Control of Aquatic Diseases

1. Control of Aquatic Diseases

2. 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

3. 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 won’t be effective

4. 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.

5. 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

6. 2) Quarantine and Restriction of Movement • Programs not typically effective because farmers won’t 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.

7. 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 (< 11 C), brown trout to whirling disease, new strains of L. vannamei resistant to WSSV • common problem: breeding in resistance usually means breeding out growth

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

9. 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 R&D required • “registration of a single compound for one type of use costs about $1.5 million and 1.5-3 years elapsed time”

10. 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)

11. 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 ---> market) • information on dose must appear on tags • real limitation on use, originally intended to curb only indiscriminate use

12. 6) External Treatments • Controls pathogenic agents on outside surface of fish or from water • requires immersion under quality environmental conditions • 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

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

14. External Treatments: dip on the run • Strong chemical concentration via inflow water • chemical rapidly enters water • applicable to troughs, tanks, raceways • advantage: don’t have to turn off water • disadvantage: uneven distribution

15. 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

16. 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

17. 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 difficult

18. 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 regs

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

20. 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 containers) • chemicals: iodophores (Argentyne) 100 ppm for 10-15 min

21. 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 contamination • proper hatchery design limits spread

22. 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

23. 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 vectors • critical: use only seed from SPF or high-health facilities • stocks monitored periodically for disease using rapid methodologies • infection of facility = shut-down, complete disinfection (chlorine gas, formaldehyde, etc.)

24. 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)

25. Regulatory Issues

26. Approval Requirements for New Drugs • Approval comes from either the EPA or the FDA • requires scientific research and administrative tasks • 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?

27. 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 (MIC’s) • develop a standardized test battery of isolates • isolates are representative bacterial strains + two references • acceptable MIC’s are less than 2 ppm

28. 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 levels • if effective: dose response • hard to show with shrimp because they have no obligate bacterial pathogens

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

30. 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

31. 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

32. 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

33. 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

34. 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 species • each successive use could increase proportion of drug-resistant microbes

35. 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

36. 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

37. Investigational New Aquaculture Drug Applications (INADA’s) • If this is approved, you can use an unapproved aquaculture drug • INADA’s 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

38. New Animal Drug Applications (NADA) • INADA’s lead to NADA’s • NADA’s 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, NADA’s are submitted by pharmaceutical companies manufacturing the drug