病史
患猫是室内单饲养，未接触其他猫只，正在接种疫苗，包括白血病毒（FeLV）疫苗。饲主在约2个月龄时，从动物收容所收养该猫，当时FeLV测试和免疫缺陷病毒（FIV）的酶联免疫吸附测定（ELISA）结果呈阴性。猫曾在1岁和3岁时贫血，输血、四环素、和免疫抑制药物治疗后反应良好。2次发作时都没有进行具体的诊断，给予6个月的环磷酰胺。送诊前1个月前表现正常。
临床症状是非特异性的，包括嗜睡，厌食，体重损失，大便正常但偏少。严重贫血被确诊，治疗开始时使用强的松（7.5毫克口服 q 12 h），环磷酰胺（12毫克口服 4天7），强力霉素（25毫克口服q 12 h），补充维生素或铁。治疗1个月后猫没有反应，需要进行更详细的检查。
体格检查
猫（体重3.2公斤）安静，警惕性高；体温和呼吸频率无异常。主要的异常有心动过速（230次/分），III或VI级左胸骨缘心脏收缩期杂音，患猫看上去很苍白是比较主要的异常。
实验室检查
FeLV/FIV混合的ELISA检测和大型猫血巴尔通体（Mycoplasma haemofelis）的聚合酶链反应检测均正常。其他的初始诊断包括全血细胞计数，生化分析，尿液分析。有轻微的多染性红细胞；其他异常结果如下表所示。
实验室检查结果

项目	结果	参考范围
红细胞（×10^6 /μL）	1.47	50-100
红细胞压积（%）	7

24-45

平均红细胞血红蛋白浓度（%）	37.9	30-36
淋巴细胞（×10^3 /μL）	0.85	1.5-7.0
有核红细胞（/μL）	212	-
网织红细胞（×10^4 /μL）	60,000	-
血浆尿素氮（mg/dl)	35	15-29
球蛋白(g/dl)	4.1	2.3-3.8
丙氨酸转氨酶（U / L）	236	20-170
尿比重	1.039	-

诊断：与FeLV病毒感染有关的巨幼红细胞性贫血
稳定后，制作骨髓涂片进行细胞学检查，间接荧光免疫试验（IFA）检测FeLV。骨髓穿刺显示总体细胞减少，尽管估计的外周血小板数量正常，巨核细胞是稀少的。粒红比增加到10:1。尽管骨髓细胞成长是正常的，但有大量的与红系细胞线相关的巨成红细胞变化（见下图）。骨髓IFA检测FeLV的结果呈阳性。
骨髓穿刺，瑞氏吉姆萨染色。这个样本包含罕见的巨核细胞增生。粒红比是10：1。尽管骨髓细胞生长成熟过程是正常的，但有大量的与红系细胞线相关的巨成红细胞变化。巨幼红细胞（箭头）是大号的红细胞前体。它们的不成熟、不规则、淡染的细胞核中含有不规则的染色质团块，表明细胞核和细胞质成熟并不同步（放大500倍后图像）。

三个不同的场合使用ELISA检测猫FeLV结果呈阴性。虽然病毒抗原检测是FeLV感染推荐的诊断方法，以及常用的ELISA法检测p27核心抗原是相当敏感的，但如果感染局限于骨髓（潜伏感染），ELISA检测外周样品的结果是阴性的。虽然与FeLV感染相关的疾病一般是与病毒血症有关，但其有时只出现在骨髓。在这些情况下，诊断结果取决于骨髓中病毒的鉴定，这种病毒鉴定通常依赖于骨髓样本IFA试验结果。

贫血是FeLV感染常见的并发症，可通过几种不同的机制发生。根据不同的机制，FeLV相关的贫血可能是再生或非再生的，而且可能与多种红细胞形态特征有关。因免疫抑制的原因，FeLV测试呈阳性的猫更容易感染各种病毒，细菌，原虫，或真菌微生物。这些并发感染可直接（例如猫血巴尔通体病）或间接（例如炎症疾病）导致贫血。淋巴增生性或骨髓增生性疾病是FeLV感染相关的贫血发生的其他原因，如骨髓纤维化。FeLV也可能引起贫血，通过选择性消耗骨髓红细胞集落形成单位或抑制红细胞集落单位分化。

Medical history

The affected cats are kept alone indoors and have not been exposed to other cats. They are being vaccinated, including the leukemia virus (FeLV) vaccine. The owner adopted the cat from an animal shelter at about 2 months of age when FeLV tests and enzyme linked immunosorbent assay (ELISA) for immunodeficiency virus (FIV) were negative. The cats were anaemic at 1 and 3 years of age and responded well to transfusions, tetracycline, and immunosuppressive drugs. At the time of both attacks, no specific diagnosis was made and cyclophosphamide was given for 6 months. Normal performance 1 month before admission.

