Publications

parasites of domestic and wild animals in south africa. l. ixodid ticks infesting horses and donkeys.	the aim of the study was to determine the species spectrum of ixodid ticks that infest horses and donkeys in south africa and to identify those species that act as vectors of disease to domestic livestock. ticks were collected opportunistically from 391 horses countrywide by their owners or grooms, or by veterinary students and staff at the faculty of veterinary science, university of pretoria. ticks were also collected from 76 donkeys in limpopo province, 2 in gauteng province and 1 in north we ...	2017	28281774
molecular detection of zoonotic tick-borne pathogens from ticks collected from ruminants in four south african provinces.	ticks carry and transmit a remarkable array of pathogens including bacteria, protozoa and viruses, which may be of veterinary and/or of medical significance. with little to no information regarding the presence of tick-borne zoonotic pathogens or their known vectors in southern africa, the aim of our study was to screen for anaplasma phagocytophilum, borrelia burgdorferi, coxiella burnetii, rickettsia species and ehrlichia ruminantium in ticks collected and identified from ruminants in the easte ...	2015	26227797
veterinary extension on sampling techniques related to heartwater research.	heartwater, a tick-borne disease caused by ehrlichia ruminantium, is considered to be a significant cause of mortality amongst domestic and wild ruminants in south africa. the main vector is amblyomma hebraeum and although previous epidemiological studies have outlined endemic areas based on mortalities, these have been limited by diagnostic methods which relied mainly on positive brain smears. the indirect fluorescent antibody test (ifa) has a low specificity for heartwater organisms as it cros ...	2010	21247042
climate changes and suitability for the ticks amblyomma hebraeum and amblyomma variegatum (ixodidae) in zimbabwe (1974-1999).	the spread of amblyomma hebraeum has been reported in zimbabwe. at the same time there was little or no spread in the distribution of amblyomma variegatum. this paper examines the climatic cycles and their trends in the period 1974-1999 with a view to explaining the abiotic causes of this spread, and of forecasting the likely tendency in climate suitability for both tick species. an annual data-set of rainfall and air temperature was used as a source for climate, together with a habitat-modeling ...	2008	18083309
amblyomma variegatum in cattle in marie galante, french antilles: prevalence, control measures, and infection by ehrlichia ruminantium.	we report marie galante as one of the caribbean islands most heavily infested by the tropical bont tick (tbt) amblyomma variegatum which is associated with two major diseases of ruminants: heartwater and dermatophilosis. in 2005, a survey was undertaken to assess the prevalence of tbt infestation in cattle, the prevalence of ehrlichia ruminantium infection in tbts, and the tick control measures implemented by livestock owners. a random sample of 195 cattle herds out of 1885 recorded on the islan ...	2008	18406061
a quantitative real-time pcr assay for ehrlichia ruminantium using pcs20.	heartwater is a tick borne disease that affects ruminants and wild animals in africa south of the sahara. it is caused by ehrlichia ruminantium and transmitted by the tick amblyomma hebraeum. the protocols currently used to detect heartwater take several days to complete. here, we describe the development of a pcs20 quantitative real-time pcr taqman probe assay to detect e. ruminantium in livestock blood and ticks from the field. the assay is based on the conserved pcs20 gene region of e. rumina ...	2008	18511221
science and popular participation in the investigation of heartwater in south africa, c. 1870-1950.	during the late nineteenth century, settler farmers in southern africa identified heartwater as a damaging disease of small stock and cattle. they advanced various explanations of the disease, including the theory that it was caused by the bite of ticks. around 1900, the american entomologist c.p. lousbury demonstrated that heartwater was transmitted by the bont tick. he also worked out the life cycle and life habits of the tick. subsequently, farmers developed methods of controlling ticks by di ...	2008	20055238
