Tick (Ixodes holocyclus) paralysis in the dog – quantitative studies on immunity following artificial infestation with the tick

SUMMARY Beagles have been immunised against the paralysing effects of the Australian paralysis tick Ixodes holycyclus by allowing female ticks to feed on these dogs. Complete immunity to the toxic effects of lethal numbers of feeding ticks has persisted in these beagles for at least 53 weeks and in similarly-immunised foxhounds for at least 102 weeks, during which periods the beagles and foxhounds were kept free of ticks. Serum antitoxin titres increased to a maximum value (hyperimmunity) of 46 antitoxin units/mL with a minimum number of 11 ticks feeding simultaneously. Titres declined to a low level after 12 to 14 weeks of freedom from tick infestation but increased again on reinfestation with ticks. Large numbers of ticks (up to 60) appeared to be required after several stimulation/relaxation cycles to obtain hyperimmune levels of antitoxin in serum. The serum antitoxin titre appeared to be a good indicator of effective immunity to tick paralysis during the initial development of hyperimmunity but was less indicative thereafter, as dogs whose serum antitoxin titres had reached an apparent maximum remained immune to tick paralysis after titres had decreased to low levels. There was no evidence of cutaneous hypersensitivity or any other tick rejection mechanism that could account for this effect.     

Suspected tick paralysis (Ixodes holocyclus) in a Miniature Horse

A 9‐year‐old Miniature Horse gelding infested with ticks (Ixodes holocyclus) was presented with flaccid motor paralysis causing recumbency. Neurological examination and other diagnostic tests did not identify an alternative aetiology, leading to a presumptive diagnosis of tick paralysis. The gelding was treated with tick antiserum and intensive supportive care. He made a gradual recovery over the 48 h following presentation and was discharged without further complications. This case report describes in detail the clinical signs and successful treatment of a Miniature Horse with flaccid paralysis caused by suspected envenomation by Ixodes holocyclus.     

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.     

Tick (Ixodes holocydus) paralysis in the dog – induction of immunity by injection of toxin

SUMMARY Three beagle dogs were immunised against the paralysing effects of holocyclotoxin, using toxic extracts derived from salivary glands of the Australian paralysis tick, Ixodes holocydus. Upon subsequent challenge with four ED50, 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. holocydus ticks had fed, showed no symptoms but a control beagle became paralysed after 4 I. holocydus females fed on it. Treatment was instituted immediately upon the onset of clinical signs and the dog recovered uneventfully.     

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.     

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.     

Distributions of the paralysis ticks Ixodes cornuatus and Ixodes holocyclus in south-eastern Australia

OBJECTIVE: To describe the actual and potential geographic distributions of Ixodes cornuatus and I holocyclus in south-eastern Australia. PROCEDURE: Examination of ticks from museum collections and trapped animals were made. (Bioclimatic analysis BIOCLIM) was used to predict potential distributions. RESULTS: I holocyclus was collected from rodents (Rattus fuscipes, R lutreolus, R rattus), wombats (Vombatus ursinus), cats and dogs in Gippsland and I cornuatus was collected from rodents (R fuscipes), wombats, cats and dogs in central Victoria. All life-cycle stages of both species were collected during the warmer months of the year. The known distribution of the two species was established from specimens in museum collections and suggested that a boundary between the two may exist in eastern Gippsland. BIOCLIM suggested that the area immediately to the east of Melbourne was climatically suitable for I holocyclus, although no endemic foci of infection are currently known from this region. The potential distribution of I cornuatus included east Gippsland and the Otway Ranges, areas in which the tick is not currently known to occur. CONCLUSIONS: I holocyclus and I cornuatus have more restricted distributions than current collections suggest and therefore may have the possibility to extend their geographical ranges in the future.     

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 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.     

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.     

