Disease Control and Prevention Principles

Course Description

• This course introduces core concepts and principles in disease control and prevention
• Students learn about infectious disease surveillance data, disease transmission, and outbreak investigation
• The course focuses on understanding interactions within and between the agent, host, and environment

Course Objectives

• Students should be able to comprehend biological concepts of diseases
• Students should be able to recognize properties of different pathogens and pathogenesis mechanisms
• Students should be able to understand disease control and prevention principles
• Students should be able to identify and describe public health issues linked to major diseases in Ghana
• Students should be able to understand strategies and interventions to control and prevent diseases in Ghana

Course Content

• Includes disease principles, diagnosis, and detection
• Includes disease control and prevention principles
• Includes antibiotic resistance
• Includes prevention of disease spread and vaccinology
• Includes therapeutics and emergency responses to emerging diseases
• Includes strategies and interventions for control and management

Overview of Diseases

• Disease is any harmful deviation from an organism's normal structural or functional state
• Such deviations are generally associated with signs and symptoms, differing from physical injury
• Pathology: The study of disease
• Etiology: Determination of a disease's cause

Types of Diseases

• Communicable: Can be transmitted from one organism to another
• Non-communicable: Not infectious and generally develop slowly

Communicable Diseases

• Illness is caused by a specific infectious agent or its toxic products
• Illness arises through transmission of the agent or its products
• Transmission routes include infected persons, animals, or inanimate sources to susceptible hosts
• Transmission can occur directly or indirectly through intermediate hosts, vectors, or contact with the inanimate environment
• Examples of transmission routes include airborne (TB, measles, meningitis), water/foodborne (cholera, typhoid), helmintic (guinea worm, roundworm), vector-borne (yellow fever, malaria), sexually transmitted (HIV/AIDS), contact (ringworm, Yaws), animal-transmitted (rabies), and other (tetanus)

Non-communicable Diseases

• Usually long-lasting, progress slowly, often referred to as chronic diseases
• They can arise from environmental exposures or genetic abnormalities, and may be evident at birth or later in life
• The World Health Organization (WHO) identifies four major types:
  • Cancer
  • Cardiovascular disease (e.g., heart attack, stroke)
  • Chronic respiratory diseases (e.g., asthma)
  • Diabetes mellitus
• These four groups account for 82% of all deaths from non-communicable disease

Epidemiologic Terminologies Associated with Infectious Diseases

• Communicable Disease: Illness due to a specific infectious agent or its toxins. Arises through transmission from infected sources to susceptible hosts via direct or indirect routes
• Host: A person or other living organism (including birds and arthropods) that harbours or nourishes an infectious agent under natural conditions -Definitive (primary) host: A host where a parasite attains maturity or passes its sexual stage - Example: The female Anopheles mosquito is the primary host for the malarial parasite Plasmodium
  • Secondary (intermediate) host: A host in which a parasite is in a larval or asexual state
    • Example: Humans are the secondary host for malaria parasites
  • Transport/paratenic host is a carrier where the organism lives but does not undergo development
    • Example: Freshwater shrimp, flatworms, and frogs.
  • Reservoir host: Any animal infected by a parasite, serving as a source of infection
    • Hosts can be humans, animals, or the environment
    • Example: Soil is the reservoir for Clostridium botulinum
  • Accidental Host: An organism, that does not allow transmission to the definitive host, thereby preventing the parsite completing its development -Examples include humans with fish parasite and ticks

Additional Terminologies

• Reservoir: Any person, animal, arthropod, plant, soil, or substance where an infectious agent lives and multiplies, acting as a source of infection
• Infection: The entry, development, and multiplication of an infectious agent in a human or animal body
• Infective dose: The quantity of the organism needed to cause clinical disease
• Infectiousness: The relative ease with which an infectious agent is transmitted to other hosts
• Contamination: The presence of an infectious agent on a body surface, clothes, beddings, toys, surgical instruments/dressings, other articles or substances, including water and food
• Infestation: The lodgment, development, and reproduction of arthropods on the surface of the body or in clothing (e.g., lice, itch mite)
• Contagious Disease: A disease transmitted through contact such as scabies, trachoma, STD and leprosy
• Vector: An insect or any living carrier transporting an infectious agent from an infected individual to a susceptible individual, their food, or immediate surroundings

Incidence and Prevalence

• Incidence: Occurrence of new cases of a disease within a population during a specific period
• Prevalence: Total number of existing cases (old and new) in a population at a particular time

Epidemic, Endemic, Hyperendemic, and Holoendemic

• Epidemic: The unusual occurrence of disease, specific health-related behavior, or other health-related events in a community, exceeding expected occurrence
  • (epi= upon; demos= people)
  • Can occur in endemic states
• Endemic: The constant presence of a disease or infectious agent within a given geographic area or population group, or the usual/expected frequency of disease in a population
  • (En = in; demos = people)
• Hyperendemic: Disease is constantly present at high incidence/prevalence, affecting all age groups.
• Holoendemic: High infection levels begin early in life and affect most of the child population, leading to equilibrium where adults commonly show evidence of the disease than children do (e.g., malaria)

