Secretory antibody responses in cattle infected with foot-and-mouth disease virus.

Antibody responses in serum, saliva, nasal secretions, or esophageal-pharyngeal fluid of foot-and-mouth disease virus-infected steers were examined by single radial immunodiffusion and mouse-neutralization tests. In steers infected with type O foot-and-mouth disease virus, high serum antibody titers were detected within 10 days after infection. Antibody was first detected in saliva at 30 days and gradually increased to a plateau at about 90 days. Small amounts of antibody continued to be secreted in saliva and in nasal secretions for at least 6 months. Antibody was not detected in esophageal-pharyngeal fluid. The major antibody activity in secretions was due to secretory immunoglobulin A as revealed by radioimmunoelectrophoresis.     

Failure to induce mucosal disease in cattle persistently infected with bovine viral diarrhea virus by treatment with adrenocorticotropic hormone

Recent research has shown that cattle that develop mucosal disease (MD) often, if not always, have been persistently infected with bovine viral diarrhea virus (BVDV) since birth. The purpose of the present study was to determine whether MD could be induced by immunosuppression of persistently BVDV-infected cattle. For that purpose, adrenocorticotropic hormone (ACTH) was injected intramuscularly, twice daily for 5 consecutive days in 4 persistently BVDV-infected cattle and in 3 control cattle. Before the ACTH treatment, the numbers of leukocytes, neutrophils and mononuclear cells (MNC) per litre of blood in BVDV-infected cattle were in the same range as in the controls. Similarly, the proportions of B cells, T cells, monocytes and Fcγ⁺ cells (cells with receptor for the Fc part of IgG) were the same in the 2 groups of animals. On the other hand, the proliferative response to mitogen stimulation of MNC obtained from the control animals was twice as high as the corresponding value of the persistently BVDV-infected cattle.In all animals, ACTH treatment caused increased Cortisol concentrations, leukocytosis, neutrophilia and decreased mitogen-induced lymphocyte stimulation. However, the MNC count and the proportions of B cells, T cells, Fcγ⁺ cells and monocytes remained unaltered. In spite of the immunosuppression, indicated by the decrease in mitogen-induced lymphocyte stimulation. ACTH treatment did not provoke any clinical signs of MD in the persistently BVDV-infected cattle.     

Detection of foot-and-mouth disease virus infected cattle using infrared thermography

In this study, infrared thermography (IRT) was assessed as a means of detecting foot-and-mouth disease virus (FMDV)-infected cattle before and after the development of clinical signs. Preliminary IRT imaging demonstrated that foot temperatures increased in FMDV-infected animals. The maximum foot temperatures of healthy (n = 53), directly inoculated (DI) (n = 12), contact (CT) (n = 6), and vaccine trial (VT) (n = 21) cattle were measured over the course of FMD infection. A cut-off value was established at 34.4 °C (sensitivity = 61.1%, specificity = 87.7%) with the aim of detecting FMDV-infected animals both before and after clinical signs were observed. Seven of 12 (58%) DI and 3/6 (50%) CT animals showed maximum foot temperatures exceeding the 34.4 °C cut-off before the development of foot vesicles. In contrast, only 5/21 (24%) VT animals displayed pre-clinical foot temperatures above this cut-off possibly indicating partial vaccine protection of this group. These results show IRT as a promising screening technology to quickly identify potentially infected animals for confirmatory diagnostic testing during FMD outbreaks. Further evaluation of this technology is needed to determine the value of IRT in detecting animals with mild clinical signs or sub-clinical infections.     

Kinetics of immune response to foot-and-mouth disease virus (type Asia 1) in experimental cattle

Humoral and mucosal (secretory antibody)immune response to FMDV type Asia 1 in cattle was analyzed after vaccination and infection using virus neutralizing test (VNT). Vaccination (1/16th the usual dose) failed to protect cattle from generalized clinical disease following experimental FMDV Asia 1 infection. Our results showed that infection induced higher and prolonged serum antibody titres indicating antigen mass is important for optimal immune response. Experimental FMDV infection induced significant secretory antibody (mucosal) response in cattle. Though, there was no difference in the serum antibody response between the cattle that developed generalized infection (unprotected) and those with only localized infection (protected), secretory antibody response differed, wherein the unprotected cattle had higher secretory response than protected cattle. Thus, FMDV Asia 1 infection stimulates a similar serum antibody response and a unique secretory antibody response among the infected cattle. An erratum to this article can be found at     

Border disease in sheep caused by transmission of virus from cattle persistently infected with bovine virus diarrhoea virus.

