Feline leukemia virus infection: a clinical and epidemiological enigma
Feline Leukemia Virus (FeLV) is a gamma-retrovirus found worldwide in domestic cats, as well as in small wild cats. It is associated with a variety of serious and sometimes fatal diseases, including anemia, immunosuppression and certain cancers. First described over 55 years ago, FeLV has received intense research interest, which has led to increasingly robust diagnostic tests and effective vaccines. Although the prevalence of this infection in domestic cats has declined in many geographic areas, the disease remains a puzzle and can spread rapidly, especially among naive ‘multiple cat’ populations such as shelters and catteries, as well as in pets. houses with several cats. An important goal in order to further reduce the prevalence is to understand the FeLV status of each cat at risk of infection.
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A cutting-edge Premier Review published in the Journal of Feline Medicine and Surgery This month aims to bring diagnostic expertise to veterinarians in practice by examining recent knowledge about the pathogenesis of infections, acquired using molecular techniques.1 Writing for an international audience of veterinary practitioners and feline researchers, the professors Regina Hofmann-Lehmann, University of Zurich, Switzerland, and Katrin Hartmann, LMU Munich, Germany, explain that not only are there several different outcomes of FeLV infection, but these can vary in the weather. Newly classified as “progressive”, “regressive”, “focal” and “abortive” infection, the authors describe how it can be helpful to think of these findings in terms of a set of equilibrium scales, along with the immune response. the cat on one side and the virus on the other.
From an epidemiological point of view, it is the progressively infected cat that is the most significant. In these infections, the virus has the upper hand – these cats release a large number of FeLV particles and pose a risk of infection to other cats. Regardless of their state of health, progressively infected cats should be separated from naive FeLV companions. From a clinical point of view, progressively infected cats are also a priority: they are at high risk of succumbing to a potentially fatal disease; however, if properly cared for, many can continue to live healthy and happy lives, sometimes for years to come.
Of the other possible outcomes, abortion infection is the most favorable for the cat – these cats have strong anti-FeLV immunity. Cats regressively infected will have developed a partially effective antiviral immune response that can control the virus; however, they probably never completely clear the infection and can shed the virus, and therefore pose a risk of infection, in the early phase of infection or when reactivated. In focal infection, which is relatively rare, the cat’s immune system maintains viral replication sequestered in certain tissues.
When it comes to FeLV testing, seemingly confusing or “jarring” test results are not uncommon, especially in the early phase of infection, and can pose considerable challenges to the practitioner who needs to establish FeLV status and implement appropriate therapeutic and epidemiological measures. The authors discuss the most frequently used methods for the detection of FeLV, including the free FeLV p27 antigen test, the viral RNA test, and the FeLV provirus test, focusing on when to test and how to interpret a positive or negative result. The detection of anti-FeLV antibodies, including a point-of-care test for FeLV p15E recently introduced to the European market, is also discussed. A diagnostic algorithm produced by the European Cat Disease Advisory Council (ABCD) that provides advice on which test to choose in which scenario is incorporated in the review article.
1. Hofmann-Lehmann R and Hartmann K. Infection with feline leukemia virus: a practical approach to diagnosis. J Feline Med Surg 2020; 22: 831-846. Read it for free at: https://journals.sagepub.com/doi/abs/10.1177/1098612X20941785
2. Little S, Levy J, Hartmann K, et al. AAFP Feline Retrovirus Screening and Management 2020 Guidelines. J Feline Med Surg 2020; 22: 5-30. Read it for free at: https://journals.sagepub.com/doi/abs/10.1177/1098612X19895940