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Objectives of Host-Microbe Relationships

• Understanding the relationships between agent, host, and environment is essential
• Enumerating different symbiotic relationships is important
• Recognizing the frequency and distribution of diseases is key
• Learning about the transmission modes of common infectious diseases is necessary
• Comprehending human immune defenses provides a critical foundation

Overview of Host-Microbe Interactions

• Humans are constantly exposed to microbes in their environment, often without harm
• Microbes colonizing the body can become part of the normal flora or cause infection/disease
• Normal flora includes bacteria, fungi, and protozoa residing naturally in the skin, gastrointestinal tract, mucous membranes, and genitourinary tracts and provide a stabilizing balance
• Pathogens harm the body's tissues through virulence factors
• Infections occur when pathogens access, adhere to, grow in, and disrupt the body's tissues

Pathology, Infection, and Disease

• Pathology is the scientific study of disease, where pathos means suffering, and logos means science
• Etiology refers to the cause of a disease
• Pathogenesis is the manner in which a disease develops
• Infection is the invasion or colonization of the body by pathogenic microorganisms
• Disease occurs when an infection results in any change from a state of health

Normal Microbiota

• Animals (Humans included) are generally free of microbes in utero
• At birth, normal and characteristic microbial populations begin to establish themselves
• Newborns are first exposed to microorganisms (lactobacilli) from the mother's vagina, which colonizes the newborn's intestines
• Additional bacteria are acquired from food
• Microorganisms persist throughout life, increasing or decreasing in response to environmental conditions, which contributes to disease

Normal vs. Transient Microbiota

• Normal microbiota permanently colonize but do not produce disease under normal conditions
• Transient microbiota are present temporarily (days, weeks, or months) and then disappear

Normal Microbiota and the Host

• Microbial antagonism (competitive exclusion) allows normal microbiota to prevent harmful microorganism overgrowth by competing for nutrients, producing harmful substances for invaders, and or affecting environmental conditions (pH and available oxygen)
• Disease occurs when the balance between normal and pathogenic microbes is upset

Normal Microbiota in a Human

• The human body hosts diverse normal microbiota in various regions
• The conjunctiva hosts coagulase-negative staphylococci, Haemophilus, Staphylococcus aureus, and Streptococcus
• The nose contains coagulase-negative staphylococci, Viridans streptococci, Staphylococcus aureus, Neisseria, Haemophilus, and Streptococcus pneumonia
• The outer ear harbors coagulase-negative staphylococci, diphtheroids, and Pseudomonas species
• Mouth and Oropharynx have Viridans streptococci, coagulase-negative staphylococci, Veillonella, Fusobacterium, Treponema, Porphyromonas, Prevotella, Neisseria, Branhamella catarrhalis, Streptococcus pneumonia, beta-hemolytic streptococci, Candida, Haemophilus, Diphtheroids, Actinomyces, Eikenella corrodens, and Staphylococcus aureus
• Stomach features Streptococcus, Staphylococcus, Lactobacillus, and Peptostreptococcus.
• The urethea contains coagulase-negative staphylococci, diphtheroids, Streptococcus, Mycobacterium, Bacteroides, Fusobacterium, and Peptostreptococcus
• The vagina features Lactobacillus, Peptostreptococcus, Diphtheroids, Streptococcus, Clostridium, Bacteroides, Candida, and Gardnerella vaginalis
• The skin contains coagulase-negative staphylococci, diphtheroids (Propionibacterium acnes), Staphylococcus aureus, Streptococcus, Bacillus, Malassezia furfur, Candida, and Mycobacterium
• The small intestine hosts Lactobacillus, Bacteroides, Clostridium, Mycobacterium, Enterococci and Enterobacteriaceae
• The large intestine hosts Bacteroids, Fusobacterium, Clostridium, Peptostreptococcus, Escherichia coli, Klebsiella, Proteus, Lactobacillus, Enterococci, Streptococcus, Pseudomonas, Acinetobacter, coagulase-negative staphylococci, Staphylococcus aureus, Mycobacterium, and Actinomyces

Symbiosis

• Symbiosis refers to the relationship between normal microbiota and the host
• It is defined as living together of of two or more organisms where at least one is dependent upon the other
• Interactive associations include mutualism, commensalism and parasitism

Mutualism

• Describes an association where both organisms benefit from the association
• Partners include microbe/microbe, microbe/plant, and microbe/animal

