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Control of Aquatic Diseases


... minimum impact on the environment really restricted to certain user groups New Animal Drug ... R&D required registration of a single compound ... – PowerPoint PPT presentation

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Title: Control of Aquatic Diseases

Control of Aquatic Diseases
Various Methodolgies Allowing Control
  • Test and Slaughter
  • Quarantine and Restriction of Movement
  • Immunization and Disease Resistance
  • Destruction or Reduction of Intermediate Hosts
  • Drug Therapy
  • External Treatments
  • Systemic Treatments
  • Hatchery Sanitation

1) Test and Slaughter
  • Requires testing population for pathogenic agent
  • If found, entire herd is destroyed
  • Carcasses disposed in a manner preventing further
    spread of agent
  • Effective when absolute control is needed
  • agent has no known treatment
  • agent is exotic
  • fish have high levels of agent
  • Often requires legislation to be effective
  • which agents require mandatory slaughter?
  • must include all policies
  • requires indemnification or wont be effective

2) Quarantine and Restriction of Movement
  • Restricts all movements of fish between drainage
    systems and between hatcheries -or-
  • Fish transport requires detention of fish in
    suspected area for length of time equal to
    incubation period of suspected agent
  • If no disease develops, fish moved
  • If disease develops, fish are rejected.

2) Quarantine and Restriction of Movement
  • Applies to whole animal, parts, or products
  • easy to suggest on paper, hard to abide by
  • Why? How can you practically hold fish outside
    your facility for the incubation period?
  • What about latent carriers?
  • Q/R also applies to all fish/shrimp imports
  • inspections carried out by certified inspectors
  • sampling assumes 5 prevalence in lot
  • sampling level ensures 95 chance of recovering
    one infected individual
  • could be infected but probably not

2) Quarantine and Restriction of Movement
  • Programs not typically effective because farmers
    wont pay for inspections if not required by law
  • Interstate transport laws are fairly loose
    (Idaho has no regulations)
  • True inspections programs are best handled by
    large institutions (e.g., public aquaria)
  • For permitting import of shrimp in Texas, you can
    only have one species (L. vannamei) and it must
    be SPF for TSV, white spot, IHHNV and Vibrio sp.

3) Immunization and Disease Resistance
  • Vaccines have proven useful to traditional
    agricultured species, humans, traditional species
  • not so effective for most aquacultured species
  • fish not very immuno-competent at low temps
  • limited methodologies for mass immunization
  • breeding/genetic programs in place for disease
    resistance rainbows resistant to furunculosis
    at low temps (lt 11 C), brown trout to whirling
    disease, new strains of L. vannamei resistant to
  • common problem breeding in resistance usually
    means breeding out growth

4) Destruction/Reduction of Other Hosts in Life
  • Can be effective against most metazoan parasites
  • you can try to eliminate some snails, keep birds
  • difficult to eradicate vertebrates most are
  • Belizean example of eradication

5) Drug Therapy
  • Typical method of dealing with outbreaks of
    infectious diseases in fish/shrimp
  • unfortunate for various reasons development of
    resistance, cost, approval issues
  • money limited potential volume of sales
    prohibits most companies from doing the RD
  • registration of a single compound for one type
    of use costs about 1.5 million and 1.5-3 years
    elapsed time

Federal Food, Drug and Cosmetic Act (1915)
  • Revised in 1956
  • limited use of many substances until safety to
    animals established
  • all compounds used must be registered as safe for
    use by FDA
  • GRAS generally recognized as safe
  • testing efficacy, toxicity, tissue residence
    time (food implications)

Revised Act (1956)
  • Applied to previous, but also included section on
    food additives
  • really targeting feeds
  • feed additives require additional registration
  • dosage (what is effective?)
  • withdrawal time (last dose ---gt market)
  • information on dose must appear on tags
  • real limitation on use, originally intended to
    curb only indiscriminate use

6) External Treatments
  • Controls pathogenic agents on outside surface of
    fish or from water
  • requires immersion under quality environmental
  • chemical effective but at lower-than-lethal level
    (e.g., chlorine not good for this use)
  • miscible in water
  • resist absorption by fish
  • usable for multiple treatments
  • cheap

