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These studies were conducted to investigate the possible role of certain aspects of the on-host ecology and off-host survival of the sheep scab mite, Psoroptes ovis, in the dissemination of infestation. All developmental stages of the mite occurred in the fleece both proximally or distal to the skin of infested Merino and Dorper sheep. A larger proportion of mites was present in the fleece of Dorper sheep distal to the skin in the late afternoon and early morning than at other times during the day. Immature and adult mites readily transferred to tufts of wool or hair placed on infested sheep of both breeds. No mites could be found on wool or hair rubbed off onto tree trunks or branches or other structures in enclosures housing heavily infested sheep, nor could any mites be collected from the soil of these enclosures, whereas more than 80% of mites artificially seeded onto soil samples were recovered. The longest mean off-host survival times for larvae, nymphs, and male and ovigerous female mites were recorded at 10 degrees C, and were 9.25 days (RH = 90%), 15 days (RH = 33% and 75%), 10.5 days (RH = 75% and 90%) and 11.25 days (RH = 90%) respectively. Under natural climatic conditions ovigerous females in glass vials containing Merino wool survived for 17 days compared to 15 days for females in vials without wool; this difference was, however, not significant. The mean off-host pre-hatch period for eggs varied between 5.9 days (T = 25 degrees C and RH = 33%) and 22.1 days (T = 10 degrees C and RH = 75%), while the longest time individual eggs took to hatch at the latter temperature and RH was 31 days.

Five Merino and five Dorper sheep were artificially infested with the sheep scab mite Psoroptes ovis and the effect of infestation on their haematology, serum protein levels and live mass recorded for a period of 14 weeks. The reaction of the Merino sheep to infestation was more severe than that of the Dorper sheep. Haematological values fluctuated within the normal range during the assessment period. The mean haemoglobin concentration of the Merino sheep declined until antiparastic treatment was administered 10 weeks after infestation, after which it gradually increased. The lymphocyte counts of both breeds of sheep declined from 2 weeks to 10 weeks post-infestation, but increased after treatment, while the highest eosinophil counts were recorded in the Merino sheep at the height of the acute disease 8-10 weeks post-infestation. Serum albumin values for both breeds and serum globulin values for the Merino sheep were higher than normal during the entire 14-week observation period. A decrease in serum albumin and an increase in serum globulin concentration occurred at the height of infestation in both breeds. The mean live mass of a second group of five infested Merino sheep decreased by 6.4 kg over a 16-week period compared to a gain of 4.56 kg for five infested Dorper sheep.

A single Merino sheep, artificially infested with the sheep scab mite, Psoroptes ovis, and a similarly infested Dorper sheep were placed with 9 uninfested Merino or 9 uninfested Dorper sheep respectively during winter and the rate of spread of infestation on the uninfested sheep observed. The same procedure was repeated in summer. It took 14 and 8 weeks respectively in winter before all sheep in the 2 groups displayed lesions of sheep scab, whereas in summer it took 10 and 12 weeks before all sheep had lesions.

Sheep scab mites, Psoroptes ovis, collected from a Merino donor sheep, were used to infest Merino and Dorper sheep, and Angora and Boer goats. Mites were placed on the sheep on 1 or 2 occasions and on 5 occasions on the goats. All the animals were examined at regular intervals for the presence of scab lesions and living mites. Both sheep breeds developed lesions, but those on the Merino sheep were always larger than those on the Dorper sheep at the same intervals after infestation. None of the goats developed lesions or showed signs of irritation, or harboured any mites.

