BigBrother Public health textbook part 1 :: 2nd edition

COMMUNITY

For 2nd year

1 Concept of Health

Outlines

 Understand the definition of health.

 Study the different dimensions of health.

 Know the spectrum of health.

Health Definition

Health Dimensions

There are five dimensions of health: physical, mental, emotional, spiritual, and social.

WHO definition of health: “a state of complete physical, mental and social well-being and not merely the absence of disease or infirmity” Holistic

These five 5 dimensions of health provide a full picture of health as a change in any dimension affects the others.

Physical Mental

The physical dimension of health refers to the bodily aspect of health. It refers to the more traditional definitions of health as the absence of disease and injury.

It ranges in quality along a continuum where a combination of diseases such as cancer, diabetes, cardiovascular disease or hypertension are at one end and a person who is at optimum physical condition (think health not fitness) is at the other.

Mental health refers to the cognitive aspect of health. It’s often linked to or includes emotional health, to distinguish the two. Mental health is more the functioning of the brain, while emotional health refers to the person’s mood often connected to their hormones. Then it includes many mental health issues such as Alzheimer’s and dementia. It refers to the person’s ability to use their brain and think. This may be to solve problems or to recall information, but the focus is on the cognitive aspect of the person.

It can affect the other dimensions as a decline in physical health can result in a decline in other forms of health. E.g. a person who suddenly gets the flu is often isolated socially as to not infect others, struggles to focus in order to study or learn anything new, and may feel sad as a result of their isolation.

An increase in MH can come as a result of increased physical activity, and good MH can then lead to an increase in selfesteem as mental performance improves. Greater self-esteem then leads to more confidence in social situations and can lead one to ask the larger questions about life leading to increased spiritual health.

Emotional

Emotional health is about the person’s mood or general emotional state. It is our ability to recognize and express feelings adequately. It relates to your self-esteem as well as your ability control your emotions to maintain a realistic perspective on situations.

Spiritual

Spiritual health relates to our sense of overall purpose in life. People often find this purpose from a belief or faith system, while others create their own purpose.

The relationship between emotional and mental health is clear and as such some illnesses relate to both, such as: depression and anxiety.

A person who has purpose to life is said to be healthier than those who don’t see a purpose to life.

Spiritual health will very easily affect emotional and mental health as having a purpose in life can help you to apply yourself to achieving goals.

Emotional health affects the other dimensions of health as a person with a good self-esteem is more confident in social settings, makes friends quickly and often performs better in physical activity.

Having a purpose to live can also help to maintain a proper perspective on life and overcome adversity. Often people who are spiritual meet together regularly around their spiritual purpose, which helps to improve their social health.

The social dimension of health refers to our ability to make and maintain meaningful relationships with others. Good social health includes not only having relationships but behaving appropriately within them and maintaining socially acceptable standards.

Social health affects the other dimensions of health in many ways. A bad social life can lead a person to question their purpose in life or feel isolated and unwanted. Such feelings can demotivate people from physical activity and lead them towards depression.

The basic social unit of relationship is the family, and these relationships impact a person's life the most. Other key relationships are close friends, social networks, teachers, and youth leaders.

Spectrum of Health

 Health and disease lie along a continuum & there is no single cut of point. The lowest point on health-disease spectrum is death and the highest composes the WHO definition of positive health.

 Health fluctuates within range of optimal wellbeing to various level of dysfunction. The transition from optimal health to illness is often gradual & where one state ends other states begins.

A figure showing the spectrum of Health

 The spectrum of health emphasizes that individual health state is not static, it's a dynamic phenomenon & a process of continuous change.

Well-being Concept

Well-being is a positive outcome that is meaningful for people and for many sectors of society, because it tells us that people perceive that their lives are going well. Good living conditions (e.g., housing, employment) are fundamental to well-being. Tracking these conditions is important for public policy. However, many indicators that measure living conditions fail to measure what people think and feel about their lives, such as the quality of their relationships, their positive emotions and resilience, the realization of their potential, or their overall satisfaction with life i.e., their “well-being”

Well-being generally includes global judgments of life satisfaction and feelings ranging from depression to joy

There is no consensus around a single definition of well-being, but there is general agreement that at minimum, well-being includes the presence of positive emotions and moods (e.g., contentment, happiness), the absence of negative emotions (e.g., depression, anxiety), satisfaction with life, fulfillment and positive functioning. In simple terms, well-being can be described as judging life positively and feeling good. For public health purposes, physical well-being (e.g., feeling very healthy and full of energy) is also viewed as critical to overall well-being.

Different aspects of well-being that include the following:

Physical well-being

Economic well-being

Social well-being

Emotional well-being

Psychological well-being

Development & Activity

Engaging activities and work

• Engaging activities and work.

Domain specific satisfaction

Life satisfaction

• Engaging activities and work.

Concept of Quality life

Quality of life (QOL) is defined by the World Health Organization as ‘individuals' perception of their position in life in the context of the culture and value systems in which they live, and in relation to their goals, expectations, standards and concerns.

Determinants of health

[1] The social and economic environment. [2] The physical environment.

[3] The person’s individual characteristics and behaviors.

The context of people’s lives determines their health, and so blaming individuals for having poor health or crediting them for good health is inappropriate. Individuals are unlikely to be able to directly control many of the determinants of health. These determinants or things that make people healthy or not include the above factors, and many others:

Income and social status: higher income and social status are linked to better health. The greater the gap between the richest and poorest people, the greater the differences in health.

Education: low education levels are linked with poor health, more stress & lower selfconfidence.

Culture: customs and traditions, and the beliefs of the family and community all affect health.

Health services: access and use of services that prevent and treat disease influences health

Gender: men and women suffer from different types of diseases at different ages.

Social support

networks: greater support from families, friends and communities is linked to better health.

Genetics: inheritance plays a part in determining lifespan, healthiness and the likelihood of developing certain illnesses.

