Tick paralysis: another lethal tick-borne disease.
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Paralysis of domestic stock by the paralysis tick Ixodes holocyclus is chiefly a disease of young animals (especially calves) and of non-habituated stock introduced into tick-infested country in spring. The tick has a wide host range, but its principal hosts are bandicoots. The tick has one generation per year and the adult female, which causes almost all paralysis, is abundant in spring and early summer and occurs most commonly in overgrown or regrowth country where bandicoots are abundant. The distribution and behavior of the long and the short-nosed bandicoots are reviewed. The number of ticks required to induce paralysis in cattle and the protection from paralysis afforded by prior experience of the tick are discussed.
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.
Allergic reactions to Ixodes holocyclus are well recognized but poorly defined. Tick-bite reactions in 42 individuals in this study fell into six classes. Skin-prick tests and radioimmunoassay (RIA) indicated that all systemic hypersensitivity (class 3) and atypical reactions (class 4) were IgE-mediated. Some 73% of the large local reactions (class 2) and only 12.5% of the small local reactions (class 1) were associated with IgE specific for tick allergens. Subjects who reported heavy exposure to tick-bite were more likely to have positive RIA values (P less than 0.05). There was an association between the individual's atopic status and tick allergy (P greater than 0.05).
A patient with tick paralysis had motor and sensory nerve conduction studies before and after removal of an engorged tick. The amplitudes of muscle action potentials evoked by stimulation of motor nerves were reduced initially, returning to normal after the tick was removed. Distal motor and sensory latencies also shortened after removal, and conduction velocities were improved 6 months later. Direct stimulation of muscle produced a normal response, and tests of neuromuscular transmission were normal, including the response to edrophonium. These findings are compatible with experimental results showing effects of the toxin on motor nerve terminals as well as on large sensory and motor nerves.
The pathophysiology and clinical manifestations of tick paralysis in North America and Australia are reviewed. Clinical and electrodiagnostic findings in tick paralysis are contrasted with those that occur in other diffuse lower motor neuron disorders, and the disease in North America is compared with the more severe form of the disease that occurs along the east coast of Australia. A detailed account of the treatment of animals afflicted with tick paralysis is presented.
Electrophysiologic measurements in a 9-year-old girl with tick paralysis demonstrated a prolonged distal latency and a decremental response to 30 Hz stimulation. The nerve conduction determinations became normal after clinical recovery. The pathophysiologic process of this disease seems to be within the peripheral nerve although a central site of action of tick toxin cannot be completely excluded. Tick paralysis should be considered in the individual who develops ascending paralysis.
Reviewed are 3 cases of tick paralysis in children each with a different presentation. One child presented with an ascending flaccid weakness, another with weakness and cerebellar signs, and a third with pure cerebellar signs. Ixodes scapularis, the black-legged deer tick, was the offending tick in Case 3 and apparently has not been previously reported to cause paralysis in humans. Because of the potential for a fatal outcome, it is imperative to consider tick paralysis in any child with an ascending flaccid weakness or acute ataxia.
Significant differences in the distribution of brown paralysis ticks on various age classes of Angora goats were recorded. In kids, most (greater than 98%) of the ticks attached to the head and ears, whereas in older groups, in addition to the ears, a high proportion (greater than 20%) of ticks also attached to the ventral side of the neck. There were significant differences in the mean infestation densities of both male and female R. punctatus in kids and older animals. These differences were, however, only significant for the first two sample dates involving kids, and are probably related to behavioural attributes of the kids which enhance tick/host contact. Newly born Angora goat kids are considered a high-risk group with regard to paralysis caused by the brown paralysis tick. Methods of avoiding mortality amongst kids are suggested.
Spatial distribution of the Karoo paralysis tick (Ixodes rubicundus) has been studied in a paralysis enzootic area of the southwestern Orange Free State. Significantly more females than males were collected from the vegetation. Most ticks (99%) used grass as questing sites at a height of approximately 45 cm (range 10-97 cm), which correlates with the size of host animals. No significant differences between the questing height of male and female ticks were evident. The ticks were found on most of the grass species present and, except for the genus Eragrostis, no specific preference was evident. When questing, the capitulum of I. rubicundus is usually (90%) directed towards the ground. Seventy-eight percent of the ticks occurred singly on a specific grassblade or flowerhead. In those cases where two ticks occurred together, no sexual aggregation was evident. Most ticks occurred under or close (mean = 62 cm) to the crown cover of specific shrub or tree species. These plant species were characterized by a dense crown cover with a mat of decaying leaf litter underneath. The preference of the tick for wild olive trees (Olea europaea africana) suggests that, except for the physical characteristics of this tree species, host factors may also be important. Significantly more ticks were distributed on the cooler, more protected southern sides of vegetation in comparison to the northern sides.
One hundred seventeen Dermacentor variabilis were removed from the head and back of a grey fox (Urocyon cinereoargenteus) showing paresis and diminished motor reflexes of the hind limbs. Rapid and total recovery led to a diagnosis of tick paralysis.
An outbreak of suspected tick paralysis occurred in one-humped camels in Southern Darfur, the Sudan, between latitudes 11-12 degrees N and longitudes 24-25 degrees E, when the camels were herded in tick infested areas. It involved 251 camels of different ages, in ten herds causing 34.3% mortality. The symptoms were incoordination of movements, unsteady gait and recumbency followed by death or recovery. Hyalomma adults and/or Rhipicephalus nymphs and adults were incriminated to be the cause of the disease. Transient paralysis in a guinea pig was produced after experimental feeding of ticks. Removal of the camels from the tick infested areas and treatment against the ectoparasites with Lindane at the concentration of 0.23% contributed to controlling the disease.
The blocking conditions appropriate for Western blot identification of allergens of the Australian paralysis tick, Ixodes holocyclus, have been investigated. The results suggest that human serum is a potent blocking agent which may have wide application in the immunodetection of antigens.
Clinical and serologic evidence of Lyme disease in Australia, including the typical rash, erythema migrans, has been reported. The vector tick transmitting Borrelia burgdorferi in Australia, however, has not been determined. The Australian paralysis tick, Ixodes holocyclus, is a logical candidate vector of the Lyme disease spirochete in Australia; therefore, we tested the ability of I. holocyclus to acquire and maintain a North American isolate of B. burgdorferi. Larval I. holocyclus ingested spirochetes, but none of 84 derived nymphs were infected. These experiments should be repeated with Australian strains of spirochetes.
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