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Biomedical subjects

R M Newson

Publications and source records attributed to R M Newson.

At least 19 recordsLinked to original sources
PubMed1993

Host resistance in cattle tick control.

Cattle ticks are an important constraint on the livestock industry, particularly in tropical and subtropical areas, mainly because of the diseases they transmit and the costs of control. Conventional control is by means of acaricides; although there are still serious drawbacks, these can be minimized by a strategic approach. In this review Julio de Castro and Robin Newson look at alternatives. One is to make use of the host's innate abilities. In the simplest situation, where no control measures are applied, the animals develop their own protective immunity against ticks and tick-borne diseases (TBDs). Alternatively, breeds of cattle with naturally high resistance to ticks can be used, enhanced by selection. Methods of immunizing cattle against ticks are also under development. Ideally, ticks should be managed at an economically acceptable level by a combination of techniques, supported where necessary by vaccination against TBDs.

Journal Article↗
PubMed1991

Predation of free-living engorged female Rhipicephalus appendiculatus.

In experiments done over a period of 1 1/2 years using engorged female Rhipicephalus appendiculatus tethered in a grass plot, 42% predation was observed in long grass (40-60 cm), and 36% in short grass (6-10 cm). Deaths due to environmental factors were 4.8% and 6.8% in long and short grass, respectively. Six groups of animals were confirmed to be predators of the ticks, namely: ants, spiders, rodents, birds, lizards and shrews. The implications of these results in making tick population models, and the possibility of using predators in integrated tick-control packages are discussed.

Animals↗
PubMed1991

Tick infestations on Zebu cattle in western Kenya: host resistance to Rhipicephalus appendiculatus (Acari: Ixodidae).

Tick-susceptible Friesian steers were used as bait animals to assess the availability of adult Rhipicephalus appendiculatus Neumann on the pasture. Assuming that initial gross pickup rates of ticks by cattle were similar, the numbers of female ticks that attached and the numbers that subsequently fed to maturity on individual cattle were compared based on data obtained from bait animals. The proportion of successful attachments on high-resistance (HR) cattle (0.30) was significantly less than that on the low-resistance (LR) animals (0.51). Similarly, the proportion of attached ticks that fed to maturity also was significantly lower on HR animals (0.15) than on LR animals (0.33). Female survival was calculated as the product of these two parameters. On the HR cattle, female survival (0.05) was significantly less than on LR (0.18). About 12% of the cattle had low resistance, and up to 73% of the females survived on them. These animals were responsible for much of the tick multiplication in the field population.

Animals↗
PubMed1989

Development of resistance in calves to nymphs of Rhipicephalus appendiculatus (Acarina:Ixodidae) during test feeds.

A test of host resistance to infestation by the tick Rhipicephalus appendiculatus was repeated 5 times, at weekly intervals, on 2 initially susceptible calves. One hundred nymphs (NN) were used each time. Pairs of tick-susceptible rabbits served as controls. The engorged NN were weighed, then allowed to moult individually, and the sex of each was noted after emergence of the adult. During the course of the experiment there was a significant reduction in mean engorged weight (especially in the pre-male NN) and also in the length of the feeding period, and a downward trend in the percentage of NN which engorged. There was a significant increase in the percentage of engorged NN that moulted. Pre-male NN were significantly heavier than pre-female NN after feeding on susceptible hosts, but though mean feeding times were the same, they took 1-2 days longer to moult than pre-females at 28 degrees C. It was concluded that the test itself could induce resistance if applied to fully susceptible calves.

Analysis of Variance↗
PubMed1989

Resistance in cattle against Rhipicephalus appendiculatus with an assessment of cross-resistance to R. pulchellus (Acari: Ixodidae).

A comparison of the yield of engorged nymphs of Rhipicephalus appendiculatus and R. pulchellus was carried out between cattle highly resistant to R. appendiculatus but susceptible to R. pulchellus, and cattle and rabbits susceptible to both species. Resistant cattle yielded fewer and smaller R. appendiculatus nymphs than either susceptible cattle or rabbits. More nymphs of both tick species dropped from susceptible cattle but no differences were detected in the mean weight of engorged R. pulchellus nymphs fed on R. appendiculatus-resistant and susceptible cattle, although resistant animals yielded more nymphs of R. pulchellus than of R. appendiculatus. An acute inflammatory reaction, accompanied by intense pruritus and grooming, was observed in the ears of the resistant cattle infested with R. appendiculatus, but no reaction was detected in the opposite ears where R. pulchellus was feeding. The low cross-resistance between these two closely related tick species suggests that different antigens may be involved in the development of resistance in cattle to different tick species.

