Studies on the Decline of Bovine Virus Diarrhoea Virus (BVD V) Maternal Antibodies and Detectability of BVDV in Persistently Infected Calves

Persistently infected (PI) animals play a significant role in spread and transmission of bovine virus diarrhoea virus (B VD V) (Duffell & Harkness 1985). The identification and removal of PI cattle from the herd is of great importance in the control of BVDV. Although PI animals often show various degrees of growth retardation and unthrifty appearance, a significant proportion is clinically normal. PI animals are often seronegative (Duffell & Harkness 1985), but calves may be tested seropositive because of the presence of maternal immunity (Meyling & Jensen 1988). The passively derived BVDV antibodies may interfere with the ability to detect virus. Considering the importance of early recognition of PI calves, it is essential to determine the earliest time when PI animals can safely be diagnosed in the herd.     

An attempt to predict anergy in tuberculosis suspect cynomolgus monkeys.

Acid-fast microorganisms were identified from the tuberculous lesions of a male cynomolgus monkey (Macaca fascicularis). Twenty-two other cynomolgus monkeys housed in the same room were presumed exposed to tuberculosis (Mycobacterium spp.). In addition to standard intradermal (ID) tuberculin testing, clinicians attempted to evaluate the immune status of these monkeys in order to identify animals exhibiting false negative (anergy) ID tuberculin tests. Twenty-one of the potentially exposed monkeys were immunized with tetanus toxoid (TT). Tetanus antitoxin (TAT) titers were measured before and after immunization. The delayed cutaneous hypersensitivity (DCH) reaction to TT was evaluated using a commercially available human test panel. Some animals did not exhibit a DCH reaction to TT. At necropsy 1 of the 21 animals exhibited tuberculous lesions, and acid-fast microorganisms were identified on direct smears of lymphatic tissue of a second animal. Although reported to be of value in assessing the cellular immune status of rhesus monkeys (Macaca mulatta), the delayed cutaneous hypersensitivity response to tetanus toxoid was not helpful during this outbreak in identifying cynomolgus monkeys infected with M. tuberculosis, or in interpreting suspect ID tuberculin tests.     

Maternal antibody blocks humoral but not T cell responses to BVDV.

Bovine viral diarrhoea virus (BVDV) contributes significantly to health-related economic losses in the beef and dairy industry. Antibodies of maternal origin can be protective against BVDV infection, however, calves with low titres of maternal antibody or that do not receive colostrum may be at risk for acute BVDV infection. Interference by high titres of maternal antibodies prevents the development of an antibody response following vaccination with either a killed or attenuated BVDV vaccine. However, the T cell mediated immune response to BVDV may be generated in the absence of a detectable serum neutralizing antibody response. Two trials were conducted to evaluate the potential to elicit T cell mediated immune responses to BVDV in calves with circulating maternal antibody to BVDV. In the first trial, calves with high levels of circulating maternal antibody to BVDV 1 and BVDV 2 were experimentally infected with BVDV 2 (strain 1373) at two to five weeks of age. The T-cell mediated immune responses of the experimentally infected calves and non-infected calves were monitored monthly until circulating maternal antibody was no longer detectable in either treatment group. Calves experimentally infected with BVDV developed BVDV specific CD4(+), CD8(+), and delta T cell responses while high levels of maternal antibody were circulating. A second challenge with BVDV 2 (strain 1373) was performed in the experimentally infected and control calves once maternal antibody could no longer be detected. Previous exposure to BVDV in the presence of maternal antibody protected calves from clinical signs of acute BVDV infection compared to the control calves. In the second trial, three groups of calves with circulating maternal antibody to BVDV were given either a modified live vaccine (MLV) containing BVDV 1 and BVDV 2, a killed vaccine containing BVDV 1 and BVDV 2, or no vaccine, at seven weeks of age. Serum neutralizing antibody levels and antigen specific T cell responses were monitored for 14 weeks following vaccination. Calves vaccinated with MLV BVDV developed BVDV 1 and BVDV 2 specific CD4(+)T cell responses, and BVDV 2 specific gammadelta T cell responses, in the presence of maternal antibody. Vaccination with killed BVDV did not result in the generation of measurable antigen specific T cell immune responses. In this trial, a second vaccination was performed at 14 weeks to determine whether an anamnestic antibody response could be generated when calves were vaccinated in the presence of maternal antibody. Calves vaccinated with either a MLV or killed BVDV vaccine while they had maternal antibody developed an anamnestic antibody response to BVDV 2 upon subsequent vaccination. The results of these trials indicate that vaccinating young calves against BVD while maternal antibody is present may generate BVDV specific memory T and B cells. The data also demonstrated that seronegative calves with memory T and B cells specific for BVDV may be immune to challenge with virulent BVDV.     

