Saturday, May 18, 2013

Cancer in Cats: Feline Leukemia

Cancer in Cats: Feline Leukemia

My series for Pet Cancer Awareness Month continues with a Q&A on leukemia in cats. Strictly speaking, leukemia is a cancer affecting the white blood cells. But the virus that causes it, also known as FeLV, is a retrovirus that can also cause several other fatal diseases in cats. Because the terms are used so interchangeably, this post will discuss them both.

Retroviruses produce an enzyme that allows these viruses to insert copies of their genetic material into the cells they infect. Rather than killing the body's healthy cells, they transform them into cells like themselves. This is how these viruses multiply in an infected cat's body. The feline immunodeficiency virus (FIV) is another type of retrovirus, although its cells are more oval in shape, whereas FeLV cells are circular. The two retroviruses have several other distinct differences, chiefly that a cat infected with FIV may never develop any symptoms, whereas an FeLV+ cat will develop some type of disease related to the virus.

Is There a Difference Between Leukemia and FeLV?

Yes. Leukemia is a type of cancer. It causes the number of white blood cells, or leukocytes, in the blood to be far higher or lower than normal. It can cause failure of the cat's immune system or the development of tumors. About a third of all the cats who die from tumors die from a tumor caused by leukemia, and about 1% to 2% of all cats have leukemia.

In a healthy cat's body, the leukocytes help the immune system fight off infections. These white blood cells either consume pathogens trying to invade the body, or they produce antibodies that will attack them. Leukocytes are produced in the body's bone marrow, spleen, thymus, lymph nodes, and tonsils. There are five different types of them, each with a specialized function.

Leukemia tends to mainly alter the lymphocytes (the cells produced in the lymph nodes that mark invading cells for destruction) and neutrophils (the immune system's first responders to inflammation). The virus also damages the cells in the bone marrow that produce blood platelets (megakaryocytes) and the red blood cells that carry oxygen to the body's cells (erythrocytes).

FeLV (Feline Leukemia Virus) is a retrovirus that can cause other diseases in addition to leukemia. Approximately 2%-3% of all cats in the US have it. Because retroviruses can integrate themselves into a cat's DNA, they affect many things beyond the blood. There are actually four subgroups of FeLV. Which disease it causes depends on the particular subgroup of the virus.

  1. Subgroup A is the original form of the virus that exists in all cats infected with it. This type is easily passed from one cat to another. It is less likely to cause the symptoms of actual cancer than the other three types. But along with the FeLV-A virus, in every infected cat, one of the other subgroups of the virus also exists.
  2. Subgroup B causes tumors, or lymphosarcoma, also known as lymphoma, which we discussed in an earlier post this month
  3. Subgroup C is the one that causes leukemia: damage to and depletion of red blood cells (severe anemia) and a proliferation of white blood cells.
  4. Subgroup T attacks the lymphocytes, causing a variety of seemingly unrelated, non-cancerous conditions that include arthritis, spontaneous abortion in pregnant queens, and suppression of the immune system that leaves the cat vulnerable to many other diseases.
When testing for FeLV in your cat, all subgroups of the virus can be detected, but testing does not reveal which of the four are present in your cat.

How Can My Cat Get FeLV?

Cats catch the FeLV virus by being exposed to the saliva, tears, and nasal secretions of infected cats. Other bodily fluids (e.g., urine, feces, milk) also contain the virus. If your cat has close contact with another cat who has the virus, your healthy cat can become infected with it. Mutual grooming is one means. Fighting with other cats is a leading cause of transmission, as a bite wound puts highly infectious saliva directly into the bloodstream. Mating is another, since male cats may bite females during this act. Sharing litter boxes or food and water dishes is less of a concern, but can still spread the virus.

Kittens can also get the virus from their mother while still in the womb, through the placenta. After being born, they're still being exposed to the virus during nursing, through their mother's milk. Some kittens exposed to it this way will fight off the virus and never develop actual leukemia. Others will carry the virus, but could appear perfectly healthy for many years before the disease progresses to one of the other three types. Aside from kittens, who are highly susceptible, elderly cats are more susceptible to infection with FeLV.

