Pathogen Case Studies Flashcards
Why could STIs be easy to control?
As infection is linked to human social and sexual behaviour, we have more opportunity to stop infection (e.g. condoms) (it is difficult to control human behaviours however).
What are 3 reasons to why STIs are increasing in numbers still?
- Use of pill has replaced barrier methods of contraception that help prevent spread of STIs.
- Change in public attitudes to sex – increased numbers of sexual partners in many western countries, as well as dating apps, leading to more opportunities for STIs to spread.
- Other factors: Problems of drug resistant strains of bacteria, poor attendance at STI clinics by some infected individuals, lack of appropriate sex education advice, introduction of Viagra has increased STIs in old people homes etc.
What are the 3 major bacterial STIs in the UK, the bacteria that causes it, and what is a common property of all of these bacteria?
- Gonorrhoea – Neisseria gonorroheae
- Syphilis – Treponema pallidum
- Chlamydia – Chlamydia trachomatis
> All of these bacteria are highly host-adapted strict pathogens and cannot survive long outside of the human body (non-commensal). They are spread directly from person-to-person with no animal reservoir.
What are 5 general properties of Neisseria Gonorrhoeae?
- Gram negative (outer-membrane) coccus, characteristically seen as diplococci in samples of discharge (2 cells stuck together after cell division)
- Non-motile
- Humans are the only host: No animal reservoir. Transmission is directly from person-person
- Poor survival outside the human (can be grown as pure culture)
- Intimate mucosal contact is needed for transmission (vagina, penis, throat and rectal mucosa).
What are the symptoms of Gonorrhoea in a) Males b) Females?
a) Male: Thick urethral discharge.
b) Pain on urination Female: vaginal discharge
What can cause Gonorrhoea to lead to more serious complications and some examples?
> Up to 50% of infected females may be asymptomatic or only have mild initial symptoms. They may not seek treatment and this can lead to serious complications:
- Pelvic Inflammatory Disease (PID)
- Damage to fallopian tubes, leading to infertility
- Passed to baby at birth making them blind (why screens are needed on pregnant women)
Describe the protein involved in the early and later stages of infection of Neisseria gonorrhoeae (for Gonorrhoea)
- Initial attachment through long ranged Pili (not high affinity but reach long distances)
- Outer membrane proteins mediate interment attachments
a. Protein II- OM (Opacity protein) protein
for intimate attachments
b. Capsule- Helps resist phagocytosis
c. Protein I- Outer membrane porin
needed for survival in phagocytes - Later stage of infection
a. IgA protease- destroys secretory IgA
b. Transferrin/ lactoferrin binding proteins-
Fe uptake (won’t be a lot of iron present in
sex mucosal surfaces)
c. LPS/LOS- Inflammation at site of
infection (pain)
Why are so many surface proteins on Neisseria gonorrhoeae involved in adhesion onto epithelial cells lining the urethra or vagina?
Good adhesion is essential for a mucosal pathogen in this environment to prevent being dislodged by urine flow
What is the gonococcal strategy for evading the immune system?
- Molecular Mimicry
>The LPS can be modified by attaching sialic acid residues (very common in human cells) to it (sialylation) so that it “looks” like host tissue to the immune system and so does not provoke an immune response. - Antigenic variation
>Many of the surface proteins (e.g. pilin PilE and PII) are highly immunogenic, but gonococci can continuously produce sequence variants (able to vary sequence of proteins so antibodies don’t recognise them) that make it difficult for the immune system
Describe how antigenic variation is present in the Pilin of Neisseria gonorrhoeae and how this is done
> The variable region of Pilin (section detected by antibodies and T-cells) varies in populations of Neisseria gonorrhoeae so is difficult for immune system to target.
> PilE encodes for the major subunit of Pilin. pilS is similar to PilE but sequence variation with many different copies with changed sequences.
PilE is expressed with different recombined silent genes (pilS genes).
Why is tracing and treatment important for Gonorrhoea?
As asymptomatic carriers are major reservoirs of infection in the human population (up to 50% of females, and 10% of males)
What antibiotics is Neisseria gonorrhoeae a) resistant to b) resistance becoming more common to?
a) Penicillin and Fluoroquinolones
b) Cephalosporins
Describe the morphology of Treponema Pallidum
Spiral with flagellum in periplasmic space.
What disease does Treponema Pallidum cause?
Syphilis
What disease does Neisseria gonorrhoeae cause?
Gonorrhoea
What are the general properties of Treponema pallidum?
- Fragile
- Slow growing
- Poor survival outside host
What phylum does Treponema pallidum belong to?
Spirochaetes due to spiral shape
How is infection of Treponema pallidum caused and what are the mortality rates?
> Infection requires intimate sexual contact, and is aided by minute tissue abrasions that occur during sex
> Infection is CHRONIC and in untreated cases may last decades, with maybe 30-50% mortality.
Describe the stages of Syphilis infection
Occurs over a very long time frame (Stages go from more localised to disseminated)
- Primary Syphilis (can jum straight to latent phase)
>Chancre sores (short lived sores) - Secondary Syphilis
>Rash, fever, neuro symptoms - Latent
>No symptoms
>Can go back and repeat secondary Syphilis many times.
§ First 3 are early syphilis (under a year)
- Tertiary stage
>5-50 years
>50% fatality.
>Gumma (a nodule or tumour-like growth in organs), bone, cardiac, nerve disease
What are 5 ways T.pallidum survives in the host long-term?
- Lack of endo- and exotoxins
>T. pallidum lacks LPS, the endotoxin found in the outer membranes of many Gram-negative bacteria. The attachment of T. pallidum to cells does not harm the cells. - Invasion of “immune-privileged” tissues
>Cells in CNS, eye, and placenta, where there is less surveillance by the host’s innate immune system. - Ability to maintain infection with few organisms
>Maintaining infection with very few organisms in anatomical sites distant from one another, T. pallidum may prevent its clearance by failing to trigger the host’s immune response, which was may require a “critical antigenic mass”. - Lack of surface antigens
>Only rare integral proteins in its outer membrane (less antigens) - Low iron requirements, ability to obtain sequestered iron
> may be able to acquire iron from host proteins. It may also overcome the iron sequestration problem by using enzymes that need metals other than iron as their cofactors.
>Also it lacks an electron transport chain, which is made up of enzymes that use iron as a cofactor, which decreases its overall demand for iron.
What is used to treat Syphilis and why is it difficult?
> Penicillin
> Because the bacterium is so slow growing it is essential that a high level of penicillin is maintained in the body for several weeks (to make sure all cells are dead); many people give up and keep the disease.
How does Syphilis infection effect HIV infection?
Infection with syphilis makes it several times more likely that HIV infection occurs.
What is the structure of Chlamydia and what issues does this cause?
Small wall-less bacteria (still gram negative) which are obligate intracellular parasites (cannot be cultured on agar in lab, cannot survive outside host cell- virus like)
