Tick toxicity in cats caused by Ixodes species in Australia: a review of published literature

Tick toxicity in cats caused by Ixodes holocyclus and related species is a common medical condition on the east coast of Australia. Intoxication typically causes a flaccid ascending neuromuscular paralysis and clinical signs can include anxiety, dysphonia, hind limb weakness and/or ataxia, pupillary dilation, respiratory signs and possible bladder voiding dysfunction. Diagnosis is made with a combination of appropriate clinical signs and visualisation of tick(s) on a thorough body search. Cases are classified clinically using a scoring system, which grades neuromuscular weakness and respiratory compromise. The mainstays of treatment are tick removal, administration of tick antitoxin serum and intensive supportive care. Given a prompt and appropriate management regimen, prognosis is good, according to available literature. Most of the literature concerning tick toxicity in cats is anecdotal in nature and an evidence-based review of what is known of this condition has not previously been published.

Long QT syndrome in dogs with tick toxicity (Ixodes holocyclus)

OBJECTIVE

To evaluate cardiac electrical function in dogs with tick toxicity.

DESIGN

A prospective clinical investigation of 39 client-owned dogs treated for naturally occurring tick toxicity.

PROCEDURE

An ECG was performed on each dog on several occasions; at admission to hospital with tick toxicity, 24 h later, at discharge from hospital when clinically normal and approximately 12 months later.

RESULTS

The mean QT interval corrected for heart rate (QTc) was prolonged at admission, 24 h and at discharge compared to the QTc measured 12 months later. T wave morphology was altered in dogs at admission. All other parameters were within normal limits.

CONCLUSIONS

The prolonged QTc interval and altered T wave morphology of dogs with tick toxicity reflects delayed cardiac repolarisation and is comparable with long QT syndrome (LQTS) in people who are predisposed to polymorphic ventricular tachycardia and sudden death. Resolution of ECG changes lagged behind clinical recovery.

Sweating sickness: relative curative effect of hyperimmune serum and a precipitated immunoglobulin suspension and immunoblot identification of proposed immunodominant tick salivary gland proteins

Although of low morbidity, sweating sickness is readily induced in calves by infestation with positive Hyalomma truncatum adult ticks. This epitheliotrophic disease has no specific cure except by the administration of hyperimmune serum obtained from animals which have recovered and are subsequently immune to the disease. Treatment with hyperimmune serum, however, has associated problems of donor availability, possible serum contamination and i.v. administration of a relatively large volume. This paper compares the treatment and cure of sweating sickness using unrefined hyperimmune serum and that of an experimental suspension. The latter proved relatively inefficient probably due to a low concentration of effective immunoglobulins. Immunoblot analyses of the sera of affected animals, using tick salivary glands as antigen during the course of the trial revealed 4 tick salivary gland proteins with molecular masses of between 27-33 kDa. These are proposed as being associated with sweating sickness immunodominance.

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.

Infestation in the dog by the paralysis tick, Ixodes holocyclus. 4. Cardiovascular effects

To determine the extent and significance of changes in heart rate and rhythm noticed previously in dogs paralysed with Ixodes holocyclus, two studies were undertaken. In one the electrocardiogram was recorded at stages throughout the disease and the traces analysed for changes, while in the second a detailed study of the effect of Ixodes holocyclus on the cardiovascular system was undertaken. The electrocardiographic changes were extremely variable between stages and between dogs. Generally, if a dysrhythmia occurred in stages 1, 2 or 3 it tended to be sinus tachycardia, ventricular tachycardia or sinus arrest. In stage 4 sinus arrest, sinus bradycardia, or sinus or ventricular tachycardia were the prominent dysrhythmias, whereas in stage 5 sinus bradycardia predominated. Cardiovascular measurements indicated an increase in peripheral vascular resistance leading to a significant elevation in mean arterial pressure at all stages of the disease. Cardiac output was decreased significantly only at stage 2, although it was below the control measurements at all stages. Pulmonary arterial pressure was significantly elevated at stages 2, 3 and 4 due most probably to an increase in pulmonary vascular resistance. Myocardial contractility was not significantly changed throughout the disease. The changes observed in the electrocardiogram and the cardiovascular system in stages 1, 2 and 3 are unlikely to be due to hypoxia and could represent dysfunction of the autonomic nervous system. During stages 4 and 5 oxygen levels were below normal and the bradycardia seen terminally is almost certainly due to hypoxaemia.(ABSTRACT TRUNCATED AT 250 WORDS)