Partial suppression of cell mediated immunity in chromoblastomycosis

The cellular immune response of 8 patients from the Brazilian Amazon region with chromoblastomycosis was analyzed. Primary immunological responses of patients were tested by contact sensitization to 2,4-dinitro-chlorobenzene (DNCB), or rejection of first set skin allografts. 2 of 8 patients were reactive to DNCB after sensitization, and skin allograft rejection occured in an average of 14 days. Capacity of patients to mount recall immunological responses was measured by skin testing with two fungal antigens and three bacterial antigens. Delayed skin reaction to trichophytin and Candida antigens was negative in the majority of the patients. However, reactivity to mycobacterial (tuberculin), and bacterial (staphylococcal, streptococcal) antigen was high, or only slightly diminished respectively. The data suggest that patients with chromoblastomycosis have suppressed nonspecific, cell mediated immunity for some antigens (skin allografts, DNCB, fungal antigens), while reactivity to bacterial and mycobacterial antigens is not impaired.     

Bovine maternal,fetal and neonatal responses to bovine viral diarrhea virus infections

Due to the affinity of BVDV for the fetus and for cells of lymphatic organs of infected cattle, reproductive failure or immunosuppression, respectively, are likely consequences of BVDV infections of susceptible cattle. Infection of susceptible pregnant cattle with noncytopathic (ncp) BVDV results in transplacental infection with induction of maternal and fetal innate and adaptive immune responses. Differences in maternal innate and adaptive immune responses are evident in late gestation between cows carrying fetuses persistently-infected (PI) with BVDV and cows with fetuses transiently-infected with BVDV. Fetal innate and adaptive immune responses to ncp BVDV infection are defined by fetal age and developmental stage of the fetal immune system. Since a functional fetal adaptive immune response does not occur in the early fetus, immunotolerance to ncp BVDV is established, virus replicates unrestricted in fetal tissues and calves are born immunotolerant and PI with the virus. In the last trimester of gestation, the fetal immune system is adequately developed to respond in an efficacious manner, most commonly resulting in the birth of a clinically normal calf with pre-colostral antibodies. Immunosuppression due to postnatal acute ncp BVDV infections of susceptible calves may contribute to the occurrence and severity of multi-factorial respiratory tract and enteric diseases.     

Greater numbers of nucleotide substitutions are introduced into the genomic RNA of bovine viral diarrhea virus during acute infections of pregnant cattle than of non-pregnant cattle

ABSTRACT: BACKGROUND: Bovine viral diarrhea virus (BVDV) strains circulating in livestock herds show significant sequence variation. Conventional wisdom states that most sequence variation arises during acute infections in response to immune or other environmental pressures. A recent study showed that more nucleotide changes were introduced into the BVDV genomic RNA during the establishment of a single fetal persistent infection than following a series of acute infections of naive cattle. However, it was not known if nucleotide changes were introduce when the virus crossed the placenta and infected the fetus or during the acute infection of the dam. METHODS: The sequence of the open reading frame (ORF) from viruses isolated from four acutely infected pregnant heifers following exposure to persistently infected (PI) calves was compared to the sequences of the virus from the progenitor PI calf and the virus from the resulting progeny PI calf to determine when genetic change was introduced. This was compared to genetic change found in viruses isolated from a pregnant PI cow and its PI calf, and in three viruses isolated from acutely infected, non-pregnant cattle exposed to PI calves. RESULTS: Most genetic changes previously identified between the progenitor and progeny PI viruses were in place in the acute phase viruses isolated from the dams six days post-exposure to the progenitor PI calf. Additionally, each progeny PI virus had two to three unique nucleotide substitutions that were introduced in crossing the placenta and infection of the fetus. The nucleotide sequence of two acute phase viruses isolated from steers exposed to PI calves revealed that six and seven nucleotide changes were introduced during the acute infection. The sequence of the BVDV-2 virus isolated from an acute infection of a PI calf (BVDV-1a) co-housed with a BVDV-2 PI calf had ten nucleotides that were different from the progenitor PI virus. Finally, twenty nucleotide changes were identified in the PI virus of a calf born to a PI dam. CONCLUSIONS: These results demonstrate that nucleotide changes are introduced into the BVDV infecting pregnant cattle at rates of 2.3 to 8 fold higher then during the acute infection of non-pregnant animals.     

