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Aquaculture Disease Processes. Dr. Craig Kasper FAS 2253/FAS 2253L. Description of Syllabus. Course Number and Title: FAS 2253/FAS 2253L, Aquacultural Disease Processes Lecture Time/Location: TTH/9:30-1045am/BSC 212 Lab Time/Location: TH/11:00a-12:40p/BSC 212

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aquaculture disease processes

Aquaculture Disease Processes

Dr. Craig Kasper

FAS 2253/FAS 2253L

description of syllabus
Description of Syllabus
  • Course Number and Title: FAS 2253/FAS 2253L, Aquacultural Disease Processes
  • Lecture Time/Location: TTH/9:30-1045am/BSC 212
  • Lab Time/Location: TH/11:00a-12:40p/BSC 212
  • Instructor: Dr. Craig Kasper, BHUM 111, 253-7881, [email protected]
description of syllabus3
Description of Syllabus
  • Exposure to fundamental and current disease/health issues pertaining to the production of aquaculture crops
  • Prevention of diseases via practical diagnosis and real-world decision making!!
  • Covers: anatomy and physiology, immunology, virology, bacterial diseases, nutritional diseases, parasitology, mycoses, larval diseases and general health management
  • Text: Fish Disease and Diagnosis (Noga, Blackwell Publishers).
  • Additional readings will be on reserve in the library.
  • Course will consist of weekly two-hour lectures (2) followed by a two-hour practical lab.
  • You will need “grubby” clothes on lab day
  • No open-toed shoes in lab!!
  • Labs may require observation and checking on samples outside class period
syllabus lecture outline
Syllabus: lecture outline

Date Topic

8/24 Introduction to Disease

8/29 Signs vs. Symptoms? What’s the difference?

8/31 Immune Response in Aquaculture Animals, Part 1

9/5 Immune Response in Aquaculture Animals, Part 2

9/7 Diseases of a Non-infectious Nature (Nutritional)

9/12 Exam 1

9/14 Common Viral Pathogens of Aquaculture Organisms, Part 1

9/19 Common Viral Pathogens of Aquaculture Organisms, Part 2

9/21 Common Bacterial Pathogens of Aquaculture Organisms, Part 1

9/26 Common Bacterial Pathogens of Aquaculture Organisms, Part 2

9/28 Exam 2

10/3 Probiotic Bacteria (Part 1)

10/5 Probiotic Bacteria (Part 2)

10/10 Molds and Fungi (Part 1)

10/12 Molds and Fungi (Part 2)

10/17 Exam 3

Date Topic

10/19 Protozoans and Parasites Part 1

10/24 Protozoans and Parasites Part 2

10/26Exam 4

10/31 Aquaculture Health Programs

11/2 Design of High Health Facilities/HACCP/Biosecurity

11/7 Practical Considerations

11/9 Regulations, Drugs and the FDA

11/14Exam 5

11/16 Treatments

11/21 Ethics in treating fish.

11/23 Case Study (Real World Example)

11/28 Case Study (Real World Example)

11/30 Thanksgiving Break (No Class)

12/2 Presentations

12/7 Presentations

12/9 Final Exam (non-cumulative)

lecture 1 introduction to disease
Lecture 1: Introduction to Disease
  • What is disease?
  • Types of diseases
  • Dynamics of infectious disease
  • Epizootiology of infectious diseases
  • What you have to do to be a disease agent
  • Disease reservoirs
  • Transmission
  • The host
  • Stages in an epizootic
what is disease
What is Disease?
  • Definition: any alteration of the body or one of its organs so as to disturb normal physiological function
  • opposite of health = unhealthy or dysfunctional
why are diseases of such concern in aquaculture
Why are diseases of such concern in aquaculture?
  • 1990: WSSV, a virus, devastates shrimp culture in China, $600 million lost
  • 1971: Flexibacter columnaris, a bacterium, kills 14 million wild fish in Klamath Lake
  • the Idaho trout industry loses 10 cents on every dollar made to disease (death, weight loss)
  • future of finfish and shrimp culture may hinge on our ability to control vibriosis*

*more on “vibrio” in a later lecture!

