Help clients stay optimistic when FeLV results are positive
You just ran a point-of-care (PoC) test for feline leukemia virus (FeLV), and the results are positive. Now what?
Tell the owners not to panic
An FeLV-positive cat can live a long and healthy life, often without any veterinary intervention. So make sure owners understand that this is not a death sentence.
Perform a confirmatory test
All PoC tests have been shown to yield false positive results.1 But keep in mind that all FeLV tests—PoC tests, polymerase chain reaction (PCR) testing or immunofluorescent antibody (IFA) testing—have some intrinsic inaccuracy, making it difficult to resolve discordant results with absolute certainty. Nonetheless, confirmation is essential.
Let clients know their cat is not alone
In a recent study of 62,301 cats from 1,396 clinics and 127 shelters, the prevalence rate for FeLV seropositive tests was 3.1% in North America.1 This translates to about 3 million cats. Adult age, outdoor access, clinical disease and sexually intact male status were risk factors. The rate of infection is similar to the last decade, meaning that prevention and surveillance have been somewhat unsuccessful. This preventable virus places cats at risk for an array of diseases and premature death. Every cat should be tested and at-risk cats should be vaccinated with a demonstrably effective vaccine.
Step clients through what happens next
Viral infection with FeLV can result in a variety of outcomes. Some cats contain the infection and show a regressive course, while others stay viremic and succumb to the infection within a few years. In regressive infection, cats cease producing productive virus and circulating p27 antigen but still carry provirus detectable by PCR tests. These cats initially test positive for soluble p27 antigen and then revert to antigen-negative status, do not shed infectious virus and are less likely to develop FeLV-associated diseases. Regressive cats can still shed virus via blood transfusions and may occasionally relapse into productive infection and illness. Thus, healthy FeLV-positive cats should be treated like any other healthy cat and kept indoors.
Investigate your treatment options
With the advent of many antiretroviral therapies in the treatment of human immunodeficiency virus (HIV), a number of these new drugs have been proposed for FeLV. Properly designed trials and clear evidence of efficacy, however, remains elusive.2 Zidovudine, for example, showed promise in in vitro testing but not in vivo. Similarly, adefovir, tenofovir, ribavirin and raltegravir have been shown to be effective in vitro with no supporting in vivo data.2 Thus, antiretroviral therapy is only indicated in exceptional cases due to lack of proven efficacy of many antivirals and their toxicity at this time. Level 1 evidence-based clinical trials are needed to evaluate these drugs as there may be some in the long list of drugs currently being used for HIV that may prove safe and effective.
The focus of treatment for FeLV-positive cats with clinical signs of illness remains focused on looking for underlying disease. Anemias, for example, should prompt investigation for Mycoplasma species before initiating glucocorticoid therapy to which some cats respond. A diagnosis of lymphoma may carry a more guarded prognosis in these cats. Nonetheless, a typical chemotherapy protocol should be undertaken. If the patient has neurologic signs, cryptococcosis, lymphoma and toxoplasmosis should be ruled out. If neurologic signs are thought to be caused by FeLV, zidovudine (AZT; 5 mg/kg orally every 12 hours) may be helpful.
Recurring infections should be treated aggressively. In addition to standard therapy, feline interferon-omega, available in Japan, Australia and Europe, may be helpful. In a placebo-controlled field study, 48 cats infected with FeLV were treated with high-dose feline interferon-omega at 1 X 106 every 24 hours given subcutaneously on five consecutive days. The treatment was repeated two more times with weeks between each treatment. This therapy reduced clinical signs and increased survival. However, no virus parameters were measured.2 There are, as yet, no studies demonstrating efficacy when given orally.
1. Burling AN, Levy JK, Scott HM, et al. Seroprevalence of feline leukemia virus and feline immunodeficiency virus in cats in the United States and Canada and risk factors for seropositivity. J Am Vet Med Assoc 2017;251(2):187-194.
2. Hartmann K. Efficacy of antiviral chemotherapy for retrovirus-infected cats. What does the current literature tell us? J Feline Med Surg 2015;17:925-939.