Tick paralysis in the Karoo areas of South Africa

Abstract

1. Four forms of tick paralysis in South Africa may be distinguished, which differ as regards the clinical picture and are associated with four distinct tick species. 2. The literature dealing with tick paralysis in South Africa is briefly reviewed. 3. The seasonal occurrence of the adults, nymphae and larvae of I. rubicundus is given. 4. The adult is both nocturnal and diurnal and it is possible to demonstrate a peak in diurnal activity between 10 a.m. and 2 p.m. 5. The immature stages are exclusively nocturnal. 6. The influence of temperature upon larval activity is demonstrated graphically. 7. A host list is given which shows that the Menotyphla and Lagomorpha play the main role as hosts of the immature stages. The Artiodactyla constitute the main hosts of the adult tick amongst the wild animals. The tick is not found on birds. 8. The attachment sites of the adult stages on adult sheep and lambs are given and the chances of reaching full engorgement on the different regions of the body of the sheep arc discussed. The preferential sites for I. rubicundus and I. ricinus are compared and the differences in habit of these two species on sheep described. 9. The time required by the female to reach full engorgement in different situations on the bodies of sheep is given. 10. The stages of engorgement normally observed are described and exceptions to this rule are discussed. 11. The percentage of females that fail to reach full engorgement on sheep is shown to increase with the time the sheep spends in tick-infested veld. 12. The influence of copulation upon the rate of engorgement is discussed. 13. The use of tethered sheep in tick-infested veld as a means of tick survey is discussed. 14. An improvement on the standard technique of dragging for ticks, for use in the Karoo shrub, is described. 15. The attraction of different materials to I. rubicundus tested by the dragging technique in the field has been investigated. 16. Seven species of ticks found during the course of dragging are noted. 17. The uniformity of distribution of I. rubicundus larvae in the field is discussed. 18. The factors responsible for the losses of ticks from the apparatus during the course of dragging are demonstrated graphically and discussed. 19. A map showing the distribution of I. rubicundus and the occurrence of tick paralysis in relation to veld (pasture) types in a selected area in the Sneeuberg Range is included. 20. The ecological investigations of overseas workers on other tick species are reviewed briefly for comparison with the findings relating to I. rubicundus in South Africa. 21. An association between tick incidence and deterioration of pasture in the case of I. rubicundus is found to follow a pattern similar to that of I. ricinus in Britain. 22. The hatching and survival of the larvae of I. rubicundus are shown to represent phases of the life-cycle more susceptible to unsuitable environment than any other stage. 23. Experimental studies on the hatching and survival of eggs placed in decaying plant material under certain shrubs and rank grasses are described and compared with the differences observed when grasses are not allowed to become rank. 24. Significant differences in tick densities are shown to occur in different naturally-infested veld types. Sweet-grass mountain veld, constituting the original coverage of all mountains in the area under investigation, is not suited to the completion of the life-cycle of the tick. 25. The role played by Rhus erosa in the creation of suitable environmental conditions for the tick is pointed out. 26. The time required for bringing about an alteration in the existing plant associations by applying different methods of pasture management is discussed. 27. The influence of the regular dipping of sheep upon the incidence of I. rubicundus is demonstrated. 28. The exclusion of sheep from tick-infested camps during the active season of I. rubicundus is shown to have no effect upon the incidence of the tick. 29. The influence of veld fires upon the tick is pointed out. 30. The recommendations of other investigators for the control of I. rubicundus by dipping are compared with the application of dipping to the control of I. ricinus. 31. The specific efficacy of insecticides against the tick as found by a laboratory method, the ability of the insecticide to diffuse along the wool fibres and the quantity of insecticide deposited in the fleece rather than the concentration of the wash in the dipping tank, are shown to be the decisive factors governing the period of protection obtained against I. rubicundus. 32. BHC is shown to be capable of protecting woolled sheep against I. rubicundus for a period exceeding 18 weeks when 4·75 gm. of the gamma isomer is deposited per sheep. 33. Dieldrin is shown to protect woolled sheep for approximately 11 weeks when 7 gm. of the active ingredient is deposited per sheep. 34. The protection of sheep against Rhipicephalus evertsi and Hyalomma spp. by BHC has been tested. 35. The experience gained in the application of the foot- or walk-through bath for sheep is given.