Disease monograph: Feline Leukemia Part 1: What is it?

Feline Leukemia Virus is a disease is transmitted between cats by a virus. The Feline Leukemia virus is a retrovirus from a family of viruses called oncornaviruses - viruses that cause the development of cancers (among other effects). A retrovirus is a virus that interacts with the genetic material of its host in order to reproduce. Feline Leukemia Virus (FeLV) causes immunosuppression, or failure of the body's natural defenses, in many feline species - the domestic cat is most susceptible, but large cat species such as lynxes, Florida panthers, cheetahs and lions have also been reportedly infected. This virus is not known to pass between non-feline species, so humans and dogs appear to be safe.

How is Feline Leukemia transmitted?

Electron micrograph of FeLV - from Wikipedia

The virus is shed in the saliva of an infected cat, and to some degree in respiratory secretions. Most cats receive the virus through the mouth. Generally, it is considered that the virus is transmitted through long term contact with an infected individual - such as sharing litterboxes and food bowls, mutual grooming, or through a bite. Mating behavior may also transmit the virus. Additionally, kittens can contract FeLV from their mother in utero and be positive from birth, or they can contract the virus through their mother's milk. Petting a feline leukemia positive cat and then petting a non-infected cat will not transmit the disease.

The frequency of FeLV positive cats varies greatly between areas. In some areas, the incidence can be as high as 70% in large multi-cat homes where cats have outdoor access. In single-cat, indoor homes, the prevalence is around 3% (3 in 10 cats). FeLV tends to be more common in urban cats (up to 40%) than in rural cats (up to 6%), because cats live in higher population densities and therefore have more contact with each other.

Healthy cats that test positive should not be allowed to roam outside, because they can infect other cats they come across. Additionally, other cats that live in the same household should be vaccinated, and it is recommended that the FeLV positive cat not have contact with the other cats because no vaccine is 100% effective, and the FeLV positive cat may spread other diseases that their weakened immune system allows them to contract.

Signs and symptoms

Not all cats that contract the feline leukemia virus actually develop "leukemia" (cancer of the white blood cells - specifically in the bone marrow), but leukemia is one of the cluster of diseases and symptoms that can develop when a cat is infected with this virus. Common symptoms of FeLV include poor appetite, poor coat and skin condition, fever, lethargy, weight loss, and anemia. Anemia is present in about 25% of all FeLV-related illness. Fifty percent of infected cats that become ill develop immunosuppression, or immune system failure, to some degree.

Various organ diseases can develop, such as liver or intestinal disease. Many cats may experience prolonged healing times after surgery or wounds. Additional signs may include uneven pupil size (anisocoria), swollen lymph nodes (lymphadenopathy), various secondary infections (bladder, skin, respiratory tract - bacterial or viral origins), gingivitis, stomatitis, diarrhea, jaundice, and a type of cancer called lymphosarcoma. Cats that are infected with FeLV are 50 times more likely to develop lymphosarcoma than non-infected cats. Lymphosarcoma (sometimes called lymphoma) is a cancer that consists primarily of a type of white blood cell called "lymphocytes". It can affect almost any organ in the body, but in young cats, it often appears in the chest cavity. In older cats, lymphoma of the intestinal tract is more common. Often in intestinal cases, there is no obvious mass or lump to find, but instead a generalized thickening of the intestine.

• Pale gums (or pale nail beds)
• Jaundice - yellow color to eyes, mouth, ears or other exposed skin and/or extremely dark, staining urine

  

  Jaundice coloring the roof of a cat's mouth

• Enlarged lymph nodes
• Chronic infections of respiratory tract, bladder or skin
• Gingivitis
• Weight loss/poor appetite
• Fever
• Poor coat
• Progressive weakness/sleepiness/lethargy/reclusiveness/hiding
• Diarrhea
• Vomiting
• Dehydration
• Breathing difficulty
• Reproductive problems - sterility, miscarriage

There are four possible paths the disease can take in an infected cat. These potential outcomes depend on the amount of virus the cat is exposed to, the strain of the virus (there are 4 unique strains of FeLV), the cat's initial health level (the effectiveness of his immune system and the presence of any other health complications), and age.