types of diseases
Types of Diseases
  • infectious: diseases due to the action of microorganisms (animal or plant):
    • viruses: CCV, WSSV, TSV, YHV
    • bacteria: Vibrio sp.
    • protozoans
    • metazoans
    • fungi: Saprolegnia sp.
    • crustaceans: O. Isopoda
types of diseases11
Types of Diseases

2) non-infectious: diseases due to non-living causes (environmental, other)

  • even a moderately adverse environment can lead to stress, stress leads to epizootics
  • a very adverse environment can cause disease and mortalities directly (e.g., nitrogen gas bubble disease, brown blood disease)
  • the “other” category refers to nutritional, genetic and developmental diseases
types of diseases12
Types of Diseases

3) treatable vs. non-treatable

  • non-treatable diseases are some of the worst
  • include pathogens such as viruses, drug-resistant bacteria, myxozoans
  • white spot syndrome virus (shrimp) has no known treatment
  • Vibrio sp.: because of rampant over-use of antibiotics in Central America, South America, new, more virulent strains are developing
dynamics of infectious diseases
Dynamics of Infectious Diseases
  • First mode of infection demonstrated by Robert Koch (1876) and his work with Bacillus anthracis(anthrax)
  • reached epidemic proportions in cattle, sheep and other domesticated animals
  • also can occur in man (as we are well aware!)
  • Koch showed that a bacterium caused the disease by using the following method:
koch s method postulates
Koch’s Method (Postulates)
  • 1) find the organism common to all infected animals, demonstrate its absence in healthy ones
  • 2) isolate the organism in pure culture
  • 3) reproduce the disease in suitable experimental animals
  • 4) reisolate the same organism from experimentally infected animals
dynamics of disease germ theory
Dynamics of Disease: Germ Theory
  • Koch’s work lead to what is known as the germ theory: germs cause disease
  • if you have germs you are diseased
  • Renes Dubos (1955) refined the concept in the following statement:

“There are many situations in which the microbe is a constant and ubiquitous component of the environment but causes disease only when some weakening of the patient by another factor allows infection to proceed unrestrained, at least for a while. Theories of disease must account for the surprising fact that, in any community, a large percentage of healthy and normal individuals continually harbor potentially pathogenic microbes without suffering any symptoms or lesions.”