Transplacental antibodies. Part II: Maternal antibodies against the toxins of C. diphtheriae and C. tetani

Examinations of 297 sera for diphtheria antitoxin and 160 sera for tetanus antitoxin were carried out in 1981. All sera were obtained from the cord blood of mothers between 15 and 34 years of age. The mothers were divided into four age groups each of which was further subdivided into the primipara and multipara subgroups. The aim was to assess the age-specific variations in response to active immunization against diphtheria and tetanus. The protective level of diphtheria antitoxin (at least 0.01 I.U./ml) was recorded in the serum of 96.3% of examinees and the rates of seropositivity were found to fall with increasing age. The protective level of tetanus antitoxin (at least 0.1 I.U./ml) was found in the serum of 95.2% of mothers. The serologic response encountered in groups of older mothers was a clear-cut demonstration that the country-wide mass immunization against tetanus carried out between 1974 and 1975 was highly effective and fully justified. The variations in the diphtheria and tetanus antitoxin levels found in the primipara and multipara subgroups were not statistically significant.     

An Experimental Study of a Concurrent Primary Infection with Bovine Respiratory Syncytial Virus (BRSV) and Bovine Viral Diarrhoea Virus (BVDV) in Calves

Experimental infections with bovine respiratory syncytial virus (BRSV) and bovine viral diarrhoea virus (BVDV) were performed to study the effect of concurrent BRSV and BVDV infections. Twelve seronegative calves, in 3 groups, were inoculated on a single occasion with pure BRSV (group A), BRSV and noncytopathogenic BVDV (group B) or mock infected (group C). Mild respiratory symptoms were recorded 4 to 5 days post inoculation (dpi) in group A and group B calves. One calf in group A was severely affected and required medical treatment. In group B, fever (40.7-41.4 °C) was prominent 7 to 8 dpi. Only calves in group B were BVDV positive in purified lymphocytes at 2 to 14 dpi and showed increased serum interferon levels, with a peak at 4 dpi, indicating BVDV to be responsible for inducing the rise. BRSV was detected in lung lavage fluids up to 7 dpi for group A calves, compared to 11 dpi for group B and calves in this group also seroconverted later displaying lower BRSV titers. The time lag before an antibody response and the titers recorded in group B, indicated that the duration of BVDV infection in lymphocytes negatively influenced the capacity to mount a BRSV antibody response. kw|Keywords|k]cattle; k]respiratory disease; k]interferon; k]PCR     

Lack of Virus Transmission from Bovine Viral Diarrhoea Virus Infected Calves to Susceptible Peers

None of 14 calves not previously exposed to BVDV became infected after being forced to have nose-to-nose contact with a group of 5 calves primarily infected with BVDV These were 5 male calves primarily infected with a type I BVDV strain, after nose-to-nose contact with a persistently viraemic calf. All 5 became infected and were clinically affected. They were slightly depressed and pyretic at 8–9 days postinfection, with a body temperature of up to 41.6°C, but no medical treatment was required. Seroconversions to BVDV were detected in these calves at 14 to 21 days postinfection. The 14 healthy calves, proved to be free from BVD virus – as well as antibodies, were introduced 2 by 2 into the group of 5 primarily infected calves on days 4, 7, 14, 21, 28, 35 and 42 after the 5 calves had been in contact with the persistently BVDV-infected calf. Each pair of calves stayed within the primarily infected group for 2 days. None of these 14 calves seroconverted to BVDV.     