an attenuated ehrlichia ruminantium (welgevonden stock) vaccine protects small ruminants against virulent heartwater challenge.	heartwater is a tick-borne disease of ruminants caused by the intracellular rickettsia ehrlichia ruminantium. the only commercially available immunization procedure involves infecting animals with cryopreserved sheep blood containing virulent e. ruminantium organisms, followed by treatment with tetracyclines when fever develops. the virulent welgevonden stock of e. ruminantium was attenuated by continuous propagation of the organisms in a canine macrophage-monocyte cell line (dh82), followed by ...	2005	15705474
comparing the detection of exposure to ehrlichia ruminantium infection on a heartwater-endemic farm by the pcs20 polymerase chain reaction assay and an indirect map1-b enzyme linked immunosorbent assay.	detection of heartwater is not always easy especially because all the serological assays so far available either have poor sensitivity or specificity. the indirect map-1b elisa has been reported to be the most specific test for heartwater, although it does also detect antibodies to some closely related ehrlichial agents. this study was undertaken to compare two methods for the detection of heartwater infection caused by the ehrlichial agent ehrlichia (cowdria) ruminantium. fifteen cattle on a he ...	2003	14621319
introduction of the exotic tick amblyomma hebraeum into florida on a human host.	a resident of florida returned from a short visit to southern africa to find a male amblyomma hebraeum tick attached to the skin behind her knee. amblyomma hebraeum is a major vector of 2 pathogens that cause important diseases in southern africa, heartwater of ruminants and african tick-bite fever of humans. the tick was tested by polymerase chain reaction assay for evidence of infection with cowdria ruminantium and rickettsia africae (the causative agents of heart-water and african tick-bite f ...	2002	12197136
the prevalence of cowdria ruminantium in free-living adult amblyomma hebraeum collected at a communal grazing area and in 2 wildlife reserves in south africa.	in order to detect the prevalence of cowdria ruminantium in the vector tick, amblyomma hebraeum, free-living, unfed adult ticks were collected with the aid of pheromone/co2 traps. ticks were collected at the rietgat communal grazing area, as well as in the southwestern kruger national park and in the songimvelo game reserve, all located in heartwater-endemic areas of south africa. the presence of c. ruminantium in these ticks was determined by polymerase chain reaction (pcr) analysis. ticks from ...	2002	12515301
antibody responses to map 1b and other cowdria ruminantium antigens are down regulated in cattle challenged with tick-transmitted heartwater.	serological diagnosis of heartwater or cowdria ruminantium infection has been hampered by severe cross-reactions with antibody responses to related ehrlichial agents. a map 1b indirect enzyme-linked immunosorbent assay that has an improved specificity and sensitivity for detection of immunoglobulin g (igg) antibodies has been developed to overcome this constraint (a. h. m. van vliet, b. a. m. van der zeijst, e. camus, s. m. mahan, d. martinez, and f. jongejan, j. clin. microbiol. 33:2405-2410, 1 ...	2001	11238227
resistance of leopard tortoises and helmeted guineafowl to cowdria ruminantium infection (heartwater).	experimental infection trials were conducted to investigate susceptibility of leopard tortoises (geochelone pardalis) and helmeted guineafowl (numida meleagris) to infection with cowdria ruminantium, the causative agent of heartwater, a tickborne disease of domestic and wild ruminants. ten guineafowl were inoculated intravenously with a virulent dose of c. ruminantium derived from bovine endothelial cell cultures, and four leopard tortoises were exposed to c. ruminantium infection by the feeding ...	2001	11423187
competence of the african tortoise tick, amblyomma marmoreum (acari: ixodidae), as a vector of the agent of heartwater (cowdria ruminantium).	the ability of the african tortoise tick, amblyomma marmoreum, to acquire and transmit cowdria ruminantium infection was investigated experimentally with transmission trials and with a c. ruminantium-specific polymerase chain reaction (pcr) detection assay. laboratory-reared a. marmoreum larvae and nymphs were fed on small ruminants with clinical heartwater. after molting, the resultant nymphs were fed on cowdria ruminantium-naive sheep (n = 3), and the adults were ground and inoculated intraven ...	2000	10864237