If a cat tests positive for FeLV, one of the following will occur:

1) IMMUNITY - Some cats are able to fight off the virus and become immune. Some of these cats completely eliminate all traces of the virus from their bodies. The cat may have some mild signs of illness - fever, poor appetite, large lymph nodes, lethargy for up to 10 days and then recover. This outcome occurs about 40% of the time, and is more likely in adults than in kittens.

2) PROGRESSIVE INFECTION - The second possibility is that the cat may become infected and develop a compromised immune system. The cat may have a short illness and recover enough to be outwardly healthy for 2-3 years in 50% of the cases. This outcome occurs about 30% of the time, and is more common in kittens than in adult cats. The bone marrow, which produces new blood cells, becomes infected and each new blood cell that is produced will contain more virus, creating a "persistent viremia" or constant presence of virus in the bloodstream. The infection is progressive, gradually taking hold in various body organs. Lymphoma is the final stage of the disease.

3) LATENT INFECTION -  Up to 30% of the time, cats will develop a latent infection. These cats may test positive at first, and then test negative 3-4 weeks later. The virus does not kill the cat's cells once it is inserted into the cellular DNA, but sits in wait. Eventually the body may reject these abnormal cells or the cat will become sick. While healthy, these cats will continue test negative on FeLV tests, but if vaccinated, will not be protected. Pregnant cats with latent infection may test FeLV negative but produce FeLV positive kittens. A latent infection may eventually result in immunity or may develop into active infection at some point in the future. Many cats with lymphoma (a common end-stage of FeLV) do still carry some FeLV DNA and are suspected by some to be latently infected with Feline Leukemia Virus.

4)  CARRIER STATE - Others may experience a "regressive infection" and continue to harbor the virus or particles of virus in a few cells, but the virus cannot replicate. In these cats, there is rarely any sign of illness, and they do not shed the virus. This outcome is extremely rare, occuring only about 1-2% of the time. These cats will test positive on ELISA test but negative on IFA tests. They may remain asymptomatic for a long time, even years. These cats are considered "carriers", and while they may never get sick, they can infect other cats. Eventually, these cats may develop active infection or develop latent infection. 

Feline Sense and Scents-ability: Part 4: Sight

SIGHT

Despite those huge, luminous eyes that sometimes seem to glow in the dark, a cat’s sense of sight is probably its least important sense next to taste! Cats can thrive with only one eye or even no eyes! Without sight, a cat relies on its sense of touch and hearing to map out the world, just like a human would.

The glow that you see in your cat’s eyes is light reflecting off a membrane lining the retina that collects and amplifies light called the tapetum lucidum. Because of this membrane, cats can see in as little as 1/6^th the light that humans need to see – but they still can’t see in complete darkness. Cats have many more rod light receptors than cone light receptors in their retina. Rod receptors are good at sensing motion and seeing in low-light conditions. Cones are the light receptors that sense color variation. What this means is that in order to see so well in so little light, cats sacrifice some clarity of vision, but they are much more skilled at sensing tiny motions, have extremely well-developed depth perception and much more acute low-light vision. They also have 200 degrees of visual field vs. human 180 degrees but their field of binocular vision is slightly narrower than ours. What a human can see clearly at 100 feet, a cat can only see clearly as far as 20 feet.

People often wonder if cats can see colors. They can, but their perception of color is much more limited than ours. They have dichromatic vision, meaning that they have two types of cone light receptors in their eyes - yellow/green and blue. Humans have trichromatic vision, meaning that in addition to the color receptors that cats have, we also have receptors that sense the color red. Cats can tell the difference between green, blue and yellow, but probably have difficulty distinguishing between red and green. Cats are able to distinguish between colors at the blue end of the spectrum (long wavelengths) better than between colors near the red end of the spectrum (short wavelengths).

Photo interpretation by Nicolay Lamm (http://www.wired.com/2013/10/cats-eye-view/)

While color and field of vision are limited, a cat seems to be exquisitely sensitive to sensing motion, or changes within the field of vision. It is thought by some that instead of seeing fluid motion, cats may see a "stop-motion" view of the world, giving their brain time to compare each "scene" to the one before and process minute differences between each image.

Cat Flip Book from matthieu scanlon on Vimeo.

A cat’s eyes can indicate a lot about its mood – the cat’s pupils dilate up to five times their normal size when it is frightened or threatened, or about to pounce. When cats are content, they squint their eyes.