Physical environment: safe water and clean air, healthy workplaces, safe houses, communities and roads all contribute to good health.

Employment and working conditions: people in employment are healthier, particularly those who have more control over their working conditions.

Employment and working conditions: people in employment are healthier, particularly those who have more control over their working conditions.

Personal behavior and coping skills: balanced eating, keeping active, smoking, drinking, and how we deal with life’s stresses and challenges all affect health.

Conceptofdisease 2

outlines:

Definitionofdisease

Theoriesofdiseasecausation

Stagesofdisease

Icebergphenomenon

Definitionofdisease

-Diseaseisusuallyconsideredtheoppositeofhealth,adeviationfromthe normalfunction.

AccordingtoWebster→“Aconditioninwhichbodyhealthisimpaired,a departurefromastateofhealth,andalterationofthehumanbody interruptingtheperformanceofvitalfunctions”.

Accordingtoanecologicalview→“Amaladjustmentofthehuman organismtotheenvironment”.

Thekeytofindingremediesforthecureofdiseases,necessitatesan understandingofthecauseofthedisease.Butourperceptionofdisease causationhasundergoneavastalterationwiththeever-changingadvancement ofscienceanditscontributiontohealth.

Theoriesofdisease causation

-Ourexplanationofdiseasecausationisbasedonsomanytheories:

Theoriesofthepre-modernera.

Germtheoryofdisease.(discussed)

Biomedicalmodel.

Epidemiologicaltriad.(discussed)

Dever’sepidemiologicalmodel.

Theoryofmulti-factorialcausation.(discussed)

Webofcausation.

Wheelofdiseasecausation.

Othertheories.

Germtheoryofdisease

-ThedemonstrationofbacterialpresenceintheairbyLouisPasteurandAnthrax iscausedbybacteriabytheturnofthe18thcenturycausedadrasticshiftinthe understandingofdiseasecausation.

-Thus,focusfromempiricalcausessuchasbadairandwrathofGodwasaltered toscientificallyplausiblecauseslikethepresenceofspecificmicroorganisms.

-Thegermtheoryimpliesthecausaleffectisonetoone,i.e.,asingle microorganismistheculpritbehindaspecificdisease.e.g.,Mycobacterium tuberculosisbacteriaandtheoccurrenceoftuberculosis.

-Butthatseldomisthecase,asmanydiseasescannotbeexplainedbythisoneto-onecausalrelationbutinreality,aninteractionofvariousothercontributory factors.

Multi-factorialcausation

-Pettenkoferproposedthatdiseaseisaresultofmanyfactorsasopposedto germtheorywheretheideaofasinglecausewasused.

-Improvementsinpublichealthandmedicinebroughtaboutadeclinein communicablediseases.Butothernon-communicableailmentswereonarise whichcouldnotbeexplainedbasedonthegermtheoryofdisease.

-Hencesinglecausewasdeemedtobeoversimplifyingetiologyofadisease wherefactorssuchassocial,cultural,genetics,andeconomicfactorswere overlooked.

-Alsohavingmultiplecausesforadiseasemeantnumerousmethodsof preventingthatdisease.Butitwasessentialtoprioritizethesequenceof modificationofthecausalfactorstotacklethediseasecausation.

-Thisrepresentstheinteractionbetweenanagent,hostorpersonsand environmentorplacewithinaspecifictimedimension.Theepidemiological triadcanbeappliedtonon-infectiousdiseaseswheretheagentcouldbe ‘unhealthybehaviors,unsafepractices,orunintendedexposurestohazardous substances’

-Thetriadconsistsofanexternalagent,asusceptiblehost,and anenvironmentthatbringsthehostandagenttogether.Thediseaseresults fromtheinteractionbetweentheagentandthesusceptiblehostinan environmentthatsupportstransmissionoftheagentfromasourcetothathost. -Agent,host,andenvironmentalfactorsinterrelateinavarietyofcomplexways toproducedisease.

-Differentdiseasesrequiredifferentbalancesandinteractionsofthesethree components.

-Developmentofappropriate,practical,andeffectivepublichealthmeasuresto controlorpreventdiseaseusuallyrequiresassessmentofallthreecomponents andtheirinteractions.

1)Agent:

originallyreferredtoaninfectiousmicroorganismorpathogen:avirus, bacterium,parasite,orothermicrobe.Generally,theagentmustbepresentfor diseasetooccur;however,presenceofthatagentaloneisnotalwayssufficient tocausedisease.

Avarietyoffactorsinfluencewhetherexposuretoanorganismwillresultin disease,includingtheorganism’spathogenicity(abilitytocausedisease)and dose.

Overtime,theconceptofagenthasbeenbroadenedtoincludechemicaland physicalcausesofdiseaseorinjuryi.e.,

chemicalcontaminants(suchastheL-tryptophancontaminantresponsible foreosinophilia-myalgiasyndrome).

physicalforces(suchasrepetitivemechanicalforcesassociatedwithcarpal tunnelsyndrome).

Whiletheepidemiologictriadservesasausefulmodelformanydiseases,ithas proveninadequateforcardiovasculardisease,cancer,andotherdiseasesthat appeartohavemultiplecontributingcauseswithoutasinglenecessaryone.

2)Host(Thehumanwhocangetthedisease):

Avarietyoffactorsintrinsictothehost,calledriskfactors,caninfluencean individual’sexposure,susceptibility,orresponsetoacausativeagent.

-Opportunitiesforexposureareofteninfluencedbybehaviorssuchas:

a.Sexualpractices

b.Hygiene

c.Ageandsex

d.Otherpersonalchoices

-Susceptibilityandresponsetoanagentareinfluencedbyfactorssuchas:

a.Geneticcomposition

b.Nutritionalandimmunologicstatus

c.Anatomicstructure

d.Presenceofdiseaseormedications

e.Psychologicalmakeup

3)Environment:

Extrinsicfactorsthataffecttheagentandtheopportunityforexposure

Physicalfactors→geologyandclimate.

