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Biomedical subjects

A M Spickett

Publications and source records attributed to A M Spickett.

At least 37 records · Page 2Linked to original sources
PubMed1991

Drag-sampling of free-living ixodid ticks in the Kruger National Park.

Free-living ticks were collected by means of drag-sampling in 32 of the 35 landscape zones of the Kruger National Park during a period of 1 calendar month. Of the 18,199 specimens collected, 99.53% were larvae, 0.05% nymphs and 0.42% adults. Fourteen species were collected. Amblyomma hebraeum followed by Boophilus decoloratus, predominated, both in distribution and abundance. Large variations were encountered between drags. There was no correlation between the numbers of larvae collected and time of day, temperature, grass length, vegetation biomass estimates and subzone type.

Animals↗
PubMed1990

Fitting the Gompertz function to dose-response data of larval tick populations.

Samples of 6, 1st generation larval populations of Boophilus decoloratus, originating from field collected females, were subjected to increasing doses of the organophosphate acaricide, Dioxathion. The dose-response relationship for 3 populations showed random heterogeneity, while systematic deviations from the linear probit lines were observed for the other 3 populations. Logistic and Gompertz regressions were also fitted for all 6 populations. Probit regressions fitted best for 2 populations exhibiting heterogeneous responses. The logistic regression fitted best for 1 population with heterogeneous responses and 1 population with systematic deviating responses. The Gompertz regression fitted best for the 2 remaining populations exhibiting systematic deviating responses. The Gompertz function may be useful in describing the dose-response relationship obtained for certain acaricidal toxicity tests.

Animals↗
PubMed1990

On sampling tick populations: the problem of overdispersion.

Data collected on both free-living and parasitic tick populations are likely to be overdispersed. The use of means from few replicate samples of overdispersed data as quantitative estimators of tick population density is in turn likely to lead to inaccurate interpretations which may be scientifically misleading. In this paper ways of estimating overdispersion are listed and suggestions for the use of correct statistical tests for handling overdispersed data are given.

Animals↗
PubMed1990

The prehatch period and larval survival of Boophilus decoloratus (Koch, 1844) (Acarina: Ixodidae) under natural conditions in the Transvaal, South Africa.

Studies were made on the duration of the prehatch period of Boophilus decoloratus and on the subsequent survival and viability of larvae under natural conditions. The length of the prehatch and larval survival periods was found to be inversely dependent on increased temperature. A high initial temperature at the time of female drop decreased the prehatch period further, resulting in synchronous hatching of eggs laid at different times. Oviposition occurred but no eggs hatched during mid-winter months with mean temperatures below 10 degrees C. Eggs laid after mid-winter hatched because of the higher temperatures during subsequent months. Diapause occurs at the egg stage in areas with mean winter temperatures below 10 degrees C. Larvae survived for 10-35 weeks during periods of high and low seasonal temperatures respectively. Larval viability decreased concomitantly with larval survival. The results suggest that pasture spelling alone would be impractical as a control measure for this tick species.

Animals↗
PubMed1989

Resistance of Nguni, Bonsmara and Hereford cattle to ticks in a Bushveld region of South Africa.

Counts of engorged female ticks on naturally infested cattle over a 2 year period, showed that indigenous Nguni cattle harboured significantly fewer Amblyomma hebraeum, Boophilus decoloratus and Hyalomma spp. during periods of peak abundance than either Bonsmara or Hereford cattle. Fewer abscesses, associated with tick bite, were also present in the Nguni cattle. Individual tick resistance indices, determined after artificial tick infestation in the field, could not be correlated with hair length, skin thickness or conglutinin titres. The consistently large percentage of Nguni cattle showing high tick resistance according to index determinations, indicates a superior level of natural immunity in this breed. The relative incidence of individuals in high, medium and low resistance classes reflected an increase in resistance with exposure to ticks and the potential for the selection for tick resistance within all 3 breeds.

Animals↗
PubMed1989

Unusual hepatic parenchymal crystalloid material and biliary microliths in goats.

Investigation into an outbreak of suspected photosensitivity in Boer goats grazing green oats (Avena sativa) led to the finding of microscopical parenchymal crystaloid material and biliary microliths in the livers of 3 ewes that were killed for necropsy. Neither Tribulus terrestris nor Panicum spp. occurred on the farm. Further investigation resulted in the isolation, from leaf spots on the oat leaves, of the fungus Drechslera campanulata, cultures of which have been shown to be highly toxic to sheep, goats and calves. The hepatic parenchymal crystalloid material, which did not invoke any inflammatory reaction, occurred intracellularly in hepatocytes and extracellulary in sinusoids and central veins. Histochemically, this material reacted positively for calcium and free fatty acids and ranged from nonbirefringent, grey spicules to birefringent, glass-like sheaved crystals. A distinctive feature in the livers of the 3 goats was the presence of periductal concentric fibrosis and cast-like biliary microliths which occasionally contained a core of birefringent crystalloid material morphologically and histochemically different from that seen in the parenchyma. An aetiological relationship between the presence of highly toxic D. campanulata isolates on green oats and the hepatopathy with biliary microliths and calcium-free fatty acid crystalloids is possible.

Animals↗
PubMed1989

Paralysis of laboratory rabbits by nymphae of Ixodes rubicundus, Neumann 1904 (Acarina: Ixodidae) and some effects on the life-cycle following feeding under different temperature conditions.

Feeding under constant cold conditions resulted in a marginal shortening of feeding period and a major shortening of the subsequent developmental phase of all stages of Ixodes rubicundus Neumann 1904, the Karoo paralysis tick. Paralysis occurred in laboratory rabbits when nymphae were fed on them under constant warm, constant cold and fluctuating ambient winter conditions. This paralysis was found to be dependent on infestation rate and feeding conditions. Under constant cold conditions paralysis resulted from lower levels of infestation than under warm or under fluctuating winter conditions. Neurological parameters used in assessing the progression of the paresis are discussed.

