Disease interactions in wild and farmed fish

1

Disease Interactions Between Farmed and Wild Fish
- Fiction Fact
Kevin H. Amos , National Aquatic Animal Health
Coordinator NOAA Aquaculture Program NOAA
Fisheries Brown Bag Seminar Silver Spring,
Maryland October 11, 2007
2
The Case of the Sickly Salmon
3
Indictment 1

• Lo and behold, now we have Atlantic salmon in
  this state and now we have viruses (VHS virus) we
  have never seen before.
• Rob Zuanich, Commercial fisherman, Seattle
  Post Intelligencer, 2/28/89

4
Indictment 2

• It doesnt take too much gray matter to put two
  and two together. You have to ask how the thing
  (VHS virus) leap-frogs from Europe to Puget
  Sound. The common denominator would be Atlantic
  salmon.
• Jerry Grover, Regional Administrator, USFWS
• Seattle Post Intelligencer, 2/28/89

5
Indictment 3

• escaped Atlantic salmon spread diseases to wild
  salmon
• Educational Column, Seattle Post Intelligencer,
• 9/28/03

6
Indictment 4

• Mathematically coupled data setsindicate
  farm-origin lice induced 9-95 mortality in
  several sympatric wild chum and pink salmon
  populations
• Krkosek et al, Proceedings of the National
  Academy of Science, October 17,2006.

7
Guilty as charged?

• Or, are we rushing to judgment?

8
The Complexity of Disease

• Pathogen factors
• Host factors
• Environmental factors

9
Pathogen Factors

• Virulence
• Quantity
• Viability
• Reservoirs
• Intermediate life stages or alternate hosts

10
Host Factors

• Species susceptibility
• Individual susceptibility
• General health of host (nutrition, immunity)
• Age, size, stage in life history
• Prior exposure, vaccination, natural immunization
• Time of year
• Number relative density of cohorts
• Other infections, primary and secondary

11
Environmental Factors Impacts on host and
pathogen

• Season
• Temperature
• Water chemistry (chemical biological)
• Tides and currents
• Food supply for host
• Presence of other infected hosts, currently or
  previously Overlap Theory

12
Essentials to Cause a Disease Outbreak A
Perfect Storm

• Adequate number of susceptible hosts
• Adequate number of viable, virulent pathogens
• Environmental conditions which favor the
  pathogen, but compromise the host

13
The Culprits Infectious Pathogens

• Bacteria - BKD
• Virus - VHS
• Parasites - Sea lice, Gyros

14
BKD in wild female Chinook
15
EM of RhabdovirusVHSV (strain IV a)
16
Sea Lice
17
Gyro
18
What do all these pathogens have in common?

• A natural source exists in the wild
• Were not introduced into the region by farmed
  fish
• None of the pathogens are exotics

19
Do disease outbreaks occur-

• In marine pens? Yes!
• In wild salmon stocks? Yes!
• In species other than salmon? Yes!
• Due to pathogen transmission from wild fish to
  cultured fish? Yes!
• In wild fish due to farmed fish? Maybe.

20
The Evidence

• Evidence presented will be science-based.
• The sciences of epidemiology and pathology will
  form the cornerstones of our case.

21
Word of caution on cause and effect!

• When you hear the clattering of hooves, dont
  assume its a zebra most likely it is a horse!

22
Crime scenes in marine pens and in the wild

• VHS in the Pacific Great Lakes
• Sea lice
• Gyros in Norway/Baltic

23
Facts - VHS virus

• VHS causes disease in RB trout in Europe
• VHSV first isolated in U.S. in wild Pacific
  salmon in 1988
• VHSV determined to be native pathogen in Pacific
  Ocean
• Major outbreaks occur in the wild in pilchard,
  herring and mackerel
• New strain of VHS (IV b) in Great Lakes
• No virus or disease in farmed fish!

24
Broughton Archipelago

• Sea lice observed on sick wild salmon fry in 2001
  
• Near-record low pink returns in 2002
• Sea lice known to exist on farmed salmon
• Conclusion by some Low return of pinks in 2002
  due to mortality caused by lice from farms.

25
Pink adult returns to Broughton
26
Facts - Sea lice

• High prevalence in wild salmon
• Natural disease episodes recorded prior to marine
  aquaculture 1906, 1918, 1971.
• Found in non-salmon hosts (Jones)
• Lice load relatively low on farms
• No measurable impact on wild salmon populations
  (Beamish)

27
Other Theories for Pink Crash in 2002

• Feast begets famine redd superimposition,
  disease transmission on redds, poor nutrition due
  to competition.
• Higher than usual number of fry resulted
  exacerbated lice situation
• Event(s) on the high sea unrelated to lice

28
Gyros

• Govt. of Norway imported infected juvenile
  salmon from the Baltic to govt. hatchery.
• Norwegian stocks naïve to G. salaris
• Baltic stocks resistant to G. salaris
• Lack of bio-security allowed Gyros to spread
  within Norway.
• Huge impacts due to disease mortality and
  eradication efforts

29
Risky Business - Imports

• Exotic diseases have been introduced by commerce
  (G. salaris, WSSV)
• Caution! New discoveries often not new (as
  the case of VHS in NW)

30
Summary of Evidence

• Pathogen does not equal disease!
• Natural prevalence of pathogens in wild fish
  significant
• Juveniles stocked in marine pens are
  pathogen-free
• Exotics pathogens pose a significant risk

31
Judgment

• Evidence insufficient to link farmed fish to
  disease outbreaks in wild Pacific salmon
• Evidence suggests wild fish are the major source
  of pathogens
• Disease outbreaks occur in all populations of
  wild and cultured aquatic animals when we have
  the Perfect Storm

32
The Sentence

• Bio-security at farms is crucial
• Investigate causes of fish kills farmed and
  wild
• Implement a national aquatic animal health plan
  (NAAHP)

33
Objectives of NAAHP

• Protect wild and cultured animals
• Facilitate safe and legal trade
• Ensure availability of diagnostic and health
  certification services
• Define roles and responsibilities
• Meet U.S. obligations (OIE and WTO)

34
Fact

• Kevin S. Amos of PPBES fame is not my evil twin
  brother, even though we were both born in the
  same hospital in Lincoln, Nebraska.

35
Acknowledgments

• The following have contributed to this
  presentation - Thanks!
• WDFW, DFO, Jim Chacko, Jim Winton, Ted Meyer,
  Garth Traxler, Scott LaPatra, Gail Kurath, Bill
  Batts, Pacific Fisheries Resource Conservation
  Council, BC Salmon Farmers, ADFG, Richard
  Beamish.