2 Lec - infectious process .ppt

ILOs By the end of this lecture, you should be able to: •Understand Infectious Disease Process. •Understand Dynamics of Infectious Disease Transmission. Infection • The entry and development or multiplication of an infectious agent in an organism, including the body of man or animals • Body respo...

ILOs By the end of this lecture, you should be able to: •Understand Infectious Disease Process. •Understand Dynamics of Infectious Disease Transmission. Infection • The entry and development or multiplication of an infectious agent in an organism, including the body of man or animals • Body responds in form of Immune response or disease • An infection does not always cause illness Infectious disease • A disease due an infectious agent • Contagious or non-contagious Communicable disease Definition 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, vector or the inanimate environment. Dynamics of infectious diseases Introducti on Infectious Agent Reservoir Portal of exit Mode of Transmiss ion Incubatio n Period Period of Communicabi lity Susceptibi lity & Resistance Disease transmission takes place through the interaction of the following:  Infectious agent  Reservoir  Portal of entry and exit  Modes of Transmission  Incubation Period  Period of Communicability Dynamics of infectious diseases Introducti on Infectious agent Infectious Agent Protozoa (Plasmodi um species) Reservoir Portal of exit Viruses Mode of Transmiss ion Incubatio n Period Period of Communicabi lity Susceptibi lity & Resistance Metazo a (filaria) Infectious agent Rickettsi ae Fungi Bacteria and their toxins Dynamics of infectious diseases Introducti on Infectious Agent Reservoir It is the natural habitat in which the organism survives and multiplies and is completely dependent upon for survival. Reservoir There are three reservoirs for infectious agents: Portal of exit Mode of Transmiss ion Incubatio n Period Period of Communicabi lity Susceptibi lity & Resistance Source of infection • Source of infection: The person, animal, object, or substance from which an infectious agent passes or is disseminated to the host • Reservoir is defined as “ any person, animal, arthropod, plant, soil or substance, in which an infectious agent lives and multiplies on which it depends primarily for survival and where it reproduces itself in such a manner that it can be transmitted to a susceptible host • Not always synonymous Dynamics of infectious diseases Introducti on Infectious Agent Reservoir Portal of exit Mode of Transmiss ion Incubatio n Period Period of Communicabi lity Susceptibi lity & Resistance 1. Human Reservoir: Certain infectious agents can only live and multiply inside the human body (examples include Smallpox virus, Poliovirus and S. typhi and paratyphi). The human reservoir may be a case or carrier. Dynamics of infectious diseases Introducti on Carriers are classified according to: Infectious Agent Reservoir Portal of exit Mode of Transmiss ion Incubatio n Period Period of Communicabi lity Susceptibi lity & Resistance Carrie r Dynamics of infectious diseases Introducti on Infectious Agent Reservoir Portal of exit Mode of Transmiss ion Incubatio n Period Period of Communicabi lity Susceptibi lity & Resistance I. Carrier Classification by Type: Dynamics of infectious diseases Introducti on Infectious Agent Reservoir Portal of exit Mode of Transmiss ion Incubatio n Period Period of Communicabi lity Susceptibi lity & Resistance II. Carrier Classification by Duration: Incubation Period Animal reservoir: • Zoonoses: refers to an infectious disease that is transmissible under natural conditions from vertebrate animals to humans. Environmental Reservoir • Soil, plants & water Dynamics of infectious diseases Introducti on Infectious Agent Reservoir Portal of exit Mode of Transmiss ion Incubatio n Period Period of Communicabi lity Susceptibi lity & Resistance Epidemiological importance of carriers as a source of infection: 1) 2) 3) 4) 5) 6) They are not recognized to people or even themselves. They move freely in the community. Their number may be greater than cases. Infectivity may persist for a long time (years). The diagnosis needs laboratory investigations. The danger of carrier in some occupations dealing with community members, e.g., food-handlers, nurses, teachers ticket collectors. Portal of entry • • • • Respiratory tract Alimentary tract Genitourinary tract Skin • • The portal of entry refers to the manner in which a pathogen enters a susceptible host. The portal of entry must provide access to tissues in which the pathogen can multiply or a toxin can act. Often, infectious agents use the same portal to enter a new host that