Phagocytosis of horse erythrocytes treated with equine infectious anemia virus by cultivated horse leukocytes

Development and evaluation of a blocking ELISA for serological diagnosis of equine infectious anemia

Equine infectious anemia (EIA) is an important viral disease characterized by persistent infection in equids worldwide. Most EIA cases are life-long virus carriers with low antibody reactions and without the appearance of clinical symptoms. A serological test with high sensitivity and specificity is required to detect inapparent infection. In this study, a B-cell common epitope-based blocking ELISA (bELISA) was developed using a monoclonal antibody together with the EIAV p26 protein labelled with HRP. The test has been evaluated against the standard and with field serum samples globally. This bELISA test can be completed within 75 min, and the sensitivity is higher than those of either the AGID or one commercial cELISA kit. This bELISA assay was 8-16 times more analytically sensitive than AGID, and 2 to 4 times more analytically sensitive than one cELISA kit by testing three sera from the USA, Argentina, and China, respectively. The 353 serum samples from Argentina were tested, in comparison with AGID, the diagnostic sensitivity and specificity of our bELISA assay were 100% (154/154) and 97.0% (193/199), respectively, and the accuracy of the bELISA test was 98.3%. The bELISA test developed in this study is a rapid, sensitive, specific method for the detection of EIAV infection, and could be a promising candidate for use in the monitoring of the EIA epidemic worldwide. KEY POINTS: • A universal epitope-based blocking enzyme-linked immunosorbent assay (bELISA) was developed for detection of antibodies to EIAV. • The bELISA assay can be used to test EIAV serum samples from different regions of the world including North America, South America, Europe, and Asia. • The bELISA assay was evaluated in three different international labs and showed a better performance than other commercial kits.

Equine infectious anemia in 2014: live with it or eradicate it?

In the absence of an effective vaccine, the success of the test and removal approach for the control of equine infectious anemia (EIA) cannot be overstated, at least in those areas where testing has been traditionally routine. This article addresses 4 main aspects: what has been learned about EIA virus, host control of its replication, and inapparent carriers; international status regarding the control of EIA; diagnostic and laboratory investigation; and reducing the spread of blood-borne infections by veterinarians. An attempt is made to put these issues into practical contemporary perspectives for the equine practitioner.

Differential effects of virulent and avirulent equine infectious anemia virus on macrophage cytokine expression

Equine infectious anemia virus (EIAV) causes rapid development of acute disease followed by recurring episodes of fever, thrombocytopenia, and viremia. Most infected equid eventually bring the virus under immunological control. We recently reported the development of an equine-specific ribonuclease protection assay (RPA) to quantitate mRNA levels of 10 cytokines. Using this newly developed RPA, we now show significant differences in cytokine induction in equine monocyte-derived macrophages (EMDM) exposed to virulent and avirulent EIAV. Virulent EIAV17 induced significant increases in interleukin (IL)-1alpha, IL-1beta, IL-6, IL-10, and tumor necrosis factor (TNF)-alpha by 0.5-1 h postinfection (hpi). In contrast, the avirulent virus failed to induce any of the tested cytokines above that of control levels. These data show a direct correlation between cytokine dysregulation and EIAV pathogenesis.

Equine infectious anemia

The ability of EIAV to persistently infect horses in the face of a profound immune response by the host makes it a potentially devastating disease for the horse population of the United States. Its ability to evade host immune defenses by lying dormant in apparently healthy animals and by rapidly changing its antigenic determinants is proving to be a major obstacle to vaccine development. Because most infected horses appear clinically normal and a large proportion of horses in this country remain untested, the virus is not likely to be eradicated in the near future. Yet, for the same reason, because most horses infected with EIAV appear clinically normal, there is a tendency for the horse industry to become complacent in its efforts to control the virus. The cooperation of horse owners, veterinarians, and regulatory officials is necessary to keep the threat of EIA in check in the United States.

Immune-mediated thrombocytopenia in horses infected with equine infectious anemia virus

An adult horse infected with a virulent, cell culture-adapted strain of equine infectious anemia virus (EIAV) developed cyclical thrombocytopenia in which the nadir of platelet counts coincided with peak febrile responses. In order to investigate the mechanism of thrombocytopenia during acute febrile episodes, four adult horses were experimentally infected with the wild-type Wyoming strain of EIAV. Platelet counts decreased from baseline as rectal temperature increased. Serum reverse transcriptase activity increased above background levels in all horses, coincident with increase in rectal temperature. All horses developed an EIAV-specific immune response detectable by Western immunoblot by postinfection day 10. Increases in platelet-associated immunoglobulins G and M were detectable by direct fluorescent-antibody test and flow cytometric assay. Viral replication in bone marrow megakaryocytes was not detectable by in situ hybridization. Results suggest an immune-mediated mechanism of thrombocytopenia in horses infected with EIAV. Despite an inability to identify virion particles in association with platelet-bound antibody, the cyclical nature of the thrombocytopenia and the occurrence of a marked cell-free viremia concomitant with fever and thrombocytopenia suggest immune complex deposition on platelets. We propose that clearance of virus and antibody-coated platelets from the peripheral circulation by hepatic Kupffer cells and splenic macrophages may target infectious virus particles, in the form of immune complexes, to host cells most permissive for in vivo viral replication.

Phagocytosis of opsonized fluorescent microspheres by equine polymorphonuclear leukocytes

Equine blood polymorphonuclear leukocytes (PMN) were isolated by buffy coat and hypotonic lysis of residual erythrocytes. A highly reproducible method is described for measuring the uptake of opsonized latex microspheres by equine PMN using flowcytometry. The use of cytochalasin D allowed for differentiation of ingested from attached particles. The kinetics of phagocytosis in vitro is shown for different experimental conditions. We developed an assay for evaluation of phagocytic capacity of PMN which allows the assessment of drugs for their influence on phagocytosis in vivo as well as in vitro.

Complement-mediated hemolysis of horse erythrocytes treated with equine infectious anemia virus

Horse erythrocytes treated with equine infectious anemia virus hemagglutinin were found to be lysed after incubation with fresh horse serum at 37 degrees C. Fresh guinea pig serum induced more efficient hemolysis than horse serum. Direct immunofluorescence test revealed the adsorption of complement factors on the surface of the erythrocytes. Calcium and magnesium ions were necessary for the hemolysis to take place. Antibody against equine infectious anemia virus enhanced the virus-induced complement-mediated hemolysis. These observations indicated that the classical pathway of complement activation was responsible for this virus-induced hemolysis and suggest the possibility that virus antigen, anti-viral antibody and complement may play an important role in the genesis of the anemia of horses infected with the equine infectious anemia virus.