Cell-associated Viremia Research Articles

Immunization with the immediate-early tegument protein (open reading frame 62) of varicella-zoster virus protects guinea pigs against virus challenge.

The IE62 protein, the primary regulatory protein of varicella-zoster virus (VZV) and the major component of the virion tegument, was an effective immunogen in the guinea pig model of VZV infection, whereas the ORF 29 gene product, a nonstructural DNA replication protein, did not elicit protection. All animals immunized with the ORF 29 protein had cell-associated viremia compared with 2 of 11 guinea pigs given the IE62 protein (P = 0.005). VZV was detected in ganglia from 38% of the animals given the ORF 29 protein and 44% of the control animals compared with 9% of the animals immunized with the IE62 protein (P = 0.04). In contrast to the IE62 protein, immunization with the ORF 29 protein did not prime the animals for an enhanced T-cell response upon challenge with infectious virus. The VZV IE62 protein has potential value as a vaccine component.

Human Retroviruses and Neoplastic Disease

Human retroviral infections result in significant neoplastic disease. Human T cell lymphotropic virus I (HTLV-I), the first human retrovirus to be discovered, is associated with the development of acute T cell leukemia with characteristic hypercalcemia and skin lesions after many years of chronic infection of CD4+ cells. HTLV-I also produces myelopathy. A minor T cell immunodeficiency occurs in HTLV-I acute T cell leukemia with associated strongyloidiasis and Pneumocystis carinii pneumonia. Human T cell lymphotropic virus II (HTLV-II) is found to be endemic in Amerindians and intravenous drug users (IVDUs) and has been linked to some cases of hairy-cell leukemia. HTLV-II infects the CD8+ population, with significant cell-associated viremia. Clinical neurological disease is rare, with one patient with myelopathy having been described. Immunodeficiency does not seem to occur. Human immunodeficiency virus 1 (HIV-1) produces aggressive large cell and Burkitt's lymphoma in as many as 10% of HIV-1-infected patients. More than 20% of homosexual men infected with HIV-1 develop Kaposi's sarcoma (KS). The pathogenesis of KS is better understood through studying KS-like cell lines that induce angiogenic factors. In some patients HIV-1 and HTLV-I or HTLV-II infections occur concomitantly. HIV-1 accelerates the tumorigenesis of HTLV-I and produces unusual skin diseases when combined with HTLV-II. Immunodeficiency occurs in all HIV-1-infected patients.

The acute retroviral syndrome and the pathogenesis of HIV-1 infection

The acute retroviral syndrome associated with primary HIV-1 infection is characterized by clinical signs of immune activation, multi-system dysfunction, and high levels of cell-associated and plasma viremia, p24 antigenemia, and proviral burden. Clinical abnormalities associated with acute HIV-1 infection and measures of viral burden and replication generally decline in concert with seroconversion. Despite clearance of virus, patients experiencing severe forms of the acute retroviral syndrome appear to have a poorer prognosis than patients with asymptomatic primary infection. This accelerated natural history may be due to the virulence of strains causing symptomatic infection, sequelae of initial high-titer viremia and consequent high viral burden, or immune depletion through immunopathologic mechanisms accelerated by strong antigenic stimulus in primary infection. Early intervention with anti-retroviral and immune modulatory agents has the potential to alter the natural history of patients with this syndrome.

Responses of ponies to equid herpesvirus-1 Iscom vaccination and challenge with virus of the homologous strain

An experimental ( Iscom) vaccine previously shown to protect hamsters from lethal challenge with equid herpesvirus-1 ( Ehv-1), was tested in horses. Vaccination with Ehv-1 Iscoms induced serum antibodies to the major virus glycoproteins gp10, 13, 14, 17, 18 and 21/22a, whereas antibody responses to gp2 were weak or absent. High levels of virus neutralising antibody of long duration were induced, but did not prevent challenge infection with virus of the homologous strain. However, in the vaccinated ponies there was a significant reduction in clinical signs, nasal virus excretion and cell associated viraemia compared with age-matched unvaccinated controls. There was a strong correlation between pre-challenge levels of serum virus neutralising antibody and the duration and total amount of virus excreted from the nasopharynx.

