INFECTIOUS DISEASE 1 Bacteria viruses protozoans fungi and

INFECTIOUS DISEASE 1

Bacteria, viruses, protozoans, fungi, and other parasites called pathogens are capable of causing a change that disrupts the homeostasis in the body 2

Any disease caused by the presence of pathogens in the body is called an infectious disease. The main sources of pathogens are soil, contaminated water, and infected animals, ………. . 3

Not all microorganisms are pathogenic; your body is host to billions of microorganisms, most of which are bacteria. These microorganisms have a symbiotic relationship with your body helping to keep harmful bacteria and other microorganisms from growing. 4

If beneficial organisms are eliminated from your body, pathogens can establish themselves and cause infectious disease. In addition, if beneficial organisms enter areas of the body where they are not normally found, these formerly harmless organisms can become potential pathogens 5

SYMBIOTIC RELATIONSHIPS Symbiosis means “to live together” Describes the relationship between microorganisms and their host commensalism is a class of relationships between two organisms where one organism benefits without affecting the other. It can be compared with mutualism, in which both organisms benefit and parasitism, where one benefits while the other is harmed 6

TRANSMISSION OF DISEASE Pathogens can be transmitted to a host from a reservoir by four main ways. 1. By direct contact; exchange of body fluid. 2. By an object; people handle contaminate objects then touch face, nose, eyes, etc… 3. Through the air; person coughs or sneezes spreading droplets which are then inhaled 4. By a vector; insects such as mosquitos, ticks spread pathogens between hosts or reservoirs 7

PORTALS OF ENTRY Sites through which pathogens enter the body Four major types Skin Mucous membranes Placenta Parenteral route 8

MANIFESTATIONS OF DISEASE Symptoms – subjective characteristics of disease felt only by the patient Signs – objective manifestations of disease that can be observed or measured by others Syndrome – group of symptoms and signs that characterize a disease or abnormal condition Asymptomatic, or subclinical, infections lack symptoms but may still have signs of infection 9

VIRULENCE FACTORS OF INFECTIOUS DISEASE Pathogenicity – ability of a microorganism to cause disease Virulence – degree of pathogenicity Virulence factors contribute to an organisms virulence Adhesion factors Biofilms Extracellular enzymes Toxins Antiphagocytic factors 10

Adhesion factors • The majority of bacterial pathogens exploit specific adhesion to host cells as their main virulence factor. • A large number of bacterial adhesins with individual receptor specificities have been identified. • Many bacterial pathogens are able to express an array of different adhesins. • Expression of these adhesins at different phases during infection play the most important role in adhesion based virulence. 11

Biofilms form when bacteria adhere to surfaces in some form of watery environment and begin to excrete a slimy, gluelike substance that can stick to all kinds of materials–metals, plastics, soil particles, medical implant materials, biological tissues. Biofilms can be formed by a single bacterial species, but biofilms more often consist of many species of bacteria, as well as fungi, algae, protozoa, debris, and corrosion products. Essentially, a biofilm may form on any surface exposed to bacteria and some amount of water. Dental plaque is a yellowish biofilm that builds up on the teeth. 12

EXTRACELLULAR ENZYMES Enzymes secreted by the pathogen Dissolve structural chemicals in the body Help pathogen maintain infection, invade further, and avoid body defenses 13

TOXINS Chemicals that harm tissues or trigger host immune responses that cause damage Toxemia refers to toxins in the bloodstream that are carried beyond the site of infection Two types Exotoxins Endotoxins 14

ANTIPHAGOCYTIC FACTORS Certain factors prevent phagocytosis by the host’s phagocytic cells Bacterial capsule Often composed of chemicals found in the body and not recognized as foreign Can be slippery making it difficult for phagocytes to engulf the bacteria Antiphagocytic chemicals Some prevent fusion of lysosome and phagocytic vesicles 15 Leukocidins directly destroy phagocytic white blood cells

THE STAGES OF INFECTIOUS DISEASE Following infection, sequence of events called the disease process occurs Many infectious diseases have five stages following infection. (Not all diseases have all five stages) Incubation period Prodromal period Illness Decline 16 Convalescence

