A retrovirus carries an enzyme that causes reverse transcription, a normally occurring process. RNA is normally copied by pairing up with DNA. An RNA retrovirus ffools the DNA into copying the viral RNA so more of the retrovirus can be created. As long as the virus can replicate its own RNA it can thrive. According to Erin Miller and the team responsible for the "Feline Leukemia Virus FAQ," "A retrovirus is a parasite at the genetic level, a DNA tapeworm, if you will."
According to Cornell University there are three important differences between FIV and FeLV. First, the morphology or shape of the viral particals is different. The FeLV virus is circular while the FIV particals are elongated. The viruses are very genetically different. The two have structuralproteins that are different in size and composition.
The Feline Leukemia Virus is transmitted more readily than the Feline Immunodeficiency Virus. FeLV is transmitted via saliva, mucus, urin, feces, and blood. The most likely methods of transmission are mutual grooming, biting, and fighting. Other means of transmission are sneezing, hissing, sharing food and water bowls, and sharing litter boxes. Kittens of aan FeLV positive queen will be FeLV positive. Neonatal kittens are 100% susceptible to catching the virus from one exposure. Eight week old weanlings are 85% susceptible from one exposure. Ther is some indication that FeLV can cause abortions in queens.
The FIV virus is not as eassily spread as FeLV. Unlike FeLV, FIV is not transmitted by such casual contact as using the same food and water bowls. It is transmitted very well by bite wounds and blood transfusions. Free roaming male cats have a higher infection rate because they are usually more agressive. Sexual transmission of the disease is uncommon. Transmission from a queen to her kittens is unusual, but does occaisionally occur. To date it is unclear whether infection occurs during gestation or as kittens ingest infected milk.
Cornell University states that the "Clinical signs of FeLV include anemia, jaundice, depression, wight loss, decreased appetite, diarrhea or constipation, blood in 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 can cause breakdown of the immune response system in effect destroying the cat's natural defenses. The virus has the ability to move into the bone marrow where both red and white blood cells are produced. Once in the marrow, the virus can enjoy a latency period of several years. Some FeLV cats are struck by cancer. The tumors in such cats can cause cloudy eyes, vomiting, constipation, liver disease, kidney disease, respiratory distress, intestinal inflammation with diarrhea, and neurological abnormalities.
After initial infection of FIV, usually several weeks, the cat will have a mild fever and enlargment of the lymph nodes. This stage may even go undetected by the cat's owner unless the lymph nodes become greatly enlarged. The clinical signs are diverse because they include a wide array of secondary infections. Some symptons are depression, poor coat condition, persistent fever, and loss of appetite. Inflammation and infection of gums (gingivitis) and mouth (stomatitis), skin infection, urinary bladder infection, and upper respiratory tract infection, diarrhea, and infection of the intestinal tract are common problems. Some inflammation in eye tissues are common but not apparent. Weight loss is slow and progressive. In the later stages of the disease, chronic wasting occurs. As with FeLV, the FIV virus can have a latency period of many years where the infected cat will appear normal and healthy.
Diagnosis of FeLV and FIV infected cats is importantt. There are two common types of blood tests used tfor detecting FeLV. The first is the Enzyme-Linked Immunosorbent Assay (ELISA) which is a kit test which can be performed in a veterinary clinic. The second is the Immunofluorexcence Assay (IFA), also known as the Hardy Slide Test. This test must be sent to a diagnostic laboratory. According to Cornell University, "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)." When a cat has tested positive for FeLV at a veterinarian's office by use of the ELISA test, a second test should be done with the IFA test.
FIV is diagnosed based on history, clincal signs, and an FIV antibody test. This test can be done at a veterinarian's office. The test should be confirmed with a test of a different format, usually one done by a diagnostic laboratory. If the cat tsts negative, a follow up test should be done eight to twelve weeks later. This amount of time would allow for the antibodies to appear. Some cats may take even longer before they develop detectable levels of antibodies.
No cure is available for either Feline Leukemia of Feline Immunodeficiency Vius. Vaccinations are available for FeLV. No vaccination is 100% effective, but it is estimated that they have 75-85% effectiveness. This means that a cat will be able to fight off and infection 7-8 times out of ten. The vaccination gives the cate a MUCH better chance of not becoming persistently infected by FeLV. No vaccination exhists for FIV. Prevention of FeLV with the vaccine is important. Both diseases can be prevented by keeping cats indoors or in enclosed catteries.
No specific treatment is recommended for FIV. Drugs used to fight Human Immunodeficiency Virus (HIV) such as AZT have strong side effects in cats and are often lethal. If AZT is used, it is very expensive. Some symptoms can be treated individually. The best strategy involves supportive care. This includes antimicrobial drugs, intravenous drugs, blood transfusions, and feeding high caloric dietary supplements. In literature, there are also arguements agains vaccinating, massive doses of antibiotics, steroids, or AZT. This argument states that these are potentially fatal to a cat in the actual AIDS stages of FIV. A homeopathic alternative is to feed the cat highly nutritional food with pleanty of supplements. The cat MUST be made and indoors only cat to protect it from illness and to protect other cats from the disease.
