Miscellaneous Flashcards
What type of virus is HIV?
Retrovirus. These are enveloped viruses.
In what should you especially consider HIV?
Think of testing for HIV infection when faced with recurrent shingles, candidiasis etc.
Multi-dermatomal shingles
Unexplained lymphadenopathy
Unexplained weight loss or diarrhoea, night sweats, PUO
Oral/oesophageal candidiasis or hairy leukoplakia
Flu-like illness, rash, meningitis
Unexplained blood dyscrasias.
What HIV screening test is preferred?
Venous blood sample.
What do 4th generation HIV tests detect?
p24 antigens and HIV antibodies.
They will detect the vast majority of infections at 4 weeks. If negative, repeat at 8 weeks if high suspicion.
What are HIV point of care tests?
Finger prick blood. Lower sensitivity and specificity. Gives false positive and negative results.
What is the natural history of HIV?
- Primary infection
- Acute HIV syndrome, wide dissemination of virus, seeding of lymphoid organs (acute rise in HIV RNA then fall and fall in CD4 count followed by a gradual rise)
- Clinical latency
- Constitutional symptoms (progressive generalised lymphadenoapthy)
- Opportunistic diseases (AIDS when CD4<200)
- Death.
What happens to CD4+ T lymphocyte count from clinical latency to death?
Decreases.
What happens to HIV RNA between clinical latency and death?
Increases. Increases rapidly from constitutional symptoms to death.
When is high risk of transmission of HIV?
The first month or so post infection due to the high viraemia.
After initial exposure of HIV, how long is the average period that somebody is asymptomatic for?
Seven years.
How is RNA copied into DNA?
Reverse transcriptase.
What group of viruses does HIV-1 and HIV-2 belong to?
Lentivirus.
How many HIV subtypes are there?
9.
How do viruses replicate?
- Attachment: viral and cell receptors e.g. HIV (gp120 and CD4)
- Cell entry: only central viral ‘core’ carrying the nucleic acid and some associated proteins enter the host cell
- Interaction with host cells: use cell materials (enzymes, amino acids, nucleotides) for their replication
- Replication: may localise in the nucleus, cytoplasm or both. Production of progeny viral nucleic acid and proteins
- Assembly: occurs in the nucleus (e.g. herpesviruses), in the cytoplasm (e.g. poliovirus) or at cell membrane (e.g. influenza virus)
- Release: by bursting open (lysis) of the cell or by ‘leaking’ (exocytosis) from the cell over a period of time e.g. HIV.
What immune response do CD4 T cells act in?
Acquired immune response.
What is the gold of CD4 T cells?
They are responsible for organising, recruiting and facilitating the maturation of B antibody producing cells and T CD8 killer cells.
What types of T helper cells do CD4 T cells mature into?
On presentation of antigen CD4 cells mature into two types of t helper cell.
1. T helper cell 1 produces specific interleukins (IL 4, 5, 10,13 ) that cause maturation of B lymphocytes into plasma cells. The plasma cells then produce specific antibodies IgG etc against the specific antigen in question. This allows a more prolonged and effective antibody response.
2. T helper cell 2 produces IFN alpha and TNF. These cytokines activate further CD8 cells, turning them into Cytotoxic T lymphocytes (CTL) and NK cells. CTLs then produce an enzyme ( perforin ) that directly kill cells with antigen on /in.
Note IFN alpha is an important cytokine in the bodies defence against TB
CD8 Killer T cells Act as direct killer cells by killing any cell that is seen to be infected with the specific foreign agent.
What does HIV result in?
The death of CD4+ T lymphocytes.
What does HIV replicate within?
CD4 T cells.
What is the structure of a virus?
Lipid envelope around outside
Protein capsid
Nucleic acid in centre
Virion associated polymerase in the centre.
How does HIV replicate?
- HIV binds via gp120 envelope glycoprotein, to CD4 receptors on T helper cells, monocytes, macrophages and neural cells
- CD4+ cells migrate to lymphoid tissue, where virus replicates
- New viruses are released, and infect new CD4+ cells
- As infection progresses, depletion or impaired function of CD4+ cells and immunity
- After cell entry, viral reverse transcriptase makes DNA copy of RNA genome
- Viral integrase enzymes integrates this into host DNA
- Viral RNA is spliced, core viral proteins are synthesized, then cleaved by viral protease into enzymes and building blocks of the virus
- Completed viruses are then released by budding
- Number of circulating viruses (viral load) predicts progression to AIDS.
What are the 9 steps of HIV replication?
