Risk factors for Brucella spp. infection In dairy cattle farms in Asmara, State of Eritrea

A cross-sectional study was conducted to identify risk factors for herd infection by Brucella spp. in dairy cattle in the suburbs of Asmara, Eritrea. Data were collected from 64 herds, randomly selected from a total of 99 herds with a minimum herd size of 9 cows. A questionnaire was used to gather data on management, hygiene and herd structure. Serum samples collected from all pregnant heifers, cows and bulls, were screened for Brucella infection by the Rose Bengal test (RBT), and all RBT-positive sera re-tested with the complement-fixation test (CFT) for confirmation. A seropositive herd was defined as one in which at least one animal tested positive in the CFT. There were 23 (36%) positive herds among the 64 studied. Both multiple logistic and multiple betabinomial regression modeling were used to analyze the data. Mixed-breed herds, compared to single (exotic)-breed herds, were found to be independently associated with increased herd seroprevalence (OR=5.2, 95% confidence interval 1. 4-18.7) in the multiple logistic model with the herd infection status as the dependent variable. The importance of this variable was supported by the multiple betabinomial regression model (OR=3.3, 1.4-7.6) with animal-level prevalence within herd as the outcome variable. Both models also revealed the presence of a negative association between seropositivity and cattle stocking density.

Ehrlichia (Cytoecetes) phagocytophila predisposes to severe contagious ecthyma (Orf ) in lambs

Eight lambs experimentally infected with Ehrlichia (Cytoecetes) phagocytophila 7 days before exposure to orf virus were compared with control lambs infected with orf virus alone. The dually infected animals differed from the controls in showing skin lesions of greater severity, prolonged viral shedding, and lower antibody titres. Infection with E. phagocytophila had no significant effect on virus-specific lymphocyte proliferation. Such proliferation was detected in the peripheral blood of all lambs as early as 7 days after exposure to orf virus.

Lymphocyte responses to mitogens and rickettsial antigens in sheep experimentally infected with Ehrlichia (Cytoecetes) phagocytophila

Infection of sheep with Ehrlichia (Cytoecetes) phagocytophila, the causative agent of tick-borne fever (TBF), was characterised by a significant reduction in lymphocyte reactivity to the mitogens phytohaemagglutinin, concanavalin A, pokeweed mitogen and Escherichia coli lipopolysaccharide during the period of rickettsiaemia. The addition of the prostaglandin inhibitor, indomethacin, or the nitric oxide inhibitor, N(G)-monomethyl-L-arginine, had no significant effect on the suppressive effects of E. phagocytophila on lymphocyte reactivity to the mitogens. However, peripheral blood lymphocytes obtained from primed sheep proliferated in the presence of live or heat-inactivated E. phagocytophila. Antigen-specific proliferation was detected in lymphocytes samples obtained 11 to 21 days post-inoculation with E. phagocytophila.

Inhibition of phagosome-lysosome fusion in ovine polymorphonuclear leucocytes by Ehrlichia (Cytoecetes) phagocytophila

Ehrlichia (Cytoecetes) phagocytophila, the causative agent of tick-borne fever, is an intracellular bacterium that survives and multiplies within granulocytes and monocytes. In the present study, the possible fusion of lysosomes with phagosomes containing E. phagocytophila was investigated in poly-morphonuclear (PMN) cells of sheep infected with the agent, acid phosphatase cytochemistry and cationized ferritin being used as markers of primary and secondary lysosomal enzymes. Latex beads or Candida albicans were incubated with infected and uninfected PMN cells and labelled with the same lysosomal markers. Lysosomal enzymes labelled with the markers were commonly found in phagosomes containing latex beads or C. albicans, but there was no evidence of phagosome-lysosome (P-L) fusion in phagosomes containing E. phagocytophila. It was significant that in cells that contained E. phagocytophila, latex beads and C. albicans, P-L fusion occurred only in phagosomes containing latex beads or C. albicans. However, evidence of P-L fusion with phagosomes containing E. phagocytophila was obtained when PMN cells were incubated with oxytetracycline, which is known to inhibit synthesis of bacterial proteins. These findings indicate that E. phagocytophila is capable of inhibiting P-L fusion and that oxytetracycline depresses this capability.