comparison of efficacy of american and african amblyomma ticks as vectors of heartwater (cowdria ruminantium) infection by molecular analyses and transmission trials.	the ability of amblyomma americanum, amblyomma cajennense, amblyomma maculatum, and amblyomma variegatum to acquire and transmit cowdria ruminantium infection was investigated. uninfected nymphs were fed on clinically reacting c. ruminantium-infected sheep and then analyzed for infection by specific dna detection assays and by tick transmission trials. by polymerase chain reaction (pcr), the mean infection prevalence of a. maculatum ticks (50.7%) was similar to that of a. variegatum, elevage str ...	2000	10701562
detection of the agent of heartwater, cowdria ruminantium, in amblyomma ticks by pcr: validation and application of the assay to field ticks.	we have previously reported that the pcs20 pcr detection assay for cowdria ruminantium, the causative agent of heartwater disease of ruminants, is more sensitive than xenodiagnosis and the pcs20 dna probe for the detection of infection in the vector amblyomma ticks. here, we further assessed the reliability of the pcr assay and applied it to field ticks. the assay detected dna of 37 isolates of c. ruminantium originating from sites throughout the distribution of heartwater and had a specificity ...	2000	10747140
the occurrence of theileria and cowdria parasites in african buffalo (syncerus caffer) and their associated amblyomma hebraeum ticks.	the polymerase chain reaction and oligonucleotide probing were used to detect theileria and cowdria species in dna extracted from blood and ticks recovered from 24 african buffalo during a gamecapture operation in the kruger national park, south africa. species-specific probing indicated that all but one of the buffalo were carrying at least one theileria species. indirect fluorescent antibody (ifa) serology indicated that all animals had been exposed to theileria parva infection but only 33% we ...	1999	10631711
evaluation of 16s, map1 and pcs20 probes for detection of cowdria and ehrlichia species.	a panel of 16s ribosomal rna gene probes has been developed for the study of the epidemiology of heartwater; five of these detect different cowdria genotypes, one detects five distinct genotypes; one detects any group iii ehrlichia species other than cowdria and one detects any group ii ehrlichia species. these probes have been used on pcr-amplified rickettsial 16s rrna genes from over 200 amblyomma hebraeum ticks. control ticks were laboratory-reared and either uninfected or fed on sheep experi ...	1999	10355799
susceptibility and carrier status of impala, sable, and tsessebe for cowdria ruminantium infection (heartwater).	three species of wild african ruminants, impala (aepyceros melampus), sable (hippotragus equinus), and tsessebe (damaliscus lunatus), were experimentally inoculated with in vitro culture-derived cowdria ruminantium organisms, the tick-borne causative agent of heartwater in domestic ruminants, to determine their susceptibility to infection. no clinical disease was observed in any of the ruminants. however, c. ruminantium was detected in the sable by the transmission of heartwater to susceptible s ...	1999	10386439
cowdria ruminantium infection in ticks in the kruger national park.	adult amblyomma hebraeum ticks, the principle vector of heartwater (cowdriosis) of domestic ruminants in southern africa, were collected in pheromone traps placed in kruger national park, an exclusively wildlife sanctuary in south africa. these ticks transmitted cowdria ruminantium, the rickettsial agent causing heartwater, to a susceptible goat, resulting in acute, fatal disease. c ruminantium was isolated in bovine endothelial cell culture from the plasma of this animal during the febrile stag ...	1999	10515616
prevalence of cowdria ruminantium infection in amblyomma hebraeum ticks from heartwater-endemic areas of zimbabwe.	analysis of the transmission dynamics of cowdria ruminantium, the tick-borne rickettsial agent of heartwater in ruminants, requires accurate measures of infection in vector populations. to obtain these, amblomnia hebraeum ticks were collected at two heartwater-endemic locations in the lowveld and highveld regions of zimbabwe and assessed for c. ruminantium infection with specific polymerase chain reaction (pcr) and dna probe detection assays. at the lowveld site, 11.2% (50/446) of adult ticks an ...	1999	10579452
