|
How is FeLV
spread from cat to cat? |
The feline leukemia virus is
excreted in saliva and tears and possibly the urine and feces
of infected cats. Prolonged, extensive cat-to-cat contact is
required for efficient spread, because the virus is rapidly
inactivated by warmth and drying. |
|
How long can a
cat survive with FeLV disease? |
A cat with FeLV disease may
live for several weeks to several months, depending on how
advanced the disease is at the time of diagnosis. However, it
is impossible to tell how long any particular cat will
survive. |
|
Can a cat
become immune to FeLV? |
A significant percentage of adult cats
that are exposed to the virus develop immunity and do not
become persistently viremic (i.e., will not carry the virus
indefinitely in the blood and bone marrow). Usually those
cats live out a normal life span. However, in some the virus
may remain sequestered for a variable period of time
somewhere in the body. It is thus conceivable that FeLV might
break out and cause disease at a later date, after the cats
have been stressed, or perhaps medicated with drugs that
suppress the immune system. |
|
Can my
children or I become infected with FeLV if our cat is
infected? What about our dog? |
Although the possibility that FeLV can be
transmitted to human beings and cause disease cannot be ruled
out completely, there certainly is no evidence to date that
transmission does occur, despite decades of extensive
research. Also, there is no known association of FeLV with
acquired immune deficiency syndrome (AIDS) in human beings.
It is true that FeLV can be grown in human cells in culture;
the same is true of other infectious disease agents that
nevertheless do not produce disease in human beings.
Similarly there is no evidence that FeLV is carried by, or
causes any illness, in dogs. |
| Clinical
Signs |
|
What are the
clinical signs? |
Common clinical signs produced by FeLV
include anemia, jaundice, depression, weight loss, decreased
appetite, diarrhea or constipation, blood in the stool,
enlarged lymph nodes, respiratory distress, decreased
stamina, excessive drinking and urination, fetal resorption,
abortion, infertility, birth of "fading" kittens, and a
syndrome resembling panleukopenia ("cat distemper"). FeLV
also interferes with the cat's natural ability to ward off
infectious disease agents, so that almost any severe, chronic
illness may lead your veterinarian to suspect FeLV.
Cancer occurs in some FeLV-infected cats. In
those cats the tumor masses may cause such problems as
respiratory distress; intestinal inflammation with diarrhea,
vomiting or constipation; liver or kidney disease; cloudy
eyes; and neurologic abnormalities. |
| FeLV Tests
& Interpretation |
|
What do the
FeLV test results mean? |
Two types of FeLV blood tests are in
common use: the enzyme-linked immunosorbent assay (ELISA, or
kit test, which can be performed in your veterinarian's
office) and the immunofluorescence assay (IFA, also called
the Hardy test or slide test, which must be sent out to a
diagnostic laboratory). Both tests detect a protein component
of the virus as it circulates in the bloodstream, either free
in the serum (ELISA test) or within infected white blood
cells (IFA test). Interpretation of a positive or negative
test depends on which of these two tests your veterinarian
has selected.
The feline leukemia virus is present in the
blood (a condition known as viremia) during two different
stages of the infection. The ELISA test can detect the
primary viremia—the stage before the bone marrow has become
infected, when the cat's immune system still has an
opportunity to ward off the virus. The ELISA test can also
detect the virus in the secondary viremia stage - when the
virus has invaded the bone marrow, thus establishing a firm
and lifelong foothold within the cat.
By contrast, the IFA test detects
circulating viruses primarily during the second stage. Once
the infection progresses to that stage, it has passed a
"point of no return." Thus the majority of cats testing
positive by the IFA test remain positive for life. Those
cats, as well as most of those that are ELISA-positive, are
shedding FeLV in the saliva and are infectious for other
cats.
