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Two types of diseases


infectious disease ( is an interplay or a war btwn parasite and host) invasion or colonization of the body by pathogenic microbes


Four types of infectious agents

fungi, parasites, bacteria and viruses


Routes of infectious disease transmission

Direct transmission

vertically, parent to offspring genetically or by passing infection from mother to child

horizontal, transferred to other members of the same or different species through non hereditary means


disease can be indirectly tranferred

Vector, alive and transfer a disease

vehicles, transferred through food or water

fomites, non living object that transfer disease


Parasite Relationship

-live in symbiotic relationship (two organisms living together


Symbiotic relationship

-mutualism, both species benefit in interaction

-commensalism, one species benefits and another don't gain or harmed

-parasitism, one species benefits and another is harmed



- specific; sense of certain microbes - protozoans, worms flukes- infect our bodies

-General; sense of host-parasite relationship- microbes are parasites when they cause disease


Parasite effect on host

-Colonization, microbe is present and multiplying at a mucosal surface and is negligible -Infection, multiplication on the microbe in the host, no substantial effect on the host -Disease, microbe is present and multiplying with clear adverse effect on the host


Parasites pathogenicity (ability to cause disease)

Kinds of pathogens

-Frank pathogen/primary, when present always cause disease

-Opportunistic pathogens, causes disease in certain hosts or under certain conditions

-nonpathogenic, not associated with disease


Routes or entry for invading pathogens

Skin, Mucous membranes, Placenta, Parenteral route


classifying infectious disease

-symptoms, changes in body function

-Signs, changes or measure an observer can observe

-syndrome, group of symptoms or signs

-communicable disease, easily spread from person to another

-non communicable disease, not spread from host to another


" Frequency of occurrence

-Incidence, number of pple in population who develop a disease during a particular time period

-prevalence, number of pple in a population who develop a disease at a spcecifed time regardless of when it appeared

-Sporadic disease-occurs only occasionally

-endemic disease- always present in population

-epidemic disease - many pple within population develop disease in a short time

-Pandemic disease - an epidemic that occurs world wide


classifying infectious diseases by severity and duration

-Acute disease - develops rapidly but last only short time

-Chronic disease - develops slowly and the body reactions may be less severe; long lasting

-Subacute disease - intermediate btwn acute and chronic

-Latent disease, causative agent remains inactive for some time but then becomes active to produce symptoms


" by how they damage the host

-local infection, invading microbes are limited to a small area of the body

-Systemic/generalized infection, microbes or their products are spread throughout the body by the blood or lymph

-Focal infection, agents of a local infection enter blood and spread to other parts of body where they remain confined

- Sepsis, toxic inflammatory condition

-Septicemia, multiplication of pathogens in blood

***bacteremia-bacteria in blood, Toxemia-toxins in blood, Viremia-viuses in blood

-Primary infection, acute infection that causes initial illness

-Secondary infection, caused by opportunistic pathogen after immune system weakened


Stages of a Disease

-Incubation period, interval btwn initial infection and the first appearance of any signs or symptoms

-Prodromal period, short period of mild symptoms

-Period of illness, disease if most severe and person exhibits overt signs and symptoms (patient dies)

-Period of decline, signs and symptoms subside

-Period of convalescence, person regains strength and body returns to its pre-diseased state

-Capable of transmitting disease during all stages


Reservoirs of infection

Types of Common Reservoirs

-living or inanimate object that provides a pathogen with adequate conditions for survival and multiplication and an opportunity for transmission

1, Human-transmit pathogen without any signs or illness

2, Animal-zoonoses, occur primarily in animals and transmit to humans

3, Non-living, soil harbors fungi, water harbors salmonella


Nosocomial Infections

- acquired in the hospital, result in the microbes in the hospital, most common Staphlococcus, E coli, most common sites of infections - urinary tract>surgicalwounds>respiratory


Emerging Infectious Diseases

- Changing diseases, showing an increase in incidence in the recent past or potential to increase in the near future like anthrax, whooping cough, hepatitis, ebola, lyme disease, antibiotic resistant pneumonia, west nile virus