Biologicfactors→insectsthattransmittheagent.

Socioeconomicfactors→crowding,sanitation,andtheavailability ofhealthservices.

Naturalhistoryofdisease

oItreferstotheprogressionofadiseaseprocessinanindividualovertime,in theabsenceoftreatment.

oForexample,untreatedinfectionwithHIVcausesaspectrumofclinical problemsbeginningatthetimeofseroconversion(primaryHIV)and terminatingwithAIDSandusuallydeath.

oItisnowrecognizedthatitmaytake10yearsormoreforAIDStodevelop afterseroconversion.

oMany,ifnotmost,diseaseshaveacharacteristicnaturalhistory,although thetimeframeandspecificmanifestationsofdiseasemayvaryfrom individualtoindividualandareinfluencedbypreventiveandtherapeutic measures.

Stagesofdisease

Thefiveperiodsofdisease(sometimesreferredtoasstagesorphases)include theincubation,prodromal,illness,decline,andconvalescenceperiods.

incubationperiod

Itoccursinanacutediseaseaftertheinitialentryofthepathogenintothe host(patient)

.Itisduringthistimethepathogenbeginsmultiplyinginthehost.

However,thereareinsufficientnumbersofpathogenparticles(cellsor viruses)presenttocausesignsandsymptomsofdisease.

Incubationperiodscanvaryfromadayortwoinacutediseasetomonths oryearsinchronicdisease,dependinguponthepathogen.

Factorsinvolvedindeterminingthelengthoftheincubationperiodare diverse,andcanincludestrengthofthepathogen,strengthofthehost immunedefenses,siteofinfection,typeofinfection,andthesizeinfectious dosereceived.

Duringthisincubationperiod,thepatientisunawarethatadiseaseis beginningtodevelop.

prodromalperiod

Itoccursaftertheincubationperiod.

Duringthisphase,thepathogencontinuestomultiplyandthehostbegins toexperiencegeneralsignsandsymptomsofillness,whichtypicallyresult fromactivationoftheimmunesystem,suchasfever,pain,soreness, swelling,orinflammation.

Usually,suchsignsandsymptomsaretoogeneraltoindicateaparticular disease.

periodofillness

Itoccursaftertheprodromalperiod

Duringwhichthesignsandsymptomsofdiseasearemostobviousand severe.

periodofdecline

Itoccursaftertheillnessperiod.

Duringwhichthenumberofpathogenparticlesbeginstodecrease,and thesignsandsymptomsofillnessbegintodecline.

However,duringthedeclineperiod,patientsmaybecomesusceptibleto developingsecondaryinfectionsbecausetheirimmunesystemshavebeen weakenedbytheprimaryinfection.

periodof

convalescence

Itocucursaftertheconvalescenceperiod.

Duringthisstage,thepatientgenerallyreturnstonormalfunctions, althoughsomediseasesmayinflictpermanentdamagethatthebody cannotfullyrepair.

WhenareInfectious diseasestransmitted?

Infectiousdiseasescanbecontagious(transmissible)duringallfiveoftheperiods ofdiseaseandituponthedisease,thepathogenandthemechanismsbywhich thediseasedevelopsandprogresses.

❶Forexample,withmeningitis(infectionoftheliningofbrain),theperiodsof infectivitydependonthetypeofpathogencausingtheinfection:

Bacterialmeningitisiscontagious→theincubationperiodforuptoaweek beforetheonsetoftheprodromalperiod.

Viralmeningitisbecomecontagious→theprodromalperiodwhenthefirst signsandsymptomsappear.

❷Skinviraldiseasesassociatedwithrashes(e.g.,chickenpox,measles,rubella, roseola),patientsarecontagiousduringtheincubationperioduptoaweek beforetherashdevelops.

Incontrast,withmanyrespiratoryinfections(e.g.,colds,influenza,diphtheria, strepthroat,andpertussis)thepatientbecomescontagiouswiththeonsetofthe prodromalperiod.

❹Dependinguponthepathogen,thedisease,andtheindividualinfected, transmissioncanstilloccurduringtheperiodsofdecline,convalescence,and evenlongaftersignsandsymptomsofthediseasedisappear.

Forexample,anindividualrecoveringfromadiarrhealdiseasemaycontinueto carryandshedthepathogeninfecesforsometime,posingariskoftransmission toothersthroughdirectcontactorindirectcontact(e.g.,throughcontaminated objectsorfood).

Theanalogyoficebergisusedtodescribediseasepatternincommunity andpopulation.

Thestudyofthe"Icebergphenomenonofadisease"tellsoftheprogress (pathogenesisandspread)ofadiseasefromitssub-clinicalstagesto apparentdiseasestate.

Thetipoftheicebergrepresentswhattheclinicianssee

Thesubmergedhiddenpartiswhat'sbeingexploredandmade visiblebytheepidemiologists

Thelargehiddenpartoficebergiswhatconstitutesthemassof unrecognizeddiseaseinthepopulationanddeterminesthefate ofanydiseaseprogram.

Icebergphenomenon

Demography 3

Outlines

✓ Definitions and components of demography

✓ Demographic data and demographic transition.

✓ Population Pyramid.

Definitions Demography

Demography is the science that researches and describes a population. More concretely, demography researches the size, composition and (age) structure, as well as the geographic distribution of human populations.

In addition, demographers look at how a population develops, changes and reproduces over a certain period of time.

Three fundamental aspects are observed:

1. The birth rate (fertility)

2. The death rate (mortality).

3. Emigration and immigration (migration)

Demography does not only research the current, but it works more with the factors that can influence population change. Demographers look at the individual life courses, which means the time between birth and death, and what happens within this time. Births, deaths and migration are the core aspects of demographic analyses. Age and gender are important factors that determine these aspects.

