Rickettsiales Flashcards
How does the presence of LPS and peptidoglycan differ in Anaplasma, Rickettsia, and Ehrlichia?
- Anaplasma and Ehrlichia lack LPS
- Rickettsia has LPS
~ Anaplasma and Ehrlichia have minimal peptidoglycan
~ Rickettsia has the classical peptidoglycan (very similar to other Gram-negative bacteria)
Since Anaplasma and Ehrlichia lack LPS, what maintains cell wall stability?
acquire cholesterol from their host
What are the 2 morphotypes of Anaplasma and Ehrlichia?
- EXTRACELLULAR: dense-cored cell (DC)
- INTRACELLULAR: reticulate cell (RC- morula)
How do the intracellular morula of Anaplasma and Ehrlichia behave? How does Rickettsia compare?
replicate in vacuoles (like Chlamydia and Salmonella)
lacks 2 different life forms and does not hide in vacuoles (like Listeria and Yersinia)
Why are Rickettsiales members obligate intracellular pathogens?
- cytoplasmic membranes of Anaplasma, Ehrlichia, and Rickettsia are highly permeable
- Anaplasma, Ehrlichia, and Rickettsia cannot produce enough of their own ATP
- Anaplasma and Ehrlichia are dependent on cholesterol from their host cell to stabilize their cell envelop
How are Anaplasma and Ehrlichia transmitted?
arthropod-borne —> ticks
What are the 4 groups of Rickettsia? How is each transmitted? What 3 characteristics are used for this differentiation?
- spotted fever group - Dermacentor ticks
- ancestral group - ticks
- typhus group - fleas, lice
- transitional group - ticks, mites, fleas
- LPS serogrouping
- arthropod vectors
- clinical manifestations
What is required for Anaplasma, Ehrlichia, and Rickettsia transmission? Why?
arthropods
- cannot stay outside of a cell for a long time
- arthropods are able to directly deposit them into or near blood vessels so they can immediately infect blood cells or endothelium
How do the arthropod vectors of each Rickettsiales member transmit them?
RICKETTSIA - various arthropod larvae, nymph, and adults exhibit transstadial and transovarian transmission
ANAPLASMA, EHRLICHIA = only nymph and adult ticks undergo transstadial transmission
Why does there seem to be a predilection for ticks for Rickettsiales transmission?
ticks hunt animals for blood meal and there are at least 3 stages in their life where they have a high chance of transovarian and transstadial transmission
- TO = larvae climb onto host, get a blood meal, and engorged larvae drop in vegetation
- TS = nymph climbs onto host, gets a blood meal, and engorged nymph drops in vegetation
- TS = adult ticks climb on host, get a blood meal, and engorged females drop in vegetation where they lay eggs
What are the 4 most medically important ticks in the US?
- Rhipicephalus sanguineus - brown dog tick
- Amblyomma americanum - lone star tick
- Dermacentor variabilis - dog tick
- Ixodes scapularis - eastern black-legged tick
What are the general predilection sites for Rickettsiales in vertebrates? Specific genera?
blood cells and endothelial cells
- Anaplasma = RBC, WBC, platelets
- Ehrlichia = WBC, endothelium
- Rickettsia = endothelium
What are the 2 predilection sites of Rickettsiales in arthropods?
- midgut cells
- salivary glands
Which 3 species of Anaplasma target red blood cells? What does this cause?
- A. marginale - Rhipicephalus, Dermacentor, Hyalomma, Boophilus, Ixodes
- A. centrale - Rhipicephalus, Dermacentor
- A. ovis - Rhipicephalus, Dermacentor
ANEMIA
What species of Anaplasma targets red blood cells, monocytes, and macrophages? What does this cause?
A. bovis - Rhipicephalus, Hyalomma, Ambylomma, Haemaphysalis
anemia and leukopenia (lowers immunity —> higher chance of secondary infection)
What species does Anaplasma particularly target? What are 2 exceptions and what do they cause?
ruminants
- A. phagocytophilum - all mammals, dogs + humans (Ixodes scapularis) —> neutrophils —> leukopenia
- A. platys - dogs (Rhipicephalus, Dermacentor) —> platelets —> thrombocytopenia (bleeding)
What are the 3 species of Ehrlichia affecting dogs? What do they target?
- E. chaffeensis - Amblyomma, Dermacentor; monocytes, macrophages (ZOONOTIC)
- E. ewingii - Amblyomma, Dermacentor; neutrophils (ZOONOTIC)
- E. canis - Rhipicephalus; monocytes, macrophages
LEUKOPENIA
What 2 species of Ehrlichia affect ruminants? What do they target?
- E. chaffeensis - Amblyomma, Dermacentor; monocytes, macrophages (ZOONOTIC)
- E. ruminantum - Amblyomma; endothelium
LEUKOPENIA + VASCULITIS + THROMBOCYTOPENIA = heartwater disease
What is the major predilection site of Rickettsia? What are the 4 major species affecting humans and rodents? What disease do they cause and how are they transmitted?
blood vessels —> bleeding
- R. prowazekii - epidemic (sylvantic) typhus - lice transmit to humans and flying squirrels
- R. typhi - murine typhus - fleas transmit to humans and wild rodents
- R. akari - Rickettsial pox - mites transmit to humans and wild rodents
- Orentia tsutsugamushi - scrub typhus - mites transmit to humans and wild rodents
What 2 species of Rickettsia affect dogs and cats? Why do they cause and how are they transmitted?