Commensalism

• One organism benefits, and the other is unaffected
• Refers to the association where one partner, the commensal, benefits from the association while the other partner, the host is neither harmed nor helped
• Many body organisms are part of the normal body flora
• Disruption of normal flora may allow overgrowth disease (thrush, oral yeast, or yeast vaginitis)
• Candida spp. in the skin or the vagina may be be commensal but entry of the same organism into tissue of blood results in infection

Parasitism

• One organism, the parasite, benefits while the other or the host is harmed.
• Many disease-causing bacteria are parasites

Opportunistic Pathogens

• These pathogens cause disease when the host's defenses are compromised or when they grow in an area of the body not natural to them
• They are non-pathogenic to the normal, healthy person, with no well-developed virulence properties

Classifying Infectious Diseases

• Communicable diseases can spread from one host to another: chickenpox, measles, genital herpes, typhoid fever, and tuberculosis
• Contagious diseases easily spread from one person to another
• Non-communicable diseases do not spread from one host to another

Epidemiology Triangle Model

• This model showcases the relationship between three concepts
• The agent must be present for the disease to occur
• The host is more vulnerable to severe infectious diseases or illness
• Environmental factors influence the infectious disease's spread

Microorganisms

• These must be present for diseases to occur and include
• Algae
• Bacteria
• Fungi
• Protozoa
• Virus

Sources of Microbes

• Microbes come from various sources such as
• Air
• Soil
• Plants
• People
• Animals
• Water

Primary Biosafety Levels

• Primary biosafety levels are rated from 1 - 4 based on the infection risk and how to handle them safely
• Level 1 is a standard open bench, no special facility needed; for microbes not generally considered pathogens and will not colonize healthy people (Micrococcus luteus, Bacillus megaterium, Lactobacillus, and Saccharomyces)
• Level 2 requires Level 1 facilities and practices and trains personnel how to handle pathogens; pathogens can cause disease in healthy people but can be contained with the proper facilities (Staphylococcus aureus, Escherichia coli, Salmonella spp., Corynebacterium diphtheriae; pathogenic helminths; hepatitis A, B, and rabies viruses; Cryptococcus and Blastomyces)
• Level 3 requires a Level 2 facilities and practices but requires all manipulation be performed in safety cabinets; microbes can cause lethal disease if inhaled (Mycobacterium tuberculosis, Francisella Tularensis, Yersinia pestis, Brucella spp., Coxiella burnetii, Coccidioides immitis, and yellow fever, WEE, and AIDS viruses)
• Level 4 requires Level 3 facilities and practices but has isolated facilities with very controlled accessed; agents inhaled are highly virile and pose a extreme risk for morbidity and mortality (exotic flaviviruses; arenaviruses (Lassa fever virus); or filoviruses, including Ebola and Marburg viruses)

Equilibrium Between Population, Infectious Agent, and Environment

• A communicable disease depends on the agent and includes
• Virulence
• Infectious dose
• Susceptibility to drugs
• Mode of transmission
• Ability to adapt to change

Equilibrium Factors

• Host factors that affect communicable diseases consists of age, genetic make up, poverty, and nutritional status
• Environmental factors include shelter, altitude, humidity, sanitation, food supply, water supply, climate change, and overcrowding

Communicable Disease Cycle

• Stages include
  • Non-diseased state
  • Risk and exposure factors
  • Susceptibility to the diseases
  • Biological evidence of infection
  • Clinical illness
  • Communicable disease cycle
  • Progresses to disease, possible Death or may have
  • Recovery immortality

Notifiable Diseases Agents (A-I)

• Acute bloody diarrhea is caused by Shigella
• Acute hemorrhagic fever is caused by Dengue, Ebola virus, and Marburg virus
• Acute febrile illnesses is brought on by Leptospira interogans,
• Acute lower respiratory tract infection & pneumonia is brought on by S. pneumoniae, Haemophilus pneumonie, and Klebsiella pneumoniae
• Acute watery diarrhea is caused by rotavirus
• Cholera is caused by Vibrio cholera
• Dengue hemorrhagic fever and Diphtheria are both caused by Dengue virus
• Corynebacterium diphtheriae brings on Diphtheria
• Filariasis is caused byWuchereria bancrofti and Brugia malayi

Notifiable Diseases Agents (A-G)

