Rocky Mountain spotted fever


Tickborne infection caused by Rickettsia rickettsii.

Vertical transmission depends on a tick with an infected ovary which ensures infected tick progeny.

R rickettsii impairs tick well-being with the development of few larvae and mature ticks.

Rickettsia rickettsii in the salivary glands of a vector tick is transf2242ed into the dermis of a human with spreading and replication in endothelial cells causing a widespread vasculitis with most significant damage in the brain and lungs.

Skin manifestation develop between day three and five of the illness with typical lesions starting on the ankles and wrists and spreading proximately to the palms and soles.

Skin lesions range from maculopapular to petechial.

Skin biopsies reveal vasculitis with perivascular infiltration of neutrophils and lymphocytes.

A maculopapular rash usually occurs 2-3 days after the disease onset.

Endothelial cell damage is caused by Rickettsial organisms.

Late skin lesions may manifest with a leukocytoclastic vasculitis with neutrophil infiltrates, fibrin thrombi, and capillary wall necrosis.

Predominantly transmitted by American dog tick, Dermacentor variabilis, and the Rocky Mountain wood tick D. andersoni.

Horizontal transmission depends on transient rickettsemia in nonimmune hosts, on which uninfected ticks feed and become infected.

Incidence increased by three times between 2001-2005.

In 2005 CDC reported 1936 cases.

Cases are reported throughout the Americas.

Patients often present with muscle weakness followed by systemic illness that may include rhabdomyolysis.

1 in 3 pediatric patients and 1 in 5 adult patients require hospitalization.

With treatment 4% fatality rate and 72% hospitalization rates.

Most common fatal tickborne illness in the U.S.

Can cause pneumonia, myocarditis, renal failure, hepatitis, encephalitis, gangrene and death.

Majority of patients do not have the triad of fever, rash and history of tick bite.

Absence of tick bite history is common and the rash may appear several days after the fever.

Up to 30% of untreated patients die of the disease.

Severe illness and death associated with delayed diagnosis.

Fever, rash and tick bite are the classic features and it is best treated with doxycycline for 7 days.

50% of deaths occur within 9 days of onset of illness.

Treatment most effective when initiated within 5 days of the onset of illness.

Treatment with doxycycline should not be delayed for laboratory confirmation of the diagnosis.

Because of the nonspecific presentation diagnosis is difficult, with patients presenting with fever, myalgias, headache and a rash.

Usually 3-5 days after the illness starts a macular rash evolves into a maculopapular and then petechial pattern.

Nausea, vomiting, abdominal pain and cough may accompany the illness.

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