Rickettsiaceae, Anaplasmataceae, Coxiellaceae
- Small, intracellular pathogens
- Obligate aerobes
- Gram-negative rods that stain best with Giemsa or Gimenez stains.
- Some infections caused by these species are self-limiting
- Doxycycline can be administered to shorten illness duration and prevent complications.
Species overview
Be aware that all of these species were formerly categorized as members of Rickettsiaceae, and that intertextual variation exists.
Rickettsiaceae damages endothelial cells of blood vessels
Rickettsia rickettsii* causes
Rocky Mountain Spotted Fever
Rickettsia akari* causes rickettsial pox
Rickettsia prowazekii and Rickettsia typhi* cause different forms of typhus
Orientia tsutsugamushi* causes scrub typhus.
to damage to the endothelial cells of blood vessels.
Anaplasmataceae
Ehrlichia chaffeensis* causes human monocytic ehrlichiosis
Ehrlichia ewingii* causes human ewingii ehrlichiosis
Anaplasma phagocytophilum* causes human granulocytic anaplasmosis.
Coxiellaceae
Coxiella burnetti* causes Q fever.
Infections, Reservoirs, and Vectors
Rickettsia rickettsii
- Rocky Mountain Spotted Fever
— Fever, headache, myalgias, and, sometimes, confusion (as a result of CNS involvement).
— Patients commonly develop a
macular rash that can progress to petechiae; the
rash characteristically begins on the wrists and ankles, then spreads to the palms, soles, and trunk. This pattern of spread is a helpful distinguisher.
— Gastrointestinal involvement is possible, and can cause abdominal pain, nausea, vomiting, and/or diarrhea.
— Left untreated, disseminated vasculitis can lead to
multi-organ failure.
- Ticks and rodents are key reservoirs; hard ticks are vectors.
Rickettsia akari
— Typically less severe than Rocky Mountain Spotted Fever.
— Patients experience fever and papulovesicular rash with
eschars. Headaches and myalgia are possible.
— Rodents are the reservoirs; mites are the vectors.
Rickettsia prowazekii
—
Brill-Zinsser disease is the result of latent infection that manifests years, even decades, later.
— Patients experience fever, headache, chills, myalgia, and a
macular rash that spreads from the trunk to the extremities.
— CNS involvement is possible, and can present as confusion.
— If left untreated, vasculitis can lead to
multi-organ failure.
— Humans are the main reservoir, and the human body louse is the vector; be aware that flying squirrels and their fleas have also been described as reservoirs and vectors.
Rickettsii typhi
- Endemic typhus (aka, murine, typhus)
— Patients experience fever, headache, myalgia, and a
maculopapular rash that spreads from the trunk to the extremities.
— Gastrointestinal involvement is possible, and
more common in children.
— Cases are typically mild, but severe cases can lead to renal dysfunction or respiratory impairment (experienced as cough, dyspnea).
— Small mammals, particularly cats and rodents, are key reservoirs; their fleas are the vectors.
Orientia tsutsugamushi
— Fever, intense headahces, mylagias, and a
maculopapular rash that starts on the trunk; in some cases,
eschars will form, especially at the site of inoculation.
— Lymphadenopathy and pulmonary and neurologic involvement are common; gastrointestinal involvement may also occur.
— Reservoirs include mites (chiggers) and rodents; mites are the vector.
Ehrlichia chaffeensis
- Human monocytic ehrlichiosis
— Fever, headache, and myalgia; Coughing is common in adults.
— The
rash associated with this infection varies, and is more common in children.
— Central nervous system involvement is possible.
— Leukopenia, thrombocytopenia, and elevated transanimases.
— Deer, dogs, and other mammals are common reservoirs; soft ticks are the vector.
Anaplasma phagocytophilum
- Granulocytic anaplasmosis
— Similar symptoms and signs to human monocytic ehrlichiosis
—
Rash is rare.
— Small mammals are the reservoirs; soft ticks are the vector.
Coxiella burnettii
— Fever, headache, and myalgia, but
no rash.
— Chronic Q fever can lead to serious complications, including hepatitis, pneumonia, and subacute
endocarditis.
— Reservoirs include mammals, ticks, and birds; though ticks are a potential vector, most cases of Q fever are the result of the aerosol inhalation or consumption of the bacteria in contaminated milk.
