Responses of Fasciola hepatica infected sheep to various infection levels

The response to Fasciola hepatica was studied in sheep infected with 5, 30, 150 metacercariae. The animals were necropsied 12 weeks post-infection (p-i) for counting and measuring flukes. Cellular and humoral responses were detected by peripheral eosinophil count, peripheral blood lymphocyte proliferation with excretory-secretory products (FhESP) and ELISA. All sheep were infected at necropsy except one sheep which was infected with 5 metacercariae. Mean parasitic intensities were 40%, 44% and 27% of the infection dose in sheep infected with 5, 30, 150 metacercariae respectively. FhESP-specific lymphocyte responses of the 3 infected groups were significantly enhanced in weeks 3 and 4 p-i (p < 0.05). The kinetics of the specific humoral response were similar for the 3 infected groups but the antibody level was significantly lower in animals infected with 5 metacercariae than in the 2 other infected groups from week 5 p-i to week 12 p-i (p < 0.05). Peripheral eosinophil count was significantly enhanced (p < 0.05) in infected groups. The numbers of peripheral eosinophils were significantly different between the 3 infected groups in week 3, 4 and 6 p-i and were related to infection level. These results confirm that sheep are highly susceptible to F. hepatica infection, even when infection pressure is very low. Peripheral eosinophilia was dependent of the infection level. The immune response was similar in sheep infected with various numbers of flukes.     

A 2.9 kDa Fasciola hepatica-recombinant protein based ELISA test for the detection of current-ovine fasciolosis trickle infected

The suitability of an enzyme linked immunosorbent assay (ELISA) test with a 2.9 kDa Fasciola hepatica-recombinant protein (FhrAPS) for diagnosing early and current-ovine fasciolosis was analyzed, and compared to that obtained by using a direct ELISA for detecting F. hepatica-circulating FhES antigens and to the coprological sedimentation for fluke egg quantitation. Fourteen Gallega autochthonous breed sheep were experimentally infected with metacercariae by a trickle system (small repetitive infections) and divided into two groups: G-I represented a primary infection for 34 weeks; G-R, animals with primary infection and reinfected 18 w.a.p.i. Seven sheep were left uninfected as the control group (G-C). Serum IgG antibody values against the FhrAPS rose rapidly by 1st w.a.p.i. in all infected sheep. Antibody levels in those with primary infection (G-I, G-C) peaked at 10 weeks, diminishing slightly and levelling from 16 to 34 weeks. Those with primary infection reinfected at 18 weeks had a rebound effect with the highest values observed. Circulating F. hepatica-ES antigens were detected by the 1st w.a.p.i. in all infected groups peaking at 6 weeks, decreasing rapidly to uninfected control values by 10 weeks of infection. Faecal egg-output started 11 weeks after primary infection. An increase in the IgG antibody as well as antigen responses to the FhrAPS and to anti-FhES from the 18 w.a.p.i. was recorded in G-T and G-R after the challenge infection. Antibody levels remained high whereas antigenemia values diminished after 6 weeks. A positive significant correlation between the IgG response against the FhrAPS and the F. hepatica circulating antigens (r2 = 0.428, p = 0.001) was obtained. In conclusion, our standardized diagnostic ELISA for fasciolosis based on the detection of IgG responses to the FhrAPS would be a valuable tool to diagnosis early and current F. hepatica-infections in sheep.     

Effects of feline leukemia virus infection on neutrophil chemotaxis in vitro

A procedure for measuring in vitro feline neutrophil chemotaxis was developed, using a modified Boyden chamber apparatus and 3-microns-pore polycarbonate filters. A pooled feline serum sample was used as the chemoattractant. Chemotaxis was evaluated in 5 groups of cats: group 1-specific-pathogen-free cats that had not been exposed to feline leukemia virus (FeLV); group 2-previremic, FeLV-infected, specific-pathogen-free cats; group 3-FeLV-viremic, subclinically affected cats; group 4-FeLV-viremic, clinically affected cats; and group 5-sick cats that were not infected with FeLV. Neutrophils from the viremic, clinically affected cats had significantly lower (P less than 0.025) chemotactic responses than did those from subclinically affected, viremic cats. Conversely, neutrophils from cats that were ill due to causes other than FeLV had the highest mean chemotactic values. Among the viremic, subclinically affected cats, a linear relationship was found between age and chemotaxis, indicating that impairment of neutrophil function may be greater in younger viremic cats. However, FeLV-infected cats can not be identified on the basis of neutrophil chemotaxis.     

