Lecture 5 Flashcards
Learning Objectives
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
Chlamydiaceae: Phylogeny
- 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)
Can you get chlamydia non-sexually?
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:
- 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. - 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. - 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.
CHLAMYDIAL MORPHOLOGIes
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
GENERAL FEATURES OF CHLAMYDIACEAE
- 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
Chlamydia trachomatis
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%.
Chlamydia trachomatis diseases 1
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
Chlamydia trachomatis diseases 2
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
Chlamydia trachomatis diseases 3A
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
Chlamydia psittaci- Psittacosis/ parrot fever
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
RICKETTSIAE: PHYLOGENY
Four genera:
Rickettsia
Orientia
Coxiella
Erlichia
General Features of Rickettsiae
- 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)
Typhus
- 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
Typhus v typhoid
*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
FURTHER READING: Chlamydia/ Rickettsia
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