The effects of Ehrlichia (Cytoecetes) phagocytophila on the clinical chemistry of sheep and goats

Tick-borne fever (TBF) is a rickettsial disease of domestic and wild ruminants in temperate climates where the hard tick Ixodes ricinus is present. The disease is characterized by a high temperature and severe leukopenia. In the present study, the effects of TBF on the activity of serum alkaline phosphatase (ALP), and on the concentrations of plasma zinc, iron, total bilirubin, urea, creatinine and albumin were investigated by inoculating one group of eight sheep and one group of eight goats with the Old Sourhope (OS) strain of Ehrlichia (Cytoecetes) phagocytophila. All goats and sheep experimentally infected with E. phagocytophila reacted with fever, rickettsiaemia and leukopenia. The leukopenia was due to an acute lymphocytopenia and prolonged neutropenia. In both groups of animals. TBF was characterized by significant reductions in the activities of serum ALP and concentrations of plasma zinc, iron and albumin. However, there were significant increases in the concentrations of plasma total bilirubin, urea and creatinine in both species of animals. The reductions in ALP and iron were significantly more pronounced in sheep than in goats.

Differential haematological effects of tick-borne fever in sheep and goats

Tick-borne fever (TBF) is a rickettsial disease of domestic and wild ruminants in temperate climates. It is characterized by high fever and severe leukopenia. In the present study, the possible difference in the severity of disease in sheep and goats was investigated by inoculating one group of eight goats and one group of eight sheep with the Old Sourhope (OS) strain of Ehrlichia (Cytoecetes) phagocytophila. All sheep and goats experimentally infected with E. phagocytophila reacted with fever and rickettsiaemia, but there were significant differences between goats and sheep in the severity of clinical disease, the duration and magnitude of fever, the magnitude of rickettsiaemia and the patterns of reduction in the number of total leucocytes. Sheep reacted with fever significantly earlier than goats and the febrile period lasted for a significantly longer period. In contrast, the magnitude of rickettsiaemia was significantly higher in goats than in sheep. Infection with TBF was characterized by a transient increase in the number of neutrophils, which was quickly followed by an acute reduction in the number of lymphocytes and a prolonged reduction in the number of neutrophils in both sheep and goats. In both groups of animals, infection with TBF was also characterized by significant reductions in the total number of red blood cells (RBCs), thrombocytes and packed cell volume (PCV) and the concentration of haemoglobin (Hb). However, the mean corpuscular volume (MCV) and mean corpuscular Hb (MCH) were significantly increased in sheep only.

The effects of bovine respiratory syncytial on normal ovine lymphocyte responses to mitogens or antigens in vitro

In the present study peripheral blod mononuclear cells (MNC) obtained from normal uninfected lambs were used to study the possible effects of bovine respiratory syncytial virus (BRSV) on lymphocyte responses to the mitogens, phytohaemagglutinin (PHA), concanavalin A (Con A) and pokeweed mitogen (PWM) in vitro. Live BRSV had a depressive effect on the proliferative responses of normal MNC to PHA, Con A and PWM. Inactivated BRSV and a commercial preparation of prostaglandin E2 were also found to depress the proliferative responses of normal ovine MNC to PHA but recombinant tumour necrosis factor-alpha (TNF-alpha) had no such effect. Serum samples obtained from BRSV-infected lambs contained substances inhibitory to PHA-driven lymphocyte blastogenesis. Memory blastogenic responses to border disease virus (BDV) of lymyphocytes obtained from lambs previously primed with BDV were significantly reduced when lymphocytes were exposed to infectious BRSV.

Granulocytic Ehrlichia infection in ixodid ticks and mammals in woodlands and uplands of the U.K

The prevalence of infection with Ehrlichiae of the Ehrlichia phagocytophila genogroup (the granulocytic Ehrlichiae), in questing Ixodes ricinus ticks of U.K. upland and woodland habitats, was investigated by PCR. The prevalence of infection in the three feeding stages of I. ricinus indicated that granulocytic Ehrlichiae are transmitted transstadially with no, or inefficient, transovarial transmission. The presence of infected ticks in both habitats indicates that endemic cycles of granulocytic Ehrlichia (GE) infection are maintained by both domesticated sheep and by wild reservoirs, and coexist with endemic cycles of Borrelia burgdorferi infection. Moreover, demonstration, for the first time, of GE infection in engorged Ixodes trianguliceps ticks and blood collected from wild rodents, suggests that European wild rodents are competent reservoirs. GE infection prevalence in nymphal and adult I. ricinus was significantly greater in uplands than woodlands, which is consistent with ticks of all three feeding stages feeding on reservoir-competent sheep in uplands. In one woodland studied, pheasants are important hosts for nymphal I. ricinus but are incompetent or inefficient reservoirs, so reducing GE infection prevalence in I. ricinus ticks in this habitat. 16S rRNA sequences of GE from ticks of these U.K. habitats, showed a high degree of homology with those of granulocytic Ehrlichiae isolated from humans, but also showed some evidence of genetic diversity of granulocytic ehrlichiae in the U.K. The implications of these findings, for the taxonomy of granulocytic ehrlichiae and the potential for human infections to occur in the U.K., is discussed.