The objectives of this study were to determine the influence of application site and sheep breed on the efficacy of a flumethrin (1% m/v) solution for the control of 'bont'-legged (Hyalomma spp.) and red-legged ticks (Rhipicephalus evertsi evertsi). This study was conducted from November 1996 to February 1997 on 3 farms in the southwestern Free State Province. Two trials were conducted on Dorper sheep and 2 on Merino sheep. For each specific application 30 sheep were selected and allocated to 3 groups of 10 animals each using randomisation through minimisation, with pre-treatment total tick count as only criterion. Groups consisted of an untreated control group, a group treated with 3 ml of a flumethrin (1% m/v) solution applied only to the anogenital region, and a group treated at a dose rate of 1 mf flumethrin (1% m/v)/5 kg host body mass. The total dose volume for animals in the last group was divided into 3 equal parts and applied to the brisket/axillae, groin and anogenital regions respectively. Animals grazed under extensive farming conditions and were infested by ticks that occurred naturally in the environment. Ticks were counted and removed weekly over a 6-week period. In all 4 trials, Rhipicephalus e. evertsi was the dominant tick species, followed, in 3 of the trials, by Hyalomma spp. Efficacy (%) of control against ticks for Dorper sheep, treated only on the anogenital region, was variable, ranging between 29.5 and 97%. In Merino sheep the efficacy values ranged between 23.1 and 90 %. The site-spcific (anogenital region) efficacy of control against ticks infesting Merino sheep was in general 100% or almost 100%. In Dorper sheep the efficacy values were >80 % for 3-5 weeks. The efficacy (%) of control against ticks for sheep treated on the brisket/axillae, groin and anogenital regions was always higher compared to sheep treated only on the anogenital region. In Dorper sheep, efficacy of control was >80 % for up to 4 weeks and in Merino sheep >80 % for 6 weeks.

Karoo paralysis in South Africa is induced in livestock by feeding female Ixodes rubicundus ticks when infestation densities on hosts exceed certain critical levels. It has been shown previously that Angora goats are at a higher risk of being paralysed than Merino sheep, and such differences have been related to differences in feeding behaviour and spatial distribution of the two small-stock breeds. We hypothesized that differences in infestation densities with Karoo paralysis ticks would also occur between Merino and Dorper sheep breeds. A study was conducted under natural conditions in the south-western Free State, to compare infestation burdens of the two sheep breeds and also to investigate seasonal patterns and annual variations in variations in terms of rainfall and temperature. Ten animals of each breed ran free in an area with a known history of Karoo paralysis and were examined on an approximately fortnightly basis, from March 1992 to December 1995, to determine tick abundance. Differences between the two breeds were significant (P < 0.05) during 1992 and 1993, but not during 1994. During the first two years, peak abundance of ticks was reached earlier in Dorper than in Merino sheep, and it also reached higher levels in Dorper than in Merino sheep (mean = 17.9 and 7.3, respectively). In 1993, two Dorper, but no Merino sheep, were paralysed. Dorper sheep are clearly at a higher risk of being paralysed than are Merino sheep, and as such, they can serve as indicators of adult tick activity and hence of the time to commence prophylactic treatment. Differences between the two breeds are probably related to differences in grazing patterns. Marked variation in abundance and the time of onset of peak activity of I. rubicundus occurred over the years. Tick numbers were high in 1993 and 1995, but very low in 1992. In 1993, peak activity occurred earlier (April) than during the other years (June or July). These differences are related to differences in prevailing environmental conditions that influence tick activity in a complex manner. Heightened humidity and lower temperatures during the early stages of seasonal activity of the tick (April or May), normally result in peak abundance of ticks on hosts at that time.

Successful prophylaxis of paralysis, induced in small stock by feeding female Ixodes rubicundus, is dependent on the accurate determination of the commencement of seasonal activity by the tick. The commencement of this activity was recorded for 11 consecutive years on a farm in the south-western Free State, South Africa, and for shorter periods on other farms, some of these in regions with markedly colder climates. The colder the mean minimum atmospheric temperatures during the 2 months preceding the start to tick activity, the earlier it commenced. This could differ by 4 weeks from year to year on the same farm. In a region with a low effective temperature activity commenced between 3-8 weeks earlier than in a region with a higher effective temperature.

