Feline Leukemia Virus (FeLV) Infection

Feline leukemia virus (FeLV) is a viral infection that has a significant impact on domestic cats across the globe. The virus is caused by a retrovirus that belongs to the Gammaretrovirus genus of the Retroviridae family. FeLV infection can greatly compromise the immune system of cats, making them vulnerable to a range of secondary infections and neoplastic diseases. It poses a significant threat to the health and well-being of domestic cats. As a leader in animal disease diagnostics, BioVenic is committed to providing customers with diagnostics development as well as vaccine development services to prevent FeLV infection.

Etiology

FeLV is a single-stranded positive-strand linear RNA virus with an envelope and fibers on its surface. FeLV is divided into 3 serotypes based on different envelope antigens, namely FeLV-A, FeLV-B, and FeLV-C. Different serotypes of viruses have different pathogenicity.

• Type A is weakly pathogenic but can cause persistent viremia.
• Type B is less likely to cause viremia, but is the most pathogenic and may be the direct pathogen that induces malignant lesions and feline AIDS (FAIDS).
• Type C mainly causes developmental disorders of the red blood cell line in the bone marrow, leading to anemia.

Fig. 1 Schematic diagram of the structure of FeLV.¹

Pathogenesis

FeLV infection first requires host cell surface receptor recognition. Different subtypes recognize infected cells through different receptors. FeLV surface glycoprotein binds to host cell receptors, fuses with host cell membranes, and destroys target cells. After infection, FeLV enters the cat's bloodstream and subsequently spreads to various immune organs including bone marrow, thymus, and spleen. The virus can induce immunosuppression, resulting in impaired ability to mount an effective immune response against other pathogens. In addition, FeLV can integrate its genetic material into the host's DNA, leading to long-term viral persistence and potentially oncogenic transformation.

Transmission

• FeLV is primarily transmitted through the respiratory and gastrointestinal tract levels. FeLV is mainly excreted through saliva and enters the body through the mucous membranes of the eyes, nose, and mouth.
• Additionally, FeLV can also be transmitted vertically. FeLV can infect the fetus through the uterus and can also be transmitted through breast milk.
• Blood-sucking insects can become FeLV transmission vectors.

Signs and Symptoms

The FeLV infection can cause a variety of clinical signs and symptoms and may also lead to the development of various cancers, especially lymphomas. The manifestations can vary depending on age, the stage of infection, and the individual cat's immune response. Some cats may remain asymptomatic carriers, while others may develop severe illness.

Common clinical signs associated with FeLV infection include:

Infectious Response in Cats After Exposure to FeLV

Cats infected with FeLV develop one of three infection response categories.

• Abortive infection: FeLV antigen and nucleic acid tests in cats with this type of infection are negative and FeLV antibody tests are positive.
• Regressive infection: Cats with this infection category have strong immunity in their bodies, and they will not get sick. Although they still carry viruses in their bodies, they will not excrete viruses to the outside world.
• Progressive infections: Cats with this infection category do not have an immune response, and FeLV replicates extensively in immune organs. The FeLV-related disease appears within two to three years.

Diagnosis

BioVenic provides Immunodiagnostics and molecular diagnostics development services to clients, and generally, we recommend the following diagnostics tests to detect FeLV in cats.

• ELISA: These diagnostic tests are employed during both early and late stages of infection to detect the presence of FeLV antigen or antibodies in the blood of feline patients.
• IFA: In the later stages of infection, the test can be utilized to identify the presence of FeLV particles within white blood cells.
• PCR: The assay can be employed to detect the presence of FeLV in feline bone marrow, indicating if the virus has infected the bone marrow.

It is important to note that confirming FeLV infection typically requires more than two types of test results, and repeating the tests can enhance accuracy in diagnosis.

Treatment and Prognosis

• Regrettably, there is currently no cure available for FeLV.
• For infected cats, treatment can be symptomatic, and supportive care provided. Examples include antimicrobial therapy for secondary infection, blood transfusion, and nutritional support for anemia.
• Experimental antiviral drugs and immunomodulatory therapies are being investigated but are not yet widely available.
• Several factors affect the prognosis of FeLV-infected cats, including the stage of infection, concurrent disease, and health overall. Some cats may live for many years with proper care, while others may die quickly.

Prevention

• Vaccination is recommended for at-risk kittens and cats.
• Limit contact with FeLV-positive cats.
• Keep cats indoors and minimize contact between cats.
• FeLV is sensitive to disinfectants and can be used for regular disinfection of cattery etc.
• Regular veterinary check-ups and routine FeLV testing.

Through ongoing collaboration with veterinary professionals and organizations, BioVenic strives to improve the health and well-being of cats by developing innovative diagnostics solutions, treatment options, and preventive measures for FeLV. If you need more information, please contact us immediately.

Reference

1. Westman, M. E., et al. "Diagnosing feline immunodeficiency virus (FIV) and feline leukaemia virus (FeLV) infection: an update for clinicians." Australian veterinary journal 97.3 (2019): 47-55.