Lecture 5 Flashcards

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1
Q

Learning Objectives

A

1) To cover the impact and aetiology of Chlamydia sp (eg
C. trachomatis)

2) To cover the impact and aetiology of Rickettsia sp (eg
Rickettsia prowazekii)

1 and 2) Understand their unique life cycle/ intracellular
survival

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2
Q

Chlamydiaceae: Phylogeny

A
  • Family which once
    included 2 genera,
    Chlamydia and
    Chlamydophila
  • Single genus:
    Chlamydia

Egs:
* C. trachomatis; ocular,
genital
* C. psittaci: psittacosis
* C. pneumoniae (10-20
% CAP, cardiovascular
disease)

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3
Q

Can you get chlamydia non-sexually?

A

Yes, it is possible to contract chlamydia non-sexually, although it is primarily known as a sexually transmitted infection (STI). Here are some non-sexual routes through which chlamydia can potentially be transmitted:

  1. Vertical Transmission
    Mother to Child: Pregnant women with chlamydia can pass the infection to their newborn during childbirth. This can lead to conjunctivitis (eye infection) or pneumonia in the baby.
  2. Fomites
    Inanimate Objects: There is some evidence suggesting that chlamydia could potentially be transmitted through contaminated surfaces or objects (fomites), such as towels, linens, or medical instruments. However, this mode of transmission is considered extremely rare and is not the primary route of infection.
  3. Autoinoculation
    Self-Transmission: An infected person could potentially spread the bacteria from an infected area (e.g., genitals) to another area (e.g., eyes) through hands, although this is also considered rare.

Summary
While non-sexual transmission of chlamydia is possible, the primary route remains sexual contact. Practicing safe sex, getting regular screenings, and seeking prompt treatment if infected are essential for preventing the spread of chlamydia and other STIs. If you have concerns about chlamydia or potential exposure, it’s best to consult a healthcare professional for advice and testing.

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4
Q

CHLAMYDIAL MORPHOLOGIes

A

Elementary bodies (EB); infectious form,
metabolically inactive. electron dense, nucleoid,
granular cytoplasm, spherical,
approximately 0.2-0.3 microns in diameter- very very small

Reticular bodies (RB); intracellular
reproductive form,
metabolically active, chromatin dispersed
(transcription)- these are the forms that can reproduce
approximately 0.5-2 microns in diameter,
can divide by binary fission resulting in new
RBs- just before infection they will turn back into EBs and infect more cells

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5
Q

GENERAL FEATURES OF CHLAMYDIACEAE

A
  • Non-motile, obligate intracellular
    coccoid bacilli (circular shaped) parasites
  • Inhabit and infect, mucus membrane epithelial cells/ macrophages
  • Small enough to pass through 0.45
    micron filters
  • Cell wall: existence of peptidoglycan
    was debated until Liechti et al., 2014, A
    new metabolic cell-wall labelling method reveals peptidoglycan in Chlamydia
    trachomatis. Nature
  • Energy parasites: lack ATP-generating
    ability and must obtain from host cell
  • contain and synthesis RNA and DNA and have ribosomes, proteins and lipids however cannot generate their own ATP as they have no flavoproteins or cytochromes so must obtain it from a host cell

are obligate intracellular pathogens as they need other cells in order to replicate

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6
Q

Chlamydia trachomatis

A

The most common preventable cause of blindness due to infectious disease

  • Public health problem in 44 countries, and is responsible
    for the blindness or visual impairment of about 1.9 million
    people
  • 142 million people live in trachoma endemic areas
  • SAFE: Surgery, Antibiotics, Facial cleanliness and
    Environmental improvement
  • In 2018, 146 112 people received surgery and 89.1 million
    people were treated with antibiotics. Global-level antibiotic
    coverage in 2018 was 50%.
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7
Q

Chlamydia trachomatis diseases 1

A

Trachoma serovars (Types A, B and C)

