The
time interval between exposure and onset of KHV disease is temperature
dependent; the lower the temperature, the longer the incubation period
(time between a first exposure to the virus and the onset of disease).
KHV seems to survive at low temperatures better than high temperatures
(> 86° F), but disease caused by KHV is generally seen between 68-85°
F.
Koi
that have been exposed to KHV have 4 possible fates: a) are
not infected, i.e., are naturally resistant or are immune b) are
infected and die or c) are infected, but survive and eliminate
the virus or d) are infected and survive, but become asymptomatic
carriers. Asymptomatic carriers are healthy animals that have
viral DNA somewhere on or in their body (the site remains to be
determined) and when the right conditions (which are not completely
known) occur, the viral DNA becomes activated and begins to reproduce
more viruses. The conditions under which the virus is eliminated or
becomes latent (inactive) is still unknown. Carrier fish contain viral
DNA that can become active some time in the future and can spread the
infection to previously unexposed fish.
Stress
(including transport, parasites, poor water quality and other factors)
probably plays a role in causing fish to breakdown from the disease; KHV
is often associated with secondary diseases (i.e. Costia).
The
virus attacks epithelial cells of the koi, especially skin and gills.
This results in excessive mucus shedding, dry feeling skin, dead gill
cells (often attacked by fungus, parasites and bacteria). Affected koi
do not eat, cannot breathe, and die a slow, painful death, often lasting
weeks.
The
mortality rates of populations of koi from a pond in which
symptomatic koi were diagnosed (confirmed by laboratory
analysis) range from 50-100%.
There
is clinical evidence that suggests that KHV affects koi, but not
goldfish, but it is not known whether or not goldfish can harbor live
virus, and if so, for how long.
Diagnosis
of KHV
The
most effective way to diagnose KHV at the present time in sick fish is
by the PCR test for KHV DNA. Virus
Isolation and histology (stained slides interpreted by experts) is also
possible, but takes longer. Each test has pitfalls, and is only as
reliable as the sampling method and interpretation. All of the tests are
subject to false negatives; the PCR test can have a false positive
results. Histology is not specific for KHV. Accuracy is critical and
sometimes multiple tests must be run. This diagnosis is too important to
trust to inexperienced hands.
Current
tests are not useful in finding KHV in healthy carrier fish.
However, directly exposing KHV free koi to healthy suspected carrier
fish (at temperatures between 68-80°) might cause disease in the KHV
free koi within a few weeks (or up to 3 months), which can be tested for
KHV. The technique is not failsafe. However, since there is no reliable
laboratory method of detecting carriers by any other means, this method
could be tried. Obviously, a test that does not cost of lives of
innocent koi would be welcome.
Treatment
of KHV Disease
There
is no cure or treatment for KHV viral infection at this time.
Treatments (chloramine T or potassium permanganate treatment for
secondary bacterial gill disease, fungal and parasite control;
antibiotic treatment for internal secondary bacterial infections; salt
for relief of overhydration; vitamin C for immune support), might help
koi overcome secondary problems, but they should not be interpreted to
mean than they cure KHV disease. There is no cure. At temperatures <
65 ° F, koi generally do not die or show symptoms of KHV infection, but
infected fish will develop signs of KHV disease when the temperature
reaches optimum for this virus (68-80°). Raising the temperature to
> 86° F might increase the number of survivors. There are still no
documented scientific reports to establish reliable treatment guidelines
at this time, but chloramine T or potassium permanganate treatments may
also be beneficial by reducing the number of live viruses in the water.
Sick fish might not survive the treatments; surviving fish might have
permanent injuries. Treatment can be costly. Individually valuable and
privately owned fish might be worth the effort, but it is not cost
effective for most dealers. Furthermore, surviving koi must be
considered to be carriers until proven otherwise, and therefore, should
not be shown, sold, or transferred without advising the new owners that
these are KHV survivors.
Prevention
of KHV Exposure
It
is highly recommended that owners quarantine all new and any returning
(i.e., having been outside the system) fish at the owner's home. There
is good evidence to assume that all koi have been exposed to one
or more disease causing agents, and that through proper care and
management, the losses of koi to disease can be greatly reduced.
However, unlike other infectious diseases that can be cured or treated
effectively, viruses are incurable, and KHV is associated with high
mortalities and permanent carrier fish. Therefore, quarantine is the
best defense against KHV at this time.
