Feline immunodeficiency virus
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Feline immunodeficiency virus (FIV) is a lentivirus that affects domesticated housecats worldwide and is the causative agent of feline AIDS. Approximately 11% [1] of cats worldwide, and about 2.5% of cats in the USA, [2] are infected with FIV. FIV differs taxonomically from two other feline retroviruses, feline leukemia virus (FeLV) and feline foamy virus (FFV) and is more closely related to human immunodeficiency virus HIV. Within FIV, five subtypes have been identified based on amino acid sequence differences coding for the viral envelope. FIV is the only non-primate lentivirus to cause an AIDS-like syndrome, but FIV is not always a death sentence for cats, as they can live relatively healthily as carriers and transmitters of the disease for many years. A vaccine is available although its efficacy remains uncertain, and cats will test positive for FIV antibodies after vaccination.[3]
FIV was first discovered in 1986 in a colony of cats that had a high prevalence of opportunistic infections and degenerative conditions, and has since been identified as an endemic disease in domestic cat populations worldwide [4].
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[edit] Transmission
The primary modes of FIV transmission are deep bite wounds and scratches, where the infected cat's saliva enters the other cat's bloodstream. FIV may also be transmitted from pregnant females to their offspring in utero.[5] This differs from FeLV, which may be spread by more casual, non-aggressive contact since the virus is also present at mucosal surfaces such as those in the mouth, rectum, and vagina, so casual contact cannot be ruled out as a potential transmission.
[edit] Testing
Veterinarians will check a cat's history, look for clinical signs, and possibly administer a blood test for FIV antibodies. FIV affects 2-3% of cats in the US and testing is readily available. It should be noted that this testing identifies those cats that carry the FIV antibody, and does not detect the actual virus. Therefore, a positive test does not necessarily mean the cat is a carrier of FIV.
False positives occur when the cat carries the antibody (which is harmless), but does not carry the actual virus. The most frequent occurrence of this is when kittens are tested after ingesting the antibodies from mother's milk, and when testing cats that have been previously vaccinated for FIV. For this reason, neither kittens under 8 weeks, nor cats that have been previously vaccinated are tested.
Kittens and young cats that test positive for the FIV antibody may test negative at a later time due to seroreversion, provided they have never been infected with FIV and have never been immunized with the FIV vaccine.
Cats that have been vaccinated will test positive for the FIV antibody for the rest of their life due to seroconversion, even though they are not infected. Therefore, testing of strays or adopted cats is inconclusive, since it is impossible to know whether or not they have been vaccinated in the past. For these reasons, a positive FIV antibody test by itself should never be used as criteria for euthanasia.[6]
Tests can be performed in a vet's office with results in minutes, allowing for quick consultation. Early detection helps maintain the cat's health and prevents spreading infection to other cats. With proper care, infected cats can live long and healthy lives.[7]
The American Association of Feline Practitioners, an organization of veterinarians with a special interest in the health of cats, urges regular testing but not euthanasia of infected cats. Infected cats can live for years if diagnosed early and managed properly.
[edit] Vaccine
A vaccine for FIV is available (ATCvet code: QI06), and was developed using isolates of two of the five FIV subtypes (or clades): A and D.[8] The vaccine was shown to be moderately protective (82% of cats were protected) against subtype A FIV,[9] but a later study showed it to offer no protection against subtype A.[10] It has shown 100% effectiveness against two different subtype B FIV strains.[11][12] Vaccination will cause cats to have positive results on FIV tests, making diagnosis more difficult. For these reasons the vaccine is considered "non-core", and the decision to vaccinate should be made after discussion with a veterinarian and consideration of the risks vs. the effectiveness.[13]
[edit] Approved treatment
In 2006, the United States Department of Agriculture issued a conditional license for a new treatment aid termed Lymphocyte T-Cell Immune Modulator[14]. Lymphocyte T-Cell Immune Modulator is manufactured by T-Cyte Therapeutics, Inc., exclusively licensed by IMULAN BioTherapeutics, LLC and distributed in the United States by ProLabs Animal Health (www.prolabsanimalhealth.com).