Examples of demography:

1. Age of death: A death within the first years of life and a death at the age of 93 have very different consequences for the human population. Both influence, however, the development of the overall life expectancy of a population and its age structure.

2. Age of mother at first birth: It makes a big difference if a woman is a 22year-old or a 36-year-old when she has her first child. The chances that she will have more children in the course of her life are much higher in the first case than in the second. In that respect, populations where the average age of mothers at first birth is low tend to have higher rates of fertility and larger family sizes.

3. Gender distribution among newborns: When there are inequalities in the gender distribution among newborns for one or more generations, meaning a clearly identified difference in the number of new-born boys and girls, then this will have an impact on their life courses later on. For example, there are fewer partners available to start a family, which can then impact the birth rate.

In addition to age and gender, there are other factors that can interact in population development over a certain period of time:

For example, marital status in the reproductive phase of life, when men and women can reproduce, can influence the birth rate, as can the level of education of women and their opportunities in the labor market.

Demographic Data

1- Censuses:

Aim to enumerate the whole population of a defined geographical area. They collect individual-level data on the population’s characteristics that refer to a single point in time. As well as collecting data on the size and composition of the population, most censuses also ask about moves in a fixed period of time before the enumeration. In countries where vital statistics data are incomplete, questions may also be asked about fertility and mortality. Countries that issue identity numbers and require their population to report their place of residence can maintain continuous population registers. In a few European countries these registers now fuse the functions of the registration system with those of the census.

2- Surveys:

In particular,in countries where registration of vital events is incomplete national sample surveys are the main source of vital statistics.

Demographic Transition

Demographers explain the past changes in the population through a theory, or rather a model, known as the “Demographic Transition Theory”. This theory of “Demographic Transition” describes how birth and mortality rates have changed during transition situations, and builds upon the experiences of western Europe in the last two hundred years. This model seeks to summarize the demographic experiences of as many countries as possible within a theoretical framework.

The “Demographic Transition” functions like this:

1. In the first stage

the birth and mortality rates are very high. Many people are born, but within the same population, many people also die, particularly at a young age,specifically newborns and infants. This results in either very low or even no population growth: There are many births, but this is countered by the high death rate.

2. In the second stage

Mortality rate begins to decrease.Due to scientific and social advancements, fewer people die in the early life stages and they also live longer. During such periods when the mortality already begins to decrease and the birth rate continues to be very high, the population significantly increases temporarily.

3. In the third stage

After some time, the birth rate begins to decline: People bring fewer and fewer children into the world. Parents do not have to have as many children as before since children no longer present an economic benefit. Now is when the birth rate begins to drastically decline.

4. In the fourth stage

Both the mortality and the birth rates are low: Less people are dying (or rather they are living longer) and they have fewer children. As a result, the population growth is low or is close to approaching zero.

5. In the fifth stage

The birth rate begins to slowly grow again. The increase does not reach the same level as it was before, but the birth rate gets closer to two children per woman. The population grows either very slowly or stays at zero. Although population growth is very low, both in the phase before the actual “Demographic Transition” and in the phase after it, the two phases differ considerably in regards to the age composition of the population

➢ Before the “Demographic Transition”, there are numerous births and many deaths, the latter also at younger ages. This results in a population with a “young” age structure with a high proportion of children and a small proportion of older people.

➢ After the “Demographic Transition”, fewer children are born, but the majority of them live until a very high age. This results in a population with an “older” age structure. This is what is meant by “population ageing”.

NOTE

The beginning, ending and length of the “Demographic Transition” differs by country.

Definition:

A population pyramid or "age-gender-pyramid" is a graphical illustration of the distribution of a population (typically that of a country or region of the world) by age groups and gender.

❖ It typically forms the shape of a pyramid when the population is growing. Males are usually shown on the left and females on the right, and they may be measured by count or as a percentage of the total population.

❖ This tool can be used to visualize the age of a particular population. It is also used in ecology to determine the overall age distribution of a population; an indication of the reproductive capabilities and likelihood of the continuation of a species.

❖ Each country will have a different population pyramid. However, population pyramids can be categorized into three types: stationary, expansive, or constrictive. These types have been identified by the fertility and mortality rates of a country.

Population Pyramid

Types:

“Expansive” or “Expanding” population pyramid

➢ A pyramid can be described as stationary if the percentages of population (age and sex) remain approximately constant over time.

➢ In a stationary population, the numbers of births and death roughly balance one another.

“Stationary” or “constant” population pyramid

➢ A population pyramid that is very wide at the younger ages, characteristic of countries with a high birth rate and perhaps low life expectancy.

➢ The population is said to be fastgrowing, and the size of each birth cohort increases each year.

“Constrictive” or “Declining” population pyramid

➢ Population pyramid that is narrowed at the bottom. The population is generally older on average, as the country has long life expectancy, a low death rate, but also a low birth rate

➢ In future there may be high dependency ratio due to reducing numbers at working ages. This is a typical pattern for a very developed country, with a high level of education, easy access to and incentive to use birth control, good health care.

4 General concepts in epidemiology of communicable diseases

Outlines

 Definition of infection

 Chain of infection

Infection : is the invasion of an organism's body tissues by disease causing agents, their multiplication, and the reaction of host tissues to the infectious agents and the toxins they produce.

 An infectious disease, also known as a transmissible disease or communicable disease, is an illness resulting from an infection.

 Infections can be caused by a wide range of pathogens, most prominently bacteria and viruses. Hosts can fight infections using their immune system. Mammalian hosts react to infections with an innate response, often involving inflammation, followed by an adaptive response.

 Specific medications used to treat infections include antibiotics, antivirals, antifungals, antiprotozoal, and anthelminthic. Infectious diseases resulted in 9.2 million deaths in 2013 (about 17% of all deaths).