Neutrophil adherence and movement in poorly and well-controlled diabetic dogs

Neutrophil adherence, random movement, and chemotaxis were quantitated in healthy nondiabetic dogs and in dogs with experimentally induced diabetes mellitus. On the basis of glycosylated serum protein values, the diabetic dogs were subdivided into well-controlled and poorly controlled groups. Neutrophil adherence was decreased significantly in poorly controlled diabetic dogs, but significant differences in neutrophil adherences were not found between nondiabetic and well-controlled diabetic dogs. Significant differences in neutrophil random or chemotactic movements were not found between non-diabetic and diabetic dogs. The decreased neutrophil adherence observed in poorly controlled diabetic dogs may predispose these animals to bacterial infection. Therefore, stringent regulation of blood glucose concentrations may decrease the frequency of secondary bacterial infections in spontaneous diabetes mellitus in dogs.     

Bluetongue virus serotypes 20 and 17 infections in sheep: Comparison of clinical and serological responses

The clinical, virological and serological responses of sheep infected with an Australian bluetongue virus (BTV) isolate (serotype 20) were compared to responses in sheep inoculated with an American bluetongue isolate (serotype 17) with which it had shown cross-reactions in serum neutralization tests. In sheep inoculated with BTV 20, clinical signs were very mild and viremia was first detected by day 5; virus was isolated intermittently for a further 2 to 3 days. Neutralizing and precipitating antibodies were first detected in the serum of the sheep between 2 to 3 weeks following inoculation. In contrast, sheep inoculated with BTV 17 showed pyrexia and severe hyperemia of the nasolabial area and oral mucosa from day 7 to 17. Viremia was first detected on day 3 and extended to day 20, while the appearance and titers of serum antibodies was similar in both groups.After challenge with BTV 17 the sheep in both groups remained clinically normal, and virus was not detected in the blood; however, serum neutralizing antibody titers to both viruses increased 2 weeks after challenge and the mean titer of the two groups ranged from 1:250 to 1:640.     

Bovine sire effects on daughters' in vitro blood neutrophil functions, lymphocyte blastogenesis, serum complement and conglutinin levels

Blood neutrophil functions, lymphocyte blastogenic responses, serum complement, and serum conglutinin activity of 98 lactating Holstein cows from two genetic lines were evaluated. The genetic lines were produced in a selection experiment that created and perpetuated genetic differences in milk production for up to seven generations. No significant differences between the two genetic lines of cows were found for neutrophil function, lymphocyte blastogenic responses, serum complement levels, or serum conglutinin levels. Significant differences between sire progeny groups within lines were found for unstimulated and mitogen-stimulated lymphocyte blastogenesis (P less than 0.0001), and almost all neutrophil functions (antibody independent neutrophil cytotoxicity, antibody dependent neutrophil cytotoxicity, ingestion of bacteria, iodination, chemiluminescence, chemokinesis, and chemotaxis (P less than or equal to 0.05)). Sire progeny group differences (P less than or equal to 0.0001) within lines for serum complement and conglutinin activity were also found. Neutrophil chemiluminescence activity (positive relationship; P less than or equal to 0.001), concanavalin A-stimulated lymphocyte blastogenesis (positive relationship; P less than or equal to 0.004), and serum conglutinin activity levels (negative relationship; P less than or equal to 0.01) each had small but significant associations with the total milk somatic cell count. Cows seropositive for bovine leukosis virus had increased resting and mitogen-stimulated lymphocyte blastogenic activity and were associated with increased in vitro neutrophil random migration and production of superoxide anion. Estimates of genetic parameters of various immune cell functions, of serum complement and of conglutinin levels for daughters of 11 sires with 4-6 daughters in the data set were determined. In this report, genetic variation was demonstrated for nonspecific humoral and cellular immunity.     

