Cat AIDS (Feline Immunodeficiency Virus -FIV) 

Cat AIDS (FIV - feline immunodeficiency virus) was first discovered in California in 1986. Its similarity to HIV (Human Immunodeficiency Virus - also known as AIDS) caused great alarm among cat owners. Many FIV positive cats were unnecessarily put to sleep or abandoned in shelters. The virus occurs world wide in all species of cats and affects about 5% of the total cat population. It does not cause disease in humans.

The virus damages the cat's immune system, leading to a series of secondary infections that may become fatal. It is like another virus, FeLV (Feline Leukaemia Virus) in that both viruses attack the immune system and cause similar symptoms. However, these are different viruses - infections of FeLV and FIV are unrelated.

©pic, AIDScience Vol. 2, No. 8, April 2002

Cause

FIV has probably been around for centuries. It is usually transmitted by cat bites. Therefore, cats that spend a lot of time outdoors and involved in fighting, especially undesexed male cats, are at the highest risk. But having Cat Aids isn't necessarily a death knell. Many can live for many years with the disease before succumbing to secondary infections. In some cases, FIV positive cats have lived for ten years, but five years is common. 

Diagnosis

FIV can be easily diagnosed by blood test, and most vet clinics have tests that can be done while you wait. The vet usually tests for the presence of FeLV virus, as some cats with Aids also have this virus as well and when both viruses are present, the long term prognosis is not as good. Unfortunately, a cat either has FIV or not. Blood tests for antibodies are testing the severity of the infection are pointless. 

Symptoms

About a month after infection, first symptoms which appear are minimal. There might be a period of fevers (humans experience 'night sweats' in the early stages of Aids), enlarged lymph nodes, and a low white cell count. Following this episode, the cat appears to have recovered, but in fact remains FIV positive for the rest of its life. It was once thought that the virus becomes dormant, but work with HIV in humans in the 1990s showed the opposite scenario, that the virus continues dividing in the body and it is only when the immune system begins to fail that serious symptoms show. This explains why in humans the use of anti-viral drugs (which stops the virus from dividing) has been so successful in reducing death due to Aids. Because FIV attacks the body's immune system, FIV-positive cats are less resistant to disease. Because they are viremic (large numbers of viruses in the blood), they normally present with a high fever (often >40⁰C), loss of appetite and lethargy. They also present wit other complaints such as diseases affecting the mouth, gums, bowels, respiratory system, and urinary tract. 

Treatment

Unfortunately, there is no cure for the virus itself. The use of anti-viral drugs in cats has been tested with some success but the prohibitive cost far outweighs its use. AZT has been shown to be ineffective at stopping the virus from invading the cat's body even when given immediately after infection. Fortunately, a cat diagnosed as having FIV may be treated with supportive drugs for many years. Treating symptoms as they occur, usually with broad-spectrum antibiotics support is helpful. At some point however, the immune system will begin to fail and at this stage, pneumonia or toxic shock are common causes of death. Immune supporting drugs such as Waltham Immune Support® and vitamin supplements have been shown to be helpful. Providing a balanced nutritional diet and reducing stress are also very important, as well as making sure your cat is regularly wormed and flea treated, so as to minimise the stress on its immune system. 

Prevention  

There is a vaccine now available in Australia. The protocol is for three (3) vaccinations four weeks apart.

FIV Aids vaccine 

Vaccine implications

Cats vaccinated with Fel-O-Vax® FIV develop antibodies to the inactivated virus present in the vaccine. Currently available antibody-based FIV diagnostic tests (e.g., SNAP® Feline Combo, PetChek® FIV Ab plates, and Western blot) available in the United States and Europe cannot distinguish cats vaccinated with Fel-O-Vax® FIV from FIV-infected cats or from cats that are both vaccinated and infected. Negative FIV-antibody test results remain reliable (see the 2001 Report of the AAFP/AFM Advisory Panel on Feline Retrovirus Testing and Management at http://www.aafponline.org/about/guidelines.htm). But until tests that differentiate vaccinated cats from infected cats become readily available, it will be impossible to assess the significance of positive test results. (Is a positive-testing cat infected, vaccinated, or both?) Some consequences of this ambiguity: The benefit of testing and isolating FIV-infected cats—the mainstay of reducing viral transmission—will be diminished if vaccinated cats are erroneously assumed to be non-infectious. It will be impossible to ascertain the safety of adopting positive-testing cats into households with uninfected cats. Vaccinating all the residents prior to adoption may provide some protection, but it is unrealistic to expect all vaccinates to be protected. Because infected cats—either healthy or ill—will be difficult to identify, the delivery of the specialized care they require will be significantly compromised. Kittens born to vaccinated queens will likely test positive for passively acquired FIV antibody. According to studies conducted by the manufacturer, antibody levels drop to levels that won’t interfere with test results by the time kittens reach 8 weeks-of-age. Some shelters and other facilities designed to house strays often euthanize cats with positive FIV test results, so previously vaccinated uninfected cats may needlessly undergo euthanasia. Permanently identifying cats vaccinated with Fel-O-Vax® FIV (e.g., using a microchip or tattoo) has been suggested as a means of identifying vaccinated cats, thus sparing them from euthanasia. Yet previous vaccination does not rule out infection nor prevent the subsequent placement of infected cats.

Vaccine efficacy 

FIV is commonly classified into five different subtypes (A, B, C, D, and E) based upon genetic variation within one section of the virus envelope gene. Subtypes A and B are the predominant subtypes in the United States. Substantial genetic variation exists both within and between the various subtypes (also called genotypes or clades). Experimental FIV vaccines reported thus far in the literature have demonstrated poor cross protection between subtypes (e.g., vaccines based on subtype A virus have shown decreased protection against subtype B challenge). 

As a condition of licensure, the United States Department of Agriculture (USDA) requires manufacturers to determine vaccine efficacy based upon results of laboratory studies. Accordingly, 45 eight week-old specific pathogen free kittens were randomized into two groups: 25 were vaccinated with Fel-O-Vax® FIV three times three weeks apart while 20 kittens served as non-vaccinated controls. Approximately one year later, both groups were challenged intramuscularly with a subtype A virus that differed by 10% in a portion of the envelope gene from the subtype A virus used in the vaccine. The preventable fraction (defined as the proportion of cats protected by vaccination in excess of the proportion that is naturally resistant) was calculated to be 0.82 (82%). 

Challenge models that accurately reflect “real world” exposures to infectious agents are difficult to design and control, expensive, and involve large numbers of cats. In addition, they often require several years of data collection to obtain meaningful results. Laboratory challenges of the kind required by the USDA provide necessary and valuable information, but for reasons of practicality and expense, they may not reflect vaccine performance in the field. Although these efficacy figures are encouraging, it is possible that fewer than 82% of vaccinated cats will be protected from the vast array of FIV genetic variants to which they may be exposed in nature. Therefore, while reasonable to expect that some cats vaccinated with Fel-O-Vax® FIV will be protected from infection, others certainly will not. 

Conclusion 

The absence of tests that distinguish cats vaccinated with Fel-O-Vax® FIV from infected cats, coupled with questions regarding the vaccine’s ability to induce protection against all the subtypes and strains of FIV to which cats might be exposed, makes the decision to recommend use of this product far from straightforward. It is crucial that clients are adequately informed about the vaccine’s impact on future test results, and their decision should be reached only after careful consideration of both positive and negative implications. If the decision ultimately falls in favor of vaccination, cats should test negative immediately prior to receiving Fel-O-Vax® FIV.