PubMed · 5388318
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R L Taylor. 1969. Immunogenic differences between two Anaplasma marginale isolates.. https://pubmed.ncbi.nlm.nih.gov/5388318/
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Recent applications of DNA analysis, cloning, sequencing and expression technology have resulted in significant advances in our understanding of the hemoparasite Anaplasma marginale. Analysis of 16S ribosomal RNA has confirmed a phylogenetic position close to Ehrlichia sp. and Cowdria ruminantium. Intact genomic DNA of A. marginale digested with SfiI separates into bands from 14 to 170 kbp on pulse-field gels, with a total genome size of 1200-1260 kbp and G + C content of 56 mol%. Major surface proteins (MSP1-MSP5) have been identified and DNA coding sequences are available for most of these. These data have revealed that MSPs may be quite polymorphic between different geographic isolates, may be encoded by multi-gene families, and have some similar features to other prokaryotes including signal peptidase cleavage sites and gene regulatory sequences. Homologies have been detected between MSPs and immunodominant proteins of Cowdria ruminantium. Several MSPs have been expressed to high level and purified from recombinant Escherichia coli. MSP 1, 2 and 4 have potential for the development of vaccines and MSP3 and 5 for improved diagnostic assays.
An increased number of articles on the use of nucleic acid-based hybridization techniques for diagnostic purposes have been recently published. This article reviews nucleic acid-based hybridization as an assay to detect hemoparasite infections of economic relevance in veterinary medicine. By using recombinant DNA techniques, selected clones containing inserts of Anaplasma, Babesia, Cowdria or Theileria genomic DNA sequences have been obtained, and they are now available to be utilized as specific, highly sensitive DNA or RNA probes to detect the presence of the hemoparasite DNA in an infected animal. Either in an isotopic or non-isotopic detection system, probes have allowed scientists to test for--originally in samples collected from experimentally infected animals and later in samples collected in the field--the presence of hemoparasites during the prepatent, patent, convalescent, and chronic periods of the infection in the host. Nucleic acid probes have given researchers the opportunity to carry out genomic analysis of parasite DNA to differentiate hemoparasite species and to identify genetically distinct populations among and within isolates, strains and clonal populations. Prevalence of parasite infection in the tick vector can now be accomplished more specifically with the nucleic acid probes. Lately, with the advent of the polymerase chain reaction technique, small numbers of hemoparasites can be positively identified in the vertebrate host and tick vector. These techniques can be used to assess the veterinary epidemiological situation in a particular geographical region for the planning of control measures.
Live vaccines against hemoparasitic diseases in livestock are based on parasites derived from culture (Theileria annulata), from blood of infected animals (Babesia bovis, Babesia bigemina, Anaplasma centrale, (attenuated) Anaplasma marginale and Cowdria ruminantium), and from ticks (Theileria parva). The T. annulata attenuated cultured schizont vaccine is safe for all varieties of cattle. Blood derived vaccines are recommended mainly for young cattle, the age limit varying with the different vaccines and breeds of cattle. In older animals, monitoring of the individual response is needed. Immunization against T. parva requires simultaneous or postinoculation chemotherapy. The potential for accidental transmission of disease agents exists with all blood derived vaccines. Various degrees of resistance to field infection have been reported in animals immunized with live vaccines. Nevertheless, all of them engender a level of protection against natural challenge that justifies their use in field vaccination. Chemotherapy or chemoprophylaxis may prevent establishment of infection with the vaccinal parasites, and thus may interfere with elaboration of immunity. Outbreaks of disease in vaccinated herds, caused by antigenic variants among the tick-transmitted parasites, have been observed mainly in Babesia infections. In recent years, the main efforts towards improvement of live vaccines have been in the direction of replacing blood- and tick-derived parasites by those cultured in vitro under controlled standardized conditions.