Tick bites, with transmission from the tick's salivary glands after at least 6 to 10 hours of attachment ○ Modes of transmission include the following: ○ rickettsii in nature (i.e., the dog tick, Dermacentor variabilis, in the eastern two thirds and western coast of the United States the wood tick, Dermacentor andersoni, in the Rocky Mountain states and other ticks in Mexico, Central America, and South America). Ticks are the vector and the reservoir of R. Echocardiographic studies reveal minimal myocardial dysfunction, 187 and normal pulmonary capillary wedge pressure measurements document the noncardiogenic nature of the pulmonary edema. 186 Patients with pulmonary edema with impairment of pulmonary function or acute respiratory distress syndrome may require oxygen therapy and ventilatory assistance. Pulmonary involvement is suggested by cough and radiologic changes, such as alveolar infiltrates, interstitial pneumonia, and pleural effusion. 185 Prerenal azotemia related to hypovolemia responds to intravenous hydration however, in patients with acute tubular necrosis, hemodialysis may be required. Renal failure is an important problem in severe RMSF. These changes may reflect retinal vasculitis with increased permeability and focal thrombosis. On funduscopic examination, retinal vein engorgement, arterial occlusion, flame hemorrhage, and papilledema without increased CSF pressure have been noted. 184 Sequelae occur less often in patients with early antibiotic treatment. In a more recent series of cases of children with RMSF, 15% of survivors had neurologic deficits at discharge, including global encephalopathy, ataxia, and blindness. 183 These sequelae were headache and other subjective findings, but 12 cases involved electroencephalographic abnormalities. Among 37 patients followed for 1 to 8 years after acute RMSF, including some in the preantibiotic era, 21 had residual neurologic abnormalities. In general, neurologic involvement portends a bad prognosis. The electroencephalogram may show diffuse cortical dysfunction. However, glucose concentration is low in the CSF of only 8% of patients. The cerebrospinal fluid (CSF) contains increased leukocytes in one-third of patients, with either lymphocytic or polymorphonuclear predominance 146 CSF protein concentration is increased in one-third of patients. Focal neurologic deficits, transient deafness, meningismus, and photophobia may suggest meningitis or meningoencephalitis. 181,182 Headache is usually quite severe. Careful examination seldom reveals an eschar at the site of the tick bite in RMSF. 146 Gangrene involves the digits or limbs and occasionally necessitates amputation. Skin necrosis or gangrene develops in only 4% of cases as a result of rickettsial damage to the microcirculation. Involvement of the palms and soles is considered characteristic, but it occurs in only 36% to 82% of patients who have a rash it often appears late in the course ( Figs. The rash typically begins around the wrists and ankles but may start on the trunk or be diffuse at the onset. 145,180 A delay in diagnosis is occasionally associated with the absence or late onset of rash. Rocky Mountain “spotless” fever occurs more often in older patients and in black patients. The rash, the major diagnostic sign, appears in a small fraction of patients on the first day of the disease and in only 49% during the first 3 days, usually appearing 3 to 5 days after the onset of fever and occurring in 88% to 90% of patients overall. Other signs and symptoms are frequently prominent early in the course before the onset of rash, at which time gastrointestinal involvement with nausea, vomiting, abdominal pain, diarrhea, and abdominal tenderness occurs in substantial numbers of patients this may suggest gastroenteritis or an acute abdominal condition requiring surgery. 145 The variable incidences of reported headache and myalgia in different series are likely related to the proportion of young children who may not articulate the concept of pain. The temperature is higher than 102☏ (38.9☌) in 63% of patients during the first 3 days and in 90% later. The disease usually begins with fever, myalgia, and headache, most likely the effects of proinflammatory cytokines ( Table 186.1). Variation in incubation time may be related in part to inoculum size. The incubation period of RMSF ranges from 2 to 14 days, with a median of 7 days. Bennett MD, in Mandell, Douglas, and Bennett's Principles and Practice of Infectious Diseases, 2020 Clinical Manifestations
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