Two outbreaks of border disease occurred on farms with sheep flocks and breeding cattle. The infection of the pregnant sheep was probably caused by transmission of virus from calves persistently infected with non-cytopathic bovine virus diarrhoea virus (BVDV) which were kept in close confinement with the ewes during mid-pregnancy. Border disease was also induced experimentally in eight lambs by exposing their dams at 38 to 78 days of gestation to a heifer persistently infected with BVDV. Both the natural and the experimental infections were characterised by typical signs such as 'hairy-shaker' lambs and high lamb mortality. The diagnosis was confirmed by virus isolations from live-born lambs, seroconversion and pathology. The study supports the assertion that cattle persistently infected with BVDV and in close contact with pregnant sheep, are an important source of strains of virus capable of causing border disease.     

Cohabitation of pregnant white-tailed deer and cattle persistently infected with Bovine viral diarrhea virus results in persistently infected fawns

Economic losses due to infection with Bovine viral diarrhea virus (BVDV) have prompted introduction of organized control programs. These programs primarily focus on the removal of persistently infected (PI) animals, the main source of BVDV transmission. Recently, persistent BVDV infection was demonstrated experimentally in white-tailed deer, the most abundant wild ruminant in North America. Contact of cattle and white-tailed deer may result in interspecific BVDV transmission and birth of persistently infected offspring that could be a threat to control programs. The objective of this study was to assess the potential for interspecific BVDV transmission from persistently infected cattle cohabitated with pregnant white-tailed deer. Seven female and one male white-tailed deer were captured and bred in captivity. At approximately 50 days of gestation, two cattle persistently infected with BVDV 1 were cohabitated with the deer. In a pen of approximately 0.8 ha, both species shared food and water sources for a period of 60 days. Transmission of BVDV as indicated by seroconversion was demonstrated in all exposed adult deer. Of the seven pregnancies, four resulted in offspring that were infected with BVDV. Persistent infection was demonstrated in three singlet fawns by immunohistochemistry and ELISA on skin samples, PCR, and virus isolation procedures. Furthermore, two stillborn fetuses were apparently persistently infected. This is the first report of BVDV transmission from cattle to white-tailed deer using a model of natural challenge. Under appropriate circumstances, BVDV may efficiently cross the species barrier to cause transplacental infection and persistently infected offspring in a wildlife species.     

Response of cattle persistently infected with bovine virus diarrhoea virus to bovine leukosis virus

Six cattle persistently infected with bovine virus diarrhoea virus (BVDV) and seronegative, and two control, virus negative seropositive cattle were inoculated with lymphocytes infected with bovine leukosis virus (BLV). The two controls produced a normal immune response to BLV, developing antibodies at four and five weeks after inoculation. Two of the six cattle persistently infected with BVDV developed a strong antibody response by six weeks after inoculation with BLV. Four developed a depressed response to BLV, characterised in three by a 'hooking' reaction in the immunodiffusion test which persisted in successive bleedings but was interspersed occasionally by a weak positive reaction. In one of these animals, a series of 'hooking' reactions was followed by a number of negative results. The fourth animal remained serologically negative until 16 weeks after inoculation when a 'hooking' reaction was observed followed by a series of negative results. BLV was isolated from all the cattle persistently infected with BVDV at 42 or 58 weeks after inoculation regardless of whether the serum samples gave negative, 'hooking', weak positive or positive reactions in the immunodiffusion test. BLV was consistently isolated from the nasal secretions of a steer which was BVDV negative but seropositive. The possibility of decreased immune responsiveness to BLV in animals persistently infected with BVDV should be considered when formulating regulations governing the testing of animals for freedom from BLV.     

