9/22/2009 Case 1: Rocky mountain spotted fever

Presented by: Dr. Roy Rhodes - Robert Wood Johnson University Hospital

Clinical History:

A 3 year old boy with a history of animal bites at a picnic near Trenton developed fever, rash and multiorgan failure and died  At autopsy, there was extensive edema of scalp, eyelids, neck, hands and scrotum.  The lungs (right 240 gram, left 210 gram) were congested and edematous.  There was a liter of serous ascitic fluid.  The liver (540 grams) had capsular petechiae.  The 190 gram spleen had a recent infarct.  There was mild brain swelling and a temporal lobe was soft and friable along the autopsy saw cut.

Pertinent previous history:  The animal bites were tick bites, especially on the scalp. 

Autopsy revealed microglial nodules and a perivascular angiitis.  Morulae (multiple aggregates of membrane-bound organisms within a macrophage) were seen on the Giemsa stain.  The differential diagnosis included Rocky Mountain Spotted Fever (RMSF) and meningococcemia. 

Diagnostic Notes:

The diagnosis was Rocky Mountain Spotted Fever, with DNA testing positive for R. rickettsia.  RMSP causes an angiocentric inflammatory process, which is the key finding.  There may also be microglial nodules subarachnoid inflammation and recent infarcts.  Transmission occurs via Dermacentor ticks; in the West, Dermacentor andersoni is responsible.  The dog tick, Dermacentor variabilis also carries the organism and RMSF is endemic in the entire USA with most reported cases in children.  Cases from the Southeast and NYC are noteworthy.  Therapy is tetracycline and chloramphenicol.  Mortality is 3-5%.


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