Infection of conjunctival
epithelial cells, repeated
clinical/subclinical infection
and cell infiltration can cause
cornea to cloud/scar

Transmitted by flies, fomites,
touch

Favours hot, dry climates

can cause corneal opacity

trachomatous scarring which is scarring underneath eyelids

trachomatous trichiasis causes eyelashes to grow in towards the eye

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8
Q

Chlamydia trachomatis diseases 2

A

Inclusion conjunctivitis (Types
D to K)
Neonatal form: Inclusion
blenorrhoea can develop when
infant is in birth canal and
appears 5-12 days after birth.
Can precede infant pneumonia
(can also develop
independently).

Adult form: associated with
sexual contact via STD form,
also from swimming pools
contaminated with chlamydia
from genital secretions
(“swimming pool conjunctivitis”)

these can be treated with antibiotics

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9
Q

Chlamydia trachomatis diseases 3A

A

Genital chlamydiasis
Men: Urethritis (NGU), 7-28 days after
infection, mild burning, more frequent
need to urinate, white discharge from
penis

Epididymitis, proctitis, Rieter’s
syndrome, lymphogranuloma
venereum (LGV, climatic buboe)

Women: urethritis, cervicitis, PID,
infertility, ectopic pregnancy, premature
delivery, postpartum fever, LGV

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10
Q

Chlamydia psittaci- Psittacosis/ parrot fever

A

Isolated from over 100 avian species,
esp cockatiels and parakeets
EB very resistant (eg in feed for 2
months)

Most patients develop symptoms after
10 days

Severity of clinical signs range from
Non-apparent to flu-like to severe
pneumonia (30-60 year olds)

Risk groups, occupational disease,
pigeon farmers, pet shop owners,
veterinarians, poultry workers etc

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11
Q

RICKETTSIAE: PHYLOGENY

A

Four genera:
Rickettsia
Orientia
Coxiella
Erlichia

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12
Q

General Features of Rickettsiae

A
  • Obligate intracellular pathogens
  • Small coccoids or rods (0.3 by 1-2
    microns) incredibly small
  • Fastidious cannot grow on microbiological media, some grow on embryonated eggs or in tissue
    culture cells
  • Structurally similar to gram negative cells (have LPS and PG
    cell walls)
  • Multiply by binary fission only in
    infected cells
  • with the exception of coxiella all are Transmitted by arthropod vectors (eg
    ticks, mites, lice, fleas)
    Coxiella (Q fever)
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13
Q

Typhus

A
  • Caused by Rickettsia prowazekii
  • Arrives in Europe in 1489 via
    soldiers returning from Cyprus
  • In 1557-59 an outbreak in England
    killed 10% of the population
  • Transmitted by Pediculus humanus
    corporis (infected faeces)
  • Incubation 7-14 days, high fever,
    chills, headache, may lead to coma
  • Macular eruption 5-6 days after
    onset which is spots all over the skin
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14
Q

Typhus v typhoid

A

*Typhus: , cough, headache, joint and muscle pain, nausea, chills, confusion, low blood pressure (eg Rickettsia typhi or prowazekii)

*Typhoid (aka resembling typhus): Abdominal tenderness, agitation, bloody stool, chills, confusion, delirium, hallucinations, nose bleeds and fatigue (Salmonella typhi)

Vector: Flea/ what you had for tea
Treatment: Fluids and antibiotics, oxygen

Prevention: Good hygiene, insect repellants, insecticides, vaccine

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15
Q

FURTHER READING: Chlamydia/ Rickettsia

A

Elwell, C., Mirrashidi, K. and Engel, J., (2016) Chlamydia
cell biology and pathogenesis. Nature Reviews
Microbiology 16: 385-400

Thiriot et al., Hacking the host: exploitation of
macrophage polarization by intracellular bacterial
pathogens, Pathogens and Disease, Volume 78, Issue 1,
February 2020,
ftaa009, https://doi.org/10.1093/femspd/ftaa009

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