FeLV, a retrovirus, is
the most important infectious disease agent producing fatal illness in
domestic cats today.
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.
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.
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.
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.
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.
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. 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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