There
is good reason to recommend English style koi shows and advise against
Japanese style koi shows. Field cases of
KHV had a common factor: koi had been in direct contact with other koi
(newly purchased, or recently shown in a Japanese style koi show) and
then entered a pond without quarantine. Recently transported fish are
stressed (which is believed to be underlying facilitator of KHV disease)
and koi are moved more often in a Japanese style koi show. KHV is
suspected to be present in koi populations from many countries, and
current evidence suggests that no county of origin should be considered
free of the virus. There seems to be no justification for showing koi in
Japanese style koi shows where the fish are in direct contact with many
koi from many places. While the tradition and beauty of a Japanese style
koi show would be missed by many, preserving tradition is not worth the
potential risk of harming all of the beautiful animals that the show was
designed to appreciate and honor. Since koi are truly domestic animals
and often loved pets, we owe it to them to protect their health.
There
is little documented information about how KHV is transmitted (i.e. by
water, direct contact with infected fish, through an intermediate host
etc) or about how long, and under what conditions the virus will live
away from the host. The virus may be transmitted by water or nets
(short term and minimal contact), but disease outbreaks are
definitely linked to direct fish to fish contact.. Herpes
viruses are killed by routine disinfection, so KHV is assumed to be
likewise susceptible. Therefore, a good disinfection procedure that is
used regularly and correctly is an essential part of a disease
prevention program.
-
Be an educated hobbyist. Quarantine your
fish. Ask your dealer about their quarantine and disease control
practices, and work with dealers who quarantine and have routine
established veterinary care. Each inspection, quarantine and disease
prevention program reduces the risk of KHV. Watch for updates about the
virus and control measures such as vaccinated fish, resistant fish or
populations of KHV free fish, which might become available in the near
future. Attend seminars about KHV or work with qualified professionals
who are up to date on this disease. If KHV is suspected, get
professional help. This disease is too deadly to be missed and too
costly to be wrong. The best way to control KHV is by having
breeders, dealers, veterinarians, researchers and hobbyists working
together so that the hobby remains fun for all.
A
QUARANTINE PROTOCOL FOR KOI HOBBYISTS TO REDUCE THE RISK OF KOI HERPES
VIRUS (KHV) INFECTION
Quarantine
alone will not prevent the spread of KHV, but it will reduce the risk
Quarantine, when used as part of a comprehensive disease prevention
program, is the single best current method of preventing many different
types of infectious diseases from entering a koi pond. The following
quarantine protocol represents current thinking and experience of
several knowledgeable experts in the scientific, veterinary and hobby
community and will likely uncover most KHV infected koi. It is not
failsafe, and all koi owners are strongly advised to seek professional
advice when dealing with this disease. However, it is a very important
first step in reducing the risk of introducing KHV into a pond.
System
requirements
Quarantine
is forced isolation. Therefore, a suitable place for this isolation
needs to be prepared. Excellent conditions and good water quality is
essential because no quarantine is better that quarantine in a system
that has poor conditions.
Details
of how to build several different quarantine systems will be given the
May/June '03 issue ofKoiUSA.
The
quarantine system needs to:
-Be
adequate in size and shape - round is better than square
-Be
free of initial pathogens — sanitize the system prior to use, or use a
system known to be disease free.
-Be
in a safe place - the environment should be tranquil and not subject to
extremes
-Have
a working bio filter - nearly a must and a definite advantage -
otherwise daily water changes and ammonia binders are required.
-Have
the capacity to heat the water to 70- 75 degrees F.
-Be
located a sufficient distance or have barriers such that other areas are
not easily contaminated by water or equipment used in and/or around the
system.
-Have
adequate disinfection - see separate disinfection section.
-If
the 'heat method' is intended to be employed in an attempt to increase
survivors ofKHV, provisions to heat the tank water to 86° F need to be
available.
The
protocol
Under
ideal conditions, the water in the quarantine tank water should be the
same temperature and pH as the water in which the koi has been swimming
over the last couple of weeks. If this is not possible, then try to get
as close to temperature as practical remembering that koi tolerate a
rise in water temperature better than a drop.
The
koi to be isolated should be contained in a transport bag with adequate
water and oxygen and floated in the isolation tank water for 20 to 30
minutes to allow for temperature equilibrium between the water in the
bag and in the tank.
Fish
(but not transport water) should be released into a properly sized
container (koi tub) of clean quarantine tank water and subsequently the
fish should be quickly transferred to the tank. If the hobbyist is not
competent to handle the fish with bare hands, the transport bag should
be used to transfer the koi and should contain as little water as
possible, the goal being to minimize the amount of transport water put
into the quarantine tank.
The
fish should be kept quiet and under cover of Styrofoam or pvc pipes
The
temperature of the water in the Q-tank should be adjusted and held
between 70° to 75° F for a period of no less than three weeks. During
the temperature adjustment period, the temperature should not drop or
raise more than 5° F per day.
Do
not feed the koi for the first few days. Then, if the fish appear
hungry, start feeding a little twice per day.
