Highlights from World Disease Chapters 11, 12, and 13

public health

concerned with health of the public (ex: populations)

Epidemiology

a branch of medical science that discovers the source, cause and control of infectious disease and other health problems in populations

epidemiology

core science of public health

Epidemiologists

challenged to determine why an outbreak of disease occurs at a particular time and/or particular place

epi

upon

demos

people

logos

study

results of epidemiological studies

identify risk factors for disease and targets for preventive healthcare (high BP is a risk factors for neurodegenerative and cardiovascular disease)

Disease pattern

the occurrence of disease- related events by time, place and personal characteristics

Disease incidence

the number and rate of disease in the population

pattern by time

seasonal occurrence, annual occurrence, daily, weekly or even hourly occurrence during an epidemic

pattern by place

includes geographic variation, urban-rural differences and locations of worksites or schools, densely populated and congregate settings with cramped housing units

patterns by personal

characteristics including demographic factors like preexisting conditions, age, race, sex, marital status, socioeconomic status as well as behaviors and environmental exposures

The two fundamental measures of disease occurrence

prevalence and incidence

Prevalence

measures the proportion of persons in a population who have a particular disease at a particular time

COVID19 prevalence rate in US 2023 (population 328M)

103.8/328= 31.6%

COVID19 prevalence rate in US 2022 (population 328M)

80.2/328= 24%

COVID19 prevalence rate in US 2021 (population 328M)

46.5/328= 14%

Incidence proportion

the proportion of an initially disease-free population that develops disease or dies during a specified (usually limited) period of time

Variations of incidence

attack rate, risk, probability of getting disease

incidence

new cases that occurred during a given time period/population

incidence conveys:

information about the risk of contracting the disease

prevalence indicates:

how widespread the disease is

prevalence and incidence tend to go hand and hand with

short lived illness, like the common cold, and diseases that kill those affected swiftly, like rabies

R0

The average number of secondary infections produced when one infected individual is introduced into a host population where everyone is susceptible

(measures the potential for transmission and epidemic outbreak)

R0 is calculated by:

using individual-level contact tracing data obtained at the onset of the epidemic. Once an individual-level contact tracing data obtained at the onset of the epidemic. Once an individual is diagnosed, his/her contacts are traced and tested. R0 is then computed by averaging over the number of secondary cases of many diagnosed individuals

R0 of an infectious disease predicts:

if an emerging infectious disease can spread in a population; what proportion of the population should be immunized through vaccination to eradicate a disease

The higher R0,

the stronger is disease spreading

The R0 for measles in a susceptible population

We expect each new case of measles to produce 15 new secondary cases

John Snow (mid-late 1800s)

the father of epidemiology as we understand it

In the 17th century, deadly cholera epidemics were happening in many countries and continents

Cholera outbreak

1854, 500 deaths in 10 days

Sporadic

refers to a disease that occurs infrequently and irregularly (tetanus, rabies, etc)

Endemic

regularly found at a steady level in a particular location, baseline (common cold, etc)

epidemic

sudden increase in morbidity (illness rate) and mortality (death rate) above the norm expected (plague, etc)

pandemic

epidemic that has spread across continents (1918 influenza, HIV/AIDS)

Epidemics: the types

common source

epidemics involve contact with a single contamination source (contaminated water, John Snow)

propagated epidemics

result from person to person contact (mumps, chicken pox, COVID19)

propagate in the community

an infectious disease must reach and strike many hosts. This is achieved by a chain of events linked into a so-called disease cycle

interferes with the disease

targeting the chain of events linked into a so-called disease cycle

microbe-host interactions

occur at the core of the disease cycle

Reservoir

a side in nature/a habitat in which microbes can survive and possibly multiple

reservoirs

prime targets for preventing, minimizing and eliminating existing and potential epidemics

pathogens where humans are the only known reservoir

smallpox, gonorrhea, measles, polio, etc. those pathogens are easier to eradicate

Active carriers:

individuals who have a microbial disease

healthy carriers

have no symptoms and may unwillingly pass the disease onto others

chronic carriers

continue to harbor the microbe after recovery, this state can continue indefinitely without illness. Treatments may include long term antibiotics

Zoonoses

domestic and wild animals serve as reservoirs for ~150 species of pathogenic microbes that can affect humans and cause zoonotic diseases

eradication of zoonotic disease

requires eradication of their reservoirs- a goal hard to achieve

Primates

animals closely related to humans

nonliving reservoirs

soil, water, food

Cycle of microbial disease

1.Pathogen

2. Reservoir (source) of pathogen

3. Transmissible to susceptible host

4.Portal of entry into susceptible host

5.Portal of exit out of susceptible host

Transmission

the mechanism by which an infectious agent is spread into a susceptible person

Direct transmission

microbes are transferred from portals of exit to portals of entry

Horizontal: person-to-person, animal-to-person

contact, touch (blood, facilitated by mucus membranes, kissing, sneezing, sex, etc), animal bites (rabies virus directly transmitted from saliva onto skin cut)

Vertical: mother to child

transplacental (from mothers to offspring via placenta- AIDS, measles, chickenpox), in breast milk, via birth canals (STD)

indirect transmission

microbes pass from reservoir (or source) to an intermediate agen and then to a host

vehichleborne

via food, water, biological products (organs, blood/products transfusion) and fomites (inanimate objects)

airborne

aerosols of water or dust particles (less than 4 um) in the air; unlike droplets (10um or larger) aerosols remain airborne for extended periods

vectorborne

phylum arthropoda (ticks, flies, mosquitoes, lice and fleas), which also includes class insects (chagas' kissing bug)

Mechanical vectors

perform passive transmission on feet, insect body, when microbes do not invade, multiply or develop in the vector