Modulation of leukocyte populations and immune responses in sheep experimentally infected with Anaplasma (formerly Ehrlichia) phagocytophilum

Anaplasma phagocytophilum infection in sheep is characterized by an immune suppression as indicated by impaired antibody response, reduced lymphocyte response and reduced oxidative burst. The effect of A. phagocytophilum infection on leucocyte populations, especially lymphocytes, was therefore investigated in six sheep experimentally infected with A. phagocytophilum, and compared with leucocyte populations from control animals.To investigate the ability of the infection to interfere with the cellular and humoral responses to specific antigens, the animals were vaccinated with commercial vaccines at the time of experimental infection, and monitored for 56 days.There were reduced percentages of gammadelta T-cells and CD4+ T-cells in peripheral blood of infected animals throughout the study period, and these cell populations showed a down-regulation of CD25 expression; while there was a relative increase in CD8+ T-cells. The reduction in CD25+ gammadelta T-cells involved a subpopulation of WC1+ gammadelta T-cells. During the first 2 weeks of the study there were reduced percentages of B-cells and leukocytes expressing MHC II and CD11b, though this decrease changed to a relative increase later in the study. The relative reductions in leucocyte populations corresponded with the observed leucopenia during the first 3 weeks post-infection, which involved lymphocyte, neutrophil and eosinophil subsets [Vet. Immunol. Immunopathol. 86 (2002) 183]. There was a reduced expression of CD11b and CD14 on granulocytes during the first 2 weeks of the study, which corresponded with the previously reported leucopenia involving neutrophils and eosinophils. Antibody responses to vaccines, lymphocyte in vitro proliferative responses to antigens and mitogens, and in vitro IFN-gamma responses to antigens were reduced up to 4 weeks after infection.     

Observations on blood leucocytes and lymphocyte subsets in sheep infected with bovine leukaemia virus: a progressive study

Haematological parameters and reactivity of lymphocyte antigens to monoclonal antibodies were studied over a 10-month period in sheep experimentally infected with bovine leukaemia virus (BLV). BLV-inoculated animals seroconverted within 1 month and showed a significant lymphocytosis 2-6 weeks after infection. Control animals inoculated with BLV-free lymphocytes showed a stronger and more immediate neutrophil response than those inoculated with BLV-positive lymphocytes. One month after infection, BLV-inoculated sheep showed a relative increase of cells bearing antigens T4, T6, T8 and T19, and 10 months into the trial, MHC II lymphocytes increased, T6 remained elevated, but T4 helper cells were significantly decreased in number. Lymphoma tissue showed the presence of T8 cells, and lymph nodes from seroconverted sheep had areas of concentrated T4 staining cells. These results demonstrate responses in cellular immune mechanisms to infection with BLV.     

Host responses during experimental infection with Fasciola gigantica or Fasciola hepatica in Merino sheep I. Comparative immunological and plasma biochemical changes during early infection