Early Pathogenesis of Disease Caused by SIVsmmPBjl4 Molecular Clone 1.9 in Macaques

We have studied the early pathogenesis of infection by molecular clone 1.9 of SIVsmmPBj14 in pig-tailed and cynomolgus macaques. Like the uncloned PBj14 parent, SIVsmmPBj14-1.9 consistently induced an acute clinical syndrome characterized by behavioral depression, fever, profuse diarrhea, dehydration, lymphadenopathy, splenomegaly, and mucocutaneous exanthema that began at 7 days postinfection (DPI). The acute clinical disease coincided with a marked cell-associated and cell-free viremia, during which SIV p27 was demonstrated in 4 to 68% of circulating mononuclear leukocytes between 4 and 17 DPI. Also characteristic were monocytosis and reductions in CD4+ and CD8+ T lymphocytes, as well as CD20+ B lymphocytes. The most profound depletion occurred in the CD44hi subset of CD4+ T cells. Unlike animals infected previously with uncloned or biologically cloned PBj14, however, all SIVsmmPBj14-1.9-infected macaques survived the acute-phase disease to progress to a chronic, largely asymptomatic phase of infection. Recovery from the acute-phase disease correlated with down modulation of virus replication and the appearance of antibodies to SIV Env and Gag proteins. Similar to the PBj14 parent, PBj14-1.9 targeted to intestine, spleen, bone marrow, lymph node, and cerebellum. Saliva contained substantial quantities of infectious virus and no viral antibodies during the early phase of infection. By contrast, saliva from chronically infected animals usually contained antibodies but no virus. This study extends previous work demonstrating that the acute clinical syndrome produced by SIVsmmPBj14 in pig-tailed macaques represents a unique model of lentiviral pathogenesis.

Protection against Marek's disease by a fowlpox virus recombinant expressing the glycoprotein B of Marek's disease virus.

Fowlpox virus (FPV) recombinants expressing the glycoprotein B and the phosphorylated protein (pp38) of the GA strain of Marek's disease virus (MDV) were assayed for their ability to protect chickens against challenge with virulent MDV. The recombinant FPV expressing the glycoprotein B gene elicited neutralizing antibodies against MDV, significantly reduced the level of cell-associated viremia, and, similar to the conventional herpesvirus of turkeys, protected chickens against challenge with the GA strain and the highly virulent RB1B and Md5 strains of MDV. The recombinant FPV expressing the pp38 gene failed to either elicit neutralizing antibodies against MDV or protect the vaccinated chickens against challenge with MDV.

Investigations on course and outcome of phocine distemper virus infection in harbour seals (Phoca vitulina) exposed to polychlorinated biphenyls. Virological and serological investigations.

The influence of polychlorinated biphenyls (PCBs) on phocine distemper virus (PDV) infections in harbour seals (Phoca vitulina) was studied. Six out of ten seals had been conditioned with a defined mixture of PCB-congeners for several weeks. Following exposure to the cell culture-propagated PDV isolate 2558/Han 88 the complete clinical picture of "1988 seal plague" was provoked in all ten seals inoculated. Four out of six PCB-conditioned seals and two out of four seals not loaded with PCBs succumbed to the infection within three weeks post inoculation. With regard to the clinical course, duration of cell-associated viremia, PDV-antigen distribution in tissues of fatally infected seals and the humoral immune response to PDV no differences between PCB-loaded and unloaded seals were recognized. Evidence was obtained that the pathogenesis of experimental PDV-infection in harbour seals shares some features with those of canine distemper in terrestrial carnivores. In contrast, however, to experimental distemper infection of gnotobiotic dogs prompt development of high titres of PDV-specific IgG did not correlate with recovery from infection.

Epizootiological aspects of type 1 and type 4 equine herpesvirus infections among horse populations.

