Fish Diseases Lesson 2 Factors Involved in the Outbreak of Disease.
-
Upload
christiana-gordon -
Category
Documents
-
view
242 -
download
3
Transcript of Fish Diseases Lesson 2 Factors Involved in the Outbreak of Disease.
Fish DiseasesFish DiseasesLesson 2Lesson 2
Factors Involved in the Factors Involved in the Outbreak of DiseaseOutbreak of Disease
Factors Involved in the Factors Involved in the Outbreak of DiseaseOutbreak of Disease
A susceptible hostA susceptible host
A virulent pathogenA virulent pathogen
Proper environmental Proper environmental conditionsconditions
1. A susceptible host1. A susceptible host Good diet and clean water supply Good diet and clean water supply
Avoid introducing fish from another Avoid introducing fish from another hatchery - Quarantinehatchery - Quarantine
Host’s defense systemHost’s defense system
Fishes’ Lines of DefenseFishes’ Lines of Defense
Mechanical - Skin, Scales and Mucus Mechanical - Skin, Scales and Mucus
Physiological - Physiological - – White blood cells (Phagocytosis) White blood cells (Phagocytosis) – Liver detoxifies chemicals from waterLiver detoxifies chemicals from water– Local Tissue reactionsLocal Tissue reactions
Immune systemImmune system– Active against bacteria, parasites & virusesActive against bacteria, parasites & viruses
2. Virulent Pathogen2. Virulent Pathogen
Not all bacteria cause diseaseNot all bacteria cause disease
Some strains of known fish Some strains of known fish pathogens may not always cause pathogens may not always cause diseasedisease
Bacteria can become more virulent Bacteria can become more virulent by being “passed through” a fishby being “passed through” a fish
3. Adverse Environment3. Adverse Environment
Changes in environmentChanges in environment Certain temps favor or hinder Certain temps favor or hinder
pathogenpathogen Facility design - tanks vs pondsFacility design - tanks vs ponds Biological factorsBiological factors
– Hatcheries with well water vs surface Hatcheries with well water vs surface waterwater
Critical Levels of Water Critical Levels of Water QualityQuality
OxygenOxygen NitritesNitrites AmmoniaAmmonia Total AlkalinityTotal Alkalinity Total HardnessTotal Hardness pHpH TemperatureTemperature
Critical TemperaturesCritical Temperatures
Optimum varies with speciesOptimum varies with species– Tilapia - above 21 C (70 F)Tilapia - above 21 C (70 F)– Trout - 10-16 C (50-61 F)Trout - 10-16 C (50-61 F)– Catfish 10-30 C Optimum 25-30 C Catfish 10-30 C Optimum 25-30 C
(77-86)(77-86)
Critical Temps for Critical Temps for PathogensPathogens
Ichthyopthirius Multifilis (Ich)Ichthyopthirius Multifilis (Ich)– Most severe 20-22 C ( 68-72 F)Most severe 20-22 C ( 68-72 F)– Can occur down to 5 CCan occur down to 5 C– Seldom above 23 C ( 73)Seldom above 23 C ( 73)
Channel Catfish Virus (CCV)Channel Catfish Virus (CCV)– occurs above 23 Coccurs above 23 C
Enteric Septicemia (ESC) -Enteric Septicemia (ESC) -– 23-27 C (73-81)23-27 C (73-81)
Aeromonas 25-30 C (77-86)Aeromonas 25-30 C (77-86)
Factors in Disease Factors in Disease DevelopmentDevelopment
1. 1. SSource of infectionource of infection 2. 2. MMode (method) of infectionode (method) of infection 3. 3. PPortal of entryortal of entry 4. 4. VVirulence of the organismirulence of the organism 5. 5. RResistance of the hostesistance of the host
Source of InfectionSource of Infection
Infected fish, dead fish , sick fish, Infected fish, dead fish , sick fish, carrierscarriers
Infected fish eggs from carrier Infected fish eggs from carrier broodstockbroodstock
Contaminated water supplyContaminated water supply Contaminated FeedContaminated Feed Man and his activities Man and his activities
Mode of TransmissionMode of Transmission
Through the waterThrough the water– water with all the waste products water with all the waste products
from the fish make ideal conditions from the fish make ideal conditions for pathogens to survivefor pathogens to survive
Portal of EntryPortal of Entry
Gills - parasites can pierce gills and Gills - parasites can pierce gills and bacteria can enterbacteria can enter
Skin - breaks in skin and mucus by Skin - breaks in skin and mucus by parasites or handlingparasites or handling
Ingestion-Don’t feed wild, uncooked fishIngestion-Don’t feed wild, uncooked fish
Virulence of PathogenVirulence of Pathogen
Varies by species of virus or Varies by species of virus or bacteriabacteria
Different strainsDifferent strains
Pass-through effectPass-through effect
Resistance of HostResistance of Host
Different than immunity Different than immunity – Immunity is acquired by previous Immunity is acquired by previous
exposure to the infectionexposure to the infection
Natural Resistance Natural Resistance – substances in the fishsubstances in the fish– Non-specific Non-specific
Factors EffectingFactors Effecting Natural Resistance Natural Resistance
White Blood cells White Blood cells Tissue integrityTissue integrity NutritionNutrition Age of AnimalAge of Animal Strain of species Strain of species TemperatureTemperature
ResistanceResistance
Does not mean that the animal Does not mean that the animal cannot be infected, but that cannot be infected, but that the host has the ability to the host has the ability to subdue the pathogen to the subdue the pathogen to the point where it will not cause point where it will not cause disease.disease.