Lab 8: Epidemiology

epidemiology

"the study of what is upon us"; the study of the distribution (frequencies or patterns) and determinants (causes or risk factors) of disease (pathogens or accidents/natural disasters) in human populations (neighborhood, school, country)

epidemiology applied to animals

veterinary epidemiology or epidemizoology

infectious disease

disorders caused by microorganisms (bacteria, viruses, and fungi)

how can infectious disease spread 

communicably (person to person, flu/covid), vector (intermediary organism such as flea spreading bubonic plague), contaminated food or water (E.coli contamination) 

what can epidemiology also be applied to

chronic diseases such as heart disease and cancers or natural disasters that can be natural or manmade

disaster epidemiology

explores long and short terms health effects of disasters and predicts the consequences of future disasters

epidemic

occurrence of disease cases in excess of normal expectancy within a certain area (ie whooping cough in US 2010/2013)

pandemic

when the diseases spreads globally to one or more continents (flu/hiv)

pandemic definition

disagreement over definition, refers to distribution, says nothing about virulence or severity of diseases

WHO

World Health Organization adds “unconfined global spread” and “large scale severe diseases or deaths) to definition of pandemic, ie, COVID 

endemic

disease prevention in population at consistent levels, ie chicken pox in US

index case

first case of infection in outbreak

common source epidemics 

contaminated food, water, inanimate objects, cause for epidemics to occur rapidly but subside quickly, many new cases after initial case, but then number of cases drops when source is removed, ie salmonella

host to host epidemics

direct contacts with individual or through vectors, occur slowly and subside slowly, ie COVID 19

herd immunity 

when a certain portion of a population is vaccinated or immune to an infectious agent, an outbreak is unlikely and the few who are still susceptible in the community (children’s less than 1 years old in measles, mumps, and rubella and immunocompromised people) are somewhat protected 

measles

highly contagious (nose and throat mucus), lives up to 2 hours in air or surfaces, and 90% of people unvaccinated people exposed can become infected 

common systems of measles

high fever, runny nose, cough, red and watery eyes, rash

common complications of measles 

diarrhea, ear infections 

severe complications of measles

pneumonia, encephalitis

measles in the US

in 1950s there were 3-4 million infections with 400-500 deaths with all children infected by the age of 15, then in 1963 the first vaccine was licensed, in 1978 the CDC set 1982 as goal for elimination, and in 2000 measles were declared eliminated in the US

disease elimination 

the absence of continuous diseases transmission for >12 months (no longer endemic) in the presence of a surveillance system that has been performing well 

disease eradication

there are no more cases of a particular disease occurring naturally worldwide (smallpox)

overview of measles trends in US in past 40 years 

in 70s federal government expanded financial support for vaccine programs (including measles) but funding weened in 80s and many low income people could not afford to vaccinate their children so between 1989-91' there were over 55000 measles cases in US which caused congress to create vaccine for children program in 1993 to help fund immunization for low income household

first state to require measles booster

New York, increased vaccine effect from 93-97%

what led to elimination of measles in US

strong immunization programs in the year 2000

measles 2019 and 2025

we haven’t had many cases since 1992, before elimination, as of October 1, 2025 we have had 1618 measles cases in US

2019 measles outbreak 

continuous disease transmission that led us to almost lose elimination status 

2020 measles 

low measles because quarantine caused people to stay home and caused under reported cases of measles and covid measures slowed down spread of other infectious diseases; infants missed their measles vaccine this year and experts worried there would be influx of measles in future

why is measles high in 2025

vaccine hesitancy caused by Andrew Wakefield incorrectly linking vaccines to autism

what state wants to ban vaccine mandates for children in school 

florida but this is bad because to develop herd immunity 95% of the population needs to have vaccine and current estimate for % of people in florida vaccine is 88%

eradication of small pox 

vaccine was originally developed in 1800s and there was decline in cases and in 1967 WHO declared their intensified small pox eradication program and in 1980 small pox was eradicated, live samples of small pox being stored by CDC in atlanta and a lab in russia both being monitered by WHO

vector borne diseases

have a pathogen, vector, and host

pathogen

agent that causes disease such as bacteria, viruses, protists, nematodes, and fungi

vector 

organism that spreads a pathogen such as mosquitoes, ticks, and fleas 

host

organism that harbors a pathogen and is typically required for a pathogen to complete its life cycle, can be humans, rats and birds

Malaria

protozoan plasmodium spp (malaria ancient disease) is the pathogen, mosquitoes are the vector, and people are the host, in almost half of the worlds population is at risk for contracting the disease, not an endemic in US but does have mosquitoes capable of transmitting the pathogen 

West Nile virus

West Nile virus is the pathogen, mosquitoes are the vector, and birds are the host, first isolated in 1937 in Uganda and was found in north america in 1999 and since has become the most prevalent mosquito born disease in US, American birds are not immune because its from another continent and american birds have not developed any defenses against it but some species are more susceptible such as crows and jays

b. burgdorferi 

Lyme disease is the pathogens, black legged ticks are the vectors, and white footed rats are the hosts, deers are not good at harboring the diseases, originally misdiagnosed and thought to be juvenile arthritis 

