Lecture 5

Question 1

increases in population density

Answer 1

Industrial Revolution –> demographic transition

Sanitary problems:
- accumulation of sewage, grey water, garbage. Provision of clean water, food, energy
- solutions: management systems = sewers systems, garage management, clean water supply

Public health problems - solutions for the masses:
- hospitals
- public health campaigns (e.g., vaccination)

Question 2

Helping the enemy (pathogens)

Answer 2

The short generational time of most pathogens result in the rapid evolution of new reproductive and transmission strategies

Our strategies to fight them, turns out, can also help them

Hospitals have contributed to a outbreaks of highly virulent strains of E Coli, salmonella, staphylococcus and streptococcus bacteria

Question 3

one the positive side, hospitals contribute to the origins of epidemiology

Answer 3

it was outbreaks of infectious diseases that gave place to epidemiology as one of the main components of the modern health sciences

Question 4

The birth of quantitative epidemiology (and modern medicine) are linked to?

Answer 4

• the understanding that human health and disease patterns follow mathematical laws (William Farr)

In sum, the emergence of medical maths lead to the emergence and establishment of epidemiology as a field

Question 5

Evolutionary epidemiology

Answer 5

“A particle of small-pox matter, so minute as to be borne by the wind, must multiply itself many thousandfold in a person thus inoculated; and so with the contagious matter of scarlet fever. It has recently been ascertained that a minute portion of the mucous discharge from an animal infected with rinderpest, if placed in the blood of a healthy ox, increases so fast that in a short space of time ‘the whole mass of blood, weighing many pounds, is infected, and every small particle of that blood contains enough poison to give, within less than fort-eight hours, the disease to another animal”

Question 6

Epidemiology today

Answer 6

A discipline that studies the causes of disease looking at WHO is affected, WHERE diseases occur, WHEN they occur and the social, environmental and lifestyle correlation of disease occurrence

Question 7

what is disease?

Answer 7

a biomedically measurable lesion, or an anatomical or physiological “irregularity”

Question 8

what is epidemiology?

Answer 8

a discipline that studies the causes of lesions, or anatomical or physiological irregularities looking at WHO is affected, WHERE diseases occur, WHEN they occur and the social, environmental, dietary and lifestyle correlates of disease occurrence

Question 9

disease “traditional biomedical” approach

Answer 9

Dichotomous

• individuals are healthy or sick

Question 10

The limit between health and disease is not always clear

Answer 10

Conventional criteria = Functional impairment

Conventional Critiera: rely on observable symptoms and measurable impairments in function

Functional impairment: describes a decrease in an individual’s ability to perform normal daily activities or functions

• suffering
• statistical deviance
• physical lesion

Often correlate but are not sufficient to diagnosed a disorder

Question 11

illness from the perspective of the individual

Answer 11

Experience of being unwell entails the experience of suffering
The experience of suffering varies across cultures

Main categories:
- somatic experiences
- mental dysfunction
- suffering due to misfortune

• On occasion the carrier of the illness is not the one suffering, as it happens sometimes with some psychiatric conditions
• On occasion illness can be associated with higher reproductive success

Question 12

Antisocial personality disorder (psychopathies)

Answer 12

• deceitful and manipulative
• superficial charm but lack empathy. contemptuous of the feelings, rights, and suffering of others

Question 13

How do psychopaths fare in life?

Answer 13

• 50% go through life undiagnosed and undetected
• Those scoring higher in Psychopathic Checklist - Revised (PCL-R) tend to be rated higher in physical attractiveness and have higher number of children
• In addition, psychopathic offenders score lower than non-psychopathic offenders on fluctuating asymmetry, a reliable measure of past developmental perturbations

Now that this type of behaviour could be “biologically” adaptive does not mean we have to accept it or tolerate it - the natural fallacy

Some cognitive mechanisms are hypothesised to have evolved because they allow us to detect psychopaths. Furthermore, we have develop legal tools to protect the rest of us from them.

Question 14

Most traditional approachs to health challenges tend to focus on 2 things

Answer 14

1. treatment of immediate symptoms
2. proximate causes (mechanisms)

Question 15

Evolutionary perspective - Why pain, fever, cancer, and negative emotions?

Answer 15

Ultimate: evolutionary origin and function of the reaction

Why pain, fever, cancer, and negative emotions?

Because, despite their obvious costs, they increase the chances of surviving those challenges. Fever creates a poor environment for bacteria to survive and reproduce. Pain helps avoid injury or further tissue damage. Cell duplication allows tissue healing. Negative emotions help note negative social situations and can promote taking action to change their course.

Question 16

health status from an evolutionary perspective

Answer 16

Health status: is multidimensional, and a spectrum, it is not binary

The integrity and function of the body can be affected by various factors, including:
- lesions
- genetic mutations
- malfunction
- environmental challenges (physical or social)

Those changes in health status may result in undesirable, painful or uncomfortable outcomes

To decide if those undesirable outcomes can be avoided and develop strategies to prevent them or reduce their impact is useful to understand their ultimate causes

Question 17

A wholistic perspective should include:

Answer 17

A full explanation. An analysis of both proximate and ultimate explanations

• it would be mistake to focus only one of the two types of causation or to study them independently

Question 18

evolutionary theory and its contribution to epidemiology

Answer 18

to solve undesirable, painful, or uncomfortable outcomes is important to investigate and differentiate between “true malfunction” and the “uncomfortable secondary effects” (side effects) of adaptations.

