Eradicating viruses Flashcards
What are the animal equivalents of the following viral diseases: smallpox, measles, and polio?
- small pox –> camel pox
- measles –> rinderpest virus
- polio –> enteroviruses
what virus causes small pox?
variola virus
what are the two forms of smallpox?
- variola major
- variola minor
how does smallpox spread?
aersols and through fomites
describe the disease course of variola major
- incubation period: 1-2 weeks
- prodrome: few days, not very contagious, high fever, malaise, headache
- early rash: 4 days, highly infectious, lesions appear all over
- pustular rash: 5 days, contagious, lesions become postules
- postules and scabs: 5 days, contagious, pustules scab over
- resolving scabs: 6 days, contagious, scabs retain some virus
- scabs resolve: no longer infectious, scarring
what are the other types of small pox?
- modified smallpox: mild, usually previously vaccinated with poor take, low mortality
- flat smallpox: severe, sunburn like features, high mortality
- hemorrhagic smallpox: few lesions, extensive hemorrhagic manifestations, inflammatory shock, 100% lethal
flat and hemorrhagic are probably due to pre-existing immune deficiences including pregnancy
what’s the difference between monkeypox and smallpox?
- smaller mortality
- fewer lesions
- differential diagnosis: PCR, serology
- endemic to central/west africa
- zoonotic, small rodent reservoir, bushmeat trade
describe the sequelae of smallpox
- pock marks, scarring
- blindness
- limb deformities
- lifelong resistance
describe the biology of variola virus
- poxvirus (orthopoxvirus family)
- large dsDNA virus
- encodes immunosuppressive virulence factors
- large brick-shaped viruses – can be seen under a light microscope
what is the smallest orthopoxvirus?
variola virus (VARV)
how has smallpox shaped faith?
many religions have gods devoted to smallpox
where did smallpox originate from? what about variola minor?
- possibly Nile valley, fertile crescent, rome’s granary
- minor: spread from africa to the americas by the slave trade
how did we date the emergence of smallpox?
using a molecular clock and DNA from a 370 year old lithuanian mummy
describe the course of smallpox in Peru: 1524
- 1524: smallpox arrives
- 25: smallpox kills the inca, huayna capac, and his heir dies soon afterwards –> civil war
- 33: Pizzaro exploits the chaos and brutally conquers the territory
what plagues caused the destruction of central and south american civilization
- smallpox
- measles
- typhus
- influenza
- yellow fever
what was the Great Dying in Austrailia?
- british colonists brought smallpox on arrival day
- an endemic ensued
- children and pregnant women were especially vulnerable
- waves of disease moved westward over the 19th century, traveleres encountered scarred and blinded survivors
how did the great dying cause a little ice age?
epidemics killed 100 million people in the 16th-17th century, the forests grow back on abandoned fields –> CO2 was absorbed by the new forests and the world cools
what factors favour elimination of smallpox
- cheap, safe, and effective vaccine producing long-lived immunity (no cold chain needed)
- easily detected/reported
- no persistent infections or permanent reservoir
why did the american campaign against quebec fail?
- british forces were routinely variolated, americans not so
- american troops got sick and their campaign failed
which virus, discovered by Jenner, was ultimately used to eradicate smallpox?
vaccinia virus
what is the origin of vaccinia virus?
likely a horsepox and not a cowpox
how and why was Jenner’s vaccine improved upon?
- jenner’s vaccine was originally passaged in humans –> spread other diseases like syphillus
- vaccine farms arose and “calf lymph” was used throughout the eradication era
when was smallpox declared eradicated? how did we achieve eradication?
- 1979
- world-wide mandatory vaccination campaigns plus aggressive search and discovery tactica
- late stages: ring vaccination plus bounties for new cases
what are practical challenges to vaccination?
- wars
- corruption
- incompetence
- religious and tribal feuds
- mistrust
- individual versus community rights
- poverty
what are the special rules for handling variola virus?
- only two sites are allowed to store and study variola virus: BSL4 requirements, archives are stored frozen with armed guards
- centers must report what they are doing every year to WHO
- only research relating to drug, vaccine and/or diagnosistic development is allowed
- no lab can retain clones or DNAs comprising >25% of the genome
- engineering variola genes into other poxviruses is illegal
- in canada, possession of variola is a criminal offence under the pathogens and toxins act
what are the two labs with variola now?
CDC Atlanta, US
VECTOR, Russia
what type of virus in rinderpest?
(-)ssRNA virus
describe the disease caused by rinderpest
- respiratory virus
- highly contagious
- causes oozing sores in the mouth, eyes, respiratory, and urogenital tracts
- symptoms include diarrhea, dehydration and death
- young animals are the most sensitive and immune for life
- affects cattle, sheep, goats, and wild game
- 90% mortality
why was it feasible to eradicate rinderpest?
- vaccine protects from all three lineages
- Ro was lowerish, so herd immunity suffices
- high impact disease –> encourages cooperation
what was the original method used in europe to control rinderpest?
mass slaughter
what were the special tactics used to help eliminate rinderpest?
- PCR helped track origins of outbreaks
- serological testing measured vaccination and infection rates
- isolated reservoirs in ethiopia, sudan, yemen, pakistan and india were picked as priority targets
- UNICEF partnership helped recruit community liason officers – trained as vaccinators and vets, gaining trust and providing access to confict zones
when was rinderpest declared eradicated it, what were some challenges to eliminating it?
- 2011
- wildlife reservoirs
- mistrust
- tribal feuds
- wars
- poverty
where is rinderpest being held now?
- AU-PANVAC, ethiopia
- National institute of animal health, japan
describe some general featurs of poliovirus: disease, family, route of transmission. who’s at risk, seuquelae
- causes poliomyelitis
- picornaviridae
- oral-fecal route
- can estabilsh carrier stages
- children under 5 are at greatest risk
- can cause permanent paralysis
what are the two polio vaccines?
- sabin: live attenuated, oral vax
- salk: killed injectable vax
what polio strains are circulating today, which is the major one?
- wt
- cVDPV1
- cVDPV2 (most)
how many mutations are requred to create a cVDPV2 polio strain, how long does this take?
6 mutations –> about a year
what recent change to the polio vaccine makes it much harder for it to revert?
CpG codons were used to replace synonymous codons in the capsid genes + 5’UTR was altered –> makes it hard to revert
what is the next virus we are looking to eliminate?
peste des petite ruminants (PPR)