An FeLV positive cat MUST be made an indoors only cat. FeLV is highly communicable and needs to be kept away from other cats. Being indoors will also reduce the amount of stress the infected cat must deal with which helps keep the cat healthy. NEVER breed and FeLV cat whether it is male of female. The infected cats should continue to receive its vaccinations with exception of the FeLV vaccination. According to Cornell University, "A variety of chemotherapeutic regimens have been developed, and in certain cases those regimens can produce temporary remission, depending on the physical condition of the cat tand the type of disease that is present. Chemotherapeutic drugs are very potent, and their effects must be monitored carefully to avoid overdosing the patient." Antiviral compounds including interferon can be used to treat FeLV positive cats. They are still experimental, but are more safe than chemotherapeutic agents.
Steroids are also used for FeLV positive cats. The steroids can reduce the numbers of some white blood cells. According to Cornell University " 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." Solid tumors caused by FeLV can be combated by Prednisolone which can act directly against the cells of some solid tumors. Excessive destruction of red blood cells and anemia can be caused by FeLV. Steroids can inhibit the cells that are normally responsible for destroying the red blood cells.
Research is ongoing to find an effective way to combat FeLV. Some studies invove the virus itself. A complete understanding of the virus may lead to clues on how to destoy it or its infectious process. New vaccines, therapies, and diagnostic tests are constantly being evaluated.
One case of FIV research involves some big cats, namely lions. Moreover, the interest lies in the fact that the virus does not kill lions. Virginia Morell, a writer for "Discover Magazine" gave the account of Craig Packer and Stephen O'Brien. Packer has studied the lions of the Serengeti for over a decade. O'Brien works for the National Cancer Institute. In 1990, it was discovered that many of Packer's lions were infected with FIV. O'Brien has determined that 84% of the Serengeti lions harbor the virus. There was however no trace of FeLV.
The cats seem to have developed some sort of balance between themselves and the virus. The cat's resistance to the virus may hold a key to fighting the epidemic in domestic cats and humans. About 25 cat species around the world have their own strain of the disease. Domestic cats ae the only ones on which the disease has a detrimental effect.
O'Brien has already achieved a first in immunodeficiency research. He has begun to trace the geneology of the virus back millions of years by comparing the genetic sequences of each strain. The possibility is that HIV is a fairly new strain that evolved from older strains such as FIV. We however do not want to wait a millennia for HIV to achieve symbiosis with its host. At O'Brien's laboratory, there are six deep freezers containing over 5,000 vials containing tissue, blood cells, serum, and semen from animals throught the world. In his collection are thirty two of thirty seven cat species. This library helps to support research on how animals evolve resistance to new viruses. Many of the samples date back a decade or more. Now when there is an epidemic among animls, many times the population's medical history can be traced to see if this has occurred previously.
O'Brien uses a centrifuge to separate the red blood cells, white blood cells, and serum. At the lab, the serum is tested for FIV antibodies and they determine which of the cats are carrying the disease. In the DNA of infected whie cells is the segment where FIV has inserted its own genes. The virus' polymerase gene is then sought out by using genetic probes. The segmente can then be prepared so that a cojmputer can map out its base pair sequence.
Using this information, O'Brien has mapped ou a history of the diseaee. Each strain has its own distinct gene sequence. The closer the sequences, the less time the strains have had to diverge. Accoding to this research, "FIV has been with the cats a long time, long enough to evolve their own strains of the virus." The virus probably infected the feline famiily some 6 million to 3 million years ago when the separate species began to form. There are three distinct FIV lineages in the lion population alone. O'Brien believes that domestic cats are fairly new to the virus' repertoire. Maybe within the past 1,000 years since the domestic cat actually developes AIDS.
O'Brien's research can also give clues to HIV. Most of the suspected relation is mostly speculation thus far. They are similar, and yet very different. For example, HIV has twice the number of genes as FIV. O'Brien thinks that a possible explanation for this is that when the virus jumps to a new host, it acquires new genes. Since FIV is more primitive than HIV, FIV has had pleanty of time to gather genes on its way to becoming HIV. This is again just an idea.
What they hope to gain by all the research on lions and their relatives is an outlet for combating HIV. FIV does not kill lions. Somewhere along their evolutionary path, the catws or the virus has changed in such a way as to allow a symbiotic relationship. Researchers want to find out if there is a way of finding out what happened and if it can be done in humans. One of the first clues may be finding out why lions go unharmed by FIV while the disease destroys domestic cats. By mapping the genomes of both lions and domestic cats and their strains of FIV, the researchers hope to find what gene or genes make lions resistant to FIV. In lions, their T cells combat the virus. In humans and domestic cats, T cells put up a good fight but are killed. This highly experimental research will help cats help humans.
This research is geared toward finding a genetic solution for FIV and HIV. The lions let us know that the virus is not a new threat. It has shown that they were successful even with the disease. Maybe humans are on their way to coevolution with the disease, and maybe a cure will be found for FeLV. The only difference is humans don't want to wait around for it to happen, they want to make it happen.
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