L102a: bacterial pathogens in fish

What percentage of fish are lost to infectious disease?

30%

What groups do we divide infectious disease into?

1. Bacterial

2. Parasitic

3. Viral

4. Fungal

5. Non-infectious disease

How can we calculate constant pressure of disease?

P = NV/R

• P = probability of developing pathogens

• N = number of pathogenic organisms

• V = virulence of organisms

• R = resistance of the host

What is the relationship of disease severity and pathogen number?

Increased pathogen number → increased disease severity

What are genetic and physiologic factors of host resistance?

1. Genetic propensity for disease resistance

2. Stress → immunosuppression

What are things that can stress the fish?

1. High density

2. Non-optimal husbandry

3. Changes in environment (ESPECIALLY TEMPERATURE)

What are gross signs of bacterial infection (septicemia)?

1. Internal hemorrhage

2. Hemorrhage at base of fis

3. Exophalmia (bulging eyes)

4. Ascites or dropsy

5. Granulomatous inflammation

6. External necrosis

What are the two organs that will be most informative for culturing a fish with septicemia?

1. Kidney

2. Spleen

THESE ARE THE BLOOD FILTERING ORGANS

Why is culturing fish skin extremely difficult?

Fish have massive bacterial flora on the skin due to constant exposure of skin to environment

what direction approach can we do to culture the spleen?

Lateral

what direction approach can we do to culture the kidney?

Laterally and dorsally

What causes the majority of bacterial infections in aquarium fish?

Opportunistic (secondary) bacteria as they are widespread in their environment

When will opportunistic bacteria strike to cause disease in the fish?

Cause disease when fish are injured, stressed, and/or immunosuppressed

What do opportunistic bacterial infections often result in the fish?

Skin or gill lesions that progress to septicemia

What type of bacteria are most of the opportunistic bacteria?

Gram-negative rods

What specific opportunistic bacterial infections often is the most problematic, widely distributed, and zoonotic?

Aeromonads

What are the specific Aeromonads strains?

1. Aeromonas hydrophilic

2. A. Sobria

3. A. Caviae

What are the names of opportunistic bacteria that lead to infections?

1. Aeromonads

2. Pseudomonas spp.

3. Plesiomonas shigelloides

How would you describe the lesion in the following fish?

Multifocal hemorrhagic dermatitis consistent with bacterial infection

How would you describe the lesion in the following fish?

Focal ulcerative dermatitis consistent with bacterial infection

List the primary pathogens

1. Mycobacteria spp.

2. Vibrio spp.

3. Streptococcus spp.

4. Francisella noatunesis

5. Flavobacteria spp. / Tenacibaculum martitum

Flavobacterium spp.

Yellow pigmented filamentous bacteria associated with disease in freshwater fish

What other names can Flavobacterium columnare be called?

1. Columnaris disease

2. Cotton / wool mouth

3. Saddleback

Where will Flavobacterium columnare in freshwater typically infect?

Infects the gills and skin then will progress to septicemia

What temperature will Flavobacterium columnare typically infect freshwater fish?

Historically a warm water disease (above 20 *C) but emerging in cold water fish

What bacteria is responsible for the signs in the following fish?

Flavobacterium columnare in freshwater fish

How do we diagnose F. Columnare in fish?

• Gill clip and skin scrape wet mounts

• Long filamentous bacteria that produce “haystacks”

What bacteria is shown on the wet mount slide?

• F. Columnare

• HAYSTACK APPEARANCE

What bacteria is THE “bacterial gill disease”?

Flavobacterium branchiophilum

What is the mechanism of action of Flavobacterium branchiophilum?

Bacteria remain SUPERFICIAL but produce a toxin that results in acute vasoconstriction → hypoxia and hyperplasia of the fish

What is the treatment of F. columnare?

Oral or injectable antibiotics

What is the treatment of Flavobacterium branchiophilum?

Immersion treatment in formalin, Chloramine-T, hydrogen peroxide

What bacteria is shown on the following slides?

Flavobacterium branchiophilum

Which will streptococcus spp. infect?

• Both wild and captive fish

• Both freshwater and saltwater fish

• INFORMS YOU IT IS NOT HOST SPECIFIC

What clinical signs will appear in fish infected with streptococcus spp?

• Fibrinous lesions systemically

• High bacterial loads in the brain

What is streptococcus associated with wild marine fish often attributed to?

Environmental conditions such as:

1. Temperature changes

2. Freshwater run-off into ocean

MCQ: What pathogen would be most effectively treated with immersion antimicrobials?

Flavobacterium branchiophilum

What type of environment does Vibrio spp. (vibriosis) infect?

Saltwater pathogen

What clinical signs will be seen in fish infected with vibrio spp?

Skin lesions and signs of sepsis

What situations will vibrio spp. be epizootic?

1. Stressed or immunocompromised fish

2. Ingestion of diseased or asymptomatic fish

3. Contamination of wounds

What bacteria causes “Fish Tuberculosis”?

Mycobacteria spp.

What are the clinical signs of a mycobacteria spp. infection?

Often chronic wasting disease with prominent granulomas (especially in the liver) in individual fish

What fish environment are there high incidences of mycobacteria spp infection?

1. Aquarium fish

2. Laboratory fish

What bacteria is responsible for the following lesion?

Mycobacteria spp

Why is mycobacteria spp. infection extremely difficult to manage?

1. Bacteria is an INTRACELLULAR pathogen that causes granulomatous formation that is unresponsive to antibiotics

2. Destroys the biofilm in the fish’s environment → hard to eradicate

What bacteria causes Fish Handler’s Disease?

Mycobacteria spp. but will not cause systemic disease in humans

What type of fish are the only fish where antibiotics are licensed for use in the USA in the treatment of bacterial disease?

Foodfish

What do we do for the treatment of bacterial disease in aquarium fish?

1. Off-label and minor use-minor species FDA regulations apply = more flexibility in treatment

2. ALWAYS HAVE ANTIBIOTICS OR GRAM NEGATIVE BACTERIA ON HAND (THESE ARE THE OPPORTUNISTIC PATHOGENS)

What are alternative strategies for endemic bacteria used in aquaculture?

1. Vaccines

2. Selective breeding programs

MCQ: what characteristic makes mycobacteriosis so difficult to treat in infected fish?

Intracellular infections result in granuloma infection

MCQ: what management strategy is best for opportunistic bacterial pathogens in an aquarium setting?

Optimal fish husbandry

MCQ: what management strategy is best for primary bacterial pathogens in an aquarium setting?

Biosecurity

What steps are done prior to the entrance of new fish?

1. Collect thorough history from animal source

2. Quarantine 30-60 days prior to introduction

3. Comprehensive fish exam and prophylactic treatment for parasites

4. Maintain strict biosecurity SOPs

List the biosecurity SOPs

1. System specific equipment and people

2. Disinfection of equipment with bleach or iodine (RINSE WELLNESS SINCE TOXIC TO FISH)

3. Foot baths

4. Wellness documented records to trace infections