R.F. Cook

Tissue Sites of Persistent Infection and Active Replication of Equine Infectious Anemia Virus during Acute Disease and Asymptomatic Infection in Experimentally Infected Equids

ABSTRACT Equine infectious anemia virus (EIAV) infection of horses is characterized by recurring cycles of disease and viremia that typically progress to an inapparent infection in which clinical symptoms are absent as host immune responses maintain control of virus replication indefinitely. The dynamics of EIAV viremia and its association with disease cycles have been well characterized, but there has been to date no comprehensive quantitative analyses of the specific tissue sites of EIAV infection and replication in experimentally infected equids during acute disease episodes and during asymptomatic infections in long-term inapparent carriers. To characterize the in vivo site(s) of viral infection and replication, we developed a quantitative competitive PCR assay capable of detecting 10 copies of viral DNA and a quantitative competitive reverse transcription-PCR assay with a sensitivity of about 30 copies of viral singly spliced mRNA. Animals were experimentally infected with one of two reference viruses: the animal-passaged field isolate designated EIAVWyo and the virulent cell-adapted strain designated EIAVPV. Tissues and blood cells were isolated during the initial acute disease or from asymptomatic animals and analyzed for viral DNA and RNA levels by the respective quantitative assays. The results of these experiments demonstrated that the appearance of clinical symptoms in experimentally infected equids coincided with rapid widespread seeding of viral infection and replication in a variety of tissues. During acute disease, the predominant cellular site of viral infection and replication was the spleen, which typically accounted for over 90% of the cellular viral burden. In asymptomatic animals, viral DNA and RNA persisted in virtually all tissues tested, but at extremely low levels, a finding indicative of tight but incomplete immune control of EIAV replication. During all disease states, peripheral blood mononuclear cells (PBMC) were found to harbor less than 1% of the cellular viral burden. These quantitative studies demonstrate that tissues, rather than PBMC, constitute the predominant sites of virus replication during acute disease in infected equids and serve as resilient reservoirs of virus infection, even in the presence of highly effective immune responses that maintain a stringent control of virus replication in long-term inapparent carriers. Thus, these observations with EIAV, a predominantly macrophage-tropic lentivirus, highlight the role of tissues in sequestering lentiviral infections from host immune surveillance.

Equine infectious anemia and equine infectious anemia virus in 2013: A review

A detailed description of equine infectious anemia virus and host responses to it are presented. Current control and eradication of the infection are discussed with suggestions for improvements to increase their effectiveness.

Differential responses of Equus caballus and Equus asinus to infection with two pathogenic strains of equine infectious anemia virus.

Most in vivo studies with equine infectious anemia virus (EIAV) have been performed in horses and ponies (Equus caballus) with little published information available detailing the clinical responses of donkeys (Equus asinus) to infection with this virus. Consequently, donkeys were inoculated with two strains of EIAV (EIAV(PV) and EIAV(WY)) which have been documented to produce disease in E. caballus. Four ponies, 561, 562, 564 and 567 and two donkeys, 3 and 5 were infected with EIAV(PV) and one horse (94-10) and one donkey (4) were infected with EIAV(WY). Although the horse and ponies all experienced clinical signs of disease, which in some cases were severe, the donkeys remained asymptomatic throughout a 365-day observation period, except for mild transient reductions in platelet counts. The results from serological assays, virus isolation from plasma and detection of plasma-associated viral RNA by RT-PCR, indicated that initial replication of EIAV(PV) and EIAV(WY) was lower in donkeys than in horses and ponies. This conclusion was confirmed using competitive RT-PCR, in which viral RNA levels in the plasma of EIAV(PV)-infected ponies was up to 100,000-fold higher than in infected donkeys during the first 20 days post-infection (dpi). Similar results were obtained in the EIAV(WY)-infected animals, in which viral RNA burdens in the donkey at 20 dpi were 1000-fold less than in the horse. However, infection of donkey and horse monocyte-derived macrophage cultures with EIAV(PV) demonstrated that these cells in vitro were equally susceptible to virus-induced cytopathic effects and yielded similar levels of progeny virus. This result suggests that factors other than host cell permissiveness mediate the clinical differences observed between horses and donkeys infected with EIAV(PV) or EIAV(WY).

Complex Interactions between the Major and Minor Envelope Proteins of Equine Arteritis Virus Determine Its Tropism for Equine CD3+ T Lymphocytes and CD14+ Monocytes

ABSTRACT Extensive cell culture passage of the virulent Bucyrus (VB) strain of equine arteritis virus (EAV) to produce the modified live virus (MLV) vaccine strain has altered its tropism for equine CD3+ T lymphocytes and CD14+ monocytes. The VB strain primarily infects CD14+ monocytes and a small subpopulation of CD3+ T lymphocytes (predominantly CD4+ T lymphocytes), as determined by dual-color flow cytometry. In contrast, the MLV vaccine strain has a significantly reduced ability to infect CD14+ monocytes and has lost its capability to infect CD3+ T lymphocytes. Using a panel of five recombinant chimeric viruses, we demonstrated that interactions among the GP2, GP3, GP4, GP5, and M envelope proteins play a major role in determining the CD14+ monocyte tropism while the tropism for CD3+ T lymphocytes is determined by the GP2, GP4, GP5, and M envelope proteins but not the GP3 protein. The data clearly suggest that there are intricate interactions among these envelope proteins that affect the binding of EAV to different cell receptors on CD3+ T lymphocytes and CD14+ monocytes. This study shows, for the first time, that CD3+ T lymphocytes may play an important role in the pathogenesis of equine viral arteritis when horses are infected with the virulent strains of EAV.

