I am sharing 'PRINCIPLES OF DC-1' with you

BPH 118: Principles of Disease Control 2 Credit Hours  COURSE OUTLINE Introduction Course Description This course provides an introduction to core concepts and principles in disease control and prevention. Students will be introduced to infectious disease surveillance data, d...

BPH 118: Principles of Disease Control 2 Credit Hours  COURSE OUTLINE Introduction Course Description This course provides an introduction to core concepts and principles in disease control and prevention. Students will be introduced to infectious disease surveillance data, disease transmission, and outbreak investigation. The framework underpinning this course is the understanding and application of the interactions within and between the agent, host and environment.  COURSE OUTLINE Course Objectives At the end of this course, students should be able to: understand biological concepts of diseases, recognize the properties of different types of pathogens and the mechanisms of pathogenesis, understand the principles of control and prevention of diseases, identify and describe current public health issues related to the most important diseases in Ghana, appreciate strategies and interventions put in place to control and prevent diseases in Ghana.  COURSE OUTLINE Course Content Disease principle, diagnosis and detection. Disease control and prevention principles Antibiotic resistance Prevention of disease spread/ vaccinology Therapeutics, emergency responses to emerging diseases Strategies and interventions for control and management  OVERVIEW OF DISEASES. Disease, any harmful deviation from the normal structural or functional state of an organism, generally associated with certain signs and symptoms and differing in nature from physical injury.  OVERVIEW OF DISEASES The study of disease is called pathology. It involves the determination of the cause (etiology) of the disease, the understanding of the mechanisms of its development(pathogenesis), the structural changes associated with the disease process (morphological changes), and the functional consequences of those changes. Correctly identifying the cause of a disease is necessary to identifying the proper course of treatment.  TYPES OF DISEASES 1. COMMUNICABLE 2. NON-COMMUNICABLE  1. COMMUNICABLE Communicable Disease (synonym: infectious, transmissible disease) - An illness due to a specific infectious agent or its toxic products that arises through transmission of that agent or its products from an infected person, animal or inanimate source to a susceptible host either directly or indirectly through an intermediate plant or animal host, through a vector, or through contact with the inanimate environment.  1. COMMUNICABLE CONT. Airborne diseases e.g. TB, measles, meningitis Water and food borne diseases e.g. cholera, typhoid Helmintic diseases e.g. guinea worm, round worm Vector borne diseases e.g. yellow fever, malaria  COMMUNICABLE DISEASES cont, Sexually transmitted diseases e.g. HIV/AIDS Contact diseases e.g. ringworm, Yaws Diseases transmitted by animals e.g. rabies Other diseases e.g. tetanus  Non-communicable diseases Noncommunicable disease Noncommunicable diseases generally are long- lasting and progress slowly, and thus they are sometimes also referred to as chronic diseases. They can arise from environmental exposures or from genetically determined abnormalities, which may be evident at birth or which may become apparent later in life.  Non-communicable diseases The World Health Organization (WHO) has identified four major types of noncommunicable disease: Cancer cardiovascular disease (e.g., hear attack, stroke) chronic respiratory diseases (e.g., asthma) diabetes mellitus WHO estimates that, combined, these four groups of conditions account for 82 percent of all deaths from noncommunicable disease.  Epidemiologic terminologies associated with infectious diseases Communicable disease A communicable disease is an illness due to a specific infectious (biological) agent or its toxic products that arises through transmission of that agent or its products from an infected person, animal or inanimate source to a susceptible host either directly or indirectly through an intermediate plant or animal host, through a vector, or through contact with the inanimate environment.  Host A person or other living animals, including birds and arthropods, that harbours or nourishes an infectious agent under natural conditions. Types include: - definitive (primary) host : when a parasite attains its maturity or passes its sexual stage. Example: The primary host of the malarial parasite Plasmodium is the female Anopheles. - Secondary (intermediate) host: those in which a parasite is in a larval or asexual state  Host Example: The secondary host of malarial parasites is the human body, where the malaria parasite uses the host's red blood cells to produce male and female gametocytes, which are taken by the female Anopheles mosquito on biting a malaria-infected person to produce sporozoites in its gut  Host - Transport/paratenic host: is a carrier in which the organism remains alive but does not undergo development. Example incudes freshwater shrimp, flatworms and frogs - reservoire host: its any animal (species) that is infected by a parasite and which serves as a source of infection for man or other species. Reservoire includes humans, animals and the environment. For example, the reservoir of Clostridium botulinum is soil, but the source of most botulism infections is improperly canned food containing C. botulinum spores.  