1. Factors Involved in the Outbreak of Disease
Fish Diseases Lesson 2
Factors Involved in the Outbreak of Disease

2. Factors Involved in the Outbreak of Disease
A susceptible host
A virulent pathogen
Proper environmental conditions

3. 1. A susceptible host Good diet and clean water supply
Avoid introducing fish from another hatchery - Quarantine
Host’s defense system

4. Fishes’ Lines of Defense
Mechanical - Skin, Scales and Mucus
Physiological -
White blood cells (Phagocytosis)
Liver detoxifies chemicals from water
Local Tissue reactions
Immune system
Active against bacteria, parasites & viruses

9. 2. Virulent Pathogen Not all bacteria cause disease
Some strains of known fish pathogens may not always cause disease
Bacteria can become more virulent by being “passed through” a fish

10. 3. Adverse Environment Changes in environment
Certain temps favor or hinder pathogen
Facility design - tanks vs ponds
Biological factors
Hatcheries with well water vs surface water

11. Critical Levels of Water Quality
Oxygen
Nitrites
Ammonia
Total Alkalinity
Total Hardness pH
Temperature

12. Critical Temperatures
Optimum varies with species
Tilapia - above 21 C (70 F)
Trout C (50-61 F)
Catfish C Optimum C (77-86)

13. Critical Temps for Pathogens
Ichthyopthirius Multifilis (Ich)
Most severe C ( F)
Can occur down to 5 C
Seldom above 23 C ( 73)
Channel Catfish Virus (CCV)
occurs above 23 C
Enteric Septicemia (ESC) -
23-27 C (73-81)
Aeromonas C (77-86)

14. Factors in Disease Development
1. Source of infection
2. Mode (method) of infection
3. Portal of entry
4. Virulence of the organism
5. Resistance of the host
Break the Chain

15. Source of Infection Infected fish, dead fish , sick fish, carriers
Infected fish eggs from carrier broodstock
Contaminated water supply
Contaminated Feed
Man and his activities

16. Mode of Transmission Through the water
water with all the waste products from the fish make ideal conditions for pathogens to survive

17. Portal of Entry Break the Chain
Gills - parasites can pierce gills and bacteria can enter
Skin - breaks in skin and mucus by parasites or handling
Ingestion-Don’t feed wild, uncooked fish
Break the Chain

18. Virulence of Pathogen Varies by species of virus or bacteria
Different strains
Pass-through effect

19. Resistance of Host Different than immunity Natural Resistance
Immunity is acquired by previous exposure to the infection
Natural Resistance
substances in the fish
Non-specific

20. Factors Effecting Natural Resistance
White Blood cells
Tissue integrity
Nutrition
Age of Animal
Strain of species
Temperature

21. Resistance
Does not mean that the animal cannot be infected, but that the host has the ability to subdue the pathogen to the point where it will not cause disease.