Page 941 - Clinical Small Animal Internal Medicine

87 Feline Leukemia Virus 879

Transmission during birth and nursing constitutes the found to be FeLV provirus positive and FeLV antigen
VetBooks.ir greatest risk of producing live, viremic kittens. There is negative. Provirus PCR testing is positive sooner (1–2
weeks) after FeLV exposure than antigen detection in
some evidence that regressively infected queens may
pass virus on to their kittens either in utero or in milk.
Some specialized laboratories offer RT‐PCR for the
Neonatal kittens are at risk of rapidly progressive infec- blood.
tion with clinical manifestations of hypothermia, dehy- detection of viral RNA. The detection of viral RNA in the
dration, failure to nurse, and early mortality, collectively saliva correlates well with the detection of antigen in
termed “fading kitten syndrome.” It is likely that trans- the blood of infected cats. However, FeLV viral RNA in
mission from infected queens to their kittens is the single saliva and blood of experimentally infected cats was
greatest source of FeLV infections. found as early as one week after FeLV exposure, at least
Although neurologic disorders associated with FeLV two weeks before antigen detection in the blood.
are most often caused by compression of the brain and
spinal cord by lymphoma tumor tissue, a mechanism for Testing Cats for FeLV Infection
neuropathology is also suspected to result in peripheral
neuropathies, urinary incontinence, and ocular pathol- ● Test sick cats for the presence of FeLV antigenemia/
ogy, including anisocoria, mydriasis, Horner syndrome, viremia (using antigen tests, virus isolation, RT‐PCR
and central blindness even in the absence of visible com- from saliva).
pressive lesions on diagnostic imaging. If antineoplastic – Any cat that tests FeLV positive: retest the cat after
therapy is planned, it is important to distinguish neopla- 1–2 months to determine whether progressive or
sia from neuropathy. regressive infection prevails. Quarantine the cat dur-
Stomatitis is more classically associated with feline ing this period since the cat is a FeLV infection source
immunodeficiency virus (FIV) infection, but FeLV infec- for other cats. This procedure may be repeated if cir-
tion can also predispose cats to chronic ulcerative prolif- cumstances permit and/or the testing interval may
erative gingivostomatitis. Clinical sequelae include pain, be discussed with the cat owner.
anorexia, and tooth loss. An immune‐mediated mecha- ● Test healthy cats for the presence of FeLV antigene-
nism is likely, particularly in combination with co‐infec- mia/viremia (using antigen tests, virus isolation,
tions such as feline calicivirus. RT‐PCR from saliva).
– Prior to the first FeLV vaccination, testing is recom-
mended for every cat; prior to the second vaccina-
Diagnosis tion (booster of basic immunization), testing is
recommended if the cat may have been exposed to
The outcome of a FeLV infection can be characterized FeLV in the last 4–8 weeks.
using the results from virus isolation, immunofluores- – If the cat is at high risk for FeLV (outdoor access,
cence assays, detection of FeLV p27 capsid antigen in multicat environment, any husbandry with chang-
serum or plasma, and detection of FeLV provirus or ing cats, etc.).
viral RNA in the blood or some tissues by molecular – If the cat has moved to a new environment (new
assays. Serologic assays for the detection of FeLV‐spe- home, shelter, cattery, etc.): if the cat tests negative,
cific antibodies are currently not routinely used. quarantine (keep from other cats and any potential
Antigenemia (presence of p27 capsid antigen) is a FeLV exposure) and retest after 4–6 weeks for
marker of infection and in most, but not all cats, a absence of FeLV antigen prior to introduction into
parameter for viremia (presence of replication‐compe- the new environment.
tent virus). Detection of viremia by virus isolation is – Any cat that tests FeLV positive: retest the cat after
not widely available, laborious, and time consuming. In 1–2 months to determine whether progressive or
contrast, antigenemia can be easily detected using regressive infection prevails. Quarantine the cat dur-
enzyme‐linked immunosorbent assay (ELISA) in a spe- ing this period since the cat is a FeLV infection source
cialized laboratory or by rapid point‐of‐care tests. for other cats. This procedure may be repeated if cir-
Most cats will test antigen positive within 3–6 weeks cumstances permit and/or the testing interval may
after FeLV exposure. The detection of FeLV provirus in be discussed with the cat owner.
the peripheral blood or certain tissues like bone mar- ● Test healthy cats for the presence of FeLV provirus in
row using RT‐PCR is more sensitive than the detection the blood (PCR). Confirmatory of positive or ques-
of antigenemia or viremia to demonstrate previous tionable antigen tests; true antigen‐positive samples
FeLV exposure. Thus, a certain proportion of pet cats are highly provirus positive.
can be found to be PCR positive but antigen negative. – Early infection: provirus PCR from blood tests
In an early study in Switzerland, 10% of pet cats were earlier positive than antigen tests.