Molecular characterization of the Israeli B. bigemina vaccine strain and field isolates

The present study demonstrated the genetic character of the Israeli Babesia bigemina vaccine strain and field isolates, based on rap-1a and rap-1c gene sequences. The RAP-1a of blood-derived Israeli B. bigemina field isolates shared 100% amino acid sequence identity. However, comparison of RAP-1c from various Israeli B. bigemina field isolates revealed that the total sequence identity among the field isolates ranged from 98.2 to 100%. High identity was observed when RAP-1a sequences from the Israeli vaccine strain and field isolates were compared with RAP-1a from Egypt, Syria, Mexico and South Africa, while, the Israeli RAP-1c sequences showed the highest identity to the Mexican isolate JG-29 and to the PR isolate from Puerto-Rico. Based on sequence variations between the rap-1a of the vaccine strain and that of the field isolate, and between the rap-1c of the vaccine strain and that of the field isolates, nPCR-RFLP procedures were developed that enable, for the first time differentiation between the Israeli B. bigemina vaccine strain and field-infection isolates. These assays could serve as fast and sensitive methods for detection and differentiation between Israeli B. bigemina vaccine strains and field isolates, as well as for epidemiological investigations.

Differentiation between Israeli B. bovis vaccine strain and field isolates

The present study demonstrated for the first time the ability to distinguish between the Israeli Babesia bovis vaccine strain and field isolates. The existence of an additional EcoRI restriction site in the rhoptry-associated protein-1 (rap-1) gene, which is unique to the Israeli vaccine strain, and the abolition of one of the HaeIII restriction sites in the rap-1 gene of the vaccine strain enabled distinction between the Israeli B. bovis vaccine strain and field isolates, and this was the basis for polymerase chain reaction (PCR)-restriction fragment length polymorphism (RFLP) development. ClustalW sequence alignment of RAP-1-deduced amino acids of the Israeli B. bovis strains and of field isolates showed that the total sequence identity among the RAP-1 amino acid sequences ranged from 97.5% to 100%. However, comparison between amino acids of RAP-1 of the Israeli vaccine strain and of field isolates, on the one hand, and B. bovis strains from Argentina, Mexico, Brazil, and USA, on the other hand, revealed 90% identity. The PCR-RFLP assay offered the great advantage of being able to distinguish between vaccine and field isolates in mixtures and provide new insight into the molecular epidemiology of B. bovis infections in Israel.

Concomitant infection of cattle with the vaccine strain Anaplasma marginale ss centrale and field strains of A. marginale

Bovine anaplasmosis, caused by Anaplasma marginale, the intraerythrocytic rickettsia, is controlled by vaccination with live Anaplasma marginale ss centrale (A. centrale), a subspecies of relatively low pathogenicity. We have experimentally demonstrated that an animal primarily infected with A. marginale, or with the related vaccine subspecies A. centrale can be infected with the heterologous subspecies, and carries both bacteria. The co-infection was detected in experimentally cross-infected calves for up to 3 months after the last inoculation with the heterologous subspecies. The occurrence of characteristic cyclic rickettsemia of A. centrale and A. marginale was observed by examination of Giemsa-stained blood smears, or by the presence of specific rickettsial DNA confirmed in PCR assays based on specific msp1a and msp4 for A. marginale, and on specifically designed msp3 and msp4 primers for A. centrale. Sequence analysis of msp4-specific fragments for each subspecies revealed the presence of dual infection in both calves on days 30 and 60 after cross-inoculation with the heterologous Anaplasma subspecies. The experimental cross-infection of calves clearly demonstrated that the concept of "infection exclusion" does not apply to Anaplasma infection in cattle; as there was no infection exclusion of A. marginale in A. centrale-infected cattle, and vice versa. The present results confirmed our previous findings that cattle grazing in an anaplasmosis-endemic field were subject to concomitant infection with both the vaccine A. centrale and the field A. marginale strains.