Leukocyte profile of cattle persistently infected with bovine viral diarrhea virus

Animals acutely infected with bovine viral diarrhea virus (BVDV) exhibit transient immunosuppression as a result of the virus' predilection for cells that play critical roles in the host immune system. Acute BVDV infections have major effects on thymic and follicular T-lymphocytes, as well as follicular B-lymphocytes, often resulting in severe reduction in circulating numbers of lymphocytes and suppression of functional activities of these cells. Granulocytes and monocytes are equally susceptible to BVDV infections with reduction in numbers and suppression functions. However, there is limited information on the leukocyte profile of cattle persistently infected (PI) with BVDV. This study reports on phagocytic activities of granulocytes and monocytes as well as immunophenotyping by flow cytometric analysis of leukocytes isolated from healthy non-PI (NPI) and PI animals. No significant differences were found between the leukocyte profiles and the phagocytic activities of PI animals when compared to a group of healthy NPI animals.     

Estimation of the transmission of foot-and-mouth disease virus from infected sheep to cattle

The quantitative role of sheep in the transmission of foot-and-mouth disease virus (FMDV) is not well known. To estimate the role of sheep in the transmission of FMDV, a direct contact transmission experiment with 10 groups of animals each consisting of 2 infected lambs and 1 contact calf was performed. Secretions and excretions (oral swabs, blood, urine, faeces and probang samples) from all animals were tested for the presence of FMDV by virus isolation (VI) and/or RT-PCR. Serum was tested for the presence of antibodies against FMDV. To estimate FMDV transmission, the VI, RT-PCR and serology results were used. The partial reproduction ratio R₀^p i.e. the average number of new infections caused by one infected sheep introduced into a population of susceptible cattle, was estimated using either data of the whole infection chain of the experimental epidemics (the transient state method) or the final sizes of the experimental epidemics (the final size method). Using the transient state method, R₀^p was estimated as 1.0 (95% CI 0.2 - 6.0) using virus isolation results and 1.4 (95% CI 0.3 - 8.0) using RT-PCR results. Using the final size method, R₀^p was estimated as 0.9 (95% CI 0.2 - 3.0). Finally, R₀^p was compared to the R₀’s obtained in previous transmission studies with sheep or cattle only. This comparison showed that the infectivity of sheep is lower than that of cattle and that sheep and cattle are similarly susceptible to FMD. These results indicate that in a mixed population of sheep and cattle, sheep play a more limited role in the transmission of FMDV than cattle.     

The immune response in cattle infected with Tritrichomonas foetus

Holando-Argentina calves (males and females) were experimentally infected with Tritrichomonas foetus var. Belfast (T. foetus) by introducing 10(7) protozoa into the preputial and vaginal cavities, in order to analyse the course of the immune response to infection. Samples of serum, vaginal mucus and preputial secretion were taken periodically and assayed by means of microagglutination of living protozoa. The serum antibody titre, which averaged 32 before infection and was equivalent to titres in a non-infected group, increased to 512 in the heifers 11 weeks later and to 128 in the bulls 4 months post-infection. Agglutinating antibodies were not detected in the preputial cavity, but heifers showed antibodies in the vaginal mucus and became trichomoniasis free after 4 months. Conversely, genital secretions from the bulls gave rise to positive cultures during the whole period of experimentation. The intradermal sensitivity was checked using a soluble antigen from T. foetus. The diameter of the papula increased up to three times in heifers, while in bulls the results were no different than those from the non-infected group. Serum antibodies were of the IgG2 subclass, while those isolated from vaginal mucus were characterized as IgG1, an opsonizing antibody. Heifers were refractory to challenge infection after 1 year. The poor immune response in bulls is consistent with their role as carriers of T. foetus.     

Genetic variation of foot-and-mouth disease virus isolates recovered from persistently infected water buffalo (Bubalus bubalis)

Genetic variation of foot-and-mouth disease virus (FMDV) isolates, serotype O, recovered serially over a 1-year period from persistently infected buffalos was assessed. The persistent state was established experimentally with plaque-purified FMDV, strain O(1)Campos, in five buffalos (Bubalus bubalis). Viral isolates collected from esophageal-pharyngeal (EP) fluids for up to 71 weeks after infection were analyzed at different times by nucleotide sequencing and T(1) RNase oligonucleotide fingerprinting to assess variability in the VP1-coding region and in the complete genome, respectively. Genetic variation increased, although irregularly, with time after infection. The highest values observed for the VP1-coding region and for the whole genome were 2.5% and 1.8%, respectively. High rates of fixation of mutations were observed using both methodologies, reaching values of 0.65 substitutions per nucleotide per year (s/nt/y) and 0.44s/nt/y for nucleotide sequencing and oligonucleotide fingerprinting, respectively, when selected samples recovered at close time periods were analyzed. The data herein indicate that complex mixtures of genotypes may arise during FMDV type O persistent infection in water buffalos, which can act as viral reservoirs and also represent a potential source of viral variants. These results fit within the quasi-species dynamics described for FMDV, in which viral populations are constituted by related, non-identical genomes that evolve independently from each other, and may predominate at a given time.     