Over
the entire period of quarantine, be sure to monitor water parameters,
particularly ammonia, nitrite, pH alkalinity, and temperature and make
any necessary adjustments and/or take appropriate measures.
Water
changes are usually beneficial, are recommended and a minimum of 10% per
day is advisable. Always dechlorinate new water used for water changes
and use an ammonia binder if the water contains chloramines and you are
changing over 20% or if you do not have a working bio-converter on the
system.
The
fish should be maintained at 70° to 75° F for no less than three weeks
and a much better period would be three months. The longer the
quarantine period, the more likely infected fish will be revealed.
At
some time during the quarantine period, a fish of "lesser
desirability" from your pond should be placed in the tank with the
new arrival(s). Koi are social animals, and need companions. However, if
there are more than one koi in quarantine, the pond fish can be added
after 1-3 weeks in quarantine, and the population kept for 3 weeks to 3
months more. By waiting until 3 weeks, many diseases, including KHV will
become obvious, and can be eliminated before any pond fish are at risk.
During
the period of quarantine, periodically check (or have a professional
check) for any other abnormal or disease conditions. It is advisable to
have a complete and accurate diagnosis of conditions found in
quarantine, make sure that the quarantine system has good water quality
and follow expert advice for keeping koi healthy. Monitor the tank daily
and if any fish (new or old) shows the symptoms typical of KHV, call a
qualified veterinarian to take samples and submit them to a qualified
lab for testing. For a list of qualified veterinarians, see the AKCA web
site at: www.akca.org and follow the "KHA" link then
the "Referral Veterinarians" link. If maintained at the 70°
to 75° F temperature with no attempt to otherwise support the fish or
suppress opportunistic pathogens, about 10% of the fish should be
expected to survive.
KHV
infected koi may be euthanized (humanely killed) and disposed of
properly to prevent spread, or an attempt may be made to save the fish.
One method reported successful in saving a substantial percentage of KHV
infected koi is to elevate the temperature of the tank water to 86° F
until the fish recovers. Others (see previous section) involve adding
chemicals to the water to treat the symptoms of sick fish and possibly
to prevent transmission of virus. Remember there is no cure for KHV.
DISINFECTION
Using
separate equipment for separate systems is best but when that is not
possible or practical or if disease has invaded a system and ponds and
equipment need to be disinfected, the following should prove helpful.
Household
bleach, a sodium hypochlorite solution (usually 5.25%), is a good
disinfectant particularly for ponds (without fish) and for infrequent or
once-off disinfecting of lager equipment. The recommended concentrations
are 200 ppm (-145 ml or 5 oz per 10 gallons) for one hour and 10 ppm
(-725 ml or 3 cups per 1,000 gallons) for 24 hours'. Bleach is toxic to
fish but can be neutralized with sodium thiosulfate ("STS" - a
dechlorinator). Use STS at the rate of 1 gram per 10 liters of water'
(-380 grams or 0.81 pounds per 1,000 gallons of water) to neutralize
sodium hypochlorite at 200 ppm. Bleach can quickly degrade nets and
other equipment. A material that is much gentler on equipment and good
choice for general sanitizing of nets, tubs and smaller equipment is
benzalkonium chloride ("BZK"), a quaternary ammonium chloride
compound.
For
some years, many koi shows have used BZK to disinfect equipment. The
typical dose used there is about 200 ppm. That dosing was chosen because
it is effective against many pathogens and is not lethal to koi in short
term dips of that concentration. If the risk of accidentally placing koi
in a disinfecting tank is small, a higher concentration can be used to
provide faster action, i.e., 250 to 500 ppm for 20 to 30 minutes' or
1000 ppm for one minute2 .If 50% BZK is purchased, a
disinfecting solution of-400 ppm may be prepared by placing 3.0 ml of
50% BZK in each gallon of water. To avoid large amounts of foam, the BZK
concentrate should be added to the water and not vice versa. Containers
for dipping equipment should be large enough to handle any and all
equipment anticipated to need disinfecting. If there is a risk of
significant contaminants entering the dipping container, care should be
taken to cover the container when not in use. BZK is available in a 50%
solution from Argent Labs.
Western Quat
(quaternary ammonium chloride, -10% solution) is
available from Aquatic Eco-Systems. Or, see your local veterinarian for
specific uses and disinfection protocols. Disinfection does not work if
not used properly; it works best when used as part of a comprehensive
disease prevention program.
Equipment
that is dirty or has organics on its surface should be thoroughly
cleaned prior to disinfecting as contaminants can protect pathogens from
the disinfectants and organics tend to combine with and "use
up" the active ingredients of disinfecting solutions or protect
pathogens from it.
Dispose
of plants from infected KHV infected ponds.