Preparation of chicken IgY against recombinant E2 protein of bovine viral diarrhea virus (BVDV) and development of ELISA and ICA for BVDV detection

Bovine viral diarrhea virus (BVDV) infects cattle and may lead to persistent infection (PI). The PI animals harbor BVDV throughout their life and become immune tolerant against BVDV. Thus, diagnosis of this virus in herd is highly important. Recombinant E2 protein expression (using pET-32a in Escherichia coli) was confirmed by SDS-PAGE and Western blotting; then purified by Ni⁺ affinity chromatography. Chickens were immunized with BVDV-E2 protein, and IgY antibodies were extracted from egg yolk by PEG-6000. The peak titer of anti-BVDV-E2-IgY was 1:128,000 after the fifth immunization. IgY-based enzyme-linked immuno sorbent assay (ELISA) and immunochromatographic assay (ICA) were further developed. Coincidence of ELISA and ICA test with RT-PCR was 95.45 and 90.91%, respectively. The anti-BVDV-E2 IgY could be used in routine screening of BVDV infection. Besides, it can also be applicable while licensing and/or using live vaccines; screening of imported products containing bovine serum and strong surveillance of BVDV outbreaks.     

Restoration of host defense mechanisms in man by levamisole

Levamisole, a broad-spectrum anthelmintic, increased the delayed hypersensitivity skin reaction to tuberculin and to DNCB in about one third of the patients. Levamisole and the racemate tetramisole temporarily increased serum antibody titres in response to vaccination against influenza.     

BVD Virus Antigens in Tissues of Persistently Viraemic,Clinically Normal Cattle: Implications for the Pathogenesis of Clinically Fatal Disease

The cellular events involved in precipitation of the clinically fatal outcome of an infection with bovine viral diarrhoea virus (BVDV) remain unresolved, though it is now known that this course of the infection, Mucosal Disease (MD), only occurs in calves persistently infected with non-cytopathic BVDV. In studies aimed at elucidating the pathogenesis of MD, the distribution of BVDV antigens and infectious virus in tissues of persistently infected, clinically normal calves was investigated. Virus antigen was detected in most tissues, in epithelial and immune cells. No signs of an inflammatory response were detected and cytopathological changes were subtle or absent. The infection may nevertheless create a cell-environment which will enhance replication of cytopathic virus. Variations in the clinical, pathomorphologies and virological appearance of MD-cases may depend on both the host-reactions, including virus-induced immunopathology, and the virus-strain combinations in a putative mixed infection.     

The impact of BVDV infection on adaptive immunity

Bovine viral diarrhea virus (BVDV) causes immunosuppression of the adaptive immune response. The level of suppression of the adaptive immune response is strain dependent. The early events of antigen presentation require activation of toll-like receptors that results in the release of pro-inflammatory cytokines. Non-cytopathic (ncp) BVDV infection stimulates cytokines from macrophages in vitro but the effect of BVDV infection in vivo on macrophages or in vitro with monocytes is not clear. Antigen presentation is decreased and co-stimulatory molecules are down regulated. T-lymphocytes numbers are reduced following BVDV infection in a strain dependent manner. There is recruitment of lymphocytes to the bronchial alveolar space following cytopathic (cp) BVDV infection. Depletion of T-lymphocytes occurs in the lymphoid tissue and is strain dependent. BVDV cp T-lymphocyte responses appear to be primarily a T helper 1 response while the response following ncp BVDV induces a T helper 2 response. Cytotoxic T-lymphocytes (CTL), an important BVDV defense mechanism are compromised. The major neutralizing antigens are well characterized but cross-protection between strains is variable. PI animals have normal adaptive immune responses with the exception of the PI strain immunotolerance and mucosal disease may be a function of the level of gamma delta T cells.     