• Leprosy is caused by Mycobacterium leprae
• Leptospirosis is caused by Leptospira interrogans
• Malaria is caused by P. falciparum
• Measles is caused by measles virs.
• Meningococcal infection is caused by Neisseria meningitidis
• Neonatal and Non-neonatal tetanus are brought on by Clostridium tetani
• Paralytic shellfish poisoning (PSP) is caused by toxin-contaminated bivalve and shellfish and crustaceans
• Rabies (human) is caused by the rabies virus
• Schistosomiasis is triggered by Schistosoma japonicum
• Typhoid & paratyphoid fever is caused by Salmonella typhi and Salmonella paratyphi.
• Viral encephalitis is caused by HSV and Japanese encephalitis
• Viral hepatitis is caused Hepatitis A, B, and C
• Viral meningitis is caused by HSV.
• Whooping cough is caused by Bordetella pertussis

Occurrence of a Disease

• Symptoms are body function changes, such as pain and malaise (a vague feeling of body discomfort)
• Signs are the objective changes the physician can observe and measure (lesions, swelling, fever, and paralysis)
• Syndrome is a group of symptoms or signs accompanying a particular disease

Incidence and Prevalence

• The incidence is the number of people in a population who develop a new disease during a particular time period
• The prevalence is the number of people in a population who develop a disease at a specified time, regardless of when it first appeared (includes old and new cases)

Frequency and Distribution of Disease

• Sporadic diseases occur occasionally in a population at irregular intervals
• Endemic diseases are continually present at a steady level in a population
• An outbreak is a slight increase in the disease level above endemic level

Epidemic & Pandemic

• An epidemic disease is acquired by many hosts in a given area in a short time and features a sudden increase of morbidity (illness rate) and mortality (death rate) above the normal level
• A pandemic disease is a worldwide epidemic

Conditions for an Epidemic/Outbreak

• An epidemic or outbreak will only occur if
• A host- susceptibility (host or reservoir)
• Virulence of the infectious agent i.e bacteria, virus, parasite, or fungi are not eliminated
• Environment that promotes the exposure are upset

Virulence

• Is the ability of an organism to infect the host and cause a disease
• Virulence factors are molecules expressed and secreted
• Colonize the host
• Evade or inhibit the immune responses of the host
• Enter into or out of a host cell
• Obtain nutrition from the host

Virulence Factors that promote bacterial colonization

• Use motility to disseminate within to other host cells
• Adhere to host and resist physical removal
• Invade host cells
• Compete for iron and other nutrients
• Resist immune defenses such as phagocytosis and completement
• Evade adaptive immune defenses

Herd Immunity

• This occurs when a large fraction of the population is immune to a given disease, making it difficult for the disease to spread

Severity or Duration of a Disease

• Acute diseases develop rapidly but last only a short time (e.g. influenza)
• Chronic disease develops more slowly, and the body's reactions are less severe, but it continues or recurs for long periods (e.g., Infectious mononucleosis and hepatitis B)
• Subacute diseases are mediate between acute and chronic (e.g., subacute sclerosing panencephalitis)
• Latent diseases are when the causative agent the agent remains inactive for a time but becomes active to produce symptoms of the disease (e.g., Shingles)

Extent of Host Involvement

• Local infections feature invading microorganisms limited to a small area of the body (e.g., boils and abscesses)
• Systemic (generalized) infections are when organisms or their products spread throughout the body via the blood or lymph (e.g., Measles)
• Sepsis is a toxic inflammatory condition arising from the spread of microbes (especially bacteria) or their toxins from a focus of infection

Septicemia

• Also called blood poisoning, is a systemic infection arising from the multiplication of pathogens in the blood
• Bacteremia
• Toxemia
• Viremia

Other Types of Infections

• Primary infections are acute infections that cause the initial illness
• Secondary infections are is caused by an opportunistic pathogen after the primary infection has weakened the body's defenses
• Subclinical (inapparent) infections do not cause any noticeable illness

Predisposing Factors

• Alter the course of a disease and makes the body more susceptible
• Gender (females have higher incidence of urinary tract infections than males, males have higher rates of pneumonia and meningitis)
• Genetic background
• Climate and weather
• Inadequate nutrition

Other Predisposing Factors

• Fatigue
• Age
• Environment
• Habits
• Lifestyle
  • Occupation
  • Pre-existing illness
  • Chemotherapy
  • Emotional disturbances

Patterns of Disease - Stages of a Disease

• Incubation period (no signs or symptoms)
• Prodromal period (mild signs or symptoms)
• Period of illness (most severe signs and symptoms)
• Period of decline (signs and symptoms)
• Period of convalescence

Spread of Infection

• Reservoir - Source of where infection can occur
  • Living (Animal or human)
    • Inanimate (object)
    • Non-living (soil and water)

Carries and Zoonoses

• Carries Harbors the organisms but no signs of illness
• Zoonoses - Diseases that can occur primarily in animal that get transmitted to humans