pcr detection of cowdria ruminantium infection in ticks and animals from heartwater-endemic regions of zimbabwe.	the development of a pcr assay for the detection of cowdria ruminantium infection in ticks has been previously described. here we report a further evaluation of this assay by comparison with a dna probe and with the mouse inoculation assay (mia). application of the pcr assay in determining the prevalence of infection in ruminants and ticks from heartwater-endemic areas of zimbabwe is also described. one hundred uninfected and 120 infected amblyomma hebraeum ticks were analyzed by pcr, dna probe ...	1998	9668453
investigating the epidemiology of heartwater (cowdria ruminantium infection) by means of a transmission dynamics model.	a mathematical model of the transmission dynamics of cowdria ruminantium by the ixodid tick amblyomma hebraeum in the bovine host is developed and used to investigate the epidemiology of heartwater across a range of vector challenge. the processes described are supported by empirical data. the pattern of outcome measures (incidence, case-fatality and proportion of infected hosts) predicted agrees with those described anecdotally from field experience and empirical observation, and demonstrates t ...	1998	9695100
demonstration of a carrier state for cowdria ruminantium in wild ruminants from africa.	four wild african ruminants, eland (taurotragus oryx), giraffe (giraffa camelopardalis), kudu (tragephalus strepsiceros strepsiceros), and blue wildebeest (connochaetes taurinus), were experimentally infected with the rickettsia cowdria ruminantium, the tickborne agent causing heartwater in domestic ruminants. the infections were established, and c. ruminantium was transmitted to naive small ruminants by the vector amblyomma hebraeum when transmission attempts were made at days 128 (eland and wi ...	1998	9706566
the distribution of heartwater in the highveld of zimbabwe, 1980-1997.	heartwater, the tick-borne disease caused by the rickettsia cowdria ruminantium has historically been confined to the southern and western lowvelds of zimbabwe. since 1986, however, cases of heartwater have been diagnosed with increasing frequency in the central and eastern regions of the previously heartwater-free highveld plateau. during the same period, collections of the two major tick vectors of heartwater in zimbabwe, amblyomma hebraeum and amblyomma variegatum, were made for the first tim ...	1998	9809322
distributions of the vectors of heartwater, amblyomma hebraeum and amblyomma variegatum (acari: ixodidae), in zimbabwe.	the tick vectors of heartwater (cowdria ruminantium infection) in zimbabwe, amblyomma hebraeum and amblyomma variegatum, historically were believed to be confined to the low-lying regions of the south and north-west of the country. however, country-wide surveys performed in 1975-1980 and 1988-1991 demonstrated that both species were also established in western parts of the highveld plateau and had started to encroach on the predominantly heartwater-free central and eastern highveld regions. to d ...	1998	10030008
development and evaluation of pcr assay for detection of low levels of cowdria ruminantium infection in amblyomma ticks not detected by dna probe.	the sensitivities of a pcr assay and a dna probe assay were compared for the detection of cowdria ruminantium in amblyomma ticks that were fed on c. ruminantium-infected, clinically reacting, and recovered carrier animals. the pcr assay and dna probe detected infection in 86.0 and 37.0%, respectively, of 100 ticks fed on a febrile animal. in 75 ticks fed on carrier animals, pcr and the dna probe detected infection in 28.0 and 1.33% of ticks, respectively. this demonstrates that the dna probe has ...	1995	7699036
laboratory reared amblyomma hebraeum and amblyomma variegatum ticks differ in their susceptibility to infection with cowdria ruminantium.	the susceptibility of laboratory reared zimbabwean amblyomma hebraeum and a. variegatum ticks to infection with geographically distinct cowdria ruminantium strains was investigated by feeding both species simultaneously on individual sheep infected with one of the four strains (crystal springs [zimbabwe], ball 3 [south africa], gardel [guadeloupe] and nigeria [nigeria]). a. hebraeum ticks demonstrated a high susceptibility to infection with all four c. ruminantium strains. in comparison, a. vari ...	1995	7589273