The chain of infection

In order for a communicable infectious disease to occur, there are six requisites for its perpetuation namely:

I. Presence of a microbiologic agent.

II. Presence of a reservoir and source

III. An outlet (portal of exit) from the reservoir.

IV. A suitable mode of transmission.

V. A portal of entry.

VI. Presence of a susceptible host.

I. Microbiologic agent:

The mystery of infectious diseases was solved late in the 19th Century by the discovery of the micro-organisms of some diseases by Pasteur and Koch. The microorganisms responsible for the causation of infectious diseases are classified into bacteria, viruses, rickettsia, fungi, protozoa, and Parasites.

Bacteria: 1

 Bacteria are a varied group of unicellular micro-organisms which vary in size from a fraction of a micron to about 12 microns. some of the bacteria may form spores (sporiolate) e.g. chlostridium tetani, chlostridium botulinum and anthrax bacilli.

 The Spores are highly resistant and may remain viable in the soil for a long time.

 Bacteria responsible for human diseases are classified morphologically into:

 Cocci e.g. pneumococci, meningococci, staphylococci, streptococci.

 Bacilli: The most important bacilli are those of the bowel. Examples are salmonella typhi and para typhi, shigella, brucella, corynebacterium diphtheria and tubercle bacilli. Some bacilli can grow anaerobic as tetanus and gas gangrene bacilli.

 Spirochaetes: The spirochaetes that are pathogenic to man include:

• Treponemas e.g. T. pallidum (Syphilis).

Borrelias e.g. B. recurrentis (louse borne relapsing fever) and

B. duttoni (Tick borne relapsing fever),

Leptospiras e.g. L. icterohaemorrhagica (Weil's disease).

 Vibrio e.g. V.cholera.

2 Viruses

 These are minute micro-organisms which multiply within suitable living cells and cannot be seen by the ordinary microscope. They vary in size from 20300 mill microns.

 Viruses are the causative agents of a large number of diseases including measles, mumps, chicken pox, influenza, common cold, poliomyelitis, small pox, yellow fever, dengue fever, and herpes zoster.

 Rickettsiae can only grow in living cells Like viruses but they can be seen under the ordinary microscope.

 Rickettsiae are usually transmitted to man by biting insects

 rickettsia burnetti is transmitted to man by air or milk.

The main diseases caused by rickettsiae include:

3 Rickettsia

Rocky Mountain spotted fever

4 Protozoa

these are unicellular animals. Four human diseases of public health importance are caused by protozoa:

 Malaria (Plasmodium malariae).

 Amoebic dysentery. (Entamoeba histolytica).

 Sleeping sickness (Trypanosomas).

 Kala azar (Leishmania).

Murine typhus

Scrub typhus of western Pacific

Trench fever

Quintana Louse

5 Parasites

These are animals which live on or within other organisms. Examples of human diseases caused by parasites include Bilharziasis by bilharzia worms, Elephantiasis by filaria worms, Hook worm infections as Ancylostomiasis by anchlostoma worms and Hydatid disease by taenia echinococcus.

II. Reservoirs and sources of infection

 The reservoir of infection may be man, animals, soil or inanimate organic matter in which the infectious agent, lives, and depends on primarily for survival and multiplies in a way that enables it to be transmitted to a susceptible host. Man himself is the most frequent reservoir of most of the infectious agents that are pathogenic to man.

 Source of infection is person, object or substance from which an infectious agent passes immediately to the host. If transfer is direct from the reservoir to the host, in this case the reservoir is the source of infection e.g. in measles.

The source may be

A vehicle : e.g. contaminated water in typhoid fever.

A vector : e.g. infective mosquito in malaria.

Contaminated articles: e.g. A toy or other utensils in case of diphtheria.

Reservoirs of infection are classified into:

1. Cases:

 These are the main reservoir of infection whether typical or subclinical (in apparent, missed).

 The microorganisms leave the cases with the secretions or excretions connected with the organ or tissue in which they are present.

 In apparent cases are those cases in which infection is so mild that it is not recognized clinically.

 However, evidence of infection could be demonstrated by laboratory methods.

 In fact, infection causing subclinical cases is the rule rather than the exception in many diseases and amount to 90% or more of all the infections e.g. in poliomyelitis.

2. Carriers

 A carrier is a person who harbors a specific infectious agent without showing symptoms of clinical disease.

 Carriers are dangerous reservoirs of infection because:

 The carrier and his contacts are unaware of the fact that he can infect them and consequently they do not take any precautions.

 A carrier does not display any clinical manifestations.

 It is not always easy to discover carriers because laboratory examinations, which may not always be easy or practical, are usually required.

It is not always possible to deal with carriers effectively e.g. if the typhoid carrier is the housewife who could not be prevented from preparation, and handling of food.

Classification of carriers

Chronologically (according to duration of carriage or according to the place of carriage).

1. Chronologically : Chronologically carriers are classified into:

A. Contact carriers: These are persons who are in direct contact with infective cases e.g. doctors, nurses, parents of an ill person, or servants. The main characteristic of this type is that the period of carriage ends as soon as the patient is cured.

B. Incubating carriers: They are persons who discharge the micro-organisms during the incubation period e.g. in the case of measles, mumps, infective hepatitis and poliomyelitis.

C. Convalescent carriers: They are defined as persons who discharge the microorganisms during the convalescence period.

They are the commonest type of carriers.

 Sometimes the carriers may remain so after the convalescence period i.e. post convalescent carriers as in typhoid fever (they amount to about 5% by the end of the third month).

 This is why release samples are required after clinical cure before releasing patients suffering from diseases in which a carrier state is known to develop.

 As a rule the patient is not discharged until it is p roved by the laboratory means that the samples are free from the infectious agent on three consecutive bacteriological examinations.

2. According to the duration of carriage: carriers are classified into:

A. Temporary carriers: they are persons who carry the microorganism for a period less than three months (except in typhoid, where the period is for less than one year).

