MIIM30011 2024 L24 - Syphilis & Chlamydia PDF

Chlamydia & Syphilis Dr Sacha Pidot [email protected] www.pidotlab.com  By the end of this lecture you should be able to: To understand the key features of the diseases syphilis and chlamydia To understand the major biological and molecular factors that make Trepon...

Chlamydia & Syphilis Dr Sacha Pidot [email protected] www.pidotlab.com  By the end of this lecture you should be able to: To understand the key features of the diseases syphilis and chlamydia To understand the major biological and molecular factors that make Treponema pallidum and Chlamydia trachomatis such successful pathogens  Chlamydia The most common STI in the world – 200,000+ cases in UK in 2017 (c.f. 7000 cases of syphilis) Caused by Chlamydia trachomatis Asymptomatic in 80% of individuals – Can lead to blocked fallopian tubes – Induction of male infertility?? Only recognized as a specific STI in 1970s – Little to no history before this time Exclusive human pathogen Transmitted via sexual contact and vertical transmission  Chlamydia – disease symptoms In females – cervix most commonly infected → cervicitis, urethritis, pelvic inflammatory disease, perihepatitis, or proctitis. – if untreated, increases risk of infertility and ectopic pregnancy. – infants born vaginally to mothers with genital Chlamydia trachomatis may develop conjunctivitis and/or pneumonia. In males – urethritis, epididymitis, prostatitis, proctitis, or reactive arthritis In both sexes – conjunctivitis, pharyngitis, and lymphogranuloma venereum (enlarged lymph nodes) https://teachmeobgyn.com/sexual-health/sexually-transmitted-infections/chlamydia/  Chlamydia trachomatis – serovars Chlamydia trachomatis – Gram-negative, anaerobic – obligate intracellular parasites – 18 serovars that correlate with multiple medical conditions: Serovars A, B, Ba, and C: ocular infection → chronic conjunctivitis, can cause blindness Serovars D-K: Genital tract infections, neonatal infections Serovars L1-L3: Lymphogranuloma venereum (LGV)  Chlamydia trachomatis – life cycle Two developmental forms – elementary body (EB) – infectious form, taken up by host cells – reticulate body (RB) – differentiates from EB, replicative form inside host cells  Chlamydia trachomatis – life cycle Elementary Bodies – infectious form – Spherical, ~0.2 μm diameter – Osmotically stable, less permeable than RBs → environmentally resistant – Preloaded with virulence factors type III secretion effectors involved in internalization – EBs internalized following epithelial attachment Enter a vacuole, known as an inclusion – EBs invade by receptor-mediated endocytosis and block targeting of inclusion to lysosomal pathway Panzetta et al, 2018, Front Microbiol  Chlamydia trachomatis – life cycle Reticulate Bodies – replicative form – Spherical ~0.8 μm diameter – Not infectious – Not stable outside of the host cell – Actively replicate inside the host cell – RBs are enriched in proteins involved in nutrient uptake, ATP generation and translation Panzetta et al, 2018, Front Microbiol Chlamydia trachomatis – life cycle Elwell et al, 2016, Nat Rev Microbiol  Chlamydia trachomatis – intracellular niche The inclusion: – Migrates to microtubule organizing centre Effectors possibly tether inclusion to dynein and/or centrosomes – Regulates fusion and membrane dynamics Inhibits lysosome fusion, but promotes fusion with nutrient rich vesicles » Promoted by bacterial Inc proteins Recruits Rab proteins – master regulators of vesicle fusion Interacts with SNARE proteins – some C. trachomatis produced proteins contain SNARE-like domains – Scavenges nutrients – esp. lipids C. trachomatis has eukaryotic lipids in membrane Acquired from Golgi and other vesicles – Interacts with other organelles Lipid droplets and peroxisomes – possible sources of triacylglycerol and enzymes Mitochondria – may be used to acquire energy smooth ER – may facilitate lipid transport Chlamydia trachomatis – modifying the host response Premature host-cell death limits replication – Chlamydia activate pro-survival pathways and inhibit apoptotic