Page 1525 - Small Animal Internal Medicine, 6th Edition

CHAPTER 96 Polysystemic Viral Diseases 1497

occasionally identified in peripheral blood smears, effusions, et al., 2015). Thus results support the recommendation to
and CSF. optimally use FeLV antigen-negative and provirus DNA-
VetBooks.ir FeLV antigens in neutrophils and platelets by immunofluo- negative cats as blood donors (Wardrop et al., 2016)
Most cats with suspected FeLV infection are screened for
Treatment
rescent antibody (IFA) testing or in whole blood, plasma,
serum, saliva, or tears by ELISA. Blood or plasma may be Antiretroviral drugs that could be potentially used for the
the most accurate fluids to assess in ELISA tests. There are management of cats with clinical disease related to FeLV
multiple point of care tests around the world, and results can have been reviewed (Hartmann et al., 2015). Several antivi-
vary between tests and between the same test in two different ral agents have been proposed for the treatment of FeLV; the
studies (Hartmann et al., 2007; Westman et al., 2017; Levy reverse transcriptase inhibitor AZT has been studied the
et al., 2017; Liu et al., 2016; Krecic et al., 2018). IFA results most. Unfortunately, administration of AZT to persistently
are not positive until the bone marrow has been infected. viremic cats does not appear to clear viremia in most, and it
Generally, the results of IFA testing are accurate more than had minimal benefits for clinically ill cats in a study (Hart-
95% of the time. False-negative reactions may occur when mann et al., 2002). Interferons have an effect against FeLV in
leukopenia or thrombocytopenia prevents evaluation of an vivo and in vitro (Collado et al., 2007; de Mari et al., 2004)
adequate number of cells. False-positive reactions can occur and lessen clinical disease in FeLV-infected cats by immune
if the blood smears submitted for evaluation are too thick. A modulation as described for FIV (Domenech et al., 2011;
positive IFA result indicates that the cat is viremic and con- Leal and Gil, 2016; Pedretti et al., 2006). Immunotherapy
tagious; approximately 90% of cats with positive IFA results with drugs compounds such as Staphylococcus protein A,
are viremic for life. The rare combination of IFA-positive and Propionibacterium acnes, or acemannan have been pur-
ELISA-negative results suggests technique-related artifact. ported to improve clinical signs in some cats, but controlled
The virus can be detected in serum by ELISA before infec- studies are lacking.
tion of bone marrow and can therefore be positive in some Chemotherapy should be administered to cats with FeLV-
cats during early progressive stages of infection or during associated neoplasia (see Chapters 76 and 79). Opportunistic
early latent infection, even though IFA results are negative. agents should be managed as indicated; the upper dose range
Other possibilities for discordant results (ELISA-positive, and duration of antibiotic therapy are generally required.
IFA-negative) are false-positive ELISA results or false- Supportive therapies such as hematinic agents, vitamin B 12 ,
negative IFA results. Cats with positive ELISA results and folic acid, anabolic steroids, and erythropoietin generally
negative IFA results should be isolated until retested 4 to 6 have been unsuccessful in the management of nonregenera-
weeks later because progression to persistent viremia and tive anemia. Blood transfusion is required in many cases.
epithelial cell infection may be occurring. Cats with immune-mediated hemolytic anemia require
ELISA-positive cats that revert to negative have developed immunosuppressive therapy, but this may activate virus
focal (latent) infections or regressive infection. Virus isola- replication. The prognosis for persistently viremic cats is
tion, IFA performed on bone marrow cells, immunohisto- guarded; the majority die within 2 to 3 years.
chemical staining of tissues for FeLV antigen, and PCR can
be used to confirm focal or regressive infection in some cats. Prevention and Zoonotic Aspects
Cats with focal or regressive infection are not likely conta- Avoiding contact with FeLV by housing cats indoors is the
gious to other cats by direct contact, but infected queens may best form of prevention. Potential fomites such as water
pass the virus to kittens during gestation or parturition, or bowls and litter pans should not be shared by seropositive
by milk. Cats with regressive or focal infection can be immu- and seronegative cats. Testing and removal of seroposi-
nodeficient and may become viremic (IFA- and ELISA- tive cats can result in virus-free catteries and multiple-cat
positive) after administration of glucocorticoids, or after households.
extreme stress. Because of variations in challenge study methods and
A delay of 1 to 2 weeks generally occurs after the onset of the difficulty of assessing the preventable fraction of a
viremia before ELISA tear and saliva test results become disease with a relatively low infection rate, long subclini-
positive; therefore these test results can be negative even cal phase, and multiple field strains, the efficacy of indi-
when results with serum are positive and so are not generally vidual vaccines continues to be in question (see Chapter
not recommended for use unless blood cannot be collected. 93). In one recent study, all three FeLV vaccines studied
Antibody titers to FeLV envelope antigens (neutralizing anti- gave similar efficacies (Grosenbaugh et al., 2017). Vac-
body) and against virus-transformed tumor cells have been cination of cats not previously exposed to FeLV should
detected in research studies, but the diagnostic and prognos- be considered in cats at high risk (i.e., contact with other
tic significance of results from these tests is unknown. Real- cats), but owners should be warned of the potential effi-
time PCR assays are more sensitive than conventional PCR cacy of less than 100%. Cats with persistent FeLV viremia
for FeLV infections, but testing is not standardized amongst do not benefit from vaccination. Vaccination is related to
most laboratories in the United States (Torres et al., 2005). the development of fibrosarcoma in some cats (see Chapter
FeLV has been transmitted by blood from some cats that 93). Cats developing these tumors may be genetically
are FeLV provirus-positive, p27 antigen-negative (Nesina predisposed.