Infestation in the dog by the paralysis tick, Ixodes holocyclus. 5. Treatment

In this study the value of drugs administered with hyperimmune serum in the treatment of advanced disease produced by Ixodes holocyclus was compared under controlled conditions. All control dogs died rapidly whereas one dog survived and 3 dogs died after receiving hyperimmune serum alone. When promethazine hydrochloride was administered with hyperimmune serum 2 dogs recovered rapidly while the remaining 2 died. Administration of dexamethasone and hyperimmune serum allowed 3 dogs to survive while administration of phenoxybenzamine hydrochloride in conjunction with hyperimmune serum allowed rapid recovery of all 4 dogs. Phenoxybenzamine hydrochloride, an alpha-adrenergic blocking drug, was chosen because of its potential to attenuate the arterial hypertension previously reported (Ilkiw et al 1988). The survival of all dogs together with the rapid return to normality indicated that this drug was beneficial in the treatment of dogs with advanced signs of tick paralysis.

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.

An undescribed Rhipicephalus species associated with field paralysis of Angora goats

Paralysis of Angora goat kids caused by adult ticks, which most probably belong to an undescribed species of the Rhipicephalus pravus group, is described. Confirmed cases of paralysis occurred in the south-western Orange Free State between the second half of September and the first half of November as well as during the first half of February. The mean female tick burdens (mean = 21.4) of paralysed Angora kids were significantly higher than those of healthy kids (mean = 4.4). The predilection attachment site of the adult ticks was the ears of the goats. The elephant shrew Elephantulus myurus is a preferred host of the immature stages whereas the scrub hare Lepus saxatilis serves as an important host for the adult ticks.

Infestation in the dog by the paralysis tick Ixodes holocyclus. 3. Respiratory effects

To assess respiratory function in dogs with tick paralysis, respiratory measurements were recorded on 14 dogs experimentally infested with Ixodes holocyclus. There was a progressive fall in respiratory rate with no change in tidal volume, which resulted in a significant fall in minute respiratory volume in the latter stages of the disease. The fall in respiratory rate was possibly central in origin and was accompanied by an increased alveolar-arterial oxygen tension difference, probably caused by pulmonary congestion and oedema. The "grunting" respiration seen in tick paralysis was due to closure of the vocal cords during expiration and could represent an attempt to re-expand collapsed parts of the lung.

Infestation in the dog by the paralysis tick Ixodes holocyclus. 2. Blood-gas and pH, haematological and biochemical findings

Arterial blood-gas and pH, haematological and biochemical estimations were carried out on 8 dogs infested with Ixodes holocyclus and 2 uninfested controls. The arterial blood-gas and pH measurements did not change significantly until the dogs were recumbent and unable to lift their heads. When affected dogs became moribund, moderate hypoxaemia with acute ventilatory failure was present. The significant haematological and biochemical abnormalities were difficult to interpret individually, but taken together could reflect sympathetic stimulation of the adrenal cortex or medulla.

Infestation in the dog by the paralysis tick Ixodes holocyclus. 1. Clinical and histological findings

Under laboratory conditions 8 dogs were infested with Ixodes holocyclus and the clinical signs and histological findings were recorded. Seven of the dogs developed clinical signs of the disease, died and were subjected to a post-mortem examination, while the eighth dog remained normal. The clinical signs were consistent between animals and enabled the course of the disease to be subdivided into 5 stages to facilitate analysis of data in future experiments. The most prominent feature of the disease was dysfunction of the efferent motor system although some disturbance of the afferent pathways and involvement of the autonomic nervous system did occur. The period elapsing between attachment of the ticks and onset of signs varied from 5.5 to 7 days, while the mean duration of the disease was 23.3 h. The histopathology demonstrated moderate to severe congestion of the liver, kidney and lungs, and in some lung sections pulmonary oedema was present.

Further studies of the clinical pathology of sweating sickness in cattle

Experimentally-induced cases of sweating sickness in calves were used in an effort to correlate the blood chemistry with some of the known pathological changes. Results showed that the "sweating" associated with necrotic dermatitis did not alter blood electrolyte levels. Laboratory evidence of a disseminated intravascular coagulopathy was found which correlated with the microthrombi described in cases of sweating sickness. A high blood cortisol level was found in one of the animals that died from the disease and could possibly be used as a prognostic indicator in clinical cases. Recommendations are made with regard to the supportive treatment based on the clinical pathological findings.

