Detection of antibodies to bovine leukemia virus in bovine milk samples with an ELISA involving two monoclonal antibodies.

An indirect enzyme-linked immunosorbent assay was used to detect antibody to bovine leukemia virus (BLV). In the assay the gp51 antigen was selectively adsorbed to the solid phase using a monoclonal capture antibody. Specific antibodies in milk or serum samples were revealed by the addition of a monoclonal antibovine IgG 1 conjugated to peroxidase. All milk samples from animals found positive by serum testing were shown to be positive. BLV-positive milk samples were detected when added to pools of negative samples.

Safety of a temperature-sensitive vaccine strain of bovine viral diarrhea virus in pregnant cows.

Safety tests were conducted in 78 pregnant cows vaccinated with a commercial preparation of a temperature-sensitive vaccine strain of bovine viral diarrhea (BVD) virus. After vaccination, seroconversion was detected in 33 (97%) of 34 cattle that did not have antibodies against BVD virus. Overall, 43 (91%) of 47 cows with prevaccination titers less than or equal to 4 seroconverted. During the test period, cows did not become naturally infected with BVD virus, and BVD-associated reactions to the vaccine were not observed in vaccinated cows. Calves born to vaccinated cows did not have clinical signs of fetal BVD. Precolostral blood samples collected from the progeny of cows that were seronegative at vaccination were free of antibody against BVD virus. Bovine viral diarrhea virus was not isolated from the cattle evaluated in the present study.

The neurovirulence of human and animal rotaviruses in cercopithecus monkeys.

Cercopithecus monkeys were inoculated according to the specifications of neurovirulence safety test for live rubella virus vaccine with RIT 4237, a rotavirus vaccine candidate. RIT 4237 is a high passage level of the Nebraska Calf Diarrhoea Virus (NCDV). The histological findings in the first test indicated some involvement of the central nervous system. The same test was therefore repeated with RIT 4237, with a lower passage level of the NCDV strain, and with the 'Wa' strain, a human virus grown in tissue culture. Clinical signs and histological findings were concordant and demonstrated that all the viruses were moderately neurovirulent. As in the poliovirus neurovirulence test, the histological lesions depended mainly upon a correct inoculation in the lumbar cord. RIT 4237 was found to have the same degree of neurovirulence as the low-passage NCDV or as the 'Wa' strain.

Clinical evaluation of a temperature-sensitive bovine viral diarrhea vaccine strain.

A naturally occurring strain of bovine viral diarrhea (BVD) virus was chemically treated to produce a genetically stable, temperature-sensitive mutant, designated RIT 4350. The RIT 4350 strain had a restrictive growth temperature of 39.5 C, so that systemic replication or fetal infection was not detected after parenteral administration in cattle. The RIT 4350 strain was tested as a cell culture-adapted vaccine in healthy heifers, immunodepressed calves, and pregnant cows. In a pathogenicity test in 5 healthy heifers, vaccination with 10 times the field dose resulted in seroconversion, but produced no clinical signs of disease or leukopenia. In a pathogenicity test in immunodepressed calves, 7 test animals were treated with dexamethasone and inoculated with 10 times the field dose. The calves developed mild enteric signs, but virus isolation attempts were negative. Following vaccination, the immunodepressed vaccinated calves were challenge exposed with the Osloss strain of BVD virus; all these vaccinated calves remained healthy. Two of 68 postchallenge serum samples from vaccinated calves were positive for BVD virus, compared with 9 of 20 samples from control calves. In another pathogenicity test, 7 pregnant cows vaccinated with 4 times the field dose seroconverted, remained clinically healthy, and delivered healthy calves.

Protection studies in colostrum-deprived piglets of a bovine rotavirus vaccine candidate using human rotavirus strains for challenge.

Studies were performed to evaluate the potential use of the bovine RIT 4237 rotavirus strain as a vaccine candidate against infection with human rotaviruses. Initial experiments revealed that colostrum-deprived piglets were susceptible to infection with several human strains, except for those belonging to subgroup 1. Subsequently, different immunization procedures with RIT 4237 were studied in this animal model. It was found that a two-dose administration, either given intramuscularly (twice) or once intramuscularly and once intragastrically, was necessary to induce a significant serum antibody response. Finally, the protective effect of the latter vaccination schedules against subgroup 2 and 3 rotavirus strains of human origin was evaluated by artificial challenge. In both cases, prior administration of live RIT 4237 significantly decreased fecal shedding of the challenge virus when compared with control animals.

