KHV Testing for Koi: PCR Test Guide

By KoiQuanta Editorial Team|Updated Mar 2026

PCR KHV testing has a sensitivity of over 95% when samples are collected correctly. That sensitivity means a negative PCR result from a properly collected sample provides strong evidence the fish is not shedding active KHV. A poorly collected or incorrectly stored sample produces an unreliable result regardless of the test's inherent accuracy. Sample collection and handling are as important as the test itself.

KoiQuanta supports lab test result entry linked to fish and koi quarantine program records. No competitor integrates lab test result management in this way.

TL;DR

Koi Herpesvirus (KHV), also known as Cyprinid herpesvirus 3 (CyHV-3), is a highly contagious and typically fatal viral disease affecting koi and common carp (Cyprinus carpio).
First described in Israel in 1998, it has since spread globally through the international koi trade.
If fish show these signs between 16-25°C, KHV testing is urgent.
Turnaround is typically 3-7 working days for standard testing.
Test all fish on arrival before quarantine begins 2.
Hold through at least one complete cycle in the temperature risk window (16-25°C) 3.
Turnaround is typically 3-7 working days.

What Is KHV?

Koi Herpesvirus (KHV), also known as Cyprinid herpesvirus 3 (CyHV-3), is a highly contagious and typically fatal viral disease affecting koi and common carp (Cyprinus carpio). First described in Israel in 1998, it has since spread globally through the international koi trade.

Key characteristics:

Mortality rates of 70-90% in naive (previously unexposed) populations
Temperature-dependent: active and most contagious at 16-25°C
Latent infection: fish that survive KHV exposure may remain carriers that shed virus under stress or during temperature fluctuations into the risk window
No effective treatment: KHV is managed through prevention and containment, not cure
Notifiable disease in many countries: suspect cases may require regulatory reporting

KHV is the primary reason why quarantine for imported koi - especially from Japan and other high-prevalence regions - should be taken seriously. A single KHV-positive fish introduced to a naive collection can kill the entire pond.

When to Test for KHV

Importing koi from high-risk regions (Japan, Israel, Eastern Europe): Test before completion of import quarantine. Many professional operations test all imports before discharge from quarantine.

Fish showing clinical signs in the temperature risk window: KHV clinical signs include sudden high mortality, lethargy, gathering at the surface, white/necrotic patches on the gills, sunken eyes, and skin haemorrhage. If fish show these signs between 16-25°C, KHV testing is urgent.

Purchasing high-value koi from unknown sources: For fish valued at £500+, testing before purchase or as a purchase condition is reasonable risk management.

Confirming disease freedom before sale: Dealers selling high-value fish or fish to buyers who require health certification may need to confirm KHV-negative status.

Post-mortality investigation: After unexplained mortality in the temperature risk window, testing surviving fish and fresh post-mortem samples helps confirm or rule out KHV.

How PCR KHV Testing Works

PCR (Polymerase Chain Reaction) testing amplifies specific sequences of KHV DNA to detectable levels. Even small quantities of viral DNA in a sample can be detected reliably. This makes PCR the most sensitive available method for KHV detection.

There are two main variants:

Conventional PCR: Detects presence or absence of the viral sequence
Quantitative PCR (qPCR): Detects presence and estimates viral load (how much virus is present)

qPCR is increasingly standard in diagnostic labs because viral load information provides additional interpretation context.

How to Collect KHV Test Samples

Sample types accepted by most labs:

Gill swab (preferred for live fish): A sterile swab rubbed gently along the gill arch of a live fish. The gills are the primary site of KHV replication and the highest sensitivity sample for active infection. Requires a fish veterinarian or experienced handler - the fish must be restrained and the operculum lifted to access the gill.

Swab from kidney or spleen (post-mortem): Internal organ tissue from a freshly dead fish provides the highest sensitivity sample. Kidney and spleen are the preferred tissues.

Blood sample: Some labs accept blood samples. Requires a vet for collection.

Whole fresh dead fish: Some labs will perform the sampling from a fresh (not frozen) dead fish sent directly. The lab extracts tissue samples internally.