The dissemination of equine herpesvirus types 1 (EHV-1) and 4 (EHV-4) among various horse populations in Japan was investigated through the isolation and typing of virus strains from horses with respiratory diseases. Type specific monoclonal antibody pools were used for the typing of isolates. The 42 strains of EHV-1 and 64 strains of EHV-4 were isolated from 4593 nasal swabs and/or blood plasma samples collected from 3326 horses during a period from 1979 to 1990. All the strains of EHV-1 were isolated from racehorses only and during the winter season exclusively, when the epizootic of respiratory diseases occurred among racehorse populations at two Training Centers of the Japan Racing Association. In contrast, the strains of EHV-4 were isolated from horses irrespective of the season, facility, or horse population; foals and yearlings in breeding farms and our institute, rearing horses in rearing farms, and racehorses. Especially, 4 strains of EHV-4 were isolated from plasma samples containing buffy coat cells. We believe this is the first reported case of EHV-4 cell-associated viremia in the world. All 87 strains isolated from aborted fetuses were identified as EHV-1. The results suggest that EHV-1 is responsible for epizootic respiratory diseases in racehorses in the winter and abortion among mares at the late stage of gestation, and that EHV-4 causes respiratory diseases throughout the year among all horse populations.

Clinical signs and humoral immune response in horses following equine herpesvirus type-1 infection and their susceptibility to equine herpesvirus type-4 challenge

A group of three horses was experimentally infected with equine herpesvirus type 1 ( EHV-1) and showed clinical signs characterised by a biphasic febrile response, leucopenia and cell associated viraemia accompanied by virus shedding from the nasopharynx. A second exposure to the virus 18 days later resulted in the isolation of virus from the nasopharynx of one horse. This and a further group of three EHV-1 seropositive horses were subsequently infected with equine herpesvirus type 4 ( EHV-4) 147 days after the initial EHV-1 infection and virus was shed from the nasopharynx in the absence of clinical disease. Following the first EHV-1 infection, virus specific immunoglobulin M (IgM) was present by day 5 and remained high until the second exposure at day 18 at which point levels decreased. In contrast, EHV-1 specific IgG, detected at day 6 peaked at day 18, after which time levels remained high. Virus neutralising antibodies and antibodies able to mediate antibody-dependent cellular cytotoxicity were present by day 10. The immune response to EHV-1 is discussed with reference to the disease.

Postexposure Immunotherapy of Simian Immunodeficiency Virus (SIV) Infected Rhesus With an SIV Immunogen

An inactivated whole simian immunodeficiency virus (SIV) immunogen given to healthy, seropositive rhesus macaques 4 months after infection had no effect on the humoral immune response to SIV, the presence of antigenemia, cell-associated viremia, or disease course. Further immunotherapeutic trials in this highly susceptible animal model should be carried out sooner after exposure, before significant loss of CD4 cells has occurred. The SIV infected macaque model will continue to serve an essential role in development and testing of anti-AIDS drugs and immunogens.

Viremia and neutralizing antibody response in infants with exanthem subitum

Mononuclear cell-associated viremia caused by human herpesvirus type 6 was detected in 39 (66%) of 59 blood samples from 38 children with exanthem subitum between day 0 and day 7 of the disease. The rate of virus isolation from mononuclear cells was 100% (26/26) on days 0 to 2 (just before appearance of skin rash), 82% (9/11) on day 3, 20% (2/10) on day 4, 7% (2/12) on days 5 to 7, and 0% (0/37) on day 8 and thereafter. The cell-free virus was detected in blood in 10 (21%) of 47 blood samples during the same period. The antibody activity to the virus, evaluated by a newly developed neutralization assay, was first detected on day 3 of the disease with a positive rate of 18% (2/11). It became 60% (6/10) on day 4, 75% (9/12) on days 5 to 7, and 100% on day 8 and thereafter. Thus the disappearance of the virus from blood was associated with the induction of specific immunity to the virus.