Understanding this difference is critical to avoid suppressing natural defences

Question 19

How do we study health and disease at the population level?

Answer 19

Collection of Epidemiological data
- analysis of vital statistics on morbidity (disease) and mortality (death)
- analysis of large-scale population surveys and surveillance (CDC, WHO)

Governments, religious authorities, nurses, doctors, and local health centres collect this data

Question 20

Two main “quantifiable” outcomes

Answer 20

• measures of morbidity
• measures of mortality

Question 21

Measures of morbidity

Answer 21

incidence and prevalence of a disease (population and time-specific measures)

Question 22

what is incidence?

Answer 22

number of NEW cases during a particular time interval

IR = # of new cases of a disease during a specific time period / # of people at risk for developing the disease during that time period

Example: post-partum psychosis is estimated to be in 1 in 500 to 1000 new mothers. The key is in the denominator

Question 23

what is prevalence?

Answer 23

the total number of ALL (old and new) cases of a disease in a given population during a particular time interval

Prevalence rate = # of ALL cases of a disease present in a pop during a specific time period regardless of when they contracted the disease / # of people at risk for the disease

Question 24

incidence VS prevalence

Answer 24

the difference between prevalence and incidence is largest when evaluating chronic conditions (e.g.: COVID vs diabetes)

Question 25

Epidemiological Study Designs

Answer 25

Four most commonly used:
1. Randomised trials
2. cohort studies
3. case-control studies
4. cross-sectional studies

Question 26

Randomised trials

Answer 26

• study population
• divide into two groups (treatment 1 and treatment 2)
• divided both treatment groups into two more groups each (affected and no change)

dividing into two treatment groups is random allocation

Question 27

Cohort studies

Answer 27

following the same individuals through time

• select study population
• divided into two groups: exposed and unexposed
• exposed divides into: develop health condition and do not develop health condition
• unexposed divides into: develop health condition and do not develop health condition

Question 28

Example of prospective cohort study: effects of parental divorce on prevalence of chronic stress symptoms

Answer 28

• Babies born in the US in 2005
• divide into two groups: parents divorce during childhood AND parents do not divorce during childhood
• divide two groups again into: develop symptoms and no symptoms

A research study that follows over time groups of individuals who are alike in many ways but differ by a certain characteristic

Question 29

Example of retrospective cohort study: effects of baby feeding experience on the development of obesity in adolescence

Answer 29

• people born between 1950 and 1980
• divide into two groups: breast fed AND bottle fed
• divide these two groups into: develop obesity or no obesity

A retrospective cohort study looks back in time. It uses preexisting secondary research data to examine the relationship between an exposure and an outcome. Data is collected after the outcome you’re studying has already occurred

Question 30

Naturalistic longitudinal studies focus on normative variation - another form of cohort study

Answer 30

• select study population
• divide into 4 groups: chronic natural exposures - natural variability
• three groups: within and between variability at age 1, age 2, and age 3.

Question 31

Case-control study

Answer 31

• select study population
• divide into: cases (with disease) AND control (disease free): called disease status
• divide these new groups into: exposed AND unexposed

Example: effect of # of menstrual cycles during reproductive years because of contraceptive use and development of breast cancer (BC)
- study pop: post-menopausal women
- divide into cases (with BC) AND control (no BC): disease status
- divide the cases and control into: high # of menstrual cycles and low # of menstrual cycles

Question 32

cross-sectional studies: snapshot approach

Answer 32

• select study pop
• divide into: age group 1-4 exposed, and age group 1-4 unexposed

Question 33

what is infectious disease?

Answer 33

communicable disease
- Caused by specific agents or their toxic products which are transmitted from one person to another, directly or indirectly

Question 34

what are noninfectious diseases?

Answer 34

Not transmitted from person to person (e.g., cancer, genetic diseases, allergies, nutritional diseases)

Question 35

what is endemic?

Answer 35

presence of a certain disease at a relatively constant level at all times (e.g., malaria is endemic in Africa, Changas disease in South America)

Question 36

what is epidemic?

Answer 36

When the number of cases in a fairly localised area suddenly increase above the expected level for a short time (e.g., avian flu in Asia since early 2000s or mumps in Ireland 2018-19)

Question 37

what is a pandemic?