Animals↗
PubMed1989

Parasites of domestic and wild animals in South Africa. XXIV. Arthropod parasites of bushbuck and common duiker in the Weza State Forest, Natal.

One bushbuck, Tragelaphus scriptus, and 1 common duiker, Sylvicapra grimmia, were shot each month from May 1983 to May 1984 in the Weza State Forest, Natal, i.e. a total of 13 animals of each species. The bushbuck were infested with 8 ixodid tick species, 2 louse species and a louse-fly species. The common duiker harboured 7 tick species and 2 louse species. Ticks of the genus Ixodes were the most numerous and prevalent on both antelope species, but no pattern of seasonal abundance was evident. Although only small numbers were recovered, adult Haemaphysalis aciculifer were present from September to February, nymphs of Rhipicephalus appendiculatus from May to September, and adult Rhipicephalus lunulatus from December to March. The louse-fly, Lipoptena paradoxa, was recovered from some of the bushbuck from October to May.

Animals↗
PubMed1988

A survey of Karoo tick paralysis in South Africa.

Recent research interest in Karoo tick paralysis and its vector. Ixodes rubicundus, prompted this survey to determine the economic implications of this disease. The survey indicated relatively high losses caused by the condition, identified the stock involved and provided data on the incidence of paralysis and on the control methods employed. Recommendations are made to institute chemical control earlier in the season to attempt better containment of the problem.

Animals↗
PubMed1987

The natural control of heartwater vectors.

Socio-economic factors and environmental considerations have increasingly encouraged the search for methods of tick control other than acaricidal treatment. Biological control management regimes have, so far, not proved to be sound replacements for acaricides. The major natural control methods employed successfully at present are host resistance and pasture management. The former has been extensively studied and utilized in a one-host-tick situation, and its potential specificity for the Amblyomma species is discussed. Pasture management in the form of tick-resistant plants and habitat modification affecting vector ecology and viability is discussed, as is host availability. Parasites and predators affecting tick populations are gleaned over with the accent on predacious birds (Buphagus species) which may play a limited role in integrated control programmes. Reference is made to the possibilities of genetic manipulation, problems accompanying the implementation of sterile male techniques, and hybrid sterility. In conclusion, a plea is made to ensure a thorough understanding of target vector ecology before any control measures are employed. This should be preferably from an integrated point of view rather than from a standpoint of unilateral reliance.

Animals↗
PubMed1985

An in vivo comparison of the efficacy of the heartwater blood and ground-up tick suspension vaccines in calves.

Two groups of calves were respectively immunized with heartwater blood (BV) and ground-up tick suspension (GUTS) vaccine. A third group was left unimmunized as controls. No difference in the immune status conferred could be demonstrated between the 2 vaccines at 6 months and 12 months challenge after vaccination. An index, based on the rectal temperature before and during the reaction, was calculated as an aid in evaluating the data. In practice, the evaluation of heartwater vaccination by challenge is more effective at 12 months than at 6 months after vaccination. No effective difference was demonstrated between the 2 vaccines in their immunizing efficacy.

Animals↗
PubMed1984

Electron microscopic observations on the luminal surface of teat cup liners of milking machines used under South African conditions.

An investigation undertaken with the aid of scanning electron microscopy (SEM) on new and used teat cup liners revealed the generally poor quality of luminal surfaces. Even those of the brand-new distributor controls showed significant faults in the evenness and continuity of the liner surface. A hundred and 500 milkings apparently tend to aggravate faults like cracks, pores, grooves and pits, because of the general brittleness of some of the teat cup liners. The poor quality of the liners investigated raises various questions about the method of distribution of teat cup liners and serious concern about the role they play in predisposing bovine udders to mastitogenic infections, spreading mastitis, affecting the production and quality of milk, increasing the cost of milk production and reducing profits of dairy farming.

Dairying↗
PubMed1981

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 fatal to all the pathogenic organisms.

Animals↗
PubMed1981

Ixodes (Afrixodes) matopi n. sp. (Acarina: Ixodidae): a tick found aggregating on pre-orbital gland scent marks of the klipspringer in Zimbabwe.

Ixodes (Afrixodes) matopi n. sp. is described from females and males collected off twigs bearing deposits of intraspecific communication marks secreted by the pre-orbital glands of the klipspringer Oreotragus oreotragus and from laboratory-reared immature specimens. One female was also found on a goat. The 4 collections were all from Zimbabwe, 3 of them from Matabeleland South Province and the fourth from Inyanga District, Zimbabwe.

Animals↗
PubMed1981

Ecological studies on Ixodes (Afrixodes) matopi Spickett, Keirans, Norval & Clifford, 1980 (Acarina: Ixodidae).

Ixodes (Afrixodes) matopi occurs in association with the klipspringer (Oreotragus oreotragus) in rocky areas in Zimbabwe. The adult ticks are specific parasites of this antelope and the immature stages feed on klipspringers, hydraxes (Procavia capensis and Heterohyrax brucei) and red rock hares (Pronolagus crassicaudatus). Adults are active only in the wet season and prior to feeding are found on bushes growing adjacent to rocks. The ticks aggregate on twigs which have been marked with the secretions of the pre-orbital glands of klipspringers. Larvae are evident in greatest numbers in the latter part of the wet season and nymphs in the cool dry season. Unfed larvae and nymphs occur predominantly on mats of humid leaf litter in the cracks and gaps between rocks, and both show well-defined patterns of daily activity.

Animals↗