Rickettsiaceae

Obligate intracellular parasite Gram negative pleomorphic rods Parasite of arthropods – fleas, lice, ticks and

mites. No Human to human transmission.

TICK FLEA LICE MITE

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Virulence of Rickettsiae Adherence to the Host Cell inoculated into the dermis of the skin by a tick bite or through damaged skin from the feces of lice or fleas spread through the bloodstream and infect the endothelium Invasion of Host Cells attaching to the host cell membrane, rickettsiae are phagocytosed by the host cell quickly escape from the phagosome membrane and enter the cytoplasm Movement within and Release from the Host Cell Typhus group rickettsiae are released from host cells by lysis of the cells. Spotted fever group rickettsiae escape from the cell by stimulating polymerization of host cell-derived actin tails, which propel them through the cytoplasm and into tips of membranous extrusions, from which they emerge.

Organism Disease Vector Reservoir

Distribution

E chaffeensis Human monocytic ehrlichiosis

Lone Star tick

White tailed deer

Southeastern, Mid-Atlantic and South Central United States

E. ewingii

Primarily a dog disease Human granulocytic ehrlichiosis

Lone Star tick

White tailed deer

Southeastern, Mid-Atlantic and South Central United States

A. phagocytophilum

Human granulocytic anaplasmosis (human anaplasmosis)

Deer and dog ticks

Small mammals

Wisconsin, Minnesota, Connecticut

E. sennetsu Sennetsu fever Fish infected by trematod

mammals Japan

Disease Organism Vector Reservoir

Rocky Mountain spotted fever

R. rickettsii Tick Ticks, wild rodents

Ehrlichiosis E. chaffeensis E. ewingii

Tick Deer Deer Small mammals

Anaplasmosis A. phagocytophilum Tick Deer Deer Small mammals

Rickettsialpox R. akari Mite Mites, wild rodents

Scrub typhus R. tsutsugamushi Mite Mites, wild rodents

Epidemic typhus R. prowazekii Louse Humans, squirrel fleas, flying squirrels

Murine typhus R. typhi Flea Wild rodents

Q fever C. burnetii None Cattle, sheep, goats, cats

Rickettsial diseases

Epidemic Typhus

•Fever/chills •Myalgia •Headache •Rash (No eschar) – all over body except palm sole & face.

Endemic Typhus

•Fever •Myalgia •Headache •Rash (No eschar) Trunk> extremities

•Milder form of illness.

Scrub Typhus

•Fever •Headache •Rash with eschar •Lymphadeno-pathy

Indian Tick

Typhus

•Fever •Headache •Rash with eschar, first appear on wrist and ankle.

Q-fever

•Fever •Headache •Fatigue •Pneumonia • No Rash

Rickettsial diseases

Rocky Mountain Spotted Fever

•Fever •Headache •Rash (No eschar) – first appear on wrist & ankle •Palms & soles involved •Systemic Complications – R/S, CVS, CNS, Renal, Hepatic

Rickettsial Pox

•Mild Illness •Fever •Headache •Vesicular Rash with eschar •Lymphadenopathy •Resemblance to chicken pox

Weil-Felix Proteus Agglutination Test

Weil-Felix test- Based on the antigenic cross reactions among

rickettsial antigens, mostly LPS, and Proteus vulgaris strains

OX19 and OX2, and Proteus mirabilis OXK .

Procedure: Serum is diluted in three separate series of tubes followed by the addition of equal amount of OX19,OX2,OXK in 3 separate series of tubes. Incubation at 370C for overnight. Observe for agglutination.

Weil –Felix Reaction

OX 19 OX 2 OX K

Epidemic typhus +++ + -

Endemic typhus +++ ± -

Tick born spotted fever

++ ++ -

Scrub typhus - - ++

Treatment

Treatment should be started early in the first week of illness.

Doxycycline (first choice)

Tetracycline (alternate)