effects of tick infestation and tick-borne disease infections (heartwater, anaplasmosis and babesiosis) on the lactation and weight gain of mashona cattle in south-eastern zimbabwe.	the effects of ticks and tick-borne disease infections on the lactation and weight gain of mashona cattle were studied at mbizi quarantine station in the south-eastern lowveld of zimbabwe. twenty-nine mashona cows were allocated to 2 balanced groups and kept in separate paddocks at a stocking rate of one animal per 8 ha. one group received regular acaricide treatment to control bont (amblyomma hebraeum) and other ticks. the other group was left untreated. the cows were artificially inseminated. ...	1995	7502343
the relationship between tick (amblyomma hebraeum) infestation and immunity to heartwater (cowdria ruminantium infection) in calves in zimbabwe.	the occurrence of endemic stability for heartwater (cowdria ruminantium infection) is a controversial issue, because the means by which young cattle and other neonatal ruminants become infected and acquire immunity to the disease have never been adequately explained. we conducted a study in a heartwater-endemic area in southeastern zimbabwe to investigate the relationships between calf immunity to c. ruminatium, infestations of the tick vector amblyomma hebraeum and dam, colostral and calf antib ...	1995	8533273
factors affecting the distributions of the ticks amblyomma hebraeum and a. variegatum in zimbabwe: implications of reduced acaricide usage.	the ticks amblyomma hebraeum and a. variegatum are the main vectors of heartwater, a disease of ruminants caused by cowdria ruminantium, in the agricultural areas of zimbabwe. at present, a. hebraeum is widely distributed in the dry southern lowveld, and occurs in at least seven foci in the higher rainfall highveld. amblyomma variegatum occurs in the zambezi valley and surrounding dry lowveld areas in the northwest. the distribution of a. hebraeum has changed considerably over the past 70 years, ...	1994	7628253
the detection of antibodies cross-reacting with cowdria ruminantium in the sera of domestic ruminants in regions of south africa where amblyomma hebraeum does not occur.	high levels of seropositivity, in all probability attributable to ehrlichia, were recorded in the serum of domestic ruminants throughout districts in south africa where amblyomma hebraeum, the vector of the heartwater agent, does not occur. the antibodies, detected with the indirect fluorescent antibody (ifa) and the indirect elisa tests, cross-reacted with cowdria ruminantium, which was used as antigen in both tests. a combination of the ifa and elisa tests, currently employed to detect antibod ...	1994	7501358
the relationship between cowdria and ehrlichia: change in the behaviour of ehrlichial agents passaged through amblyomma hebraeum.	following an earlier report that an ehrlichia-like agent isolated from an adult hyalomma truncatum female became more pathogenic and elicited a disease in sheep indistinguishable from heartwater after having been passaged through amblyomma hebraeum, a similar phenomenon is herewith recorded. an ehrlichial agent demonstrated in the blood smear of a serologically positive, naturally infected lamb, changed in behaviour and assumed the characteristics of cowdria after passage through a. hebraeum. cr ...	1993	8134623
antibodies to cowdria ruminantium in mozambican goats and cattle detected by immunofluorescence using endothelial cell culture antigen.	endothelial cell cultures, established from bovine umbilical cord arteries and subsequently infected with cowdria ruminantium, were used as antigen in the indirect fluorescent antibody test. bovine sera (374) and caprine sera (388) collected in 6 provinces of mozambique were tested. overall, 30.4% of goat sera had antibodies to cowdria, and 43% of sera collected from cattle. north of the river save, where the tick amblyomma variegatum is highly prevalent, overall percentages of positive sera wer ...	1993	8236490
an immunoblotting diagnostic assay for heartwater based on the immunodominant 32-kilodalton protein of cowdria ruminantium detects false positives in field sera.	heartwater, a major constraint to improved livestock production in zimbabwe, threatens to invade areas which have been previously unaffected. to monitor its spread in zimbabwe, an immunoblotting diagnostic assay based on the responses of animals to the immunodominant, conserved 32-kda protein of cowdria ruminantium was evaluated. in this assay, no false reactions were detected with sera known to be positive and negative, but sera from some cattle, sheep, and goats from heartwater-free areas of z ...	1993	8253974
