Koi Herpes Virus (KHV)

1. Koi Herpes Virus (KHV) Allen C. Riggs DVM, MS Aquaculture Development Program- Disease Prevention (ADP-DP) Hawaii Department of Agriculture

2. What is KHV? • Cyprinid herpesvirus-3 or CyHV-3 • DNA virus – family Herpesviridae • Susceptible species – Common carp (Cyprinus carpio carpio), Koi (Cyprinus carpio koi) and Ghost carp (C. carpio goi) • Resistant species – common goldfish (Carassius auratus) and grass carp (Ctenopharyngodon idella)

3. KHV mortality patterns: • 80 – 90% mortality in susceptible populations • Clinical disease occurs must commonly when water temperatures are between 22 – 27C (72 – 81F) • However new cases have been reported in lower water temperatures down to 18C (64F)

4. Signs of KHV: • Non-specific • Gill mottling with white necrotic patches dispersed between normal red gill tissue • Bleeding gills • Sunken eyes • Skin lesions • Notched nose

6. Methods of transmission: • Direct contact with infected fish • Direct contact with fluids from infected fish • Direct contact with water or mud which infected fish had been exposed to • Fomites/vectors from contaminated systems

7. How do fish become infected? • Infective virus enters susceptible fish through gills, skin and possibly gut • Depending upon water temperature, susceptible fish that get exposed may become infected and die • OR may survive the initial outbreak and become carriers

8. Latent carriers • Survivors of initial infection typically never show clinical signs again • However they are still infected and can spread disease to susceptible fish • This latent carrier possibility is what makes KHV especially problematic to commercial dealers *

9. Water temperature and KHV: • Clinical KHV disease has an average incubation period of 14 days following naïve fish exposed to infected or carrier fish • Most mortalities occur between 22 and 25.5C (72 -78F) • Virtually no mortalities above 30C (86F) • New cases have shown clinical outbreaks in temperatures below 21C (70F)

10. How to confirm KHV infection: • No one can tell by just looking at the fish! • Laboratory tests are required • Direct methods – actually detect the virus or “pieces” of its genetic material • Indirect methods detect antibodies produced by the fish after exposure to the virus

11. Direct methods • Virus isolation (growing the virus) on KoiFin (KF) cell lines • Polymerase chain reaction (PCR) • Best samples from alive then euthanized fish – posterior kidney • Non-lethal samples of blood, feces or gill clips can be used but results are often less reliable

17. Indirect methods: • Enzyme-linked immunosorbent assay (ELISA) • Virus neutralization (VN) • Non-lethal sample using blood • A positive ELISA or VN indicates that a fish has antibodies ( protective immune product) against KHV virus*

18. No test answers all KHV questions! • Negative tests by either direct or indirect methods do NOT mean fish are not carriers • No test definitely detects all carriers or survivors of outbreaks • Using diagnostic tests as a part of a combined preventive strategy is currently the most practical and cost effective

19. Why can’t the diagnostic tests give a definitive answer? • PCR is the preferred test for confirmation of active clinical infection – fish are sick and dying • PCR can detect some latent carriers but not all – surveillance screening of “normal” populations OR fish in quarantine • PCR is the most economical and easiest to implement

20. What about the antibody tests? • Fish that have antibodies against KHV mean that they have been exposed to the virus at some time in the past • Two possibilities – active infection with outbreak just starting OR latent carrier • Antibody producing immune cells take time to ramp up with new infections – false negatives • Same cells may slow down or stop antibody production if non-lethal infection occurred a long time ago and fish no longer sick – false negative on carrier state

21. Individual vs population screening: • Antibody testing is the preferred method for detecting carrier status in valuable individuals * • But what about testing groups of 10, 100 or 1000 fish? • Unless you test them all by antibody detection methods and get all true negative results each time – can NOT be 100% sure

22. How to prevent KHV: • Quarantine (Q) • Water temperature in between 21 – 27C (70 – 80F) …… 24C (75F)* • 30 day minimum time period • “Reverse quarantine” after 30 days initial Q period • Diagnostic screening tests

23. Quarantine • Definition • Separate tank or pond w/ separate water & filtration system • Preferably located away from the main pond • Time Period 4-6 weeks

24. Can KHV be treated? • No treatment for KHV! • Virus can remain viable for 3 days in water without fish hosts • Common disinfection protocols can eliminate the virus from contaminated systems and equipment

25. Regulatory Concerns with KHV: • 2007 – World Organization for Animal Health (OIE) added KHV to the notifiable disease list for finfish • USDA-APHIS asks accredited veterinarians and diagnostic labs to report positive cases to the AVIC of the state in which the case occurred

26. Regulatory Concerns with KHV: • USDA-APHIS has no mandatory requirements on KHV status for koi moving interstate or international • No mandatory depopulation for positive KHV fish • KHV now a Hawaii State reportable disease – positive cases must be reported to the Hawaii State Veterinarian

27. Spring Viremia of Carp (SVC) • RNA virus • Affects koi & goldfish • Mortality up to 70% in affected populations • Temperature range 12-24°C 54-72°F • OIE reportable disease • FAD and mandatory depopulation required by both State and USDA-APHIS

28. New USDA Guidelines for SVC • 8 spp. of fish that are susceptible to SVC are now under USDA oversight for importation into the U.S. • Required documents • USDA import permit (form VS-135) • Veterinary health certificate from the exporting country • USDA VS Port Veterinarian must inspect each shipment at entry port