Many cats with feline leukemia will also experience reproductive difficulties. Kittens of affected queens may die before birth or shortly afterwards. Evidence of neurologic disease may also be observed (Lutz, 2012). Neurologic signs associated with FeLV include ataxia, weakness, anisocoria, para- or tetraparesis, behavioral changes, and urinary incontinence. These signs may be attributed to FeLV- associated polyneuropathy or lymphoma (Fenimore, 2014). There have also been reports of immune-complex deposition leading to polyarthritis and glomerulonephritis in FeLV-positive cats (Lister, 2015a). When a cat with FeLV develops kidney disease, however, it is also important to consider the possibility that renal failure may be caused by renal lymphoma (Fenimore, 2014). Diagnostic testing may be required to distinguish between lymphoma and glomerulonephritis as the cause of a cat’s renal disease. tests negative either was not exposed to FeLV, is immune to FeLV, developed a regressive infection, or is very early in the course of infection (Hofmann-Lehmann & Hartmann, 2020). In the case of recent exposure, repeating the test in six weeks should be considered (Hofmann-Lehmann & Hartmann, 2020). If this approach is chosen, the cat should be quarantined until the test is repeated. In many cases, however, a negative FeLV can be interpreted to mean that the cat is not infected with FeLV, and no further testing is needed. The challenge arises in cats that test positive on the FeLV ELISA test. Although the FeLV ELISA test is regarded as specific, it is important to remember that the predictive value of a positive test is inversely related to the prevalence of a disease. Feline leukemia has a relatively low prevalence, especially in healthy, client-owned cats. Therefore, false positive results on the FeLV ELISA may be common, especially in low-prevalence areas (Litster, 2015a). Everyone on the veterinary team must understand this risk of false positives in order to avoid jumping to conclusions and offer accurate client education when a positive result arises. All positive FeLV ELISA results require confirmatory testing; a positive result does not necessarily mean that a cat is truly infected. There are several simple ways to confirm a positive FeLV ELISA test. One option is to perform a second FeLV ELISA test, using a different in-house test brand or a reference laboratory (Hofmann-Lehmann & Hartmann, 2020). Alternatively, confirmatory testing can be submitted to a reference laboratory in the form of a saliva RT-PCR test or a blood provirus PCR test. Cats should be quarantined while these confirmatory tests are being performed; this will ensure that they do not spread the virus if they are truly infected. If a cat tests positive on both an in-house ELISA and a confirmatory test, they can be diagnosed with FeLV. The next question, however, is whether they will experience a regressive infection or a progressive infection. In order to assess this, an ELISA test should be repeated six weeks later (Hofmann-Lehmann & Hartmann, 2020). If the cat is negative after six weeks, the cat can be presumed to have a regressive infection. If the cat remains positive at six weeks, however, the cat may have a progressive infection. Cats that test positive at six weeks should be retested again after an additional six weeks, or three months after their initial FeLV-positive test (Hofmann-Lehmann & Hartmann, 2020). Continued positive results indicate a progressive infection. It is important to keep in mind, however, that not all FeLV- infected cats will go on to develop a progressive infection.
Because of immunosuppression, FeLV-infected cats may also present with recurrent or resistant infections involving any part of the body. Infected cats may present with recurrent upper respiratory infections, which may be either viral or bacterial in nature. Many FeLV-positive cats develop chronic stomatitis associated with bacterial infections or chronic calicivirus that cannot be cleared because of immunosuppression (Fenimore, 2014). Chronic enteritis may also develop, leading to vomiting and diarrhea. This enteritis typically resembles that seen with panleukopenia and is often caused by bacterial overgrowth (Fenimore, 2014). Clinical icterus may also be seen in FeLV-infected cats. This icterus may be hepatic or prehepatic. Prehepatic icterus may be caused by immune-mediated red blood cell destruction or secondary Mycoplasma haemofelis infection. Hepatic disease may be attributed to lymphoma, Toxoplasma gondii infection, or hepatic lipidosis (Fenimore, 2014). Diagnosis of FeLV There are many different potential manifestations of FeLV infection. Therefore, it is important that all sick cats be tested for FeLV. Especially strong indications for FeLV testing include complete blood cell count abnormalities (anemia, leukopenia, leukocytosis, thrombocytopenia, thrombocytosis, pancytopenia, and/or leukemia), chronic oral infections (gingivitis, stomatitis), uveitis, immune-complex deposition (evidence of polyarthritis or glomerulonephritis), other signs of immunodeficiency, reproductive problems, or neurologic disease. Cats that have been exposed, or potentially exposed, to FeLV should also be tested, especially before they are introduced to uninfected cats. Testing is recommended for all newly adopted cats and cats who have been in contact with a known FeLV-positive cat. It can take up to six weeks for FeLV to be detectable in peripheral blood on an in- house ELISA test after infection, so in-house FeLV testing should occur approximately six weeks after a suspected FeLV exposure. High-risk, unvaccinated cats should be tested on an annual basis. This includes outdoor cats, cats living with a FeLV- positive housemate, cats living in a rescue/shelter setting, and cats living with homes with frequent changes in housemates. Early diagnosis allows for early interventions that can aid in the management of FeLV, along with allowing infected cats to be quarantined. Among healthy cats, it is also important to test for FeLV before FeLV vaccination. The FeLV vaccine does not cause a false positive on diagnostic testing, but FeLV status should still be determined before vaccination. This allows clients to make an educated decision regarding the expected benefits of vaccination. Additionally, testing before vaccination will be beneficial in the case that there is ever a suspected vaccine failure. While there are a wide variety of indications for FeLV testing, obtaining an accurate diagnosis can sometimes present a diagnostic challenge (Hofmann-Lehmann & Hartmann, 2020). In the veterinary clinic, the p27 ELISA antigen test is often used as an initial in-house test to screen for FeLV antigen in the blood of infected cats. The p27 antigen is the major core component of FeLV, and its presence indicates viremia (Lutz, 2012). This test is sensitive, specific, convenient, and affordable, making it a mainstay in many veterinary practices. However, this test does have limitations. A negative FeLV ELISA test can be trusted; it indicates that the cat does not have circulating FeLV antigen at the time of testing (Hofmann-Lehmann & Hartmann, 2020). A cat that
EliteLearning.com/Veterinarian
Book Code: VFL1526
Page 62
Powered by FlippingBook