Sources of Disease

• For organisms to be pathogenic they must be able to maintain ability to infect and replication
  • site to Reservoir
  • The object, place or person from which the organisms pass to the host is called the Source - Sometimes reservoir and source are the same

Reservoirs of Infection

• these represent Sites in nature where microbes survive (and can multiply and cause continual sources of infection
  • Animals Living reservoirs (rabies,lyme disease)
  • Humans Living reservoirs (Small pox, gonorrhea) - Fomite Non-living reservoirs -soil, water (botulism,tetanus)

Human Sources

• only transfer human only infections
  • Human infections only Small pox, gonorrhea, Measles, Typhoid fever
  • Active carriers can be acutely if
• Convalescent carriers are are recovering from a disease
• Healthy carriers
  • do not show symptoms of the disease but harbor the organisms
  • inapparent infections or latent diseases Example: Typhoid Mary

Animal Sources

• Zoonosis
  • e.g. Rabies,Leptospirosis,Japanese encephalitis

Insect Sources

• Biological source are Insects vector
• Insects transfer organisms to humans or animals Insects are required for part of the developmental cycle of the organism

Insect Source - Mechanical Vectors

• Organisms are carried on the appendages of the insect

Non Living Reservoir

• Some bacteria produce harmful toxins to water and soil food sources agents infectious to man

Reservoirs

• Soil, water and Food are reservoir
  • Spores can be inhaled, then germinate, multiply and produce disease

Sources of Diseases in Water, Food and Fomites

• Sources of Disease in Water
  • water source for disease transmission
  • can be fecally infected
    • water borne pathogens and can enter through the sweat abraded skin
• Sources of Disease in Food
  • Analysis must confirm the food as the source of the disease
    • Improper storage temperatures, poor hygiene, contaminated equipment
• Fomite (catheters, needles etc)
  • Inanimate objects other than food

Transmission of Diseases

• 3 major Routes
  • Contact
  • Vehicle
  • Vectors
• Transmission of disease can occur through
  • Person to person
  • Contact to nonliving -Droplet transmission

Modes of transmission through contact

• Direct (Requires close association)
• indirect (through fomites, water) Airborne (aerosols) Vector

Mode of Transmissions

• Direct

• Requires close association

  • Between Infected and susceptible host -Person — to -> person example sex,kissing, sneeze

• Indirect • From one through intermediate (food and water)

Vehicle Transmission

• Waterborne transmission-water contaminated with aUntreated or poorly treated sewage (cholera,
  • waterborne shigellosis,and leptospirosis)

Food borne transmission-transmitted in foods that -Are Incompletely cooked,Poorly refrigerated or Prepared under unsanitary conditions

• (food -Poisoning and tapeworm infestation)

  • Airborne transmission -spread agents infection By droplet nuclei in dust that t ravel more than I meter From the reservoir to the host

• Transmission of disease agents by medium – Water, food or air

• Other media include aBlood and other body fluids, drugs, and intravenous fluids.

Vector Transmission

Vectors – animals that carry pathogens from animal to a host.

Arthropods – most important group of disease vectors

Mechanical transmission

Biological transmission

Epidemical of Vectors

• Arthropods -Invertebrate wiht jointed appendages -ticks, flies, mosquitioes and fleas carry disease Ticks carries-plague

Vector Types

Mechanical vector

Biological vector

• Microbe proliferates In arthropod
• Necessary component in the life cycle of the microbe

Sometimes transovarian transmission

Cycle of Disease

• cycle that transfer source into transmission of communicable disease
  • Portal to Exit
  • Disease

Portals are the route of disease in transmission from one host to another

Skin

• Mucous membranes: respiratory tract, intestinal tract, urinary tract, genital tract -Blood

Body Fights Infections

• Physical barriers

  • Defenses Physical and Physlologic

  • Aquired and Inate in the body

Infectious Agents

  -   Size: small to large agents that the body tries to confronts

10 to 1000 the size that the body deals With

Human Defense on Infection

• Physical Barriers Skin mucus membranes
• innnate immunity
• acquired immunity

Skin and mucus membrane

– Skin is the largest organ in the body. -Skin creates a Physical barrier

• Mucus provides enzymes with protection

Epithelial Cells protect

• blood barrier Inflammation and phagocytosis

Aquired and Inate immunity

• Phases of inate and aquired immunity
  • 6 to 12 hours inate
• aquired at 1 to 3 days and back to ination

Immune System 1 ,2,3 Line of Dence

• Immune system in line of denence
• First , second , third degree depend on if pathogen comes or goes based on size or strength of body