they used to exit the source host. For example, influenza virus exits the respiratory tract of the source host and enters the respiratory tract of the new host. In contrast, many pathogens that cause gastroenteritis follow a so-called “fecal-oral” route because they exit the source host in feces, are carried on inadequately washed hands to a vehicle such as food, water, or utensil, and enter a new host through the mouth. Other portals of entry include the skin (hookworm), mucous membranes (syphilis), and blood (hepatitis B, human immunodeficiency virus). Dynamics of infectious diseases Introducti on Infectious Agent Reservoir Portal of exit Mode of Transmiss ion Incubatio n Period Period of Communicabi lity Susceptibi lity & Resistance Portal of Exit Portal of exit of the infectious agent from the reservoir may be: • Portal of exit is the path by which a pathogen leaves its host. The portal of exit usually corresponds to the site where the pathogen is localized. • For example, influenza viruses and Mycobacterium tuberculosis exit the respiratory tract, schistosomes through urine, cholera vibrios in feces, Sarcoptes scabiei in scabies skin lesions, and enterovirus 70, a cause of hemorrhagic conjunctivitis, in conjunctival secretions. • Some bloodborne agents can exit by crossing the placenta from mother to fetus (rubella, syphilis, toxoplasmosis), while others exit through cuts or needles in the skin (hepatitis B) or blood-sucking arthropods (malaria). Dynamics of infectious diseases Introducti on Mode of Transmission Infectious Agent It is the route through which infectious agent is transmitted to the host. Reservoir Portal of exit Mode of Transmiss ion Incubatio n Period Period of Communicabi lity Susceptibi lity & Resistance Modes of Transmission Dynamics of infectious diseases Classification of Modes of Transmission: It may be classified into direct and indirect transmissio Infectious Introducti on Agent Reservoir Portal of exit Mode of Transmiss ion Incubatio n Period Period of Communicabi lity Susceptibi lity & Resistance • • • In direct transmission, an infectious agent is transferred from a reservoir to a susceptible host by direct contact or droplet spread. Direct contact occurs through skin-to-skin contact, kissing, and sexual intercourse. Direct contact also refers to contact with soil or vegetation harboring infectious organisms. Thus, infectious mononucleosis (“kissing disease”) and gonorrhea are spread from person to person by direct contact. Hookworm is spread by direct contact with contaminated soil. Droplet spread refers to spray with relatively large, short-range aerosols produced by sneezing, coughing, or even talking. Droplet spread is classified as direct because transmission is by direct spray over a few feet, before the droplets fall to the ground. Pertussis and meningococcal infection are examples of diseases transmitted from an infectious patient to a susceptible host by droplet spread. Dynamics of infectious diseases Classification of Modes of Transmission: Introducti on Infectious Agent Reservoir Portal of exit Mode of Transmiss ion Incubatio n Period Period of Communicabi lity Susceptibi lity & Resistance • Indirect transmission refers to the transfer of an infectious agent from a reservoir to a host by suspended air particles, inanimate objects (vehicles), or animate intermediaries (vectors). • Airborne transmission occurs when infectious agents are carried by dust or droplet nuclei suspended in air. Airborne dust includes material that has settled on surfaces and become resuspended by air currents as well as infectious particles blown from the soil by the wind. Droplet nuclei are dried residue of less than 5 microns in size. In contrast to droplets that fall to the ground within a few feet, droplet nuclei may remain suspended in the air for long periods of time and may be blown over great distances. Measles, for example, has occurred in children who came into a physician’s office after a child with measles had left, because the measles virus remained suspended in the air. • • Vehicles that may indirectly transmit an infectious agent include food, water, biologic products (blood), and fomites (inanimate objects such as handkerchiefs, bedding, or surgical scalpels). A vehicle may passively carry a pathogen — as food or water may carry hepatitis A virus. Alternatively, the vehicle may provide an environment in which the agent grows, multiplies, or produces toxin — as improperly canned foods provide an environment that supports production of botulinum toxin by Clostridium botulinum. Vectors such as mosquitoes, fleas, and ticks may carry an infectious agent through purely mechanical means or may