Pandemic, Exotic, Sporadic, Nosocomial, and Opportunistic

• Pandemic: An epidemic occurring worldwide, crossing international boundaries, and affecting a large number of people, such as influenza pandemics
• Exotic diseases are imported into a country where they do not otherwise occur (e.g., rabies in the UK)
• Sporadic: Cases of disease occur in a scattered or isolated way in a given area
  • Cases occur irregularly and infrequently, showing little connection to each other or a common source of infection (e.g., polio, meningococcal meningitis, tetanus)
  • A sporadic disease could become the starting point of an epidemic if conditions become favorable
• Nosocomial: Infections are acquired in a hospital by a patient who did not have the infection upon admission. This includes infections appearing post-discharge and among facility staff
  • Examples include infection of surgical wounds, hepatitis B, and urinary tract infections
• Opportunistic: Infection by organisms that exploit a defect in host defense (e.g., immunity)
  • These are common in AIDS, and include Herpes simplex, cytomegalovirus, M. tuberculosis

Cases, Carriers, Incubation and Latent Periods

• Case: A person in the population identified as having a disease, health disorder, or condition under investigation
• Index case: The first identified case in a population
• Carrier: A person or animal harboring a specific infectious agent without clinical disease, serving as a potential source of infection to others
• To form a carrier state, three elements must occur:
  • The presence of the disease agent in the body
  • The absence of recognizable symptoms and signs of disease
  • The shedding of the disease agent in the discharge or excretions
• Incubation period: The time from exposure to the development of disease or time interval between invasion by an infectious agent and the appearance of the first sign or symptom of disease
• Latent period: The period between exposure and the onset of infectiousness, which can be shorter or longer than the incubation period

Infectious Disease Process (Chain of Transmission)

• Infectious disease results from the interaction of the agent, host, and environment, involving 6 components:
  • Causative (etiologic) agent
  • Reservoir of the agent
  • Portal of exit from the reservoir
  • Mode of transmission of the agent to the new host
  • Portal of entry to the new host
  • Susceptible host

Definition of Epidemiology

• Epidemiology: The study of the distribution and determinants of health-related states and events in populations, and the application of this study to control health problems (Last, 1983)
• Present epidemiological approach is based upon the interactions of the host, causative agent, and environment expressed as the epidemiological model

Interaction Between Agent, Host, and Environment

• Different diseases are common at different times and in different places.
• Understanding requires considering the disease organism (AGENT), the people they infect (HOST), and their surroundings (ENVIRONMENT)
• Epidemiological Triad is Demographic, Biological and Socioeconomic Characteristics of - Agent, Host and Environment.

The Agent

• Refers to factors whose presence leads to a disease state in an individual
• In infectious diseases, the agent is biologic, but can be physical, chemical, or a nutrient in other disease conditions
• An agent may manifest itself through its absence. E.g. lack of vitamin A can manifest in night blindness
• A biologic agent needs a suitable environment to grow and multiply to be able to spread and infect another host
• A natural balance exists between the agent, host, and environment, influencing each other/ This explains the relationship that must exist for a disease to occur.

The Host

• They are affected by their environment
  • The host (man) may live in a hot and wet climate in which there will be mosquitoes
• They can change the environment
  • By draining swamps or moving out of the hot or wet climate

The Environment

• They can affect the causative agent
  • Climatic changes from wet to dry season influence the abundance of mosquitoes and for that matter plasmodium parasite, which is the agent for malaria
• When the balance between these three (agent, host and environment) are constant there will be a fairly steady number of people getting sick all the time from a particular disease (these diseases are said to be endemic)
• When the balance between the host, agent and the environment are shifted in favour of the agent, e.g. when many non-immune children have been born in an area, a large number of cases of mealses may occur in a short time (these diseases are called epidemic)
• If the balance is shifted against the agent, so that the agent cannot thrive, the disease will be controlled and the number of cases will be smaller

Control of Disease

• To be able to control a given disease, it is necessary to understand the factors which will affect the balance between the host, the agent and the environment and to know what can be done to tip the balance in favour of the host

Phases of Disease Progression

• Stage of susceptibility
• Sub-clinical stage
• Clinical stage
• Disability stage

Stage of Susceptibility

• The disease condition has not yet developed.
• Conditions that will favour occurrence e.g. exposure to cold, general fatigue, alcoholism etc will increase risk of getting pneumonia.
• Some risks factors can be altered whiles others cannot be altered.
  • E.g. smoking can be altered, age & sex cannot be altered

Sub Clinical Stage

• The person has been infected or has the disease but shows no signs or symptoms and he does not know that he has that disease.
• The sub clinical stage may lead to recovery without the person developing any clinical stage or it may lead to the clinical stage.

Clinical Stage

• The person shows signs and symptoms of the disease.
• For infectious disease, the time between infection and the appearance of symptoms and signs of illness is called Incubation period
• The shorter incubation period, the more rapidly the disease can spread or die out in the community
• There are various possible outcomes like recover, disability or death

Disability Stage

• This refers to the stage after the disease has run its course. Some diseases resolve completely without defect.
• Others however leave some considerable damage or disability.