Answer 37

when number of cases increased worldwide (e.g., AIDS, COVID-19)

Question 38

key traits of infectious diseases

Answer 38

• transmissibility
• virulence

Question 39

transmissibility

Answer 39

• Rate at which an infection spreads
• Usually depends on the density of hosts and the virulent of parasite population

Question 40

Virulence

Answer 40

• The relative effect of a pathogen on its host’s health
• The ability of any agent of infection to produce disease. A measure of the severity of the disease a pathogen is capable of causing

Question 41

Types of transmission

Answer 41

Directly transmitted diseases: transmission via direct contact between hosts
- Horizontal transmission: any form of transmission that is NOT maternal and through direct contact between individuals (touching, sexual intercourse, sneezing, sharing salvia, etc)
- Vertical transmission: maternal transmission from mother to offspring (giving baby HIV through breast feeding or pregnancy)

Indirectly transmitted diseases: vehicle-borne and vector-borne

Question 42

Examples of direct transmission of diseases

Answer 42

Respiratory: flu, chicken pox, measles
Sexual: HIV, genital herpes, syphilis, gonorrhoea
Direct physical contact: diphtheria, herpes

Question 43

Examples of indirect transmission

Answer 43

Vechile-borne
- water-borne: cholera, hepatitis, typhoid fever
- food-borne: botulism, salmonellosis, tapeworm
- soil-borne: hookworm, tetanus
- needle-sharing: hepatitis B, HIV

Vector-borne
- mosquitoes: malaria, dengue fever, yellow fever
- ticks: Lyme disease
- fleas: bubonic plague
- lice: louse-borne typhus fever
- flies: leishmaniasis, trypanosomiasis

Question 44

Virulence, evolution and ecology in the context of pathogens

Answer 44

Pathogens are pathogens because of their cost to the host

If there were no cost to the host, they would not be consider a pathogen or parasite but a symbiont (Symbionts are organisms that live in close association with the host and typically provide some benefit to the host, such as aiding in digestion or providing protection)

The evolution of pathogens: Pathogens that effectively exploit host resources and reproduce without killing their hosts too quickly may have a selective advantage

The ecological environment: Factors such as population density, host behavior, and environmental conditions can influence how pathogens spread and how virulent they become.

The costs imposed on hosts by pathogens can be viewed through a cost-benefit lens. Pathogens must balance the benefits of exploiting host resources with the potential costs of harming the host. If the cost becomes too high, it may lead to host death, which can ultimately jeopardize the pathogen’s own survival and transmission.

Question 45

Advantages of an evolutionary perspective

Answer 45

• ultimate causes of patterns of virulence and transmission
• focus on LH of parasites and hosts

Question 46

An evolutionary perspective

Answer 46

• virulence is the product of complex interactions among evolutionary, ecological and epidemiological processes
• evolutionary and ecological changes affecting population dynamics of disease, such as spatial structuring, within-host dynamics, polymorphism in host resistance, host longevity and population size, can impose selective pressures on virulence

Question 47

LH and fitness of parasites

Answer 47

• parasites have evolved life-history tradeoffs that maximise their fitness (including reproduction and transmission strategies)
• natural selection leads to the optimisation of virulence strategies, which should vary according to the environment
• humans and parasites Life History strategies have co-evolved through generations with the parasites having the advantage of their shorter life spans
• we can study which factors alter the parasites transmission and virulence patterns
• if we can control the environment we can control their transmission and virulence strategies

Question 48

progression of infection and symptoms

Answer 48

• Onset of infection
• latent period
• incubation period
• becomes infectious
• infectious period - beings to show symptoms
• symptomatic illness - no longer able to transmit infection
• symptoms disappear

Question 49

LH factors affecting virulence

Answer 49

• parasites face life-history tradeoffs between host survival and fecundity, given that greater host exploitation is likely to increase transmission rate but also to reduce host survival and, hence, the time available for transmission
• simultaneously, hosts face life-history tradeoffs between the cost of resistance and the risk of infection

Question 50

modes of transmission and virulence

Answer 50

Vertical (mother-child) transmission: reduce virulence relative to horizontal transmission
- tends to depend on host survival and reproduction

• some parasites may be able to alter their hosts behaviour

Question 51

transmission patterns and virulence

Answer 51

in order to be transmitted horizontally (individual to individual) the parasites have to get their hosts to interact with as many other potential hosts as possible

Trade-offs: speed, virulence, and transmission opportunities

• fast transmission may lead to increase virulence

Question 52

Parasites with a direct and indirect life cycle

Answer 52

Parasites with a direct life cycle requires only one definitive host to complete its life cycle. Parasite may induce changes in the host’s behavior that promote greater social contact with other individuals of the same species (aggression and risky behaviour). Example: Rabies

Pathogens with an indirect life cycle require more than one host species to complete their life cycle. Pathogens can alter the behavior of their prey-hosts in ways that make them more susceptible to predation (risky behaviour and altered sensory perception.

Question 53

sex, transmission patterns and virulence

Answer 53

For STDS the sexual behaviour of the host is critical to a pathogen

• Organisms tend to avoid mating with sick individuals, usually identified by their aspect and behaviour. Yet the production of those identifiable traits can be avoided by some parasites

Question 54

In summary

Answer 54

in order to develop preventative strategies and treatments is critically important to understand the parasites life cycle and the strategies it uses to reach its hosts (genetic, physiological or behavioural)