pathways – Chlamydia slow progression of the host cell cycle Effectors modulate microtubule assembly and centrosome duplication and clustering – Chlamydia dampen DNA damage response Infection induces double-strand DNA breaks Chlamydia trachomatis – modifying the host response Binding of Chlamydia induces inflammatory response – BUT, Chlamydia block NF-kB activation – T3SS effectors downregulate IFNγ expression Chlamydia modify host transcriptome and proteome Chlamydia trachomatis – modifying the host response Elwell et al, 2016, Nat Rev Microbiol  Chlamydia trachomatis – genomics First genome finished by Sanger sequencing (1998) – One of the first bacterial genomes to be sequenced Very small → 1.04 Mb genome + 7.4kb plasmid – Typical of reductive evolution, intracellular lifestyle and parasitism – Plasmid important for in vivo growth Many “essential” bacterial genes missing – Missing FtsZ (cell division), DNA damage repair, synthesis of essential amino acids/nucleotides Little evidence of HGT – Remember RB is locked away in vacuole Thomson et al, 2007, Genome Res  Chlamydia trachomatis – genomics High synteny between different serotypes – BUT, non-synonymous mutations and pseudogenes differentiate strains causing different diseases Hadfield et al, 2017, Curr Top Micro Immunol Chlamydia – Diagnosis PCR test is most sensitive – Targets region of the C. trachomatis plasmid – Can be used on swabs from suspected infections Direct cell culture also available – 60-80% sensitivity Serology not useful Point of care tests available – Not sufficiently sensitive or specific Chlamydia – treatment Azithromycin or doxycycline primarily used – ≥97% cure rate – However, 50–70% of cases are asymptomatic problem for efforts to control C. trachomatis High incidence of reinfection – immunity to new infection not provided by previous infection Reports of antibiotic resistant strains, but these have not become widespread  Syphilis – A sexually transmitted disease Caused by Treponema pallidum subsp pallidum - a spirochaete Disease course – Primary, secondary, latent and tertiary Can be over >10 years “The great imitator” Primary syphilis – “Active infection” – Incubation period = 9 – 90 days – Characteristic skin lesions – “chancre” Highly infectious – contain many live spirochaetes – Usually on genitals or other sites involved in sexual contact – Typically painless and resolve spontaneously Radolf et al, 2016, Nat Rev Micro  Syphilis – A sexually transmitted disease Secondary stage – Fever, mucosal lesions – mild rash - normally on palms and soles of feet – Still sexually transmissible Latent phase (asymptomatic) – Can last many years (>10!) – Infectious early on in this phase Tertiary syphilis – Systemic symptoms – Visceral lesions (gummas), cardiac damage, neurological conditions (neurosyphilis), eye involvement, bone damage Peeling et al, 2017, Nat Rev Dis Primers  Neurosyphilis and ocular syphilis Can occur at any stage of infection – Not commonly seen now with early treatment T. palldium enters CSF early after infection “General paralysis of the insane” Asylums in the 19th century Symptoms include: – chronic meningitis – neurological disturbance – progressive dementia, psychosis HIV increases risk of neuro-ophthalmic complications Syphilis – Vertical transmission Mother → child transmission Can be transmitted to foetus through the placenta – Congenital syphilis Higher rate of infant mortaility/stillbirth – A leading cause of preventable stillbirths Infants often preterm, low birthweight, have signs that mimic sepsis Opportunity for eradication of mother-to-child tranmission – Has been achieved in some countries  Syphilis - epidemiology ~17.7 million cases worldwide (2012) – 5.6 million new cases per year – >60% of disease burden in low/middle income countries Prevalence – Decreasing in heterosexual population – But, problematic in populations with risky sexual behaviours Sex workers, MSM, multiple sex partners, drug use – Increasing prevalence in MSM since 1998 – Rise of “hook-up” apps Peeling et al, 2017, Nat Rev Dis Primers  T. pallidum - general features G-ve but lacks LPS – Outer membrane phospholipids different to other G-ves – Lipoproteins not on surface Slow growth (>30hrs doubling time) Microaerophilic, 34 degrees C Endoflagella – x 3 from one end Until recently, could only be cultured in rabbit testicles – Since 2018, can now be cultured in cells - rabbit cell culture Limited surface exposed antigens – facilitates invasion and dissemination Peeling et al, 2017, Nat Rev Dis Primers  T. pallidum – lack of immunogenicity General lack of immunogenicity related to limited exposure of surface proteins – Avoids triggering host immune response – Evades antibodies → facilitates persistence Surface thought to be “antigenically inert” → too simplistic, as antibodies to surface are generated Poor target antigenicity, production of lipoprotein “decoys”, heterogeneous populations in infections Antibodies are produced, but insufficient to clear the pathogen – Can also hide in various niches → Immunological “cat and mouse” game BamA – transports outer membrane proteins TprK – immune evasion, antigenic variation to outer membrane TP0751 - protease Peeling et al, 2017, Nat Rev Dis Primers  T. pallidum – invasion and transmission T. pallidum enters through skin abrasions – Initial adherence to epithelial cells – Organisms multiply below epithelium and disseminate through lymph and blood – Penetrate through intracellular junctions – powered by motility and proteolytic activity of TP0751 – Infection then becomes systemic – also disseminates rapidly to CSF Transmitted through microabrasions (cuts) during sexual activity – >10 organisms required to cause infection Peeling et al, 2017, Nat Rev Dis Primers  T. pallidum genomics Actually 3 x subspecies Treponema pallidum subsp. pallidum → syphilis T. p. subsp. endemicum → bejel or endemic syphilis T. p. subsp. pertenue → yaws – Subspecies cannot be distingiuished by morphologic, biochemical features or antigenicity differentiation primarily based on clinical features of disease Genomes of all subspecies are ~1.14 Mbp (i.e. very small!) – 0.2% difference at nt level between all 3 subspecies (~2300 nts!) – Limited metabolic capacity, many genes for transporters Reflects an adaptation to mammalian tissues Human restricted pathogen - humans are only reservoir of T. pallidum T. pallidum - genomics T. pallidum has dispensed with most biosynthetic machinery No oxidative phosphorylation – No need for iron or cytochromes But many transporters – Used to scavenge molecules from host – includes amino acids  Diagnosis of syphillis Detection mainly by serology – But inability to distinguish between subspecies (e.g. yaws or bejel) Methods: – Darkfield microscopy – >75% sensitivity, >94% specificity But needs special equipment – Direct fluorescent antibody staining - >73% sensitivity, 100% specific Uses monoclonal antibody to specific T. pallidum protein – Immunohistochemistry – 49-92% sensitive, 100% specific Used fixed tissue sections stained with specific T. pallidum antibodies – PCR becoming more common, but no agreed upon standard – Point of care tests also becoming more available Detect anti-T. pallidum antibodies Most are lateral-flow tests - like pregnancy stick test BUT, cannot always differentiate prior treated infection from current infection Syphilis treatment and prevention Historically, treated with Salvarsan – First synthetic antibacterial compound – BUT - contained arsenic! Now → Treatment = β-lactams – Penicillin is the primary treatment choice for all stages of syphilis – Penicillin resistance has not been observed – Exposed partners also require treatment Prevention – screening, treatment in high risk settings, safe sex education → contacting cases Summary Syphilis and chlamydia are caused by human- restricted pathogens – But, both of these pathogens cause disease in different ways (intra- vs extra-cellular infection, etc) Consequences of both of these pathogens can be severe if undetected and untreated Finally… Take 2 minutes and write down: – What was the most important thing you learned today? – What questions remain in your mind?