Isolation of Neospora caninum from dairy zero grazing cattle in Israel

First Israeli Neospora caninum isolates were obtained from brain tissues of aborted fetuses (NcIs491 and NcIs580) from dairy farms endemic for neosporosis and maintaining cattle on zero grazing. Tissues from different parts of the fetus brains were used to infect Vero cells. Tachyzoites of N. caninum were first observed in cultures from days 30 and 32 after infection. To confirm the identity of the isolated parasites, DNA extracts from brains and cultures were tested by PCR with specific primers based on the Nc5 gene. Specific fragments were amplified by PCR from infected cultures of both fetuses on day 25. Susceptible seronegative gerbils (Meriones tristrami) were inoculated intraperitoneally with 10(3) to 10(5) tenfold dilutions of subculture tachyzoites. The inoculated gerbils developed specific antibodies to N. caninum, with end-point serum dilution of 1:4096 in the IFA assay, whereas no neurological signs or deaths were seen during 4 months of observation.

Babesia bigemina: attenuation of an Uzbek isolate for immunization of cattle with live calf- or culture-derived parasites

The virulence of an Uzbek isolate of Babesia bigemina, obtained from infected Boophilus annulatus ticks from an endemic area in Uzbekistan, was attenuated for immunization of cattle with autochthonous calf- or culture-derived parasites in Uzbekistan. After four "slow passages" in vivo the virulence was reduced, as evidenced by the response of calves inoculated with an experimental live frozen vaccine produced from the following passage. The vaccine was safe and protective against homologous virulent challenge under laboratory conditions. The culture-derived experimental vaccine was produced from cultures initiated after 3 passages in vivo followed by 22 passages in vitro. The cultured parasites did not elicit any clinical sign, but inoculated calves seroconverted following vaccination and were protected against the virulent homologous challenge. Both calf- and culture-derived vaccines were safe for cattle grazing in an endemic area in Uzbekistan. Despite the high polymorphism of B. bigemina, as reported from various geographical regions, the Central Asian strain was attenuated similarly to those that form the basis of the existing live B. bigemina vaccines in other parts of the world.

Application of PCR for Detection of Clostridium botulinum Type D in Bovine Samples

Diagnosis of botulism in cows is obtained by detecting the neurotoxin and/or Clostridium botulinum in the suspected animal. The standard method for detecting the toxin is the mouse bioassay. However, in recent years, the use of mice has become very costly and inconvenient in some facilities, and public pressure has been increasing to find alternatives to live animal bioassays. In this manuscript, we describe the use of the polymerase chain reaction (PCR) procedures in the diagnosis field cases of bovine type D botulism. Bovine samples from clinical cases diagnosed as C. botulinum type D according by clinical symptoms and bioassay resulted in expected PCR product ( approximately 497 bp) similar to the C. botulinum type D NCTC 8265 strain while the gene product was confirmed by sequence data.

Molecular and serological detection of A. centrale- and A. marginale-infected cattle grazing within an endemic area

A reverse line blot hybridization (RLB) one-stage nested PCR (nPCR) for Anaplasma centrale and a nested PCR for Anaplasma marginale were used to detect infected cattle grazing within an endemic region in Israel. A novel set of PCR primers and oligonucleotide probes based on a 16S ribosomal RNA gene was designed for RLB detection of both Anaplasma species, and the performance of the molecular assays compared. The immunofluorescent antibody test (IFA) was used to detect antibodies to both Anaplasma species, whereas, a highly sensitive and specific competitive enzyme-linked immunosorbent assay (cELISA) was used to detect antibodies in A. centrale-vaccinated cattle. The RLB and the nested PCR procedures showed bacteremia with sensitivity of 50 infected erythrocytes per milliliter. Up to 93% of the A. centrale vaccinates carried specific antibodies that were detected by cELISA, and up to 71% of the vaccinated cattle were found to be naturally infected with A. marginale according to the PCR and the RLB assays. Nevertheless, no severe outbreaks of A. marginale infection occurred among vaccinated herds in this endemic region. It appears that both, molecular tools and serology are useful for evaluation of the vaccine efficacy. In the light of wide natural field infection with A. marginale, strong recommendations to continue the A. centrale vaccination program regime will continue until a new generation of non-blood-based vaccine will be developed.

