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

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

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

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

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

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

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

Critical Temperatures Optimum varies with species Tilapia - above 21 C (70 F) Trout - 10-16 C (50-61 F) Catfish 10-30 C Optimum 25-30 C (77-86)

Critical Temps for Pathogens Ichthyopthirius Multifilis (Ich) Most severe 20-22 C ( 68-72 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 25-30 C (77-86)

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

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

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

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

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

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

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

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.