Synthetic pyrethroid pour-on compounds have been developed for use on cattle but many are now also registered for the control of ectoparasites on small ruminants. The breed of small livestock has been known to influence the efficacy of various pour-ons and we hypothesized that differences in the duration of protection afforded by a synthetic pyrethroid pour-on against ticks on small livestock, would be greatest between hairy and woolly breeds. Angora goats with mohair, Dorper sheep with hairy wool, and Merino sheep with wool were treated with 1% m/v deltamethrin pour-on with an oil base at a dosage rate of 1 ml 5 kg-1 body mass. The duration of effective protection against Ixodes rubicundus, the Karoo paralysis tick, was determined under field conditions. Angora goats proved to be the highest risk group, but were afforded the least protection. Efficacy never reached 100% in this group and within 3 weeks the goats were already at risk of paralysis. Dorper sheep were afforded above 90% protection for 3 weeks and 85% after 4 weeks. In the case of the Merino sheep efficacy of protection remained above 90% up to 7 weeks post-treatment and was still 87% during Week 8. Differences in the amount of sebum and suint in the epidermis of the different breeds may be responsible for differences in the rate of spread and the rate of dilution of the active compound in the epidermis.

Hyalomma ticks were collected from Merino and black-headed Dorper sheep and their attachment preferences determined. The preferred site of attachment for Hyalomma marginatum rufipes on both Dorper and Merino sheep was the anogenital and inguinal areas (75-76%). On Dorper sheep, H. truncatum attached predominantly to the anogenital and inguinal areas (67.7%). On Merino sheep, most adults of this species attached to the feet (26%). Almost equal percentages also attached to the anogenital/inguinal and brisket areas (21.6 and 22.9%, respectively). These differences should be considered when pour-on acaricides are applied to different breeds of sheep.

An outbreak of lameness amongst Merino lambs, associated with the presence of Hyalomma ticks, was investigated on a farm in the south-western Free State, South Africa. The purpose was to follow the progress of the condition and to determine the extent of involvement of the two Hyalomma species which occur in the region. The flock of experimental sheep (n = 460) ranged free in natural veld under extensive farming conditions. During September and October 1993, adult ewes and lambs in this flock were examined at weekly intervals to determine tick identity, abundance and attachment-site preferences on lame and unaffected animals. Lameness occurred only among lambs, of which 68 were affected during the 8-week period. Hyalomma ticks tended to aggregate and mean numbers of ticks/aggregation were significantly higher on lame lambs (mean = 11.3) than on either the unaffected lambs (mean = 6.9) or the ewes (mean = 7.1). Most tick aggregations (72.4%) on the lame lambs occurred on the lower legs and feet, 34 out of 55 of these on the fetlocks or interdigital clefts. Hyalomma truncatum dominated (> 97%) on all animals examined. Only 15.8% of the Hyalomma marginatum rufipes recovered from the lame animals were attached to the legs. At two other localities at which H. marginatum rufipes was more abundant, or even dominant, few ticks attached to the lower legs or feet. Those that did were mostly H. truncatum (> 90%). Both H. marginatum rufipes and H. truncatum may attach to the same ventral and anogenital body regions, but H. truncatum has a tendency to attach also to the feet and lower legs. Although attachment of one or a few ticks in the axillar region or upper legs may cause lameness in sheep, the attachment of ticks to the interdigital clefts and fetlocks almost always causes lameness. The latter condition is more likely to occur in regions where H. truncatum dominates.

Paralysis caused by feeding female Ixodes rubicundus ticks is a major problem in large areas of South Africa. As the life cycle of the tick extends over a period of 2 years, it was hypothesized that strategic treatment of sheep with an acaricide over a 2 year period, timed to kill most engorging females, should markedly lower the biotic potential of the tick. Two flocks of sheep grazing in separate paddocks known to be infested with I. rubicundus were treated either strategically or on a threshold basis (i.e. only when tick challenge exceeded a predetermined critical level in terms of paralysis) for a 2 year period. The tick burdens of untreated control sheep running with the two flocks were monitored over a 4 year period and their seasonal dynamics determined. The times at which peak infestations occurred were similar for both flocks of sheep, but significant differences in mean tick burdens between the two flocks were recorded. Tick numbers on sheep in the strategically treated flock did not decrease during the third and fourth years of the trial as was expected. Possible reasons for this were low stocking densities, especially during times of peak abundance of adults and the presence of wild hosts which maintained tick populations.