support growth or changes in the agent. Examples of mechanical transmission are flies carrying Shigella on their appendages and fleas carrying Yersinia pestis, the causative agent of plague, in their gut. In contrast, in biologic transmission, the causative agent of malaria or guinea worm disease undergoes maturation in an intermediate host before it can be transmitted to humans Dynamics of infectious diseases Introducti on Infectious Agent Reservoir Incubation Period It is the time interval between invasion by an infectious agent and appearance of the first sign or symptom of the disease. Portal of exit Mode of Transmiss ion Incubatio n Period Period of Communicabi lity Susceptibi lity & Resistance Exposu re Appearance of symptoms /signs Dynamics of infectious diseases Introducti on Infectious Agent Reservoir Portal of exit Mode of Transmiss ion Incubatio n Period Period of Communicabi lity Susceptibi lity & Resistance The length of the Incubation Period: It is characteristic of each disease. There is a minimum incubation period for every disease before which no illness can occur. It varies from one person to another with the same disease as it depends on Level of the immunity of the host, the microbial load introduced into the host, the virulence of the microorganism Latent period • Non infectious diseases • Period from disease initiation to disease detection Dynamics of infectious diseases Introducti on Infectious Agent Reservoir Portal of exit Mode of Transmiss ion Incubatio n Period Period of Communicabi lity Susceptibi lity & Resistance Epidemiological importance of incubation period 1-Preventive measures Carried out during the incubation period to prevent occurrence of the disease or at least ameliorate its severity: Dynamics of infectious diseases Introducti on Infectious Agent Reservoir Portal of exit Mode of Transmiss ion Incubatio n Period Period of Communicabi lity Susceptibi lity & Resistance Epidemiological importance of incubation period (cont.) 2- Measures for contacts: by •Surveillance disease. of contact with communicable • List & Supervision: Observation for the longest incubation period to detect the disease as early as possible, treatment can be started in a suitable time before complications start. Dynamics of infectious diseases Introducti on Epidemiological importance of incubation period (cont.) Infectious Agent Reservoir Portal of exit Mode of Transmiss ion Incubatio n Period Period of Communicabi lity Susceptibi lity & Resistance 3-Qurantinable Measures: • In Qurantinable diseases (cholera, Yellow Fever, plague) having a valid certificate of immunization or else he is put in the quarantine till the end of the international incubation period, provided that no signs or symptoms of the disease appeared through out the isolation period. Dynamics of infectious diseases Introducti on Infectious Agent Reservoir Portal of exit Mode of Transmiss ion Incubatio n Period Period of Communicabi lity Susceptibi lity & Resistance Epidemiological importance of incubation period (cont.) 4-Diagnostic Measures Tracing the source of infection and contacts especially for diseases with a short incubation period as in the case of food poisoning. Dynamics of infectious diseases Introducti on Infectious Agent Reservoir Portal of exit Mode of Transmiss ion Epidemiological importance of incubation period (cont.) 5- Prognostic measures: • By Estimating the prognosis of a disease. In some diseases as tetanus and rabies, the shorter the incubation period, the worse the prognosis of the disease Long IP Incubatio n Period Period of Communicabi lity Susceptibi lity & Resistance Intermediate IP Short IP Dynamics of infectious diseases Introducti on Period of Communicability Infectious Agent • • Reservoir Portal of exit Mode of Transmiss ion Incubatio n Period Period of Communicabi lity Susceptibi lity & Resistance It is the time during which an infectious agent may be transferred directly or indirectly from an infected person to another person. It might include part of the incubation period, the whole disease and /or convalescence Example: Period of Communicability of Mumps = 21 days Dynamics of infectious diseases Introducti on Importance of Period of communicability: Infectious Agent • Preventive measures may be taken during this period to prevent transmission of disease through:  Isolation of the patient during the period of communicability eg. Measles( 4days before onset of rash and 4 days after appearance of rash).  