Lecture 7 Host Microbe Interaction

–routinely reside on body’s surfaces

•some can cause disease should opportunity arise (opportunistic)

•can leave individuals vulnerable to.invasion–Individuals said to be immunocompromised

•Skin, mucous membranes are barriers

–Also host complex ecosystem of microorganisms “living together” or symbiosis

Resident microbiota and Transient.microbiota

–Important to human health

sites for extended periods

temporarily

protection against pathogens

•Covering of binding sites prevents attachment

•Consumption of available nutrients

•Production of compounds toxic to other bacteria

intestinal microbiota,allow overgrowth of toxin-producing Clostridium difficile.`

–Stimulation of adaptive immune system

•Mice reared in microbe-free environmenthave greatly underdeveloped mucosal-associated lymphoid tissue (MALT);antibodies against normal microbiota bind to pathogens as well

•Immune system learns to lessen response to many microbes that routinely inhabit gut as well as food–Basis of hygiene hypothesis, which proposes insufficient exposure to microbes can lead to allergies

•Exposed to microbes during passagethrough birth canal

•These take up residence; others fromfood, humans, environment soon also become established on newborn

Changes occur in response tophysiological variations within host (e.g., hormonal changes) and as result ofactivities of host (e.g., consuming food

–characterized by high fat and renedcarbohydrate and sugar content

–Correlated to increasing rate of obesity in the population

–Sugar substitutes are also increasing (i.e., aspartame)

from lean mice

•(consideredlean)

(consideredlean)

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–Consume more food–Have higher body fat content/weight

+/+mice

•Increasein the genus Firmicutes ,decrease in the genus Baceteriodetes

•Ob/ob miceare more efficient at harvesting energy from food

–Phosphotransferase systems

–Fructose and mannose metabolism,

–Glycolysis/gluco-neogenesis,

–But depleted of genes required for starch and sucrose metabolism

•These changes may be associated with increase in energy entering into the host buthow?

•is that the ability to metabolizes and uptake fructose (a main sugar in Westerndiet) by bacteria is very low

•This stimulates the the production of short chain fatty acids, which is sensed by the the human body

•In response, the human body secretes leptin,which slows the movement of food through the intestine and activates fructose transporter

•Leads to increased absorption of energy from food passing through intestine

•Howinfectious agents spread from person to person (place to place) Trackingthe spread of the disease

•study of disease patterns in populations

•Examining infections once they have occurred•Treating infection once they have occurred•Mechanistic understanding of both sides

–collect,compile data about sources of disease and risk factors

•Design infection control strategies,prevent or predict spread of disease

•Use expertise in diverse disciplines including ecology, microbiology, sociology, statistics, and psychology

•Many of our daily habits (handwashing, waste disposal) based on work

•Communicable (contagious) diseases and •Non-communicable diseases

–Transmitted from one host to another

•e.g.,measles, colds, influenza

–Transmission determined by interactionsbetween environment, pathogen, and host

•Control of any of these factors may breakinfection cycle

–Do not spread from host to host

•Microorganisms most often arise from individual’s normal microbiota or environment

Attackrate

Incidencerate

Prevalence

–is percentage of people who become ill inpopulation after exposure

•Reflects infectious dose, immune statusof population

–is number of new cases/time/population

•Measure of risk of an individualcontracting a disease

–is total number of cases at any time orfor a specific period in a given population

•Reflects overall impact of disease on society; includes old and new cases, as well as duration of disease

Both expressed as cases per 100,000people

–is incidence of disease in population atrisk•Contagious diseases (e.g., influenza)often have high morbidity rate: infected individual may transmit to several

–is overall death rate in population

•In developed countries, most oftenassociated with non-communicable diseases (e.g., cancer, heart attack)

•Communicable diseases major cause ofdeath in developing countries

–is percentage of population that diesfrom a specific disease

•Plague, Ebola feared because of very highrate

–constantly present in population•E.g., common cold, measles in UnitedStates

–is unusually large number of cases

•Can be from introduced or endemic disease

–is group of casesat specific time and population

–is global •(e.g., AIDS)

–Natural habitat in which pathogen lives

•In or on animal, human, or in environment(soil, water)