Vaccination with glutaraldehyde-fixed bovine respiratory syncytial virus (BRSV)-infected cells stimulates a better immune response in lambs than vaccination with heat-inactivated cell-free BRSV

The lamb model was used to investigate the possible protective effects of vaccination with inactivated viral antigens against experimental infection with bovine respiratory syncytial virus. Two groups of eight lambs were vaccinated with either glutaraldehyde-inactivated cell-associated virus or heat-inactivated cell-free virus and subsequently challenged with live virus, along with a group of naive lambs. The virus was shed for significantly longer periods, and the virus titres in nasal secretions were significantly higher in the group of naive lambs than in the two groups of vaccinated lambs. The period of virus-shedding in nasal secretions and virus titres was significantly lower (p < 0.01) in the group of lambs immunized with the cell-associated preparation. The same antigen stimulated better cellular immune responses as measured by virus-specific cytotoxicity or by virus-specific lymphocyte proliferation. However, priming with inactivated vaccines had no significant effect on lymphocyte responses to phytohaemagglutinin, which was found to be significantly reduced (p < 0.01) following challenge with live virus.

Granulocytic ehrlichiosis: an emerging or rediscovered tick-borne disease?

The Ehrlichieae are gram-negative obligately intracellular bacterial pathogens. They can be divided into at least three genogroups on the basis of 16S rRNA gene sequences, but are also classified by target cell specificity. A group of granulocytic ehrlichiae primarily infect neutrophils and fall into genogroup II. The granulocytic ehrlichiae are subdivided by their target hosts, i.e., Ehrlichia phagocytophila in cattle and sheep, E. equi in horses, and the agents of human (HGE) and llama (LGE) granulocytic ehrlichioses. However, these subdivisions may give a false impression, as all these species are closely related both antigenically and on the basis of 16S rRNA operon sequence. In addition, cross-species transmission can occur naturally or by experimental infection. The vectors for these granulocytic ehrlichiae are hard-bodied ixodid ticks, and the reservoir hosts are probably wild rodents, deer and sheep. In each host, this illness presents as a febrile disease which can be followed by immunosuppression leading to secondary infections.

In-vitro studies on mechanisms of immunosuppression associated with bovine respiratory syncytial virus

Bovine respiratory syncytial virus (BRSV) depressed the proliferative reactivity of normal ovine peripheral blood lymphocytes to phytohaemagglutinin (PHA). This BRSV-induced reduction in proliferative reactivity was not reversed or ameliorated by the addition of (1) indomethacin or flunixin meglumine, substances known to inhibit the production of prostaglandins, or (2) the cytokines, interleukin-1 (IL-1) and interleukin-2 (IL-2), or (3) rat growth factor. The results suggest that the suppression of ovine lymphocyte reactivity to PHA associated with BRSV was not caused by the release of cyclooxygenase products such as prostaglandins, or the production of inhibitors of IL-1 or IL-2.

The effects of bovine respiratory syncytial virus on the phagocytic and antigen-presenting capacity of peripheral blood monocytes and monocytic cell lines derived from lambs and calves

Human respiratory syncytial virus and bovine respiratory syncytial virus (BRSV) suppress lymphocyte responses to mitogens. In the present study, the possible effects of BRSV on some functions of antigen-presenting cells (APC) were investigated by exposing ovine monocytic cells to the virus before their use as APC. The depletion of monocytes from peripheral blood mononuclear cells resulted in the near total abrogation of proliferative responses to phytohaemagglutinin (PHA). Reactivity was restored by the addition of homologous monocytic cells derived from ovine peripheral blood monocytes as APC. The exposure of these monocytic cells to BRSV for 48 h before their use as APC significantly reduced the proliferative responses of uninfected ovine lymphocytes to PHA. Furthermore, the exposure of bovine peripheral blood monocytes and bovine and ovine monocytic cell lines to BRSV for 48 h reduced their capacity to phagocytize latex beads.