detection of cowdria ruminantium by means of a dna probe, pcs20 in infected bont ticks, amblyomma hebraeum, the major vector of heartwater in southern africa.	a dna probe, pcs20, previously described for use in detection of cowdria ruminantium infections in amblyomma variegatum (the principal vector of heartwater) hybridized with c. ruminantium dna in organs of laboratory-infected a. hebraeum adult ticks (the major southern african vector of heartwater). the probe hybridized with c. ruminantium dna in 46/49 midguts from male ticks and 26/29 from females, thus indicating infection. corresponding salivary glands were less heavily infected, but infection ...	1993	8432329
adult amblyomma hebraeum burdens and heartwater endemic stability in cattle.	several conclusions of importance to studies on the epidemiology of heartwater were drawn from an investigation in which the numbers of adult amblyomma hebraeum ticks, to which a closed herd of hereford cattle were exposed over a period of 6 1/2 years, were manipulated. with a tick cowdria ruminantium infection rate of 3-5%, an endemically stable situation was created by dipping the herd only when an average of 10 adult male and female a. hebraeum ticks were counted on 10 animals. when the avera ...	1992	1513597
comparison of the attachment rates of males of the ticks amblyomma hebraeum and a. variegatum to cattle, sheep and rabbits in the absence of aggregation-attachment pheromone.	losses in domestic ruminants caused by heartwater (cowdria ruminantium infection) in zimbabwe and mozambique are greater when the vector is amblyomma hebraeum than when the vector is a. variegatum. it has been suggested that the epidemiology of the disease may be influenced by the rates at which unfed adults of these two tick species attach to uninfested hosts (i.e. in the absence of the male-produced aggregation-attachment pheromone [aap]). in this study we confined unfed males of a. hebraeum a ...	1992	1446569
ultrastructural morphology of cowdria ruminantium in midgut epithelial cells of adult amblyomma hebraeum female ticks.	amblyomma hebraeum male and female ticks, experimentally infected as larvae with the ball 3 stock of cowdria ruminantium, were fed on a heartwater susceptible sheep. the initial attachment of the males was required as a pre-requisite for female attachment. reticulate bodies were the predominant morphologic form of cowdria observed in gut epithelial cells after 1-3 days of feeding. single intermediate bodies and no elementary bodies were observed. organisms were found within a membrane-bound vacu ...	1991	1923381
infection rates with cowdria ruminantium of nymphs and adults of the bont tick amblyomma hebraeum collected in the field in zimbabwe.	cowdria ruminantium (heatwater) infection rates of field populations of the bont tick, amblyomma hebraeum, were determined at two locations in the southern lowveld of zimbabwe. at mbizi quarantine station, unfed adult males and females, and nymphs were collected at intervals over a 2-year period using traps. at lemco ranch, engorged nymphs were collected on three occasions from weaner calves and allowed to moult to adults. the unfed ticks were fed in small pools on heartwater-susceptible sheep, ...	1990	2399648
increased pathogenicity of an ehrlichia-like agent after passage through amblyomma hebraeum: a preliminary report.	after being passaged through 3 generations of amblyomma hebraeum, an ehrlichia-like agent isolated from an adult hyalomma truncatum female became more pathogenic and elicited a disease in sheep indistinguishable from heartwater. cross-immunity between this agent and several stocks of cowdria ruminantium and high levels of antibody elicited by the agent against 2 stocks of c. ruminantium in the indirect fluorescent antibody test, confirmed its close relationship to cowdria.	1990	2293132
pheromone-mediation of host-selection in bont ticks (amblyomma hebraeum koch).	the bont tick, amblyomma hebraeum, is the principal vector to southern african ruminants of heartwater (cowdria ruminantium infection). the role of feeding male ticks, which emit an aggregation-attachment pheromone, in attracting unfed ticks to cattle was investigated. calves infested with feeding male ticks were more attractive to unfed adult ticks than were uninfested calves. the presence of the pheromone on previously infested cattle apparently allows unfed ticks to discriminate between hosts ...	1989	2911745
