Affects: Cats
Feline immunodeficiency virus (FIV) is a lentivirus that affects cats worldwide with 2.5% to 4.4% of felines being infected.
FIV was first isolated in 1986, by Niels C. Pedersen and Janet K. Yamamoto at the UC Davis School of Veterinary Medicine in a colony of cats that had a high prevalence of opportunistic infections and degenerative conditions, and was originally called feline T-lymphotropic virus. It has since been identified in domestic cats.
Transmission: The primary mode of transmission is via deep bite wounds, in which the infected cat's saliva enters the other cat's tissues. FIV may also be transmitted from pregnant females to their offspring in utero; however, this vertical transmission is considered to be relatively rare, based on the small number of FIV-infected kittens and adolescents. This differs from feline leukemia virus (FeLV), which may be spread by more-casual, nonaggressive contact, such as mutual grooming and sharing of food bowls.
Risk factors for infection include male sex, adulthood, and outdoor access. One case study conducted in São Paulo found that 75% of FIV-infected cats were males. Higher rates of infection in males than females occur because males defending their territory bite more frequently.
Transmission And Susceptibility: FIV is more rampant in non-Panthera lineages, such as lynxes, bobcats, cheetahs, and pumas, compared to Panthera species like lions, leopards, jaguars, and tigers. Studies indicate that lynxes are more susceptible to FIV due to higher levels of the A3Z3 protein, part of the APOBEC3 family, which limits virus replication in felids. However, A3Z3 mutations do not significantly alter viral genes, suggesting that other genetic or environmental factors may influence the virus's effects.
Members of the Panthera genus exhibit higher levels of protective protein expression, potentially mitigating the severity of infection. Additionally, carnivorous diets contribute to FIV transmission, as larger wild felids may contract the virus by consuming smaller, infected prey species, increasing the rates of infection.
Treatment Options: In 2006, the United States Department of Agriculture issued a conditional license for a new treatment aid termed Lymphocyte T-Cell Immunomodulator (LTCI). Lymphocyte T-Cell Immunomodulator is manufactured and distributed exclusively by T-Cyte Therapeutics, Inc.
Lymphocyte T-Cell Immunomodulator 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 anemia (reduced oxygen-carrying ability in the blood), opportunistic infection, lymphocytopenia, granulocytopenia, or thrombocytopenia (low levels of lymphocytes, granulocytes, and platelets respectively, the first two are types of white blood cell). The absence of any observed adverse events in several animal species suggests that the product has a very low toxicity profile.
Lymphocyte T-Cell Immunomodulator is a potent regulator of CD-4 lymphocyte production and function. It has been shown to increase lymphocyte numbers and Interleukin 2 production in animals. It is a single-chain polypeptide and 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 (freeze-dried) 1 microgram dose. Reconstitution in sterile diluent produces a solution for subcutaneous injection.
Vaccine: As with HIV, the development of an effective vaccine against FIV is difficult because of the high number of, and differences between, variations of the virus strains. "Single-strain" vaccines, i.e., vaccines that only protect against a single virus variant, have already demonstrated a good efficacy against homologous FIV strains. A dual-subtype vaccine for FIV released in 2002 called Fel-O-Vax made it possible to immunize cats against more FIV strains. It was developed using inactivated isolates of two of the five FIV subtypes (or clades): A Petaluma and D Shizuoka. The vaccine was shown to be moderately protective (82% of cats were protected) against subtype A FIV, but a later study showed it to offer no protection against subtype A. It has shown 100% effectiveness against two different subtype B FIV strains. 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.