Biological vectors:

represent a necessary part of the life cycle of a pathogen, transmission is an active process

Food intoxication (food poisoning):

ingestion of bacterial toxins (with or without the microbe being present)

Foodborne infection (disease):

bacteria multiply in the intestinal tract and secrete toxins (enterotoxins) and may invade cells of the intestinal tract

Clostridium botulinum:

a g+ obligate anaerobe bacillus, spores in soil

Botulism

caused by the botulinum neurotoxin

botulinim toxin

performed in improperly canned veggies, sausage, cured pork and ham, smoked fish and canned salmon

therapy

antitoxin and mechanical ventilation

botox

release wrinkles, reduce muscle overactivity

lethal dose of botulinum toxin for a human

typical grain of sands weight, 1kg would be enough to kill the entire population

Staphylococcal food poisoning is caused by toxins from

staphylococcus aureus, a g+ coccus, commensal opportunistic for humans. Non-spore forming, not motile

S. aureus

Found in human skin, in the node, armpit, groin and other areas with estimated prevalence of 20-30% for persistent and 60% for intermittent colonizations

Foods with staphylococcal toxins:

meat, poultry, egg and dairy, salads, cream filled pastries & cakes, sandwich fillings

Staphylococcal food poisoning

result from the consumption of sufficient amount of one or more preformed enterotoxins. The toxin, not the bacterium acts in the small intestine and causes inflammation and swelling

Salmonellosis

is caused by several species of g- bacilli in the genus

Salmonellosis in baby foods and peanut butter and unknown source

outbreak in 2007-2008, 400 deaths, 2,088 cases

Salmonella typhi

most deadly of salmonella, secretes typhoid toxin & causes typhoid fever, transmission via fecal matter-contaminated foods or hands

typhoid mary

early 1900s was a healthy asymptomatic carrier of salmonella typhi

cholera intoxixation

caused by the exotoxin secreted by the g- curved rod vibrio cholera, Rehydration must be instituted quickly to avert death

Whooping cough

caused by the g- coccobacillus

Humans and primates are the reservoir, threat to children under age 4

Transmission direct via droplets

Bacilli bind to epithelial cells in upper respiratory tract

symptoms: runny nose, fever and mild cough- followed by weeks of severe coughing (may last for 10 weeks)

Diphtheria

caused by an exotoxin produced by the g+ bacillus

Diphtheria transmission

via droplets and fomites

Kills epithelial cells which accumulate forming a leathery pseudomembrane

Death by suffocation may result

Toxin diffuses into the bloodstream and may cause widespread damage

S. pyogenes

can cause the life-threatening flesh-eating disease, or necrotizing fasciitis

Flesh eating disease

occurs in cuts, bruises. Bacteria secretes flesh-destroying enzymes and toxins cause tissue necrosis at a speed 3 cm/h

Necrotizing fasciitis are (650 to 800 cases annually in the US), non contagious

Treatment: antibiotics, skin grafts, amputations, hyperbaric oxygen therapy

Tuberculosis

An ancient disease, remains the leading cause of infectious death worldwide

About 10M people are infected with an annual death toll of 2M

About 8M new cases develop annually made even worse by multiple drug resistant strains

Plague (black death)

is caused by the g- bacillus, yersinia pestis: one of the most virulent bacteria known

ID is a single bacillus

Multiple virulence factors produces

Multiple transmission mechanisms

Multiple portals of entry

No spores but extremely hardy, infectious after many weeks in soil and other surfaces

first pandemic of the plague

plague of justinian 6th-8th centuries

second pandemic of the plague

black death 14th century

third pandemic of the plague

monder plague 18th-20th century

black death

profound effects on the course of European history, Mass deaths, suffering, lack of understanding caused horror and resulted in massacring of lepers, romani jews, causes great social and economic upheaval between 1350 and 1400

Incidence and mortality rates of plague

Incidence rate in the US 6-7 year, mortality rate is 1/year

Global incidence rates 1,000 to 2,000 cases per year, highest in Africa

Transmission of plague to an uninfected individual can be completed by

Droplet contact

Physical contact

Indirect contact: contaminated surface

Airborne transmission

Fecal-oral transmission

Vector borne transmission: insects or other animals

bubonic plague

Most common form, contracted by an infected rodent or flea bites

Usually contracted by an infected rodent or flea bites

The bacilli infect the lymph nodes of groin, armpits and neck causing inflammation and swelling (buboes)

Untreated, it can spread into the bloodstream (causing septicemic) or into the liver and lungs (causing pneumonic)

pneumonic

Bacilli from lymph can either enter the bloodstream and colonize lungs, causing pneumonic plague which can then be transmitted to others by coughing and through saliva

Approaches 100% fatality without early treatment

Vaccine is protective for only a few months and is only given to persons at high risk

septicemic plague

Results from the spread of bacteria from the lungs to other parts of the body

Acquired by contact of contaminated hands, food or objects withe the mucous membranes of the nose or throat

100% fatal

MRSA bacteria

Staphylococcus aureus is the most virulent of the staph, g+

Methicillin resistant s. Aureus (MRSA) are the leading cause of nosocomial infections in the United States

gastroenteritis

stomach and abdominal pain, diarrhea, vomiting,and abdominal cramps

Hepatitis

Inflammation of the liver, usually caused by a viral infection, that causes fever, loss of appetite, jaundice, fatigue, and altered liver function.

jaundice

yellowing of the skin and the whites of the eyes caused by an accumulation of bile pigment (bilirubin) in the blood

viral hepatitis

A, B,C, D, and E (D and E are not as common in the US)

Indirect vehicleborne

Hepatitis A and E