Micro- Vector Borne Infections Flashcards
What 2 genera are considered to be in the Rickettsiaceae family?
What 4 genera are in the Anaplasmataceae family?
Rickettsia:
- rickettsia
- orientia
Anaplasmatacaeae
- anaplasma
- ehrlichia
- neorickettsia
- wolbachia
Rickettsia genera has more than 30 species associated with human disease. The genera is further broken down into what 2 groups?
- spotted fever group
2. typhus group
Orientia only has one species. What is it and what does it cause?
O. tsutsugamushi
It causes scrub typhus
What is the size, shape, and gram stain capacity of Rickettsia and Orientia?
What is required to grow the in vitro? Why?
They are small, pleomorphic gram negative coccobacilli
They contain non-toxic LPS and peptidoglycan.
To grow in vitro, they require living cells like yolk sac of embryonated eggs or tissue culture cell lines because they are OBLIGATE INTRACELLULAR parasites
Rickettsia species are found worldwide. Each species has a specific arthropod vecor and one or ore animal reservoirs. What are the 4 arthropod vectors?
- hard tick–RMSF, tick typhus
- mites– richettsialpox, scrub typhus
- lice–
- fleas– endemic typhus
What intracellular parasite causes RMSF?
What is the primary reservoir?
Where are endemic areas in the US?
What is the seasonal preference and arthropod vector?
Intracellular parasite: Rickettsia Rickettsii
Primary reservoir: rodents [although other mammals can be hosts as well]
Endemic areas: 1. Mid-Atlantic states 2. Texas, Oklahoma - Lonestar tick 3. Southeastern US - Dog tick [in the west, it is the wood tick]
Seasonal preference: spring/summer
How does transmission of the infection differ from Lyme disease in the Ixode tick vs. Rickettsia Rickettsii in the wood, lone star and dog ticks?
Rickettsia is maintained by transovarial transmission [Vertical].
Lyme disease is not maintained by vertical transmission
What intracellular parasite causes rickettsialpox?
What is the natural reservoir? arthropod vector?
What are the 2 ways the infection is maintained?
What environment does it occur in?
Rickettsia akari
Natural reservoir: wild rodents/mice
Arthropod vector: mite
Maintained by:
- mice-to-mice transfer via mites
- maintained in mites via vertical transmission
Environment: worldwide, but prefers drier environment
What disease is caused by:
R. conorii
R. australis
R. africae
Where do they occur? What is the arthropod vector?
Tick Typhus in the Mediterranean, Australia and Africa respectively.
Vector: brown dog tick
What are the two forms of typhus?
What is the vector for each type?
What intracellular parasite causes each?
What is the main reservoir of each?
- Epidemic
- human louse borne
- R. prowazekii
- reservoir : humans [crowding, poor hygiene, poverty] or squirrels [southern flying squirrel] - Endemic
- flea-borne [the rat flea]
- R. typhi
- reservoir: rats, mice, rodents in Texas, southern border states
What is the intracellular parasite and reservoir/vector of scrub typhus?
How is the parasite maintained?
Orientia tsutsugamushi
Reservoir/vector: mite
Maintained by transovarial transmission
What is the pathogenesis of Rickettsia?
- infecting organism is introduced to human host by a bite, but the tick must stay attached for 24-48 hrs to transmit the Rickettsia
- local replication
- bacteremic spread
- enters host cell by stimulating phagocytosis, then degrading the phagosome using bacterial phospholipase to enter cytoplasm
Where do the following grow within the host cell?
How are they released?
- spotted fever group [rickettsii, akari, africa, australis, coronii]
- orientia
- typhus group [prowazekii, typhi]
Why does this difference exist?
- grow in the cytoplasm and released by membrane protrusion
- grow in the nucleus and released from membrane protrusion
- grow in cytoplasm and released by lysis of host cell
Spotted fever group has the ability to polymerize actin.
How do Rickettsia get energy?
- make their own ATP via TCA cycle
2. parasitize the host cell ATP by means of bacterial ATP translocase
What are the primary sites of replication in Rickettsia infection?
Vascular endothelium leading to:
1. vasculitis due to cell dysfunction and death leading to capillary damage and leaking of blood cells into perivascular tissue –> petechial hemorrhage
- exposed subendothelium activates clotting cascade leading to thrombosis and necrosis
In general ALL rickettsial infections are characterized by what features?
