Page 940 - Clinical Small Animal Internal Medicine

878 Section 9 Infectious Disease

Epidemiology supporting stromal cells. Platelet dysfunction, thrombo-
VetBooks.ir The prevalence of FeLV infection documented in cross‐ cytopenia, and neutropenia are all possible sequelae.
Lymphoma is the most frequently diagnosed malig-
nancy of cats. Tumors such as lymphoma and lymphoid
sectional surveys in North America has been declining
throughout the past three decades and is attributed to leukemia develop in as many as 30% of cats with pro-
testing and vaccination efforts. In the United States, 3.1% gressive FeLV infections. Regressive infections are also
of cats in a large, nationwide dataset tested positive for implicated in the occurrence of these tumors in the
FeLV in 2010, with increased risk among outdoor cats, absence of viremia, but cats with progressive infections
unneutered males, and cats with other disease condi- may face an increased risk of lymphoma development as
tions (particularly respiratory disease, oral disease, and high as 60‐fold. Most American cats with mediastinal,
abscessation). Prevalence was highest in the midwestern multicentric, or spinal forms of lymphoma are FeLV pos-
and western regions of the United States and lowest in itive. However, these forms of lymphoma are becoming
the northeast. Seroprevalence surveys of varying statisti- less common as the prevalence of FeLV decreases.
cal power have found rates of positive test results to Diffuse gastrointestinal (GI) lymphoma (small cell; T cell
range from 3.6% in Germany and Canada to 4.6% in origin) is now more likely to be found in FeLV‐negative
Egypt and 24.5% in Thailand. cats of middle or older age and can be difficult to differ-
In a national (United States) study, FeLV infection was entiate from inflammatory bowel disease. Fibrosarcomas
diagnosed in 9% of cats undergoing treatment for bite and quasi‐neoplastic disorders such as multiple carti-
wounds, approximately three times the rate for cats in laginous exostoses (osteochondromatosis) can be asso-
general. FeLV is considered to be an age‐dependent dis- ciated with FeLV.
ease; young kittens are at higher risk of progressive infec- Leukemia is characterized by the neoplastic prolifera-
tion and more rapid disease progression, whereas adults tion of hematopoietic cells originating in the bone mar-
display some degree of age resistance. However, trans- row, including neutrophils, basophils, eosinophils,
mission can occur at any age, and factors affecting clini- monocytes, lymphocytes, megakaryocytes, and erythro-
cal course of disease are complex and incompletely cytes. Feline leukemias are strongly associated with FeLV
understood. infection and typically involve neoplastic cells circulat-
ing in the blood. Lymphoid leukemias are further classi-
fied as acute and chronic. Acute lymphocytic leukemia is
Signalment characterized by lymphoblasts circulating in the blood,
whereas chronic lymphocytic leukemias have an
increased number of circulating lymphocytes with
The susceptibility of domestic cats for FeLV infection mature morphology.
varies and is mainly age dependent. Kittens are more The immunosuppression caused by FeLV creates
prone to develop progressive FeLV infection than adult increased susceptibility to bacterial, fungal, protozoal,
cats. and viral infections. Numbers of neutrophils and lym-
phocytes in the peripheral blood of affected cats may be
reduced, and those cells that are present may be dysfunc-
History and Clinical Signs tional. Many FeLV‐positive cats have low concentrations
of complement which may contribute to FeLV‐associ-
Feline leukemia virus‐related disorders are numerous ated immunodeficiency and oncogenicity, as comple-
and include anemia, neoplasia, immunosuppression, ment is vital for antibody‐mediated tumor cell lysis.
immune‐mediated diseases, reproductive problems, Immune complexes formed in the presence of moder-
enteritis, neurologic dysfunction, and stomatitis. Some ate antigen excess can cause systemic vasculitis, glomer-
FeLV‐B‐infected cats develop lymphoid malignancies, ulonephritis, polyarthritis, and a variety of other immune
while FeLV‐C infection is associated with the develop- disorders. In FeLV‐infected cats, immune complexes
ment of aplastic anemia. FeLV‐T is a T cell tropic cyto- form under conditions in which FeLV antigens are abun-
pathic virus that causes lymphoid depletion and dant and anti‐FeLV IgG antibodies are sparse, a situation
immunodeficiency in infected cats. ideal for the development of immune‐mediated disease.
The anemia caused by FeLV is typically nonregenera- Reproductive problems are commonly associated with
tive and normochromic. Less commonly, macrocytosis FeLV infection. Fetal death, resorption, and placental
or regenerative hemolytic anemia is seen in 10% of involution may occur in the middle trimester of preg-
FeLV‐induced anemia cases. The cause of nonregenera- nancy, presumably as a result of in utero infection of
tive anemia is usually bone marrow suppression due to fetuses by virus transported across the placenta in mater-
viral infection of the hematopoietic stem cells and the nal leukocytes. Abortion typically occurs in late gestation.