APBI 419 - Module 1

Disease

any change in structure / function of a body that presents particular set of signs that’re different from what is considered normal state

for a disease to occur:

• fish must become susceptible to orgs or agents causing disease

• hosts must be present

• agent (chemical or biological) must be capable of causing disease outcome and be in a dose big enough to incite negative host response

• environment is essential element determining whether or not disease occurs

• host + agent + environment determines likelihood of serious / irreversible disease

Health

extent that indiv / group is able to satisfy needs + cope with environment changes

Infection

detrimental colonization of a host org by a foreign species resulting in host response

• the infecting org tries to use host resources to multiply; @ host's expense

• the pathogen will interfere w/ normal functioning of host

• may lead to chronic wounds + maybe death

• the host's general response to infection = inflammation + mounting of immune response

Pathogen

any disease-producing microorg; bacteria, viruses, fungi, and parasites

• not normal flora

• under specific circumstances of changed host susceptibility / movement of normal flora to unusual body locations, normal flora bacteria can become pathogens

Obligate

sub-type of pathogen

depends on host for survival

Opportunistic/facultative

sub-type of pathogen

might require host tissues as part of normal life cycle

Pathogenicity

ability of org to induce disease

Virulence

ability of infectious agent to invade host tissues and cause disease; severity

• highly virulent - causes severe disease / death

• varies between + within species / strain; depends on host response to org

Cause of disease

• what brings about a condition or produces an effect

  • caused by interaction of host, disease causing agent, + shared environment

  • results when certain combo of risk factors develops

Risk factor

• any host, agent, environmental factor that increases probability that adverse health effect will happen

  • has to be multiple factors to cause disease

  • factors cause disease under certain circumstances

  • if interactions between the 3 vary, it can make it hard to predict outcome of changes in risk factors

Necessary factors

•  those required to produce disease

  • like certain diseases can't occur without certain bacteria

Contagious

•  refers to easily transmitted

  • microorg can be infectious without being contagious

Infectious

• ability of a pathogen to cause disease

  • can be highly contagious while being relatively non-infectious

  • a pathogen can be highly infectious while not being really contagious

OR

• disease causing agent

  • infectious agents incite host response designed to eliminate invading orgs

Transmission

transfer of a pathogenic agent from infected host to uninfected one

Vertical transmission

spread of infection parent → offspring during development → fertilization

Horizontal transmission

 transmission @ any other life stage

Parasite

animal that lives on/in another animal (the host) @ expense of the animal

Infestation

considering macro-parasites (worms or lice); this term used interchangeably w/ infection but principles of interaction w/ host are similar

Disease control

• actions taken to reduce probability of occurrence of disease in indivs; to reduce incidence of disease in pops

Disinfection

• destruction of pathogenic orgs associated w/ inanimate objects / on the external surface of fish or eggs

  • physical or chemical means

Sterilization

complete elimination of all viable orgs

Sanitization

inhibition of growth

Mutualistic

•  host and microbe pop benefit

  • ex. bacteria in gastrointestinal tract of vertebrates

Reservoirs (carriers)

• Pathogens can be present in fish without causing disease

  • fish can suppress pathogen enough so it's latent (present but not acting; dormant)

    • those reservoirs = silent sources

  • fish don't appear ill despite some degree of host response and may act as carriers

Asymptomatic infections

•  don't cause signs that're readily observed

  • asymptomatic fish are capable of shedding infectious orgs and are termed as carriers

  • they might not display signs of disease but are capable of transmitting infectious disease to other fish in system

• Infections can be _____ @ time of initial infection, mid-infection, upon recovery

Subclinical infections

infection that doesn't result in obvious clinical signs but does reduce the productivity of affected indivs or pops