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Flashcards in Scenario 15 Deck (102)
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What memory immunity is stored in varicella?

VZV specific IgA and IgG antibodies and CD8/4 T cells (needed to prevent reactivation)


What is zoster?

Reactivation of latent VZV painful vesicles (1-2 vesicles) most commonly thoracic


How is zoster transmitted?

Spread by resp and skin lesions and congenital infection of fetus in first 20 weeks


When should post exposure prophylaxis be given?

Pregnant, immunocompromised or neonate of seronegative mother


What treatment should be used in zoster?

First line antiviral agents- aciclovir, valaciclovir and famciclovir


How are virus' detected?

Electron microscopy , cytopathic effect, cmv, protein antigen, nucleic acid (PCR, ELISA)
Specific antigen response- serology, seroconversion


What is therapeutic index?

Minimum cell toxic dose/ minimum virus inhibitory dose= at least 10


What are examples of nucleoside analogues?

Aciclovir, ganciclovir


What are examples of nucleotide analogues?



How does aciclovir work?

Nucleoside analogue, competitive substrate for viral DNA polymerase inhibiting viral DNA polymerase and terminating the chain


How is aciclovir selective to infected DNA?

Preferential monophosphorylation- infected has 40-50x more phosphorylation, cellular DNA less susceptible (no viral DNA polymerase), effective chain termination due to lack of OH group


What are the issues with aciclovir?

poor oral absorptuon, short half life (need 5 a day) 85% excreted in urine
Use valaciclovir- 80% taken up


Why are some cells resistant?

Virus thymidine kinase absent or viral DNA polymerase altered


How does ganciclovir work?

Requires tri phosphorylation to active form. Works by inhibiton of CMV polymerase, not a chain terminator- need to add valine to be absorbed


Why is resistance to anti-retroviral therapy so high?

Error rate high so lots of mutations, selective pressure exerted if treatment stopped then resistant strain becomes latent


What are the targets for RNA anti-virals?

Viral proteases, viral surface proteins, immune modulation


What is advised after a splenectomy?

Prophylaxis and immunisation


What is defects in humoral immunity?

Immunoglobulin deficiency, congential B cell deficiencies
Frequent ear and sinus infection, infants fail to grow, pneumonias, obsesses, chronic enterovirus meninenephalitis, increased incidence of autoimmun and CT disorders


How do we prevent infection in defect in humoral immunity?

Ig replacement therapies


What infections are likely in people with congenital complement abnormalities?

Resembles hypospeism- streptoccocus pneumoniae, haemophilus influenzare, nisseria meningitidis)


What is defect in neutrophil number defined as?

less than 1x10^9 /l
May occur after haemopoetic stem cell transplantation, chemo, immunosuppresion, haematological malignancy, prolonged placement of catheters


What are the risks after solid organ transplantation?

Immediately after upper/lower RTIs but long term need lifelong immunosuppression, risk of transmitting infection i the organ and some inevitable CMV, toxoplasma- need prophylaxis


What is cytomegalovirus?

Transmitted by intimate contact 50% of adults, majority asymptomatic
If donor positive and recipient negative- primary infection
If donor negative recipient positive- reactivation
If both positive- recurrent infection


What is CD4?

A cell surface molecule which is on T helper cells and expressed on dendritic cells and macrophages. Stabilises a T helper 1 cells interaction with MHC class II and recruits signalling molecule, T helper 2 cells stimulate b cells for antibody production and aids CD8 T cells.


How are the number of CD4 cells depleted?

Direct cytopathicity of the virus, killing by specific cytotoxic T cells, memory pool particularly depleted


What is the host response in HIV infection?

CD4 count fails early and functional impairment of CTL response, cytotoxic T cells can kill HIV infected cells and HIV specific neutralising antibody response- antigenic diversity of HIV is a challenge


What is a primary immunodeficiency?

Innate defect at a genetic/ developmental level- failure to produce a class of antibody/ complement./ enzymes


What is a secondary immunodeficiency?

Factors not innate to the patient, nutrition, malignancies, aging, drugs, stress, splectomy


What are the steps of the formation of a HIV provirus?

Reverse transcriptase copies an RNA template onto dsDNA copy then covalent insertion of viral DNA into the genome of the infected cell (cant be cured)


What is the genetic organisation of a retrovirus?

9 genes synthesising 3 polyproteins
Gag- group specific antigen- viral core proteins, matrix, capsid
Pol- polymerase- enzymes, protease, reverse transcriptase, integrase
Env- envelope glycoprotein