Lymphocyte T-Cell Immune Modulator is intended as an aid in the treatment of cats infected with feline leukemia virus (FeLV) and/or feline immunodeficiency virus (FIV), and the associated symptoms of lymphocytopenia, opportunistic infection, anemia, granulocytopenia, or thrombocytopenia. The absence of any observed adverse events in several animal species, suggests that the product has a very low toxicity profile.
Lymphocyte T-Cell Immune Modulator is a potent regulator of CD-4 lymphocyte production and function.[15] It has been shown to increase lymphocyte numbers and Interleukin 2 production in animals.[16]
Lymphocyte T-Cell Immune Modulator is a single chain polypeptide. It is a strongly cationic glycoprotein, and is purified with cation exchange resin. Purification of protein from bovine-derived stromal cell supernatants produces a substantially homogeneous factor, free of extraneous materials. The bovine protein is homologous with other mammalian species and is a homogeneous 50 kDa glycoprotein with an isoelectric point of 6.5. The protein is prepared in a lyophilized 1 microgram dose. Reconstitution in sterile diluent produces a solution for subcutaneous injection.[17]
[edit] Effects
FIV can attack the immune system of cats, much like the human immunodeficiency virus (HIV) can attack the immune system of human beings. FIV infects many cell types in its host, including CD4+ and CD8+ T lymphocytes, B lymphocytes, and macrophages. FIV can be tolerated well by cats, but can eventually lead to debilitation of the immune system in its feline hosts by the infection and exhaustion of T-helper (CD4+) cells.
FIV and HIV are both lentiviruses; however, neither can infect the other's usual host: humans cannot be infected by FIV nor can cats be infected by HIV. FIV is transmitted primarily through saliva (bites), such as those incurred during territorial battles between males. Cats housed exclusively indoors are much less likely to be infected, provided they do not come in contact with infected cats.
Consensus whether there is a need to euthanize FIV infected cats has not been established. The American Associations of Feline Practitioners, as well as many feral cat organizations, recommend against euthanizing FIV+ cats, or even spending funds to test for the virus, as spaying or neutering cats seems to effectively control transmission - as neutered cats are less likely to engage in territorial fights. A vigilant pet owner who treats secondary infections can assist an infected cat to live a reasonably long life. The chance that an FIV infected cat will pass the disease on to other cats within a household remains, and increases with serious fighting or biting (American Association of Feline Practitioners 2002). There is a quantifiable risk that cats living outside of a home can spread the disease to others and can also spread the disease in a group setting in a shelter. Cats living alone as a single pet, rarely left to roam free, pose a diminished, but not non-existent risk.
The disease occurs in three stages: First is the Acute Stage (1-2 months after transmission) in which fever, depression, and generalized lymphadenopathy are observed (Wise 2005). Second is the Subclinical Stage (4 weeks to X months after transmission), in which symptoms of the disease decrease or disappear; however, all cats remain viremic for life. Third is the Chronic Stage, in which cats eventually succumb to chronic infections due to suppressed immune system function. Cats may incur stomatitis, odontoclasia, periodontitis, gingivitis, rhinitis, conjunctivitis, pneumonitis, enteritis, and dermatitis in the later stages of infection. FIV+ cats are less likely to develop AIDS-like symptoms than HIV+ humans.
FIV infects other feline species, and in fact is endemic in some large wild cats, such as African lions. Unlike domestic cats, these species do not necessarily exhibit symptoms, perhaps because they have developed evolutionary mutations that confer resistance.
[edit] See also
[edit] References
- ^ Richards, J (2005). "Feline immunodeficiency virus vaccine: Implications for diagnostic testing and disease management". Biologicals 33: 215. doi:.
- ^ Zislin, A (2005). "Feline immunodeficiency virus vaccine: A rational paradigm for clinical decision-making". Biologicals 33: 219. doi:.
