Week 6 (disease control and prevention) Flashcards
2 diseases that have ever been fully eradicated
Smallpox and Rinderpest
Smallpox
virus spread human to human (R0 = 5-7), typically through face-to-face contact or items contaminated with fluid from scabs; 10-14 day incubation period
Smallpox symptoms
-Starts with nonspecific symptoms (like common cold), but within a few days a widespread rash would develop
-After a few weeks, pustules would form over body (including inside mouth), eventually crusting over and falling off (scars would remain for life, could also cause blindness)
-Mortality rate ~30% for more virulent disease strain, no effective treatment
Smallpox historic distribution
-Historically endemic in Africa, Europe, and Asia, brought to the Americas by colonists (with devastating effects)
-Estimated to have killed hundreds of millions of people (at least) in course of human history
Adaptive immunity
-longer lag of response speed
-high specificity to antigens
-higher response potency
-rapid amplified response
-B and T lymphocytes, antibodies, and activated T cells
Innate immunity
-immediate response speed
-low specificity to antigen
-lower response potency
-no memory and same response
-epithelial barriers, macrophages, dendritic cells, mast cells, granulocytes
Vaccine
-takes advantage of the immune system’s ability to recognize and remember pathogens (adaptive immunity)
-Introduce a safe version of the pathogen (or piece of the pathogen) to teach the immune system how to recognize it in the future
-ensures that the future exposure to the pathogen results in a rapid and effective immune response, protects from developing the full-blown period
Contemporary vaccine history
-first contemporary vaccine attributed to Edward Jenner in 1796 for smallpox, observed milkmaids less likely to get smallpox and hypothesized due to exposed to cowpox
-Injected jame Phipps with cowpox pus, waited for him to become infected, then injected him with smallpox, no disease
Attenuation
make inactive, safe version of the virus
Component vaccine
use part of the pathogen
Why vaccines take so long to develop
-Most vaccines fail to work at all
-less than 10% are ever approved for public use
-Even if it does work, must ensure it is safe and effective
-Must avoid harmful side effects
-Once developed, must still spend time and money to produce and distribute
Herd immunity
-enough people recover from the disease and develop immunity or are vaccinated (which confers immunity) to prevent further infection speed
-Protects the most vulnerable of society (very old, very young, immunocompromised)
Vaccine limitations
-Must maintain high vaccination rates to ensure herd immunity
-hard to develop vaccines for:
–Diseases that don’t affect high income countries or many people
–Pathogens that mutate rapidly
–Large, complex pathogens (multicellular parasites)
–Pathogens with multiple life stages and hosts (malaria)
–Novel or poorly studied pathogens
What facilitated smallpox eradication
-The virus is human-specific, no non-human reservoirs
-Disease symptoms clearly visible and recognizable (no need for lab test)
-Effective vaccine available (heat stable and offered protection for 5-10 years)
-Other regions had successfully eliminated virus, demonstrating that it was possible
-There was political will and financial backing to support eradication efforts
WHO eradication campaign strategy
-Involved high levels of international cooperation: hundreds of individuals from WHO leadership, young health workers
-Vaccinate at least 80% of the population (in hopes of achieving herd immunity)
-Establish effective surveillance network to quickly identify novel smallpox cases and contain disease spread (ring vaccination)
-Regularly distribute surveillance reports, tracking progress and novel containment strategies
When was smallpox eradicated
1980
Jacobsen v Massachusetts (1905)
Court ruled that Massachusetts acted within its power to enforce laws to protect public health and mandate vaccines
Control
interventions to restrict infection transmissions at a group level (locally dependent)
Eradication
-complete absence of an infection, globally
-Noninfectious diseases cannot be eradicated
Elimination
the absence of disease transmission in a specific area
Extinction
pathogen no longer exists in any form, but practically impossible to demonstrate
Consideration in control efforts
-Environment: how well can pathogens survive outside the human host in a particular area and remain infective
-Reservoirs: can the pathogen “hide” in a nonhuman host and later infect humans?
-Transmission: is the pathogen airborne? Is it spread through body fluids? Can it survive on surfaces? How contagious is it
-Host resistance: once infected/immunized, do people develop long-lasting immunity to reinfection
Components of control and eradication efforts
-Surveillance: effective system in place to monitor disease patterns and quickly identify novel cases
-Interventions: prevent disease transmission (cost and social acceptance must be considered)
-Certification: independent, trusted groups must certify disease absence
Types of disease interventions
testing, contact tracing, quarantine