RESERVOIRS OF INFECTION Most pathogens cannot survive long outside of their host Sites where pathogens are maintained as a source of infection are termed reservoirs of infection Three types of reservoirs Animal reservoir Human carriers Nonliving reservoir 17

ANIMAL RESERVOIRS Zoonoses – diseases that are naturally spread from their usual animal host to humans Acquire zoonoses through various routes Direct contact with animal or its waste Eating animals Bloodsucking arthropods Humans are usually dead end host to zoonotic pathogens 18

Disease a pattern of response by a living organism to some form of invasion by a foreign substance or injury which causes an alteration of the organisms normal functioning also – an abnormal state in which the body is not capable of responding to or carrying on its normally required functions Pathogens organisms or substances such as bacteria, viruses, or parasites that are capable of producing diseases Pathogenic means disease causing or producing Pathogenicity describes the potential ability and strength of a pathogenic substance to cause disease Pathogenesis the development, production, or process of generating a disease 19

Endemic/Enzootic: the ongoing, usual level of, or constant presence of a disease in a given population Hyperendemic: persistent level of activity beyond or above the expected prevalence Holoendemic: a disease that is highly prevalent in a population and is commonly acquired early in life in most all of the children of the population 20

Epidemic/Epizootic : outbreak or occurrence of one specific disease from a single source, in a group population, community, or geographical area, in excess of the usual level of expectancy Pandemic/Panzootic: epidemic that is widespread across a country, continent, or large populace, possible worldwide Incidence: is a measure of the risk of developing some new condition within a specified period of time. Although sometimes loosely expressed simply as the number of new cases during some time period. Incidence proportion : (also known as cumulative incidence) is the number of new cases within a specified time period divided by the size of the population initially at risk. For example, if a population initially contains 1, 000 non-diseased persons and 28 develop a condition over two years of observation, the incidence proportion is 28 cases per 1, 000 persons, i. e. 2. 8% 21

Prevalence: the number of people within a population who have a certain disease at a given point in time Point prevalence: how many cases of a disease exist in a group of people at that moment. prevalence relies on 2 factors: How many people have had the disease in the past Duration of the disease in the population The difference between prevalence and incidence can be summarized thus: prevalence answers "How many animals have this disease right now ((old and new))? " and incidence answers "How many animals per year newly acquire this disease? ". 22

Contagious disease is a disease that is passed from one animals to another either by direct contact or through an object that the infected person has touched. Some examples of this type of diseases are measles and chicken poxwhich can quickly pass on to one person to another. This is why it is seen that if a person catches chicken pox, some more members of his family also fall prey to this disease if they do not take precaution. Non contagious diseases that are not able to be spread from animals to animals. Genetic diseases, cancers, mental disorders, autoimmune diseases and heart disease are some of the many diseases 23 that aren't contagious

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Infectious Diseases and the Process of Infection: the growth/multiplication of a microbe in a host • Infection does not always result in injury of the host (disease) • Two main classes of infection by site: – localized – generalized (disseminated; systemic) 25

Localized Infections • Organism enters the body and reaches target site of infection • Organism adheres to or enters host cells and multiplies at site of infection • Infection spreads within the site (e. g. , respiratory tract; intestines) • Symptoms of illness appear • Organism does not spread through the lymphatic system or reach the bloodstream • Infection subsides due to host defenses (e. g. , immunity) • Agent eliminated from the body; infected cells replaced; "cure" 26

Generalized Infections • Organism enters the body and reaches target site of initial infection • Organism adheres to or enters host cells and multiplies at initial site of infection • Infection spreads within site and to other sites via tissues, lymphatic system, bloodstream (bacteremia, viremia, etc. ) and possibly other routes • Symptoms of illness may appear • Organisms infect other organs, tissues and cells; more spread via bloodstream • Symptoms of illness become severe • Host defenses eliminate organisms leading to cure or disease continues, possibly leading to irreversible damage or death 27

Outcomes of Infection Microbes differ in their ability to produce the different outcomes of infection: (i) infection without illness; (ii) infection with illness; (with or without long-term sequelae) (iii) infection, illness and then death 28