MRI safety: everyone's job.

It seems that in most hospitals, the MRI department is the only department charged with ensuring MRI safety. Unfortunately, it took the tragic loss of a patient's life in a New York hospital has served to bring the topic of MRI safety forward in the minds of many healthcare leaders. Of course, safety in the MR imaging suite has long merited the attention it is now receiving. Medical professionals agree it should receive the very highest of priority. However, bringing that goal from concept to reality is a real challenge--one that St. Luke's Episcopal Hospital in Houston, Texas, accepted and met. Our success, we believe, resulted from promoting MRI safety as a hospital-wide concern and investigating and then implementing several specific measures to maximize patient safety. In addition to our own evaluation of existing procedures and policies, St. Luke's enlisted the help of two outside consultants to perform separate comprehensive MR safety evaluations of our facility. Among the suggestions offered by the consultants was improvement in our MRI safety form. Taking the safety form on the MRIsafety.com Web site as a guide, we made certain modifications to our form, then met with our nursing councils to gain their input. The result has been a dramatic increase in compliance. All MRI technologists must have the backing of management--and know that they have it. Management must empower the technical staff to adhere to safety principles, even when it means enforcing safety rules with physicians. Disseminating MR safety information to the appropriate personnel in a health facility can be a daunting task. We found video to be the most effective means of presenting MR safety information. Some MR vendors can supply a safety video that gives excellent examples of non-MRI safe equipment. The MR supervisor will find it beneficial to distribute the video to any department that might have access to the MRI suite. Today at St. Luke's, MRI safety is not a topic for annual review; instead, it is on the minds of our staff with each and every patient.

The effects of the bont tick, Amblyomma hebraeum, on milk production of Sanga and Sanga x Brahman cattle.

The effects of adults on the bont tick, Amblyomma hebraeum on the milk production of Sanga and Sanga x zebu (Brahman) cattle were measured over a period of 11 weeks in the low veld of Zimbabwe in the summer of 1986. Four groups of lactating cows, consisting of two breeds, each divided into a high and low tick treatment, were exposed to very low or high challenges of ticks and their milk production measured by weighing their calves before and after suckling. The liveweight gains (LWG) of the calves were also measured. Tick burdens on the infested groups averaged around fourteen engorging females of A.hebraeum per day, which amounted to infestations of about 150 adult ticks. This is greater than most observed field infestations. This caused no significant reduction in milk yield or calf growth over the whole period, provided the teats of the dams had not been damaged by ticks. Mismothering occurred when teats were damaged. No breed differences were observed so all data was pooled for further analysis. Average calf LWGs of the high tick groups were reduced by 2.2 kg (P < 0.01) during one 4-week period but overall the 3.9 kg difference in LWG of the tick treatment groups was not quite significant (P < 0.10). Although there was a poor relationship between tick numbers and reduced milk yield or calf LWG, the effects were always in the direction expected. The effects averaged 6 +/- 10 g reduction of milk and 2.6 +/- 1.8 g loss of LWG of calves for every female tick that engorged. it was concluded that milk production is not an important consideration when estimating the losses in production caused by A.hebraeum on Brahman x Sanga or Sanga breeds of cattle. Losses due to teat or udder damage could be much more important and need to be quantified.

The effects of the brown ear-tick, Rhipicephalus appendiculatus, on milk production in dairy cattle.

The effect is reported of artificially controlled levels of infestation with adults of Rhipicephalus appendiculatus on the milk yield of twenty commercial Bos taurus dairy cattle on a high plane of nutrition and eighteen crossbred B.taurus x Sanga cattle on a lower plane of nutrition on the highveld of Zimbabwe. The results showed no significant effect on milk yield of infestations averaging twenty engorging ticks per animal per day, despite severe ear damage in some animals. They indicate that milk production of dairy cattle under commercial management is not sensitive to infestation with R.appendiculatus. The results have important implications for management of ticks in Africa, but need to be interpreted within the context of the control of tick-borne diseases.