The effects of virus-specific antibodies on the replication of bovine respiratory syncytial virus in vitro and on clinical disease and immune responses in lambs

Low concentrations of antibodies, specific to human respiratory syncytial virus (RSV) have been shown to enhance virus replication in human monocytic cell lines by several workers. In the present study, replication of bovine RSV in ovine peripheral blood monocytes was shown to be enhanced in the presence of low concentration of bovine RSV-specific antibodies. Antibodies had no enhancing effect on virus replication in secondary lamb testis cells or monocytic cell lines derived from peripheral blood monocytes. The possible effects of low titres of bovine RSV-specific antibodies on the development of clinical disease were examined by inoculating groups of lambs with a mixture of virus and antibodies and assessing the severity of clinical disease and by measuring venous oxygen (PO2) and carbon dioxide (PCO2) tensions, as hypoxia has been associated with respiratory diseases. Inoculation of bovine RSV and virus-specific antibody complexes to lambs did not enhance clinical disease and had no effect on the clinical chemistry, haematology and PO2 and PCO2 tensions. Groups of lambs inoculated with virus alone or virus-antibody complexes developed significant humoral and cellular immune responses. There was no significant difference in the cellular immune responses of lambs exposed to virus alone and lambs exposed to virus-antibody mixture, as measured by virus-specific lymphocyte transformation or by cytotoxicity assays but the period of virus shedding was longer in lambs inoculated with a mixture of virus and immune serum.

Replication of bovine respiratory syncytial virus in bovine and ovine peripheral blood lymphocytes and monocytes and monocytic cell lines

The present study compared the replication of bovine respiratory syncytial virus (BRSV) in bovine and ovine peripheral blood mononuclear cells, ovine and bovine monocytic cell lines and ovine alveolar macrophages. Low titres of virus were detected in ovine and bovine lymphocytes and monocytes 24-96 h post-exposure to the virus but there was no apparent replication of the virus in ovine alveolar macrophages during the culture period. The virus replicated to higher but statistically insignificant titres in ovine and bovine peripheral blood monocytes than in lymphocytes, with lymphocytes yielding peak titres significantly earlier. The secondary cell lines obtained from ovine liver and bone marrow also supported the replication of BRSV to high titres. The titres of BRSV in ovine and bovine lymphocytes and monocytes were significantly lower than in secondary cell lines. The addition of human recombinant tumour necrosis factor alpha after exposure to the virus or pre-incubation of ovine or bovine monocytic cells with either human recombinant interleukin 2 or phorbol myristate acetate before exposure to BRSV, did not significantly affect virus titre. Pre-incubation of cells with indomethacin or actinomycin significantly lowered virus titre (p < 0.05).

Immune responses of lambs to the fusion (F) glycoprotein of bovine respiratory syncytial virus expressed on insect cells infected with a recombinant baculovirus

A group of lambs was immunized with the F protein of bovine respiratory syncytial virus expressed in a baculovirus (Bac-F) and their humoral and cellular immune responses to bovine RSV studied before and after challenge with infectious bovine RSV. Immunization with Bac-F resulted in significant humoral immune responses as measured by virus neutralization and cellular immune responses as measured by lympho-proliferation against inactivated bovine RSV and specific cytotoxicity against autologous targets. Challenge infection with bovine RSV was characterized by significant anamnestic responses in Bac-F immunized lambs and virus shedding in nasal secretions was significantly lower in Bac-F immunized lambs than in control lambs.

Immunoglobulins of camel (Camelus dromedarius) colostrum

Immunoglobulins G, M and A were identified in dromedary camel colostra by acid precipitation, gel filtration and fast-protein liquid chromatography (ion exchange). Heavy and light chains were identified by polyacrylamide gel electrophoresis and Western blotting. IgG subclasses (IgG1, IgG2 and IgG3) were isolated by DEAE ion-exchange chromatography and shown to have different electrophoretic mobilities. Cross-reactivity of camel IgA with IgA of other species was determined by enzyme-linked immunosorbent assay (ELISA). Most of the immunoglobulin content was IgG, but a molecule identifiable as IgA was detected and purified. It would appear that in the camel, as in cattle, IgG is the major secretory immunoglobulin of colostrum.