Among healthy cats, some can apparently fight off FeLV naturally when exposed to it. These cats may run a slight fever, have swollen lymph nodes, lose their appetite, and become lethargic as their bodies fight the virus, usually for no more than 10 days. This happens about 40% of the time in adult cats and around 70% in kittens. These cats may shed the virus for several months in their bodily fluids, but the infection is usually completely gone within six months. They will live a normal, healthy life and never suffer any symptoms.

About 30% of cats exposed to FeLV will develop an active infection of the virus that will eventually be fatal. These cats typically develop actual leukemia, with all its associated symptoms. White blood cells are greatly increased, but they are defective due to having been altered by the virus. This has the effect of suppressing the cat's immune system, making him more susceptible to all types of diseases caused by bacteria, viruses, fungi, and protozoa.

The remaining 30% of cats will carry the virus, but test negative for it. They may develop lymphoma that is actually caused by the undetected presence of FeLV in their bodies. Typically, the tumors will be in the cat's chest, spleen, kidneys, or spinal area. These cats will not respond as well to treatment of the lymphoma as would a cat that is not infected with FeLV. This is especially true if the tumor is of the acute lymphoblastic leukemia (ALL) type, which involves immature white blood cells that develop quickly.

FeLV is not contagious to humans or other types of pets, only to other cats. The main danger to a human who has an FeLV+ cat is to the pocketbook! (And, of course, to the emotions.)

How Can I Tell For Sure If My Cat Has the FeLV Virus?

Your veterinarian will need to take a blood sample from your cat and test it. This is known as the ELISA (enzyme-linked immunosorbent assay) test and can be done right in your vet's office. The virus protein will show up in your cat's blood. It can be detected within a few days after a cat becomes infected with the virus. Vets typically do this test as part of a cat's initial blood work on a patient's first visit.

There is a second test, known as IFA (indirect immunofluorescent antibody assay), that requires processing by a specialized laboratory. It checks for signs of the virus protein in the white blood cells. If your cat is showing strong symptoms of FeLV infection but the ELISA test is negative, your vet may want to send a sample off for this test. It's also used to verify a positive ELISA test before a final diagnosis is made.

Cats with a positive IFA result do not have a good long-term prognosis. They are considered "persistently viremic," meaning that the disease will progressively become worse until it kills them. Most cats are already in this stage when the disease is discovered.

A needle biopsy may be done to extract some cells from any masses, lymph nodes, or body cavity fluids. The final diagnosis of FeLV infection will be made after microscopic examination of these tissue biopsies to look for cancerous cells.

What Are the Symptoms of Leukemia?

In the early stages, your cat likely would show no symptoms and may appear perfectly healthy. Within two to four weeks of infection, however, the virus is already at work, getting established and replicating itself within your cat's body. The cat may have a mild fever and seem like he doesn't feel well. As discussed above, if your cat is successful in fighting off the virus, these may be the only symptoms ever exhibited, and your cat may go on to live a normal, healthy life.

The lymph nodes may be slightly swollen, especially in the neck area, since the virus first establishes itself there. As the virus injects itself into more and more of the cat's blood cells, you may notice that your cat will alternate between being well and having some type of illness. There's typically a loss of appetite that will lead to weight loss. There is usually some vomiting and diarrhea, as well. The diarrhea may be bloody.

Because the cat isn't getting proper nutrition, the coat will begin to appear dull and in poor condition. You may notice that your cat's gums and the inside of his mouth appear pale from anemia. Your vet may discover a persistent fever as your cat's immune system becomes more active with the overabundance of white blood cells.

Inside your cat's body, the disease is causing all the blood vessels to swell and the joints to become arthritic. The intestines are swelling. The blood vessels in the kidneys are swelling and there is increased albumin being released into the cat's blood. White blood cells are abundant, but they have been damaged so they can't function properly. Red blood cells may be abnormally large. In about 10% of affected cats, the red blood cells will actually rupture and release the hemoglobin in them that carries oxygen to the cells. There may be painful, abnormal bony growths developing in the connective tissues.

