, myalgia, and a macular rash that moves from the trunk to the extremities but does NOT go onto the hands or feet. It often relapses, so long-term follow-up is important for these patients.
Next, we’ll talk about Murine Typhus, which causes a high fever, chills, severe headaches, maculopapular rash that starts on the truck and goes to the extremities. This normally resides in humans and possibly flying squirrels (because that’s a thing), and is transmitted to humans through the bite of the human louse.
It’s important to begin empiric treatment with doxycyline if you suspect a rickettisal illness, and then wait for a confirmatory test. Diagnosis is typically via serology but this takes several weeks for the antibody levels to reach detectable levels. It’s also possible to take a skin biopsy of the rash, to look for the organism or perform NAAT. One thing that you can do rapidly is the Weil-Felix agglutination test which is when you mix the patient serum with the O antigens from Proteus spp. If the patient has a Rickettsial infection, the anti-Rickettsia antibodies will cross react with the Proteus antigens and cause agglutination. This will help you differentiate the Rickettsial illnesses from other causes of fever and rashes.
A 45-year-old female presented to the emergency department in Texas with fevers, headache, arthalgias, nausea, dyspnea, ataxia, worsening confusion, and neck pain for the past 7 days. Vital signs reveal a heart rate of 135 beats/min, and a blood pressure of 84/53 mmHg. Physical examination reveals a diffuse macular rash, that has spread to the palms of the hands and soles of the feet. The patient’s spouse explains that the rash first started at her wrists and moved up her arms to her torso. A Kernig test is negative. The patient’s spouse also reveals that she has multiple bug bites while in her bed which most likely came from her pet dogs which were not up-to-date on monthly flea and tick medications. Laboratory studies reveal a positive Weil-Felix agglutination test. Which of the following is the most likely causative agent?
A. Coxiella brunetii
B. Rickettsia typhi
C. Rickettsia prowazekii
D. Rickettsia rickettsii
First, diagnose the patient.
This patient is presenting with fever, headache, arthralgia, nausea, neck pain, dyspnea, and neurological dysfunctions including ataxia, increasing confusion.
Negative Kernig test points away from meningoencephalitis, but it should definitely still be in the back of your mind, just in case.
A history of bug bites that might be flea or tick, the progression of the rash, and the geographical location of Texas, and the positive Weil-Felix test all help to suggest a diagnosis of: Rocky Mountain Spotted Fever.
A. Coxiella brunetii is the causative agent of Q fever. It will case fever, headache,and myalgias and might progress into pneumonia. It doesn’t present with a rash, and it would also have a negative Weil-Felix reaction.
B. Rickettsia typhi presents with fever, chills, severe headache, and would have a positive Weil-Felix test, but the rash for Epidemic Typhus starts on the trunk and moves to the extremities. This rash does not travel onto the palms or soles.
C. Rickettsia prowazekii presents with fever, chills, severe headache, and would have a positive Weil-Felix test, but the rash for Murine Typhus starts on the trunk and moves to the extremities. This rash also does not travel onto the palms or soles.
D. Rickettsia rickettsii presents with fever, chills, headache, and a rash that moves from the extremities inward. This rash will travel onto the palms and soles.
Therefore,
A 22-year-old male presents to the emergency department with a two-week history of intermittent fevers, headache, fatigue, malaise, nausea, vomiting, and non-productive cough. Three days prior to presentation, a rash began to develop on his upper torso and spread to cover his entire body. Vital signs show a pulse of 136 beats/min. Physical examination revealed a petechial rash covering his entire body, but sparing his palms, soles, and face. His condition began to deteriorate until he was admitted to the intensive care unit for severe sepsis. His family is pretty sure that his pet cats have fleas. Laboratory studies reveal the presence of anti-Rickettsia spp. IgM antibodies. What is the most appropriate treatment?
A. Vancomycin
B. Doxycyline
C. Erythromycin
D. Hydroxyquinolone
First, diagnose the patient.
This patient is presenting with fever, headache, malaise and a rash, which can be caused by many different infectious organisms. The rash progresses from the truck to the extremities, and did not travel onto the palms or soles. The lab was able to find the presence of antibodies against Rickettsia spp. is highly suggestive of Murine Typhus.
All Rickettsia spp. infections are best treated with doxycyline because they are obligate intracellular organisms.
Therefore,
Reference:
https://microbewiki.kenyon.edu/index.php/Rickettsia
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6091339/pdf/amjcaserep-19-917.pdf
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6320554/
The Bradley Lab 