Host-microbe Host-microbe

relationshipsrelationshipsDisease processesDisease processesEpidemiologyEpidemiologyNosocomial infectionsNosocomial infections

Introduction to Immunity

Host-Microbe Relationships

What do the following terms mean? Pathogen Host Symbiosis

Symbiosis includes: mutualism commensalism parasitism

Example of Mutualism: Bacteria on The Human Skin

Contamination, Infection, & Disease

Contamination: the presence of microbes

Infection: the multiplication of any parasitic organism in or on a host

Disease: a change in the state of health in which tissues/organs are disrupted or damaged.

Can be viewed as a sequence of increasing severity (contamination infection disease)

Pathogenicity vs. Virulence

Pathogenicity: the ability of an organism to cause disease

Virulence: the intensity (or degree) to which an organism causes disease

Microflora (Flora, Microbiota)Organisms that live on or in the body but under

normal circumstances do not cause disease

Types: Resident microflora

(normal flora): comprise microbes that are always present in or on the human body

Transient microflora: microbes that can be present under certain conditions in any of the locations where resident microflora are found

Opportunistic Organisms

Organisms that do not normally cause disease, but take advantage of particular opportunities to cause disease.

Immunocompromised individuals commonly become infected with opportunistic organisms

Kinds of Diseases

Human diseases are caused by infectious agents, structural or functional genetic defects, environmental factors, or any combination of these causes

Infectious Diseases: caused by infectious agents such as bacteria, viruses, fungi, protozoa, & helminths

Noninfectious Diseases: caused by any factor other than infectious organisms

Microbiology focuses on Infectious Diseases Communicable disease: a disease that can

be transmitted from one person to another What are examples of communicable microbial diseases?

Noncommunicable disease: a disease that cannot be transmitted from one person to anotherWhat are examples of noncommunicable microbial diseases?

Types of Infectious Diseases

Acute: develops rapidly & runs its course quickly (measles & cold)

Chronic: develops more slowly than an acute disease, is usually less severe, & persists for a long, indeterminate period (tuberculosis)

Subacute: intermediate between an acute & a chronic disease (gingivitis)

Latent: characterized by periods of inactivity either before signs & symptoms appear (herpes virus)

Stages of an Infectious Disease

Incubation period: time between infection & appearance of signs and symptoms

Prodromal phase: a short period of nonspecific, often mild, symptoms (malaise and headache)

Invasive phase: period when the individual experiences the typical signs & symptoms of the disease

Acme: period during invasive phase where

symptoms & signs are most severe Decline phase: the period of illness when host

defenses & effects of treatment overcome the pathogen

Convalescent period: tissues are repaired, healing takes place, & body regains strength & recovers

Stages of an Infectious Disease

Signs, Symptoms, & Syndromes

Most diseases are recognized by signs & symptoms

Sign: a characteristic of a disease that can be observed by examining the patient (e.g. swelling, redness, rashes, coughing, pus, runny nose, vomiting)

Symptom: a characteristic of a disease that can be observed or felt only by the patient (e.g. pain, shortness of breath, nausea, sore throat, headache)

Syndrome: a combination of signs & symptoms occurring together & are indicative of a particular disease or abnormal condition

Sequelae: even after recovery, some diseases leave after-effects (e.g. valve damage)

Epidemiology, Incidence & Prevelance

Epidemiology: the study of factors & mechanisms involved in the frequency & spread of diseases & health-related problems

Etiology: the assignment or study of causes and origins of a disease

Incidence of a disease: the number of new cases contracted within a set population during a specific period of time

Prevalence of a disease: the total number of people infected within the population at any time

Diseases in Populations

Endemic: disease is present continually in the population of a particular geographic area

Epidemic: a higher-than-normal incidence of a disease in a population

Pandemic: worldwide disease

The Spread of Cholera

Began in Peru in 1991

Moved to Columbia & Ecuador

Late 1992: epidemic spread to Venezuela, Bolivia, Chile, & Brazil in South America

Then to Guatemala, Honduras, Panama, Nicaragua, & El Salvador in Central America

Reservoirs of Infection

Reservoirs: Sites in which organisms can persist & maintain their ability to infect

