NAME OF DISEASE:         Rocky Mountain Spotted Fever
                                            Tick typhus
                                            Fievre boutonneuse
                                            Kenya tick typhus
                                            Queensland tick typhus
                                            South African tick bite fever
                                            Indian tick typhus

ETIOLOGICAL AGENT:

    Rickettsia rickettsii, an obligate intracellular parasite which grows in both the cytoplasm and nucleus. The vector is a tick, Dermacentor andersoni.
 

PATHOGENESIS AND PATHOLOGY:

    The microscopic pathology of the rickettsial diseases is characteristic. The rickettsias multiply within the endothelial cells lining the small blood vessels. Endothelial proliferation and perivascular infiltration lead to leakage and thrombosis. Such vascular lesions in the skin produce the rash; identical lesions in the meninges probably account for the headache. The focal lesions tend to be particularly severe in RMSF. Thromboses and necrosis of arteriolar walls lead to the rupture of vessels and consequent petechial or large hemorrhages. Degenerative changes in muscles frequently occur in RMSF but are rare in other rickettsial diseases.
 

MANIFESTATIONS:

    Fever, headache, rash, toxicity, mental confusion, and myalgia constitute the principal clinical features of RMSF. The incubation time between tick bite and the onset of illness is usually 2-6 days, but it may be as long as 2 weeks. The onset may be gradual or abrupt. The fever rises rapidly, and it is characteristically high and spiking in most patients. Temperature peaks of 105-106°F are common, as are dramatic morning remissions of as much as 3-5 degrees. The pattern of fever may also be persistently high, holding at 102-104°F.

    The rash is almost invariably the earliest dependable diagnostic sign, occurring by the second or third day of illness in most patients. Occasionally, the rash may be delayed until the sixth day or later. Characteristically, the initial lesions are small erythematous macules that blanch on pressure. The lesions rapidly become maculopapular and petechial in untreated patients. Almost invariably, the rash first appears on the wrists and ankles, spreading within a few hours up the extremities to the trunk. Throughout the illness, the rash remains more marked on the extremities. A highly diagnostic feature of the rash, and of RMSF itself, is the regular occurrence of the rash on the palms and soles.

    The headache is described as extremely severe by patients old enough to give a history. It begins soon after onset, and it is intense, continuous, and intractable to all therapy. Toxicity is also a salient feature of the disease. The patient is restless, irritable, and apprehensive. In severe cases, there may be progression to mental confusion, delirium, and coma.

    Muscle tenderness is common. Patients characteristically complain bitterly when their calf or thigh muscles are squeezed. Edema, if present, may be generalized, but it is usually limited to the extremities or the face.

    Other signs include stiff neck, conjunctival suffusion, and oral exanthema. Enlargement of the spleen or liver is relatively infrequent. Local lesions (eschars with regional adenitis), although common in the other spotted fevers, are rarely seen in RMSF.
 

DIAGNOSIS:

    1.     Serology

            A.     Complement fixation     )     Antibodies first occur
            B.     Weil-Felix                     )     between 8 - 12 days

            C. Immunofluorescence of biopsy material (4-5 days)

    2.     Blood parameters

            A.     Leukocyte count (normal during first week and then progressing to 11,000 -
                    30,000/mm³)

            B.     Thrombocytopenia (decrease in number of platelets)

    3.     Isolation of organism

            A.     Inoculation of embryonated egg

            B.     Inoculation of guinea pig
 

DIFFERENTIAL DIAGNOSIS:

    1.     Measles - the measles rash does not involve the palms and soles. It is not a petechial
            rash and it spreads from head to trunk to extremities. Koplic spots (small red spots with a
            bluish-white speck at the center) occur on the buccal mucosa.

    2.     Meningococcemia - rash first occurs at skin pressure points, always petechial. Don't wait to
            differentiate - start chloramphenicol therapy immediately.
 

TREATMENT:

    Loading doses of chloramphenicol until the fever subsides, then half that amount for 3 more days. Tetracycline can also be used. SULFONAMIDES ARE CONTRAINDICATED. Infuse platelet concentrates to correct thrombocytopenia.
 

PREVENTION:

    1.     Control ticks

    2.     Killed vaccine - 2 doses one month apart. Annual booster after that.