Antigens of bovine respiratory syncytial virus in peripheral blood lymphocytes of experimentally infected lambs

Eight lambs were experimentally infected with bovine respiratory syncytial virus (RSV) and the distribution of viral antigen in lymphocyte subpopulations studied by flow cytometry. Experimental infection with bovine RSV was characterised by significant changes in lymphocyte subpopulations. Infection was followed by a significant (P <0.001) reduction in the number of cells expressing the OvCD5 epitope (T cells), due to a fall in the number of cells expressing the OvCD4 epitope (helper) and those expressing the OvWC1 epitope (gamma/delta) 3-7 days post-inoculation. There was a significant increase in the number of OvCD5+ cells expressing the OvCD8 epitope (cytotoxic/suppressor) later. Flow cytometric analysis with bovine RSV-specific monoclonal antibodies revealed that viral antigens were present in all lymphocyte subpopulations but the main targets were T cells in general and OvCD4+ cells in particular. Challenge of primed lambs with bovine RSV had similar effects over a shorter period, followed by significant rises in the number of OvCD45+ (B) cells and OvCD5+ (T cells). Viral antigens were also present in lymphocytes subsets following challenge.

Cell-mediated immune responses of lambs to experimental infection with bovine respiratory syncytial virus

Primary infection of lambs with bovine respiratory syncytial virus (RSV) was characterised by the presence of virus-specific cytotoxic cells in the peripheral blood as early as 5 days post-infection. These effector cells lysed virus-infected autologous targets in a self-restricted manner. Depletion techniques revealed that cytotoxic activity was largely due to OvCD8+ cells. Neutrophils obtained from experimentally infected lambs 5 to 10 days post-inoculation exhibited significant cytotoxic activity in the presence of bovine RSV-specific antiserum. During the same period there was a significant lymphoproliferative response to live or inactivated bovine RSV. Lymphoproliferative and cytotoxic activity coincided with the clearance of the virus from nasal secretions.

Serology of Orthopoxvirus cameli infection in dromedary camels: analysis by ELISA and western blotting

An enzyme-linked immunosorbent assay (ELISA) was developed, together with a Western blotting technique, for the detection of total and IgG and IgM antibodies to camelpox virus (Orthopoxvirus cameli) in camel (Camelus dromedarius) sera and for identifying the seroreactive antigens of the virus. A total of 520 camels from different regions in Libya were tested. The overall seropositivity rate in the examined herds was 9.8%, and varied between herds from 0 to 30%. Two viral antigenic determinants (31 and 35 kDa) were shared by the Western blotting patterns of all the positive camel sera tested. The developed ELISA assay showed ability to differentiate between orthopox and parapoxvirus infections in camels. It is considered that the ELISA technique is justified for serodiagnosis of camelpox in the camel and could be easily modified and usefully applied to other species at risk of poxvirus infection.

Replication of bovine respiratory syncytial virus in ovine peripheral blood lymphocytes and monocytes in vitro

Adherent and non-adherent mononuclear cells obtained from the peripheral blood of normal lambs supported the replication of bovine respiratory syncytial virus in vitro. Sequential treatment of monocytes with phorbol ester acetate (PMA) enhanced their ability to support viral replication. After exposure in vitro for 24 h, viral antigens were present in 47 +/- 4.5% of monocytes and 32 +/- 3% of lymphocytes. Treatment of monocytes with PMA resulted in the increase of the proportion of cells expressing viral antigen and in the titre of infectious virus.

Immune responses of the camel (Camelus dromedarius) to contagious ecthyma (Orf) virus infection

An enzyme-linked immunosorbent assay (ELISA) was developed together with a western blotting technique for the detection of total and specific IgG and IgM antibodies to the contagious ecthyma (orf) virus in camel (Camelus dromedarius) sera and for identifying the seroreactive antigens of the virus. An outbreak of generalised contagious ecthyma in camels was diagnosed for the first time in Libya; the seropositivity rate in a herd with clinically affected camels was 37.9% (and was related to clinical signs) and in apparently normal herds was 0% to 6.8%. Two viral antigenic determinants (22 and 40 kDa) were shared by the western blotting patterns of all the positive camel sera tested, another viral antigenic component of 28 kDa was shared by the positive sera with high ELISA titres. Very close similarity was seen with the western blot of orf-positive sheep sera. It is considered that the ELISA technique was valid for orf serodiagnosis in the camel and could be usefully applied to other species at risk of orf infection.

