Rickettsial diseases Flashcards
Where do all rickettsial diseases come from?
Arthropod hosts (tick, flea, louse, or mite) which is part of their life cycle
What are the major rickettsiae and what are their target cells they infect?
rickettsia (endothelium), Orientia (endothelium), Ehrlichia (monocytes or neutrophils), Anaplasma (neutrophils) and Coxiella (macrophages)
What is the pathogenesis of rocky mountain spotted fever?
Rickettsia spreads through the bloodstream and injures the host endothelial cells by the other membrane protein B. Ultimately, endothelium injury occurs via toxic reactive oxygen species. This increased vascular permeability is what leads to the petechiae, purpura, and vasculitis seen in spotted fever as well as the damage to target end organs (meningoencephalitis, and pulmonary edema/pneumonitis.
What does rocky mountain spotted fever look like clinically?
It begins with fever, headache, myalgias, nausea, vomiting and abdominal pain. The rash usually occurs on days 3-6. Thrombocytopenia and hyponatremia can occur. The rash occurs on the wrists and ankles and has a centripetal spread. Later macules/papules on the palms/soles
What are the 3 main types of rickettsial disease?
Spotted fever group, typhus group, and scrub group
What organisms make up the spotted fever group?
R. Rickettsii, R. conorii, R. akari, R. Africa, R. japonica, and R. australis
What organisms make up the typhus group of diseases?
R. typhi and R. prowazekii
What organisms make up the scrub typhus group?
R. tstsagamushi
How common is a rash in the spotted fevers, typhus group, and scrub typhus rickettsial infections?
85-100% of the time in spotted fevers, 50-80% of the time in typhus group and 50% of the time in scrub typhus
Is an eschar seen at the inoculation site in rocky mountain spotted fever?
NO! This is an important and constant feature seen in most of the spotted fever group and scrub typhus but not in RMSF and typhus group infections
Which rickettsial diseases have the worst mortality?
Severe: RMSF (25% if untreated, 4% if treated)>epidemic typhus (15% if untreated and 3% if treated)>Mediterranean spotted fever (3-5% mortality>endemic typhus and rickettsial pox which are benign
What two ticks cause RMSF and what areas do they cause the disease in?
Dermacentor variabilis is the #1 vector. This is in the eastern 2/3 of the US and the pacific coast
- Dermacentor andersoni is the #2 vector and is in the rocky mountain states
- Rhipicephalus sanguineus is in the southwestern US
What area is normally spared by the rash in RMSF?
The face
What is the treatment for RMSF?
Doxycycline is the tx of choice for everyone, even children
The only exception is pregnant women who should get chloramphenicol
What percentage of patients with RMSF remember the tick bite?
60% of patients recall tick bite
What rickettsiae causes the Mediterranean spotted fever “Boutonneuse fever”?
R. conorii
What tick usually carries R. conorii leading to Mediterranean fever?
Rhipicephalus sanguineus (brown dog tick)
Clinical features of Mediterranean spotted fever?
Presents with necrotic papule at the site of the tick bite. This then spreads to become a maculopapular eruption favoring the legs
First-line treatment for Mediterranean spotted fever?
Doxycycline
For mild disease in children you can use azithromycin and clarithromycin
What bacteria causes Rickettsialpox?
R. akari
Which tick carries R. akari for rickettsialpox?
Liponyssoides sanguineus (house mouse mite)
What is the clinical presentation of Rickettsialpox?
Within 48 hours a papulovesicle appears at the site of the bite. This progresses to an escar in the majority of pts (>90%)
- fever and systemic sx’s with widespread cutaneous eruption including the face, trunk, and extremities of red macules and papulovesicles with hemorrhagic crusts occur. Can have mouth involvement
Note the involvement of the face, as compared to RMSF which spares the face
What three diseases are considered the spotted fevers in rickettsial disease?
Rocky Mountain spotted fever (RMSF), Mediterranean spotted fever and rickettsialpox
What three diseases are included in the typhus group of rickettsial disease?
Endemic/murine typhus, cat flea typhus, epidemic typhus
What bacteria causes endemic/murine typhus?
R. typhi
What is the vector for endemic/murine typhus (R. typhi)?
Xenopsylla cheopis (oriental rate flea)
Note: this is also the vector for the bubonic plague
Clinical presentation of endemic/murine typhus?
Presents with fever and similar symptoms to the spotted fever diseases plus erythematous macules and papules that start in the axillae
What is the treatment for endemic/murine typhus?
Doxycycline
What bacteria causes cat flea typhus?
R. felis
What is the vector for cat flea typhus?
Ctenocephalides felis (cat flea)
Clinical presentation of cat flea typhus?
Identical to murine/endemic typhus (similar to spotted fevers but lesions start in the axillae).
Treatment for cat flea typhus?
Doxycycline
What is the bacteria that causes epidemic typhus?
R. prowazekii
What is the vector for epidemic typhus/R prowesekii?
Pediculus humanus var. corporis (human body louse)
What conditions predispose to epidemic typhus?
Crowded living conditions
What is Brill-Zinsser disease?
recurrence of latent epidemic typhus infection (occurs decades later)
What is flying squirrel typhus?
It is a type of epidemic typhus that can be caused by coming in contact with flying squirrels and their fleas/lice
Treatment for epidemic typhus?
Doxycycline
What bacteria causes scrub typhus?
Orientia tsutsugamushi
What is the vector for bush typhus/Orientia tsutsugamushi?
Larval trombiculid mites (chiggers)
Clinical presentation of bush typhus?
Eschars form over the bite sites. This progresses to fever, lymphadenopathy, and a macular rash that starts in the axillae and has centripetal spread.
Treatment for bush typhus?
Doxycycline, in pregnant women = azithromycin
Most common geographic location of bush typhus?
Asia
What bacteria causes human monocytic ehrlichiosis?
Ehrlichia chaffeensis
What is the vector for ehrlichiosis?
Amblyomma americanum (lone star tick)
Clinical presentation of ehrlichiosis?
Most common in the southern US
- Presents with fever, myalgias, thrombocytopenia, leukopenia, and maculopapular or petichael rash that is most common on the trunk and extremities
Mortality = 3%
No eschar at the site of innoculation
What is the treatment for ehrlichiosis?
Doxycycline
What is the reservoir for ehrlichia chaffeensis?
White tailed deer
What bacteria causes Human granulocytic anaplasmosis?
Anaplasma phagocytophilum
What is the vector for anaplasma phagocytophilum?
Ixodes scapularis and ixodes pacificus (same as lyme disease and babesiosis)
Clinical presentation of anaplasmosis?
It is similar to ehrlichiosis (fever, myalgias, thrombocytopenia, leukopenia, but there is a lesser chance of rash and decreased mortality. Can have peripheral neuropathy
Commonly occurs as a co-infection with Lyme or babesiosis