the carrier status of sheep, cattle and african buffalo recovered from heartwater.	sheep, cattle and the african buffalo (syncerus caffer) were shown to remain carriers of heart-water (caused by cowdria ruminantium) for long periods after recovery; 223, 246 and 161 days, respectively. transmission was achieved using adults of the southern african bont tick (amblyomma hebraeum) that had fed as nymphs on recovered animals. our findings differ from those of other workers who attempted transmission using nymphs that had fed as larvae on recovered animals or with blood from recover ...	1989	2617830
the role of males of the bont tick (amblyomma hebraeum) in the transmission of cowdria ruminantium (heartwater).	the role of males of the bont tick (amblyomma hebraeum) in the transmission of cowdria ruminantium (heartwater) was investigated. transstadial (nymph to adult) and intrastadial transmission were demonstrated. males transferred from live or dead hosts to live hosts were shown to transmit c. ruminantium repeatedly. it was concluded that male transmission is of importance in the epidemiology of heartwater.	1989	2588467
the presence of cowdria ruminantium antigen in various tissues of amblyomma hebraeum imagines as detected by an enzyme-linked immunosorbent assay.	investigation into the presence of c. ruminantium antigen, using an enzyme-linked immunosorbent assay (elisa) in various tick tissues and haemolymph of adult amblyomma hebraeum ticks revealed that the organism invades a number of body parts and can be demonstrated in a. hebraeum. in females, the gut, salivary glands, hypodermis and synganglion and in males, the salivary glands and gut showed the highest concentration.	1988	3217097
distinctive staining of colonies of cowdria ruminantium in midguts of amblyomma hebraeum.	mallory's phloxine-methylene blue stain was used to differentiate colonies of cowdria ruminantium in midgut epithelial cells of nymphal amblyomma hebraeum that had been infected as larvae. gut tissues were collected from nymphs that had fed on a susceptible sheep and were fixed in formol-saline on the day of repletion. paraffin sections, 3-4 micron thick, were then stained and this rendered colonies and cell nuclei densely blue against a uniformly pink background of tick tissues. colonies were e ...	1987	2452397
ultrastructural features of cowdria ruminantium in midgut epithelial cells and salivary glands of nymphal amblyomma hebraeum.	colonies of cowdria ruminantium were studied in midgut epithelial cells and salivary gland acini of nymphal amblyomma hebraeum that were infected experimentally as larvae. colonies were found in both tissues and studied with light and electron microscopy. colonies observed within gut cells frequently contained 2 types of the organism: electron-dense and reticulated forms. the morphology of colonies from salivary glands, as seen with light microscopy, varied from compact, densely-staining, small ...	1987	3587934
purification of cowdria ruminantium by density gradient centrifugation.	the isolation of cowdria ruminantium by differential and isopycnic density gradient centrifugation is reviewed with special reference to the suitability of percoll as density gradient medium. infected sheep brain, amblyomma hebraeum nymphae and various mouse organs were used as starting material. by these methods, partially purified viable populations of the organism with distinctly different densities were obtained. the conclusions are based upon results of analyses of density fractions by inoc ...	1987	3329312
control of induced infestations of adult amblyomma hebraeum with sustained release ivermectin.	the efficacy of ivermectin, administered in a sustained release formulation by intraruminal pumps at approximate daily dose rates of 20, 40 and 60 micrograms/kg, was evaluated in 16 cattle against induced infestations of 3 strains of adult amblyomma hebraeum. engorged female ticks were mass-measured and incubated, and reproductive data recorded. there was an increase in mortality of male and female ticks compared to that of controls with increasing daily dose of ivermectin, and a decrease in the ...	1987	3295646
problems with the interpretation of epidemiological data in heartwater: a study on 23 farms.	in an epidemiological study undertaken on 23 farms where heartwater occurs endemically, it was found that on an overall average, antibodies to cowdria ruminantium were detected in 64.3% of the cattle, 6 adult amblyomma hebraeum ticks were counted per animal and 7.0% of ticks were infected with the heartwater agent. it was found that the seropositivity of the animals was determined largely by the tick loads to which they were subjected and that the influence of the tick c. ruminantium infection r ...	1987	3448573
