FIV stands for feline immunodeficiency virus, just like HIV stands for human immunodeficiency virus, which can progressively lead to AIDS (acquired immunodeficiency syndrome) in cats.
Humans cannot be infected with FIV. FIV is a cats-only infection.

Clinical signs can start as soon as 6 to 8 weeks after infection. Clinical signs vary widely and are commonly associated with opportunistic infections as FIV positive cats are immunosuppressed. Cats can also appear normal for years after infection. During this period of time they can infect other cats. Clinical signs include, but are not limited to: Fever, lethargy, going off food and/or water Redness and swelling of the gums and oral cavity Enlarged lymph nodes Eye diseases Neurological diseases: behavioural changes, seizures, unable to walk properly The above signs are not specific for FIV, and can also be caused by other various diseases. 

There are several modes of transmission of FIV:
Deep bite wounds from fighting are a major and most common mode of virus transmission. Therefore, outdoor, intact, male cats are most likely to be infected. In-utero infection (womb) are rare, but kittens of infected queens (mother cat) have circulating FIV antibodies due to passive transfer of antibodies. Sexual transmission and through improperly screened blood transfusion. FIV transmission does not occur through casual contact (sharing of feed bowl or snuggling).  

How do I prevent my cat from FIV?
Exposure to infected cats can be prevented by keeping cats indoors so they are not at risk of being bitten by FIV positive cats. Avoid adopting FIV positive cats into multi-cat households, especially if they might bite and fight with FIV negative cats.

How do I know if my cat has FIV?
FIV is mainly diagnosed by performing a screening antibody blood test, which is fairly accurate because most cats infected with FIV become lifetime carriers.

Which cats should be tested?
All cats and kittens should be tested on their first veterinary visit regardless of age because a negative result is reliable. Kittens may test positive due to maternal antibodies, thus, those who test positive should be retested after 6 months of age. Cats with possible recent exposure to FIV positive cats (cat fight with bite wounds). Antibodies usually appear within 2-4 weeks after exposure, but some cats do not produce antibodies for up to 1 year. Any sick cat, even if tested to be negative before. Cats at risk of contracting disease (e.g. outdoor cats, cats recently mated to cats with unknown FIV status, cats living with FIV positive cats) should be retested yearly.

Vaccination
It is currently only recommended to consider vaccinating a cat against FIV only if it is at high-risk of being infected. There are several reasons why the FIV vaccine is a non-core vaccine: The current vaccination for FIV only vaccinates against 2 out of the 5 strains of FIV. There is limited information as to the effectiveness of the vaccine. A cat that is vaccinated against FIV will test positive for the disease on the screening blood test as with an infected cat. It is thus not possible to tell a vaccinated and infected cat apart if it’s FIV vaccination history is unknown.

Living with a FIV positive cat
Some lifestyle changes will probably be needed if you have an FIV positive cat.

Keep your Cat Indoors Only
By knowing that your cat has an infectious disease, the responsible thing as the owner is to prevent the spread of this disease in your community. This means that a normally outdoor cat has to be kept indoors to prevent contact with other cats within the community. This may post as a challenge to cats that are used to being outdoors.

No raw food
All FIV positive cats should not be on a raw diet. This is due to uncooked foods, especially meat, can harbour parasites and pathogens that a cat with a normal immune system might be able to tackle, but an FIV positive cat might not.

General Monitoring 
The FIV positive cat should have a check-up at least twice a year with an annual full blood panel and a urine tests. It is also important to be vigilant of any changes in an FIV positive cat. Small changes that might not post a significant risk to a normal cat should probably be thoroughly investigated in an FIV positive cat.