Accidental host Dead-end, incidental, or accidental host – an organism that generally does not allow transmission to the definitive host, thereby preventing the parasite from completing its development. Accidental hosts can be any kind of host. Examples of accidental hosts include humans with fish parasites (likely a result of diet), and ticks, which can feed on humans as accidental hosts, rather than their normal deer or forest animal hosts  Reservoir Any person, animal, arthropod, plant, soil, or substance, or a combination of these, in which an infectious agent normally lives and multiplies, on which it depends primarily for survival, and may serve as a source of infection to susceptible host. It is the natural habitat of the infectious agent.  Infection Infection is the entry and development or multiplication of an infectious agent in the body of man or animals. Infective dose: The infective dose is the quantity of the organism needed to cause clinical disease. Infectiousness - Indicates the relative ease with which an infectious agent is transmitted to other hosts. Contamination:The presence of an infectious agent on a body surface, on or in clothes, beddings, toys, surgical instruments or dressings, or other articles or substances including water and food  Infestation It is the lodgment, development and reproduction of arthropods on the surface of the body or in the clothing, e.g. lice, itch mite.  Contagious disease A contagious disease is the one that is transmitted through contact. Examples include scabies, trachoma, STD and leprosy.  Vector of infection An insect or any living carrier that transports an infectious agent from an infected individual or its wastes to a susceptible individual or its food or immediate surroundings. Both biological and mechanical transmissions are encountered. Incidence and prevalence of infectious diseases Incidence of an infectious disease: Is the occurrence of new cases of a disease within a particular population or group during a specified period of time. Prevalence of an infectious disease: The total number of cases or of persons ill (old and new) in existence in a specified population at a particular time in a given geographical area.  Epidemic “The unusual occurrence of disease in a community, specific health related behavior, or other health related events clearly in excess of expected occurrence” (epi= upon; demos= people) Epidemics can occur upon endemic states too.  Endemic It refers to the constant presence of a disease or infectious agent within a given geographic area or population group. OR It is the usual or expected frequency of disease within a population. (En = in; demos = people) Hyperendemic and holoendemic The term “hyperendemic” expresses that the disease is constantly present at high incidence and/or prevalence rate and affects all age groups equally. The term “holoendemic” expresses a high level of infection beginning early in life and affecting most of the child population, leading to a state of equilibrium such that the adult population shows evidence of the disease much less commonly than do the children (e.g. malaria)  Pandemic and Exotic An epidemic occurring worldwide or over a very wide area, crossing international boundaries, and usually affecting a large number of people. e.g. Influenza pandemics. Exotic diseases are those which are imported into a country in which they do not otherwise occur, as for example, rabies in the UK.  Sporadic It is the occurrence of cases of disease in a scattered or isolated way in a given geographical area. The cases occur irregularly, haphazardly from time to time, and generally infrequently. The cases are few and separated widely in time and place that they show no or little connection with each other, nor a recognizable common source of infection e.g. polio, meningococcal meningitis, tetanus…. However, a sporadic disease could be the starting point of an epidemic when the conditions are favorable for its spread.  Nosocomial infections Nosocomial (hospital acquired) is an infection occurring in a patient in a hospital or other health care facility in whom the infection was not present or incubating at the time of admission. Includes infections acquired in the hospital but appearing after discharge, and also such infections among the staff of the facility. Examples include infection of surgical wounds, hepatitis B and urinary tract infetions.  Opportunistic infection This is infection by organisms that take the opportunity provided by a defect in host defense (e.g. immunity) to infect the host and thus cause disease. For example, opportunistic infections are very common in AIDS. Organisms include Herpes simplex, cytomegalovirus, M. tuberculosis….  