morphology and development of cowdria ruminantium in amblyomma ticks.	the morphology and development of cowdria ruminantium have been studied in amblyomma hebraeum and a. variegatum. colonies of c. ruminantium have so far been demonstrated microscopically in gut, salivary gland cells, haemocytes and malphighian tubules of infected amblyomma ticks. colonies in gut cells were seen in both unfed and feeding ticks but colonies in salivary gland acini were observed only in nymphs that had fed for 4 days. although the predominant type seen in both tick stages was the re ...	1987	3448559
heartwater. the artificial transmission of cowdria ruminantium in domestic ruminants and mice.	the artificial transmission of cowdria ruminantium with infected blood, organ homogenates, peritoneal macrophages, tick stabilate and tissue culture cells is discussed. organ homogenates prepared from the myocardium, spleen, kidneys and liver of diseased animals are commonly used to infect mice. the efficacy of organ homogenates as a source of c. ruminantium depends on factors such as the route of inoculation and the heartwater isolate used. heartwater is artificially transmitted with infected t ...	1987	3329318
purification of cowdria ruminantium by lectin cellular affinity chromatography.	this review covers the isolation of cowdria ruminantium by lectin cellular affinity chromatography from different amblyomma hebraeum sources. cellular affinity chromatography has been reviewed with special attention being given to the application of this technique in the isolation of rickettsiae.	1987	3329313
isolation of cowdria ruminantium by means of percoll density gradient centrifugation and detection by an enzyme-linked immunosorbent assay.	the isolation of cowdria ruminantium by means of percoll density gradient centrifugation permits the recovery of partially purified viable populations of the organism possessing distinctly different densities. these conclusions are based upon results of analyses of density fractions by intravenous inoculation into sheep, protein determination, electron microscopy and enzyme-linked immunosorbent assay. morphological differences were observed in the density fractions obtained from infected brain t ...	1986	3014417
the detection of antibodies to cowdria ruminantium in serum and c. ruminantium antigen in amblyomma hebraeum by an enzyme-linked immunosorbent assay.	a sensitive and reliable enzyme-linked immunosorbent assay for the detection of antibodies to cowdria ruminantium in serum and c. ruminantium antigen in amblyomma hebraeum nymphae is described. for the screening of antibodies, c. ruminantium from a. hebraeum nymphae, partially purified by wheat-germ lectin affinity chromatography, was used as antigen. to screen nymph populations, sera from either ball 3 strain-infected sheep or kumm-strain infected mice were used. by using appropriate controls t ...	1986	3960490
proof of transovarial transmission of cowdria ruminantium by amblyomma herbraeum.	transovarial transmission of cowdria ruminantium by amblyomma hebraeum does occur in certain instances. both the transovarial and the filial infection rates appear to be very low. the infection may reappear only in the adults or nymphae, or in all 3 stages of the tick's life cycle.	1986	3960489
a method for determining the cowdria ruminantium infection rate of amblyomma hebraeum: effects in mice injected with tick homogenates.	amblyomma hebraeum ticks, collected in the field and individually homogenized, were injected into mice. thirteen out of 240 ticks were shown to be infected with the heartwater agent. antibodies against cowdria ruminantium were detected in the sera of the mice by means of the indirect fluorescent antibody test. giemsa-stained smears, prepared from the haemocytes of the ticks, revealed morphologically different forms of the heartwater agent. a strain of c. ruminantium, designated the welgevonden s ...	1985	3900855
some effects of 60co irradiation on cowdria ruminantium in its tick host amblyomma hebraeum koch (acarina: ixodidae).	an attempt was made to attenuate cowdria ruminantium by irradiation of the nymphal stage of its tick host, amblyomma hebraeum. the irradiated nymphs were homogenized and serial dilutions of the resultant suspension were injected intravenously into heartwater-susceptible sheep. no attenuation could be demonstrated but the results indicate that progressively more micro-organisms will be destroyed the higher the irradiation dosage applied, and that dosages between 20 and 30 kilorad apparently prove ...	1981	7279384