Rocky Mountain spotted fever

Rocky Mountain spotted fever is a tick-borne infection of the Americas. It causes fever, headache, and myalgia with maculopapular rash on the 3rd to 5th days (in the season and locality of tick activity). Petechiae are associated with end organ damage. Effective antibiotics are available.

CASES/YEAR
28,020 (US); 50,000 (Global)
CATEGORY
Arthropod-Borne
AGENT TYPE
Rickettsiae
OTHER NAMES
Rickettsia rickettsii infection; North American tick typhus; New World spotted fever; Tickborne typhus fever; Sao Paulo fever;
ACUITY
Acute-Severe
INCUBATION
2-14 days with a median of 7 days; [PPID, p. 2352]
INITIAL SYMPTOMS
Fever, headache, myalgia with maculopapular rash on the 3rd to 5th days (in the season and locality of tick activity); [CCDM]
PRECAUTIONS
Standard; "Not transmitted from person to person except through transfusion, rarely." [CDC 2007 Guideline for Isolation Precautions]
COMMENTS
FINDINGS:
The rash includes the palms and soles in about 30% of cases and spreads to the trunk. Patients develop a petechial rash on or after the sixth day. Petechiae are associated with end organ damage. [CCDM, p. 515] Common findings after the initial flu-like syndrome include conjunctival injection, stiff neck, nausea/vomiting, abdominal pain, hepatomegaly, splenomegaly, and hypotension. Pneumonitis (cough, rales, and pulmonary infiltrates) occurs in about 17% to 30% of patients. Encephalitis with confusion, lethargy, and delirium occur in over 25% of patients. Patients may also have ataxia, seizures, and coma. The CSF shows evidence of meningitis. Severe hemorrhage occurs "very infrequently." Laboratory abnormalities include abnormal liver and kidney function tests, hyponatremia (56% to 91% of patients), proteinuria, microscopic hematuria, mild thrombocytopenia, and increased bands (immature neutrophils). Over 30% of patients have elevated bilirubin levels, and jaundice is a sign of fulminant disease. Acute renal failure following hypotension is also common. Myocarditis is a rare complication. [ID, p. 1473-80] R. rickettsia targets the vascular endothelial cells resulting in edema, hypovolemia, ischemia, and tissue injury. Eye findings include retinal vein engorgement, flame hemorrhages, and papilledema with normal CSF pressure in some cases. Rhabdomyolysis has been reported occasionally. [Harrison ID, p. 690-1]

Chest x-ray findings include infiltrates and pleural effusions. Other findings are lymphadenopathy (27%), diarrhea, (20%), and anemia (5%-24%). Leukopenia, thrombocytopenia, and elevated liver enzymes are common. In 1/3 of cases, CSF shows increased leukocytes with a predominance of either lymphocytes or neutrophils. G6PD deficiency is a risk factor for hemolytic anemia and fulminant disease. In a series of pediatric cases, 15% of survivors had neurological deficits at discharge with encephalopathy, ataxia, and blindness. [PPID, p. 2352, Table 186.1]

EPIDEMIOLOGY:
Tick bites are typically painless and often not recognized. Cases have been reported from breaks in the skin contaminated by crushed ticks or tick feces. The natural animal reservoirs are ticks. Dogs, rodents, and other animals may become infected. [CCDM] Goats, sheep, and rabbits are also reservoirs. [PPID 7th Ed., p. 4002] Fatality rates without treatment: Rocky Mountain (20-25%); [Cohen, p. 1667t]
DIAGNOSTIC
Paired sera; Skin biopsy (immunostain or PCR); [CCDM] DFA of skin biopsy S/S of about 70%/100%; IgM appears by day 3-8, peaks at 1 mo, & lasts 3-4 mo.; [Wallach, p. 1146] DFA skin biopsy rapid & may be available in hospital; Paired sera (IFA); [ABX Guide]
SCOPE
Canada, USA, Mexico, Central America, Colombia, Brazil, and Argentina; [CCDM]
SIGNS & SYMPTOMS
  • >arthralgia
  • >fever
  • >myalgia
  • G abdominal pain
  • G blood in stool
  • G diarrhea
  • G hematemesis
  • G hepatomegaly
  • G jaundice
  • G liver function test, abnormal
  • G nausea, vomiting
  • H anemia
  • H hemolysis
  • H leukopenia
  • H lymphadenopathy
  • H splenomegaly
  • H thrombocytopenia
  • N confusion, delirium
  • N headache
  • N lethargy
  • N seizure
  • N stiff neck
  • O conjunctivitis, acute
  • R cough
  • S papules or plaques
  • S petechiae and ecchymoses
  • S rash (exanthem)
  • S rash on palms
  • U hematuria
  • X lung infiltrates
  • X pleural effusions
  • *acute renal failure
  • *ARDS
  • *bleeding tendency
  • *blindness
  • *cranial neuropathy
  • *encephalitis
  • *meningitis
  • *myelitis
  • *myocarditis
  • *paralysis
  • *pneumonia
  • *pneumonitis
  • *pulmonary edema
  • *rhabdomyolysis
  • *shock
  • *stupor, coma
  • *uveitis
ANTIMICROBIC

Yes

VACCINE

No

ENTRY
VECTOR
Ticks
RESERVOIR
Cattle, Goats and Sheep, Dogs, Rabbits, Rodents, Wild Animals
RISK FACTORS
  • Travel to endemic area
  • Victim--air release of infectious agents
  • Work in a medical or research lab
  • Work or play in tick-infested area
DRUG LINK
Merck Manual: Rocky Mountain Spotted Fever
REFERENCES FOR CASES/YEAR
1. (US) Published in MMWR 2011 = 2802; Use correction factor of 10 for reported diseases: 2802 X 10 = 28,020;
2. (Global) Most cases in mid-Atlantic and southern states, but also reported in Canada, Central America, and South America; Guesstimate from US rate: 50,000;