Rocky Mountain Spotted Fever (RMSF)

• Rickettsiae are very short, rod-shaped intracellular parasites.
• A life-threatening disease caused by Rickettsiae typically occurs in the southeastern United States.
• Rickettsial infections are most common in children during the spring and early summer due to tick activity.
• Ticks are the primary vector of Rickettsia rickettsii in the U.S., with the tick population acting as a reservoir, transmitting the organism between ticks.
• Rickettsial organisms enter through the skin and spread via the bloodstream, infecting vascular endothelium in organs.

Rocky Mountain Spotted Fever (RMSF)

• RMSF is caused by Rickettsia rickettsii.
• RMSF symptoms include: fever, headache, myalgia, and prostration.
• A rash appears 2–6 days after the onset of symptoms.
• The rash starts on the hands and feet and spreads inward to the trunk.
• Severe cases of RMSF can cause DIC, edema, and circulatory collapse.
• Central nervous system involvement can lead to delirium, coma, and seizures.
• Diagnosis of RMSF involves serology, typically indirect immunofluorescence or ELISA.
• An acute-phase serologic titer of ≥1:128 is considered diagnostic.
• Tissue biopsy with special stains from the rash site can aid in diagnosis.
• The Weil-Felix test is of historical interest only and not used due to low sensitivity/specificity.
• Rickettsiae are best visualized using a Giemsa stain under a light microscope.
• Rickettsiae must be grown in cell culture, embryonated eggs, or experimental animals.
• The first-line treatment for all Rickettsial diseases is doxycycline.
• For children, pregnant women, and individuals with tetracycline allergies, chloramphenicol is used due to contraindications with doxycycline.
• Prevention of tick exposure involves wearing protective clothing, using insect repellents, and performing frequent skin checks.
• Ticks must be attached for several hours to transmit RMSF.

Epidemic Typhus

• Epidemic Typhus is caused by Rickettsia prowazekii and transmitted by body lice.
• It is mainly found in Central and South America, Africa, and less commonly in the U.S.
• Outbreaks occur in crowded, unsanitary living conditions.
• Symptoms include high fever, chills, headache, and prostration.
• The rash spreads from the trunk to the extremities (opposite of RMSF).
• Older individuals experience more severe symptoms.
• CNS dysfunction, myocarditis, and death are complications.
• Personal hygiene and delousing with DDT are methods of prevention.

Endemic (Murine) Typhus

• Endemic Typhus is caused by Rickettsia typhi.
• Rats and fleas are the primary reservoirs and vectors, with cats and cat fleas also playing a role in the U.S.
• Seen mainly in Texas and Southern California.
• Symptoms are similar to epidemic typhus but milder.

Scrub Typhus

• Scrub Typhus is caused by Orientia tsutsugamushi.
• It is found in Eastern Asia, Australia, Japan, and Western Pacific islands.
• Mites transmit the disease.
• Rodents and mites are reservoirs.
• Symptoms include fever, headache, rash, and eschar (necrosis) at the bite site.

Chloramphenicol

• Chloramphenicol inhibits bacterial protein synthesis by binding to the 50S ribosomal subunit at the peptidyltransferase site.
• It is used to treat meningitis (H. influenzae, N. meningitidis, S. pneumoniae), BLP (E. coli, Klebsiella pneumoniae, H. influenzae), anaerobes (Bacteroides), and rickettsia rickettsii.
• Chloramphenicol is contraindicated in neonates due to the risk of gray baby syndrome.
• Side effects include anemia (dose-dependent), aplastic anemia (dose-independent), and gray baby syndrome (in premature infants).
• It is only used for life-threatening infections because of its toxicity, including gray baby syndrome (vomiting, lethargy, respiratory depression, and death).
• Can treat rickettsial diseases such as Rocky Mountain spotted fever.