Colorado tick fever is a tick-borne viral disease that occurs in western North America in mountainous regions >4,000 feet. It causes a flu-like syndrome. Pharyngitis and mild lymphadenopathy may occur. Reservoirs include ticks and small mammals.
CASES/YEAR
50 (US); 1,000 (Global)
OTHER NAMES
CTF; Related arboviral fevers carried by ticks: Bhanja (Africa, Asia, & Europe); Dugbe (Africa); Nairobi sheep disease (Africa, India); Quaranfil (Africa, Middle East); Huaiyangshan (Eastern Asia); Thogoto (Africa & Europe); [CCDM, 27-8]
INCUBATION
3-4 days; [CCDM, p. 31]
INITIAL SYMPTOMS
A flu-like syndrome; [CCDM] Pharyngitis and mild lymphadenopathy may occur. [PPID, p. 1244]
PRECAUTIONS
Not directly transmitted from person to person except by transfusion. [CCDM, p. 56]
COMMENTS
FINDINGS
Common symptoms of tick-borne viral diseases include headache, arthralgia, myalgia, and rash. Occasionally, patients with Colorado tick fever, Bhanja, or Thogoto have central nervous system infection. [CCDM, p. 29] Some patients have pharyngitis, vomiting, diarrhea, and/or spleen enlargement. About 5-12% of patients have a maculopapular or petechial rash. Approximately 10% of symptomatic children develop encephalitis or meningitis. Death, reported in children but not adults, was caused by hemorrhagic shock, DIC, or meningoencephalitis. The virus infects red blood cell precursors resulting in viremia for the life span of the RBCs (four months). In a persistent infection of the hematopoietic system, CTF may cause neutropenia, thrombocytopenia, and mild anemia. Older patients often have residual fatigue for weeks after resolution of the acute symptoms. [PPID, p. 1244-5; 1980-1] May be difficult to distinguish from Rocky Mountain spotted fever, but RMSF does not have biphasic fever pattern and is 20 times less common in western endemic areas. Also RMSF has typical rash, usually beginning on the 3rd to 5th day of the illness. [Cecil, p. 2223]
EPIDEMIOLOGY:
Reservoirs include ticks and small mammals. [CCDM, p. 30] A transfusion-related case has been reported. Laboratory transmitted cases have also been reported. [PPID, p. 1980]
DIAGNOSTIC
Detection of CTFV-specific IgM (2 weeks after onset of sx); RT-PCR (1st 2 wks after sx onset; [PPID, p. 1981] Detect virions in erythrocytes by immunofluorescent antibody labeling. [Cecil, p. 2223]
SCOPE
Western N. America in mountainous regions >4,000 feet; [PPID, p. 1980] Bhanja (Africa, Asia, & Europe); Dugbe (Africa); Nairobi sheep dis. (Africa, India); Quaranfil (Africa, Mideast); Huaiyangshan (E. Asia); Thogoto (Africa & Europe); [CCDM]
SIGNS & SYMPTOMS
-
>fatigue, weakness
-
>fever
-
>fever, biphasic or relapsing
-
>myalgia
-
E pharyngitis
-
G abdominal pain
-
G diarrhea
-
G nausea, vomiting
-
H anemia
-
H leukopenia
-
H lymphadenopathy
-
H splenomegaly
-
H thrombocytopenia
-
N headache
-
N lethargy
-
N paresthesia
-
S papules or plaques
-
S petechiae and ecchymoses
-
S rash (exanthem)
-
*bleeding tendency
-
*encephalitis
-
*epididymo-orchitis
-
*hepatitis
-
*meningitis
-
*myocarditis
-
*pericarditis
-
*pneumonitis
-
*shock
ENTRY
Needle (Includes Drug Abuse), Scalpel or Transfusion
SOURCE
Eating Contaminated Food, Eating Contaminated Produce
RESERVOIR
Rodents, Wild Animals
RISK FACTORS
- Have a blood transfusion
- Travel to endemic area
- Work in a medical or research lab
- Work or play in tick-infested area
REFERENCES FOR CASES/YEAR
1. (US) 83 cases reported in Arizona, Colorado, Montana, Oregon, Utah, and Wyoming between 2002 and 2012; [Cecil, p. 2223] Guesstimate: 50 cases/year;
2. (Global) Guesstimate: 20 X US cases/yr = 1000;