Smallpox and Other Eradication Programs Flashcards
What virus causes smallpox?
Variola virus
- Member of Orthopoxvirus
- Family Poxviridae
What is the normal host of the virus causing smallpox?
Humans
What are poxviruses?
- Large DNA viruses that replicate in the cytoplasm of infected cells
- The large genome contains genes which encode for numerous nonstructural proteins, several of which counteract the immune system
What are common complications of poxviruses?
- Blindness
- Pockmarks (deep pitted scars, most prominent on the face)
What is variolation?
- Developed by practitioners in Asia
- Involved blowing dried smallpox scabs into the nose, the individual contracted a mild form of the disease
- However, 1-2% of the variolated died
How did Edward Jenner introduce vaccination?
- He recognised that cowpox-infected dairy maids were immune to smallpox
- Deliberately used a Lancet and scratched two lines on James Philipp’s (8 years old) arm
What was the mechanism behind Edward Jenner’s procedures in vaccination?
- The use of Lancet attenuated the virus
- The scratching activated the innate immune response so that the deliberate infection was contained within the inoculation site
Describe the smallpox eradication campaign.
1950: Smallpox was eradicated in industrialised nations, but there were still cowpox cases around the world; Vaxinia virus was freeze dried
1967: Vaccination reduced the number of smallpox cases; WHO launched an intensified eradication plan
- Jet injectors were used, which used pressurised air to shoot the virus into the arm
- They were found expensive and ineffective
- Bifurcated needles were then preferred as they were easy to carry in the field and could be sterilised to be reused = Cost effective
Describe the poliovirus.
- A small RNA virus (picornavirus)
- ssRNA; has no envelope (unlike poxviruses), which makes them more difficult to disinfect
What does poliovirus cause?
Impaired breathing
Poliomyelitis
- A viral paralytic disease
- The Poliovirus enters the body orally and infects intestinal wall
- Virus proceeds to the blood stream and CNS, causing muscle weakness and paralysis
Most infected people are asymptomatic or have mild symptoms
What kind of vaccines were used against polio?
Inactivated vaccines and oral (live) vaccines
What was the inactivated polio vaccine (IPV)?
Salk Vaccine
- Formalin-inactivated poliovirus
Give an example of an oral poliovirus vaccine.
Sabin Vaccine
- Poliovirus is passed through nonhuman cells (monkey kidney cells) at a subphysiological temperature
- The virus alters its enzymes to adapt to the subphysiological environment
- When the virus is injected in humans, it is in a weakened (attenuated) form
- However, there is risk for the attenuated virus reverting back to its wild-type form
What is passive immunity?
- Temporary and does not engage immune response or generate memory
- Can be acquired naturally (maternal IgG crosses the placenta to foetus) or delivered artificially
- Protect individuals from subsequent infectious disease or in those who lack humoral responses
What are live attenuated vaccines?
- Microorganisms are attenuated (disabled) so they are unable to cause pathogenicity but still able to slowly and transiently grow within the inoculated host
- Provides active immunity
