FeLV

Feline leukemia (FeLV) is an infectious disease caused by a retrovirus of the subfamily Oncovirinae, capable of inducing immunosuppression, neoplasms and anemia.
It is widespread and is one of the main causes of death in cats, related to risk factors such as access to the external environment or cohabitation (catteries, breedings, shelters). Transmission mainly occurs through contact with infected organic fluids (especially saliva) and bites wounds. Vertical transmission (in utero and through milk) is also possible. Susceptibility is greater in young cats.
After initial infection, the virus replicates at the level of oropharyngeal lymphoid tissue and then in the intestinal and respiratory mucosa and salivary glands; finally it spreads to the bone marrow. This first viremic phase, which takes place in 2-4 weeks and which can present fever, discomfort and lynfoadenopathy, develops according to different clinical pictures depending on different factors: the immune status and the age of the cat, the strain and the viral concentration as well as the duration of exposure.
in this way 3 courses are possible:

1. Elimination of the virus: immunocompetent cats neutralize the virus and the infection disappears in 4-8 weeks.
2. Transitional viremia: the virus  located in the bone marrow is neutralized by the immune system (after 3 weeks of viremia), causing a latent infection that can reactivate following  a stimulus or stress reaction. At this stage cats are not infectious and reactivation becomes more uncommon as latency stage persist. However, the cellular alteration carried by the virus can lead to neoplastic diseases or myelosuppression.
3. Persistent viremia: when the immune system fails to contain the infection and this persists for more than 16 weeks the cat dies within 3 years from the diagnosis due to the development of diseases related to virus.

Diseases related to infection include malignant lymphoid neoplasms, myeloproliferative disorders, anemia (regenerative and non-regenerative), “panleukopenic-like” syndrome, various diseases related to induced immunosuppression and various immune-mediated diseases.
Atypical infections: persistent local viral replication with poor and intermittent production of antigens occurs very rarely.
Tests for the diagnosis of FeLV allow for the detection of the antigen.
The prevalence of FeLV infection has dropped significantly over the past 25 years, thanks to reliable diagnostic tests and vaccines.

FIV

Feline immunodeficiency virus (FIV) is a Lentivirus of the Retroviridae family isolated from cats and shows characteristics similar to human HIV. Transmission occurs mainly through bite or scratch wounds of infected cats while transmission through saliva, as well as transplacental and venereal transmissions are considered uncommon. Initially, the virus replicates affecting  T-helper lymphocytes (CD4 +), then T-cytotoxic lymphocytes (CD8 +), macrophages and B lymphocytes inducing a transient fever, lymphadenopathy and neutropenia followed by activation of the immune response associated with the decrease of the circulating virus. This acute phase is followed by an asymptomatic latency phase that can last for months or years during which, however, the T-helper lymphocytes progressively decrease, compromising the immune system. After several months or years, a recrudescence of the infection may arise, with the occurrence of the immunodeficiency syndrome, responsible for secondary infections, neurological disorders, neoplasms.

The diagnosis of FIV is based on the antibody detection. The antibodies are produced about 3-4 weeks after infection and last for the entire life of the animal. Kittens under 6 months can give false positive results when they absorb maternal antibodies (from positive mothers), then the antibodies are eliminated and after four months they return to be negative.