The effects of the brown ear-tick, Rhipicephalus appendiculatus, on milk production of Sanga cattle.

Lactating Sanga cows of the Mashona breed from Zimbabwe, receiving either a low or high level of nutritional supplement, were exposed to two levels of infestation of adults of the brown ear-tick, Rhipicephalus appendiculatus in the highveld of Zimbabwe. The effect of the ticks on the milk yield was measured over an 11-week period during the rainy season from January to April 1986. A technique in which calves were weighed before and after suckling was used to estimate milk yield. There were significant treatment effects of ticks (P < 0.05) on milk production but no significant differences in liveweight gain between calves from tick-free and tick-infested dams. The loss in milk production was poorly related to the number of female ticks that engorged, being 9 g (SEM 4) per tick. A Friesian x Hereford (Bos taurus) reference group of cattle carried 50% more ticks than the Mashona cows, illustrating a difference in resistance between the breeds. Thirteen screw-worm (Chrysomya bezziana) strikes were recorded amongst the thirty-two Mashona cows compared with twenty-one amongst the ten Friesian x Hereford animals between January and the end of March.

Infestations of the bont tick Amblyomma hebraeum (Acari: Ixodidae) on different breeds of cattle in Zimbabwe.

Infestations of adults and nymphs of Amblyomma hebraeum were counted on Brahman (Br), Brahman x Simmental (BS), Sanga (Sa) and Hereford (He) steers exposed to infested pastures at Mbizi in southern Zimbabwe in 1986-1987. Herefords were always the most heavily infested, while the Sanga tended to carry the fewest ticks with the Brahman and Brahman x Simmental groups being in between. The ratios of the engorged females on the four breeds were 2.3:1.4:1.4:1.0 for He:Br:BS:Sa. The ratios of the standard nymphs were 2.2:1.4:1.7:1.0 for He:Br:BS:Sa. The results confirm earlier observations in Africa and support the view that there are genetic differences between breeds in the expression of resistance to this tick species.

In vitro adherence of erythrocytes infected with Babesia bigemina and Babesia rodhaini to thrombospondin.

The adherence of erythrocytes infected with Babesia bigemina and Babesia rodhaini to thrombospondin (TSP) in vitro is demonstrated. Blood with a range of parasitaemias was used and counts of cells which bound to TSP on plastic were significantly different from the controls with both Babesia species. These studies indicated that TSP receptors are present on the surface of red blood cells infected with the two Babesia species, although these parasites do not alter the membranes of infected erythrocytes obviously and do not cause cerebral symptoms in their hosts. Erythrocytes infected with either B. bigemina or B. rodhaini do not adhere to other erythrocytes in vivo, probably because these parasites induce mild infections in their hosts, but they can adhere to TSP in vitro.

Acquired resistance of sheep to larvae of Lucilia cuprina, assessed in vivo and in vitro.

The effect on subsequent larval survival of infesting sheep repeatedly with larvae of Lucilia cuprina was assayed in vivo and in vitro. One in vivo assay technique, in which implanted larvae were grown to third instar, indicated a significant reduction in larval survival; another in vivo technique, in which larvae were allowed to develop to second instar in small aluminium rings attached to the sheep, indicated no reduction in larval growth or survival. Larvae of Lucilia cuprina grown in vitro on media containing sera from previously infested sheep were significantly retarded in growth after 20 h compared with controls; no difference was detected when larvae were allowed to develop to pupation on two changes of the same media. No significant differences in survival of larvae either to 20 h or to pupation were obtained between the two treatments. ELISA antibody levels against crude soluble larval material were significantly higher for sera from infested sheep than for control sera, and the regression of antibody level on mean larval weight obtained after 20 h growth in vitro was significant. The immunoglobulin fraction isolated from sera of infested sheep significantly retarded larval growth when incorporated with normal serum in growth media. These results are consistent with an effect of specific anti-larval antibody produced by sheep in response to infestation.

