L95 Rickets Flashcards
Rickettsia Host
- Blood-feeding arthropods may serve as both hosts and vectors
- Humans are typically accidental hosts
Two families in Rickettsiaceae Order?
- Rickettsiacceae
2. Anaplamataceae
Properties of the Rickettsiaceae
morphology etc
-Gram-negative, pleomorphic coccobacilli
• Glycocalyx is a slime layer
-Induce phagocytosis to enter host cells
• Escape phagosome
• Grow in cytoplasm and/or nucleus
-Can only be grown in cell culture
-Most survive only for short times outside of vector or mammalian host
• Quickly destroyed by heat, drying & bactericidal compounds
4 Rickettsial species with specific arthropod or insect hosts
- American dog tick (don’t need to know the microbe)
- House mouse mite
- Human body louse
- Cat flea
Rickettsial pathogenesis
• Rickettsiae multiply in endothelial cells of small blood vessels of the skin
and other organs
• Resulting damage leads to necrotizing vasculitis
• Major pathophysiologic effect: increased microvascular permeability
• Consequences: edema, hypovolemia, hypoalbuminemia, thrombo-
cytopenia, hypotension, reduced perfusion, multi-organ dysfunction
4 Rickettsia we need to know
R. rickettsii (RMSF) -Rocky Mountain spotted fever -Western Hemisphere R. akari -Rickettsialpox -Worldwide R. prowazekii -Epidemic typhus -Worldwide R. typhi -Murine (endemic) typhus -Western Hemisphere Worldwide
R. rickettsii
RMSF Mammalian reservoirs: Rodents, rabbits, (dogs?) Arthropod vectors (in USA): --American dog tick --Rocky Mtn. wood tick --Brown dog tick (Important in AZ!)
RMSF Hosts
Wild Rodents
R. rickettsii and RMSF: Disease
Incubation period: 2 – 14 d
Signs/Symptoms:
Fever & severe headache (often w/ sudden onset); other non-specific signs/symptoms: myalgia, nausea, vomiting, etc. (see notes)
Rash (2 – 5 d after onset of fever; absent in ~10% cases) - often begins on wrists, forearms & ankles
- spreads to trunk (centripetal spread)
What type of rash is a bad sign with RMSF?
if the macular rash becomes petechial
R. rickettsii and RMSF: Disease
Complications:
Mortality rate:
Complications: Myocarditis, CNS dysfunction, renal failure, gangrene, pneumonia, and others (see notes)
Mortality rate: 20 – 40% without treatment 2 – 5% with treatment
Early treatment decreases severity of disease & risk of death!
R. akari
-rickettsialpox
-cities, mice
Arthropod vector: House mouse mite
• Transovarial transmission occurs in the mite
rickettsialpox: phases
1st phase: red papule at bite site which becomes vesicular & then forms an eschar
2nd phase: 3 – 7 d after skin lesion appears, abrupt onset of fever and severe headache; other signs/symptoms may occur, e.g., chills, rigors & profuse sweating, myalgia
Rash: 2 – 3 d after onset of fever; generalized pox-like rash that can include palms & soles
Self-limited within 2 – 3 wk, even without treatment; no mortality
R. prowazekii
(louse-borne) typhus
Is the feeding or defecating what causes disease?
Most common mode of transmission: infectious louse feces are scratched into a louse bite wound
R. prowazekii and epidemic typhus: Epidemiology
Mammalian reservoir: Humans
Arthropod vector: Human body louse
NO transovarial transmission in lice!
R. prowazekii and epidemic typhus: Disease
Incubation period: 7 – 14 d
Signs/Symptoms: Sudden onset of fever & severe headache;
tachypnea, myalgia, & other signs/symptoms may occur
Rash: 4 – 7 d after onset of fever (absent in ~20% of cases) - often begins on trunk
- spreads to extremities (centrifugal spread)
Bad if it becomes petechial
R. prowazekii and epidemic typhus: Disease
Complications:
Mortality rate:
Complications: CNS dysfunction, myocarditis, pneumonia, renal failure, gangrene, multi-organ system failure
Mortality rate: 20 – 60% without treatment 3 – 4% with treatment
Early treatment decreases severity of disease & risk of death!
R. prowazekii: Brill-Zinnser disease and sylvatic typhus
Brill-Zinnser disease (recrudescent typhus)
- recurrent form, can develop decades after initial infection
- symptoms less severe; rarely fatal
Sylvatic epidemic typhus (aka sylvatic typhus)
- small number of cases, primarily in eastern USA
- symptoms less severe; no reported fatalities
- reservoir: southern flying squirrel
- likely vector: squirrel flea
R. typhi and murine (endemic) typhus: Epidemiology
Worldwide distribution, especially in urban & coastal port regions
• USA: 50 – 100 cases/yr, primarily in southern TX and southern CA
Mammalian reservoirs: Rats, mice, cats, opossums
Arthropod vectors: Fleas
• Transmission: Infectious flea feces inoculated into flea bite • Transovarial transmission occurs in fleas
Cat flea
R. typhi and murine (endemic) typhus: Disease
Incubation period: 7 – 14 d
Signs/symptoms similar to those of epidemic typhus, but typically less severe and of shorter duration
• Rash occurs in ~50% of cases
• Respiratory involvement occurs in ~30% patients
• Low mortality (4% without treatment; <1% with treatment)
Maculopapular rash
Diagnosis of rickettsioses
Presumptive diagnosis based on clinical presentation and patient history
Confirmatory diagnosis
• Serology (detectable titers after 1st week of infection) • Indirect immunofluorescent antibody (IFA) test
• Rash biopsy – PCR; immunohistochemical (IHC) stain
Treatment & prevention of rickettsioses
Treatment
• DOC: Doxycycline
• Chloramphenicol if doxycycline is contraindicated
Treatment should not be delayed – do not wait for lab results or if initial results (e.g., PCR) are negative!
Prevention • Avoidance of arthropod vectors • Prompt removal of attached arthropods • Control of reservoirs/vectors • Rodent control • Tick and flea control • Mass delousing w/ insecticide to control epidemic typhus • Vaccine for epidemic typhus no longer produced/available in USA
Properties of the Anaplasmataceae
Gram-negative, pleomorphic coccobacilli • Peptidoglycan reduced/absent • Slime layer glycocalyx Infect bone marrow-derived cells • Primarily target circulating leukocytes • Multiply w/in membrane-bound compartments, forming structures called morulae
How do you distinguish between rickettsia and anaplasmosis with a stain?
Anaplasma stay in leukocytes and stain as “morulae”
Vectors of the Anaplasmataceae
Lone star tick
Blacklegged tick
NO transovarial transmission in ticks
Which anaplasmatoacceae will we study?
We will consider…
• Ehrlichia chaffeensis, which infects monocytes/macrophages and causes
human monocytic ehrlichiosis (HME)
• Anaplasma phagocytophilum, which infects neutrophils and causes human
granulocytic anaplasmosis (HGA)
Ehrlichia chaffeensis and human monocytic ehrlichiosis (HME): Epidemiology
Worldwide distribution
• USA: ~500 - 1000 cases/yr within the last decade, primarily from southeastern & south-central US
• True incidence likely higher; estimated that appx. two-thirds of infections are asymptomatic (seroprevalence survey)
E. chaffeensis and HME: Epidemiology
Mammalian reservoirs:
Tick vectors (in USA) :
Mammalian reservoirs: White-tailed deer, dogs, coyotes, other mammals
Tick vectors (in USA) : Lone star tick, other tick species