dynamics of disease stress
Dynamics of Disease: stress
  • Definition: any stimulus (physical, chemical or environmental) which tends to disrupt homeostasis in an animal.
  • The animal must then expend more energy to maintain homeostasis: less energy to combat disease
  • Aquatic organisms are fundamentally different from terrestrials: they are immersed in their environment, can’t go somewhere else
  • some disease agents are almost always present in the water (ubiquitous)
  • examples: Aeromonas sp., Pseudomonas sp., Vibrio sp.
dynamics of infectious disease how it occurs
Dynamics of Infectious Disease: how it occurs
  • Three-set model:
    • susceptible host
    • pathogenic agent
    • environment unfavorable to host/favorable to agent
  • exceptions??: extremely large numbers of bacteria, extremely virulent agent
  • stress throws a wrench into it all
dynamics of infectious diseases18
Dynamics of Infectious Diseases
  • infection  parasitism  disease (infection can result from parasitism, but neither necessarily results in disease
  • symbiosis: any association between 2 species involving an exchange of matter and energy
  • commensalism: symbiosis in which one partner benefits, the other is neutral
  • parasitism: symbiosis in which the parasite (usually smaller) is metabolically dependent on the host (larger); some harm intuitive, but not necessary
epizootiology of infectious diseases terminology
Epizootiology of Infectious Diseases: terminology
  • epidemiology: branch of medicine describing occurrence, distribution and types of diseases in populations of animals at distinct periods of time and at particular places (usually refers to humans)
  • epizootiology: same as above (non-human)
  • epidemiology is the study of the who, what, when, where, how and why of disease outbreaks
epizootiology of disease outbreak terminology
Epizootiology of Disease: outbreak terminology
  • enzootic vs. epizootic (endemic vs. epidemic)
  • incidence: frequency of disease in a population over time in relation to the population in which it occurs (cases/yr)
  • rate: number of new cases per number of population (per thousand)
  • prevalence: the expression of the frequency of a disease at a particular point in time in relation to the population in which it occurs (%)
  • proportion: number affected/population
  • mortality: the percentage expression of the frequency of deaths over a period of time in the total population (not a rate, a proportion)
how to become a disease agent 6 commandments of parasitism
How to Become a Disease Agent:6 Commandments of Parasitism
  • Find a proper host
  • Somehow get in or access inside
  • Find a home
  • Be fruitful and multiply
  • Get out once done or developed
  • Be transmitted to a new host
  • all this obviously involves specificity in the host:parasite relationship
host parasite specificity
Host:Parasite Specificity
  • Specificity is required for steps 1 and 3, above (find a proper host, find a home inside)
  • host specificity example: Shasta rainbow trout are highly susceptible to Ceratomyxa shastawhile Crystal Lake individuals are completely resistant
  • reason: physiological specificity (the host must meet all of the metabolic requirements of the agent without destroying it immunologically)
host parasite specificity23
Host:Parasite Specificity
  • Another example: Why are centrarchids infected with black spot metacercariae while walleyes aren’t?
  • Answer: ecological specificity -- the host and agent must overlap in time and space
  • Another type of specificity: tissue specificity
for next time
For Next Time….
  • Will continue with introduction to disease
  • Check books on reserve in the library….
  • Lab tonight: fish interna/exeternal anatomy, we provide dissection kits, etc.
potential for disease via infection contributors
Potential for Disease via Infection: contributors
  • numberof organisms (overwhelming)
  • infectivity (ability to get in)
  • virulence (ability to produce disease)
  • susceptibility of the host
  • agent’s ability to overcome host’s defenses
  • level of stress (REM!)
  • probablility of disease (Theobald Smith Model) = (# agents x virulence of agents)÷(resistance of host)
possible fates of an agent within its host
Possible Fates of an Agent within its Host
  • host dies: agent proliferates, overwhelms host, good parasites don’t do this, $$$$$
  • host lives: largely dependent on stress
    • host gets sick, but recovers (defense worked)
    • host doesn’t get sick (agent not virulent, wrong host)
    • survivors:
      • agent either eliminated or
      • carrier state established (host infected, but no obvious disease, big problem)
        • latent(not easily observed)
        • patent (ongoing/observable)
mortality curves bell shaped
Mortality Curves: bell shaped
  • Infectious agent or toxic substance moves into the population and then, after time, no longer affects events in population.
  • Transmission is horizontal with width of curve proportional to incubation time and period of communicability.

Agent??: typically bacterial

mortality curves sigmoidal
Mortality Curves: sigmoidal
  • Slight deviation from bell-shaped curve due to lag period in course of disease (lag phase of growth)
  • Also, periods in which the disease is not communicable.


Agent??: typically bacterial

mortality curves point source
Mortality Curves: point source
  • Population at risk was exposed to agent at a single point in time.
  • All susceptible members affected.
  • Highly virulent infectious type disease of toxic agent
  • Exposure to toxin.

Agent??: chemical, viral

mortality curves plateau shaped
Mortality Curves: plateau- shaped
  • Indicates exposure over a long period of time
  • slow incubation
  • slow transmission

Agent??: possibly nutritional

mortality curves multiple spiked
Mortality Curves: multiple spiked
  • Due to frequent but intermittent exposure to disease agent
  • Data usually or eventually indicate plateau effect
  • Must take care re frequency of sample

Agent??: physical parameter (e.g., low D.O.)