Clinical symptoms are nonspecific, including lethargy, anorexia, weight loss, normal but minor bowel movements. Severe anemia was diagnosed and treatment began with prednisone (7.5 mg oral q 12 h), cyclophosphamide (12 mg oral q 12 h), doxycycline (25 mg oral q 12 h), and vitamin or iron supplementation. The cat did not respond after 1 month of treatment and needed more detailed examination.

Physical check

Cats (weighing 3.2kg) are quiet and alert. Body temperature and respiratory rate were not abnormal. The main abnormalities were tachycardia (230 beats/min), grade III or VI left sternal margin systolic murmurs, and pale cat appearance.

Laboratory inspection

Both FeLV/FIV ELISA and Mycoplasma haemofelis polymerase chain reaction tests were normal. Other initial diagnoses include full blood count, biochemical analysis, and urine analysis. Slightly polychromatic erythrocytes; Other abnormal results are shown in the table below.

Laboratory results

project

The results of

Reference range

Red blood cell (x 10^6 / mul)

1.47

50-100.

Hematocrit (%)

7

24-45

Mean erythrocyte hemoglobin concentration (%)

37.9

30-36

Lymphocyte (x 10^3 / mul)

0.85

1.5-7.0

Nuclear red cells (/ mul)

212

-

Reticulocyte (x 10^4 / mul)

60000

-

Plasma urea nitrogen (mg/dl)

35

15-29

Globulin (g/dl)

4.1

2.3-3.8

Alanine transaminase (U/L)

236

20-170.

Urine specific gravity

1.039

-

Diagnosis: megaloblastic anemia associated with FeLV infection

After stabilization, a bone marrow smear was prepared for cytology, and FeLV was detected by indirect fluorescence immunoassay (IFA). Bone marrow aspiration revealed an overall cytopenia, although the estimated number of peripheral plaques was normal and megakaryocytes were rare. The grain red ratio increased to 10:1. Although marrow cell growth is normal, there are numerous megaloblasts associated with the erythroid line (see figure). Bone marrow IFA tested positive for FeLV.

Medullary puncture, reijsa stain. This sample contains rare megakaryocyte proliferation. The grain red ratio is 10:1. Although the process of marrow cell growth and maturation is normal, there are numerous megaloblasts associated with the erythroid line. Megaloblastic cells (arrows) are large progenitors of red blood cells. Their immature, irregular, lightly stained nuclei contain irregular chromatin clumps, indicating that the nuclei and cytoplasm are out of sync when they mature (image at 500x magnification).

ELISA tests for FeLV were negative on three different occasions. Although virus antigen detection is the preferred diagnostic method for FeLV infection, and the commonly used ELISA method for detecting p27 core antigen is quite sensitive, ELISA results for peripheral samples are negative if the infection is confined to the bone marrow (latent infection). Although diseases associated with FeLV infection are generally associated with viremia, they sometimes occur only in the bone marrow. In these cases, the diagnosis depends on the identification of the virus in the bone marrow, which usually relies on the results of the IFA test of the bone marrow sample.

Anemia is a common complication of FeLV infection and can occur through several different mechanisms. Depending on the mechanism, felv-related anemia may be regenerative or non-regenerative and may be associated with a variety of erythrocyte morphological characteristics. Cats that test positive for FeLV are more likely to be infected with various viruses, bacteria, protozoa, or fungal microorganisms due to immunosuppression. These concurrent infections can lead directly (e.g., bartonella disease in cats) or indirectly (e.g., inflammatory disease) to anemia. Lymphoproliferative or myeloproliferative diseases are other causes of anemia associated with FeLV infection, such as myelofibrosis. FeLV may also cause anemia by selectively consuming bone marrow erythrocyte colony forming units or inhibiting the differentiation of erythrocyte colony units.