West Nile virus cycle 

mosquito feed off infected bird and picks up virus then proceeds to feed off another bird which inject their saliva into the host and facilitates the transfer of the virus, humans and horses are incidental hosts because they can become infected with virus but mosquitoes cannot pick of the virus from them so the west typically likes to stay in birds and mosquitoes

pathogen where humans are the main host 

dengue and zika virus 

the plague

has not been eradicated, pathogen is bacteria yerisina pestis, vector are oriental rat fleas, and hosts are black rats

how is the plague spread 

when the flea pick up bacteria from infected host the bacteria multiply in the throat of the flea which prevents any food from reaching the fleas gut causing the flea to starve and go into feeding frenzy and the flea will jump host to host trying to feed and by doing so can potentially affect several different organisms

bubonic plague

most common, infects lymph nodes, bacteria multiply in lymph nodes which causes nodes to become swollen and painful resulting in lumps called bubos; 50% fatality rate when left untreated and spread through bite of infected flea

septicemic plague 

infects blood, causes tissue death resulting in blackened skin on the nose, toes and fingers; 100% fatal if left untreated and is spread from bite of flea or can develop from untreated case of bubonic plague

pneumonic plague

infects lungs, most dangerous form of plague because can spread person to person through infectious droplets from coughing; can develop form untreated bubonic or septicemic plague and near 100% fatal if untreated

when is the body and mind balanced in old medicine

when humors are balanced, sickeness caused by humans being out of balance or by miasma (bad air) which believed to lead to imbalance of humors

humors in old medicine

Hypocretes theorized that there were four humor that when in balance resulted in healthy body and mind; yellow bile, black bile. phlegm, and blood

what was believed to cause sickness in old medicine 

miasma, foul air 

how long were beliefs of old medicine accepted

until the mid 19th century

the plague doctor

in high demand during plague pandemic and usually underqualified people did the job; treated victims, disposed of bodies, and reported deaths

blood letting 

method used by plague doctors to release blood and restore balance to humors; used leeches or other methods

what kind of costume did the plague doctor wear

waxed leather garments covering the entire body, a cane to indirectly contact patient, and a bird shaped mask filled with herbs to protect from miasma (17th century)

what did the Black Death create 

the middle class, during the plague millions of serf or the working poor were killed which resulted in a shortage of and higher demand of workers and the poor were able to negotiate higher pay and raises in social status which eventually led to the end of the feudal system

the plague in present day US

1-17 cases a year, primarily in rural west

plague as category A disease 

it can cause high mortality, it is communicable, can cause public panic and requires special action for public health preparedness

coronaviruses

have large family of viruses, only seven coronaviruses are known to cause disease in humans four of which are mild and the other three are SARS, MERS and COVID-19

zoonotic 

can be transmitted between animals and people 

what can coronoviruses cause

disease with mild to severe upper respiratory tract illnesses, and common colds like SARS, MERS, and Covid 19

SARS (2002-2004)

occurred in china from the masked palm civet (harvested for meat) to human and caused over 8000 cases and 774 deaths, disappeared due to isolation and quarantine

MERS (2012-present) 

occurs in Saudi Arabia from camels (handling them) to humans and results in over 2,500 cases and 866 deaths, higher mortality than others but not contagious 

COVID 19

occurred in china, pneumonia of unknown cause, started in bats then to intermediary pangolins  or maybe raccoon dogs to humans, and caused 7.1 million deaths worldwide

pangolins 

armadillo like animal that is used in traditional chinese medicine; currently endangered and hunting them is illegal

phases of vaccine development

exploratory stage, preclinical stage, clinical develop with 3 phases, regulatory review and approval, manufacturing, and quality control

US protocol vaccine development

first is exploratory stage where basic lab research is conducted then pre-clinical stage where researchers typically perform animal testing, here they access safety and ability to perform an immune response then in order to move into clinical trials researchers must submit application for approval from the FDA then approval moves into clinal trials

clinical development phase 1 

phase I is where small number of healthy volunteers 20-100 receive the vaccine under carefully monitered conditions these trials help to determine dose levels and side effects

clinical development phase II 

involves large group of healthy volunteers several hundred people and in this stage looking to identify common side effect and check for signs of effective immune response

clinical development phase III 

involves thousands of volunteers representing diverse populations; in this phase double blind placebo studies are conducted and researchers are looking at safety and size effects, after phase 3 is completed researchers send in an application to the FDA for vaccine approval then they move onto manufacturing and quality control

how long does the vaccine process take 

normally take 10-15 years but took about 1 year to produce COVID vaccine because researchers took short cuts that did not need to sacrifice safety

COVID vaccine development sped up 

development sped up because used research from SARS and MERS research to sped up exploratory and pre-clinical stages and were jumping into human clinical trials before completing animal studies, clinical trials sped up because some studies combines the phase I and phase II trial or moved onto to phase II before phase I finished or had phase I and II run concurrently, approval sped up because, vaccine approvals are usually long but FDA developed emergency use authorization (EUA) to facilitate the avaliablity and use of products during emergency; full FDA approval typically more data needed than to obtained EUA ex: Pfizer vaccine fully approved while moderna and J&J vaccine not as used and not have full approval, vaccine manufacturing sped up because vaccine are being produced before clinical trials complete; manufacturing typically doesn't happen until after approval because of money cost

current mRNA vaccines in the US 

Pfizer BioNTech, moderna

protein based vaccines in the US

novavax

viral vectors in the US

Johnson and johnson’ janssen (no longer available in US)

what does vaccine efficacy do over time 

declines 

what do viral mutations do

make vaccines less effective

what do new vaccines address

new variants

vaccines updated

vaccines need to be updated because vaccine efficacy declines over time as viral mutations make vaccines less effective; new vaccines can address new variants ex: booster for omicron strain of COVID