Chapter 6:Microbe-Human Interactions:

Infection and Disease

Lecturer: Eng. Mohamed Ali, B.s.c & M. Eng.

College of Agriculture, University of Hargeisa.Course: Microbiology

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Chapter 6 Contents:1. Normal Microflora

2. Progress of Infectiona) Pathogenicity

b) Portals of entry

c) Mode of Transmission

d) Process of infections and disease

e) Portals of exit

3. Disease Prevention: Hygiene

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1- NORMAL MCIR0FLORA

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Human Host (normal flora)

- Human body constant contact with microbe, some invade & multiply in body

- wide range of microbe can inhabit our body

- What is normal flora?- Microbes that inhabit in our body but do not

harm the host

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Normal Flora

• microbes that are normally found on or in the human body without causing disease.

• internal organs & tissues & fluids are microbe-free (no flora microbes available in our sterile part of our the body- eig internal organs).

• Normal Flora is harmful if they reached the sterile part of our body e-g internal organs

• Bacterial flora benefit host by preventing overgrowth of harmful microbes

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Resident Flora

• Bacterial flora benefit host by preventing overgrowth of harmful microbes – microbial antagonism

• Endogenous infections – occur when normal flora is introduced to a site that was previously sterile, and it cause disease.

• Pathogen: Microorganism capable cause a disease.

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normal flora

• Beneficial outcome– Removed by immune system– Microbial antagonism

• Adverse effects– Escape immune system– Multiply and disrupt sterile tissue– Cause a disease to internal organs

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The benefits and adverse effects of microbial contact.

Association between microbes and humans.10

2-Progress of infection: Major Factors in the Development of an Infection

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Progress of an Infection:

a) Pathogenicity

b) Portals of entry

c) Mode of Transmission

d) Process of infections and disease

e) Portals of exit

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a) Pathogenicity

Pathogenicity: Ability of microbes to cause infection

Virulence : degree to which microbe can invade and damage host tissue

Two types of virulence:

• True pathogens

• Opportunistic pathogens

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True or opportunistic pathogen• True pathogen: Cause disease in healthy

individuals

• Associated with a specific and recognizable disease. E-g – Influenza virus, plague bacillus, malarial

protozoan

• Opportunistic Pathogen:

• Cause disease in immune compromised host

• Gain access (injury) to sterile regions 14

Factors that predispose a person to infections.

Factors that weaken host defenses and increase susceptibility to infections15

b) Portals of entry

• Microbes enter in body by various transmission methods

• Most pathogens have specific portals on entry1) Skin2) Gastrointestinal tract3) Respiratory tract4) Urogenital 5) Placenta

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Skin

• example: mosquito bite skin and cause Malaria

• enters body through bite skin

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Gastrointestinal tract

• Salmonella, Shigella, Vibrio

• Viruses – polio, hepatitis A

• Protozoan – Giardia lamblia

• Enter via ingestion or the anal route

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Respiratory tract

• Streptococcus pneumoniae– Sore throat, meningitis

• Fungi – Cryptococcus– pneumonia

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Urogenital

• Numerous sexual transmitted diseases (STDs)• Virus – human papillomavirus

– Genital warts

• Protozoan – Trichomonas– trichomoniasis

• Bacteria – Neisseriagonorrhoeae– Gonorrhea

• Acquire by intercourse or intimate contact

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Common STDs which include viruses, protozoan, fungi, and bacteria.

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Placenta

• Some bacteria can penetrate the placenta barrier– Syphilis spirochete

• Birth canal – Herpes simplex virus

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A fetus can acquire an infection from the mother via transplacental infections.

Transplacental infection of the fetus.23

1) Contact Transmission

a) Direct Contact Transmission Person to person transmission. No intermediate

object is involved. Examples: Touching, kissing.

a) Indirect Contact Transmission Agent is transferred via a nonliving object. Examples: towels, eating utensils, thermometers,

stethoscopes, bedding, clothes, money, and syringes.

a) Droplet Transmission Microbes are spread in mucus droplets that

travel short distance (less than 1 meter). Examples: sneezing, coughing, talking and

laughing.