B. Chronic carriers: In this type of carriers the person harbors the microorganism for years.

Carriers may discharge the microorganisms continuously without intermission or the microorganism may not be shown in the carrier's excreta for a period of time to appear again latter and hence named intermittent carriers.

This is why suspected persons should be examined three times consecutively before excluding the carrier state.

3. According to the place of carriage :

carriers are classified into:

Stool carriers : e.g. Typhoid and paratyphoid bacilli. virus hepatitis and amoebic cysts.

Upper respiratory tract carriers : e.g. Meningococcal, diphtheria bacilli, streptococci and staphylococci.

Urinary carriers : e.g. typhoid and paratyphoid bacilli and Brucella melitensis.

Skin carriers : e.g. staphylococci. This also include nasal carriers because the lining of the nose is nothing but a fold of skin.

Dangerous group of carriers:

Certain occupational groups giving public services or care of vulnerable:

 Food handlers.

 Nurses in care of children.

 Hospital personnel.

 School personnel.

3. Animals:

 Although animals have their special infectious diseases. Some of these diseases can be transmitted to man under naturalconditions (such an infection is called a zoonosis).

 Transmission of infection from animal to man could be by contact as in some of the skin diseases of fungal origin or through eating the flesh or products of infected animals as in salmonella and brucella infection or by a vector as in plague and yellow fever.

 The most important zoonosis is: Rabies, bovine tuberculosis, undulant fever, salmonellosis, Q fever, bubonic plague, tape worm infection and anthrax

4. Other reservoirs of infection:

 In addition to the three main reservoirs discussed above, the soil is considered the reservoir in coccidioidomycosis, histoplasomosis and probably in blastomycosis. These organisms can propagate in the soil. In the case of tetanus and botulism, animals are considered the reservoir and the spores, the infective stage, are to be found in the soil.

 Arthropods are considered reservoirs if the agent passes from one generation to the other transovarian as in the case of ticks in tick berne relapsing fever.

 The microorganisms have to leave the reservoir of infection through the portal of exit.

 In general, the microorganisms come out with the secretions or excretions connected with the place in which the organism is present i.e. by a natural outlet. The organisms may leave the reservoir by (unnatural) outlets as by insect bites or other rare methods as during bloodletting.

The following are the different portals of exits:

III. Portal of exit:

 The microorganisms leave the bowel with the fecal material in diseases that affect primarily the digestive tract e.g. typhoid, paratyphoid and bacillary dysentery, the eggs of ascaris, ancylostoma, B. mansoni. Sometimes, the microorganisms may leave the gastro intestinal tract with the vomitus in diseases where vomiting is a main manifestation as in the case of cholera and food poisoning.

 Infection may be in the intestinal wall itself or in any of the organs connected with the bowel e.g. the gall bladder in enterica.

 The microorganisms may leave the body of the reservoir with the urine.

 This occurs in some diseases in which infection is general and the organism is present in the blood as in typhoid and undulant fever and also occur when infection is local in the genito-urinary tract as in case of gonorrhea and other venereal diseases and in urinary typhoid carriers, or when the eggs of a parasite are extruded during urination as in schistosoma haematobium.

Skin lesions may be one of the manifestations of a general disease e.g. chicken pox (and small pox in the past) or they may be the main disease manifestation as in impetigo and other bacterial infections of the skin. Also, discharges from the conjunctival sac are of specific importance in case of acute and chronic conjunctivitis.

3. Discharges from skin and/or mucous membrane lesions

1. The alimentary canal

2. The urinary tract

4. The respiratory tract

 The respiratory tract is the portal of exit in measles, influenza, whooping cough, common cold, diphtheria (laryngeal and nasal types), mumps, pulmonary tuberculosis, streptococcal throat infections (sore throat, tonsillitis and scarlet fever), small pox, chicken pox pneumonias and pneumonic plague.

 The microorganisms leave the respiratory tract of cases or the carriers during coughing, sneezing, talking or even during ordinary respiration.

 Microorganisms leave the respiratory tract in what is known as infective droplets.

 The very small droplets are more dangerous than the large ones, because they are more likely to remain suspended in the air and reach the susceptible host.

 Most droplets from the respiratory tract are expelled in a downward direction (during speaking at 20-25o and during coughing at 45o) therefore contaminating clothes, short people and children.

 It should be noticed that the mouth is more important than the nose as an exit for microorganisms except if the lesion is in the nose

 Even in case of sneezing, the mouth contributes more than the nose. Microorganisms present in nasal secretions spread more by indirect contact through handkerchiefs, bed cloth and fingers.

5. In-utero transmission

Some of the micro-organisms can reach the fetus in uterus e.g. the viruses of German measles, small pox, the spirochetes of syphilis

6.

By insect bites

 The microorganisms are found in the peripheral circulation of man and or animals in some diseases. At the same time, some specific insects may suck these agents with the infected blood meal.

 The agents then develop and/or multiply in the tissues of the specific vector which becomes infective latter (after a certain period referred to as the extrinsic incubation period).

The following are of public health importance among the blood sucking insects which play a role as vectors in the transmission of human diseases:

 Mosquitoes: The anopheles transmit malaria, aides transmit yellow fever, dengue fever and viral haemorrhagic fevers and the culicines transmit filariasis, west Nile fever and virus encephalitis.

 Lice: transmit epidemic typhus, epidemic louse borne relapsing fever and trench fever.

 Fleas: Transmit plague and murine typhus.

 Ticks: Transmit tick borne relapsing fever, rocky mountain Spotted fever and tick fever.

 Sand Flies: Transmit kala azar and sand fly fever.

 Tse Tse Flies: Transmit trypanosomiasis.

Modes of Transmission

The mode of transmission of an infectious disease is the mechanism by which an infectious agent is transported from the reservoir or the source to the susceptible host.

• A particular infectious agent may be transmitted to a susceptible host through different modes of transmission.

• Such variations have their implications on the epidemiology, prevention and control of the disease in question.

