Infectious Diseases - Pre-reading

Question 1

What are transmissible spongiform encephalopathies (TSEs)?

Answer 1

a group of progressive, invariably fatal, conditions that are associated with prions and affect the brain (encephalopathies) and nervous system of many animals, including humans, cattle, and sheep.

Question 2

What are prions?

Answer 2

An infectious agent made of misfolded proteins with the ability to transmit their misfolded shape onto normal variants of the same protein. They characterize several fatal and transmissible neurodegenerative diseases in humans and many other animals e.g. TSEs

Question 3

What is “positive” in the bacterial gram testing?

Answer 3

Pepticoglycan wall - a massive, thick wall will stain positive.

Question 4

What are the 3 types of fungi?

Answer 4

1. Yeasts - single cells but many form biofilms, reproduce by budding, some can can form elongated filament like buds
2. Moulds - grow as filaments (hyphae), produce spores
3. Dimorphic fungi

Question 5

What is the infectious cause of otitis externa?

Why is it difficult to treat?

Answer 5

Psuedomonas aeruginosa

Forms a protective biofilm, resistant to many abx

Question 6

What is this organism?

Answer 6

Gram positive and in pairs = strep. pnuemoniae

Question 7

Which is the most haemolytic and most virulent strep?

Give examples of each

Answer 7

Beta-haemolytic - strep pyogenes

Alpha-haemolytic - strep pneumoniae

Question 8

What are the common colonisers of the upper airways, skin and urinary tract?

• Pharyngitis
• Pneumonia
• Skin and soft tissue infections
• Urinary tract infections

Answer 8

• Pharyngitis: Group A strep
• Pneumonia: S. pneumoniae
• Skin and soft tissue infections: Beta-haemolytic streptococci (especially Group A Strep)
• Urinary tract infections: Group B strep, enterococci

Question 9

what gram positive cocci causes UTI in young women?

Answer 9

Staphylococcus saprophyticus

Question 10

Name 3 invasive fungal infections from environmental fungi (collonise airway etc only transiently)

Answer 10

1. Invasive aspergillosis
2. Pneumocystis jiroveci pneumonia
3. Cryptococcal meningitis

Question 11

How many blood cultures do you need to take?

Answer 11

2 sets (of 2 bottles) from 2 different sites

Total blood volume 10-20ml

Question 12

What is a test that if negative rules out candidaemia?

Answer 12

Beta-D-glucan test

Question 13

What test is used to diagnose some resp viruses?

Answer 13

NAAT

Question 14

What is the HIV window period?

how long is it nowadays?

Answer 14

The window period is time between potential exposure to HIV infection and the point when the test will give an accurate result.

2-3 weeks

Question 15

What is initiation of treatment prior to determination of a firm diagnosis • typically broad-spectrum (wide wild guess) abx?

Answer 15

Empiric therapy

Question 16

What are some bacterial causes of traveller’s diarrhoea? (yessc)

Answer 16

YESSC:

1. Yersinia enterocolitica,
2. E.coli O157:H7
3. Shigella,
4. Salmonella,
5. Campylobacter

(e.coli and shigella → shiga toxin → HUS haemolytic anaemia + AKI + thrombocytopaenia)

Question 17

What is dysentry?

Answer 17

intestinal inflammation, primarily of the colon.

It can lead to mild or severe stomach cramps and severe diarrhea with mucus or blood in the feces.

Without adequate hydration, it can be fatal.

Question 18

What is the most common cause of dysentry?

Answer 18

Infection with the Shigella bacillus

Question 19

What is Guillan-Barre Syndrome?

Answer 19

a rapid-onset muscle weakness caused by the immune system damaging the peripheral nervous system.

The initial symptoms are typically changes in sensation or pain along with muscle weakness, beginning in the feet and hands.

Question 20

Where is the most common source for candidaemia?

Answer 20

Gut flora

Candida can translocate from the gut into the bloodstream if the epithelial lining becomes damaged microscopically (sepsis) or macroscopically (perforation, obstruction, necrosis).

Question 21

How are fungal infections classified? Give an example of each

Answer 21

Superficial

These infections can occur in anyone and are common. People with immunocompromise are however more at risk and can have a more severe presentation. Examples include patients with HIV or diabetes.

• Oral and vaginal thrush - caused by Candida sp.
• Tinea, for example athlete’s foot (tinea pedis) or ringworm (tinea capitis) - caused by the dermatophyte group.
• Fungal nail infection (onychomycosis) - caused by the dermatophyte group.
• Pityriasis versicolor - caused by Malessezia furfur.

Subcutaneous

These infections are not common in the UK and occur mainly in tropical countries. They affect the dermis, subcutaneous tissue and adjacent bones and there is often some degree of immunocompromise.

Deep

These infections occur in people who are immunocompromised. They may be receiving drugs to suppress their immune systems e.g. cancer chemotherapy and infliximab, or may have advanced HIV.

• Invasive Candida sp. - e.g. candidaemia in ICU patients with central lines that have bypassed the barrier made by the skin.
• Invasive Aspergillus fumigatus - patients who have had transplants or chemotherapy.
• Pneumocystis jirovecii pneumonia (PCP) - patients who have HIV or low lymphocytes.
• Cryptococcal meningitis - patients who have HIV or other severe immunosuppression. Caused by Cryptococcus neoformans.

