{"id":25990,"date":"2021-10-08T18:57:34","date_gmt":"2021-10-08T18:57:34","guid":{"rendered":"https:\/\/todaysveterinarypractice.com\/?p=24546"},"modified":"2022-02-09T20:11:31","modified_gmt":"2022-02-09T20:11:31","slug":"feline-leukemia-virus-vaccination","status":"publish","type":"post","link":"https:\/\/navc.sitepreview.app\/todaysveterinarypractice.com\/preventive-medicine\/feline-leukemia-virus-vaccination\/","title":{"rendered":"Feline Leukemia Virus Vaccination"},"content":{"rendered":"

Feline leukemia virus (FeLV) is a gammaretrovirus and one of the most common causes of infectious disease in cats worldwide. Various studies estimate the prevalence of FeLV to be between 2% and 3.5% in the United States and Canada. The development and use of accurate diagnostic tests and vaccinations has led to a decrease in the prevalence of FeLV since its discovery more than 50 years ago; however, the seroprevalence has not changed in the past decade.1,2<\/sup>\u00a0<\/span><\/span><\/p>\n

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The Vaccination Station series<\/a> is brought to you by Merck Animal Health, the manufacturers of Nobivac\u00ae.<\/p>\n

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FeLV infection can spread rapidly in the feline population if vigilant preventive and early diagnostic protocols are not maintained. The course of FeLV infection is a delicate balance between the cat\u2019s immune system and the virus, and possible outcomes include progressive, regressive, abortive, or focal infection. Following recommended guidelines for diagnosing and preventing FeLV will help prevent a resurgence of this disease.\u00a0<\/span><\/span><\/p>\n

Feline Leukemia Virus<\/h2>\n

FeLV Exposure and Transmission\u00a0<\/span><\/h3>\n

FeLV is an enveloped virus with a single-stranded RNA genome that uses reverse transcriptase to convert the viral RNA genome into a DNA form. The DNA form is then integrated into the host\u2019s cells by the enzyme integrase. This integrated DNA is known as the \u201cprovirus.\u201d3<\/sup><\/span><\/p>\n

Primary transmission of FeLV is through salivary shedding, although it can also be found in urine, feces, and milk. FeLV is not stable in the environment, so transmission is generally through communal contact between cats who are socially friendly, groom each other, and share resources, or aggressive interactions between cats that result in bite wounds. In addition to horizontal transmission, FeLV can be transmitted vertically from an infected queen to her kittens. The virus may also be spread via blood transfusions.\u00a0<\/span><\/span><\/p>\n

Male cats, as well as cats that live outdoors or are intact, are at a higher risk for exposure. FeLV infection is much more prevalent in sick cats, and if healthy cats are eliminated from survey results, the prevalence of FeLV increases to 38%.3<\/sup><\/span><\/p>\n

FeLV Outcomes<\/h3>\n

FeLV replicates in the tonsils and local lymph nodes of exposed cats and then spreads through the body via infected lymphocytes and monocytes. This is the primary viremia stage. Eventually the virus infects the bone marrow and is integrated into neutrophils and platelets, which then circulate in the bloodstream. This is the secondary viremia stage.1,4<\/sup>\u00a0<\/span><\/span><\/p>\n

While cats of all ages can become infected with FeLV, kittens are much more likely to develop a progressive infection. Cats with progressive FeLV infections are persistently viremic, constantly shed millions of viral particles in their saliva, and are an infection risk to other cats. They should be kept separately from FeLV-na\u00efve cats, even if the infected cat appears otherwise healthy. Cats with progressive FeLV infections are most likely to develop FeLV-associated disease, such as lymphoma, bone marrow disorders, immune-mediated diseases, or susceptibility to secondary infections. These cats frequently die within 3\u00a0years of diagnosis.3,5<\/sup><\/span><\/p>\n

Older cats usually develop a regressive or abortive infection, and if they develop a progressive infection, they appear to have milder signs.3<\/sup> Cats diagnosed with a regressive infection have recovered from the primary viremia and generally avoid infection of the bone marrow. Antigenemia typically clears within 3 months, though the FeLV provirus still circulates in peripheral blood. These cats usually do not develop FeLV-associated disease, although the potential exists for the virus to be reactivated if the cat becomes immunocompromised, and viral shedding could recur.4<\/sup> The potential for reactivation decreases over time after exposure, although it is never completely eliminated.3<\/sup><\/span><\/p>\n

Cats with an abortive FeLV infection can be harder to diagnose. The virus is contained before provirus integration takes place, and the cats never become viremic. These cats develop FeLV-neutralizing antibodies and a strong immunity to FeLV. They will not develop FeLV-associated disease, and they have the same life expectancy as cats that have never been exposed to FeLV.3<\/sup>\u00a0<\/span><\/span><\/p>\n

Focal or atypical FeLV infections are very rare and can be challenging to diagnose because they may cause discordant test results. A queen with a focal infection in the mammary glands could pass the infection to her kittens during nursing. The neonates may then develop fading kitten syndrome and die soon after birth.5<\/sup><\/span><\/p>\n

FeLV Diagnostic Tests and Interpretation<\/h3>\n

A variety of tests are available to diagnose FeLV, and it is important to understand what the results signify to determine a prognosis and management plan for an infected cat. The American Association of Feline Practitioners (AAFP<\/a>) recommends screening all cats for FeLV at any of the points listed in <\/span>BOX 1<\/span><\/strong>.\u00a0<\/span><\/span><\/p>\n

BOX 1 When to Screen Cats for Feline Leukemia Virus (FeLV)6<\/sup><\/div>
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