- ^ Statement on Felovax at www.aafponline.org
- ^ Zislin, A (2005). "Feline immunodeficiency virus vaccine: A rational paradigm for clinical decision-making". Biologicals 33: 219. doi:.
- ^ American Association of Feline Practitioners (2002). "Feline Immunodeficiency Virus". Cornell Feline Health Center. Cornell University, College of Veterinary Medicine. http://www.vet.cornell.edu/fhc/brochures/fiv.html. Retrieved on 2008-11-12.
- ^ Statement on Felovax at www.aafponline.org
- ^ KittyTest.com. http://www.kittytest.com/fiv.jsp
- ^ Levy, J (2008), "2008 American Association of Feline Practitioners' feline retrovirus management guidelines", Journal of Feline Medicine & Surgery 10: 300, doi:
- ^ Huang, C.; Conlee, D.; Loop, J.; Champ, D.; Gill, M.; Chu, H.J. (2004), "Efficacy and safety of a feline immunodeficiency virus vaccine", Animal Health Research Reviews 5: 295–300, doi:
- ^ Dunham, S.P.; Bruce, J.; Mackay, S.; Golder, M.; Jarrett, O.; Neil, J.C. (2006), "Limited efficacy of an inactivated feline immunodeficiency virus vaccine.", Veterinary Record 158: 561–562
- ^ Kusuhara, H.; Hohdatsu, T.; Okumura, M.; Sato, K.; Suzuki, Y.; Motokawa, K.; Gemma, T.; Watanabe, R.; et al. (2005), "Dual-subtype vaccine (Fel-O-Vax FIV) protects cats against contact challenge with heterologous subtype B FIV infected cats.", Veterinary Microbiology 108: 155–165, doi:
- ^ Pu, R.; Coleman, J.; Coisman, J.; Sato, E.; Tanabe, T.; Arai, M.; Yamamoto, JK. (2005), "Dual-subtype FIV vaccine (Fel-O-Vax FIV) protection against a heterologous subtype B FIV isolate.", Journal of Feline Medicine and Surgery 7: 65–70, doi:
- ^ Levy, J (2008), "2008 American Association of Feline Practitioners' feline retrovirus management guidelines", Journal of Feline Medicine & Surgery 10: 300–316, doi:
- ^ United States Department of Agriculture. Veterinary Biological Products; Licensees and Permittees, December 2006. [1]
- ^ Beardsley, et al. "Induction of T-Cell Maturation by a Cloned Line of Thymic Epithelium (TEPI) Immunology 80: pp. 6005-6009, (Oct. 1983).
- ^ Beardsley, Terry R. Patent # 7,196,060; Method to enhance hematopoiesis. Method to enhance hematopoiesis - Google Patents at www.google.com
- ^ Beardsley, Terry R. Patent # 5,616,554; Immune-enhancing agent for therapeutic use in immunocompromised hosts. Immune-enhancing agent for ... - Google Patents at www.google.com
- Johnson (2005), Proceedings, <http://www.ivis.org/proceedings/acvp/2005/Johnson/chapter.asp?LA=1>
- Might, Jennifer Lynne (2004), Feline Immunodeficiency Virus (FIV), <http://www.blackgiraffe.com/jmight/fiv/fiv.html>
- Wise (2005), Chapter, <http://www.ivis.org/advances/carter/Part2Chap15/chapter.asp?LA=1#fel_immuno>
- American Association of Feline Practitioners (2005), AAFP guidelines on FIV and FeLV, <http://www.aafponline.org/resources/guidelines/Felv_FIV_Guidelines.pdf>
- The Lion Research Center (2005), FIV in African Lions, <http://www.lionresearch.org/current_docs/fiv.html>
- Alley Cat Allies (2001), Should we release FIV+ cats?, <http://www.alleycat.org/pdf/shouldwerelease.pdf>
[edit] External links
- An article on FIV
- Lymphocyte T-Cell Immunomodulator (LTCI)
- FIV in lions
- American Association of Feline Practitioners guidelines on FeLV and FIV
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