Bacterial Febrile Illnesses & Rashes (Ditki Notes)

• Zoonotic illnesses typically transmit via arthropod vectors
• Details for less common species can be found in separate tutorials

Rickettsia Species

• Intracellular rods are responsible for a range of illnesses, primarily targeting the lining of small vessels

Rocky Mountain Spotted Fever

• Bacteria transmit via hard ticks
• Infection produces a rash that begins on the hands and feet before spreading to the trunk
• Ocular involvement, like conjunctivitis, is common
• Untreated, widespread vascular damage can lead to organ failure and death

Rickettsialpox

• Bacteria transmit via mites
• Infection displays an eschar (redness with a blackish scab) at the bite site and a vesiculopapular rash
• Rash resembles chicken pox
• Infection is usually mild and self-limiting

Epidemic Typhus

• Bacteria transmit via the human body louse
• Infection produces a pinkish macular rash that begins on the trunk and spreads to the extremities, spares the palms and soles
• Widespread vascular damage can lead to death
• Brill-Zinsser disease occurs when latent infection re-emerges; it is typically less severe, and rash may be absent

Endemic Typhus (Murine Typhus)

• Bacteria transmit via fleas that parasitize small mammals
• Infection is similar to epidemic typhus but milder

Borrelia Burgdorferi

• Spirochete transmits via hard ticks
• Causes Lyme Disease in the United States
• Other Borrelia species are responsible for Lyme Disease outside the United States
• Lyme disease is a multi-system inflammatory disease
• Early stages often present with localized erythema migrans (bulls-eye), flu-like symptoms like fever and headache
• Later, infection can produce multiple, smaller areas of erythema migrans
• Bacteria can spread to multiple organ systems, including the nervous system, heart, and musculoskeletal structures

Coxiella Burnetti

• Intracellular rods, not transmitted via arthropod vectors
• Bacterial endospores are inhaled from animal hides or wastes
• Not everyone who inhales the endospores will get sick
• Q fever presents with flu-like symptoms
• Pneumonia can occur in severe cases
• Q fever hepatitis has fibrin ring granulomas that may or may not have fat vacuoles inside
• Chronic Q fever may develop later
• Endocarditis is a common complication

Borrelia recurrentis and other Borrelia species

• Borrelia species that cause relapsing fever transmit via body lice and soft ticks
• Relapsing fever presents recurrent episodes of fever and septicemia due to bacterial proliferation
• Borrelia membrane proteins undergo antigenic variation, promoting cycling between bacteremia and clearance
  • Bacteremia leads to antibody formation and bacterial clearance from the blood
  • Bacteremia recedes, and the host enter an afebrile stage
  • Bacteria undergo antigenic variation, evading host antibodies and proliferating
  • The host enters a new febrile episode
• Symptoms range; mild cases may produce muscle and joint pain, abdominal tenderness, and vomiting, along with jaundice, and low platelet counts
• Severe cases can affect major organ systems, hepatic or cardiac failure, or cerebral hemorrhaging