Four to 10 Dorper sheep on each of 12 farms in the Cape Province and 3 farms in the Orange Free State were examined for adult ixodid ticks at approximately 2- to 4-weekly intervals over periods varying from 4 to 18 months, commencing during January, February or April 1989. The farms in the Cape Province were located in the north-west, south-west and south of the province. Those in the Orange Free State were situated in the north-east and in the south. The sheep in the Cape Province harboured 10 species of ixodid ticks and the seasonal abundances of Ixodes rubicundus, Rhipicephalus evertsi evertsi, Rhipicephalus gertrudae and Hyalomma truncatum were determined. The animals in the Orange Free State were infested with 7 tick species and the seasonal abundances of I. rubicundus, R. evertsi and Hyalomma marginatum rufipes were determined.

The aim of this study was to quantify the infestation densities of Karoo and brown paralysis ticks on sheep and goats and explain it in terms of the etho-ecology of these ticks and their domestic hosts. The Karoo paralysis tick usually quests from a vantage point on the vegetation whereas the brown paralysis tick displays an appetence response from the ground and mainly engages hosts that are prostrate. Both tick species are confined chiefly to hilly areas. Temporal differences in the infestation densities of the hosts within and between tick species were evident. These differences were related to disparities in the spatial distribution of the hosts, their activity patterns and the specific appetence responses of the two tick species. Differential climatological conditions affected the quality of forage in areas with a varied topography and the feeding preferences of hosts influenced tick-host sympatry and hence infestation densities.

The ratio of variance to mean (s2/means) of numbers of Ixodes rubicundus (males and females) per sheep was used as a measure of the dispersion pattern of this tick within a naturally infested population of sheep. Sheep were divided into two groups, one with previous contact with I. rubicundus and the other with no previous contact. Samples of 10 sheep from each group were searched for ticks on a weekly basis for 19 weeks during the winter of 1986. In each group, both male and female ticks had an s2/means ratio greater than 1 for the majority of observation periods indicating an aggregated dispersion pattern. The degree of aggregation was greater with increasing density of the ticks. The implications of these results are discussed both in relation to sampling procedures and potential control strategies.

With the exception of October, when no collections were made, adult ticks were collected at weekly intervals from February 1986 to January 1987 from 20 randomly selected sheep out of a flock of 60. Ixodes rubicundus was the most abundant tick and was present from April to September with a peak during May. Hyalomma marginatum rufipes was the next most numerous tick. It was recovered throughout the year with peak burdens being recorded from November to April. Small numbers of a Rhipicephalus sp. (near R. pravus) were also collected. These exhibited a major peak during February and a minor peak during August. A dipping programme to prevent the paralysis caused by I. rubicundus and the Rhipicephalus sp. (near R. pravus) is suggested.

The weights of feeding female Ixodes rubicundus attaching to sheep was studied in a natural focus of Karoo paralysis. The studies showed fewer females in the middle weight ranges and more in the heavier and lighter categories than would be expected if the distribution was normal. Weights were also strongly skewed towards the lighter females between 0 and 400 mg. No differences in the pattern of attachment weights occurred over the four experimental groups used, suggesting that previous contact of sheep with I. rubicundus had no effect on the ability of the tick to engorge.

The epidemiology of Karoo paralysis, induced by the tick Ixodes rubicundus, was investigated in a paralysis-enzootic area of the southwestern Orange Free State, Republic of South Africa. Sheep became paralysed during the last week of April and the first week of May during the 1985 and 1986 seasons, respectively. Paralysis cases were recorded up until July, but most paralysis cases occurred during the first week of May with a second but smaller peak occurring during June. Tick numbers on paralysed sheep closely followed peak periods in paralysis. A total of 65 and 50% of the naive sheep became paralysed during the 1985 and 1986 seasons, respectively. The seasonal pattern of tick infestation by female I. rubicundus was similar on both previously exposed and on naive sheep. The results of this study indicate that a certain number of ticks per kilogram host body mass is required before symptoms of paresis of paralysis are observed. In general the tick burden per kilogram host mass was significantly greater in paralysed compared to non-paralysed sheep. The range in the number of ticks per kilogram host mass may, however, overlap between non-paralysed and paralysed groups. Previously exposed or previously paralysed sheep are less susceptible to paralysis in the following year. Differences in susceptibility between individual sheep seems likely.