Vaccination of older Bos taurus bulls against bovine babesiosis

Two separate groups of Bos taurus bulls, one of 106 and the second of 27 animals, imported to Israel from areas free of Babesia bovis and Babesia bigemina, were vaccinated against babesiosis with a bivalent live attenuated vaccine. In light of the fact that routine vaccination is recommended at the weaning age, these bulls--of highly susceptible breeds--were kept under close surveillance to prevent losses that might be caused by severe clinical reactions to their vaccination at the age of 16-18 months. Seven days after vaccination, about one-third of the 106 bulls in the first group developed clinical signs of B. bigemina infection, which peaked at day 9, and then diminished from day 11, when the patent period known for B. bovis infection was observed. Because of the severe clinical responses a total of 36% of the bulls required babesicidal treatment. Despite the treatment Babesia were not sterilized: 33 and 68% of the animals remained PCR positive for B. bigemina and B. bovis, respectively. To mitigate the severe responses to vaccination, the 27 bulls of the second group were vaccinated in two-steps: they were inoculated initially with avirulent culture-derived parasites and then vaccinated with the conventional donor-derived vaccine a month later. None of the bulls in the latter group developed clinical babesiosis, all were serologically positive to B. bigemina, and 67% showed seroconversion to B. bovis. In light of the experience described here, it is suggested that sensitive older cattle be vaccinated against babesiosis by priming them with avirulent in vitro-cultured parasites and then inoculating them with the conventional donor-derived vaccines.

Molecular conservation of MSP4 and MSP5 in Anaplasma marginale and A. centrale vaccine strain

Anaplasma centrale msp4 and msp5 genes were cloned and sequenced, and the recombinant proteins were expressed. The identity between Anaplasma marginale and A. centrale MSP4 was 83% in the nucleotide sequences and 91.7% in the encoded protein sequences. A. centrale msp5 nucleotide sequences shared 86.8% identity with A. marginale msp5, and there was 92.9% homology between A. centrale and A. marginale encoded amino acids of the MSP5 protein. Southern blots hybridized with probes derived from the msp4 and msp5 central regions indicate that msp4 and msp5 of A. centrale are encoded by single copy genes. Recombinant MSP4 and MSP5 fusion proteins reacted with anti-A. marginale monoclonal antibodies ANAR76A1 and ANAF16C, respectively, demonstrating the conservation of conformation-sensitive B-cell epitopes between A. centrale and A. marginale. These data demonstrate the structural and antigenic conservation of MSP4 and MSP5 in A. centrale and A. marginale. This conservation is consistent with the cross-protective immunity between A. marginale and A. centrale and supports the development of improved vaccines based upon common outer membrane proteins.

Detection of the Anaplasma centralevaccine strain and specific differentiation from Anaplasma marginale in vaccinated and infected cattle

Bovine anaplasmosis caused by the intraerythrocytic rickettsia Anaplasma marginale is the most prevalent tick-borne disease of cattle worldwide. The most efficient method to control anaplasmosis is by vaccination using live Anaplasma centrale, a closely related species or subspecies of low pathogenicity that is capable of inducing significant protection against the more virulent A. marginale. In the present study, we applied PCR assays to detect and discriminate field infection with A. marginale from A. centrale persistently infected vaccinates. Direct and one-stage nested PCR were based on A. centrale mbp58 specific sequence, with the assay sensitivity level of 0.00001% for nested PCR performed in a single amplification step. Size polymorphism in the A. marginale msp1 alpha gene among strains was used to design a PCR capable of discriminating between the Israel T and NT strains of A. marginale and the encoded MSP1a size polymorphism was confirmed by immunoprecipitation. The detection of A. centrale in 72% of vaccinated field-grazing cattle clearly indicated that the majority of vaccinated cattle remain carriers. A. marginalewas detected in 64% of these vaccinated cattle, demonstrating that, as expected, natural transmission occurs within the endemic region. The lack of severe A. marginaleoutbreaks in this region, despite ongoing transmission, is consistent with protection being provided by widespread vaccination with A. centrale.

