Flashcards in Scenario 15 Deck (102)
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?
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)