Chlamydia psittici - MegaMicro

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Chlamydia psittici

Microbiology > Bacteriology > Intracellular bacteria > Chlamydia
a. Structure
i. Gram negative like bacteria
1. Outer membrane contains lipopolysaccharide
2. Cell envelope lacks peptidoglycan
b. Pathobiology:
i. Physiology
1. Obligate intracellular organism
a. Requires host ATP
ii. Virulence Factors
1. Like in most obligate intracellular organisms, the main virulence of these pathogens come from their ability to promote endocytosis to enter then cell while avoiding degradation once in the cell.
2. Does this through its reticular body and elementary body lifestyle
iii. Lifecycle
1. Through a reticular body (RB) and elementary body (EB)
a. When in between hosts, exists as an EB
i. Not biologically active
ii. Resistant to the environment
iii. Can exist outside the host
iv. Infectious form --> can travel from host to host
b. Next, EB attaches to cell membrane
c. Attachment triggers endocytosis of EB
d. Once in vacuole transforms to reticular body (RB)
i. Evades degradation by host cells by blocking lysosomal fusion with endosome
e. RB commandeers cell’s machinery to undergo replication
f. RB forms large inclusion within host cell
g. RB is then converted back to EB
h. Cell ruptures leading to release of EB and cycle begins again

c. Epidemiology
i. Reservoir
1. Includes Psittacine birds (thus the name)
a. Incudes parrots, parakeets and macaw
2. Aerosolized droplets are inhaled and infect lung cells of host
ii. Vectors
1. No vectors
2. Host-to-host transmission

d. Laboratory diagnosis
i. Serology is the gold standard
ii. According to the CDC, a confirmed case needs one of the following criteria:
1. Isolation of the organism by culture
a. Difficult and hazardous
2. Compatible clinical illness with a 4-fold rise in antibodies against C. psittaci
3. Detection of IgM titer of 16 or greater against C. psittaci

e. Disease manifestations
i. Most common disease caused
1. Diffuse, bilateral, interstitial pneumonia with systemic symptoms
a. Atypical from common pneumonia findings
2. In more severe cases
a. Can lead to endocarditis, meningitis, liver inflammation, joint inflammation
b. Meningitis or encephalitis can lead to neurological deficits and seizures
ii. Diagnostic methods
1. History components
a. Exposure to sick birds
b. Occupational risks
i. Those who work at pet shops
ii. Poultry industry workers
c. Abrupt onset of symptoms
i. Chest pain is a common complaint
ii. Non-productive cough (50-80% of cases)
2. Physical Exam
a. Fever between 103-105 °F
i. Pulse-temperature dissociation
b. May be hard appreciate pulmonary auscultatory changes
c. Splenomegaly
d. May see cutaneous changes
i. Horder spots
ii. Splinter hemorrhages
iii. Erythema nodosum
3. Imaging and Labs
a. Chest X-ray to help visualize pneumonia
i. Consolidation usually in lower lobe
ii. Pleural effusions seen in 50% of cases
1. Usually small and asymptomatic
b. Elevated liver enzymes
c. Leukopenia and thrombocytopenia

iii. Differential diagnoses
1. Other chlamydial Pneumonias
a. C. pneumoniae
i. Long onset of disease
ii. Less severe symptoms
1. Initial URI symptoms followed by pneumonia symptoms after 1-4 weeks
2. Less severe fever and usually subsides on its own
iii. Headaches is present in 60% of cases
1. Important non classic pneumonia finding
iv. May have sinus percussion tenderness
1. Common finding in C. pneumoniae cases
b. C. trachomatis
i. Usually presents with nasal discharge, cough and tachypnea
ii. Afebrile
iii. In 50% of  cases will see conjunctivitis and middle ear abnormalities
iv. Slow onset of symptoms

iv. Therapy
1. Antibiotic treatment
a. Tetracycline or doxycycline is treatment of choice
i. Usually for 10 days

v. Prevention and control
1. Limit handling of sick birds
a. Avoid contact with dust from bird feathers
2. Can treat imported Psittacine with feed containing chlortetracycline to treat any underlying disease and avoid human infection

Related concepts

Key Words
Reticulate body
Elementary body
Intracellular pathogen

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