What not to do:

Don't freeze samples unless the lab specifically instructs freezing (freezing degrades some sample types)
Don't use formalin-fixed samples for PCR - formalin destroys DNA
Don't use decomposed fish - DNA degrades rapidly after death

Where to Send KHV Tests

Several accredited veterinary diagnostic laboratories offer PCR KHV testing. In the UK, labs include:

CEFAS (Centre for Environment, Fisheries and Aquaculture Science) - the reference laboratory for notifiable fish diseases in England
The University of Stirling Aquaculture diagnostic services
Several private veterinary diagnostic laboratories with aquatic diagnostic capability

In the USA, several state veterinary diagnostic labs and USDA-accredited labs offer KHV PCR testing.

Most labs provide sample submission instructions, required paperwork, and turnaround times on their websites. Turnaround is typically 3-7 working days for standard testing.

Contact your fish veterinarian for lab referral - they'll know which labs have current accreditation and appropriate testing capability.

How to Interpret KHV Test Results

Negative result: The sample tested contains no detectable KHV DNA at or above the test's detection threshold. This is strong evidence against active KHV infection if the sample was collected correctly and the fish was in the temperature window for active viral replication.

A negative result does not mean the fish has never had KHV. Latently infected carrier fish may test negative when the virus is in its non-replicating latent phase.

Positive result: KHV DNA was detected in the sample. In a live fish, this indicates active viral infection. In a post-mortem sample, it confirms KHV as a factor in the death.

A positive result in a live fish is a serious finding with regulatory implications. Do not move the fish or its pond water. Contact your fish veterinarian immediately.

Equivocal or borderline result: Some tests produce results at the margin of detection. Your lab report will indicate if this is the case. A borderline result typically requires resampling and retesting, ideally at a time when the fish might be in the active temperature window.

KHV Testing in Import Quarantine

For Japanese koi imports, the most rigorous testing protocol is:

Test all fish on arrival before quarantine begins
Hold through at least one complete cycle in the temperature risk window (16-25°C)
Test again before discharge from quarantine

Testing at both ends of quarantine, with the fish exposed to the active temperature window in between, maximises the chance of detecting virus that was latent on arrival but became active during the temperature challenge.

Enter all test results in KoiQuanta, linked to the specific fish and quarantine batch. The test date, lab, result, and any viral load information should be recorded. This creates the documentation trail for import compliance and fish health records.

Frequently Asked Questions

How do I test my koi for KHV?

Arrange PCR testing through a fish veterinarian or by directly contacting an accredited veterinary diagnostic laboratory. Sample collection typically involves a gill swab from a live fish (requiring fish restraint and operculum lifting) or tissue samples from a freshly dead fish. Contact your chosen lab before sampling for their specific sample submission requirements and packaging instructions. Most labs require samples shipped in cool conditions with appropriate documentation. Turnaround is typically 3-7 working days. For imports, test on arrival and again after passing through the 16-25°C temperature window during quarantine.

Where can I get a PCR KHV test for koi?

In the UK, CEFAS is the reference laboratory for notifiable fish diseases and offers KHV PCR testing, as do several university aquaculture labs and private veterinary diagnostic services with aquatic capability. In the USA, state veterinary diagnostic labs and USDA-accredited labs offer KHV testing. Your fish veterinarian is the best referral source for a currently accredited lab with appropriate capability for your region. Most labs have sample submission instructions on their websites, including required forms and shipping requirements. Some fish vets offer to coordinate the full process - sampling, submission, and result interpretation - which simplifies the process for keepers without lab submission experience.

What does a positive KHV test mean for my collection?

A positive PCR result in a live fish means KHV DNA was detected - the fish has active KHV infection. Immediate actions: isolate the fish from all others if not already isolated, do not move any fish or pond water off your property, contact a fish veterinarian immediately, and check whether KHV is a notifiable disease requiring reporting in your jurisdiction (it is in many countries). Do not introduce any new fish. The prognosis for KHV-positive fish is poor - there is no treatment, and mortality in naive populations is 70-90%. Temperature management (moving the pond above 28°C) may reduce mortality in surviving fish but doesn't cure infection. Collection depopulation may be required depending on regulatory guidance and the extent of spread.