Molecular characterization of an unassigned Israeli Newcastle disease virus isolate

Detection of Newcastle disease virus (NDV) and avian pathotyping of NDV isolates are extremely important because the appearance of virulent virus has significant economic consequences in terms of vaccination, eradication, and the ability to export poultry products. By using nucleotide and amino acid (aa) homology analysis, we could demonstrate that a NDV broiler isolate is a velogenic virus. This analysis was done after mean death time and intracerebral pathogenicity index tests gave inconsistent results. By establishing a nucleotide sequence dendrogram, we found that the disputed Ber-Tuvia was clearly in the same group as the known Herev-Laet, a velogenic isolate. The difference between Ber-Tuvia 92 and the Herev-Laet velogenic isolate was 6% as opposed to > 16% of the meso- and lentogenic isolates. The Ber-Tuvia isolate contains the Arg/Arg and Lys/Arg aa at positions 112, 113 and 115, 116, respectively, in the fusion protein cleavage aa sequence, which is typical for virulent NDV isolates.

A ribozyme targeted to cleave the polymerase gene sequences of different foot-and-mouth disease virus (FMDV) serotypes

Vaccinations against foot-and-mouth disease virus (FMDV) has dramatically reduced the number of disease outbreaks. Nevertheless, there are still many outbreaks in different regions around the world. In an effort to find new ways to control the disease, ribozymes able to cleave FMDV were designed and tested. In this work we tested the ability of FRZ4, a ribozyme targeted to the viral polymerase gene, to cleave polymerase sequences of several FMDV. Homology analysis was used to choose target sequences which consist of two conserved GUC which lie 15 bases apart and, their flanking sequences. These were the basis for the FRZ4 ribozyme gene sequence that contains two catalytic domains. We show that polymerase sequences from A, Asia 1, C and two different O1 Israeli isolates could be specifically cleaved by FRZ4. It is suggested that FRZ4 can cleave polymerase gene sequences from any FMDV serotype.

Molecular epidemiology of foot-and-mouth disease (FMD) in Israel in 1994 and in other Middle-Eastern countries in the years 1992-1994

The reverse transcriptase-polymerase chain reaction (RT-PCR) and direct sequencing were employed in the diagnosis and typing of foot-and-mouth disease virus (FMDV) in samples taken during the 1994 disease outbreak in Israel. Using PCR, virus isolation and serological methods it was shown that the 1994 disease outbreak in Israel and other Middle-Eastern countries was caused by O1 type virus. Direct PCR sequencing of VP1 genes and homology analysis of the virus isolates revealed that there were two distinct outbreaks in Israel. The first originated in Jordan, moved to the West Bank territory and then to the Lower Galilee. The second outbreak, caused by another virus, was responsible for disease outbreaks in South Lebanon, Upper Galilee and the Golan Heights. When viral sequences of isolates from the 1993 outbreaks in Egypt and Lebanon were included in the analysis, they showed a high degree of VP1 sequence homology between themselves, suggesting a common origin.