A negative FeLV test does not imply
immunity to FeLV, nor does it indicate that a cat has never
been exposed to the virus (i.e., it is a test for virus, not
the antibody to the virus). A negative test can be found in
cats that:
- Have never been exposed to FeLV (which
is what we all hope for)
- Are incubating the virus at an earlier
stage than either test can detect (such cats might test
positive later on)
- Have overcome a previous infection and
thus have not become persistently viremic
- Were infected with the virus previously
and have developed disease, but for some reason do not have
virus in the bloodstream at the time of testing
ELISA tests are also available to detect
virus in secretions— saliva and tears. There is some degree
of variability in the tests, and some positive animals may be
missed. At this time saliva and tear tests are probably best
reserved for screening purposes (e.g., to test a number of
cats, to determine whether FeLV is present in a household or
cattery) and for testing cats that are difficult to bleed.
|
|
I received two
different test results for my cat. What does this mean? |
This is an all-too-common problem and is
called "discordant test results". As explained above, both
the IFA and ELISA tests determine the presence of FeLV in the
blood of cats, but in different "compartments" of the blood
(serum vs. white blood cells).
If the cat is positive by ELISA and
negative by IFA at the same time, it may merely be that the
virus is at the primary viremia stage, which ELISA can detect
and IFA usually cannot. A cat might also test differently at
two different times with the same test; a reversal of a
positive test to negative eight weeks later is especially
common for the ELISA test. That indicates that the cat has
successfully contained the spread of the virus, so that it
never reaches the secondary stage of viremia.
Some healthy cats may remain
ELISA-positive, IFA-negative for a prolonged period of time.
Those cats are still carrying FeLV as a sequestered infection
but are apparently not shedding it in saliva, and thus will
not transmit the virus to their feline companions.
It is also possible for a cat in the early
stages of the infection to test IFA-negative and become
positive later on. Once a cat has become IFA-positive, it is
usually positive for life (persistently viremic). Whenever
there is a discrepancy between tests, one must repeat the
tests to be sure that consistent results are obtained.
Finally, when two tests fail to agree,
there is a slim possibility that one of them is incorrect.
This is not something to base all your hopes on, but it is
true that the tests are not 100 percent accurate, and once in
a great while you might receive an incorrect result.
|
|
My cat had a
positive FeLV test, but she seems completely healthy. Will
she become sick and die? |
Even if two or more successive tests
reveal your cat to be truly positive, it will not necessarily
die. An FeLV-positive healthy cat may live for months or
years; the life expectancy is impossible to predict. Your cat
is probably shedding virus that could infect other cats,
however, and you should take precautions to reduce the chance
of spreading the disease (see "Prevention").
In addition, the body's reaction to the virus may protect it
from the primary FeLV disease problems but not from the
immune-system suppression that the virus also can cause. Your
cat thus may be much more susceptible to other infectious
diseases and will require careful monitoring and immediate
treatment should illness become apparent. |
| Treatment
|
|
Is there any
cure? |
To date there is no cure for FeLV
infection or disease. A variety of chemotherapeutic regimens
have been developed, and in certain cases those regimens can
produce a temporary remission, depending on the physical
condition of the cat and the type of disease that is present.
Those drug therapies may allow the cat to continue in a
reasonably healthy state for a period of several weeks to
several months. However, it must be understood that those are
only remissions and not permanent cures. Chemotherapeutic
drugs are very potent, and their effects must be monitored
carefully, to avoid overdosing the patient.
Various antiviral compounds including
interferon may also be used to treat cats with FeLV
infection. Those compounds, while still experimental, are
generally safer to use than chemotherapeutic agents, and may
reduce the amount of virus present in the blood of the cat,
and may extend the period of remission of clinical disease.
As yet, antiviral compounds do not produce permanent cures
for FeLV infection or disease. Hopefully, additional research
will produce effective antiviral therapies that will cure
FeLV disease. |
|
Are massive
doses of vitamin C effective against FeLV? |
There is no scientific documentation that
vitamin C cures cats of leukemia. Controlled studies of
feline viral rhinotracheitis, canine distemper, and human
respiratory infections have failed to show effectiveness of
high doses of vitamin C. Of course, a multivitamin and
mineral supplement may be helpful to any sick animal that is
not eating properly; however, there is little evidence to
support claims that such a supplement can cure any of those
conditions. Other than providing general support to the
animal's health, vitamin and mineral supplements, in our
estimation, are not effective in preventing the spread of
FeLV within a cattery and certainly will not cure an
individual cat of its infection. |
|
If there is no
cure for FeLV, why did my veterinarian prescribe steroid
treatment? |
Therapy with a steroid (such as
prednisolone) acts to decrease the numbers of some
circulating white blood cells (lymphocytes). A cat with
leukemia may have an increased number of abnormal (cancerous)
lymphocytes circulating in its bloodstream; therefore steroid
treatment may help to destroy them. Prednisolone may also act
directly against the cells of some solid tumors (such as
lymphosarcoma) that are caused by FeLV. Steroids also inhibit
the cells that are normally responsible for destroying
senescent red blood cells; that effect may help to combat the
anemia and excessive red blood cell destruction that often
accompany FeLV.