Disinfection of secretion and excreta of the patient during the period of communicability. Reservoir Portal of exit Mode of Transmiss ion Incubatio n Period Period of Communicabi lity Susceptibi lity & Resistance Dynamics of infectious diseases Introducti on Infectious Agent Reservoir Portal of exit Mode of Transmiss ion Incubatio n Period Period of Communicabi lity Susceptibi lity & Resistance Susceptibility & resistance • Some factors that increase Susceptibility to infections: Dynamics of infectious diseases/ Summary Introducti on Infectious Agent Reservoir Portal of exit Mode of Transmiss ion Incubatio n Period Period of Communicabi lity Susceptibi lity & Resistance Summary Disease transmission is affected by many factors that interact all together and influence the onset of disease, incubation period and communicability of disease. ILOs By the end of this lecture, you should be able to: •Identify methods of control of infectious diseases •Understand different control measures subjected to cases of infectious diseases •Understand different control measures subjected to contacts of cases of infectious diseases •Understand different control measures subjected to the environment where cases of infectious diseases live. Control of Infectious Diseases Introducti on Measures for Cases Measures for Controls Measures for Environme nt Introduction Definition •Measures taken for an existing disease, to limit spread of infection and its sequelae. Methods of control: •Infectious diseases are the result of interactions between factors related to the host, the etiologic agent, and the environment. Methods of control attempt to modify these factors and so depend on the epidemiology of each disease. Control of Infectious Diseases Introducti on Measures for Cases Measures for Controls Measures for Environme nt Control measures They include measures taken for case, contacts, and environment. Control of Infectious Diseases Introducti on Measures for Cases Measures for Controls Measures for Environme nt Control measures for Cases Control of Infectious Diseases Introducti on Measures for Cases Measures for Controls Measures for Environme nt a) Case finding • by screening, surveillance, periodical medical examination, pre-employment examination. Control of Infectious Diseases Introducti on b) Notification of cases: Measures for Cases • Sanitary regulations enforce The notification of infectious cases, to the local health office within 24 hours of their recognition (within 12 hours only for cholera and plague). Measures for Controls Measures for Environme nt • Value of notification: 1. To take the necessary preventive and control measures. 2. To help tracing the source of infection in outbreaks. 3. To get significant statistical data. Control of Infectious Diseases Introducti on Measures for Cases Measures for Controls Measures for Environme nt c) Isolation of cases Infectious diseases Section I: cholera, plague, typhus, relapsing fever, anthrax, yellow fever, and smallpox . Place of isolation should be isolated in a special place, whether an infectious disease hospital or a sanitary cordon . Section II Cerebrospinal can be isolated at home fever, typhoid ,paratyphoid, undulant fever, psittacosis, infective hepatitis, acute encephalitis,meningitis,T B, scarlet fever, D and poliomyelitis . after approval of the health authorities when sanitary requirements are fulfilled; otherwise the cases should isolated at hospital . Control of Infectious Diseases Introducti on c) Isolation of cases (Cont.) Measures for Cases Infectious diseases Place of isolation Measures for Controls Measures Section III: measles, are free to choose the for Environme nt place of isolation. German measles, whooping cough, mumps, chickenpox, influenza, acute pneumonia, puerperal fever, erysipelas, tetanus, bacterial food poisoning, amoebic and bacillary dysentery’s, dengue, malaria and filariasis . Control of Infectious Diseases Introducti on Types of Disinfection Measures for Cases Concurrent disinfection: Measures for Controls Measures During the course of illness,. It consists of disinfection of urine, faeces, vomit, contaminated linen, clothes, dressings, aprons… for Environme nt Terminal disinfection: It is application of disinfective measures after the patient has been removed by death or cure. Control of Infectious Diseases Introducti on Measures for Cases Measures for Controls Measures for Environme nt Measures taken for Contacts Control of Infectious Diseases Introducti on Measures for Cases Measures for Controls Measures for Environme nt Measures taken for Environment Control of Infectious Diseases/ Summary Introducti on Measures for Cases Measures for Controls Measures for Environme nt Summary Measures to control of infectious diseases transmission include: Control of Infectious Diseases/ Summary Introducti on Measures for Cases Measures for Controls Measures for Environme nt