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A Standardbred gelding and a colt were examined because of poor performance and anemia. Each horse had been given recombinant human erythropoietin (rhEPO; 4,000 IU) at least twice within the preceding 2 to 4 months. The horses had an Het of 16 and 24%, serum iron concentrations of 210 and 304 micrograms/dl (reference range, 73 to 140 micrograms/dl), total iron binding capacities of 239 and 321 micrograms/dl (reference range, 266 to 364 micrograms/dl), values for the percentage saturation of transferrin by iron of 87.9 and 94% (reference range, 20 to 52%), and serum ferritin concentrations of 255 and 355 ng/ml (reference range, 43 to 261 ng/ml), respectively. There was no clinical or laboratory evidence of immune-mediated hemolysis or an infectious or inflammatory cause of the anemia. Examination of sternebral marrow biopsy specimens revealed generalized bone marrow hypoplasia; myeloid-to-erythroid ratios were 6.7 and 3.2. Moderate-to-marked erythroid hypoplasia was diagnosed in both horses. Compared with serum from a healthy control horse, serum from the affected horses inhibited rhEPO-induced proliferation of erythroid progenitors in vitro. Results suggested that the horses had developed anti-rhEPO antibodies that cross-reacted with endogenous erythropoietin, thereby inhibiting erythropoiesis. Horses were discharged with instructions that rhEPO administration be discontinued and that dexamethasone be administered. Five months later, both horses were back in training. For 1 horse, Hct had increased to 35%, and the other horse was not available for examination.

Objective: To characterize infection of bone marrow-derived macrophages (BMDM) with equine infectious anemia virus (EIAV) by determining virus production, effects on viability, and induction of cytokines., Sample Population: BMDM obtained from bone marrow of 6 clinically normal adult horses., Procedure: BMDM were infected with EIAV at a multiplicity of infection of 8. Cell viability, percentage of cells with detectable viral protein, reverse transcriptase activity, and concentrations of infective virus (focus-forming units/ml), interleukin 6, and tumor necrosis factor-alpha were measured in culture supernatant samples obtained at various days after infection., Results: Cell viability was decreased on day 4 and was maximally decreased on day 8. The number of cells with detectable viral protein and supernatant reverse transcriptase activity increased significantly on day 4 and increased until day 6. Virus concentration (focus-forming units per milliliter) peaked on day 4 after infection and was constant thereafter. Infection with EIAV caused significant induction of interleukin 6 production by BMDM. The maximal difference was seen on day 4 after infection. Control and infected BMDM produced only negligible amounts of tumor necrosis factor-alpha., Conclusions: BMDM are useful, as a cell population, to study the effects of infection with EIAV, including cell death and induction of interleukin 6 but not tumor necrosis factor-alpha production.

We have identified congenic mouse strains that differ dramatically in resistance to infection with the murine malaria parasite Plasmodium yoelii 17X. After infection, BALB/c mice develop severe anemia and a high degree of parasitemia which sometimes results in death. The mtv-7 congenic strain BALB.D2.mlsa, however, develops only a mild degree of anemia and parasitemia. In this paper we describe the course of the disease and discuss the potential role of mtv-7 and linked loci in control of this infection. These mice differ in their response to anemia, which may contribute to their differential susceptibility to disease; however, no influence of mtv-7 reactive T cells was documented.

In diseased animals, laboratory evaluations of erythrocytes, leukocytes, and hemostasis provide important information that contributes to either narrowing the list of potential diagnoses or to determining a specific diagnosis. To adequately interpret the results of these evaluations, normal erythrocyte and leukocyte kinetics and normal hemostatic function must be understood. In addition, knowledge of common diseases resulting in abnormalities of these laboratory tests and of typical changes in these tests caused by these diseases is vital. This article has reviewed normal erythrocyte and leukocyte kinetics and normal hemostatic functions that are clinically significant and has described the laboratory abnormalities expected in common diseases affecting these functions.

As an important enzyme in DNA synthesis, dUTPase is present in a wide variety of organisms and viruses and has been identified as a component of the equine infectious anemia virus (EIAV) pol gene. The role of EIAV dUTPase, designated DU, in virus replication in vitro and in vivo was investigated with a recently described infectious molecular clone of EIAV. A deletion mutant that was deficient in dUTPase activity was constructed, and its replication kinetics was examined in fetal equine kidney (FEK) cells and primary equine bone marrow macrophage (EBMM) cells. In FEK cells, which are permissive for EIAV replication, the mutant virus replicated as well as the parental virus. In primary cultures of EBMM cells, which are primary targets of EIAV infection in vivo, the DU mutant showed delayed replication kinetics and replicated to a lower extent than did the parental virus. As the multiplicity of infection decreased, the difference between the parental and mutant viruses increased, such that at the lowest multiplicity of infection tested, there was over a 100-fold difference in virus production. The mutant virus was also much less cytopathic. The role of DU in replication in vivo was examined using a Shetland pony model of EIAV infection. Shetland ponies that were infected with the parental and mutant viruses showed transient virus RNA levels in plasma approximately 5 to 10 days postinfection. The peak virus levels in plasma (as measured by a quantitative reverse transcriptase PCR assay) were 10- to 100-fold lower in the mutant virus-infected animals than in the animals infected with the parental virus. However, ponies infected with the mutant virus mounted similar antibody responses despite the marked differences in virus replication. These studies demonstrate that EIAV DU is important for the efficient replication of the virus in macrophages in vitro and in vivo and suggests that variations in the DU sequence could markedly affect the biological and pathogenic properties of EIAV.

Direct effects of equine infectious anemia virus (EIAV) on hematopoiesis in vitro were studied. Bone marrow mononuclear cells from clinically normal horses were incubated with 100 TCID50 of EIAV/10(7) cells. These cells were cultured to assay for colonies derived from erythroid progenitors, granulocyte/monocyte progenitors, and fibroblastic progenitors. The EIAV had a selective suppressive effect on the erythroid progenitors. Colony-forming units-erythroid were suppressed to 80% of that for medium controls (P = 0.011). Burst-forming units-erythroid were suppressed to 70% of that for medium controls (P = 0.003). Significant effect was not apparent on colony-forming units-granulocyte/macrophage or on colony-forming units-fibroblastic.