Page 1523 - Small Animal Internal Medicine, 6th Edition

CHAPTER 96 Polysystemic Viral Diseases 1495

transmission is unlikely. Transplacental, lactational, and the genome of lymphoid precursors; subgroup C induction
venereal transmission are less important than casual contact. of aplastic anemia from increased secretion of tumor necro-
VetBooks.ir FeLV infection has worldwide distribution; the seropreva- sis factor-α; immunodeficiency attributable to T-lymphocyte
+
+
depletion (both CD4 and CD8 lymphocytes) or dysfunc-
lence of infection varies geographically and by the popula-
tion of cats tested. Infection is most common in outdoor
transformation; viral induction of bone marrow growth-
male cats between ages 1 and 6 years. The prevalence of tion; neutropenia; neutrophil function disorders; malignant
FeLV antigen in North America and Canada was 3.1% in promoting substances leading to myeloproliferative diseases;
a 2017 study (Burling et al., 2017), which is higher than and potentially co-infections with other retroviruses like
the 2.3% in a study reported in 2006 (Levy et al., 2006). FIV and feline foamy virus (FFV). Cats with FeLV infec-
FeLV can be detected in feces of infected fleas for 2 weeks tion or FeLV and FIV infections had significantly shorter
(Vobis et al., 2005). However, the prevalence rates for FeLV life spans than cats infected with FIV alone (Spada et al.,
vary little across regions of the United States with high and 2018). In one study, differences in viral RNA and provirus
low prevalence rates of fleas, so this is an unlikely route of tissue loads influenced the different infection outcomes like
infection. lymphoma, leukemia, and nonregenerative anemia (Helfer-
The virus replicates first in the oropharynx, followed by Hungerbuehler AK, et al., 2015). In that study, FeLV viral
dissemination through the body to the bone marrow (Table RNA and provirus DNA were detected in cats with regres-
96.3). If persistent bone marrow infection occurs, infected sive infection for up to 12 years. A closed colony of research
white blood cells and platelets leave the bone marrow with cats was used to evaluate for associations amongst FeLV,
ultimate infection of epithelial structures, including salivary FFV, feline gammaherpesvirus, and feline coronavirus. In
and lacrimal glands. Whether infection occurs after natural that study, progressive FeLV infection and FeLV-B presence
exposure to FeLV is determined by the virus subtype or were associated with higher FeLV proviral and plasma viral
strain, the virus dose, the age of the cat when exposed, and loads. Female cats were more likely to have progressive infec-
the cat’s immune responses. Using real-time PCR and antigen tions, and males were more likely to have abortive infections.
ELISA results, four classes of FeLV infection (Torres et al., Higher proviral loads of FFV associated with higher FeLV
2005; Levy et al., 2008) were defined (see Table 96.3). Some proviral and plasma viral loads, FeLV-B, and feline corona-
FeLV-exposed cats can eliminate the infection (abortive), virus. FcaGHV-1 co-infections were more likely to occur
whereas others progress to clinical illness and persistent in male cats (Powers et al., 2018). Future FeLV field studies
viremia (progressive). Other FeLV-exposed cats will develop should also include comparison with FFV and feline gam-
regressive infection characterized by antigen-negative results maherpesvirus test results.
and lower transiently positive real-time PCR results. Focal
infections are transiently antigen-positive but have persis- Clinical Features
tently positive real-time PCR results. Focal and regressive Owners generally present FeLV-infected cats for evaluation
infections can be potentially activated by the administration of nonspecific signs such as anorexia, weight loss, and
of glucocorticoids or other immunosuppressive drugs. Blood depression, or abnormalities associated with specific organ
from cats with regressive infection (provirus-positive) can systems. Of the FeLV-infected cats evaluated at necropsy,
infect previously naïve cats (Nesina et al., 2015). 23% had evidence of neoplasia (96% lymphoma/leukemia);
The pathogenesis of various syndromes induced by FeLV the remainder died from nonneoplastic diseases (Reinacher,
is complex but includes induction of lymphoma from activa- 1989). Specific clinical syndromes can result from specific
tion of oncogenes by the virus or insertion of a provirus into effects of the virus or from opportunistic infections caused

TABLE 96.3
Outcomes of FeLV Infection

FELV P27 VIRAL VIRAL PROVIRAL FELV-
OUTCOME OF ANTIGEN BLOOD TISSUE VIRAL RNA DNA IN VIRAL ASSODATED
FELV EXPOSURE IN BLOOD CULTURE CULTURE IN BLOOD BLOOD SHEDDING DISEASE
Progressive Positive Positive Positive Positive Positive Positive Likely
infection
Regressive Negative or Negative or Negative or Transiently or Positive Negative Unlikely
infection transiently transiently transiently persistently
positive positive positive positive
Abortive exposure Negative Negative Negative Not tested Negative Negative Unlikely
Focal infection Negative Negative Positive Not tested Not tested Variable Unlikely
Reprinted with permission from Levy et al., 2008.