Over time, the cat will develop oral problems. You'll notice fishy breath. The gums may become swollen due to gingivitis and some teeth develop a condition known as stomatitis, which makes them painful enough to require surgical extraction by your vet. The cat may also have a tendency to bleed more easily as the number of clotting cells in the blood decline.

If your cat is pregnant, she may spontaneously abort the litter. 60% of cats who abort litters turn out to be FeLV+. If she carries the kittens to term and they have not died in the womb, they will also be infected with the virus, having contracted it from their mother's placenta. (But, remember, some may fight it off and go on to be healthy cats.) If the queen is carrying the virus but has not yet developed symptoms, she can still pass it on to the kittens through her milk. If your breeding female (queen) is infertile, it could be due to FeLV. 68%-73% of the time, this is the case with infertile queens.

As your cat's immune system deteriorates, he will get infections on his skin or ears, and also in the urinary tract (UTIs) and upper respiratory system (URIs). The cat may avoid the litter box with each UTI because it's painful to urinate. Each infection must be treated as it occurs, with bacterial infections usually more responsive to treatment with antibiotics. Fungal and viral infections are tougher to address. There will likely be recurring diarrhea at this point, which can be worsened due to antibiotic treatment killing off the beneficial bacteria in the cat's digestive system.

The cat will begin to suffer neurological damage that can cause behavioral changes and seizures. The vision will also be affected. The cat's pupils may appear uneven in size. The cat may become incontinent. The back legs may be paralyzed. Late in the disease progress, the cat will undergo severe wasting before death.

In some very rare cases, a cat will test positive for FeLV and the virus will be multiplying in the cat's body, but it is trapped in the cat's epithelial cells because the cat is producing antibodies against it. In these cats, the ELISA test will be positive, but the IFA test negative. These cats could still eventually develop either leukemia or lymphoma from the virus.

Is There a Treatment for Leukemia in Cats?

FeLV does have a U.S.-approved drug for fighting it, known as LTCI from a company called T-Cyte. It is also used to treat FIV, and has even shown promise against FIP (feline infectious peritonitis).
This drug will not eradicate the virus from a cat's body, merely treat its effects by restoring immune function. It does this by boosting lymphocyte production and function, amplifying the production of interleukin-2 that regulates white blood cell activity, and increasing red blood cell counts to combat anemia. It does require multiple injection sessions spread out over several months. The company's website has a page you can print to take to your veterinarian in case (s)he has not heard of this drug.

In Europe, a type of Interferon marketed as Virbagen Omega is being used to treat FeLV. This is a veterinary form of Interferon that is also used to treat parvovirus in dogs, and both FeLV and FIV in cats. It may cause more diarrhea in some cats, but has reduced mortality by 20%-30%.

Once the actual leukemia develops, the only real treatment option is chemotherapy. It is effective in some cases, while others do not respond to it. Most cats who develop leukemia survive less than a year. But even if your cat is one of the lucky ones to survive, he will always continue to carry the FeLV virus in his blood.

Infections must be treated individually as they occur. Certain types of antibiotics are better for treating infections in FeLV+ cats because they also combat the Haemobartonella bacteria that can amplify the cat's anemia.

Cats who have tested positive for the FeLV virus should be kept indoors. This is not only to prevent their infecting other cats with the virus, but also for their own protection. Because FeLV weakens the cat's immune system, any type of infection will be more serious in a cat who has it.

Feeding your cat a high quality diet is also recommended. This will improve the cat's overall health and support the compromised immune system. Don't feed the cat any raw foods, as these can carry bacteria to which your cat will be more susceptible. Nutritional supplements, if you can get them in your cat, will also help.

A good oral care program will help with the gingivitis and stomatitis problems. While it won't prevent them, any help you can give your cat in keeping the mouth clean and reducing bacteria there will keep those problems at bay.

Cats who are not eating properly will likely need to be given fluids. You may be able to administer these yourself subcutaneously at home. For anemia, vets may give a blood transfusion. Other treatments will depend on the symptoms your cat exhibits.

Try to minimize stress for your FeLV+ cat. Highly stressful situations for a cat include moving to a new home, introduction of new family members or loss of family members, or overcrowding. Cats don't like change in their normal routine. Other cats intruding on their territory, which may be new cats being brought into the home, or even roaming cats they can see through a window in their yard, stress them. Wildlife such as opossums and raccoons roaming through the yard cause a cat's territorial instincts to kick in, as well.

