Seasonal occurrence of Karoo paralysis in Angora goats in relation to the infestation density of female Ixodes rubicundus

Parelaphostrongylus tenuis and other parasitic diseases of the ruminant nervous system

There are many parasites that affect the ruminant central nervous system. Clinical signs can vary dramatically based on the location and mobility of the parasite. Clinical disease can occur due to the physical presence of the parasite and the resulting host immune response or the toxin produced by the parasite. Differentiating the cause of disease is particularly important because prognosis,treatment, and subsequent control measures vary dramatically depending on the disease process. This article focuses on the pathogenesis,treatment, and control of some of the more common parasitic diseases of the ruminant central nervous system.

Ixodes rubicundus nymphs are short-day diapause-induced ticks with thermolabile sensitivity and desiccation resistance

The Karoo Paralysis tick, Ixodes rubicundus Neumann (Acari: Ixodidae), is a semi-voltine ixodid that survives stressful environmental conditions using morphogenetic diapause (eggs and engorged nymphs) and desiccation resistance. Both photoperiod and temperature influence diapause induction in the engorged nymph. Ixodes rubicundus nymphs are typical long-day photoperiodic organisms. The critical photoperiod is approximately 13.5 h light, 10.5 h dark, and they display a thermolabile response. The period between detachment and apolysis in engorged nymphs is modified by photoperiod; however, apolysis to ecdysis is not affected by photoperiod. Thus, initiation of development, but not the actual process is controlled by photoperiod. Most engorged nymphs delayed metamorphosis when exposed to short-day regimen (LD 12 : 12 h) after feeding. Nymphs exposed to pre- and post-feeding long-day regimen (LD 14 : 10 h) developed. Times for 50% of nymphs to apolyse when exposed to photoperiods of LD 14 : 10 h, 13.5 : 10.5 h, 13 : 11 h and 12 : 12 h were 28, 36, 40 and 58 days, respectively. Times for 50% of engorged nymphs to ecdyse ranged from 38 to 40 days after apolysis. Nymphs were sensitive to photoperiodic exposures before, during and after feeding. Nymphs exposed to long day (LD 14 :10 h) before and during feeding, moulted at 20 degrees C; however, most exposed to 10 degrees C followed by 20 degrees C (post-feeding) went into diapause. Both short- (10 : 14 h) and long- (14 : 10 h) day exposed engorged nymphs survived 45 days at 0% r.h. (n = 73), but diapause-destined ticks kept at 13 degrees C lost the least mass (29.5+/-9.5%, SD), while nondiapause ticks at 23 degrees C lost the most (48.7+/-8.2%, SD). Termination of diapause and transition to development probably coincides with a definite increase of water vapour uptake by engorged nymphs. Comparatively, I. rubicundus engorged nymphs are more desiccation tolerant than a North-American counterpart, Amblyomma cajennense (Fabricius) (Acari: Ixodidae), which is also semi-arid- to xeric-adapted. Diapause conveys important survival attributes that enable engorged I. rubicundus nymphs to inhabit a semi-arid environment with great temperature extremes, and to synchronize their activity periods with seasons and host utilization patterns.

Effects of castration on grooming in goats

In African antelope and North American cervids, breeding males during the rut engage in less oral self-grooming, and harbor a greater density of ticks, compared with conspecific females and non-breeding males. The purpose of this study was to experimentally test the proposition that down-regulation of self grooming in some male bovids occurs via the direct or indirect action of testosterone. Domestic dairy goats (Capra hircus) were used as a model. In Experiment 1, comparative observations conducted on twelve gonadally intact male goats (bucks), nine males castrated at 3 weeks of age (wethers), and twelve intact females (does) supported the prediction that the grooming rate of intact males would be depressed relative to wethers and does. Bucks oral groomed at one-third and one-fourth the rate of wethers and does, respectively, and they scratch groomed half as much as does. There was no significant difference between wethers and does in oral or scratch grooming rates. Experiment 2 involved castration of eleven bucks from Experiment 1, followed by 2 months of observation. Similar to the pattern of other testosterone-dependent behavioral changes after castration in adult males, there was a good deal of variation in the individual grooming response of males to castration, with increases in grooming taking 2 to 8 weeks to be manifested in ten of eleven goats. Overall, castrated males oral groomed about 3 x above their intact rates, supporting the prediction that castration removes testosterone-mediated suppression of grooming. This is the first example of alteration of grooming behavior in males by gonadal androgen, and the first demonstration of enhancement of any mammalian behavior by removal of gonadal androgen.

Interbreed differences in the efficacy of 1% deltamethrin pour-on to protect small livestock against infestation with Ixodes rubicundus (Acari:Ixodidae)

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.