The effect of the bont tick (Amblyomma hebraeum) on the weight gain of Africander steers.

The effects of the bont tick Amblyomma hebraeum on the productivity of cattle need to be quantified in order to design economically optimal control programs. Liveweight gains (LWGs) of three groups of Africander steers, maintained in the same pasture and exposed to zero, medium or high numbers of larvae, nymphs and adults of the tick, were measured. Larvae and nymphs had no significant effect on LWG but adults had a large, statistically significant effect (P less than 0.05). The tick-free group had an average LWG of 20 kg more than the heavily infested group after 3.5 months. No mortality was recorded from ticks or tick-borne diseases during the experiment. There was no relationship between the number of engorging adult female ticks counted and loss of LWG of individual animals. The latter suggests that exposure to ticks as well as engorgement by female ticks causes losses. The loss per adult female that completed engorgement was estimated, by relating the LWGs of individual animals to their tick infestations, to be 4 +/- 2 g per adult female tick. An alternative estimate, made by comparing the average LWG and tick infestations of each treatment group, was equal to 10 +/- 4 g. This latter estimate includes the effect of challenge (and rejection) as well as tick feeding and so was accepted as giving the best estimate. Screw-worm fly (Chrysomya bezziana) struck an average of 7.5% of the cattle infested with ticks in any week but the effects on the productivity of the cattle were minimized by immediate treatment. There was a significant, positive correlation between the incidence of screw-worm fly strike and the numbers of adult ticks counted on the experimental animals. The results provide data for calculating losses caused by A. hebraeum in different parts of its geographical range.

Ecological aspects of cattle tick control in central Zambia.

In ecological studies in central Zambia, both climate and ecotype affected population dynamics of tick species. Below average rainfall for several years caused a suppression in numbers of Rhipicephalus appendiculatus Neumann adults. Reduction in rainfall leading to changes in grazing patterns is thought to have been responsible for an increase in numbers of Amblyomma variegatum Fabricius adults in a grassland habitat. There were reasonable correlations between numbers of each tick species on individual hosts over 1 year old. However, there were no relationships between numbers of ticks and bovine lymphocyte antigens (BoLA).

Effect of tick control on liveweight gain of cattle in central Zambia.

Field trials were carried out during 1982-86 in two different ecotypes in central Zambia to determine the impact of tick control on the liveweight gain (LWG) of cattle. During the first 2 years of the trial a diamidide acaricide (Amitraz) sprayed at weekly intervals caused periodic depression in LWG in young animals. Thereafter a pyrethroid acaricide (cypermethrin) was used. During the 1984-85 tick season infestations of 50-120 adult Amblyomma variegatum Fabricius in untreated animals caused significant reductions in LWG. From the differences in LWG between treated and untreated cattle, the induced loss in LWG was estimated at 46-61 g per engorged female A.variegatum.

Factors affecting the survival and migration of the free-living stages of gastrointestinal nematode parasites of cattle in central Queensland.

Faecal pats containing parasitic nematode eggs were deposited monthly on worm-free pasture, from mid-1975 to early in 1979, near Rockhampton in central Queensland. Pasture samples were collected monthly from beside these pats and the number of infective larvae on the samples was counted. Cooperia spp. were the most numerous larvae on pasture all year round and Haemonchus placei were commonly present in low numbers. Small numbers of Oesophagostomum radiatum larvae were found, mostly during summer. Dung beetle activity and rainfall influenced larval populations on pasture, but temperature did not. Beetles were not active in winter, and pats deposited in spring, summer and autumn when beetles were active yielded only 42, 44 and 26%, respectively, as many larvae per 1000 eggs deposited as winter pats. Pats in which beetle activity was minimal (feeding only), moderate and intense (complete destruction), yielded 43, 10 and 6%, respectively, as many larvae per 1000 eggs as intact pats. Larval densities on pasture were highest after the first saturating rains during the spring-summer period and most of these larvae migrated from unattacked pats deposited in winter. Beetle numbers and activity increased with the summer rains and so few larvae were available to migrate onto pasture during late summer and autumn when the highest falls of rain were recorded. The regression of larval recovery on rainfall was positive and statistically significant when data collected soon after these very heavy rainfall periods were omitted from the analysis. In 1977, drought-breaking rains increased the normal larval density on pasture 10-fold because larvae in pats deposited in the last 4 months of the drought migrated onto pasture immediately after the rains. This work suggests that in summer rainfall areas where dung beetles are active, helminth control may be achieved by reducing the worm egg output from cattle during the winter.

