Feline immunodeficiency virus (FIV) was first isolated by Dr Neils Pederson and Janet K Yamamoto in 1986. FIV has been isolated from blood, saliva, milk and semen of infected cats. The virus belongs to the family of retroviridae and is classified as a lentivirus. HIV and FIV are both members of the lentivirus subfamily.

Mode of Transmission

1. Bite Wounds. Biting is the most common route of transmission. Territorial and free roaming cats are more susceptible as they frequently find themselves in cat fights.

2. Venereal transmission. While studies have shown semen from FIV positive cats can transmit the virus to seronegative females when fertilised surgically (intrauterine fertilisation), it seems in reality this is not a common mode of transmission.

3. Placental transfer or through milk. A mother can infect her kittens.

Pathophysiology

One the virus gains entry into the host, it moves through the lymphatic system to a regional lymph node. The virus then targets special white blood cells for its replication. These white blood cells (T-lymphocytes and macrophages) are essential for a healthy immune system. Over time, the virus reduced the number of these T-lymphocytes while the macrophages (the main reservoir of the virus) transport the virus to all parts of the body and are responsible for producing defects in organ function.

Clinical Signs

Typically, the initial phase of the disease is either asymptomatic or not noticed by owners. Signs can include

-enlarged lymph nodes

-loss of appetite

-fever

-lethargy

After a few days symptoms spontaneously resolve. The cat remains asymptomatic until the immune system becomes disrupted. The length of time from initial infection to clinical signs indicating loss of immunity varies from one to ten years. The average length of time is seven years.

The clinical signs then reflect generalised immune suppression:

-skin conditions (parasitic infestations, bacterial infections)

-diarrhoea

-dental and gum disease

-decreased appetite

-anaemia

-unresolved infections (respiratory, urinary, intestinal, ocular)

-mental or behavioural abnormalities (rage, dementia, roaming, seizures)

-an increase in incidence of some cancers (lymphosarcoma)

Death usually occurs from these unresolving secondary infections.

Diagnosis

If there are cllinical signs of recurrent skin, urinary and respiratory infections with some response to antibiotics, FIV must be considered. Diagnosis is confirmed by either:

-Serological (tests for antibodies against FIV). Tests are carried out in-clinic, results are fast and cost is reasonable.

-Virus isolation. This is much more time consuming, required a laboratory, is expensive and results can take a few weeks.

Treatment

No treatment is available. Care involves primarily reducing the incidence of opportunistic infections and antibiotic & antifungal treatment as required.

Tomorrow- prevalence of the virus in Australia and vaccine recommendations.

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