What is the range of incubation period?
- Fever, headache, malaise, prostration
- Skin Rash
- enlargement of spleen and liver
Incubation is 2-15 days with most lingering around 1 wk
A patient presents with a high fever, chills, headache and myalgias. He said it was rapid onset, but he didn’t seek help because he thought it was some viral thing. He had been camping in the woods last week in Georgia and wasn’t sure he cooked his food properly. About 3 to 5 days into the fever, he got a maculopapular rash on his wrists, ankles, palms&soles. The rash spread to his trunk and became petechial. He did NOT have eschar or tache noir.
What is the presumptive diagnosis?
RMSF
- endemic area [southeast-dog tick]
- fever, malaise, headache followed 3 days later by rash
- rash involves palms, soles, wrists, ankles with CENTRIPETAL SPREAD
- unlike the other rickettsial diseases, there was no eschar or tache noir marking the site where the tick bit him
What is case fatality for RMSF in elderly and children?
What increases the fatality rate?
Elderly =50%
Children= 20%
Fatality is increased by delaying until after the presentation of the rash
What characterisitic of the RMSF rash differentiates it from the other rickettsial diseases?
Centripetal nature [starts on wrists, ankles and then works inward]
How does tick typhus presentation differ from RMSF?
- milder, less fatal
- less prominent rash that usually appears on trunk
- tache noir at site of tick bite
Describe the presentation of Rickettsialpox.
Phase 1:
Papule at the site of the mite bite becomes tache noir in 7-10 days.
Phase 2:
3-7 days after tache noir, the patient gets
- fever, chills, myalgia
-regional lymphadenopathy
- stiff neck [MENINGITIS LIKE PRESENTATION]
- papulovesicular rash –> crusting
It resolves without therapy and has low mortality.
A patient presents with fever chills, myalgia, regional lymphadenopathy and a stiff neck. She has a papulovesicular rash with vesicles and crusting. Near the rash is a black spot. She said the black spot started as just a bump about 2 weeks ago.
What is it likely she has?
Rickettsialpox
Describe the pathogenesis of epidemic typhus?
When/how does the infection start?
What is incubation period?
What symptoms show up first?
How is the presentation different from RMSF?
- bite from pediculus humanus corporis which feeds and then defecates
- Feces are pruritic so the human scratches and grinds feces into the cut
- 8 day incubation
- constitutional symptoms with fever, myalgia, headache, arthralgia
- 4 to 7 days later a rash begins on the trunk and then spreads outward but SPARES palms, soles, face [unlike RMSF]
If a patient is to die of epidemic typhus, what is the usual cause?
Myocarditis or CNS complications
How does endemic typhus compare to epidemic?
Similar presentation except:
- milder
- rash restricted to chest only
What is Brill-Zinsser disease?
reactivation of epidemic typhus that occurs decades after the resolution.
It is mild and resolves with minimal sequelae
How does the incubation period, rash, presence of tache noir and systemic symptoms differ for scrub typhus and RMSF?
Scrub typhus has a longer incubation period
[10-12 days compared to a week]
Scrub typhus has a rash more similar to epidemic typhus that starts on the trunk and spreads outward WITH a tache noir where RMSF has a rash that starts peripherally and extends centrally WITHOUT tache noir.
Scrub typhus has:
- hepatosplenomegaly
- cardiac failure
- CNS effects like stroke
How are rickettsial diseases diagnosed?
- clinical presentation with good travel history
- indirect immunofluoresence test [sensitive, specific] done 4th to 8th day of disease that is done to confirm clinical
- biopsy with PCR is diagnostic but only done in reference labs
What is treatment for Rickettsia?
DRUG OF CHOICE:
- Doxycycline for 5-7 days or until patient is afebrile for 2 or more days
- started empirically because time =death or RMSF
- done even in pregnant/children b/c life»_space; discolored teeth
Chloramphenicol is used OUTSIDE the US
Where do ehrlichia and anaplasma live?
What is their size, gram stain?
Within membrane-bound vacuoles of leukocytes.
They form clustered microcolonies called morulae.
They are small coccobacilli that have dual membranes like G-, but lack LPS and peptidoglycan. They do not stain with Gram stain.
What stain can be used to identify ehrlichia and anaplasma?
