microbiology unit 4.1

abnormal state in which part or all of the body is not properly adjusted or is incapable of performing its normal functions

disease resulting from a microbial infection

the ability to cause disease

• 1. Primary Pathogen
• 2. Opportunistic Pathogen

causes disease in host is normal mode of operation

Normally non-pathogenic, but can causes disease under certain conditions

Example: perforated large intestine and gram negative bacteria

degree of pathogenicity

Characteristics of microbe that make it pathogenic

microbe growing in/on its host.

ability to establish a discrete point of infection

ability to spread from initial site of infection

study of disease in populations

John Snow....indentified contaminated water from the Board Street pump as the source of the outbreak

Florence Nightingale

number of individuals with the disease at a given time

“snap shot” of population at one time point

• number of individuals in the population who die from a particular cause in a given time interval

proportion of infected individuals who will be killed by the disease

which diseases are more significant threats at any given time in a particular populationexample: a disease with low CFR and high morbidity may be more of a threat than a very high (100%) CFR with very low morbidity

• disease is always present in the population
• •prevalence usually varies 
• •cyclic seasonal variations are common in many 
• •humans can act as reservoirs

• infected individuals are not always present in the population
• •non-human reservoirs exist 
• •isolated from populations in which it is endemic

significant increase in prevalence of a disease

outbreak of more or less limited geographic extent

outbreak that involves several continents, or world-wide

• •Many governments have agencies
• that collect and analyze epidemiological data.

• –United States: Centers for Disease Control and Prevention (CDC)
• •Headquarters in
• Atlanta, GA
• •Collects data and does research on pathogens world-wide
• •publication: Morbidity and Mortality Weekly Report (MMWR) - available free online

–cases of certain diseases must be reported to the CDC

–establish long-term patterns

–early recognition of potential outbreaks

•possibility of quick containment

–reservoirs and modes of transmission

–who is most at risk (predisposing factors)

–best methods for control

–how best to use limited resources to combat disease

• sources of disease organisms in the environment
• –Humans

•individuals showing S & S

•carriers - infected but without serious S & S

–chronic, latent, subacute, subclinical, asymptomatic, incubation

–examples: HIV, diphtheria, hepatitis, gonorrhea, streptococcal infections, typhoid fever

• •eradication may be possible for diseases with humans as the only reservoir, and if an effective vaccine is available
•    –smallpox (variola) - late 1970s
•    –poliovirus - close 

•Animals

–zoonoses: can cause disease in animals and can be transmitted to humans

•over 150 known:  Table 33.1

•control is difficult if in wild animal populations

–some have no visible effect on infected animals

•Trypanosomes and game animals in Africa

–to be a reservoir, microbes must be capable of long term survival and reproduction in these environments

• –Examples
• •soil and water
• •food

–Direct Contact

–Indirect Contact

person to person

staphylococcal infections, measles, cold viruses, influenza, STDs

–contact contaminates an inanimate object that is contacted by an uninfected host

•towels,utensils, drinking cups, money, syringes, etc

–droplet: larger mucus and saliva particles that remain airborne for only short distances

•usually less than one meter after coughing

–example: influenza

–agents on tiny particles that can remain airborne for long periods of time

•dust, mucus, saliva, aerosols

• •longer exposure
• to drying, UV, lack of nutrients

–measles, tuberculosis, Legionella, Streptococcus, fungal spores (systemic infections)

–entry by ingestion, inhalation, through cuts in skin

–Fecal/Oral transmission: exit host in feces, enter new host by ingestion of contaminated food or water

•many examples: mostly gastrointestinal diseases

–Shigella, Salmonella, enteropathogenic E. coli, cholera, Norovirus, Polio, amoebic dysentary

•associated with poor sewage and drinking water treatment, and unsanitary food preparation techniques

• Mechanical Transmission
• Biological Transmission

passive transport on surface of animal.

Ex. Houseflies and fecal microbes

specific association btwn a particular animal and a microbe.

Most vectors are blood sucking anthropods. Ex. fleas, mosquitos, tickes, flies, lice

–Vector control is often a viable strategy for control of these diseases

–Range of vector often determines where a disease can occur

–examples: Table 14.3

• •Plasmodium and
• Anopheles mosquitoes

•Rickettsias and ticks

•Typhus and lice or fleas

•Lyme disease and deer ticks

•Common Source Diseases:

–infection from contaminated, non-living source

•examples:  most food poisoning, food infections

–less likely to become epidemic/pandemic

–rapid, localized increase and rapid decline after identification and treatment of source

–spread by contact with infected individual (direct, droplet, airborne) or by vectors

–slower increase that may be less localized

–greater potential to become epidemic/pandemic

–more difficult to identify early and to control once it begins to spread

•made worse by modern transportation systems

–return of previously better controlled microbes

•drug resistance  (malaria, staph and strep)

•new pool of susceptible individuals (TB in HIV patients in US and western europe)

•breakdown in public health measures

–Evolution of microbes: new species that infect humans

•HIV

–Humans interact with the surrounding environment in new ways - changes frequency and pattern of contact with microbes.

•Lyme Disease: predator depletion and suburban lifestyle

•changes in patterns of human habitation and hemorrhagic diseases such as ebola and hantavirus

Legionnaire's Diesease and air-conditioning systems

Global warming and changes in vector ranges.