Vaccinia virus persistence in a child against the background of immune deficiency

A young girl, vaccinated against smallpox 6 years before suffered from a persistent vaccinia virus infection and a congenital skin disease, i.e. epidermolysis bullosa. The virus was isolated from skin lesions at the vaccination site and remote sites and repeatedly from the blood; it was not isolated from bone-marrow specimen, saliva, pharynx or urine. The titre of virus-neutralizing antibodies was low (1:10), immunoglobulins A, M and G were within age-related limits; antibodies against measles and tetanus were at protective levels, skin tests were positive. Staphylococcal antitoxin titre was extremely high. The child's mother, not vaccinated against smallpox, possessed vaccinia--virus-neutralizing antibodies at high titre (over 1:320). Examination of the child did not show any quantitative immune deficiency. Immune deviations were found in the lymphocyte blast-transformation reaction on stimulation with PHA and specific antigen, as well as in the nonspecific-suppression test. The possible genesis of the virus persistence and the role of the virus in the clinical course of the disease are discussed.     

Evaluation of a commercial E<Superscript>rns</Superscript>-capture ELISA for detection of BVDV in routine diagnostic cattle serum samples

Background  

Bovine viral diarrhoea virus (BVDV) is an important pathogen in cattle. The ability of the virus to cross the placenta during early pregnancy can result in the birth of persistently infected (PI) calves. These calves shed the virus during their entire lifespan and are the key transmitters of infection. Consequently, identification (and subsequent removal) of PI animals is necessary to rapidly clear infected herds from the virus. The objective of this study was to evaluate the suitability of a commercial E^rns-capture ELISA, in comparison to the indirect immunoperoxidase test (IPX), for routine diagnostic detection of BVDV within a control programme. In addition, the effect of passive immunity and heat-inactivation of the samples on the performance of the ELISA was studied.     

Reproductive and economic impact following controlled introduction of cattle persistently infected with bovine viral diarrhea virus into a naive group of heifers

The reproductive impact following controlled introduction of animals persistently infected (PI) with bovine viral diarrhea virus (BVDV) was evaluated in BVDV-naive heifers. Heifers were randomly allocated into two groups: an unexposed control herd (n = 34) and a herd exposed to five persistently infected (PI) animals for 7 mo, beginning 50 days before the breeding season (n = 34). Initiation of the BVDV-challenge was timed to mimic either direct contact with PI calves born in the previous calving season or accidental introduction of PI herd additions prior to the breeding season. The PI animals represented BVDV Types 1a (n = 3), 1b (n = 1) and 2 (n = 1). Two BVDV-free, seropositive bulls were used in each group for 78 days breeding seasons. In both groups, 33 of 34 heifers became pregnant, with similar distribution of fetal ages. Two heifers in each group aborted (etiology undetermined). In addition, one calf was born dead and one calf died 3 days post-partum in the BVDV-exposed group. One calf in the unexposed group died 4 mo post-partum. No calves, including the stillborn calf and the two calves that died prior to weaning, were persistently infected with BVDV. In summary, introduction of PI cattle to a group of BVDV-naive heifers 50 days prior to the breeding season did not negatively impact reproductive performance. To the contrary, the active immunity that developed following field exposure to BVDV provided effective reproductive and fetal protection during the breeding season and subsequent gestations, despite continuous exposure to PI animals until approximately midgestation. Although BVDV can have potentially devastating reproductive effects, timing of infection is a critical determinant in the outcome of a BVDV infection. A controlled breeding season with introduction of herd additions at less critical reproductive time points can mitigate the negative reproductive health consequences of BVDV.     

Titration of tetanus antitoxin by passive hemagglutination. II. Serological characteristics of antitoxin production in rabbits and monkeys.