Cleavage of transcripts of foot and mouth disease virus (FMDV), Asia1 serotype, by ribozymes targeted to the VP3 and VP4 genes

Two ribozyme genes were designed to cut within the VP4 and VP3 sequences of foot and mouth disease virus (FMDV) Asia1 serotype genome. The two genes were synthesized and cloned into pBluescript under the control of the T3 promoter. The ribozyme designed to cut the VP4 gene contained two catalytic sequences targeted to two GUC triplets that are 16 bases apart. The second ribozyme, intended to cut VP3, contained one catalytic sequence. Ribozymes obtained from run-off transcription from both plasmids were able to cleave viral RNA derived from runoff transcripts of plasmids carrying the proper FMDV cDNA inserts. The significance of these findings is discussed.

Detection and subtyping of foot-and-mouth disease virus in infected cattle by polymerase chain reaction and amplified VP1 sequencing

Fast and accurate detection of foot-and-mouth disease (FMD) outbreaks is needed to limit spread of the disease by proper vaccination. The use of the polymerase chain reaction (PCR) has revolutionized the way in which viral diseases are diagnosed. Sequence analysis of the amplified VP1 sequence can enable the classification of FMD virus detected in the morbid animal. PCR assays were carried out to identify the virus and its serotype in suspect animals from 2 outbreaks of FMD type O virus. Sequence analysis of the amplified VP1 cDNA showed 78% homology with O1K and over 95% homology between the samples. These findings suggest that the 2 outbreaks were due to infection with the same virus serosubtype.

Applications of the polymerase chain reaction to detect infectious bursal disease virus in naturally infected chickens

Reverse transcriptase-polymerase chain reaction was used for identification of Israeli isolates of infectious bursal disease virus (IBDV). The system was applied to tissue culture and to bursa of Fabricius from infected chickens; these latter samples had been frozen for as long as 4 years. From base homology analysis of published sequences of serotype 1 IBDV, two pairs of primers, targeted to amplify sequences from the VP2 and VP3 cistrons, were prepared. The two sets of primers could detect viruses of serotype 1. The primers directed to the cistrons could detect viral sequences from seven infected chickens. No reaction was detected with RNA extracted from bursal cells of healthy chickens or from uninfected cells. The sensitivity of the reaction was equivalent to 2.5 x 10(1) TCID50.

Nucleotide sequence of the P1 region of serotype Asia1 foot-and-mouth disease virus

Differences in the amino acid sequence of foot-and-mouth disease virus (FMDV) virion proteins (VP) among the various FMDV serotypes, particularly in the VP1 polypeptide, are the basis for antigenic diversity of this virus group. This phenomenon provides the basis for type diagnosis of FMDV by the polymerase chain reaction (PCR). In order to specifically identify the Asia1 FMDV serotype by PCR, the nucleotide sequence of its P1-coding region was determined. The sequence exhibited over 70% homology with the P1 gene segment of type O1k. The deduced amino acid sequence shares 79% homology with that of the P1 region of serotype O1k.

A possible approach to enrich cDNA yields with full-length molecules

Newcastle disease virus (NDV)-specific hemagglutinin-neuraminidase (HN) mRNAs were used as the model templates for cDNA synthesis. Polyadenylated RNAs were isolated from the particulate fraction of cytoplasmic extracts of NDV-infected cells rather than from nonfractionated extracts. The approach is based on earlier findings that eucaryotic mRNAs are present in cytoplasmic extracts in the form of ribonucleoproteins (mRNPs) rather than as free nucleic acids. The idea of the approach was to separate mRNPs from cell sap RNases prior to RNA extraction in order to minimize partial enzymatic hydrolysis of mRNAs. The presence of the 5' terminus (mRNA sense) in cDNAs synthesized was considered as an indication for the suitability of mRNA templates for cDNA synthesis. The cDNAs were synthesized and cloned in lambda gt10 phage. About 300 phages carrying the HN-specific inserts have been identified among 50,000 recombinants, and nine of them were analyzed for the presence of the HN 5' terminus. It was found that the termini are present in all the clones analyzed. The result is in an agreement with the expectation that removal of cell sap prior to RNA extraction significantly increases the suitability of RNA templates for cDNA synthesis.