Question 22

What is the scientific name for chicken pox?

What is the most common complication?

Answer 22

Primary varicella zoster infection

Pneumonitis

Question 23

What are the 4 most important herpes viruses?

Answer 23

1. Herpes simplex -1
2. Herpes Simplex 2
3. EBV
4. cytomegalovirus

Question 24

What is significant about herpes viruses?

Answer 24

Following primary infection, herpesviruses are able to become latent and establish lifelong infection. They can periodically reactivate, often when a patient’s immunity is low.

Question 25

What cancer is EBV associated with?

Answer 25

Burkitt's lymphoma

Question 26

Who does CMV (cytomegalovirus) infect?

Answer 26

CMV causes disease in patients who are immunocompromised, for example **retinitis** in patients with **HIV** , and **tissue rejection** in **transplant patients**.

Question 27

What is the difference between shingles and chickenpox?

Answer 27

Chickenpox is the primary infection whereas shingles represents reactivation of latent VZV (varicella zoster virus). Following primary infection, VZV lies dormant in single sensory nerves or dorsal root ganglia. Reactivation is usually triggered by immune compromise and leads to a rash in the area of skin supplied by these nerves - a dermatome. One or multiple dermatomes may be affected. Dermatomes do not cross the mid-line of the body.

Question 28

If a pregnant woman can't remember if she's ever had chickenpox / shingles then what should happen?

Answer 28

She should be tested for **VZV IgG.** If positive, no action is needed. If negative, then the mother is at risk becoming infected and she should be given VZV immunoglubulin (**antibodies**), to provide her with temporary passive immunity.

Question 29

How are parasites classified?

Answer 29

* **Ectoparasites** – parasites that live on the skin and hair (ecto – outside). * **Endoparasites** – parasites that live on mucosal surfaces such as the gut and in tissue (endo – within). * **Helminths** – worm-like parasites, mostly visible to the naked eye (e.g. pin worm) * **Protozoan** parasites – single-celled, eukaryotic organisms that are usually motile (e.g. malaria)

Question 30

Name 2 helminths you can catch in the UK what will you see on the bloods?

Answer 30

**Pinworm** is caused by **Enterobius** **vermicularis** and is a common helminthic infection in school-age children. Even if asymptomatic, everyone in the same house as a patient infected with pinworm should be treated with **mebendazole**. **Diphyllobothrium latum** or **fish tape worm**. Caught be eating undercooked fish or sashimi. *eosinophilia*

Question 31

Name some ectoparasites you can catch in the uk

Answer 31

Scabies (Sarcoptes scabiei) ticks lice (pubic, head, body)

Question 32

What protozoa can you catch in the UK?

Answer 32

**Toxoplasma gondii** is a common protozoan infection. Primary infection in pregnancy can be harmful to the foetus - it is a "TORCH" microorganism. Kittens shed the cysts in their faeces hence the advice to pregnant women not to clean litter trays. **Giardia lamblia** - The main symptom is watery diarrhoea and patients often complain of excessive flatulence. The symptoms can last for weeks without treatment and can sometimes cause malabsorption. The treatment for **giardiasis** is **metronidazole** or **tinidazole**. **Cryptosporidium parvum** is another gastrointestinal protazoa that causes watery diarrhoea. It mainly occurs in young children and immunocompromised patients. **Trichomonas vaginalis** is a sexually-transmitted infection that causes vaginal and urethral discharge.

Question 33

What are TORCH infections?

Answer 33

vertically transmitted infections that are capable of significantly influencing fetal and neonatal morbidity and mortality Toxoplasmosis Others (e.g., syphilis, varicella, parvovirus B19 infection, listeriosis) Rubella Cytomegaly (CMV) Herpes simplex virus (HSV) infection

Question 34

What is Strongyloidiasis? aka threadworm

Answer 34

Strongyloidiasis is an infection caused by the intestinal nematode Strongyloides stercoralis. Transmission occurs widely in tropical and subtropical areas, but also in countries with temperate climates.[1] The primary mode of infection is through larvae penetrating the skin. Strongyloides larvae migrate from subcutaneous tissues into the venous circulation, then to the lungs. Larvae migrate up the airways, are swallowed, and establish chronic infection in the intestinal tract as adults. New larvae continue this cycle within the human host creating indefinite auto-infection; meaning that, without treatment, infection is lifelong.

Question 35

What are the tests for hep B, C and HIV?

Answer 35

Hepatitis B surface antigen Hepatitis C antibody HIV antibody

Question 36

What are the common bacterial pathogens causing infective endocarditis? x5

Answer 36

1. Streptococcus viridans group (most common cause – 40-50%) 2. Staphylococcus aureus (especially acute presentation, IVDUs) 3. Staphylococcus epidermidis (mainly in prosthetic valves) 4. Streptococcus bovis is associated with colorectal cancer 5. Streptococcus mitis (viridans group streptococcus): following dental work

Question 37

What is the best choice antibiotic for empirical treatment of septic arthritis?

Answer 37

**IV flucloxacillin** ## Footnote Septic arthritis is most commonly caused by gram positive cocci, especially **Staphylococcus aureus**. As the infection is in a **deep** site, intravenous flucloxacillin is the first line choice.