Animals↗
PubMed1989

Adaptation of field strains of Rhipicephalus appendiculatus Neumann (Acarina: Ixodidae) to host resistance.

A comparison of feeding and breeding performance was made between a laboratory strain (LS) and two freshly collected field strains (FS1, FS2) of Rhipicephalus appendiculatus. The LS had been cultured for over 30 years on tick-susceptible rabbits. When fed on susceptible rabbits LS produced smaller eggs and unfed larvae, nymphs and adults than those of FS. Eggs and larvae from females engorged on cattle were larger than those from females engorged on rabbits. LS and FS females engorged on susceptible hosts were of similar weight, but the FS females were twice as heavy as LS females when tick-resistant hosts were used. A higher proportion of LS ticks than of FS ticks engorged on susceptible hosts, but a lower proportion on resistant hosts. Thus on susceptible hosts LS showed a higher reproduction efficiency than FS, but a lower one than FS on resistant hosts. The proportional reductions of engorged weights and numbers feeding successfully on resistant hosts were significantly lower for LS than FS ticks. Cross-resistance was low between LS and FS. Although all strains were affected by host resistance, it was concluded that the field strains were better adapted to withstand resistance than the laboratory strain.

Adaptation, Physiological↗
PubMed1988

Feeding performance of Amblyomma variegatum (Acarina: Ixodidae) fed repeatedly on rabbits.

Rabbits infested with different stages of Amblyomma variegatum Fabricius, 1794 became resistant to subsequent infestations by the same tick. Resistance was manifested by a reduction of 73.6% in the mean engorged weight of female ticks by the 3rd infestation. By the 5th infestation, only 70% of the nymphs engorged and their mean engorged weight was 57.7% of that of nymphs fed on tick-naive control rabbits. In the case of larvae, there was a 22.8% reduction in their mean engorged weight by the 6th infestation. Based on increases in body length while feeding on tick-naive rabbits, the nymphs could be divided into four feeding categories, i.e. Nl (unfed), N2, N3 and N4 (increasing states of engorgement). While 92-96% of ticks which dropped from susceptible rabbits fitted into feeding category N4, only 28% of those that dropped from tick-resistant rabbits fitted into that category. The remainder of the ticks fitted into categories N3 (60%) and N2 (12%). The majority of those ticks with reduced weight developed into adults which had an atypical scutal ornamentation pattern, in that an additional pair of lateral spots was regularly observed on the males. The females of such ticks deposited small numbers of eggs from which no larvae hatched.

Animals↗
PubMed1988

A climate-based model for the development of the ixodid tick, Rhipicephalus appendiculatus in East Coast fever zones.

East Coast fever (Theileria parva infection) is an important parasitic disease of cattle in East and Central Africa. Past experimental studies have provided a great deal of information on the dynamics of the life cycle of the tick vector, Rhipicephalus appendiculatus. This paper describes a mathematical model based on field observations to explain the close relationship between the tick life cycle and climate. The model provides a basis for the future study of different ECF control programmes using computer experiments.

Africa, Eastern↗
PubMed1986

Maintenance of Theileria parva parva infection in an endemic area of Kenya.

The maintenance of Theileria parva parva infection in an endemic area of Kenya on the shore of Lake Victoria was studied in the field and laboratory. High prevalences of antibodies against T. parva and T. mutans and intra-erythrocytic piroplasms were detected in local zebu (Bos indicus) cattle. The mean infection rate of Theileria parasites in the tick, Rhipicephalus appendiculatus, in field collections was 1.1%. Most of the infection was attributed to T. parva parva by application of field ticks to susceptible cattle. Five cattle, all about 1.5 years old, were purchased from local owners and transported to the laboratory. All five had oscillating antibody titres against T. parva and T. mutans and had patent theilerial infections during the subsequent 13 months. Uninfected R. appendiculatus nymphs were applied to cattle at 0, 3, 6, 9 and 13 months after transport to Muguga, and 18 out of 23 batches transmitted T. parva parva infection to cattle when 100 resultant R. appendiculatus adults were applied. Infection rates in the tick batches were usually low, with 1 salivary gland acinus infected/tick. Hence, a frequent carrier state of naturally infected cattle has been demonstrated for T. parva parva for the first time, and it is likely that this carrier state is of great importance in maintenance of T. parva parva infection in the field.

Animals↗
PubMed1985

Effects on cattle of artificial infestations with the tick Rhipicephalus appendiculatus.