Nontransmissibility of measles virus from vaccinated dogs to seronegative monkeys.

The nontransmissibility of the Edmonston strain of measles virus was demonstrated by failure to transmit the virus by aerosol from vaccinated pups to susceptible cercopithecus monkeys. Monkeys in direct contact for 3 weeks remained clinically normal and serologically negative for measles virus antibody.

RNAs of influenza virus recombinants derived from parents of known virulence for man.

Extensive use of recombinants made from A/PR/8/34 (H0N1) and wild, virulent H3N2 viruses as live influenza vaccines has provided a number of viruses of defined virulence for man. Clinical symptoms produced by these strains have ranged from febrile influenza to local coryzal symptoms or nil. A study was therefore made of the extent to which the PR8 genome had been incorporated into that of a number of the recombinants. By RNA--RNA hybridization it seemed that recombinants which had 55 per cent of greater homology with the PR8 parent were likely to conform an acceptable standard of attenuation. Those with lesser homology were frequently, but not always, clinically virulent. The technique seemed potentially useful, therefore, for screening PR8 live vaccine recombinants in vitro before giving them to volunteers.

Criteria in the evaluation of live intranasal influenza virus vaccines.

Live influenza virus vaccines should meet the following criteria: attenuation, immunogenicity, lack of spread, genetic stability, production in a suitable cell substrate, and stability during storage. In addition, they should be able to induce a wide antigenic protection. These various aspects will be discussed with reference to the "Alice" strain of live influenza A virus, which possesses all the properties for a good live attenuated virus vaccine.

Immunity studies in calves vaccinated with a multivalent live respiratory vaccine composed of I.B.R., parainfluenza 3 and bovine adenovirus type 3.

The persistence of systemic and local antibodies was studied after two intranasal administrations of the vaccine, six weeks apart. Systemic antibodies to I.B.R. and adenovirus 3 evoked by the vaccine were still present 21 weeks following the second dose of the vaccine. Inconslusive results were obtained regarding the persistence of systemic and local PI-3 antibodies because of an intercurrent natureal PI-3 infection occurring during the observation period. Local antibodies to adenovirus type 3 were found in a high percentage of vaccinated animals 21 weeks after the second dose of the vaccine, whereas local antibodies to I.B.R. remained detectable in 50% of the animals eight weeks after thesecond dose. The results of a challenge study 21 weeks after revaccination show that the presence of local and systemic antibodies prevent the multiplication of PI-3 and BAV-3 in the upper respiratory tract. Protection against I.B.R. was achieved in the absence of detectable local antibodies.

Candidate cytomegalovirus strain for human vaccination.

A strain of human cytomegalovirus called Towne was isolated in WI-38 human fibrolast cell cultures from the urine of an infected infant. It was then passaged 125 times in WI-38, including three clonings, and a pool was prepared in the same cell substrate for use as a potential live attenuated vaccine. The Towne virus has a broad antigenicity and cross-reacts with the AD-169 strain. Several markers of the Towne virus were found which differentiated it from fresh isolates. One of these was resistance of the former to trypsin. The Towne virus was tested for freedom from oncogenicity or other harmful effects in preparation for tests in humans.

Local and systemic response after simultaneous intranasal inoculation of temperature-sensitive mutants of parainfluenza 3, IBR and bovine adenovirus 3.

Triple seronegative calves were exposed by the nasal route to three (ts) mutants of bovine respiratory viruses (PI3, IBR, Adeno3). After a single exposure, they responded with significant levels of serum antibodies to the three viruses. Nasal antibodies were demonstrated for PI3 and adenovirus antigens. The failure to demonstrate nasal antibodies to IBR may be due to lack of sensitivity of the procedure used. When reexposed six weeks later, calves had sharp increases in levels of serum antibodies and developed a secondary type response at the local level for all three viruses. The persistence of the local antibodies was much longer after reexposure than after primary inoculation. This study indicates that the simultaneous application of these three (ts) viruses by the respiratory route is perfectly safe and affords a long lasting immunity towards homologous respiratory infections.