Rickettsia and Spiral Organisms Flashcards
Intracellular gram negative organisms
Rickettsia and Orientia
(Erlichia and Anaplasma)
Coxiella Burnetii (Q fever)
Spiral organisms
Treponema pallidum
Leptospira
Borrelia burgdoferi (Lyme disease)
Only seen under dark field micropscopy
Rickettsia - growth characteristics, transmission
Obligate intracellular parasite
Small (0.3x1-2 mcm)
Can’t grow on agar plates - requires tissue cultures
Readily inactivated by heat/disinfectants
Transmission:
- Spotted fever group - ticks and fleas
- tick restricted, flea worldwide
- Typhus group
- -> murine typhus - rodent flea
- -> epidemic typhus - human body louse
- Scrub typhus - larval stage of mites
Rickettsia - general pathogenesis, clinical manifestations, labs
Pathogenesis
- infect endothelial cells, especially vasculitis –> microinfarcts with necrosis and thrombosis in small vessels
Clinical manifestation depends on organ e.g. petechiae, interstitial pneumonitis, myocarditis
Site of bite may necrose and form black eschar (common in scrub typhus)
Usually 1-2 wks after arthropod bite (often at hidden skin creases/groin area)
– FEVER, RASH, HEADACHE
Lab: neutrophil + Plt low; ALT moderately high
Spotted Fever Group - species, vector, clinical presentations
Rocky mountain spotted fever
- R. rickettsii (tick borne)
- fever, headache, rash, myalgia, anorexia
- can be complicated with pneumonitis, myocarditis, renal failure, DIC, CNS involvement
Other spotted fevers
- R. japonica, R. conorii, R. felis
Typhus Group - species, vector, clinical presentations
Murine typhus
- R. typhi (flea borne)
- acute febrile illness, rash, headache
- rare fatality
Epidemic typhus
- R. prowazekii (human body louse)
- typical outbreaks where pediculosis is common
- Brill-Zinsser disease (milder form of disease)
Scrub Typhus - species, vector, clinical presentations
Orientia tsutsugamushi
Mite borne (low lying scrubs/ transitional vegetation)
SE Asia
Eschar in 20% patients
Fatality <10% if left untreated
Rickettsia - diagnosis and management
Diagnosis:
- clinical suspicion (need specific tests ordered)
- PCR
- SEROLOGY (Weil-Felix)
- -> detect anti-rickettsial Ab in patient’s serum by inducing cross reaction with Proteus OX antigens
- -> Ab detection e.g. IF stain
Spotted fever: OX2, OX19 for R. rickettsii
Murine: OX19
Epidemic: OX19
Scrub Typhus: OXK
Serology: 4x rise in Ab or single titre >512; or OXK >320 for scrub typhus
Management:
- Doxycycline 7-14 days
- Prevention by personal protection/long sleeves in rural areas, insect repellents, rodents control
- NOTIFIABLE DISEASES
Q fever - organism, geographical distribution, source, transmission, pathogenesis
Coxiella burnetii
Intracellular pleomorphic GN bacilli
Worldwide zoonotic agent - cattle, sheep, goats
(can be maintained in ticks - minor)
Transmission:
- inhalation of aerosol particles from parturient or slaughter ruminants or tick faeces
- ingestion of unpasteurised milk or milk products
- high concentration in placenta
- LOW INFECTIVE DOSE (1-10 cells only)
Pathogenesis:
- infect alveolar macrophages and cause acute or chronic infection
Q fever - clinical presentations acute and chronic
Incubation 2-5 wks
Acute Q fever:
- self limiting febrile illness (fever, headache, myalgia, night sweats, LFT derangement) ==> usually resolve in 10-14 days
- atypical pneumonia
- anicteric hepatitis (normal bilirubin, no jaundice)
- -> may develop sterilising or non-sterilising immunity –> chronic Q fever
Chronic Q fever:
- CULTURE NEGATIVE ENDOCARDITIS
- intravascular infections (not common)
- chronic granulomatous hepatitis (Doughnut granulomata)
- osteoarticular infections
- abortion, still birth
Q fever - diagnosis
Diagnosis:
- clinical suspicion (PUO + sepsis workup negative + empirical antibiotics ineffective or clear exposure history or culture negative endocarditis)
- SEROLOGY
- -> acute: 4x change in phase II IgG
- -> chronic: >800 phase I IgG
- blood or tissue PCR
- CAN’T CULTURE!
- HISTOLOGY - doughnut ring granuloma, IHC of heart valve
Q fever - management
Acute
- Doxycycline 2 wks
Chronic
- Doxycycline AND Hydroxychloroquine >18 months
(HCQ increases pH of phagolysosome which makes doxycycline bactericidal)
Pregnancy
- Septrin for duration or pregnancy
NOTIFIABLE DISEASE
Treponema pallidum - size, transmission, clinical presentations, treatment
Difficult to stain and non-cultivable
Visualised in fresh exudate by dark ground microscopy
Killed rapidly by exposure to air/desiccation
10-20 mcm long, 100-200nm width
Transmission: sexual, congenital
Clinical disease: Syphillis
Congenital syphilis
Acquired syphilis:
- incubation 9-90 days
- primary – PAINLESS genital ulcers (Chancre)
- secondary – skin rash (papulosquamous at palms and soles)
- latent – asymptomatic, slowly develop CVS and CNS complications
- neurosyphilis
Treatment: Benzathine penicillin G IM (longer/higher dose if late latent); Penicillin G high dose if neurosyphilis
Treponema pallidum - diagnosis
Microscopy
- dark ground, requiring fresh exudate from chancres (rarely done now)
SEROLOGY
- non-treponemal test (VDRL, RPR)
- -> non-specific
- -> titres can be used as markers for treatment efficacy (decreases after treatment)
- -> biological false positive if AI disease, pregnancy
- treponemal test (TPHA, TPPA)
- -> Ab remain elevated even after treatment (but not sterilising immunity)
Leptospirosis - organism, source, at risk population
Leptospira interrogans serovar icterohaemorrhagiae
Zoonosis
- direct/ indirect contact of urine of infected rodents via abrasions or cuts in the skin or conjunctiva
At risk population = sewage workers, soldiers, farmers, kayaking