It is important to remember that because
steroids and FeLV both suppress the immune system, an FeLV-positive
cat undergoing steroid therapy is especially vulnerable to
other infections. |
|
Prevention
|
|
Is there a
vaccine to protect my cat against FeLV infection? |
Several vaccines are now available to aid
in the protection of your cat against FeLV infection. The
vaccines are produced by various methods, and either contain
the inactivated ("killed") whole virus, or a subunit protein
of the virus. The principle of protection is the same for
each of these vaccines. |
|
Are the FeLV
vaccines safe? |
The FeLV vaccines are as safe as other
commonly used feline vaccines. As with any vaccine in animals
or humans, some reaction to the vaccine may occur in a
relatively small number of vaccinations. The vast majority of
cats vaccinated with FeLV vaccines will experience no
reaction at all. Occasionally, your cat will experience some
malaise for a few hours or for a day or two after
vaccination. On rare occasions, an allergic reaction to one
of the components of the vaccine may occur which will result
in fever, diarrhea, and malaise. This allergic reaction can
be treated by your veterinarian. |
|
How effective
are the FeLV vaccines? |
The FeLV vaccines are reasonably effective
in preventing persistent FeLV infection should your
vaccinated cat be exposed to the virus. No vaccine is 100
percent effective, and this is true for the FeLV vaccines.
The immune response produced by these vaccines will protect
most exposed cats from becoming infected with the virus.
Occasionally after exposure to the feline leukemia virus, a
vaccinated cat will develop a transient viremia (temporarily
become FeLV positive for up to 12 weeks), but the immune
response produced by the vaccine will control the virus such
that these cats will not develop clinical disease.
Unfortunately, a small percentage of FeLV-vaccinated cats
will not be protected against exposure to FeLV. |
|
What age
should my cat be vaccinated for FeLV? |
Kittens should be vaccinated twice
starting at nine to ten weeks of age, with the second dose of
the vaccine given three to four weeks later. Your cat should
receive annual revaccinations ("booster" vaccinations)
against FeLV. |
|
If my cat has
been vaccinated, is it safe to have this cat live with a FeLV-positive
cat? |
The FeLV vaccines are not 100 percent
effective, and thus a degree of risk occurs when a vaccinated
cat is housed with a persistently-infected cat (FeLV-positive
cat). It is recommended that FeLV-positive cats not be housed
with FeLV-negative cats, even those that have been
vaccinated. Certainly, a cat vaccinated against FeLV will
have a far greater chance of successfully withstanding an
exposure to FeLV than an unvaccinated cat. |
|
Will
vaccination interfere with the FeLV diagnostic tests?
|
No, vaccination will not interfere with
either the ELISA or IFA diagnostic tests. The vaccines do not
contain living virus, and the diagnostic tests detect a
specific protein within the virus. Antibodies against FeLV,
produced as a result of vaccination, are not detected by the
diagnostic tests. |
|
One of my cats
was just diagnosed FeLV-positive. How can I protect my other
cats from getting the disease? |
In either a cattery or a multicat
household, the most effective procedure is to test by IFA and
remove all FeLV-positive cats. The remaining FeLV-negative
cats should then be vaccinated and retested every three to
six months for the next year, and any that become positive
during that time should be removed. The household cannot be
considered "free" of FeLV until all remaining cats have
tested negative in two sequential tests taken at least three
months apart. No new cats should be brought into the
household until all the cats already there test negative
repeatedly. All new cats should test negative initially, be
quarantined for at least two months, and retest negative
before being allowed to mingle with other resident cats.