degree of infection
Degree of Infection
  • Acute: high degree of mortality in short period of time, external signs might be completely lacking (e.g., CCV, IHNV, TSV, WSSV)
  • Chronic: gradual mortality, difficult to detect a peak (Aeromonas septicemia, furunculosis)
  • Latent: disease agent present, but host shows no outward sign, little or no mortality, sometimes associated with secondary pathogen/infection (CCV and Edwardsiella ictaluri)
the reservoir concept
The Reservoir Concept
  • reservoir: the sum of all sources of the agent, the natural habitat of the agent, where the agent comes from
    • The size of the reservoir is proportional to the chance of spread of a pathogen
  • transient reservoir: situation in which the epizootic displays a seasonal pattern of either cases or carriers
  • permanent reservoir: usually associated with disease in which chronic carriers are shown
    • good example: water supply, itself
  • Definition: mode of transfer of disease to a new host
  • Method 1)direct transmission: from one host to another, either a) vertically or b) horizontally
    • vertical transmission: from parent to offspring
      • via male (Girodactylus, trematode in pipefish)
      • via female (IHN)
    • horizontal transmission: from one member of a population to another, one offspring to another
      • contact: typically water borne (e.g., fish to fish)
      • ingestion of agent or of infected aquatic
  • Method 2)indirect transmission: infection via an inanimate vehicle, vector or intermediate host
    • vehicle: an inanimate object such as handling equipment (nets, waders, etc.) or feed (e.g., aflatoxin)
    • vector or intermediate host: animate object
      • mechanical: vector is not essential to life cycle of agent
      • biological: agent spends some part of life cycle in vector(e.g., water boatman and WSSV)
disease transmission getting in the door
Disease Transmission: getting in the door

Portals of entry, not as easy as they sound:

  • ingestion: e.g., Ceratomyxa shasta, BKD, Myxobolus cerebralis
  • gill lamellae: e.g., Schizamoeba salmonis, Ichthyobodo necatur
  • lesions: bacteria (Vibrio sp.), fungi (Saprolegnia sp.)
  • active penetration: some metazoans, dinoflagellates
the host
The Host
  • The ability of a host to acquire a disease agent and demonstrate disease symptoms can be expressed both qualitatively and quantitatively
  • qualitatively: resistance(ability of a host to withstand the effects of an agent; e.g., Litopenaeus stylirostris to TSV)
  • quantitatively: susceptibility (a measure of the host’s ability to tolerate an agent)
resistance primary factors
Resistance: Primary Factors

Physical barriers, inflammation, natural immunity, acquired immunity

  • physical barriers: refers to innate characteristic of animal body to penetration (e.g., mucous slime layer, intact skin, mucous membranes, exoskeleton)
  • for fish, the mucous slime layer itself displays an immune response (phagocytic properties, antibodies)
resistance primary factors40
Resistance: Primary Factors
  • inflammation: basic response to any wound, designed to seal off the area and reduce further infection/damage
  • manifestations (humans) include swelling, reddening, loss of function, heat, pain
  • manifestations (fish) possibly include heat and pain
  • histological changes: local edema(swelling); infiltration of neutrophils (type of white blood cell produced in bone marrow) , lymphocytes (lymph proteins), macrophages; fibroplasia (formation of fibrous tissue in wounds)
resistance primary factors41
Resistance: Primary Factors

3) Immune Response

  • natural immunity: inherited (discussed in detail later)
  • acquired immunity: either active or passive
    • active: obtains antibody via contact with antigen
    • passive: antibody obtained via donor (vaccination)
  • discussed in following lecture
resistance secondary factors
Resistance: secondary factors
  • Secondary factors associated with disease resistance are either environmental in nature orsomatic (associated with host, itself)
  • environmental factors: mainly stress resulting from deviation in temperature, dissolved oxygen, ammonia; inadequate nutrition; mechanical, etc.
  • somatic factors: age, sex, species (e.g., IPN affects only largest fry, potential for exposure, immune experience via exposure, black spermataphore, TSV)
stages in epizootic
Stages in Epizootic
  • REM: epizootic is an outbreak of disease
  • incubatory: agent has penetrated host barrier, found home and multiplying
  • clinical or subclinical: host adversely affected (manifestations)
    • depression (reduced activity)
    • color change
    • interrupted feeding behavior
    • body contortions
    • respiratory change
    • mortality
stages in epizootic44
Stages in Epizootic
  • terminal: host either dies or recovers
    • exception: in some very acute, highly pathogenic diseases (e.g., MBV) death may occur so fast that obvious signs don’t develop
  • NEXT: Immune Response in Aquaculture Organisms