welcome to diseases and parasites of aquatic organisms mari-5315 dr. joe fox january 20, 2004
TRANSCRIPT
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
lag
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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(fis
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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!!