Studies on poxvirus infection in cats.

The development of clinical disease and the pathogenesis of cowpox were studied in domestic cats inoculated by a variety of routes. Intradermal titration in two cats demonstrated that as little as five pfu of cowpox virus caused a primary skin lesion. Intradermal inoculation of greater than or equal to 10(5) pfu cowpox virus resulted in severe systemic disease. Large amounts of virus (greater than or equal to 10(3) pfu/g) were isolated from skin lesions and the turbinates of cats killed at eight and 11 days post-inoculation (dpi). Lesser amounts of virus (congruent to 10(2) pfu/g) were isolated from lymphoid tissues and the lung, and small amounts of virus were isolated from various other tissues. A white cell-associated viraemia was detected from 5 dpi onwards. Skin scarification with 10(3) or 50 pfu cowpox virus enabled reproduction of the naturally-acquired disease. Cat-to-cat transmission was demonstrated from cats inoculated by skin scarification, but caused only subclinical infection in sentinel cats. Oronasal inoculation resulted in transient coryza and milder generalized disease than skin inoculation, and no transmission to sentinel cats. Preliminary investigations showed vaccinia virus (Lister strain) to be of low infectivity in cats while inoculation of ectromelia virus (Mill Hill strain) did not cause any clinical signs.

Cytomegalovirus infection in pregnancy

Cytomegalovirus (CMV) is the most common agent of prenatal (peri- and early postnatal) infection of the newborn with an incidence of 0.2–2.0% (5–10%) depending on the socio-economic status. Only one out of 20 congenitally CMV-infected newborns shows serious symptoms. Another two may reveal mental retardation and other significant handicaps in later age. Perinatal CMV infection occasionally causes atypical pneumonia, mostly combined with Pneumocystis carinii infections similar to reports of AIDS cases. The risk of vertical infection has been quantified. About 2–4% of pregnant seronegative women (40–60% of all) pass a primary, 10–20% of seropositives a recurrent CMV infection. Every third primary infection may result in vertical CMV transmission with poor prognosis in about 25% (40%) of the offspring infected (in the first half of pregnancy). Sources of vertical infection are semen, maternal cell-associated viraemia, ascending genital virus (prenatally), cervical secretion (perinatally), breast milk and saliva (early postnatally). Laboratory diagnosis of CMV infection is performed by many virological and immunological techniques for detecting viral infectivity, structural components, humoral and cellular immunoresponses. Routine diagnostic service is mainly established by virus cultivation in human fibroblasts and by ELISAs on antibodies and antigens.

Congenital Guinea Pig Infection with Attenuated Junin Virus Strains

Guinea pigs born from mothers infected before or during pregnancy with 10(3) PFU of the attenuated XJC13 or XJ0 strains of Junin virus (JV) by the intramuscular route showed 31.5% mortality that was not attributable to the mothers' clinical condition or to lack of care. There was a slight drop in mortality rate when the mothers were infected at the beginning or end of their gestation period. JV isolation from the 9 offspring killed from 1 to 125 days of age proved that virus transmitted transplacentally or soon after birth was able to persist, although titers were not higher than 10(2.7) PFU/g of tissue in various organs, including brain. Cell-associated viremia could thus account for viral spread after birth. Since an active humoral response was detected in the same animals, although Nt antibody titers were below 1:16, a state of tolerance did not exist in these congenitally infected animals. The carrier state appeared to modify guinea pig susceptibility to JV; after challenge with the pathogenic XJ strain of JV, 2 animals survived and developed normal humoral responses, while half of the remaining animals did not show typical signs of Argentine hemorrhagic fever. Although JV persistence appeared to cause no deleterious effects in surviving guinea pigs, its long-term risk remains to be determined.