The premises should be routinely scrubbed
with detergent or disinfectant and wiped down with a solution
containing four ounces of household bleach per gallon of
water (bleach is an excellent disinfectant for viruses and
other infectious disease agents). All food and water bowls,
bedding material, and litter pans should be thoroughly
cleaned and disinfected. Better yet, they should be replaced.
|
|
My one and
only cat just died of FeLV. Is it safe to bring a new cat
into my home? |
Feline leukemia virus is relatively
unstable and will not survive outside an infected cat for an
appreciable length of time. The Cornell Feline Health Center
recommends a waiting period of at least thirty days after
removal of an FeLV-positive cat before a new cat is acquired.
Other precautions that should be taken are identical to those
described above to protect healthy cats. Thoroughly disinfect
or replace the food dishes, litter pans, and bedding that
were used by the infected cat. Floors that are covered with
tile or other hard surfaces should be cleaned and then
disinfected with dilute bleach solution (4 oz. household
bleach to 1 gal. water). Thorough vacuuming of rugs, plus the
thirty-day quarantine, should be sufficient to eliminate the
virus from carpeting in the household. |
|
Should FeLV-positive
cats be destroyed? |
Removal of persistently FeLV-positive
(positive on the IFA test) cats from a household is the only
proven effective method for FeLV control. The question
naturally arises: what is to be done with such cats after
their removal? In the past, some have recommended euthanasia
(because there is no reliable means of eliminating the virus
from the cat's body, the cat itself must be destroyed, to
destroy the virus). Euthanasia has also been put forth as the
only effective means for preventing further spread of FeLV
within the cat population at large. The question of
euthanizing a positive cat is one that must be addressed in
each individual case, in consultation with the attending
veterinarian. Vaccination against FeLV does not completely
replace testing and removal as the method of choice for
controlling FeLV.
If you own only one cat and it is FeLV-positive,
euthanasia is not necessary from the standpoint of
controlling virus transmission, so long as you keep your cat
indoors and away from all other cats. You must remember,
however, that in time the cat may develop an FeLV-related
illness and become so uncomfortable that euthanasia becomes
the only humane course of action.
If you have only a few cats and are
reluctant to have a positive one destroyed, particularly if
it is clinically healthy, a strict intrahousehold quarantine
program may permit you to protect your other cats from
infection. The FeLV-positive cat must be prevented from
having any contact with the negative cats, perhaps by housing
it in a separate room within the house. Separate feeding
utensils and litter pans should be provided, and hands should
be thoroughly washed and clothing (including shoes) after
handling and caring for the positive cat. The positive cat
should never be allowed outdoors, where it might come into
contact with FeLV-negative cats and transmit the virus.
|
|
A favorite
breeding queen (now pregnant) has tested positive for FeLV.
Must she be destroyed? If so, can I wait until after her
kittens are born? |
Feline leukemia virus is transmitted from
carrier queens to their kittens either in utero or after
birth. A very high percentage of kittens born to infected
queens will succumb to FeLV infection or FeLV-related
disease. In our estimation it is absolutely essential that
you establish a test-and-removal program, so that all
persistently infected animals are removed from the cattery.
Continuing to breed FeLV-positive queens merely expands the
problem and in essence signs the death warrant of kittens
born to those queens. |
|
What is the
Cornell Feline Health Center doing to combat FeLV? |
Our research on FeLV has involved basic
studies of the virus itself; attempts to develop more
effective vaccines; and evaluations of the effectiveness of
current FeLV vaccines, therapies, and diagnostic tests. Our
efforts are directed toward eliminating forever the threat of
this devastating viral infection.
Prepared by the Cornell Feline Health
Center, Cornell University, College of Veterinary Medicine,
Ithaca, New York 14853-6401. The ultimate purpose of the Feline
Health Center is to improve the health of cats by developing
methods to prevent or cure feline diseases and by providing
continuing education to veterinarians and cat owners. Much of
that work is made possible by the financial support of friends.
©1997 by Cornell University. All rights reserved. Cornell
University is an equal opportunity, affirmative action educator
and employer. |