Detection, molecular characterization and phylogenetic analysis of full-length equine infectious anemia (EIAV) gag genes isolated from Shackleford Banks wild horses.

The genetically distinct wild horse herds inhabiting Shackleford Banks, North Carolina are probably the direct descendents of Spanish stock abandoned after failed attempts to settle mid-Atlantic coastal regions of North America in the Sixteenth Century. In a 1996 island survey, 41% of the gathered horses were discovered seropositive for Equine Infectious Anemia Virus (EIAV) with additional cases identified in 1997 and 1998. As a result of their unique genetic heritage, EIAV seropositive individuals identified in the two latter surveys were transferred to a quarantine facility on the mainland. In September 2008 two of the horses SB1 and SB2 after 10 and 11 years in quarantine respectively, developed clinical signs of EIA. In the case of SB2 these were so severe that the only humane option was euthanasia. Although SB1, survived it experienced a second clinical episode one month later. In May 2009, a third horse in quarantine, SB3, developed extremely severe clinical EIA and was euthanized. This demonstrates naturally infected long-term inapparent carriers can experience recrudescence of very severe disease many years after initial exposure to EIAV. Phylogenetic analysis of complete EIAV gag gene sequences obtained from each of three Shackleford horses demonstrated they were infected with very closely related viruses. Although these were distinguishable from all other strains examined, they belong to a monophyletic group comprising almost exclusively of New World isolates that is distinct from a number of recently characterized Central European EIAV strains.

Optimal paradigms to detect reservoirs of equine infectious anemia virus (EIAV)

Summary Today, control of equine infectious anemia (EIA) depends on the accuracy and use, in officially regulated laboratories, of the agar gel immunodiffusion (AGID) test that detects antibody against the major EIAV core protein p26. EIAV surface unit and transmembrane glycoproteins, gp90 and gp45 respectively, also stimulate antibodies that recognize highly conserved group-specific determinants. In most new infections, antibodies against gp90 are detected first, followed by those against p26 and then gp45. Generally, the first positive test in each of the official testing formats is seen within 45 days of exposure. In immunoblot tests, antibodies against gp90 are the most abundant. The immunoblot test detects antibody against multiple antigens and is the most sensitive serologic indicator of infection with EIAV. Experience with official AGID and ELISA-based test kits in a variety of situations has allowed the design of optimal paradigms for the serologic diagnosis of EIA. The strengths of the available ELISA-based test kits (sensitivity, accuracy of interpretation, and multiple antigens) and the specificity of the AGID test are both capitalized upon. An additional advantage of the ELISA kits is potential for adaptation to field use. Our success in reaching reservoirs of EIAV may depend on wider acceptance of horse-side testing, in practical and affordable formats, especially for use in remote rural areas.

Isolation and characterization of β-haemolytic-Streptococci from endometritis in mares.

The objective of this manuscript was to validate published PCR-based methods for detection of β-haemolytic Streptococci by comparison with established bacteriological techniques using 85 clinical isolates recovered from uterine swabs of mares with clinical signs of endometritis and to determine the distribution of SeeL/SeeM and SzeL/SzeM superantigens in isolates of Streptococcus equi subsp. equi (S. equi) and S. equi subsp. zooepidemicus (S. zooepidemicus). The conventional bacteriological techniques showed the vast majority of these isolates (78) were S. zooepidemicus with just 5 Streptococcus dysgalactiae subsp. equisimilis (S. equisimilis) and 2 S. equi strains detected. The PCR analyses confirmed the bacteriological results demonstrating the reliability of the 16S rRNA PCR assay for detecting Streptococci, the multiplex PCR for differentiating between S. zooepidemicus, and S. equi, and PCR assays based on streptokinase genes for identification of S. equisimilis. PCRs for genes encoding superantigens revealed seeL and seeM specific amplicons with size of approximately 800 and 810 bp respectively for the S. equi strains and for 2 S. zooepidemicus strains. To our knowledge, this is the first report of szeL and szeM possession by S. zooepidemicus isolates derived from endometritis in mares.

Development and characterization of a synthetic infectious cDNA clone of the virulent Bucyrus strain of equine arteritis virus expressing mCherry (red fluorescent protein)

Strains of equine arteritis virus (EAV) differ in their virulence phenotypes, causing anywhere from subclinical infections to severe disease in horses. Here, we describe the in silico design and de novo synthesis of a full-length infectious cDNA clone of the horse-adapted virulent Bucyrus strain (VBS) of EAV encoding mCherry along with in vitro characterization of the progeny virions (EAV sVBSmCherry) in terms of host-cell tropism, replicative capacity and stability of the mCherry coding sequences following sequential passage in cell culture. The relative stability of the mCherry sequence during sequential cell culture passage coupled with a comparable host-cell range phenotype (equine endothelial cells, CD3+ T cells and CD14+ monocytes) to parental EAV VBS suggest that EAV-sVBSmCherry-derived virus could become a valuable research tool for identification of host-cell tropism determinants and for characterization of the viral proteins involved in virus attachment and entry into different subpopulations of peripheral blood mononuclear cells. Furthermore, this study demonstrates that advances in nucleic acid synthesis technology permit synthesis of complex viral genomes with overlapping genes like those of arteriviruses, thereby circumventing the need for complicated molecular cloning techniques. In summary, de novo nucleic acid synthesis technology facilitates innovative viral vector design without the tedium and risks posed by more-conventional laboratory techniques.