Distribution of virus and tumour formation in ducks experimentally infected with reticuloendotheliosis virus

The effect of reticuloendotheliosis virus (REV) was investigated in ducks. Ducks experimentally infected at 1 day and 8 weeks of age, and ducks in-contact with these, weighed less than unaffected controls. Nine of 14 ducks inoculated at 1 day old died at a mean age of 22 weeks and seven of them had tumours. REV was isolated from almost all the organs from ducks with persistent viraemia. Ducks inoculated neonatally began laying 3 weeks later than the controls and produced a significantly lower proportion (P < 0.001) of fertile eggs. Infected ducks laid thin-shelled, rough and misshapen eggs. REV was isolated from 42 of 48 albumen samples taken from these eggs and in all three batches of duck embryo fibroblast cultures prepared from them. Following infection at 1 day of age five ducks remained tolerant and most of the remaining ducks were partially tolerant to REV infection. Cell-associated and cell-free viraemia persisted until 38 weeks of age in ducks which had a serum neutralising (SN) titre < 100. Precipitating antigenaemia gave a 100% correlation with the cell-free viraemia. Ducks infected at 8 weeks of age and ducks in-contact with the ducks infected at 1 day old showed only a cell-associated transient viraemia then promptly developed SN antibodies. However, two in-contact ducks which were viraemic by 2 weeks of age remained so until the last examination at 15 weeks of age. Possible reasons for the development of antibodies to REV in uninoculated ducks are suggested.

Turkey Herpesvirus Infection in Chickens: Induction of Lymphoproliferative Lesions and Characterization of Vaccinal Immunity against Marek's Disease

Chickens vaccinated at hatching with high doses of turkey herpesvirus (HVT) developed viremia that peaked in titer around the 12th day and gradually declined. HVT infection also induced mild microscopic lymphoproliferative lesions in the nerves and gonads. These lesions were most prominent around the 12th day and then regressed. The fact that such lesions were also induced by HVT in cyclophosphamide-treated chicks suggests that they were T-cell-dependent. Some of the cells in early HVT lesions appeared to have morphologic properties of neoplastic cells. HVT viremia and lesions were both dose-dependent and were less in chickens with maternal antibodies against Marek's disease virus (MDV). Sequential studies on chickens vaccinated with HVT and challenged with MDV showed that chickens were protected against the earliest detectable MD viremia and lymphoproliferative lesion response attributed to MD. Also, the transient necrobiotic lesions associated with productive infection of thymic lymphocytes by MDV were totally absent in vaccinated chickens. These data provide further insight on the mechanisms by which HVT protects against MD lymphoma induction. A limited oncogenic (transforming) potential of HVT as suggested by our data would provide the basis to assume that at least one component of HVT-induced immunity may be directed against tumor-specific antigens. On the other hand, our observations that HVT protects against productive MDV infection in the thymus and against cell-associated viremia are evidence for an anti-viral immune response. These hypotheses are not mutually exclusive.

Experimental infection in North American elk with epizootic hemorrhagic disease virus.

Two elk (Cervus canadensis) were inoculated intravenously with epizootic hemorrhagic disease virus. No overt signs of disease were observed in the elk although one animal had a slight febrile response. A cell associated viremia was detected in both elk, which persisted in one animal for 30 days post-inoculation. The similarities of these results to those reported for bluetongue virus infection in elk is discussed.

Intra-erythrocytic location of Colorado tick fever virus.

SUMMARY Although previous studies have shown that Colorado tick fever virus occurs only transiently in the serum, but persists for prolonged periods in the blood cell fraction of man and experimental animals, the exact nature of this cell-associated viraemia was unknown. Using virus isolation, fluorescent antibody staining, histological and electron-microscopic techniques, we have shown that persistent viraemia is predominantly due to virus contained within erythrocytes. Erythrocyte precursor cells are presumably infected in the bone marrow and are subsequently released into the blood stream, persisting for prolonged periods despite the presence of serum antibody. Virus either continues to replicate slowly or is stabilized and remains viable within the erythrocyte. Colorado tick fever virus may be a useful model virus for further study of the mechanism of blood cell infection, with implications for other arboviruses or viruses believed to be involved in leukaemia or other haematological disorders.