The relation between the natural worm burden of steers and the faecal egg count differentiated to species.

The relation between the faecal egg count and the worm burden was investigated in 104 steers of three breeds, 9-24 months of age, which were subjected to natural infection with nematode larvae from pasture at The National Cattle Breeding Station near Rockhampton in central Queensland. The worm species found were Cooperia spp., Haemonchus placei, Trichostrongylus axei, Oesophagostomum radiatum and small numbers of Bunostumum phlebotumum. The faecal egg count was found to be a reliable measure of the size of the worm burden. Steers slaughtered at 24 months of age had 90% fewer worms and 96% fewer eggs g-1 faeces (P less than 0.001) than those slaughtered at 9 months of age. Adjusted for age, the estimated faecal egg count increased 14 times (95% confidence limits 7.2, 35) for each 10-fold increase in estimated worm numbers. The proportion of each species of larvae obtained from faecal culture (larval differential count) was related to the composition of the worm burden as measured by the proportion of worms in selected maturity categories and in selected length categories for each species (P less than 0.001).

The effect of the brown ear-tick Rhipicephalus appendiculatus on the growth of Sanga and European breed cattle.

The effects of larvae, nymphs and adults of the brown ear-tick Rhipicephalus appendiculatus on the growth of Bos indicus X B. taurus (Sanga) steers and on B. taurus steers and heifers was measured by exposing groups, maintained in the same pastures, to different levels of tick challenge. Larvae and nymphs had no significant effect on liveweight gains, but adults had a large effect. Each engorging female tick counted was associated with a loss of 4 g. Their effect on the Sanga cattle was minimised by host resistance which severely limited the number of ticks feeding on them. The B. taurus animals were severely affected and suffered extensive ear damage. Both breeds were subjected to screw-worm fly (Chrysomya bezziana) strike in the lesions caused by heavy tick infestations, but the B. taurus animals were much more prone to attack. The results provide a basis for calculating losses in production caused by this species of tick which is widespread in Africa.

The grazing behaviour of cattle in relation to the sampling of infective nematode larvae on pasture.

A method of sampling pasture to estimate the numbers of infective nematode larvae to which grazing cattle were exposed was based on the grazing patterns and behavioural activities of two groups of cattle and was compared with other sampling techniques. Each group of cattle consisted of six permanent members, two members fistulated at the oesophagus and one worm-free tracer calf. Grazing time and the area where grazing occurred was not significantly different for tracer calves, fistulated cattle and permanent group members, and there was no relationship between grazing time and the live weight of cattle. Grazing time, the percentage of paddock area grazed intensively and the percentage of the paddock not grazed varied with season. The most intensively grazed areas were always visited between first light and the first rest period during mid-morning, and the plant parts and pasture species eaten could easily be identified by visual examination of these areas of the paddock. Larval recoveries per 100 g pasture ingested were estimated for comparison with the grazing area method using two other manual pasture sampling methods, a sampling method using tracer calves and one using fistulated calves. Correlations between these methods were not consistent but indicated that, given the small number of data sets, all methods were sensitive enough to estimate larval availability on pasture with the exception of the tracer calf method in the overstocked 3.4-ha paddock.

Ability of adults of Amblyomma hebraeum (Acarina: Ixodidae) to feed repeatedly on sheep and cattle.

