5-89
Principal Animal Hosts: Deer, wild rodents
Clinical Disease in Animals: Limb or joint disease, neurologic, cardiac, renal abnormalities
ID: Relapsing Fever
COL Naomi Aronson, MC, USAIntroduction: Borrelia recurrentis is a spirochete transmitted by soft ticks and crushed body lice. The soft tick
usually feeds on sleeping people in houses/cabins/caves/other dwellings. The risk of infection after infected tick
bite is about 50%. Fevers last 2-9 days, alternating with 2-4 day afebrile periods and have many, progressively
milder recurrences. The incubation period is 5-15 days.
Subjective: Symptoms
Constitutional: Acute (< 3 days): Abrupt onset fever 101-105°F, fever lasts 1-5 days then recurs multiple times,
as fever ends: chills, diaphoresis, headache, arthralgias, myalgias, nonproductive cough
Specific: Sub-acute (4-14 days): Neurologic symptoms: Bell’s palsy, deafness, visual changes mental status
changes; myocarditis (symptoms of congestive heart failure)
Focused History: Have you had on-and-off fevers lasting several days at a time? (typical pattern, but may be
seen with malaria and others) Have you had a recent tick bite? (exposure)
Objective: Signs
Using Basic Tools:
Inspection: Acute (< 3 days): Fever 101°F - 105°F that lyses with rigors, then recurs; with decreased fever,
may see 30 minutes of tachycardia and increased blood pressure followed by diaphoresis and decreased blood
pressure Sub-acute (4-14 days): 10% appear jaundiced, petechiae (if thrombocytopenic, esp. during fever) on
neck and shoulders, conjunctival hemorrhage
Auscultation: Sub-acute (4-14 days): If myocarditis develops: S3 and bibasilar rales
Palpation Sub-acute (4-14 days): Splenomegaly; if neurologic involvement: cranial nerve palsies VII/VIII, bilateral
or unilateral Bell’s palsy
Using Advanced Tools: Lab: Giemsa or Wright’s stain of a thin blood smear taken during fever may show
spirochetes with darkfield exam. Examine up to 200 oil immersion fields before considering the smear negative.
Blood smear may show thrombocytopenia, mild anemia, and a normal WBC count.
Assessment:
Differential Diagnosis:
Malaria - non-falciparum malaria may have periodic fevers; malaria parasite on blood smear and mosquito
exposure
Lyme Disease - early in infection see skin patch/target lesion of erythema migrans; low grade temperatures
usually
Leptospirosis - history of exposure to standing water/mud; usually a biphasic febrile illness with remarkable
conjunctival discharge
Dengue - mosquito-borne febrile illness with prominent myalgias, headache, diffuse rash
Meningococcus - sustained febrile infection, often fulminant; petechia that progress to purpura; often with
associated meningitis.
Ehrlichiosis - tick-borne fever infection; associated with pancytopenia on blood smear; usually no relapsing
fever pattern
Other considerations include babesiosis, typhoid, brucellosis, rickettsial infection, Colorado tick fever.