Communicable Diseases Ch. 7

Reproduction Ratio

# of new cases one diseased individual generates on average in the course of the disease's communicable period. Ex] Ebola outbreak 1 individual w/ Ebola: 3 expected to get it as well

Reservoir

'source' of pathogen in nature *Humans -infected & diseased person (~90%) -asymptomatic carrier ~infected, but not diseased person ~chronic carrier -normal microbial flora -{passive carrier} healthcare provider passing disease onto another person perhaps by not washing hands *Animals -zoonosis *Soil or water Ex] tetni found in soil -"free-living" microbes

Infectious dose

(ID) -the minimum # of particles required to establish infection -ID50=the # of microbial particles required to infect 50% of the test population

Indirect mode of disease transmission

*airborne -dust -droplet nuclei *vehicle-borne (inanimate) -food -water -other fomites Ex] bed sheets, door knobs *vector-borne (animate) -mechanical -biological

Public Health Tools to Address the burden of communicable disease

*barrier protections *immunizations protect individuals and populations *screening and case finding *treatment and contact treatment *efforts to maximize effectiveness of treatment and prevent resistance

Direct mode of disease transmission

*direct contact EX] Herpes from sex/kissing *droplet spread EX] from sneezing or coughing

biological vector VS mechanical vector

*microbe replicates to high #'s in its biological vector as part of its microbes life cycle *microbes are passively moved by mechanical vectors-microbes don't complete any part of it's life cycle during 'transit'

biological vector

*more dangerous *infected *generally interpreted to be an arthropod *EX] ticks, spiders, blood feeding insects ie.) west nile virus- mosquitos feed on an infected bird

mechanical vector

*not infected EX] fly standing on dog poo then touching potato salad

Herd immunity

*strongest thing we have -the resistance of a group to invasion and spread of an infectious agent, based on the resistance to infection of a high proportion of individual members of the group

Infectivity

*the ability of an agent to cause infection in a susceptible host -growth of the microbe within the host body -infection does NOT = disease

barrier protection against airborne transmission

*wearing a protective air-tight suit equipped with a helmet and face mask *negatively pressurized laminar flow hood *protects against airborne pathogens, or toxic vapors

vaccines currently licensed by the FDA

*whole microbe vaccines -inactivated vaccines (eg. salk polio vaccine) -attenuated vaccines (eg. sabin polio vaccine) *toxoid vaccines-neutralizes toxin if it is in your body *subunit or acellular vaccines *recombinant vaccines -immunogenic proteins produced, the purified from genetically-modified cells in culture -immunogenic genes from pathogen introduced into a non-pathogenic microbe (ie. vector) ~vector may be replication-defective or attenuated microbe

Communicable disease transmission

-a disease due to an organism such as bacteria, protozoa, or virus *Transmitted -person to person -animals to people -physical environment to human *By variety of routes -air -water -fomites -insect bites -animal bites

BSL-2

-agents are associated with human disease, hazard: percutaneous injury, ingestion, or mucous membrane exposure (eg. chlamydia, hepatitis A, Influenza A, measles, mumps, HIV)

BSL-3

-agents are indigenous or exotic, and have the potential for aerosol transmission; diseases may have serious or lethal consequences (eg. yellow fever, SARS, mycobacterium TB, bacillus antracis)

BSL-4

-pathogens are extremely dangerous, exotic agents, which pose a high risk of life-threatening disease, may be aerosol-transmitted lab infections, or related agents with an unknown risk of transmission (eg. Marburg, ebola, lassa fever, Crimean-congo hemorrhagic fever, smallpox)

virulence

-relative capacity of pathogen to damage the host -reflected in the severity of disease -not all pathogens are 'created equal'; consider *rhinovirus infection causes a common cold *ebola virus infection causes hemorrhagic fever *HIV infection, left untreated, causes Aids

