Rickettsia et. al. Flashcards
Describe the gram stain of Rickettsia. What type of stain should you use to visualize?
cocobabillary fastidious, obligate intracellular pathogen which will not show up on gram stain but can be visualized with Gimenez or Giemsa stain
What are the organisms that cause Rocky Mountain spotted fever, African tick bite fever and murine typhus (flea borne)
Rickettsia rickettsia: RMSF
Rickettsia afriae: African tick bite fever
Rickettsia mouseri: Murine typhus
What is the causative organism of Q fever?
coxiella burnetii
Describe the transmission and reservoirs of Rickettsia illness.
arthropods (insects- flea or louse and arachnid-tick or mite) serve as both host and vector and reside on the reservoir animals (dogs, mice, rats and flying squirrels)
Which two rickettsial diseases may be acquired by direct inhalation?
Q-fever (coxiella burnetii) Epidemic typhus (Rickettsia prowazekii)-- "war torn areas"
Describe the common pathogenesis of rickettsial infection. (4 main symptoms)
vasculitis caused by the invasion and multiplication of the organism in the endothelial and smooth muscle cells of of the blood vessels
thrombosis, occlusion and necrosis of blood vessel walls
thrombocytopenia with hemorrhage primarily as a result of platelet consumption
massive capillary leakage into the interstitial spaces results in edema, hypovolemia, hypotension and ARDS
What are common complications of Rickettsial illness?
encephalitis, myocarditis, and nephritis
hyponatremia due to ADH response
What is the classic triad of RMSF and where is it endemic?
fever, headache and rash (esp. of the palms, usually appearing by day 5)) typically occurring in the Southeast US with a short incubation period (2-14d)
other symptoms edema: periobital and dorm of hands/feet; conjunctival suffusion; confirmed by IFA
untreated, mortality can reach 20%
Which diseases have characteristic eschar?
no eschar with RMSF
multiple eschars with Rickettsia africae
one eschar with R. conoraii
What is the organism of epidemic typhus and how is it spread. What are the symptoms?
louse borne typhus (dies of infection after 3 wks) produces serious disease consisting of fever, severe headache, myalgic and central rash: untreated mortality ranges from 20-40% (war-torn areas, poor sanitation)
can be spread by airborne aersolation by flying squirrels
note: Brill-Sinsser disease is a mild, recrudescent form of epidemic typhus (reactivation of disease)
Who is at risk for Q fever?
veterinarians, ranchers and animal researchers whoa re in contact with infected placenta from sheep, cattle or goats
airborne transmission is also possible
What is the presentation of Q fever?
incubation period of 10-28d: fever and headache are common, 50% will develop pneumonia after inhaling, hepatitis and endocarditis can occur
What is the characteristic pathology of Q fever?
doughnut shed nocaseating granuloma–note the phase II IgM is the quickest titer to rise in Q fever then phase II IgG
What is the classic story for C. burnetti
cat giving birth under a table where poker is being played
Which are the most common travel associated Rickettsia infections and their respective organisms?
Mediterranean spotted fever: R. conorii
African tick bite fever: R. africae
Scrub typhus: O tsutsugamushi
How is Mediterranean spotted fever transmitted?
common in S. France, Spain (Europe, Africa and Asia)
requires contact with a local dog with ticks causing a mild illness with 1 eschar at site of tick bite
How is Africa tick bite fever transmitted. What is the classic presentation?
(most common rickettsiosis in travel medicine, esp from S. Africa)
is picked up while walking in the bush as cattle ticks carry the disease
headache, myalgia, disseminated rash (30%), most have inoculation scars, and over half have multiple eschars
What is the Weil-Felix Reaction?
historical lab test that identifies an insensitive and nonspecific agglutinin that measures Proteus antibodies and cross reacts with rickettsia species
What tests are used to confirm rickettsial infection?
indirect immunoflurescent antibody
indirect hemagglutination antibody
complement fixation
** it takes several weeks before antibody titers can be detected by these methods, requires 4x rise in titer or a single high titer
(PCR is promising but not widely available)
How do you treat Rickettsial disease?
early antibiotic intervention is recommend to prevent severe vascular endothelial damage
treat with doxycycline, tetracycline or chloramphenicol (risk of aplastic anemia)
you cannot wait for diagnostic testing to start treatment (treat on the basis of clinical presentation and epidemiologic risks)
Which rickettsiosis are endemic to US?
RMSF
Q fever
Murine typhus
(less common R. aquaria, R parkeri)
African tick bite fever is the most common reported by travelers