This study reports the early biochemical changes in plasma, comparative host-immune responses and parasite recovery data in Merino sheep during the first 10 weeks of infection with Fasciola gigantica and Fasciola hepatica. One group of sheep were uninfected, four groups of sheep received incremental challenge doses of F. gigantica metacercariae (50, 125, 225 and 400, respectively) and the sixth group was challenged with 250 F. hepatica metacercariae. At 10 weeks post infection (wpi), sheep challenged with F. hepatica showed the greatest fluke recovery (mean 119, range 84-166); a significantly higher biomass of parasites recovered (2.5-fold greater than the highest dose of F. gigantica); and a greater mean % parasite recovery (39.3%, range 27-55%) than any group challenged with F. gigantica. Within the groups dosed with F. gigantica a strong dose-dependent response was observed in both fluke recovery and fluke biomass with increasing dose of metacercariae. The mean % parasite recovery of F. gigantica infected groups 1-5 were 26, 23, 26 and 25%, respectively, suggesting a uniform viability of parasite establishment independent of infection dose. At 6 wpi, elevated levels of plasma GLDH were observed in the F. gigantica infected groups compared to the uninfected sheep (p<0.005) whereas the F. hepatica challenged group had four-fold higher levels of GLDH compared to the F. gigantica infected group (p<0.001). Elevated levels of GGT as an indicator of epithelial damage in the bile duct was only seen in the group challenged with F. hepatica at 10 wpi when it rose from below 100 IU/l to approximately 250 IU/l (p<0.0001) whereas no detectable increase in GGT was observed in any of the groups challenged with F. gigantica. The white blood cell response to F. hepatica infection was biphasic with the initial peak at 4 wpi and a second peak at 9 wpi, corresponding to the period of migration of juvenile fluke in the liver and the time when adult flukes are migrating into the bile duct, respectively. This biphasic response was also evident in the changes in the eosinophil counts and serum haemoglobin levels. There was a trend toward higher parasite-specific IgG2 titres in sheep infected with lower worm burdens, suggesting that higher F. gigantica or F. hepatica burdens suppress IgG2 responses. The findings of this study suggest that, in early infection in a permissive host, F. hepatica appears to be more pathogenic than F. gigantica because of its rapid increase in size and the speed of its progression through the migratory phases of its life cycle.     

Linoleic acid increases adhesion,chemotaxis, granule release,intracellular calcium mobilisation,MAPK phosphorylation and gene expression in bovine neutrophils

Neutrophils are critical to the innate immune response; therefore, the proper function of neutrophils is critical to avoid the development of certain diseases. Linoleic acid, a polyunsaturated long-chain fatty acid, is one of the most abundant long-chain fatty acids found in the plasma of cows after giving birth. In this study, we evaluated the effects of linoleic acid treatment on bovine neutrophil adhesion, chemotaxis, metalloproteinase (MMP)-9 release, CD11b expression, intracellular calcium mobilisation, mitogen-activating protein kinase (MAPK) phosphorylation and COX-2 and IL-8 expression. Bovine neutrophils isolated from healthy heifers were incubated with different concentrations of linoleic acid, and then neutrophil responses were evaluated. Our results show that the treatment of neutrophils with 100 μM linoleic acid increased their adhesion to the bovine endothelial cell line CPA47. The results of a transwell migration assay revealed that linoleic acid could also promote the chemotaxis of bovine neutrophils. Furthermore, linoleic acid treatment increased MMP-9 activity and CD11b cell surface expression in neutrophils. Fifty and 100 μM linoleic acid also increased intracellular calcium mobilisation in neutrophils loaded with Fluo-4 AM dye. Linoleic acid also rapidly (2–5 min) stimulated the phosphorylation of ERK1/2 and p38 MAPK as evaluated by immunoblot. Finally, COX-2 and IL-8 mRNA expression increased after 2 h of linoleic acid treatment. In conclusion, linoleic acid stimulates adhesion, chemotaxis, granule release and intracellular responses in bovine neutrophils.     

Hematology and clinical pathology of experimental Fascioloides magna infection in cattle and guinea pigs.

The hematologic and clinico-pathologic response to Fascioloides magna infection in cattle and guinea pigs was investigated. Twelve calves (six infected and six controls) were monitored for 26 weeks after inoculation with 1000 metacercariae. All calves remained healthy and there were no significant differences in weight gains between infected and control groups. Flukes (mean = 9.2, range 1–32) were recovered from the liver and abdominal cavity of all infected calves. The only significant response observed in the complete blood counts was an eosinophilia present in the infected calves extending from Weeks 2 to 26 post-infection. There were no significant differences in serum levels of aspartate aminotransferase and only minor increases in the levels of gamma-glutamyl transferase and sorbitol dehydrogenase.