- Attachment
- Entry
- Uncoating
- Reverse transcriptase (error prone so genetic variability)
- Genome integration
- Transcription of viral RNA
- Splicing of mRNA and translating into proteins
- Assembly of new virions
- Budding.
What cells can become infected with HIV?
CD4 T cells.
Macrophages (have CD4 and CCR5).
Possibly dendritic cells infected early on.
Occasionally: astrocytes, renal epithelial cells.
What causes AIDS?
Depletion of CD4 T cells.
How does HIV virus enter the body?
Via mucosa (vagina, rectum, intestinal, breastfeeding in infants).
What are the mechanisms of CD4 T lymphocyte depletion?
Direct cytotoxicity of directly infected cells Activation induced death Decreased production Redistribution Bystander cell killing.
What are the sanctuary sites for HIV infection?
Genital tract, central nervous system, gastrointestinal system and bone marrow.
What cells act as a reservoir for HIV?
Macrophages, microglia.
What favours HIV viral replication?
Excessive immune activation.
What did HIV-1 evolve from?
Simian immunodeficiency virus in chimpanzees.
What are infectious examples of AIDs defining conditions?
Candidiasis: oesophageal/lung Extra-pulmonary Cryptococcosis Cryptosporidiosis >1 month CMV: any organ except liver, spleen, lymph nodes Mycobacterium TB Toxoplasmosis of internal organs HSV with muco-cutaneous ulcer >1 month Pneumocystis jiroveci (carinii) pneumonia (PCP) Recurrent bacterial pneumonia.
What neoplasms are examples of AIDs defining conditions?
Invasive cervical carcinoma
Kaposi’s carcinoma
Primary CNS Lymphoma
Non-Hodgkin’s lymphoma.
What CD4 T cell count constitutes AIDs defining conditions?
<200.
What are some of the direct HIV effect AIDs defining conditions?
HIV dementia/encephalopathy
HIV associated wasting.
What is HIV seroconversion?
The period during which the body starts producing detectable levels of HIV antibodies.
What is the only symptom in HIV clinical latent phase?
Persistent generalised lymphadenopathy.
Enlarged lymph nodes involving at least 2 non-contiguous sites other than inguinal nodes.
How often should HIV +ve women have a cervical smear?
Annually.
What are the 3 respiratory diseases in HIV?
- Bacterial (often pneumococcal) pneumonia
- Tuberculosis
- Pneumocystis jiroveci pneumonia (PCP).
At what CD4 count does cerebral toxoplasmosis occur?
<100.
What are the CNS mass lesions in HIV?
Cerebral Toxoplasmosis
Primary CNS Lymphoma
Tuberculoma.
What are the ophthalmic lesions in HIV?
CMV
Toxoplasmosis
Choroidal Tuberculosis.
What are the types of meningitis in HIV?
Cryptococcal
Tuberculous
Pneumococcal.
What are the 3 HIV related neoplasms?
- Lymphoma (CD4 <100, systemic Non-Hodgkin’s lymphoma)
- Cervical neoplasia
- Kaposi’s sarcoma.
What are the 2 aims of HAART?
- Reduce viral load to <50 copies
2. Increase CD4 count.
Why does circumcision reduce the risk of HIV?
- By removing foreskin, circumcision reduces the ability of HIV to penetrate due to keratinization of the inner aspect of the remaining foreskin.
- The inner part of the foreskin contains many Langherhans cells, that are prime targets for HIV. Some of these are removed with the foreskin.
- Ulcers, characteristic of some STI’s that can facilitate HIV transmission, often occur on the foreskin. By removing the foreskin, the likelihood of acquiring these infections is reduced.
- The foreskin may suffer abrasions or inflammation during sex that could facilitate the passage of HIV.
What are the 3 drugs in HAART?
2 nucleoside reverse-transcriptase inhibitors (NRTIs) e.g. zidovudine, didanosine and lamivudine + 1 non-nucleoside reverse-transcriptase inhibitor (NNRTI).
Or 2 NRTIs + 1 Protease inhibitor (PI).
What are the 3 must haves for consent?
- Voluntary: free from pressure and incentives
- Informed: risk and benefits and alternatives
- Made by someone with capacity.
What are the 4 things someone must have to have capacity?
- Understand
- Retain
- Weigh
- Communicate their decision.
When was the Mental Capacity Act written?
2005.
What does the Mental Capacity Act state?
A person must be presumed to have capacity unless it is established that he lacks capacity.
An act done, or a decision made, under this Act for or on behalf of a person who lacks capacity, must be done, or made in his best interests.