Infectious Disease Flashcards by Sophie R Vaughan-Williams

What is the etiological agent in hepatitis B infection?

Enveloped DNA virus of the hepadnaviridae family

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Routes of transmission of hepatitis B

Vertical - From mother to child at birth (transmission is about 90% but preventative measures can be given to decrease it to approx 7%)
Horizontal:
- Sexual (more infectious then HCV and HIV)
- Blood transfusion or procedures such as dialysis or orperations.
- Needles or sharps
- Household transmission eg razors or toothbrushes

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What are the 3 antigens of clinical importance in hepatitis B?

Surface antigen (HBsAg) - found when there is a current infection
Envelope antigen (HBeAg)
Core antigen

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What are the 3 antibodies that the body produces in hepatitis B and what do they tell us ?

Surface antibody - indicated immunity following immunisation or infection
Envelope antibody -
Core antibody - found in people who have been exposed to HBV at some point but does not distinguish between present acute or chronic or past infection. Does not occur in people who have been immunised to hep B.

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Which 3 antibodies/antigens are most useful in diagnosed hep B

Surface antigen (HBsAg)
Surface antibody (HBsAb)
Core antibody (HBcAb)

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What will be seen on serological testing for someone who has been immunised to Hep B but never exposed to the virus?

HBsAg -
HBsAb +
HBcAb -

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What will be seen on serological testing for someone who has previously had a Hep B infection but it has resolved?

HBsAg -
HBsAb +
HBcAb +

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What will be seen on serological testing for someone with chronic Hep B infection?

HBsAg +
HBsAb -
HBcAb +

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What are the 4 phases of chronic Hep B infection?

Immune tolerance
Immune clearance
Immune control (inactive phase)
Immune escape (reactivation phase)

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Which phases of chronic hep B infection is treatment indicated for?

Immune clearance and immune escape

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What is hep B treated with?

Pegylated interferon alpha (weekly injections for 48 weeks)
OR
Oral Tenofovir or Entecavir daily long term

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What is the etiological agent in hepatitis c infection?

Hepacivirus in the family flaviviridae

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What is the principle mode of transmission for hep c?

Parenteral eg IV drug use, tattoos, sharing of razors or toothbrushes.

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What is the rate of vertical transmission in children born to HCV positive mothers?

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What are the typical hepatitis symptoms?

Malaise
Nausea
RUQ pain
Jaundice
Fatigue

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Extra-hepatic manifestations of HCV?

Essential mixed cryoglobulinaemia
Membranoproliferative glomerulonephritis 
Porphyria cutanea tarda
Autoimmune thyroid disease
Lichen planus
Sjogren's disease
B-cell lymphoma
Interstitial lung disease

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What are the diagnostic investigations for Hep C?

Enzyme immunoassay - positive HCV antibody

Immunoblot assay - PCR shows HCV RNA

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How many genotypes of hep c are there that tend to circulate and in which geographical areas?

6
Genotype 1,2,3 - UK
Genotype 4 - Africa and middle east
Genotype 5 - South Africa
Genotype 6 - SE Asia

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Which hep c patients are more at risk of developing end-stage liver disease?

Co-existing hepatic disease
HIV
Afro-caribbeans > Caucasians

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What does a non-invastive firboscan assess?

Liver transient elastography (stiffness)

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What screening do patients with advance fibrosis undergo?

6 monthly screening for hepatocellular carcinoma. Test include:
a-fetoprotein (a tumour marker for HCC)
Liver ultrasound

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What is the aim of treatment for hep b and hep c

Hep B - control viral replication and reduce inflammation

Hep C - curative (defined as undetectable HCV RNA in blood 12 weeks after treatment has ended)

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What is the type of drug used to treat hep c and how do they work?

Direct acting antivirals (DAAs)

They act on specific HCV viral enzymes to prevent the replication of HCV.

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What are the 3 classes of DAAs?

NS3/4A protease inhibitors (ends -previr)
NS5A inhibitors (ends -asvir)
NS5B inhibitors (ends -buvir)

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What combination of DAAs is used to treat hep c?

2 or more DAAs from 2 or more DAA drug classes

What is multi-drug resistant TB defined as?

TB that is resistant to at least isoniazid and rifampicin

Which drug out of the normal TB regime is most likely to cause liver toxicity?

Pyrazinamide

What is the normal TB treatment regime?

Rifampicin - 6/12 Isoniazid - 6/12 Pyrazinamide - 2/12 Ethambutol - 2/12

Which TB drug is most likely to cause optic neuritis?

Ethambutol

Which TB drug is most likely to cause peripheral neuropathy?

Isoniazid

Which TB drug is more likely to cause arthralgia?

Pyrazinamide

How long would you treat TB meningitis or CNS TB for?

12 months

What is the ideal diagnostic investigation of TB?

Sputum sample examined for alcohol and acid fast bacilli | Ziehl Neelson stain or Auramine Phenol staining and detection with fluorescent microscope

What test can differentiate between TB and non-TB mycobacterium?

PCR

What tests are positive in latent TB?