A total of 48 infected and 48 control guinea pigs from three separate experiments were monitored for 16 weeks after inoculation with 20 metacercariae of Fascioloides magna. Infected guinea pigs died between 7 and 114 days after infection, and flukes (ean = 2.5, range 0–13) were recovered from the liver, abdominal cavity, lungs, thoracic cavity, skeletal muscle and subcutaneous tissue. There were no differences in weight gains between infected and control guinea pigs. Complete blood counts showed increases in white blood cell, monocyte and neutrophil counts from between the third and fourteenth weeks post-infection; however, the differences were not consistently significant. Infected guinea pigs developed a significant eosinophilia and basophilia from 2 to 16 weeks post-infection. There were no significant changes in the serum levels of alanine aminotransferase or gamma-glutamyl transferase. There was an increase in the serum levels of aspartate aminotransferase beginning at 5 weeks post-infection. The response observed in the guinea pigs was similar to that reported in sheep, suggesting the suitability of the guinea pig as a model for Fascioloides magna infection in the sheep.     

Nonspecific immune response of peripheral blood neutrophils in two horse breeds (Anglo-Arabian and Spanish-Arabian): response to exercise

The aim of the present paper was: (1) to find out if there were any differences in the nonspecific immunological pattern of peripheral blood neutrophil between two breeds of horses (AA and SA); (2) to evaluate the effects of an exercise in the aerobic-anaerobic threshold. This has been observed in a group of 11 untrained horses (6 SA and 5 AA) of 2.5 years old. No statistically significant differences were found in the different stages of immune response between the rest and immediately after physical exercise to two breeds. However, the chemotaxis was significant higher at rest in the AA than SA breed. A positive correlation was found at rest between the phagocytic and oxidative metabolism activity for AA breed and a negative correlation too between the adherence and chemotaxis with phagocytic capacity, immediately after exercise test, for the same breed.     

The serum glucose and beta-hydroxybutyrate levels in sheep with experimental Fasciola hepatica and Fasciola gigantica infection

The influence of Fasciola hepatica and Fasciola gigantica infection on serum glucose and beta-hydroxybutyrate (beta-HOB) in sheep was evaluated. This was done by setting up two groups of sheep. The first group (n=13) was split in two sub-groups, one experimentally infected with F. hepatica (n=9) and the other (n=4) as uninfected control. A second group consisting of a sub-group experimentally infected with F. gigantica (n=9) the other sub-group (n=6) left as uninfected control was also set up. The results of weight gain, parasitological and serum liver enzymes activity (glutamate dehydrogenase [GLDH] and gamma glutamyltransferase [gamma-GT]) used in monitoring the infection showed that all infected animals developed fasciolosis. It was observed that a reduction in serum glucose levels was significantly lower (p<0.05) in F. hepatica infected sheep than in uninfected control sheep starting from 5 weeks post-infection (wpi) to the end of the experiment. Similar reduction was recorded in F. gigantica infected sheep between 8 and 19 wpi. In contrast, serum beta-HOB levels were elevated in F. hepatica infected sheep between 6 and 16 wpi and in F. gigantica infected sheep between 7 and 15 wpi. It would appear from these serum glucose and beta-HOB levels that fasciolosis does lead to energy deficiency (low glucose) and ketosis (increased beta-HOB). The decrease in serum glucose and increase in serum beta-HOB levels in infected sheep may help in understanding the interaction between fasciolosis and nutritional status of infected ruminants especially in young growing animals.     

Experimental maedi virus infection in sheep: early cellular and humoral immune response following parenteral inoculation

The early immune response (19 weeks) in sheep inoculated parenterally with maedi virus was studied, using the lymphocyte transformation test, immunodiffusion test, complement-fixation test, and neutralization test. Cellular immune responses were detected between 3 and 7 weeks after the sheep were inoculated. Antibodies were detected by immunodiffusion test in 3 of 5 animals in weeks 7 to 11 and by complement-fixation test in weeks 15 to 19. Neutralizing antibodies were not detected. There was no sign of virus-induced immunosuppression as determined by lymphocyte responsiveness to mitogens or by in vivo and in vitro immune responses following BCG vaccination.     