This alert kitten's dilated eyes mean it is likely going to pounce

This cat's dilated eyes mean it is ready for a fight, with ears tucked back protectively

Cats have a third eyelid or nictitating membrane that closes across the eye from the inner corner. This third eyelid is whitish in color and is usually retracted when the cat is awake. When a cat is ill, the third eyelid often becomes visible as it relaxes and covers part of the eye. Sometimes, this is due to an eye infection or injury, but it can also mean that the cat doesn't feel well in other ways.

Besides eye disorders, third eyelid elevation can also commonly be caused by fever and vestibular (inner ear) problems

Because cats don’t see well close up, it seems that cat food and toys that come in fun shapes and colors are designed more for humans enjoyment than for cats – smell, sound and motion are much more fun to them.Instead of using sight for close-up encounters, cats point their whiskers forward and use the sense of touch to guide them.

So, to better understand your cat, instead of taking a “cat’s eye view” of the world, perhaps it would be better to take a sniff and a listen, instead?

Feline Sense and Scents-ability: Part 3: Touch

TOUCH

Cats have a highly developed sense of touch. Most obviously, they have 24 vibrissae, or whiskers, grouped in 4 sets on each side of the nose. The whiskers on the face are called mystacials and the top rows can move independently from the lower rows. The whiskers above the eyebrows are called superciliary whiskers. There are also whiskers on the backs of a cat’s front legs associated with the accessory carpal gland. All these thick hairs, about 2 times thicker than the rest of a cat’s fur, and rooted 3 times deeper in the skin, are surrounded at the base by bundles of nerve receptors that send messages to a special area of the brain called the barrel cortex. There, the nerve signals create a 3-D map of the spatial environment based on a cat’s touch in a way very similar to the visual cortex’s map of the visual environment.

Cats’ whiskers also help them judge distances – from planning and executing aerial acrobatics to deciding if they will fit through small openings, and they are also a measure of a cat’s mood. Whiskers that are perked forward and spread widely apart communicate that a cat is alert and interested in the environment, possibly aggressive. Whiskers that are relaxed and positioned slightly downward indicate that the cat is feeling passive. Whiskers that are plastered back against the cat’s face indicate anger.

Cats can’t see directly underneath their noses, but they can spread their whiskers forward around their nose to form a “basket” that identifies the location of objects the cat can’t see – such as that tasty treat you just offered her. Subtle changes in air movement that move the whiskers as little as 1/200^th the width of a human hair can also help alert cats to prey they can’t see.

Rexes and Sphynx breeds tend to have very short, curly whiskers

Avoid cutting your cat’s whiskers, as they are a valuable part of how a cat “sees” the world. The whiskers of most cats (Rexes and Sphynxes excluded) are as wide as their body, so any opening that they can pass their whiskers through without resistance is an opening they can fit their body through. Cats with trimmed whiskers, or cats that are overweight run the risk of getting stuck.

Interestingly, it seems that many cats prefer to eat off of a flat or very wide, shallow dish instead of a deep, high-sided bowl because the flat dish does not interfere with their whiskers. This seems to be especially true of cats that are not feeling well.

The places on your cat's body that are most touch-sensitive are the face and the front paws. These parts of the body are your cat’s most important hunting tools.

Also, cats tend to develop surface texture preferences for everything – from litter to scratching posts, to beds. Pay careful attention to what your cat tells you – if she is not using the litter box, perhaps she doesn’t like the feel of wheat litter. If she likes to scratch on your nylon duffel bag instead of her carpet-covered scratching post, perhaps a sisal-rope post that has a little rougher texture to it would be a welcome change.

In addition to the ability to sense distance, movement and texture, cats are born with a highly developed sense of temperature sense. In the first 10 to 14 days of a kitten's life, they learn to navigate by differences in temperature. Heat receptors at the tip of a kitten’s nose detects variation in temperature as small as 0.9 degrees F, which helps the sightless infant navigate towards its mother and siblings.

Feline Sense and Scents-ability: Part 2: Taste and Smell

TASTE AND SMELL

Cats rarely chew on plants, compared to dogs, because the main draw that plants provide is their sweet sugar content. Cats not only fail to taste sweet things, they also deal with sugars poorly in other ways – among other things, they lack a sugar digestion enzyme that both dogs and people have called “glucokinase” which helps break down sugars inside the cells.