Cases A case is defined as “a person in the population or study group identified as having the particular disease, health disorder, or condition under investigation Index case : The first identified case in a population.  Carriers Is a person or animal that harbors a specific infectious agent without discernible (visible) clinical disease, and which serves as a potential source of infection to others. Three elements have to occur to form a carrier state: 1. The presence in the body of the disease agent. 2. The absence of recognizable symptoms and signs of disease. 3. The shedding of disease agent in the discharge or excretions.  Incubation and Latent periods Incubation period: time from exposure to development of disease. OR It is the time interval between invasion by an infectious agent and the appearance of the first sign or symptom of the disease in question. Latent period: the period between exposure and the onset of infectiousness (this may be shorter or longer than the incubation period).  Incubation and Latent periods Incubation period: time from exposure to development of disease. OR It is the time interval between invasion by an infectious agent and the appearance of the first sign or symptom of the disease in question. Latent period: the period between exposure and the onset of infectiousness (this may be shorter or longer than the incubation period).  THE INFECTIOUS DISEASE PROCESS (CHAIN OF TRANSMISSION) Infectious disease results from the interaction of the agents, host and the environment in a process which involves six (6) components. These six components forms the infectious disease process or the chain of transmission  Infectious disease process cont, The components are; - Causative (etiologic) agent - Reservoir of the agent - Portal of exit from the new host - Mode of transmission of the agent to the new host - Portal of entry to the new host - Susceptible host  Definition of Epidemiology Epidemiology is 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). The present epidemiological approach is based upon the interactions of the host, causative agent and environment usually expressed as the epidemiological model  The Interaction between Agent, Host and Environment Different diseases are common at different times and in different places. To understand why this is so, there is the need to consider the organism of the disease (AGENT), the people they infect (HOST) and the surroundings in which they live (ENVIRONMENT)  Epidemiologic triad (model) Demographic characteristics Biological characteristics Socioeconomic characteristics Host DISEASE Agent Environment Biological agents Physical environment Physical agents Biological environment Chemical agents Social environment Nutrient agents Mechanical agents Social agents  THE AGENT The agent refers to those factors whose presence leads to the disease state in an individual. It is biologic in infectious diseases but could also be physical, chemical or a nutrient in other disease conditions. An agent may also manifest itself through its absence. E.g. lack of vitamin A could manifest in night blindness A biologic agent needs a suitable environment to grow and multiply to be able to spread and infect another host.  AGENT cont, There is a natural balance that exists between the agent, host and the environment, and they have an influence on each other. This balance explains the relationship that must exist for a disease to occur.  THE HOST The host is affected by his environment, e.g. the host (man) may live in a hot and wet climate in which there will be mosquitoes The host can change his/her environment by draining swamps or moving out of the hot or wet climate.  THE ENVIRONMENT The environment can affect the causative agent e.g. 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)  THE ENVIRONMENT When the balance between the host, agent and the environment is 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) Therefore, if the balance is shifted against agent, so that the agent cannot thrive, the disease will be controlled and the number of cases will be smaller 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 Basically, there are four phases of disease progression Stage of susceptibility Sub clinical stage Clinical stage Disability stage  Stage of susceptibility The disease condition has not yet developed. There are conditions which will favour its future occurrence; e.g. exposure to cold, general fatigue, alcoholism etc will increase ones 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 Here 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 several outcomes of clinical stage disease i.e. recover, disability or death  Disability stage This refers to the stage after the disease had 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. Because chemicals and other substances and materials originate largely from human activities, prevention ought to be a simple matter of the application of well-established principles of industrial hygiene. In practice, however, this is often difficult to achieve. The infectious diseases may 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 and (2) by rendering the host unsusceptible. The nature of the specific preventive measures, and their efficacy varies from one disease to another. GENERAL PRINCIPLES