Essential for new human infections to occur

1. Humans2. Other animals (including insects)3. Plants4. Certain nonliving material (water & soil)

Zoonoses: diseases that can be transmitted under natural conditions to humans from other vertebrate animals (rabies)

Modes of Disease Transmission- Contact Transmission

direct contactindirect contact (fomites)droplets

Modes of Disease Modes of Disease Transmission-Transmission-Vehicle transmissionwater

air food

Droplet Transmission

Modes of Disease Modes of Disease Transmission- Transmission- Vector transmission

mechanical biological

Controlling Disease Transmission

Isolation: A patient with a communicable disease is prevented from having contact with the general population

Quarantine: the separation of “healthy” human or animal carriers from the general population when they have been exposed to a communicable disease

Modes of Disease Transmission- Summary Contact Transmission

Can be direct, indirect, or by droplets Direct contact requires body contact between

individuals Indirect contact occurs through fomites Droplet: occurs when a person coughs, sneezes, or

speaks near othersVehicle Transmission

Nonliving carrier of an infectious agent from its reservoir to a susceptible host

Water Air Food

Vector-Borne Transmission Vectors: Living organisms that transmit disease to

humans Most vectors are arthropods: ticks, flies, fleas, lice

& mosquitoes

How Fungi & Protozoa Cause Disease

Fungi Spores that are inhaled or enter cells

through a cut or wound Some fungi produce mycotoxins

Protozoa invade & reproduce in red blood cells attach to tissues & digest them Produce cysts (dormant forms) as a

means of disease transmission & trophozoites (active, multiplying forms)

Factors Affecting Disease Establishment

Portal of Entry Adhesive Factors Dose Tissue Penetration Enzymes Toxins

Toxins, enzymes, & adhesive factors are sometimes referred to as virulence factors

Portal of Entry Site of entry of microbes

Includes skin, mucous membranes, openings of the respiratory, digestive, & genitourinary systems, & crossing the placenta

May involve adhesive factors, also known as adhesins (include certain surface proteins/ glycoproteins, fimbriae, & capsules)

Portals of Exit

sites where microbes leave the body

Dose

The number of infective particles required to lead to colonization

Colonization refers to the growth & reproduction of microorganisms on host tissues

Exposure to a low dose can result in immunity

Tissue Penetration The ability of a microbe to enter host

tissue

Visible in tissue preparation

Not required for every disease

The ability of a microbe to invade tissue & damage it is known as its invasiveness

EnzymesCoagulaseStreptokinaseHyaluronidaseHemolysinsLeukocidin Collagenase

Coagulase: clots fibrin in blood plasma. Bacteria form a fibrin clot around themselves protecting them the host’s immune system (S. aureus)

Streptokinase: dissolves fibrin clots (Streptococcus)

EnzymesEnzymes

Hyaluronidase: enzyme digests hyaluronic acid

Enzymes

Hemolysins: enzymes that breakdown red blood cells (RBCs)

3 Types of hemolysis: 1- Gamma hemolyis: no breakdown of RBCs 2- Alpha (): partial breakdown of RBCs; greenish-grey coloration

3- Beta or complete hemolysis ( ): complete breakdown of RBCs; clear zones around colonies

Alpha Beta

Streptococcus pneumoniae Streptococcus pyogenes

EnzymesEnzymes

Enzymes Collagenase: enzyme that degrades

collagen (Clostridium)

Leukocidin: enzyme that degrades white blood cells

Bacterial Toxins

A substance that is poisonous to another organism

Two types:1. Exotoxin: a toxin produced by a cell

& is secreted outside the cell to affect host tissue

2. Endotoxin: a toxin that is a portion of the cell (usually the cell wall) & is released into host tissuesCharacteristic of Gram negative bacteria

Nosocomial InfectionsNosocomial Infections: an infection n infection acquired in a hospital or other acquired in a hospital or other medical facilitymedical facility

Where do the bacteria causing nosocomial infections come from?

Common Causative Agents of Nosocomial Infections

Some Common Modes of Transmission of Nosocomial Infections

Relative Frequencies of Sites of Nosocomial Infections

1.Latex gloves

2.Eye protection

3.Mask

4.Sterile Equipment

Infection Control