Feline Leukemia (FeLV), a retrovirus, is the
most important infectious disease agent producing fatal illness in domestic cats
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
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
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.
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.
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
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.
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.
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.
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.
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.
Article courtesy of the Cornell Feline
Health Center, Cornell University, College of Veterinary Medicine, Ithaca,
New York 14853-6401
Included with this article, courtesy of Steven
Slagle, DVM, is his testimonial on the effectiveness of
Transfer Factor in his
veterinary practice, and how a cat with feline leukemia fully recovered:
“Transfer factors and transfer factor Plus have turned out to be the most
effective and versatile products I have ever used in my 32-year veterinary
practice. Here are a few examples: A cat with leukemia, an oral tumor, and
posterior paralysis due to a spinal tumor, was very ill and emaciated. One month
after enhanced transfer factors (1 cap daily), there was some regression of the
oral tumor, restored appetite with some weight gain, and increased sociability.
Five months later, she continues to improve, regaining normal weight, 80%
regression of her oral tumor, and regaining use of hind legs and tail. Victor, a
10-year-old gelding, with EPM was treated with conventional drug therapy for 5
weeks and yet continued to deteriorate. At week 6, I started him on enhanced
transfer factors (6 caps/day). Within one week, he showed noticeable
improvement, and within 30 days, he was able to show. Since his full recovery 4
months ago, Victor has continued to show at his original performance level.” Dr.
Slagle says that he has used these products as stand-alone and in conjunction
with allopathic therapies in the following cases with excellent results: CANCER:
Canine lipomas, Canine/feline hepatic tumors, Equine squamous cell carcinoma,
Equine melanomas; Feline leukemia, oral tumors. VIRAL/BACTERIAL: Upper and lower
respiratory infections, Canine/feline dermatoses, Equine/bovine scours, Equine
septic arthritis, Feline abscesses.
Transfer Factor is not intended to
cure or treat disease. It is designed to enhance immune system function to
optimal levels. The immune system enhancement is responsible for any clinical