Blood smear stains like Giemsa Wright
They do not stain with gram stain because despite the fact they have 2 membranes, they lack LPS and peptidoglycan
Human monocytic ehrlichiosis is caused by what organism?
What organism causes human granulocytic ehrlichiosis?
Monocytic ehrlichiosis = E. chaffeensis
Granulocytic ehrlichiosis = Anaplasma phagocytophilum
How do ehrlichia and anaplasma get their energy?
They synthesize ATP from glutamine
How does where rickettsiae and anaplasmataceae replicate inside the cell differ?
Rickettsia = inside the cytoplasm or nucleus after using phospholipase to degrade the phagosome
Anaplasma = prevents lysosome fusion, but remains protected in the phagosome where it divides by binary fission to form the morulae
For human monocytic ehrlichiosis, what is the:
- intracellular organism
- vector
- reservoir
- regional preference
- Ehrlichiosis chaffeensis
- Lone star tick and dog tick
- Rodents
- Midwest, Mid-Atlantic, Southeast, South Central
* *Missouri and Arkansas
For human granulocytic ehrlichiosis, what is the:
- intracellular organism
- vector
- reservoir
- regional preference
- Anaplasma phagocytophilum
- Ixode tick [same as Lyme]
- rodents
- Upper Midwest, Northeast
* Wisconsin
What is the clinical course of HGE and HME?
- Tick bite
- 7 day incubation
- gradual onset fever, myalgia, headache [rash only occurs in 1/3]
- later in the course:
- anorexia/weight loss
- anemia, leukopenia from hemolysis
- abnormal LFTS
What are the 2 things done for diagnosis of HGE or HME?
- Routine blood smear to look for morulae
- only 10% of HME will have it
- only 20-80% of HGE will have it - Serology
In what 3 ways does diagnosing HGE, HME differ from diagnosing RMSF?
- HGE, HME you do NOT do culture as with RMSF
- PCR is standard for HGE, HME in endemic areas and not for RMSF
- Vasculitis is NOT observed in ehrlichiosis, but is the hallmark of RMSF
What is treatment for ehrlichiosis or anaplasma
Doxycycline
To what 2 bacteria is Coxiella phylogenetically related?
How does it gram stain?
What is its structure?
What does it require to be cultured?
It is related to legionella and francisella
It does not gram stain but is structurally similar to a Gram negative and has LPS
It is a small coccobacilliary organism that is obligate intracellular
It requires eggs or tissue culture to grow
What is the arthropod vector of coxiella?
What are the most common reservoirs?
How are humans infected? What are the 3 most common people to get infected?
Ticks carry coxiella from animal to animal NOT from animal to human.
The reservoir is large animals like cows, sheep, goats, but also domestic animals like dogs cats and sheep.
Humans get infected by inhalation of the organism that is released when milk, urine, feces or ESPECIALLY PLACENTA after parturition is left on the ground and dries.
This makes the following most likely to be infected:
- ranchers
- microbiologists
- slaughterhouse workers
What is pathogenesis of Q fever?
- Coxiella spore with VIRULENT LPS1 gets inhaled
- It is phagocytosed and lysosomal fusion occurs
- it thrives in the acidic pH of the phagolysosome and is able to go through its life cycle
- In tissue culture it has phase II LPS which is less virulent
A rancher presents with a fever that lasts 1-2 weeks with chills, headache, fatigue, sweating and muscle aches. Upon examination you notice that he has walking pneumonia and granulomatous hepatitis.
What is it likely that he has?
When will he likely experience resolution?
Acute Q fever
Can resolve spontaneously in 4 to 6 weeks
What is the incubation period for acute Q fever?
What determines the length?
10-60 days and depends on the number of spores inhaled.
1-2 spores is enough to cause infection in animal models
What are some of the key symptoms of acute Q fever?
- flu-like symptoms
- walking pneumonia
- granulomatous hepatitis [in 1/2]
What is the most common presentation of chronic Q fever?
subacute endocarditis
How is diagnosis of Q fever made?
- serological [ELISA, IFA.etc]
- acute has IgM and IgG to phase II antigens
- chronic has IgG to phase II and phase I antigens
What is treatment for Q fever?
doxycycline
[for endocarditis add rifampin]
What is prevention for Q fever?
Vaccines are given for those at high risk for infection [lab workers, meat plant, dairy workers, ranchers]
Whole cell and partially purified
The most effective vaccines have phase I LPS because this is the infective form