Because cats can’t taste sweets, they don’t really “enjoy” sugary snacks the way we would. The inclusion of carbohydrates in cat food has become a very “hot topic” in feline nutrition – while corn and other carbohydrate sources, blueberries, kelp and cranberries may contain many beneficial nutrients, cats likely do not appreciate the flavor, and in some cases it is not certain how well they digest these ingredients.

Most cats prefer canned diets in which the first several ingredients are meat-based. Canned food is better for cats than dry diets because it contains a high water content (about 80%), which helps maintain a lower urine specific gravity (less “stuff” in the urine), which helps protect the kidneys and can help prevent urinary crystals and stones. Most of the cats that we see at Exclusively Cats Veterinary Hospital who are urinating outside the box and have bladder stones or uncomfortable crystals in their urine are eating a dry-food-only diet.

Something else to note – cats do not like bitter taste any more than people do. If you use baking soda in your litter box as a deodorizer and your cat starts eliminating elsewhere, you might stop adding the baking soda to the box. It is quite bitter in taste, and while cats don’t eat litter, they do groom their paws after using the box, so can associate the bad taste of the baking soda with using the litter!

Additionally, some medications or smells that are bitter will cause your cat to drool profusely. This is a reflex that cats have developed to rid their mouths of a bad taste (often bad taste = poison, especially if your diet includes frogs and toads).

  

In 2005, a study was done that discovered the entire cat family is lacking the gene for tasting the flavor “sweet”. They have taste buds in that region of the tongue, but they do not function. Cats do taste salty, sour and bitter. Their favorite tastes are salty and sour. Some cats are drawn to “sweet” foods, but it is likely the fat content vs. the flavor that they like.

Their sense of taste is much duller than ours as well – where a human tongue has over 9,000 taste

Cat displaying flehmen expression

buds, a cat has only 473! The cat may make up for this lack of taste buds with the small Jacobson’s organ at the front of its mouth – a “vomeronasal” organ which is slightly different than either smell or taste. You can see the ducts leading to this organ in the roof of your cat’s mouth behind the upper incisors. The organ sits right at the front of the mouth and connects to the nasal passages. Snakes, elephants and horses also have this organ, among other animals. Humans, it seems, do not have a working vomeronasal organ. To use it most effectively, the cat passes air over the front of the tongue and then touches the tongue to this sensory organ to deposit pheromone molecules there. You can see your cat using this organ when it wrinkles its lips, opens its mouth and slightly sticks its tongue out when “smelling” an area where it finds an interesting smell.

With 200 million odor-sensitive cells in its nose, compared to a human’s paltry five million, a cat’s sense of smell is much more sensitive than ours. However, they don’t hold a candle to a dog’s smelling ability. Dogs have between 149 million and 300 million receptors. Still, smell is one of a cat’s more important senses. Because smell is so important to cats, a stuffed up nose can be extremely detrimental! If a cat can’t smell his food, he is highly likely to turn his nose up at it. Conversely, a scented litter that we find to be pleasantly fresh-smelling is like drowning in perfume to a cat’s sensitive schnozz.

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Meet Mr. September!

SMEAGOL

Age: 3 years

Breed: Devon Rex

Gender: Male

Weight: 9.6 pounds - excellent body condition!

Feline friends: Spaz (12 year old DLH)

Smeagol is a white, male devonshire rex of about 10 lbs.

He enjoys Whiskas temptations treats, cardboard boxes, playing fetch, stalking, and snuggles.

Sometimes he is where he is not supposed to be such as: the top of ladders, up on shelves, or on the kitchen counters. He refers to these places as “the land of above.”

He is a snuggle cat and he will make multiple attempts and whines until he gets a lap or can burrow under a blanket.

He likes to help whenever work is being done. As condo repairs happen here and there, Smeagol will always be near. He inspects everything, and anything new must meet his high standards.

Boxes are his favorite thing to play with, when a new package arrives he is there waiting for it to be opened. Sometimes he cannot wait and will assist in the opening of the package.

 

 

 

 

 

 When you meet Smeagol, he will take a while to warm up to you but once he is happy with you he will climb to the top of your shoulder and sit there. This is now his spot and he is your friend.