Types of External Treatments dips
  • Characterized as high concentration for short
    period of time
  • used on small s of fish, often routine as a
  • advantages concentration easily established,
    requires small amount
  • disadvantages have to handle all fish, can
    create situation where effective dose is higher
    than lethal dose

External Treatments dip on the run
  • Strong chemical concentration via inflow water
  • chemical rapidly enters water
  • applicable to troughs, tanks, raceways
  • advantage dont have to turn off water
  • disadvantage uneven distribution

External Treatments bath
  • Really just a prolonged dip
  • lower concentration, determined accurately by
    volume of tank, amount of chemical
  • no water exchange
  • advantage concentration known, no fish handling
  • disadvantage oxygen can decrease, NH3 can
    increase, hot-spots, must quickly remove chemical
    at end of treatment

External Treatment flow through
  • Designed to maintain constant concentraton
    flowing into tank
  • chemical dripped-in or siphoned
  • advantages no water shut-off, no handling
  • disadvantages must have even flow for even
    treatment, costly

External Treatment indefinite
  • Simple to treatment of most ponds
  • very low concentration of chemical applied
  • broken-down naturally or dissipates into air
  • must break-down quickly (problem few do)
  • advantages no handling of fish
  • disadvantages lot of chemical (), adverse
    affects on pond (kills phytos), even application

7) Systematic Treatment of Diseases
  • Compounds introduced orally thru feed
  • problem sick fish go off feed
  • drug must 1) control pathogen under internal
    conditions, 2) have effective dose lower than
    lethal dose, and 3) be cost-effective
  • applied by feed company in feeds, can be
    integrated into gelatin binder on pellet surface
  • problem even spread on pellet coat, pellets
    must be prepped daily
  • why not often used? Apathy, money, stringent FDA

8) Hatchery Sanitation
  • Purpose 1 prevention of any foreign disease
    agents from getting into hatchery
  • Purpose 2 limits disease spread to tank of

Preventive Guidelines
  • Reduces vertically-transmitted pathogens
  • 1) import only eggs, never juveniles/adults
  • 2) eggs should be from SPF/high health facilities
  • 3) wild individuals should be prohibited or all
    water, etc. needs to be disinfected
  • 4) disinfect all eggs prior to stocking hatching
    containers (also disinfect/destroy all shipping
  • chemicals iodophores (Argentyne) 100 ppm for
    10-15 min

Guidelines for Limiting Spread
  • Disinfect all hatchery and personal equipment
    after or between use (equipment must be clean
    prior to disinfection)
  • sports fishermen or farmers should never be
    allowed near facility (political issue)
  • transfer/shipping equipment, vehicles must all be
    disinfected whenever leaving grounds
  • do not overlook any possible source of
  • proper hatchery design limits spread

Part 2. Biosecurity
  • Recently, shrimp disease agents and associated
    problems have spread from foreign countries to
    the U.S.
  • major efforts established defense against disease
  • due to severity of issue, parallel efforts were
    undertaken to design production systems to
    exclude diseases
  • such systems are called biosecure
  • key issue zero water exchange

Biosecurity General Issues
  • Definition the sum of all procedures in place
    to protect shrimp from contracting, carrying and
    spreading diseases
  • critical to identify all known and potential
  • critical use only seed from SPF or high-health
  • stocks monitored periodically for disease using
    rapid methodologies
  • infection of facility shut-down, complete
    disinfection (chlorine gas, formaldehyde, etc.)

Biosecurity General Issues
  • Other potential disease sources incoming water
  • facility should be isolated from other farms,
    processing plants, capture fisheries
  • water should be recycled
  • replacement water disinfected by chlorine, ozone,
    ultraviolet light
  • avoid vectors gulls, dogs, crabs, etc.
  • feeds ( prepared vs. raw)

  • Regulatory Issues

Approval Requirements for New Drugs
  • Approval comes from either the EPA or the FDA
  • requires scientific research and administrative
  • scientific research entails learning
  • efficacy of treatment (does the compound achieve
    the desired results?)
  • can results be obtained w/out further
    jeopardizing health?
  • Does its use pose danger to humans?
  • Does the therapeutant harm the environment?