C) Mode of Transmission

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2) Vehicle Transmission: Transmission of disease via

medium such as water, food, air, blood, body fluids, and intravenous fluids.

a) Waterborne Transmission Usually caused by water

contaminated with sewage.

a) Airborne Transmission Spread of agents by droplets in

dust that travel more than 1m to host

Mode of Transmission

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3) Vector Transmission Animals that carry disease from one host to another,

Arthropods (insects) are most important animal vectors.

a) Mechanical Transmission Passive transport of pathogens on insect’s body. For

example, Bee

a) Biological Transmission Pathogen spends part of its life cycle in the vector. For

example, Mosquito

Mode of Transmission

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A mosquito is a biological vector and the common house fly is a mechanical vector.

Two types of vectors.28

D) The Process of Infection & Disease

• 4 distinct stages of clinical infections:– Incubation period – time from initial contact with the

infectious agent to the appearance of first symptoms; agent is multiplying but damage is insufficient to cause symptoms; several hours to several years

– Prodromal stage – vague feelings of discomfort; nonspecific complaints

– Period of invasion – multiplies at high levels, becomes well-established; more specific signs and symptoms

– Convalescent period – as person begins to respond to the infection, symptoms decline

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Process of infections and disease

1- Establishment:

Patterns of infection

2-Signs and symptoms:

Earliest symptoms of disease as a result of the activation of the body defenses

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Infection are classified by

a. Whether they remain at the site of inoculation (localized infection, systemic infection, focal infection)

b. Number of microbes involved in infection and the order in which they infect the body (mixed infection, primary infection, secondary infection)

c. Persistence of the infection (acute infection, chronic infection, subacute infection)

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A) Patterns of infection: • Localized infection – microbes enter the body and

remains confined to a specific tissue e-g boil• Systemic infection – infection spreads to several

sites and tissue fluids usually in the bloodstream e-g influenza

• Focal infection – when infectious agent breaks loose from a local infection and is carried to other tissues

B) Number of microbes involved:• Mixed microbe: several microbes grow

simultaneously at the infection site • Primary and secondary: initial and another infection

Establishment

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Establishment of infections vary depending on location, type of microbe, and length of time.

The occurrence of infections with regard to location, type of microbe and length of time.

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• Sign of infection refer to the objective evidence of infection

• Symptom of the infection refer to subjective evidence– Inflammation – fever, pain, soreness, swelling

• Syndrome is a disease that manifests as a predictable complex of symptom

• After the initial infection pathogens may remain in the body in a latent state and may later cause recurrent infections

• Microbes are release from the body through a specific portal of exit that allows them access to another host

Signs and symptoms

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Some commons signs and symptoms associated with infectious diseases.

Common signs and symptoms of infectious diseases37

E) Portal of exit

• Enables pathogen to spread to other hosts– Respiratory– Salivary– Skin

– Fecal

– Urogenital

– Blood

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Site at which microbes leave body. Most common Site at which microbes leave body. Most common exit portals are respiratory and gastrointestinal tracts.exit portals are respiratory and gastrointestinal tracts.

a) Respiratory Tract (Saliva): – Exit in discharges (mucus droplets) from nose and mouth.

Transmission by coughing, sneezing, spitting, etc.– Examples: Tuberculosis, influenza etc.

a) Gastrointestinal Tract (fecal): – Exit in feces or sliva.– Feces: Cholera, typhoid fever, salmonella.– Saliva: Rabies virus, herpes simplex 1.

Portal of Exit

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c) Urogenital Tract– Exit in secretions of urine

c) Skin and Wound infections– Spread through direct contact or through fomites.

c) Blood– Transmission through insects, needles, and syringes.

• Insects: Malaria, yellow fever etc.• Needles: AIDS and Hepatitis B.

Portal of Exit

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Representation of the different portals of exit.

Major portals of exit of infectious diseases.41

• Hygiene refers to conditions and practices that help to maintain health and prevent the spread of diseases. Medical hygiene therefore includes a specific set of practices associated with this preservation of health, for example environmental cleaning, sterilization of equipment, hand hygiene, water and sanitation and safe disposal of medical waste.

Disease Prevention - Hygiene

Use Use antimicrobial antimicrobial agentsagents

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