HIV Flashcards
What are the four stages of untreated HIV infection?
- Flu-like
- Feeling fine
- Falling count
- Final crisis
Which herpes virus causes Kaposi’s sarcom?
HHV8
What do ring-enhancing lesions on a head CT in HIV suggest? What do the other images show?
- Head - Toxoplasma gondii (parasite from cat faeces)
- Lungs - reticulonodular shadowing - pneumocystic pneumonia
- Retinal -
HIV also causes hairy leukoplakia - cannot be scraped off unline candidiasis
Define HIV.
HIV is a retrovirus which infects and replicates in human lymphocytes (CD4 +ve T cells) and macrophages
This leads to immune system dysfunction, opportunistic infection, and malignancy = AIDS (acquired immunodeficiency syndrome)
What is the mode of transmission of HIV?
The virus is transmitted via blood, sexual fluids, and breast milk
What are the subtypes of HIV?
Virus subtypes include HIV1 (global epidemic) and HIV2 (↓ pathogenic, predominantly West Africa).
How common is HIV? What prevalence in UK? What % is unaware of their infection?
- ~37 million adults and children are estimated to be living with hiv worldwide
- with 1.2 million deaths/yr.
- Africa has most of the disease (~26 million), most of the mortality (790 000/yr), and ~1% of the world’s wealth.
- UK: estimated ~100 000 living with HIV (=1.9/1000) including 5% of men who have sex with men (MSM).
- ~17% of those with HIV in UK are unaware of their infection.
What is the pathophysiology of HIV?
- HIV binds via GP120 envelope glycoprotein to CD4 receptors on T helper cells, monocytes, and macrophages
- CD4 cells migrate to lymphoid tissue when the virus replicates, producing millions of new virons
- These are released and in turn infect new CD4 cells
- As infection progresses, depletion or impaired function of CD4 cells leads to low immune function
- HIV is a retrovirus - encodes reverse transcriptase, allowing DNA copies to be produced from viral RNA. This is error prone –> significant mutation rate –> treatment resistance
How does HIV present?
Primary HIV infection
- Symptomatic in 80% - 2-4 weeks after infection - seroconversion illness, acute retroviral syndrome
- Flu-like illness and erythematous/maculopapular rash, fever, myalgia, pharyngitis, mucosal ulceration, headache/aseptic meningitis
- Persistant generalised lymphadenopathy (>1cm in two or more non-contiguous sites but not inguinal for >3 months)
Latent phase - asymptomatic - in latent phase of chronic HIV infection
Late - complications of immune system dysfunction/malignancy
What are the available tests for HIV?
- ELISA for HIV antibody and antigen testing - 4th generation assay test; this reduces “window period” to average ~10days.
- Rapid point-of-care testing -immunoassay kit which gives a rapid result from a finger prick or mouth swab. Only CE-marked kits should be used. Needs serological confirmation.
- Viral load - quantifies HIV RNA. Monitors response to ART. But not diagnostic due to possibility of false positive result. Confirmation of seroconversion is still required in symptomatic primary HIV.
- Nucleic acid testing/viral PCR - tests HIV RNA levels- high in early infection when antibodies might be negative. Used to test vertical transmission.
- CD4 count - not for diagnosis. Monitors immune system function and disease progression. <200cells/microlitre is the defining criteria for AIDS.
Which HIV test is used for testing vertical transmission?
Nucleic acid testing/viral PCR - used to test vertical transmission in neonates as placental transfer of maternal antibodies can affect ELISA antibody testing up to 18months of age.
What can be detected first: antigen or antibody?
Usually antigen
Antibody takes time to make
Why is diagnosis of primary HIV a unique opportunity to prevent transmission?
There is increased viral load and genital shedding - even though HIV antibody testing may be negative, HIV RNA levels are high
What defines AIDS?
CD4 count <200cells/microlitre
What are the three categories of main HIV complications?
Complications:
- complications of immune dysfunction (opportunistic infection/malignancy)
- complicating comorbidity
- complications of treatment i.e. adverse drug events