1) Production of tetanus antitoxin in rabbits and monkeys was followed by passive hemagglutination (HA) and toxin-neutralization (TN) tests. The HA activity was observed in both IgM and IgG in both animal species. 2) In rabbits, IgM antitoxin was detected as early as in 7 days, reached the maximum titer in 10--14 days, and disappeared in 3 weeks after the primary immunization. Antitoxin of IgG class was detected in 10 days, and increased gradually. The ratio of HA/TN titers ("serum ratio") was high at an early stage of primary immunization and approached the unity in 3--4 weeks. Unlike the case of guinea pigs, IgM was found to contribute greatly to this high level of ratio. Besides, most rabbits produced IgG antitoxin of high ratios at early stages of immunization. 3) The immune response of monkeys showed a pattern very similar to that of rabbits except a few days' delay in the time course of antitoxin titers. No IgG antitoxin with a high serum ratio was demonstrated. Therefore, the high serum ratio of early sera could be accounted for mainly by IgM. 4) In response to the secondary immunization, no IgM antitoxin was detected in either animal species. 5) No definite correlation between serum ratio and avidity in terms of "dilution ratio" was demonstrated. However, both the dilution ratio and serum ratio were high at an early stage of immunization and gradually decreased, though the magnitudes of the ratios were variable depending on individual animals.     

Immune responses after oral inoculation of weanling bison or beef calves with a bison or cattle isolate of Mycobacterium avium subsp. paratuberculosis

Paratuberculosis is endemic in domestic and wild ruminants worldwide. We designed the following study to compare host immune responses and pathologic changes in beef calves and bison calves after challenge with either a cattle or bison (Bison bison) strain of Mycobacterium avium subsp. paratuberculosis. In the first part of the study, six bison and six beef calves were orally inoculated with a cattle isolate of M. avium subsp. paratuberculosis over a 2 wk period. In the second part, an additional six bison and six beef calves were similarly inoculated with a bison strain of M. avium subsp. paratuberculosis. Throughout each of the studies, blood and fecal samples were taken monthly for a 6 mo infection period. Tissue samples were obtained at necropsy for culture and histopathologic analyses. Results from this study demonstrated that bison calves were more susceptible to tissue colonization than beef calves after challenge with the cattle isolate and, conversely, that beef calves were more susceptible to the bison strain of M. avium subsp. paratuberculosis. Although lesions were minimal they were most apparent in the jejunum and distal ileum. Interferon-gamma (IFN-gamma) responses were noted in some calves by 1 mo postinoculation and were sustained longer in beef calves after challenge with the bison isolate. Antibody was not detected in either beef or bison calves during the 6 mo infection period. These results indicate that the host response to strains of M. avium subsp. paratuberculosis may differ between ruminant species.     

Alternative diphtheria, tetanus and whooping cough immunization schedule to evoke a Th2 tetanus and a Th1 pertussis immune response

In a previous study, using BALB/c mice, we found that while diphtheria (D), tetanus (T) and whooping cough (Pw, whole-cell Bordetella pertussis) immunization induces a Th1/Th2 tetanus response and memory T cells able to proliferate in response to in vitro stimulation with B. pertussis, DTPa immunization induces a Th2 tetanus immune response and no memory T cells that recognize B. pertussis as stimulus. Considering that a pro-inflammatory cytokine production is not necessary for protection against tetanus and therefore should be avoided, an alternative DTP immunization schedule with minimal Pw exposure was assessed in order to obtain a Th2 tetanus response and a Th1 pertussis response. BALB/c mice were primed with DT vaccine at day 0, with Pw vaccine at day 14 and boosted with DTPa vaccine at days 21 and 28. A control group was inoculated with saline. Antibodies against B. pertussis surface antigens, tetanus and diphtheria toxoids were produced by mice. Spleen cells stimulated in vitro with B. pertussis produced IL-6 and IFNgamma. Only IL-5 was produced by cells in response to tetanus toxoid stimulation. These results are in line with the low IgG1/IgG2a ratio for pertussis antibodies compared with those corresponding to tetanus and diphtheria. The immunization protocol presented herein succeeded in producing tetanus and pertussis immune responses of Th2 and Th1 type, respectively. In contrast to previous results obtained with DTPw immunization, no IL-12 production was observed. Our findings provide direct evidence that an immunization protocol with an interval of 14 days between DT and Pw primings, followed by DTPa boosters, can induce appropriate immune responses against DTP vaccine antigens.