The Unusuals Flashcards
Description – Order Chlamydiales
Classification:
Family: Chlamydiaceae
Genera: Chlamydia, Chlamydophila
Obligate intracellular parasites
Gram-negative, but not proteobacteria
🔹 Unique Growth Cycle:
Elementary Bodies (EB)
Small, infectious, extracellular
Taken into host via receptor-mediated endocytosis
Reticulate Bodies (RB)
Larger, replicative, intracellular
Divide within endosome
Convert back to EBs for release
🔹 Key Features:
Replication entirely within endosome
Prevent phagolysosome fusion in phagocytes
No energy production: “energy parasites”
Depend on host ATP
Clinical Significance – Order Chlamydiales
Chlamydia trachomatis
A–C: Trachoma (leading preventable blindness)
L1–L3: Lymphogranuloma venereum (LGV)
D–K:
Non-gonococcal urethritis (most common bacterial STI)
Pelvic Inflammatory Disease (PID), infertility
Neonatal conjunctivitis and pneumonia
↑ Risk of HIV transmission
🔹 Chlamydophila psittaci
Zoonotic – from birds (psittacosis)
Atypical pneumonia in humans
Abortion in cattle (rare transmission from mammals to humans)
🔹 Chlamydophila pneumoniae
Human-to-human transmission (droplets)
Causes respiratory infections
Possible link with atherosclerosis and cardiac disease
🔹 Chlamydophila pecorum
Less understood
Some association with animal infections
Isolation & Identification – Order Chlamydiales
🔹 Sample Requirements:
Infected epithelial cells required
Not found in pus
🔹 Culture Methods:
Use cell lines:
McCoy, HeLa, HEp-2 (for C. pneumoniae)
Monkey kidney cells
Yolk sac of embryonated eggs
Observe inclusion bodies in host cells
🔹 Staining & Microscopy:
Giemsa stain
Iodine stain
Immunofluorescence (with or without monoclonal antibodies)
🔹 Molecular & Antigen Detection:
EIA (Enzyme Immunoassay)
PCR / LCR – commonly used for C. trachomatis
Roche multiplex detects C. trachomatis and N. gonorrhoeae
No reliable commercial tests for C. pneumoniae
🔹 Serology:
Complement fixation test used for retrospective diagnosis
Description & Habitat – Ehrlichia
Habitat & Transmission:
Found in ticks and other invertebrates
May involve fluke in fish → possible transmission through fish consumption
Commonly transmitted via Ixodes ticks
Hosts:
White-tailed deer, dogs, mice (USA)
Now detected in Queensland, Australia (Canine Ehrlichiosis)
🔹 Association with Rickettsial Diseases:
If rickettsial disease suspected in endemic areas → consider Ehrlichia
Clinical Significance – Ehrlichia
Regions:
Primarily seen in Northeastern USA
Emerging in Australia (QLD) in dogs
🔹 Disease Forms:
Human Monocytotropic Ehrlichiosis (HME):
Targets monocytes
Human Granulocytotropic Ehrlichiosis (HGE):
Targets neutrophils
🔹 Clinical Presentation:
Leucopaenia (↓ white blood cells)
Non-specific febrile illness
Severe cases in immunocompromised patients
Risk of sepsis and shock (1–3% fatality)
Isolation & Identification – Ehrlichia
🔹 Cell Culture Methods:
Canine histiocyte cell lines
THP-1 (human monocytic) and Vero cells
Human promyelocyte cell lines also used
🔹 Key Microscopy Feature:
Look for Ehrlichial morulae (berry-like intracellular clusters)
Requires an experienced haematologist
🔹 Other Diagnostic Methods:
PCR – sensitive and specific
Serology
Use a diagnostic algorithm for confirmation
🔹 Note:
No confirmed human cases reported in Australia (as of current knowledge)
Description & Taxonomy – Rickettsia
🔹 General Features:
Small, Gram-negative, aerobic coccobacilli
Obligate intracellular parasites of eukaryotic cells
Live in cytoplasm or nucleus of host cells
Transmitted by arthropod vectors (ticks, lice, fleas, mites)
Cannot grow on artificial media – must use cell culture
🔹 Taxonomy:
Rickettsial diseases caused by multiple genera:
Rickettsia
Orientia (e.g., O. tsutsugamushi)
Grouped into:
Typhus group
Spotted Fever group
Description – Anaplasma
🔹 Species:
Anaplasma phagocytophilum
Formerly known as: Ehrlichia equi, E. phagocytophilum
🔹 Morphology & Biology:
Small, Gram-negative coccus
Obligate intracellular pathogen
Infects granulocytes (a type of white blood cell)
Replicates in membrane-bound vacuoles, forming inclusions/parasitophorous vacuoles
Clinical Significance – Rickettsia
🔹 Typhus Group:
Rickettsia prowazekii (epidemic typhus)
Transmitted by human body louse
Severe illness: fever, headache, cough, delirium, rash starting on trunk
Rickettsia typhi (endemic/murine typhus)
Transmitted by rat fleas, possibly lice/mites
Milder symptoms but similar to epidemic typhus
🔹 Spotted Fever Group:
R. australis – Queensland Tick Typhus (tick bite)
R. honei – Flinders Island Spotted Fever (tick bite)
R. felis – Cat Flea Typhus (flea bite)
Orientia tsutsugamushi – Scrub Typhus
Transmitted by larval mites on rodents
Endemic in Asia and Northern Australia
Laboratory Diagnosis – Rickettsia
🔹 Diagnosis Methods:
Based on clinical suspicion + serology
Diagnostic serology:
Indirect Immunofluorescence Assay (IFA) → reference method
Other methods:
Enzyme immunoassays
Latex/plate microagglutination
🔹 Key Diagnostic Indicator:
4-fold rise in IgG titre between acute and convalescent serum samples
🔹 Notes:
Culture not routinely done – dangerous & time-consuming
IFA cannot determine species-level of causative agent
Transmission & Diagnosis – Anaplasma
🔹 Transmission:
Spread via tick bites, mainly Ixodes spp.
Same ticks that transmit Lyme disease
🔹 Diagnosis Methods:
Blood smear (to detect inclusions in granulocytes)
PCR for definitive diagnosis
Serology (paired acute/convalescent sera)
Clinical Significance – Anaplasma
🔹 Disease Caused:
Human Granulocytic Anaplasmosis (HGA)
🔹 Symptoms:
Fever
Headache
Chills
Muscle aches
Can be more severe in immunocompromised individuals
Description – Coxiella burnetii
🔹 Bacteriology:
Gram-negative, pleomorphic
Obligate intracellular pathogen
PC3 risk group organism
🔹 Growth Characteristics:
Phase I: Virulent, smooth LPS – infectious
Phase II: Avirulent, rough LPS – lab-adapted
Clinical Significance – Q Fever
🔹 Disease Caused:
Q fever – a zoonotic disease
🔹 Transmission Routes:
Aerosol from infected livestock (most common)
Shedding via faeces, birth products, milk
Involves cattle, sheep, goats
🔹 Natural & Livestock Cycles:
Wildlife ↔ ticks
Livestock ↔ ticks ↔ humans
