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At least 955 records · Page 53Linked to original sources
PubMed1997

Different organisms associated with heartwater as shown by analysis of 16S ribosomal RNA gene sequences.

Cowdria ruminantium is a rickettsial parasite which causes heartwater, a economically important disease of domestic and wild ruminants in tropical and subtropical Africa and parts of the Caribbean. Because existing diagnostic methods are unreliable, we investigated the small-subunit ribosomal RNA (srRNA) gene from heartwater-infected material to characterise the organisms present and to develop specific oligonucleotide probes for polymerase chain reaction (PCR) based diagnosis. DNA was obtained from ticks and ruminants from heartwater-free and heartwater-endemic areas from Cowdria in tissue culture. PCR was carried out using primers designed to amplify only rickettsial srRNA genes, the target region being the highly variable V1 loop. Amplicons were cloned and sequenced; 51% were C. ruminantium sequences corresponding to four genotypes, two of which were identical to previously reported C. ruminantium sequences while the other two were new. The four different Cowdria genotypes can be correlated with different phenotypes. Tissue-culture samples yielded only Cowdria genotype sequences, but an extraordinary heterogeneity of 16S sequences was obtained from field samples. In addition to Cowdria genotypes we found sequences from previously unknown Ehrlichia spp., sequences showing homology to other Rickettsiales and a variety of Pseudomonadaceae. One Ehrlichia sequence was phylogenetically closely related to Ehrlichia platys (Group II Ehrlichia) and one to Ehrlichia canis (Group III Ehrlichia). This latter sequence was from an isolate (Germishuys) made from a naturally infected sheep which, from brain smear examination and pathology, appeared to be suffering from heartwater; nevertheless no Cowdria genotype sequences were found in this isolate. In addition no Cowdria sequences were obtained from uninfected ticks. Complete 16S rRNA gene sequences were determined for two C. ruminantium genotypes and for two previously uncharacterised heartwater-associated Ehrlichia spp. Sequenced difference within the V1 loop were sufficient for the derivation of four Cowdria genotype-specific oligonucleotide probes. Four further probes were designed; one for the detection of any Cowdria genotype, one for the detection of any Group II Ehrlichia sp., one for any Group III Ehrlichia sp. and one for all Pseudomonadaceae. All the probes were specific except that for the Cowdria (Ball 3) genotype. The high prevalence (96%) in field samples of pseudomonad-like 16S sequences was the result of environmental contamination. The probes were used to screen DNA from goats in an area free of both Amblyomma ticks and clinical heartwater. A substantial proportion (42%) gave positive reactions for the apparently apathogenic Cowdria (Omatjenne), indicating that this genotype is relatively common.

Animals↗
PubMed1993

Application of enzyme-linked immunosorbent assay for epidemiological studies of diseases of livestock in the tropics of Mexico.

This study was conducted at the Centre for Research, Teaching and Extension in Tropical Livestock (Centro de Investigación, Enseñanza y Extensión en Ganadería Tropical) of the Faculty of Veterinary Medicine of the National Autonomous University of Mexico. During the latter part of 1986 and throughout 1988 and 1989, the herd of Holstein x zebu cattle at the University was tested for IgG antibodies to twenty-one viral, bacterial, rickettsial and parasitic agents. Antigens prepared from twenty infectious disease agents were used as the solid phase in an enzyme-linked immunosorbent assay, and the agar gel immunodiffusion procedure was used to test for antibodies against bovine leukaemia virus. The prevalence of IgG antibodies was high (> 50%) for bluetongue virus, Anaplasma marginale and Mycoplasma bovis. Antibodies to Brucella abortus were absent and antibodies against bovine virus diarrhoea virus and infectious bovine rhinotracheitis virus showed a very low prevalence (< 5%). Antibodies to fifteen other antigens showed intermediate prevalence (15-46%). Antibodies to Campylobacter fetus, A. marginale, bluetongue virus, bovine leukaemia virus and Haemophilus somnus displayed seasonal variations. Levels of antibody to bovine leukaemia virus, M. bovis and Listeria monocytogenes exhibited increasing secular trends while antibodies to bovine virus diarrhoea virus and C. fetus showed declining trends. Prevalence of antibodies increased with the age of animals tested. No consistent difference in antibody prevalence was found between three genotypic groups examined.

Age Factors↗
PubMed1987

[Studies in the field of tick-borne blood parasites].

A review of 'piroplasmosis' (a collective name tick-borne protozoan forms of disease of the blood (babesiasis, theileriasis) as well as rickettsial forms (anaplasmosis), written by De Blieck and published in 1916, is compared with the present state of our knowledge. Considerable progress has been made in classifying the causative agents. Moreover, the situation in the Netherlands has become much clearer. However, as regards the situation in the tropics, progress in control is rather limited and these forms of disease continue to be of major economic importance. The use of ascaricides is becoming increasingly confronted with problems and, in particular conditions, the use of cattle characterised by a considerable genetically acquired ability to produce an immune response to ticks is growing. In addition, it is hoped that it will be possible to immunise animals both against ticks and against tick-borne disease using characterised antigens produced by modern biotechnological methods in the future. Finally, a warning note is sounded that the active role of the faculty of veterinary science in the field of tropical veterinary medicine could well be reduced in the near future as a result of economies and changes of structure.

Animals↗
PubMed1995

Review of the molecular biology of Cowdria ruminantium.