Cell-mediated immune responses of lambs to challenge with bovine respiratory syncytial virus

The lamb is a good model to study the pathogenesis and immune responses to infections with respiratory syncytial virus (RSV) as lambs experimentally infected with bovine or human RSV may develop overt clinical disease. In the present study the development of cellular cytotoxic responses was studied in splenic, pulmonary and peripheral blood mononuclear cells obtained from lambs after primary and secondary infection with bovine RSV. Infection with bovine RSV was followed by the appearance of cytotoxic cells in the peripheral blood, the spleen and lung lavage fluids. These effector cells lysed virus-infected targets in a self-restricted manner. Depletion techniques revealed that cytotoxic activity was largely due to OvCD8+ cells. When effector cells obtained from primed lambs were stimulated with inactivated bovine RSV or with virus-infected cells in vitro, virus-specific cytotoxicity was significantly increased.

Monoclonal antibodies against camel (Camelus dromedarius) IgG, IgM and light chains

Monoclonal antibodies specific for camel IgG and IgM heavy chains and immunoglobulin light chains were produced by a simple, time-saving and efficient method. Popliteal lymph nodes isolated 9 days after a primary foot-pad immunisation were used as the source of antibody producing hybridoma cells. Ascites was induced in mice and ascitic fluid collected. The specificity of anti-IgG and anti-IgM monoclonal antibodies was determined by enzyme-linked immunosorbent assay (ELISA) and Western blotting. Monoclonal antibodies specifically reacting to IgG1 subclasses were demonstrated; no monoclonal antibodies specific to IgG2 or IgG3 were generated. An unexpected finding was that some class-specific monoclonal antibodies were light chain, and not heavy chain, reactive.

Distribution of Border disease virus antigen in lymphocyte subpopulations in the peripheral blood of experimentally infected lambs

Ten lambs were experimentally infected with Border disease virus and the distribution of viral antigen in lymphocyte subpopulations studied by flow cytometry. The virus was isolated in culture from the peripheral blood mononuclear cells (MNC) of all experimentally infected lambs for a mean period of 9.8 +/- 1.03 days. The peak virus titre of 3.26 log10 TCID50 per 10(6) MNC was attained Day 9 post-inoculation (pi). Viral antigen was present in peripheral blood lymphocytes of experimentally infected lambs as early as 24 h pi and continued to be detected up to Day 10 pi. The number of lymphocytes expressing viral antigen rose from 12.38 +/- 1.22% in samples taken Day 3 pi to 23.21 +/- 2.82% on those collected Day 7 pi, dropping gradually thereafter. During the peak period of infection, 12.46 +/- 2.09% of B cells, 37.71 +/- 10.96% of T cells and 52.33 +/- 8.27% of lymphocytes which were neither B nor T lymphocytes expressed viral antigen. Most of the infected lymphocytes expressed the OvCD5 (T cell) molecule. The virus affected all T cell subsets but the suppressor/cytotoxic (OvCD8+) cells appeared to be the main targets. During the peak period of infection, 54.20 +/- 6.16% of the infected T cells expressed the OvCD8 molecule, 31.58 +/- 7.12% were OvCD4+, and 12.67 +/- 6.50% were OvWC1+ (T-19+, gamma/delta).

Border disease virus antigens in lymphocyte subpopulations in the peripheral blood of persistently infected sheep

Biotinylated virus-specific antibodies were used to detect Border disease virus antigen by flow cytometry in the mononuclear cells of the peripheral blood of 15 sheep persistently infected with Border disease virus. The viral antigen was present in 12.86 +/- 4.65% (mean +/- SD) of mononuclear cells (MNC). The percentage of MNC that contained viral antigen was higher in lambs than in adult sheep, with mean rates of 22.68 +/- 5.02% and 11.65 +/- 4.39%, respectively. Depletion methods were used to estimate the distribution of viral antigen in peripheral blood lymphocyte subsets. The viral antigen was present in T-cells (OvCD5+), B-cells (LCAp220+) and non-T- and non-B-cells. Depletion studies revealed that 5.39 +/- 2.47% of the cells expressing the LCAp220 epitope (B-cells), 23.38 +/- 11.38% of those expressing the OvCD5 epitope (T-cells) and 55.07 +/- 10.93% of those which were neither B- nor T-cells were positive for viral antigen. Most (57.18 +/- 5.41%) of the T-cells containing viral antigen were cytotoxic/suppressor (OvCD8), 25.63 +/- 2.97% were helper (OvCD4) cells and 12.24 +/- 3.21% expressed the gamma/delta (OvWC1) epitope.