Arachidonic acid immunoregulation in lambs persistently infected with border disease virus

To evaluate arachidonic acid-related immunoregulatory mechanisms during long-term persistent pestivirus infection, we measured plasma contents of leukotriene C4 (LTC4), prostaglandin D2 (PGD2) and their plasma fatty acid (FA) precursor, arachidonic acid (AA), in six lambs with congenital border disease (BD). Significantly elevated average plasma LTC4 during the first half year of life was associated with increased PDG2 when compared to uninfected control lambs. Significantly elevated total plasma esterified AA stores suggest an effective BDV-mediated prostenoid immunostimulation. However, at 1 yr old, prostenoid secretion had fallen to normal (LTC4) or below normal (PGD2) levels. In contrast, there remained significantly elevated plasma esterified AA, present as available substrate for formation of these anti-viral immunoregulatory agents. These results suggested that preventing mobilization of AA from lipid stores for effective immune responses may be a viral strategy of BD virus that is associated with long term border disease effects.     

Lymphocyte blastogenesis and neutrophil function in cattle persistently infected with bovine viral diarrhea virus

Neutrophil function and mononuclear cell proliferative responses to mitogens were determined in healthy cattle and in cattle persistently infected with bovine viral diarrhea (BVD) virus. Uptake of [3H]thymidine by resting and mitogen-stimulated peripheral blood mononuclear cells was significantly lower in cattle persistently infected with BVD virus than in healthy cattle. Neutrophils from cattle persistently infected with BVD virus had significantly impaired capability to ingest Staphylococcus aureus, but were normal in respect to random migration under agarose, cytochrome C reduction, iodination, and antibody-dependent cell-mediated cytotoxicity. Impairment of neutrophil function in cattle persistently infected with BVD virus differs from impairment of neutrophil function reported in healthy cattle mounting an immune response to recent BVD virus infection.     

Study of cattle persistently infected with bovine viral diarrhea virus that lack detectable virus in serum

OBJECTIVE: To determine whether cattle persistently infected with bovine viral diarrhea virus (BVDV) that lack virus detectable in serum by use of the immunoperoxidase microtiter assay (IPMA) can transmit the virus to susceptible herdmates and determine prevalence of these cattle. DESIGN: Clinical trial and serologic survey. SAMPLE POPULATION: 2 cattle and 1,952 blood samples. PROCEDURE: A persistently infected cow in which virus could not be detected in serum was housed with a BVDV-seronegative steer. Blood and nasal swab specimens were tested via virus isolation and serum virus neutralization. Parallel WBC preparations and sera from blood samples of 1,952 adult cows were screened for BVDV by use of IPMA. RESULTS: The steer seroconverted to BVDV within 4 weeks of contact with the cow. Virus was detected in sera and WBC of 5 adult cows that were verified as persistently infected by retest 3 weeks later. Cattle persistently infected with BVDV in which virus could not be detected in both serum and WBC by use of IPMA were not found. CONCLUSION AND CLINICAL RELEVANCE: Cattle persistently infected with BVDV in which virus cannot be detected in serum by use of IPMA may serve as virus reservoirs for infecting susceptible cattle. Persistent infection was detected at a prevalence of 0.26%. Screening adult cattle by use of IPMA on serum samples appears to be a reliable means of detecting persistent infection with BVDV. Prevalence of cattle persistently infected with BVDV that have negative results of IPMA on serum is extremely low.     

Severe clinical disease induced in cattle persistently infected with noncytopathic bovine viral diarrhea virus by superinfection with cytopathic bovine viral diarrhea virus

Eight healthy cattle that were persistently infected with noncytopathic bovine viral diarrhea virus (BVDV) were inoculated with cell culture fluids that contained noncytopathic or cytopathic BVDV. A severe disease occurred after inoculation with cytopathic BVDV. The clinical signs, lesions, and immune response were consistent with those of clinical BVDV infections.