Most FeLV+ cats are not typically treated with steroids, as this can exacerbate the disease's progression. However, in those with chronic lymphocytic lymphoma (CLL) caused by FeLV, steroid treatment can send the leukemia into remission. If your cat develops an FeLV-caused lymphoma, your veterinarian will determine the type of tumor it is and treat it accordingly.

Your FeLV+ cat should see the vet every six months for a weight check, blood and urine tests, even if showing no outward symptoms. The vet will likely give your cat an anti-worm medication during these visits, to eliminate any parasites that could cause further weakness. Closely monitor the cat's health at home, as well, and get the cat to the vet if anything changes. Get any secondary infections treated promptly. Such treatments will likely be extended longer than their normal duration and may be more aggressive, due to the cat's compromised immune system.

By taking these steps, many cats can live a happy and reasonably healthy life for several years after being diagnosed with FeLV. However, 80% of all cats with a positive IFA test live less than three years  after diagnosis, so be prepared for this if your cat is FeLV+. Some people elect to have their cats euthanized when they get the diagnosis, but this may be robbing the cat of some healthy years during which you both could have enjoyed each other. As more severe symptoms develop to the point where the cat's quality of life is bad all the time, euthanasia becomes a more viable option.

Can Leukemia Be Prevented?

In many cases, yes. Keeping your cat indoors unless supervised is the first line of defense.

There is a vaccine available for FeLV that can be administered to kittens. Since it has been given more regularly to cats, the incidence of FeLV has declined dramatically. It is not effective in cats who have already been infected with the virus, so a cat should be tested for FeLV prior to receiving this vaccine. However, for cats who are 100% indoor cats and never exposed to other cats, this vaccine is not typically recommended. It has been associated with some vaccine-associated sarcomas (VASs). And it is not completely effective in preventing infection with FeLV if the cat is constantly exposed to infected cats, so even a vaccinated cat should be kept separate from any FeLV+ cats in your household.

If you discover early that your cat has been infected with FeLV, during the time known as "primary viremia," your cat may respond to treatment and never develop leukemia or lymphoma. But some cats fight off the infection naturally, even without treatment.

Any female cats who test positive for FeLV should be spayed, even if they are purebreds of good pedigree. (It's always recommended that non-pedigreed female cats be spayed regardless of their FeLV status, both to control the feline population and prevent undesirable behaviors associated with hormonal surges.) In fact, depending on the stage of the disease, a female cat with FeLV who is pregnant may suffer a miscarriage. Male cats who test positive should be neutered. This will not only prevent their passing it to females during mating, but also curb their desire to roam and fight, which spreads the virus to other males.

Keep all your healthy cats separate from any FeLV+ cats in your household. If you take in a stray or foster cat whose FeLV status is unknown, keep that cat separate from any healthy cats...and from any infected cats, in case the new cat doesn't have the virus. If one of the cats in your household tests positive for FeLV, immediately have the IFA test done on all your other cats.

If you lose a cat to FeLV, it's safest to throw away all bedding, litter boxes and food dishes before bringing a healthy cat into your home. Although the virus is fragile and doesn't live long outside a cat's body, it's better to be safe than sorry. Replace them all with new ones. If you can't do this, sterilize all the dishes and litter boxes with a bleach-water solution and wash bedding in your washer's sterilizing cycle. Vacuum all your carpets thoroughly and mop all the floors with a disinfecting agent (such as bleach-water). And make sure that any new cat you get who will be at risk for exposure to FeLV is vaccinated. Indoor-only cats who are never exposed to other cats need not be vaccinated against FeLV, although many veterinarians still recommend it in case the cat gets outside accidentally.

Sources: "Leukemia", Morris Animal Foundation; "Feline Leukemia Virus", Cornell University College of Medicine; "Feline Leukemia Virus Diseases", Pet Care Tips from Greenbrier Veterinary Hospital; "Feline Leukemia", 1-800-Pet Meds; "Overview of Feline Leukemia Virus and Related Diseases", The Merck Veterinary Manual.

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