Inflammatory cell and immune function in Merino sheep with chronic dermatophilosis

Components of inflammatory and immunological responses were compared in 17 Merino sheep with chronic dermatophilosis (Group 1) and 15 Merino sheep that had recovered from the disease (Group 2). The functions studied included: (i) total and differential white cell counts; (ii) phagocytic function and intracellular killing by neutrophils; (iii) humoral immune response to T-dependent and T-independent antigens and to Dermatophilus congolensis. (iv) lymphocyte blastogenic responses to phytohaemagglutinin; (v) bovine serum albumen and D. congolensis antigens; (vi) quantification of T-lymphocyte subsets in skin lesions resulting after re-infection with D. congolensis zoospores. After all lesions were treated and the sheep were shorn, both groups of sheep were re-infected with D. congolensis. Both groups had similar infection rate, severity of lesions and rate of resolution after re-infection. The Group 2 sheep had significantly higher primary and secondary antibody responses to killed Brucella abortus cells than Group 1 sheep, but Group 1 sheep had higher levels of specific D. congolensis antibody throughout the trial. Neutrophils from Group 1 sheep showed a higher phagocytic rate for D. congolensis zoospores than Group 2 sheep when the zoospores were opsonised by sera from the Group 1 sheep, but there was no difference in their ability to kill ingested zoospores. Although there were some differences between the groups in the proportion of lymphocytes in lesions that reacted with monoclonal antibodies to T4, T8 and T19-19 lymphocyte markers at various times after re-infection, the sheep in Group 2 consistently had higher levels of lymphocytes reacting to a monoclonal antibody for the T6 lymphocyte antigen in skin biopsies collected 9, 15 and 21 days post-inoculation (p.i.) than did sheep in Group 1. Group 2 sheep also had higher levels of epidermal cells with immunohistochemical properties of Langerhans cells at lesion sites 15 and 21 days p.i.     

A COMPARISON OF COMMERCIAL MYCOPLASMA GALLISEPTICUM ANTIGENS IN THE RAPID SERUM AGGLUTINATION TEST

Twenty-three chickens, aged 9 weeks, were housed in contact with a similar group of chickens which were infected with M. gallisepticum. The onset and development of the serum agglutinin responses which were detected by 3 commercial antigens using rapid serum agglutination tests up to 20 weeks of age, differed greatly both between the infected and in-contact groups and, within the latter group, between the antigens. Few reactions, which were weak and transient, were detected in 2 similar groups of chickens, neither infected with M. gallisepticum but 1 vaccinated at 12 and 17 weeks of age with killed Pasteurella multocida oil adjuvant vaccine.     

Late immune responses in experimental maedi

Thirteen sheep were inoculated with maedi-visna virus by respiratory or intra-cerebral (i.c.) routes and were kept in close contact with 7 uninoculated control sheep. Immune responses and virological events were followed in all 20 sheep for periods up to 3 years post-inoculation.Three out of 7 i.c. infected sheep produced no complement fixing (CF) or serum neutralising (SN) antibody, whilst all 5 infected by the respiratory route and the hyperimmunised sheep developed CF and SN antibody which persisted with fluctuating titre over the period of study.Ten out of 11 sheep, which were followed from 3 months after experimental inoculation to 16–21 months (5 sheep) or 3 years (6 sheep) after inoculation, developed transient late virus-specific cell-mediated responses with intermittent virus isolation from peripheral blood leucocytes (PBL) over the period of study.In the contract control sheep, virus was isolated from PBL of 2 sheep during the 2nd year of contact, and transient virus-specific cell-mediated responses, but no antibody responses, were detected.     

