BOD - Revision - Michaelmas - Smith - Viruses Lecture 19. PREVENTING AND TREATING VIRUS INFECTIONS Discuss, with examples, how virus infections can be controlled by vaccination, commenting on the merits and limitations of vaccination in relation to other control measures. Intro: · Viruses are obligate intracellular pathogens . Hard to treat because they live inside the body's cells · Few antiviral medicines · Vaccines can prevent infection 1. Epidemiological control: · Quarantine, isolation, slaughter · Surveillance · Sanitary engineering/food hygiene regulations * Some viruses spread via faeco-oral route e.g. poliovirus, Hep A * Good hygiene standards and clean water · Vector control * Yellow fever, Zika, dengue * Protection from bites using mosquito nets and other preventative methods · Screening of blood/blood products 2. Vaccinations: Vaccine type Attenuated Related live virus Engineered deletion mutant Pseudorabies virus Killled virus Foot and mouth disease, rabies, influenza, hep A, polio Subunit Hep B Polio, measles, mumps, rubella, yellow fever, canine distemper Marek's disease
Vaccine for: Live Yellow fever virus + Measles virus + Mumps virus + Rubella virus + Poliovirus + (Sabin) Varicella-zoster virus + Variola virus (smallpox) + (related virus) Marek's disease virus + (related virus) Canine distemper virus + Psuedorabies virus (pig herpes virus) Rinderpest virus + Hepatitis A virus + Poliovirus Rabies virus Hepatitis B virus Foot and mouth disease virus Influenza virus + Human papillomavirus + + (genetically engineered deletion mutant) dead passive + + + (Salk) + + + + · Smallpox: o Smallpox - 20th century - infected more than 300million people Edward Jenner - 1796 " Injected pus from cowpox from milkmaid in to a healthy boy " Deliberately infected with smallpox 2 weeks later > Boy survived Smallpox now eradicated (1978) · Essential factors for disease eradication: a. Virus infectious cycle must take place in a single host b. Vaccination must induce lifelong immunity · Live attenuated virus vaccines Attenuated mutants of the wild type virus: yellow fever, measles, mumps, rubella, polio (Sabin) o Live related viruses: vaccinia virus for smallpox, or turkey herpes virus for Marek's disease (tumour inducing virus of chickens) o Advantages: self-replicating (cheaper) and induce both cellular and humoral immunity that is long lived. o Progeny virions often contained at site of infection and do not spread to other sites > Produces mild/inapparent disease o Less virulent viruses selected by growth in cells other than normal host or propagation at nonphysical temperatures o Cold-adapted mutated often less pathogenic than their parental virus o Administered by injection or mouth
" Oral administration mimics natural route of infection for enteric viruses o Some viral shedding occurs - vaccinated individuals able to infect unvaccinated individuals o Reversion back to virulence possible due to mutations o Cold storage required to maintain infectivity o Induce a natural response and immunity is long lived · Inactivated/killed vaccines o Virions isolated and inactivated by chemical or physical procedures - eliminates infectivity but doesn't compromise antigenicity o Can go wrong - Salk polio virus in 1950s -more than