- R. rickettsii - Rocky Mountain spotted fever - Dermacentor and Amblyomma ticks transmit to humans, dogs, wild rodents, voles, and small mammals
- R. felis - cat flea rickettsiosis - fleas transmit to humans, cats, rodents, and opossums
What are the 5 major uses of the proteins produced by Anaplasma, Ehrlichia, and Rickettsia?
- adhesion
- internalization
- survival
- replication
- lysis of RBC or endothelial cells
What 3 proteins are used by Anaplasma, Ehrlichia, and Rickettsia for adhesion/attachment?
- outer membrane protein A - Anaplasma, Ehrlichia, Rickettsia
- outer membrane protein B - Ricketssia
- entry-triggering protein E - Anaplasma, Ehrlichia, Rickettsia
What 2 groups of proteins produced by Anaplasma, Ehrlichia, and Rickettsia are responsible for producing lipid rafts (vesicles) for engulfing red blood cells and endothelial cells membranes?
- EtpE, clathrin, caveolin-2 - Anaplasma, Ehrlichia
- clathrin, caveolin-2 - Rickettsia
What 4 proteins are produced by Anaplasma and Ehrlichia to survive in the vacuoles in the cytoplasm of host cells? Why doesn’t Rickettsia produce them?
- early endosome antigen 1
- Rab5A
- Rab7
- vacuolar-type H+ ATPase
Rickettsia survives freely in the host cytoplasm
What 3 proteins are responsible for Anaplasma and Ehrlichia survival in the cytoplasm and morula formation?
- Rab7
- transient receptor potential channels (TRP)
- ECH0825
What 2 enzymes are used by Rickettsia to destroy the vacuoles in the cytoplasm of host cells?
- hemolysin C
- phospholipase D
able to freely move and replicate in the cytoplasm of host cells
In what 4 ways can Anaplasma, Ehrlichia, and Rickettsia spread to adjacent cells from infected RBCs and endothelial cells?
- protrusion of infected cell membranes (filopodia) to enter adjacent cells without bacteria entering the extracellular space - A, E
- packed blood cells burst to spread to the adjacent cells - A, E
- phospholipase A2 lyses infected cells - R
- budding from host cell membrane - R
What are morula?
micro-colonies produced by Anaplasma and Ehrlichia when they multiply within the vacuoles in the cytoplasm of midgut or salivary gland cells of arthropods or vertebrate blood cells
Anaplasma and Ehrlichia life cycle:
Rickettsia lifecycle:
What are the 10 most common clinical symptoms of Anaplasma, Ehrlichia, and Rickettsia infection?
- fever
- malaise
- muscle aches
- headaches
- nausea
- vomiting
- fatigue
- chills
- rash
- joint pain
- very non-specific
What are 3 unique symptoms of Anaplasma and Rickettsia infection?
- jaundice - Anaplasma
- bleeding (thrombocytopenia) - Anaplasma
- blood vessel thrombosis, occlusion, and necrosis - Rickettsia
What is the cause of Rickettsia infection symptoms? What are the 6 most common symptoms?
disseminated endothelial infection due to lysis of capillaries in all organs
- vasculitis
- bleeding from skin (rash)
- bleeding from nose (epistaxis)**
- hemorrhage
- thrombosis
- blood vessel occlusion/necrosis
What are the 9 most common organ failures caused by Rickettsia that can lead to death?
- encephalitis
- myocarditis —> CHF
- pneumonia
- nephritis
- hepatitis
- rash
- edema
- hypovolemia —> shock
- thrombocytopenia from hemorrhage
What samples can be taken from humans/animals for Ricketssiales isolation?
- blood spot smear
- whole blood or serum
- skin biopsy of eschar or rash
What is the gold standard serological test for Ricketssiales identification? What else can be done?
indirect immunofluorescent IgG assay
- species-specific ELISA
- Weil Felix test
- direct visualization in tissue samples with labeled antibodies
What genes can be used on PCR to identify Rickettsiales? What 3 media can be used to culture them?
gItA, ompA, ompB, 16S genes —> quick, convenient
cell lines
1. tick cell lines - midgut cells, salivary gland cells, tick embryonic cells
2. mammalian endothelial cell lines
3. human leukemia cell lines
What is the Weil-Felix test? What is a major disadvantage to this test?
serological test using Proteus species’ LPS antigens to cause a cross-reaction with Rickettsia antigens —> coagulation = positive
low sensitivity and specificity —> will cause agglutination in the presence of Proteus and Rickettsia
What 3 species of Proteus are used in the Weil-Felix test?
- P. vulgaris OX19 - typhus group Rickettsia
- P. vulgaris OX2 - spotted fever group Rickettsia
- P. mirabilis OXK - scrub typhus group Rickettsia
What are the 3 major aspects of the iceberg concept with Anaplasma, Ehrlichia, and Rickettsia infection?
- subclinical infections are common
- reservoir vertebrate hosts are widely distributed as a source of infection
- several genera and species of arthropods may get an infection and remain infected for life in the cases of Rickettsia or pass onto offspring
What are 3 possible treatments for Rickettsiales cases?
- Doxycycline**
- Chloramphenicol
- Tetracycline
What are the best 3 ways to control and prevent Rickettsiales cases?
- kill Anaplasma, Ehrlichia, and Rickettsia by prophylactic use of Doxycycline, Chloramphenicol, or tetracycline
- kill arthropods each season using spot-on, sprays, dust, or dipping of ascaricides (pyrethroids)
- boost resistance of animals with vaccines, feeding, indoor rearing, and stress avoidance
