Topic 5 - Smallpox, Viruses, and Vaccines

Smallpox

virus

acute and stage 5 (no non-human host)

no latent stage, virus is always active in the body

mortality rate btw 30%-50%

causes a pustular rash

Smallpox timeline

appeared during the agricultural revolution

origin in cattle, could be even older from rodents in northern Africa and the Middle East

Smallpox transmission

everyone was susceptible

transmitted via inhalation of droplets from coughing, person-to-person contact, contaminated fomites

became endemic in densely populated societies

infected people died or survived and were immune → became mostly a childhood disease

populations became more resistant over time → morbidity and mortality rates went down

Fomites

Nonliving vectors

Viruses

not cellular

not alive

need host to replicate

species/organ specific (Hepatitis: liver, HIV: white blood cell, Influenza: respiratory track)

spends much of life cycle in cells

small → electron microscope necessary to see

cause illness be shutting down function of infected cells

ex: smallpox

Bacteria

cellular

alive

reproduces independently

some species specificity

mostly found in tissues and fluids, not cells

usually larger

more genetically complex

cause illness as more bacteria produce toxins and waste products

Viruses: general characteristics

nucleic (genetic) material: RNA or DNA, but never both

17nm to 300nm or 1/3 the size of a small bacterium

has protein “shell“ = capsid; some have a lipid envelope

Viruses: replication cycle

virus adsorbs to the host cell surface

virus enters the cell and uncoats

Protein synthesis

The new viruses leave by budding or rupturing the cell

Smallpox viruses

one of the largest viruses

double-stranded DNA viruses

mutates very slowly

only infects humans

200 genes

Variolation

used in Far East and Mediterranean

brought to Europe in 1715 by Lady Montague

exposure with small amounts of smallpox (dry scalps)

Edward Jenner

1796

notices that milkmaids never got smallpox during the outbreaks

he infected an 8-year old boy, risky and unethical but it worked

Eradication

Illness no longer present in a population

Conditions for eradication

stage 5 disease

has a vaccine (easy to store and administer)

public cooperation

surveillance systems

disease symptoms should be obvious

Herd immunity

if enough people are vaccinated non-vaccinated people will also be protected

Medical reasons to don’t get vaccines

allergies to components

seizure-prone

immune compromised

too young (under two)

Non-medical reason for no getting vaccines

religious beliefs

denialists

overly skeptical

First line of defense

skin and mucous membranes

non-specific

Second line of defense

Phagocytosis by macrophages

or neutrophils

non-specific

Third line of defense

Immune response

specific

White blood cells (Leukocytes)

lymphocyte

macrophage

neutrophil

eosinophil

basophil

B cell

recognizes and reacts to small free-living microorganisms such as bacteria and the toxins they produce

T cell

recognize and react to body cells that have gone awry, such as cancer cells or cells that have been invaded by viruses

can also respond to larger organisms, such as fungi and parasitic worms

Pathogen

whole disease-causing organism

Antigen

specific molecule or marker on an organism that tells your immune system to fight

Vaccines goal

use part of the pathogen (antigen) to create an immune response for future reference

How do vaccines work?

using chopped up viral parts OR

“live“ attenuated virus OR

mRNA instructions to build an antigen within the target cell

Attenuated

weakened

can still replicate and trigger an immune response, but cannot cause severe disease in a healthy person

Primary antibody response

the antibody concentration rises gradually and peaks about 2 weeks after vaccination

Secondary antibody response

the antibody concentration rises quickly, and the response is more intense. the antibody concentration remains higher for longer

Smallpox only currently stored in

Atlanta, GA (CDC)

Moscow, Russia