Asymmetrical focal neurological deficits in dogs and cats with naturally occurring tick paralysis (Ixodes holocyclus): 27 cases (1999-2006)

OBJECTIVE: To describe basic epidemiological features, clinical characteristics and outcomes of asymmetrical focal neurological deficits identified in dogs and cats with naturally occurring tick paralysis (Ixodes holocyclus). DESIGN: A retrospective study. PROCEDURE: Computer records were reviewed for all dogs and cats treated for tick paralysis between July 1999 and June 2006 at a suburban veterinary hospital in Newcastle, New South Wales. RESULTS: Neurological deficits were identified in 17/197 dogs and 10/89 cats and included unilateral facial paralysis (14 dogs; 2 cats), anisocoria (4 dogs; 7 cats), unilateral loss of the cutaneous trunci reflex (1 dog; 1 cat) and Horner's syndrome in 2 cats with anisocoria. Occurrence of deficits was not linked to season, severity of tick paralysis, breed, age, sex or body weight. With facial paralysis and anisocoria, the site of tick attachment was invariably on the head or neck and always ipsilateral to the facial paralysis. By contrast, with anisocoria alone, no consistent relationship was noted between any one pupillary dimension and the side of tick attachment. With cutaneous trunci deficits the site of tick attachment was the ipsilateral caudal axilla. Compared with recovery times from generalised signs of tick paralysis, those for facial paralysis were significantly longer (days to weeks; P < 0.001), those for anisocoria showed no significant difference (P = 0.25) and those for cutaneous trunci deficits lagged by 6 and 7 days. CONCLUSIONS: Asymmetrical focal neurological deficits are a consistent finding in a proportion of dogs and cats with naturally occurring tick paralysis due to I. holocylcus.     

The brown dog tick (Rhipicephalus sanguineus) on an imported dog

Abstract

Extract

Sir, — We wish to record the presence of the tick Rhipicephalus sanguineus on a dog imported from Australia. This tick is mainly parasitic on dogs although on rare occasions it has been collected from non-canine hosts (Roberts, 1965 Roberts, F. H. S. 1965. The taxonomie status of the species of the genera Rhipicephalus (Koch) and Boophilus (Curtice) occurring in Australia. Aust. J. Zool., 13: 491–523.  [Google Scholar]). Experimentally it has been shown capable of transmitting a wide variety of serious diseases but its role as a natural vector of many of them is unknown. In Australia it has been demostrated as being naturally infected with Coxiella burnetii (Smith, 1942 Smith, D. J. W. 1942. Studies on the epidemiology of Q Fever. Aust. J. exp. Biol. med. Sci., 20: 295–296.  [Google Scholar]) and is recorded from all continents and some oceanic islands lying between latitudes 50°N and 36°S (Roberts, 1970 Roberts, F. H. S. 1970. Australian ticks, 87–87. CSIRO.  [Google Scholar]). Auckland falls within this boundaries and therefore it is not unreasonable to suggest that R. sanguineus could become established in New Zealand.     

Retrospective study of 103 presumed cases of tick (Ixodes holocyclus) envenomation in the horse

Objective Review 103 cases of presumed tick envenomation in horses. Design Retrospective study. Method Variables, including date of presentation, age, breed, weight, presence of ticks, gait and respiration scores, duration of recumbency, treatment, outcome and complications were recorded. A series of univariable screening tests were performed and used in a multivariable logistic regression model. Results There were a total of 103 cases affecting 10 breeds, aged between 1 week and 18 years of age. Horses >6 months old and weighing >100 kg had a higher odds of death than those <6 months old and <100 kg. Cases were seen from North Queensland to the central coast of New South Wales and were more likely to present in the warmer months. There was no association between the number of ticks found on an animal and death. Horses with a higher respiratory score had higher odds of dying, but there was no association between gait score and survival. Horses recumbent >120 h after presentation had higher odds of dying. Complications were reported in 35% of horses. The odds ratio for survival was higher for horses receiving >0.5 mL/kg of tick antiserum. Overall, 74% of horses survived. Multivariable modelling was limited by the small sample size. Conclusion In general, tick envenomation in horses follows the geographic distribution of Ixodes holocyclus. Tick antiserum administered at >0.5 mL/kg increases the odds of survival. It would appear that the complications associated with managing a recumbent horse increase the odds of death.