Mantoux and interferon gamma release assay

Risk factors for TB

``` HIV Overcrowding/close contact with active case (1/3 chance of contracting from household member) Ethnic minority groups Malnutrition IV drug use Homelessness Chronic lung disease Immunosuppression ```

What are the pulmonary and constitutional symptoms sene in 90% of TB patients?

Pulmonary: Cough +/- haemoptysis, shortness of breath Constitutional sx: Fatigue, weight loss, night sweats, malaise, loss of appetite, lymphadenopathy, failure to thrive (in children)

What are the extra-pulmonary symptoms of TB?

CNS: Meningism (Neck stiffness, headache, photophobia) EYES: Choroiditis (blurred vision, red eyes) CVS: Pericarditis (chest pain, SOB) GI: Peritoneal/ilieocecal (abdo pain, mass, ascites) RENAL: Dysuria, haematuria SKIN: Lupus vulgaris MSK: Arthralgia

How are patients screened for TB in contact tracing?

Mantoux or interferon gamma release assay

What are asymptomatic children who have been in close contact with a confirmed case of TB treated with?

6 months of isoniazid

What measures are used to establish severity of HIV disease?

CD4 count | Viral load

What opportunistic infections are HIV patients with a CD4 count<200 are susceptible to?

Pneumocystis carinii pneumonia | Toxoplasmosis

How is AIDS defined?

CD4 count <200 or presence of AIDS defining illness eg opportunistic infections such as PCP, CMV, TBor setinel tumours such as Kaposi's sarcoma or lymphoma

How is HIV treated?

Highly active anti retroviral therapy (at least 3 different drugs)

HAART drug classes

Nucleoside reverse transcriptase inhibitors eg zidovudine Nucleotide reverse transcriptase inhibitors eg tenofovir Non-nucleoside reverse transcriptase inhibitors Protease inhibitors Entry inhibitors Integrase inhibitors

What prophylaxis treatment is recommended to patients with CD4 count <200?

Co-trimoxazole Nebulised pentamidine Azithromycin (if CD4 count <50)

What is the risk of pentamidine and what precaution is taken to reduce risk?

Teratogenic - given in a negative pressure side room

What precautions are taken to reduce the risk of vertical transmission form 25-40% to <1%?

Caesarean section Zidovudine monotherapy of infant for 4 weeks Exclusively formula bottle fed

What is the pathology of HIV?

It is a RNA retrovirus which, on gaining entry into a human cell, uses reverse transcriptase enzyme, to convert its RNA into viral DNA. It then proceeds to integrate itself into the host genome and replicate using the cell’s own processes. HIV can then infect any cell that expresses the CD4 receptor eg CD4 T cells, macrophages, monocytes and neurons.

What is HIV seroconversion?

The period of time during which HIV antibodies develop and become detectable. It generally takes place within a few weeks of initial infection. It is often, but not always, accompanied by flu-like symptoms including fever, malaise, maculopapular rash, myalgia and lymphadenopathy .

What differential presents similarly to HIV seroconversion?

Glandular fever (infectious mononucleosis)

3 enzymes involved in HIV infection

Reverse transcriptase Protease Integrase

Normal CD4 count

500-1500

Presentation/risks of HIV patients when CD4 count is 200-500

``` Susceptibility to shingles Oral hairy leukoplakia (EBV) Oral candidiasis Lymphadenopathy Thrush Skin infections TB ```

Cancers that patients with HIV patients are at risk of?

Kaposi's sarcoma and lymphoma

Spindle cells are characteristic of what cancer?

Kaposi's sarcoma

Infections that HIV patients with a CD4 count <50 are susceptible to?

Mycobacterium avian intracellulare | Cytomegalovirus

How to differentiate between toxoplasmosis and lymphoma?

Ring enhancing lesion on CT brain

How to you treat pneumocytis jerovecii pneumonia?

Co-trimoxazole | + Prednisolone/Hydrocortisone (if severe)

What is the diagnostic investigation for peumocystis jerovecii pneumonia?

Sputum sample - Silver stain

What is seen on chest CT for pneumocystis jerovecii pneumonia?

Ground glass appearance

What is a side effect of zidovudine?

Haemolytic anaemia

What are the 2 receptors that the HIV virus binds to?

CD4 | CCR5

What drug is used for both pre-exposure and post-exposure prophylaxis?

Truvada

What are investigations for malaria?

Thick (how much) and thin (which parasite) blood film | Antigen detection test (blood dipstick)

What are the strains of malaria?

Plasmodium falciparum Plasmodium Vivax Plasmodium Ovale Plasmodium Malariae

Why is plasmodium falciparum worse?

Sticks to blood vessel due to adhesive proteins, can cause vascular ischaemia and encephalopathy. Can give falsely low viral load.

What are the prophylactic drugs for malaria?

Doxycycline Atovoquone/Proguanil Chloroquine and proguanil (useless) Mefloquine (can cause acute psychosis)

What level of parasitaemia is severe?

>2%

What is the treatment for malaria?

IV artemisinin-based combination therapies for 7 days eg artesunate

How would you monitor response to malaria treatment?

Repeat blood films?

What are the complications of malaria?

``` Cerebral malaria AKI Hypoglycaemia Haemolytic anaemia Tissue hypoxia --> Metabolic acidosis DIC Neurological symptoms ```

Why would you give pyridoxine with the TB drugs?

Prophylaxis for isoniazid induced peripheral neuropathy

What do you find on chest X-ray for TB?

Cavitation Calcification Consolidation Fibrosis

What AIDS defining malignancy is caused by human herpes virus 8?

Kaposi's sarcoma

Infectious Disease Flashcards

(75 cards)