General information

FeLV is a retrovirus. Retroviruses are enveloped single-stranded RNA viruses. The retrovirus family is characterised by reverse transcriptase and a sometimes oncogenic potential. The reverse transcriptase “transcribes” the RNA of the virus into cDNA, which is then integrated into the genome of the host cell. This way, provirus is created, which can remain a permanent part of the genome and is responsible for the mostly persistent infections.

FeLV is transmitted directly from cat to cat. The main source of transmission is saliva. Bite injuries represent a large transmission potential because here the infectious saliva can get directly into the bloodstream. In most cases, this results in an oropharyngeal infection of the cat. The virus penetrates the mucous membranes and within two days multiplies there as well as in the tonsils and retropharyngeal lymph nodes. Through infected lymphocytes and monocytes, the virus enters the bloodstream and further into the bone marrow after about twelve days.

If cats are infected with FeLV, only a transient infection with short viraemia develops in approximately 45% of cases. The immune system is able to eliminate the virus. The cat does not fall ill. In about 30% of the infections there is a sufficient immune response to prevent virus replication, but virus elimination is not possible. A latent infection occurs. Other infectious diseases or stress can lead to viraemia reactivation.

In all other cases, persistent infection occurs which usually results in a severe and short course of the disease. The primary consequences of the infection include organ damage due to virus replication. Mostly, a FeLV-associated bone marrow depression develops. Anaemia occurs in almost 50% of FeLV-infected cats, and in about 8% of them will lead to death. This is predominantly aplastic anaemia caused by disturbed erythropoiesis. A reduced number of reticulocytes indicates aregenerative anaemia.

FIV infections are also associated with lymphoid leukosis or leukopenia.