Groups of ten cattle were exposed to 0, 40 and 400 adult Rhipicephalus appendiculatus feeding once a week for 24 weeks. Although no differences in cumulative percentage weight gain were found at the end of the experiment, animals free of ticks performed better during the first 12 weeks. A marked recovery of the 400-tick group was recorded during weeks 13-24 and after ticks were removed. Haemoglobin and packed cell volume values were lowered in tick-infested animals but no clear trends were observed in red and white blood cells. No differences between the percentages of ticks feeding in the 2 tick-infested groups on day 2 were observed but higher numbers of females were feeding on the 40-tick group on day 5. More ticks were found on day 5 after tick application to the cattle during weeks 1-6 than in the rest of the experiment. Significant correlations were found between lymph node enlargement and ear damage when they were tested against tick load. R. appendiculatus nymphs feeding on the formerly tick-infested cattle were fewer, lighter and engorged in a shorter time than those on the control animals. The possible causes for the reduction in ticks feeding, the changes in cattle weights, blood composition and development of host resistance are discussed.

Analysis of Variance↗
PubMed1985

The brown ear tick Rhipicephalus appendiculatus Neumann (Acarina: Ixodidae) and associated tick species on wild and domestic hosts at Muguga, Kenya.

During a study of an experimental population of Rhipicephalus appendiculatus and its transmission of bovine theileriosis to cattle, some supplementary information was obtained on the role of rodents and the small carnivores in the development and maintenance of R. appendiculatus populations. Observations were also made on other common tick species found on these hosts. A total of 530 individual hosts were examined during the 4-yr period, of which the majority included, among the carnivores, the white-tailed mongoose (Ichneumia albicauda), the large spotted genet (Genetta tigrina) and the zorilla (Ictonyx striatus). Among the 482 rodents 95% included Otomys irroratus, Rhabdomys pumilio and Lophuromys flavopunctatus. While all stages of R. appendiculatus thrived on cattle the role of rodents and carnivores was negligible. Similarly, while the other tick species like H. leachi group, immatures of R. hurti/jeanneli group and I. thomasae avoided cattle, they thrived on the carnivores and rodents. However, the adults of R. hurti and R. jeanneli preferred cattle to carnivores and rodents.

Animal Population Groups↗
PubMed1983

Camel production in Kenya and its constraints. II. Tick infestation.

The tick loads and tick species infesting an experimental herd, a Rendille pastoralists' herd and two ranch herds of camels, in four different areas of Kenya are described. The tick species most commonly observed were Hyalomma rufipes, Hyalomma dromedarii and Rhipicephalus pulchellus.

Animals↗
PubMed1983

Transmission of Theileria parva by a population of Rhipicephalus appendiculatus under simulated natural conditions.

A 2 hectare paddock on the Muguga Estate, Kiambu District of Kenya (altitude 2100 m) free of Theileria parva-infected ticks was seeded by applying Rhipicephalus appendiculatus nymphs to cattle infected with Theileria parva (Kiambu 4). It was estimated that over 50 000 engorged nymphs fell onto the pasture from 4 cattle with high parasitaemias during the cold season (June). Samples of these ticks were placed in plastic cylinders under the vegetation in the paddock and sexual stages of T. parva were detected in gut lumen smears in these samples up to 21 days after repletion. Zygotes were first observed to transform into kinetes on day 55 and parasites were first detected in salivary glands of adults on day 64. Moulting of the nymphs started on day 60 after repletion and was completed by day 87. Cattle introduced into the paddock showed their first infestation with adult R. appendiculatus on day 64 after repletion of the nymphs and the infestation level gradually increased. On day 76 after repletion, 17% of a sample of adult ticks infesting cattle showed salivary gland infections with T. parva and this increased to over 70% by day 150. From day 360 onwards, a decrease in both the percentage of ticks infected and the number of salivary gland acini infected/tick was noted. In addition, T. parva infections within the salivary glands required a longer period of feeding in the older ticks before they developed into sporozoites. Cycling of Theileria through ticks was prevented by the removal of female ticks before they completed repletion. Lethal challenge levels of T. parva for cattle existed in the paddock up to day 547 after repletion, after which introduced cattle showed no infection or only a sub-lethal infection. Cattle introduced into the paddock on day 808 after repletion showed no evidence of T. parva infection. The tick infestation of introduced cattle decreased markedly from day 368 and infestation had virtually ceased by day 808.

Animals↗
PubMed1980

Sweating sickness in adult cattle.

A Kenyan strain of Hyalomma truncatum was shown to cause sweating sickness in adult cattle in the laboratory. The typical lesions of moist eczema and mucous membrane changes were accompanied by a marked fall in circulating leucocytes with a severe neutropenia. Although all cattle recovered, some suffered a severe clinical disease and recovery was slow. Recovered cattle were immune to toxicosis 1 year later.

Animals↗