Studies on the ability of different strains or populations of female Rhipicephalus evertsi evertsi (Acarina:Ixodidae) to produce paralysis in sheep

Simultaneous infestation of 3-6 month-old Black-head sheep with 15 South African wild strains of Rhipicephalus evertsi evertsi males and females as well as a strain from Rwanda clearly showed that all strains are capable of inducing paralysis. Assessment of the infestation-rate of engorging female ticks during the period that their mass ranged between 15 and 21 mg/kg sheep body mass indicated that toxicity is quantitatively identical and exhibits no intraspecific gradations. The period between the beginning of infestation to the manifestation of the first clinical symptoms is, however, strain dependent: 4 days for ticks from Warmbaths, and at least 5 days for all other strains.

Investigations into the paralysis-inducing ability of Rhipicephalus evertsi mimeticus and that of hybrids between this subspecies and Rhipicephalus evertsi evertsi

Studies performed on sheep showed that Rhipicephalus evertsi mimeticus is a paralysis-competent tick species whose toxicity is either the same as, or only slightly less than that of R.e. evertsi. It was also proved that the paresis or paralysis induced by the mimeticus females is characterized by a constant incubation period which is independent of the tick infestation rate and body mass of the host, and consequently of its age. This period is entirely determined by the state of repletion of the ticks and is regulated by the date of mating. It was further proved that a precise relationship exists between an increase of engorgement or salivation activity and the intensity as well as the persistence of clinical symptoms. Thus only female ticks in the mass range of 15-21 mg are toxic. Strain-dependent differences could not be demonstrated. The infestation rates of subspecific hybrid female ticks, and of their descendants, that are necessary to produce the respective symptoms showed no differences in toxicity. When infestations were limited to a small skin area minimum paresis could frequently not be induced, even though the actual number of ticks applied was sufficient to cause lethal paralysis.

The efficacy of hyperimmune serum in the treatment of sweating sickness

Natural and experimental cases of sweating sickness were treated using a hyperimmune serum as specific treatment and hyperimmune serum combined with symptomatic and supportive treatment based on the clinicopathological changes observed in cases of sweating sickness. The treatment regimens were found to be highly effective in pigs and sheep as well as in calves, although recovery in the latter species was slower.

Tick paralysis in Brazil

From July to December 1977 and from June to November 1978 the toxic effects of Amblyomma cajennense were studied in cattle sheep and goats. Locomotor disturbances commencing as hind-limb paralysis ascended to the upper nervous centres causing paralysis. This was observed in natural infections and confirmed experimentally. Tick paralysis is reported for the first time in Brazil, manifesting itself in a different form to that usually attributed clinically to the disease. Also for the first time reference is made to tick paralysis induced by all developmental stages of A. cajennense.

Tick (Ixodes holocyclus) paralysis in the dog--induction of immunity by injection of toxin

Three beagle dogs were immunised against the paralysing effects of holocyclotoxin, using toxic extracts derived from salivary glands of the Australian paralysis tick, Ixodes holocyclus. Upon subsequent challenge with four ED50's of toxin the animals were completely immune, whereas during the early stages 2 of 3 dogs became paralysed after injection with 0.5 ED50. Three immunised beagles, on which 15 I. holocyclus ticks had fed, showed no symptoms but a control beagle became paralysed after 4 I. holocyclus females fed on it. Treatment was instituted immediately upon the onset of clinical signs and the dog recovered uneventfully.

Pyrexia in response to Rhipicephalus appendiculatus infestation in calves

Bos taurus calves free from tick-borne diseases were prophylactically treated with oxytetracycline hydrochloride and phenamidine isothionate 40% (w/v) injections and infested twice with adult Rhipicephalus appendiculatus ticks. Mono- and diphasic temperature rises were observed during primary and secondary exposures respectively with the peak occurring when the ticks were completing engorgement. However, the first rise in the secondary infestation occurred well before repletion and was associated with a hypersensitivity state. The feeding performance, viability and fecundity of female ticks were impaired during the secondary exposure.

Rhipicephalus appendiculatus: cause and vector of diseases in Africa

Rhipicephalus appendiculatus Neum. occurs mainly in the eastern and southern parts of Africa and is the principal cause and vector of some very important stock diseases in these areas. The diseases include the theilerioses, brown tick toxicosis and Nairobi sheep disease. These are briefly discussed, and emphasis is laid on the role of R. appendiculatus in their epidemiology. R. appendiculatus is a 3-host tick particularly well adapted to survive where climate and vegetation are suitable. The basic requirements and breeding potential of this tick are also discussed.

