Preventing and treating virus infections Flashcards
Public health control measures (5)
1) Quarantine (& vaccination) or slaughter
2) Surveillance - some diseases are notifiable (implementation of control measures, early detection enables swift action to stop the spread)
3) Sanitary engineering/food hygiene regulations - faecal-oral transmission reduced (poliovirus, HAV) by clean water and good hygiene
4) Control of insect vectors - mosquito (yellow fever, dengue, Zika)
5) Screening of blood and blood products - HIV, HBV, HCV
Antiviral chemotherapy overview
Viruses are all oblicate intracellular parasites that use cell biochemistry for virus replication, hence they present fewer drug targets than bacteria (which have distinct ribosomes and cell wall biochemistry), and there is the challenge of inhibiting the virus without host cell toxicity
Targets - i) virus binding to host cell ii) virus replication (enzymes involved) iii) virus assembly or dissemination
Anti-herpes virus drugs (2)
1) Acyclovir (ACV) - zovirax - active against HSV. Targets thymidine kinase (TK) and DNA polymerase. ACV is a nucleoside analogue, and it blocks DNA elongation (a chain terminator). It shows specificity as ACV is a better substrate for HSV TK than host TK. PPP-ACV is a better substrate for virus DNA pol than host DNA pol, so ACV is used in HSV-invected, but not uninfected cells
2) Ganciclovir and cidofovir - Nucleoside analogues. Shows specificity as used by virus DNA polymerase. Used in HCMV infections. Cidofovir is given intravenously and has some renal toxicity
Types of vaccine
a) Passive
b) Live
d) Dead
a) i) Immune globulin or monoclonal antibodies - eg for rabies after exposure, or infants born to HBV +ve mothers) ii) Maternal antibody - eg for measles
Advantages - immediate protection. Disadvantages - short lived (seum sickness, immune responses to foreign proteins)
b) i) Attenuated form of virulent organism - eg for yellow fever, rinderpest, polio, measles, mumps, rubella ii) Immunologically related organism - eg vaccinia for smallpox, or turkey herpes virus for Marek’s disease in chickens iii) Virulent organism through an unusual route (variolation)
Advantages - induce both T cell and antibody responses, long lasting, low cost and ease of manufacture and administration. Disadvantages - safety (may revert to virulence, or cause serious infection in immunosuppressed), heat lability, virus may shed into the environment
c) Antigen preparation lacking infectivity i) whole virus - eg rabies, polio, SARS-CoV-2 ii) specific virus proteins - eg HA for influenza, HBsAg for HBV, HPV-L1 for HPV
Advantages - safety (only if inactivation is complete). Disadvantages - requires multiple administrations to achieve solid immunity, may require adjuvants, protection for shorter duration, high cost, reduced cell-mediated immunity
a) Viruses prevented with live vaccines (10)
b) Viruses prevented with dead vaccines (8)
a) yellow fever virus, measles virus, mumps virus, rubella virus, poliovirus, VZV, canine distemper virus, Marek’s disease virus (related virus), psuedorabies virus (genetically engineered), rabies virus (genetically engineered)
b) HAV, poliovirus, rabies virus (dead or immune globulin), FMDV, influenza virus, HBV (genetically engineered or immune globulin), HPV 16/18 (genetically engineered), measles (maternal mAbs)