Antigenic profiles of recombinant proteins from Mycobacterium avium subsp. paratuberculosis in sheep with Johne's disease

Methods to improve the ELISA test to detect Mycobacterium avium subsp. paratuberculosis have been explored over several years. Previously, selected recombinant proteins of M. avium subspecies paratuberculosis were found to be immunogenic in cattle with Johne's disease. In the present study, antibody responses of infected and healthy sheep were evaluated using 18 purified recombinant proteins in an ELISA-based format for the serodiagnosis of ovine paratuberculosis. These selected recombinant proteins represent heat shock proteins, hypothetical proteins and cell surface proteins of M. avium subsp. paratuberculosis. Whereas, Map0862 (a gene uniquely present in M. avium subspecies paratuberculosis) and Map3786 encoded protein solicited the strongest antibody response in infected sheep. The protein encoded by Map2116c showed the weakest antibody response among the animals tested. Although none of the recombinant proteins detected all 11 infected sheep singly, antibodies to Map0862 were detected in 9 of 11 (81%) infected sheep. Furthermore, ovine responses to these selected antigens were assessed temporally over the course of 1 year during which we found a spiking effect rather than an incremental increase of antibody reactivity. This study evaluated multiple M. avium subsp. paratuberculosis recombinant proteins in an ELISA-based format for sheep.     

Transmission of ovine herpesvirus 2 among adult sheep

Previous studies from this laboratory have defined the pattern of acquisition of ovine herpesvirus 2 (OHV-2) in lambs under natural flock conditions. This study examined the question of whether OHV-2 could be transmitted between adult sheep. Two potential routes of transmission were examined: (1) direct inoculation of either viable leukocytes or whole blood from OHV-2 positive sheep, and (2) horizontal transmission through natural contact with OHV-2 positive sheep. Two groups of OHV-2 negative adult sheep were inoculated with material from infected sheep, one with 5x10(8) viable peripheral blood leukocytes (PBL), and the other with 100 ml of whole peripheral blood. No PCR signals were detected in any of the three sheep inoculated with the PBL during the 20 weeks following inoculation. In the group of five sheep inoculated with whole blood, two became PCR-positive at 7 and 8 weeks post-inoculation, respectively, and the remaining three sheep maintained their negative status until termination of the experiment at 20 weeks post-inoculation. In two experiments conducted in different flocks, a total of 20 adult sheep were used to examine horizontal transmission by contact; all animals became PCR-positive within 12 months of mixing the uninfected and infected animals. The results of these experiments support two conclusions. First, the susceptibility to OHV-2 is not limited to young lambs; adult sheep remain fully susceptible. Second, the fact that whole blood, but not PBL, from infected sheep was able to transmit the infection to only two of five inoculated sheep suggests that the infection in peripheral blood cells may be largely non-productive.     

Immunostimulation in mice infected with Sendai virus

The effect of Sendai virus infection on the splenic primary plaque-forming cell (PFC) response to sheep RBC in 2 strains of mice, with contrasting susceptibility to Sendai viral pneumonia, was examined. Mice were given single inoculations of sheep RBC, which varied relative to time of inoculation with Sendai virus, PFC were counted 6 days later, and were compared with PFC responses from noninfected mice. The IgM- and IgG-PFC responses were augmented in resistant C57BL/6J mice 7 and 9 days after inoculation with Sendai virus (sheep RBC given 1 and 3 days after inoculation with Sendai virus, respectively) and in susceptible DBA/2J mice 7, 9, 10, and 13 days after inoculation with Sendai virus. Augmentation was restricted mainly to IgM-, IgG3-, and IgG2b-PFC. The number of splenic background antitrinitrophenyl sheep RBC PFC in mice of both strains was examined during the course of Sendai virus infection. Only a marginal increase in background PFC was seen in C57BL/6J mice on or after viral inoculation day 11 and no change was seen in DBA/2J mice. Serum of infected mice also was examined sequentially for alpha/beta interferon (IFN). Despite vigorous lung IFN production, infected mice rarely had detectable circulating IFN. Seemingly, Sendai virus infection can induce transient hyperresponsiveness to a nonviral antigen.