Koch's Postulates

1) The organism must be shown to be present in every case of the disease by isolation of the organism 2) The organism must not be found in cases of other disease 3) once isolated, the organism must be capable of replicating the disease in an experimental animal 4) The organism must be recoverable from the animal

Modern Koch's Postulates

1) evidence of an epidemiological association 2) isolation -DNA-based technologies have advanced detection of infectious agents 3) transmissions to establish that an organism is a contributory cause of the disease

Koch's Postulates

4 postulates that together definitely establish a cause & effect for a communicable disease: -the organism must be shown to be present in every case of the disease -the organism must not be found in cases of other diseases -once isolated, the organism must be capable of replicating the disease in an experimental animal -the organism must be recoverable from the animal

How does one prove that a given microbe causes a specific disease?

Can't find an animal to react with HIV agent therefore we cannot use Koch's Postulate for HIV

infectious disease

a disease caused by an organism such as bacteria or virus.

communicable disease

a disease due to an organism such as bacteria or a virus that is transmitted person-to-person or from animals or the physical environments to humans by a variety of routes, including from air & water, contaminated articles or fomites, & insect bites & animal bites. subset of infectious disease.

disease

a disturbance, interruption or disorder of any part of the body (eg. systems, organs) such that normal body functions cannot occur

antibody

a protein produced by the body in response to a foreign antigen that can bind to the antigen & facilitate it's elimination

Modern Koch's Postulates

a set of criteria for establishing that an organism is a contributory cause of a disease, requiring evidence of an epidemiological association, isolation, & transmissions.

endemic

a term that implies that a disease is present in a community at all times but at a relatively low rate

epidemic

a term used when a disease has increased in frequency in a defined geographic area far above its usual rate

pathogenicity

ability to cause a disease

pandemic

an epidemic occurring worldwide, or over a very wide area, crossing international boundaries & affecting large # of people

case finding

as used in public health, an effort to identify and locate contacts of individuals diagnosed with a disease & evaluate them for possible treatment

ring vaccination

as used in the smallpox eradication program, immediate vaccination of populations in surrounding geographic areas after identification of a case of disease

BSL-1

biosafety level 1 laboratory -agents are not known to consistently cause disease in healthy adults (eg. canine hepatitis, nonpathogenic E. coli)

infectious disease

disease caused by microbial agents (eg. bacteria, viruses, protozoa, fungi, helminthes, prions)

case fatality rate

how many people die mortality (# dead) -------------------------- X 100 incidence (# sick with the disease

cell-mediated immunity

immunological protection that is produced by t-lymphocytes & other white blood cells that combats intracellular pathogens & tumor cells

non-communicable disease

infectious agent does not spread from one host to another

communicable disease

infectious agent, hence disease, can spread from one host to another -also called contagious disease

inactivated vaccine or dead vaccine

injection of a nonliving organism or antigens from an organism designed to develop antibodies to protect an individual from the disease

infections

invasion of host's bodily tissues by an organism such as bacteria or a virus

pathogen

microbe known to cause disease

herd immunity/population immunity

protection of an entire population from a communicable disease by obtaining individual immunity through vaccination or natural infections by a large % of the population.

passive immunity

short-term protection against a disease provided by administration of antibodies

reproduction ratio (Ro)

the # of new cases one individual with the disease generates on average over the course of the disease's communicable period

infectivity

the ability of a pathogen to enter and multiply in a susceptible host

asymptomatic transmission

the ability to transmit the disease while humans or animals are free of symptoms of the disease

route of transmission

the anatomical & physiological methods for transmission from person to person or from animal species to human

immunization

the strengthening of the immune system to prevent or control disease through exposure to anitgens or administration of antibodies

chronic carriers

those individuals without symptoms of the disease but with the ability to chronically transmit the disease

epidemiological treatment

treatment of contacts of an individual with a disease even in the absence of evidence of transmission of the disease

live vaccines (attenuated)

use of a living organism in a vaccine. Living organisms included in vaccines are expected to be attenuated or altered to greatly reduce the chances that they will themselves produce disease