Welcome to Diseases and Parasites of Aquatic

Organisms

MARI-5315

Dr. Joe Fox

January 20, 2004

Description of Syllabus

Course Number and Title: MARI-5315, Diseases and Parasites of Aquatic Organisms

Lecture Time/Location: Tuesdays, 4:30-7:00 in CS 103

Lab Time/Location: 7:00-9:00 CS 234 Instructor: Dr. Joe Fox, CS 251, TW10-12

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

Syllabus No textbook applicable (course too broad) All other readings will be on reserve or in my office course will consist of a weekly two-hour lecture followed

by a two-hour practical lab lectures are on the mariculture home page

(www.sci.tamucc.edu/pals/maric/Index/WEBPAGE/mari1.htm) you will need a lab coat (we’ll give you one) no open-toed shoes in lab labs will often require observation and checking on

samples outside class period

Syllabus: lecture outline

Lecture Date Topic

1 1/20 Introduction to Disease, Part 1

1/27 Introduction to Disease, Part 2

2 2/3 Immune Response in Aquaculture Animals

3 2/10 Diseases of a Non-infectious Nature

2/17 Exam 1

4 2/24 Common Viral Pathogens of Aquaculture Organisms, Part 1

3/2 Common Viral Pathogens of Aquaculture Organisms, Part 2

5 3/9 Common Bacterial Pathogens of Aquaculture Orgnaisms, Part 1

3/16 Spring Break – No classes.

3/23 Common Bacterial Pathogens of Aquaculture Organisms, Part 2

6 3/30 Probiotic Bacteria

4/6 Exam 2

7 4/13 Molds and Fungi

8 4/20 Protozoans and Parasites

9 4/27 Aquaculture Health Programs

10 5/4 Design of High Health Facilities

Syllabus: lab outlineLab Date Activity

1 1/20 Lab safety; Fish internal/external anatomy

2 1/27 Shrimp internal/external anatomy

3 2/3 Clinical work-up

4 2/10 Post mortem techniques

5 2/17 ELISA

6 2/24 PCR, Part 1

7 3/2 PCR, Part 2

8 3/9 Basic microbiological techniques

9 3/16 Spring Break – No lab

10 3/23 Vibrio sp. enumeration

11 3/30 Bacterial pathogen identification, classical

12 4/6 Bacterial pathogen identification, rapid methods

13 4/13 Aquaculture parasites, microscopic review

14 4/20 Aquaculture parasites, necropsy

15 4/27 Review for lab final practical exam

16 5/4 Lab Final Practical Exam

Syllabus: grading criteria

Evaluation Date % of total grade

Exam 1 2/17/04 16.67

Exam 2 4/6/04 16.67

Exam 3 5/7/04 16.67

Lab final exam 5/4/04 17.50

Lab reports Due at start of following lab period

32.50

Note: all assignments are due on time, unless w/prior consent of instructor;

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?

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 important to 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

Types of Diseases

1) 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 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 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

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)

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

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

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

Three-set model: 1. susceptible host2. pathogenic agent3. 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 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

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

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

1. Find a proper host

2. Somehow get in or access inside

3. Find a home

4. Be fruitful and multiply

5. Get out once done or developed

6. Be transmitted to a new host

7. all this obviously involves specificity in the host:parasite relationship

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 shasta while 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 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….

Will continue with introduction to disease Check books on reserve in the library…. Lab tonight: fish interna/exeternal anatomy,

we provide dissection kits, etc.

Today in MARI-5315 (Jan 20, 2004)

Texts on reserve in library (3 hr max check-out; don’t fail to turn them in on time; $3.00/hr overdue fine)

Lab tonight: we provide dissection kits Lecture: more on basics of disease

Potential for Disease via Infection: contributors

1. number of organisms (overwhelming)2. infectivity (ability to get in)3. virulence (ability to produce disease)4. susceptibility of the host5. agent’s ability to overcome host’s defenses6. 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

1. host dies: agent proliferates, overwhelms host, good parasites don’t do this, $$$$$

2. 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

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.

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Agent??: typically bacterial

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.

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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.

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Agent??: chemical, viral

Mortality Curves: plateau- shaped

Indicates exposure over a long period of time

slow incubation slow transmission

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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

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

Theoretical Cumulative Mortality Patterns

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

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

Transmission 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

a) vertical transmission: from parent to offspring via male (Girodactylus, trematode in pipefish) via female (IHN)

b) 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

Transmission

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

Portals of entry, not as easy as they sound:1. ingestion: e.g., Ceratomyxa shasta, BKD,

Myxobolus cerebralis2. gill lamellae: e.g., Schizamoeba salmonis,

Ichthyobodo necatur3. lesions: bacteria (Vibrio sp.), fungi

(Saprolegnia sp.)4. active penetration: some metazoans,

dinoflagellates

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

Physical barriers, inflammation, natural immunity, acquired immunity

1. 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 Factors

2. 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 Factors

3) Immune Response1. natural immunity: inherited (discussed in detail

later)

2. acquired immunity: either active or passivea) active: obtains antibody via contact with antigen

b) passive: antibody obtained via donor (vaccination)

discussed in following lecture

Resistance: secondary factors

Secondary factors associated with disease resistance are either environmental in nature or somatic (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 REM: epizootic is an outbreak of disease1. incubatory: agent has penetrated host barrier,

found home and multiplying2. clinical or subclinical: host adversely affected

(manifestations) depression (reduced activity) color change interrupted feeding behavior body contortions respiratory change mortality

Stages in Epizootic

3. 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

Today’s Lab: Shrimp External/Internal Anatomy

External anatomy: 30 minutes Internal anatomy: 60 minutes Read your protocol!!