•Identification important in disease control

•May be exclusive or exist in other animals, environment

•Often easier to control–E.g., smallpox

•Symptomatic or asymptomatic

obvious source of pathogens

•harder to identify, may not realize, canspread to others

–Up to 50% of women infected with Neisseria gonorrhoeae are asymptomatic, easily transmit

–Many people carry Staphylococcus aureus

•Zoonoses(zoonotic diseases) primarily exist in animals but can be transmitted to humans(e.g., plague, rabies)

•Difficult or impossible to eliminate(e.g., Clostridium)

Verticaltransmission and Horizontaltransmission

–is pregnant woman to fetus or mother toinfant during childbirth, breast feeding

is person to person via air, physicalcontact, ingestion of food or water, or vector

–handshake, sexual intercourse

•Infectious dose important (e.g., for Shigella is 10–100 cells, can happen fromhandshake)•From hands, can be ingested: fecal-oraltransmission

•Handwashing considered single most important measurefor preventing spread of infectious disease

inanimate objects, or fomites

•Clothing, table-tops, doorknobs, drinkingglases

DropletTransmission

Food and Water

Air

–respiratory droplets generally fall toground within a meter from release

-Densely populated buildings (schools,military barracks)

-Spread minimized by covering mouth whensneezing

–can become contaminated•Animal products (meat, eggs) fromanimal’s intestines•Cross-contamination: transfer from one food to another

–: respiratory diseases commonlytransmitted•Particles larger than 10 µm usually trapped by mucus

•Smaller particles can enter lungs, carrypathogens

•Talking, laughing, singing, sneezing,coughing generate

–living organisms that can carry pathogen

•Most commonly arthropods: mosquitoes,flies, fleas, lice, ticks; can carry internally or externally•Can be mechanical or biological

•Vector control important in preventingdiseases

•Ro

•Describeshow many infections will originate from one infected individual

infectionwill not spread

•infectionwill spread

–individualsthat cannot be vaccinated

–Immunocompromisedindividuals

–Veryyoung children and the elderly

•reduceRo and will break links betweenpeople in a population

microbe establishing itself on bodysurface

•Can be subclinical: no or mild symptoms

•Infectiousdisease yields noticeable impairment–Symptoms are subjective effects experienced bypatient (e.g., pain and nausea)

–Signs are objective evidence (e.g., rash, pusformation, swelling)

•Initial infection is primaryinfection

–Damage can predispose individual todeveloping a secondaryinfection

–is microbe or virus that causes diseasein otherwise healthy individual

•Diseases such as plague, malaria,measles, influenza, diphtheria, tetanus, tuberculosis, etc.

–(opportunist) causes disease only whenbody’s innate or adaptive defenses are compromised or when introduced intounusual location

•Can be members of normal microbiotaor common in environment (e.g., Pseudomonas)

refers to degree of pathogenicity

–are traits that allow microorganism tocause disease

–easily spread

number of microbes necessary to establishinfection

number of cells that infects 50% ofpopulation

~10–100 ingested Shigella

many as 10^6 ingested Salmonella entericaserotype Enteritidis–Difference partially reflects ability tosurvive stomach acid•

–time between infection and onset

•Varies considerably: few days for commoncold to even years for leprosy

Depends on growth rate, host’s condition,infectious dose

–signs and symptoms of disease

May be preceded by prodromal phase (vague symptoms)

recuperation, recovery from disease

–may harbor and spread infectiousagent for longperiods of time inabsence of signs or symptoms

–microbe limited to small area (e.g., boilcaused by Staphylococcus aureus)

–agent disseminated throughout body (e.g.,measles)

–in the blood”

•bacteria circulating in blood

–Not necessarily a disease state (e.g.,can occur transiently following vigorous tooth brushing

toxins circulating in bloodstream

viruses circulating in bloodstream

acute, life-threatening illness caused byinfectious agents or products in bloodstream

E.g., Clostridiumbotulinum, Staphylococcusaureus

•E.g., Vibriocholerae, E.coli O157:H7, Corynebacterium diphtheriae

–E.g., Mycobacteriumtuberculosis, Yersiniapestis, Salmonellaenterica

•E.g., Shigella dysenteriae,Clostridium tetani•