Control of Diseases (Prevention)

• Most diseases are preventable to a greater or lesser degree, the chief exceptions being the idiopathic diseases, such as the inherited metabolic defects.
• In the case of those diseases resulting from environmental exposures, prevention is a matter of eliminating, or sharply reducing, the factors responsible in the environment.
• Infectious diseases may be be prevented in one of two general ways:
  • (1) By preventing contact, and therefore transmission of infection, between the susceptible host and the source of infection
  • (2) By rendering the host unsusceptible.
• The nature of the specific preventive measures, and their efficacy varies from one disease to another.

General Principles of Communicable Disease Prevention and Control

• Control: Purposeful reduction of specific disease prevalence to relatively low levels of occurrence
• Objective: Complete eradication achievable through planned programs that prevent or limit transmission to susceptible individuals
• Adequate disease surveillance is essential to identify, detect, and cope with situations
• Sound epidemiologic studies and information guide prevention and control programs.

Recognition and Diagnosis

• Recognising infection and confirming diagnosis is the medical and paramedical responsibility
• Laboratory facilities support clinical diagnosis
• Promptness is vital for early and effective containment

Notification and Reporting

• Medical and paramedical staff must notify the immediate health authority of a disease
• Use form CD 1 or weekly IDSR form
• Some diseases are also notifiable internationally and the WHO
  • Including cholera, yellow fever, relapsing fever, AFP

Identification of Infection

• Identifying the source of infection
  • Investigating patients movement during the incubation period of the disease -Has patient been in contact with known or suspected cases? -Have similar symptoms developed among his associates
  • Investigating possible vehicles of spread -Is it food supply? -Is it water supply? -Is it refuse which is not properly disposed? -Is it arthropod (insect)? -Is it objects or biological products

Other Steps

• Search for carriers of diseases through testing and examination if the specimen
• The magnitude of the problem need to be identified
  • Look beyond the prescriptions of the index and secondary cases by means of organised surveys, records review etc and reach for unreported cases and other exposed persons -The revealed impact of the disease on the population (number of cases/death or groups mostly affected, geographical area affected etc)

Disease Controll Methods

• Disease control methods are specific measures that are put in place to protect individuals or groups from getting infected or when these measures have been overwhelmed that are applied to treat the cases and to limit further spread of the disease agent.
• Major activities with health education being an activity:
  • Elimination of the reservoir or source of infection -Interrupting the pathway of transmission -Protecting the susceptible hosts -Health education

Reservoir Elimination

• Involves measures to destroy the causative agent of the disease.
• The objective may be complete eradication of a significant reduction of the community reservoir
• Different means are taken based on if the reservoir exists in humans, animals, or the environment

Means of Reservoir Elimination

• The reservoir is human
  • Treatment of infected persons, both patients ad carriers For some infections, segregation of infected persons and contacts through isolation and quarantine is required
  • Isolation and quarantine may be taken for diseases which have the following epidemiologic features -High morbidity and mortality -High infectivity -Infectious cases easily recognisable -No significant reservoir or carrier -Peroid of communicability occuring clearly after the incubation period
• The reservoir is an animal -Management depends on the usefulness of the animal and intimately it is associated with man -For a pest, e.g. rat in plaque, mosquitoes in malaria, destroy all animals and exclude from human habitation -For a pet, e.g. dog in rabies, objective is to protect dogs with immunization whilst destroying the stray ones -Animals used as food should be examined and the infected ones eliminated or if possible treated while healthy ones should be protected by immunization etc Examination of animals may be done in life or after slaughter (anti-mortem or post-mortem)
• The reservoir is in Soil, water or food
  • Limit man's exposure e.g. wearing of shoes againt hookworm infection
  • Boil or chlorinate water to destroy microbes
  • Heat or cook food to destroy microbes and avoid eating contaminated food
• disinfection
  • Concurrent and terminal disinfection limits transmission of infections through destruction of the infectious agent present in discharges of patients or soiled articles

Transmission Route Interruption

• Alterations to the environment, use of pesticides
• Provision and use of safe and adequate excreta disposal facilities
• Safe and adequate disposal of domestic and industrial refuse
• Provision and use of safe and adequate water source
• Adequate housing to prevent overcrowding and ensuring adequate ventilation
• Provision of drainage of waste water
• Disinfection and sterilization

Protecting the susceptible host

• These are measures aimed at prevention of population from getting the infection.
• Immunization against specific diseases e.g: -Active immunization (tetanus, measles, TB vaccines etc) -Passive immunization (anti-tetanus serum, anti-snake serum) Use of chemoprophylaxis (drugs that prevent contacts from getting the diseases) e.g. use of SP to prevent malaria
• Personal protection -Use of insecticide treated bed nets -Use of repellants -Use of protective clothing like wearing of boots when working in cercaria infected waters
• Better nutrition

Health Education

• Education of the public on mode of spread is partially useful in disease conditions in which the transmission is mostly behavioural e.g. STIs, schistosomiasis, guinea worm