IN THE PREVENTION AND CONTROL OF COMMUNICABLE DISEASES HUSEIN ABDUL-KARIM Control of communicable diseases implies purposeful reduction of specific disease prevalence to relatively low levels of occurrence Whenever possible, the ultimate objective should be complete eradication which may be achieved by the same methods of control through a planned programme so as to prevent or limit the transmission of the infectious agent to susceptible individuals Accordingly, an adequate disease surveillance must be developed to identify, detect and cope with such situations The strategy of prevention and control programme should be based on sound epidemiologic studies and information aiming at the following principles;  1. Recognition of infection and confirmation of diagnosis Recognizing the infection and confirmation of diagnosis is the function of both the medical and paramedical who are attending to the patient(s) Laboratory facilities should be used to support clinical diagnosis. This must be prompt to effect early and effective containment measures 2. Notification of the disease to the appropriate health authority (form cd 1 or weekly idsr form) Notification of the disease is again the responsibility of the medical and paramedicals who should under any circumstances notify the immediate health authority in the district using the form CD 1 or the weekly IDSR form. Some diseases are also notifiable internationally. This is by the international sanitary regulations Some of the diseases that should be notified to WHO includes -cholera, yellow fever, relapsing fever, AFP  3. IDENTIFICATION OF SOURCE OF INFECTION The reservoir of the infectious agent must be identified in order to break the chain of transmission by; i. 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  3. IDENTIFICATION OF SOURCE OF INFECTION cont, ii. 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  4. Searching for carriers This depends on co-operation of healthy and suspected individuals It involves examination of specimen from healthy or suspected individuals and describing positions or the nature of his/her condition, the danger it constitutes to others and how he/she can minimize the danger by regarding his/her lifestyle 5. Assessment of the extent of the outbreak (define the magnitude of the problem) 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 This will reveal the impact of the disease on the population (number of cases/death or groups mostly affected, geographical area affected etc) 6. Methods of prevention and control 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. Generally, disease control methods are described under three (3) major activities with health education being an activity which is ongoing and is applied in all the methods  6. Methods of prevention and control cont, These major activities are: 1. Elimination of the reservoir or source of infection 2. Interrupting the pathway of transmission 3. Protecting the susceptible hosts 4. Health education 1. Measures towards Elimination of the reservoir or source of infection Generally, these are measures aimed at destroying the infectious agent that is causing the disease The objective is either complete eradication of disease or significant reduction in the extent of community reservoir Measures differ depending on whether reservoir is human or animal Eradication may be possible in disease in which the reservoir is an animal  a. Where the reservoir is human Treatment of infected persons, both patients and carrriers - 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 occurring clearly after the incubation period B. Where 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)  c. Where the reservoir is soil, water or food Limit man’s exposure e.g. wearing of shoes against hookworm infection Boil or chlorinate water to destroy microbes Heat or cook food to destroy microbes and avoid eating contaminated food  d. disinfection Concurrent and terminal disinfection limits transmission of infections through destruction of the infectious agent present in discharges of patients or soiled articles  2. Interrupting the transmission pathway These include varied range of environmental intervention measures aimed at breaking the link between the reservoir or source of infectious agent and the susceptible host, e.g. - Vector control through alterations of the environment and the use of pesticides - Provision and use of safe and adequate excreta disposal facilities  2. Interrupting the transmission pathway cont, - 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  3. Protecting the susceptible host These are measures aimed at preventing the population from getting infection or in case infection occurs, to prevent the development of the disease. The measures are; i. Immunization against specific diseases e.g. - Active immunization (tetanus, measles, TB vaccines etc) - Passive immunization (anti-tetanus serum, 3. Protecting the susceptible host cont, ii. Use of chemoprophylaxis (drugs that prevent contacts from getting the diseases) e.g. use of SP to prevent malaria iii. 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  4. 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