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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

Dr. Craig Kasper

FAS 2253/FAS 2253L

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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]

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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

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  • 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

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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

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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)

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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

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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

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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!

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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

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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

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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

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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:

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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

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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.”

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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.

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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

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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

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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

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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)

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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

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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)

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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

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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.

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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)

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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)

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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

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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

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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

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Mortality Curves: plateau- shaped

  • Indicates exposure over a long period of time

  • slow incubation

  • slow transmission

Agent??: possibly nutritional

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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.)

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Theoretical Cumulative Mortality Patterns

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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)

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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

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  • 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

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  • 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)

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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

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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)

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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)

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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)

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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

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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)

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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

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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