1 . Contact Transmission

Direct Contact

In the case of direct contact transmission there is actual continuity between the infected person and the susceptible host as in sexual intercourse, kissing, or other contagious personal associations.

• Examples of diseases transmitted by direct contact are the group of venereal diseases, scabies, diphtheria, rabies and infectious mononucleosis.

•In this case transmission occurs through touching contaminated objects such as toys, handkerchiefs, fomites,soiled clothing or bedding.

The infectious agent is then transmitted to the hand and/or mouth of the susceptible host, or passes through abraded skin or mucous membranes.

•In addition, surgical instruments and dressings if contaminated play a role in the transmission of infection to surgical wounds.

•The use of common towels is also important and it was shown that the incidence of certain diseases was reduced by using individual towel for each person, e.g. Trachoma and fungus infections of the skin.

Trans placental

In some diseases of the mother e.g. syphilis, the causative agent may reach the fetus trans-placental from the blood of the mother.

Droplet transmission

Droplet transmission

•Defined as the transmission of the spray emanating from an infected person during talking, sneezing or coughing directly to the mouth, nose or the conjunctiva of a susceptible person. Such droplets usually travel not more than three feet from the reservoir.

• Transmission by droplet is categorized under contact transmission since it involves reasonably close association between two or more persons.

• Examples of droplet transmission include most of the diseases of the respiratory tract and those systemic diseases in which the organism is present in the upper respiratory tract as measles. Droplets have their importance also in surgical sepsis and in puerperal fevers and the use of masks in these cases is of great value if used properly.

It should be noticed that droplet transmission prevails more in winter when people tend to aggregate in crowded places.

2 . Common vehicle transmission

A vehicle of infection may be water, food, milk, biological products (e.g. serum and plasma) or any other substance serving as an intermediate means by which an infectious agent is transmitted from a reservoir and introduced into a susceptible host through ingestion, inoculation, or by deposition on skin or mucous membranes.

Ingestion

• Examples are consuming contaminated foods and drinks

. Many diseases are transmitted by this method e.g. dysenteries, typhoid, food poisoning and cholera.

Inoculation

• As in using plasma, serum or blood transfusion, or using vaccines

hence the importance of sterile techniques in inoculations to prevent sepsis and diseases as viral hepatitis and syphilis..

Deposition

Pathogenic microorganisms or the infective stage of a parasite (bilharzia) if deposited on the skin or on the mucous membrane of the ear, nasal sinuses or the conjunctiva e.g. during swimming may lead to the development of otitis media, sinusitis or conjunctivitis..

3 . Vectors

Vectors are insects that play an important role in the transmission of human and animal diseases. Vector transmission may be mechanical or biological.

Mechanical transmission

• The insect only acts as a passive carrier of the etiologic agent of the disease picking the microorganisms from the excreta or discharges of man or animal and depositing them on food or tissues. The best example is the role played by house flies in the transmission of enteric diseases, ophthalmiasis and wound infection.

Biological transmission

Propagative:

- in which simple multiplication of the agent occurs in the vector. Examples include plague bacilli in fleas, rickettsia prowazeki in lice and the yellow fever virus in aedes mosquitoes.

This may be differentiated into:

Cyclo propagative:

- in this case the infective organisms undergo changes and multiply within the vector. The best example is the transmission of malaria parasites by anopheline mosquitoes.

Cyclodevelopmental:

-in this case the agent only develops within the vector and no multiplication takes place. The best example is the role of culicine mosquitoes in the transmission of filariasis..

4 . Air borne

Droplet Nuclei

• Droplet transmission occurs through the inhalation of the small residues that result from evaporation of droplets and remain suspended in the air of enclosed spaces. Examples of diseases transmitted in this way include pulmonary tuberculosis and surgical sepsis.

Dust

• Large droplets carrying the microorganisms usually settle down on the floor around cases or carriers or on their body surface, clothes bedding, or other articles. The mucous particles or droplets dry off and the dried residues containing microorganisms, especially those particles less than 10 microns, could be whisked from these articles into the air during activities such as making beds or cleaning the floor, or even by the simple movements of human beings and then could be inhaled by the susceptible individuals or may settle down on open wounds.

• The best examples for this method is in the transmission of staphylococci tubercle bacilli, and rickettsia burnetti.

V. Portals of entry (inlets)

inoculation through blood sucking insects or through injections.

• It is worth noticing that the portal of inlet may determine the type of pathology that may result. For instance, in case of tuberculosis and anthrax if the inlet is through the respiratory system the pulmonary types of these diseases are the result. On the other hand, if the organism enters via the intestinal tract the intestinal types are the result and if the organisms happen to enter through the skin the result would be the dermal types of these diseases.

VI. Susceptible host

A susceptible host is a person or an animal presumably not possessing immunity against a particular pathogenic agent and that reason is liable to contract the disease if exposed to its causative agent.

To conclude, exposure to infective microorganisms may or may not result infection. if infection results in detectable pathologic effect, a deviation from the normal state of health occurs and the individual is then described as suffering from an infectious disease. Infected persons include patients, subclinical infections and carries.

The following factors affect the

outcome of infection:

▪ Pathogenicity and virulence of the micro-organism.

▪ Antigenic power of the micro-organism.

▪ Duration of infectious state (period of communicability).

▪ Ease of communicability of the disease.

Pathogenicity and virulence of the 1 microorganism

• Pathogenicity means the capacity of the microorganism to produce specific pathologic effects once lodged in the host's body.

Pathogenicity can be measured by the ratio of clinical to subclinical cases.

-The higher the pathogenicity, the higher the proportion of clinical cases and the lower the proportion of subclinical cases.

- On the other hand, the term virulence is used to point out differences in pathogenicity within a group of microorganisms e.g. diphtheria bacilli are pathogenic to man but some strains (diphtheria gravis) are more virulent than others.

Virulence is measured by the case fatality rate.

- The more the virulence the higher will be the case fatality rate.