Efficacy or Effectiveness
  • First step is to test the drug against potential
    pathogens (Are they sensitive to the drugs?)
  • usually performed in vitro Minimum Inhibitory
    Concentrations (MICs)
  • develop a standardized test battery of isolates
  • isolates are representative bacterial strains
    two references
  • acceptable MICs are less than 2 ppm

Efficacy (continued)
  • Second Step assuming drug is determined safe,
    it must be effective in vivo
  • a series of dose-titration studies
  • disease intentionally induced (w/pathogen)
  • followed by administration of drug at various
  • if effective dose response
  • hard to show with shrimp because they have no
    obligate bacterial pathogens

Safety when used on Test Animal
  • Lowest dose toxic to the test animal must be
  • toxicity is more than just the lowest level
    causing mortality
  • death any other deleterious effect (e.g.,
    lethargy, poor growth, aesthetic considerations,
  • levels established by lethal concentration
    (LC), lethal dose (LD), effective concentration
    (EC), effective dose (ED)

Standardized Procedure??
  • Toxicity testing procedures for cattle are not
    that applicable to fish or shrimp
  • proposed method (Williams et al., 1992)
  • Uses therapeutic index (TI)
  • TI (highest inhibitory level of drug/lowest
    level toxic to shrimp)
  • if animals show a TI value (therapeutic index) of
    greater than 4, go on to more detailed studies in
    other stages

Human Safety Issues
  • If the drug is shown to be effective against the
    pathogen, it is assumed that some is incorporated
    into tissue
  • greatest concern how long are effective levels
    in tissue maintained?
  • Must establish withdrawal period
  • definition the amount of time a given drug
    persists in the edible flesh of treated shrimp at
    detectable levels

Human Safety Issues (continued)
  • Studies used to establish withdrawal period are
    referred to as residue or depletion studies
  • time consuming, expensive, required detailed lab
    analyses, equip, etc.
  • procedures must follow GLP good laboratory
    practices (very rigid)
  • requires FDA certified GLP lab (few in the U.S.)
  • typical lab is owned by pharmaceutical company

Environmental Safety
  • The FDA is primarily responsible for reviewing
    information to support the premise that the
    prospective drug does not harm the environment
  • they like to see data indicating that the drug
    breaks down rapidly
  • short half-life in the system
  • low effluent volume
  • effluent that is highly diluted
  • further dilution in the environment

Environmental Safety
  • The FDA is really only concerned with the
    prospective drug harming the environment as a
    direct toxicant
  • other factors should be of concern
  • direct/indirect effects on microflora in and
    outside the culture facility
  • antimicrobials can shift things towards resistant
  • each successive use could increase proportion of
    drug-resistant microbes

Administrative Procedures
  • Unfortunately, the previous scientific concerns
    are the only ones addressed for acceptance of
    newtherapeutic drugs
  • administrative tasks are more difficult than the
    scientific ones
  • myriad types of FDA applications and procedures
    that must be followed

What does the FDA Want?
  • review your protocol for testing
  • follow up with a visit
  • must respond to your application within a certain
    time limit (sometimes up to 1/2 year)
  • then they tell you that you forgot something!!
  • Keep bugging them

Investigational New Aquaculture Drug Applications
  • If this is approved, you can use an unapproved
    aquaculture drug
  • INADAs are, however, used for specific purposes,
    many restrictions
  • meaningful data
  • only under INADA protocol
  • virtually no hazard to humans (rapid degradation
    in test animals)
  • minimum impact on the environment
  • really restricted to certain user groups

New Animal Drug Applications (NADA)
  • INADAs lead to NADAs
  • NADAs provide for the submission of required
    data in support of a request to gain the approval
    of a new drug for use with animals.
  • This process is very expensive
  • Usually, NADAs are submitted by pharmaceutical
    companies manufacturing the drug