[Fatal neurological syndrome in a collared dove (Streptopelia decaocto) and fixation of ixodes pari (= I. frontalis) tick (author's transl)]

Tick paralysis is probably a common condition in wild birds, but rarely observed. The authors report the case of a collared dove (S. decaocto) presenting a fatal neurological syndrome associated with the fixation of a Ixodes pari female above the right eye. Virological studies of bird's tissues and of the tick were negative. These findings were compatible with tick paralysis or a minor equivalent of this syndrome. In addition, it was the first time that a collared dove is found as host for I. pari.

Sweating sickness in adult cattle

A Kenyan strain of Hyalomma truncatum was shown to cause sweating sickness in adult cattle in the laboratory. The typical lesions of moist eczema and mucous membrane changes were accompanied by a marked fall in circulating leucocytes with a severe neutropenia. Although all cattle recovered, some suffered a severe clinical disease and recovery was slow. Recovered cattle were immune to toxicosis 1 year later.

Tick paralysis in a western harvest mouse

An engorging female Ixodes pacificus was observed on a western harvest mouse (Reithrodontomys megalotis) in Humboldt County, California. The mouse demonstrated a flaccid paraplegia, but it appeared to recover fully after the tick was removed.

Tick paralysis in a grey fox

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.

[The vulnerability of peripheral nerves and the somatic toxin linkage in tick paralysis of chickens, caused by Argas (Persicargas) walkerae (author's transl)]

Investigations on the impulse propagation and the pattern of amplitudes of toxically by Argas (Persicargas) walkerae larvae impaired peripheral nerves were carried out under oxygen saturated and anoxic conditions. It was demonstrated, that the maximum nerve conduction velocities of the isolated N. ischiadicus were slightly lowered in the first carbogenic and anoxic phase, in comparison with normal nerves. After the second incubation the conduction velocities were, however, almost the same or even higher. The survival times of the nerves after anoxic exposure, which were determined by the temporal persistence of the potentials, revealed that this neurophysiological parameter always resulted in a higher value for the damaged nerves after every two anoxic phases. The diseased nerves therefore tolerate anoxia longer and better than do healthy nerves in respect to their excitability and in their function of impulse propagation. From these in vitro investigations it is concluded that the noxious substance responsible for the paralysis is not cell-bound, but circulates humorally. The toxin possesses membranophilic properties, but its somatic linkage is very labile.

Paralysis of calves by the tick, Ixodes Holocyclus

Adult female Ixodes holocyclus were collected from the field at Fig Tree Pocket, a Brisbane suburb, at Tamborine Mountain, Queensland and at Lismore, New South Wales, in November 1974. Females were also reared from engorged nymphs collected off bandicoots from Tamborine Mountain July 1974 and 1975. In November 1974 unexposed 2-3 week old British breed calves, weighing between 26 and 46 kg were infested with 2,4,8 or 10 ticks. Neither 2 nor 4 females per calf caused paralysis. A challenge of 8 to 10 females induced paralysis 6 to 9 days after infestation by which time most ticks had engorged. There was little difference between ticks from different geographic localities. The site of attachment had no influence on tick toxicity. In September 1975, 2-3 week old British breed and Sahiwal x Jersey calves were infested with female ticks which had moulted 2-4 weeks prior to infestation. All but one calf with 10 ticks and all calves with 4 ticks became paralysed 8 to 13 days after infestation. At the time of paralysis only 1 of the 86 ticks had engorged and the remainder were small (30 to 50 mg). The greater toxicity of the latter ticks may have been due to the different treatment of ticks prior to infestation or to variations in the production of toxin associated with slow feeding. Four of 7 paralysed calves were saved using canine antitick serum.

Paralysis in chickens caused by larvae of the poultry tick, Argas persicus

White Leghorn pullets 20 weeks old submitted to the diagnostic laboratory were found heavily infested with the larval stage of the poultry tick, Argas persicus. The birds were severely depressed and recumbent. The signs were quickly reversed when the tick larvae were removed. The rapid rate of recovery and negative results in detailed diagnostic procedures suggested that the tick larvae caused the paralysis.

Cattle and the paralysis tick Ixodes holocyclus

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.