Cowdria ruminantium is a rickettsial agent which causes heartwater, an economically important disease of livestock in the tropics and the Caribbean. Significant advances have been made in the molecular biology of C. ruminantium since its reproducible propagation in vitro in bovine endothelial cells. These advances have been targeted towards the development of improved vaccines and diagnostic tests. Several immunogenic proteins of C. ruminantium have been identified and monoclonal antibodies have been developed to some. The gene for the 21 kDa C. ruminantium protein has been cloned, characterized, sequenced and expressed to high levels to produce a recombinant analogue. This gene is conserved amongst all C. ruminantium isolates tested. The gene for the immunodominant 32 kDa protein has also been cloned recently. Analysis shows that this protein varies structurally between different C. ruminantium isolates. Recombinant protein analogues will have application in vaccine studies and subunit enzyme-linked immunosorbent assay (ELISA) developments. In the field of serology, a 32 kDa protein specific competitive ELISA (cELISA) is available and a 21 kDa protein specific direct and a cELISA is being developed. Detection of C. ruminantium in Amblyomma ticks and in animals is now possible using DNA and RNA probes and the sensitivity of these nucleic acid based assays is being maximized using polymerase chain reaction (PCR). Sequencing of the 16s rRNA gene has revealed the close phylogenetic relationship of C. ruminantium to Rickettsia, Anaplasma and Ehrlichia species. The implications of these studies will be discussed.

Animals↗
PubMed1976

Immunization against anaplasmosis and babesiosis: Part I. Evaluation of immunization using minimum infective doses under laboratory conditions.

A method of immunization against anaplasmosis and babesiosis using minimum infective doses was developed under laboratory conditions. Stabilates of Anaplasma marginale stored at -60 degrees C were found infective when diluted 10-fold to 10(-3). Stabilates of Babesia argentina and Babesia bigemina stored under the same conditions were infective when diluted 10-fold to 10(-1). Intact calves inoculated with the above dilutions of stabilates developed moderate parasitemias and recovered from infection without treatment. There was an immune response to vaccination with the formation of specific antibodies to A. marginale, B. bigemina and B. argentina as measured by the complement fixation (CF) test. All calves were found resistant to artificial challenge with lethal doses of the respective parasites.

Anaplasmosis↗
PubMed1986

Q fever vaccination of sheep: challenge of immunity in ewes.

Adult ewes (17 months of age) were vaccinated against Coxiella burnetii, using a formalin-inactivated whole cell (WC) phase I Henzerling strain vaccine or a chloroform methanol residue (CMR) vaccine. Nineteen pregnant ewes were placed in 3 categories [(i) unvaccinated, (ii) WC vaccine, and (iii) CMR vaccine] and were challenge exposed at approximately the 100th day of gestation with 210,000 plaque-forming units of C burnetii inoculated subcutaneously. Shedding of rickettsiae was measurably reduced, but was not prevented in vaccinated groups, as shown by inoculating ewes' placental tissues, amniotic fluid, and colostrum into mice, as well as by histopathologic lesions of placental tissues. The rickettsiae were shed in the placenta, amniotic fluid, or colostrum in 6 nonvaccinated ewes. In comparison, rickettsiae were detected in placental inoculations from 2 of 6 ewes in the WC vaccine group and 1 of 6 in the CMR group. In contrast to those in the vaccinated ewes, placentitis, high concentrations of rickettsiae in microscopic preparations, and weak lambs were typical for the nonvaccinated ewes.

Animals↗
PubMed1983

[A method of production of concentrated and purified vaccine against Chlamydia abortion in sheep and its testing in guinea pigs].

A method was developed for the production of a new, present day, concentrated depot-vaccine against the chlamydial abortion of sheep. Employed were a number of methods -- those with chick embryos, freezing and thawing with the use of liquid nitrogen, inactivation with formalin, purifying and concentration through differential centrifugation and supercentrifugation, with the use of an aluminum hydroxide ingredient, electron microscopy, and the respective control series, etc. The vaccine is characterized by low dosing, complete innocuity, and unreactiveness. Guinea pigs immunized singly responded with the production of complement-fixing antibodies on the 30th day of an average titer ranging from 1:32 to 1:64. Two-fold immunization on the 1st and 30th day led to the production of antibodies of average titers within the 1:256-1:512 range as established by means of CFT. The vaccine was shown to have a low prime cost.

Abortion, Veterinary↗
PubMed2006

African tick bite fever: a not-so-uncommon illness in international travelers.

BACKGROUND: African tick bite fever is a rickettsial illness that has recently emerged as a significant disease among international travelers. The vector is the Amblyomma tick, which is endemic to sub-Saharan Africa and parts of the eastern Caribbean. OBSERVATIONS: We describe a middle-aged woman who returned from a mission trip to Zimbabwe with an influenzalike illness and inoculation eschar; she also had a history of travel to a game farm. Biopsy revealed a histopathologic pattern consistent with an infectious pathogenesis. Immunohistochemical staining confirmed the presence of rickettsial organisms. In light of the patient's history, the clinical constellation of signs and symptoms, and the results of ancillary laboratory testing, a diagnosis of African tick bite fever was made. The patient was treated with doxycycline hydrochloride and had an uncomplicated course. CONCLUSIONS: This report further highlights the epidemiological and clinical features of African tick bite fever. With the increase in international travel, it is important to recognize the illness in those who have been to endemic countries and to counsel patients regarding preventive measures for planned travel.

Animals↗
PubMed1985

[Clinico-epidemiological characteristics of Q fever in the Carpathian region].

The study of the specific epidemiological and clinical features of Q fever revealed the existence of an active focus of infection among humans due to their contacts with agricultural animals in one of the districts of the region. The focus was manifested by group morbidity among the cattle-tending personnel of a dairy farm. The source of this infection was cattle. The infection was transferred mainly through the air. The disease took a moderately severe course. The study of the rickettsial contamination of humans, animals and ticks suggested the presence of the active epidemic process and made it possible to work out concrete antiepidemic measures.

Agricultural Workers' Diseases↗