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330 Feline Leukemia Virus Infection

ASSOCIATED DISORDERS • Neurologic deficits (due to FeLV-associated • Other causes of clinical signs (e.g., anemia,
Immunosuppression caused by FeLV results neuropathy) neurologic signs).
VetBooks.ir protozoal), neoplasia (mainly lymphoma), Etiology and Pathophysiology Initial Database
in secondary infections (e.g., bacterial, fungal,
Routine diagnostic testing:
• Oncornavirus (RNA virus) of the family
myelosuppression, and less common conditions
such as neurologic disorders, infertility, and
Retroviridae
○ Initial database to rule out other illnesses
fading kitten syndrome. • Once established, lifelong infection with no • CBC, serum biochemistry panel, urinalysis
cure or infections; changes are not specific to
Clinical Presentation • Three possible outcomes of FeLV infection: FeLV infection, and results often normal
DISEASE FORMS/SUBTYPES ○ Abortive infection: result of good immune in FeLV-infected cats.
• Clinical presentation in FeLV-infected cats is response. These cats develop antibodies but ○ CBC in cats with myelosuppression
usually associated with secondary diseases, such are FeLV antigen-negative (ELISA nega- can show mild to marked abnormali-
as infections, myelosuppression, or neoplasia. tive) and provirus-negative (polymerase ties, including nonregenerative anemia,
• As a result of the common use of screening chain reaction [PCR] negative). Cats neutropenia, thrombocytopenia, or
serology, infection is often detected in healthy with abortive infection are healthy, not pancytopenia.
cats. contagious, and have lifelong protection ○ Serum biochemistry profile and urinalysis
• Three major FeLV subgroups: A, B, and from new infection. are usually normal or reveal nonspecific
C. Subgroup A occurs in all infected cats. ○ Regressive infection: if less effective changes.
Subgroups B and C develop de novo from immune response, regressive infection • Radiographs and ultrasound
mutations or recombinations of subtype A develops. These cats are antigen-negative ○ Thoracic or abdominal radiographs
genome with host DNA in a FeLV-A-infected (or only positive during transient viremia and abdominal ultrasound (including
cat. Subtype B is common and associated for a short period) but provirus-positive fine-needle aspiration of mass lesions
with neoplasia. Subgroup C is rare and on PCR. They also have antibodies. In for cytologic evaluation [p. 1112])
associated with nonregenerative anemia. regressively infected cats, provirus is are performed to diagnose FeLV-
integrated into the cellular genome of associated neoplasia. A mediastinal
HISTORY, CHIEF COMPLAINT the cat, but no virus is actively pro- mass with pleural effusion on thoracic
• FeLV infection can be diagnosed incidentally duced. They do not transmit the virus radiographs is suggestive of thymic
during yearly or routine new-cat screening. (except through blood transfusions), lymphoma.
Due to the long subclinical phase, even cats but infection can be reactivated after As screening tests of choice to detect progres-
with progressive FeLV infection are often immunosuppression. If this occurs, they sive infection, fast point-of-care ELISA or
recognized before clinical signs develop. can become antigen positive and can other immunochromatography tests (using a
• Progressive infection eventually leads to develop FeLV-associated diseases. They similar technique) are used for detecting free
clinical signs months to years after infection. are usually asymptomatic, but rarely, FeLV antigen in blood. Immunofluorescence
• Signs due to secondary infections (e.g., nasal regressive infection itself can result in assay (IFA) is sometimes used for detecting
or ocular discharge) or nonspecific signs conditions in which the integrated pro- intracellular FeLV antigen in neutrophils
attributable to anemia or cancer, such as virus causes the problem (e.g., neoplasia, and platelets in blood smears or bone
weakness, lethargy, or inappetence, should myelosuppression). marrow.
prompt veterinary consultation. ○ Progressive infection: progressive infection • Diagnosis of progressive FeLV infection
• FeLV is sometimes responsible for abortion develops if there is an ineffective immune (antigen-positive, provirus-positive cats)
and infertility in infected queens response. These cats are antigen- and ○ For detection of FeLV antigen, ELISA is
• Fading kitten syndrome can occur in provirus-positive (i.e., ELISA and PCR more sensitive and detects infection earlier
newborn kittens that die within the first positive) and usually have no detectable than IFA. ELISA is the diagnostic test of
weeks of life antibodies. They will likely develop FeLV- choice for general screening.
• Various other signs can occasionally occur as a associated diseases. ○ Saliva- or tear-based antigen tests are
result of infection (e.g., urinary incontinence, not recommended (poor sensitivity due
ocular abnormalities). DIAGNOSIS to intermittent shedding).
○ Do not pool blood from multiple kittens
PHYSICAL EXAM FINDINGS Diagnostic Overview for testing (inaccurate results).
During subclinical phase, exam is unremarkable, • Progressive FeLV infection is usually diag- • Diagnosis of regressive FeLV infection
but with illness, may recognize nosed by detection of FeLV antigen by ELISA (antigen-negative, provirus-positive cats)
• General findings or other immunochromatography tests (using ○ PCR to detect the integrated provirus
○ Lymphadenopathy a similar technique). (FeLV DNA) on whole blood is the test
○ Gingivostomatitis ○ Negative results are highly reliable to rule of choice
○ Signs of opportunistic infection (due to out progressive infection in an area with ○ Very sensitive and specific
immunosuppression) low prevalence. ○ Can also be used as a confirmatory test
• Lymphoma-associated signs ○ Positive results need confirmation because for positive antigen test results
○ Dyspnea due to mediastinal lymphoma false-positive results are possible. • Diagnosis of abortive FeLV infection
and pleural effusion • Diagnosis of regressive FeLV infection (antigen-negative, provirus-negative, but
○ Diarrhea due to gastrointestinal (GI) through PCR (in blood) to detect integrated antibody-positive cats)
lymphoma FeLV provirus in an ELISA-negative cat. ○ Detection of abortive infection requires
○ Vomiting (GI lymphoma or uremia from • Diagnosis of abortive FeLV infection is detection of antibodies (test not widely
renal lymphoma) through detection of antibodies in FeLV available).
○ Icterus (hepatic lymphoma) antigen-negative, PCR-negative cats. Rarely ○ Detecting antibodies can help predict
• Myelosuppression-associated signs performed in clinical setting at present whether a cat is protected from new
○ Pallor due to nonregenerative anemia; infection.
anemia-related heart murmur, tachycardia, Differential Diagnosis ○ Can be used as an additional screening
or tachypnea • Other immunosuppressive conditions, such as test to decide if it is necessary to vaccinate
○ Hemorrhage due to thrombocytopenia feline immunodeficiency virus (FIV) infection a cat.

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