Cause:Rickettsia rickettsiae
Pathophys:Angiitis due to endothelial infection causing proliferation and thrombosis. Subclinical DIC changes in platelet and clotting system detectable even before sx (Nejm 1988;318:1021)
Carried by ticks (large and visible) from wild rodent reservoirs. Endemic in Rocky Mountain rodents; also on Cape Cod and throughout most mid-Atlantic states including Virginia and North Carolina; also seen in lab technicians working with ticks. 700-1000 cases/yr in US
Sx:Seasonal; 95% of cases between April and August. Tick bite (most recall) or dog contact. Incubation period, 5-7 d. Severe frontal headache (90%) is usually 1st sx; myalgias (80%), emesis (60%)
Si:Rash (90%), centripetal progression (extremities to trunk), palm and sole involved (in 2/12); toxic with fever leading to confusion (in 10/13); muscle tenderness, esp calf and thigh; diffuse angiitis; skin necrosis regardless of pressure points
Mortality without rx = 25%; w rx = 5%. Carditis, cerebral edema, DIC
r/o babesiosis (Babesiosis); rat bite fever (Rat Bite Fever); RICKETTSIAL POX(Nejm 1994;331:1612) from Rickettsia akari,seen all over US, initial lesion at mouse mite bite, 1-wk latency then fever, malaise, and chicken pox-like vesicular lesions, not too sick, can rx w tetracycline; other rickettsial pox in other parts of world, eg, NORTH ASIAN RICKETTSIOSIS, AFRICAN TICK BITE FEVER (Nejm 2001;344:1504), QUEENSLAND TICK TYPHUS, TYPHUS
Lab:
Hem:Thrombocytopenia (Nejm 1969;280:58) and DIC
Path: Skin bx of rash positive on immunofluorescent stain (available from CDC)
Serol: Antibody increased by immunofluorescence or microagglutination by day 15. Weil-Felix test: in Rocky Mountain spotted fever, OX2 and OX19 positive, OXK negative; in rickettsial pox, all neg
Rx: 1st, tetracycline; or 2nd, chloramphenicol