2

Antigenic power of the microorganism

This means the ability of the microorganism to initiate the develop antibodies and the associated immunity against the same type of infection. In practice, the antigenic power could be measured by:

Age specific attack rate:frequency

if the attack rate is plotted against age, it is found that in diseases caused by microorganisms of a high antigenic power e.g. measles, there is a drop in the attack rate after the young age groups. This is not the picture with diseases caused by micro-organisms of a weak antigenic power e.g. shigellosis.

The second attacks frequency

how frequent one gets two or more attacks of a certain disease. Second attacks in diseases like measles, mumps and chicken pox are not recorded, indicating a high antigenic power of their causative agents. On the other hand, common cold and other upper respiratory infections and also in diseases like syphilis and gonorrhea reinfection can occur repeatedly in the same person indicating a poor antigenic power of their causative agents.

3

Period of communicability

(Duration of infectious

(Duration of infectious state):

It is the duration of the infectious state and is defined as the time or times during which the causative agent may be transferred directly or indirectly from an infected person or animal to man. The duration of the infectious state may be short as the case in mumps or protracted as in typhoid fever where about 3% of the cases become carries for the remainder of their lives.

Ease of communicability of the disease (Duration of infectious state): 4

The ease of communicability of a particular disease is measured by the secondary attack rate. It means the attack rate of a specific disease among the remaining susceptibles within a stated period of time (usually the incubation period) after its introduction by an initial case (index case). For example, in a class room of 30 students one get measles and after two weeks 15 children fell with the disease. The medical records show that 4 students had measles before.

The secondary attack rate =

No. of secondary cases

No. of susceptible x 100

Conceptofprevention5

Outlines

Primary,secondaryandtertiaryprevention.

Healthpromotion.

Chemoprophylaxis,activeandpassiveimmunization.

Preventionandcontroltasksforcommunicableandnon-communicablediseases.

Diseaseprevention

Definition

Prevention=avoidingdiseasebeforeitstarts.

Itistheplansandmeasurestakentopreventtheonsetofadisease.



preventdisease orinjurybeforeit everOccurs.



Reducethe impactofa diseaseorinjury thathasalready occurred.

tosoftenthe impactofan ongoingillnessor injurythathas lastingeffects.

methods

Primary Secondary Tertiary

Preventing exposuresto hazardsthatcause diseaseorinjury.

alteringunhealthyor unsafebehaviors.

reducingexposure todisease-causing agents.

increasing resistanceto diseaseorinjury shouldexposure occur.

Examples

-Legislationand enforcementtoban orcontroltheuseof hazardousproducts (e.g.,asbestos)orto mandatesafeand healthypractices (e.g.,useofseatbelts andbikehelmets).

-Immunization againstinfectious diseases.

-Provisionofneeded nutritiveelements.

detectingand treatingdiseaseor injuryatanearly stagetohaltorslow itsprogress,by screening.

encouraging personalstrategies topreventreinjuryor recurrence.

implementing programstoreturn peopletotheir originalhealthand functiontoprevent longtermproblems.

helpingpeople managelong-term, often-complex healthproblemsand injuries(e.g.,chronic diseases,permanent impairments)inorder toimproveasmuch aspossibletheir abilitytofunction, theirqualityoflife andtheirlife expectancyto prevent complicationsofthe illness,including deathofthe

-Regularexamsand screeningteststodetect diseaseinitsearlieststages (e.g.,mammogramstodetect breastcancer).

-Daily,low-doseaspirins and/ordietandexercise programstopreventfurther heartattacksorstrokes.

-Disabilitylimitation:

1.Preventionof delayed consequencs

2.Treatmentand preventionof complications

-Suitablymodifiedworkso injuredorillworkerscanreturn safelytotheirjobs.

-Rehabilitation (physical,mental, socialand occupational).

NOTE

Healthpromotion

Definition:

Itistheprocessofempoweringpeopleto increasecontrolovertheirhealthandits determinantstoimprovetheirhealth.“It movesbeyondafocusonindividual behaviortowardsawiderangeofsocialand environmentalinterventions”(WHO).

p

Screeningin2ndryprevention takesplaceduringthe preclinicalphaseofanillness, afterthediseasehas developed,butbeforeclinical signsandsymptomshave appeared.

Diseasepreventionandhealthpromotionsharemanygoals,and considerableoverlapexistsbetweenfunctions.Onaconceptuallevel,itis usefultocharacterizediseasepreventionservicesasthoseprimarily concentratedwithinthehealthcaresector,andhealthpromotionservicesas thosethatdependonintersectoralactionsand/orareconcernedwiththe socialdeterminantsofhealth.

Healthpromotionincludes:

healthliteracyeffortsandmulti-sectoralactiontoincreasehealthybehaviors focusedonactivitiesforthecommunityatlargeorforpopulationsatincreased riskofnegativehealthoutcomes.

Healthpromotionusuallyaddresses:

behavioralriskfactorssuchastobaccouse,obesity,diet,andphysicalinactivity, aswellastheareasofmentalhealth,injuryprevention,drugabusecontrol, alcoholcontrol,healthbehaviorrelatedtoHIV,andsexualhealth.

2.Dietaryandnutritionalinterventiontoappropriatelytackle malnutrition,definedasaconditionthatarisesfromeatingadietin whichcertainnutrientsarelackingorinthewrongproportionsorintake istoohigh.

5.Strategiestotackle domesticviolence,including publicawareness campaigns;treatmentand protectionofvictims;and linkagewithlaenforcement andsocialservices.

Healthpromotion activities

3.Policiesandhealth servicesinterventions toaddressmental healthand substanceabuse.

4.Strategiestopromotesexualand reproductivehealth,includingthroughhealth educationandincreasedaccesstosexualand reproductivehealthandfamilyplanning services.

1.Policiesand interventionsto addresstobacco, alcohol,physical activityanddiet.