Adult Amblyomma hebraeum ticks were exposed at 14-day intervals on five sheep on 46 occasions and on three cattle on 15 occasions to determine the effects of repeated feeding. The engorged weight and percentage of ticks which fed successfully on sheep declined significantly at first but subsequently they increased. On cattle there was no progressive decline in engorged weight, although the percentage which fed successfully declined significantly and was lower than that for sheep. This decline was attributed to increased grooming by cattle and was the only apparent mechanism by which resistance was expressed.

The irradiation of babesia bovis. II. The immunogenicity of irradiated blood parasites for intact cattle and splenectomised calves.

Intraerythrocytic forms of B. bovis were exposed to 350 Grays (Gy) gamma irradiation and were then injected intravenously into intact two and three year old Hereford steers. One of 15 steers died on initial infection and subsequently six steers were given a virulent heterologous challenge three weeks after recovery; all six animals were highly immune. The remaining eight animals were kept under quarantine conditions for 10 months and were then challenged with a different virulent heterologous strain of B. bovis. Seven of eight were highly immune, but one animal died. Subsequently a further 12 steers were injected intravenously with 1 X 10(8) irradiated organisms. All showed only mild transient clinical signs. After 12 months quarantine in a tick-free area these animals were then challenged with a virulent heterologous strain and all 12 were shown to be highly immune. Irradiation reduced the infective dose from 1 X 10(8) to 2.5 X 10(3) parasites. These parasites multiplied at the same rate, and achieved the same maximum parasitaemia as the parent non-irradiated strain, but the disease produced by them was not severe. A dose of 2.5 X 10(3) non-irradiated parasites was lethal to all of the four animals which received it. It was concluded that irradiation had produced a predominantly avirulent parasite population.

Improved toxin/antitoxin assays for studies on the Australian paralysis tick Ixodes holocyclus.

Sensitive biological assays of toxin/antitoxin potency have been developed to assist in research on characterization of salivary toxins of the Australian paralysis tick Ixodes holocyclus and on immunity to tick paralysis. The toxin assay utilizes suckling mice (4-5 g); a quantitative paralysis index is applied over a range of doses. The antitoxin assay is based on an in vitro/in vivo neutralization test which required a sensitive toxin assay and methods of standardization of toxin preparations. This assay permits the monitoring of blood antibody levels in animals during the course of development and loss of immunity and is assisting a study into the feasibility of producing an anti-paralysis vaccine. The method also allows standardization of commercial tick paralysis antiserum. The methods and applications are described and comparisons made with previous assays. Sample data are examined statistically by regression and variance analyses; parallelism of dosage-response lines is tested and relative toxicities (toxin) or potencies (antiserum) calculated.

A survey for resistance in cattle ticks to acaricides.

A survey was made from late 1976 to late 1977 to determine the extent of resistance to acaricides in the cattle tick Boophilus microplus in Queensland. Questionnaires and requests for samples of ticks were forwarded to more than 900 randomly selected stock owners in the tick infested area which had been divided into 4 regions. Far North, Coastal North, Coastal Cental and South East. The response measured by the number of tick samples tested was 43%. The prevalence of resistance to organophosphorus (OP) compounds was highest in South East where 96% of the farms had OP-resistant ticks and 95% had the Biarra strain and lowest in Far North where 12% of the farms had OP-resistant ticks and 10% had the Biarra strain which was the predominant one in all regions. The highest percentages of the Ridgelands strain (35%) and the Tully strain (30%) occurred in Coastal North. The South East had the highest percentage of Mt Alford (30%). Although chlorinated hydrocarbons were banned for use in control of ticks in 1962, 49% of the farms in South East had some ticks resistant to dieldrin but in Far North it was only 2%. DDT-resistant ticks, which because of cross resistance to synthetic pyrethroids will affect the future use of this group, were present on 8% of the farms in both Coastal North and Coastal Central and 3% in South East and Far North. No resistance to the amidines, chlordimeform, chloromethiuron or amitraz was found.