Tick paralysis in dogs and cats in Australia: treatment and prevention deliverables from 100 years of research

This review of tick paralysis caused by Ixodes holocyclus in Australia addresses the question: What are the key discoveries that have enabled effective treatment and prevention of tick paralysis in dogs and cats? Critical examination of 100 years of literature reveals that arguably only three achievements have advanced treatment and prevention of tick paralysis in animals. First, the most significant treatment advance was the commercial availability of tick antiserum in the 1930s. Hyperimmune serum currently remains the only specific anti-paralysis tick therapy available to veterinarians in Australia. Second, advances in veterinary critical care have increased survival rates of the most severely affected dogs and cats. Critical care advancements have been enabled through specialised veterinary hospitals that can provide appropriate care 24 h a day, and advanced training of veterinarians, veterinary nurses and technicians. Third, perhaps that biggest advance of all in the last 100 years of research has been the commercial availability of the isooxazoline class of acaricidal preventatives in Australia specifically for I. holocyclus. This highly effective class of preventatives offers long duration of action, low cost, spot-on or oral formulations and a low rate of adverse reactions. Animal owners and veterinarians now have the most useful tool of all – a reliable preventative. This review reveals the key events in research over the last 100 years and the tortuous pathway to delivering better treatment and preventative options for this enigmatic Australian parasite.     

Long-term efficacy of a deltamethrin-impregnated collar for the control of the Australian paralysis tick, Ixodes holocyclus, on dogs

Objective To determine the duration of efficacy of a 4% deltamethrin‐impregnated collar for dogs (Scalibor® ProtectorBand, MSD Animal Health) against adult female paralysis ticks (Ixodes holocyclus). Procedures A controlled pen study was conducted. Dogs were artificially infested at 14‐day intervals with unfed adult female ticks for up to 140 days following application of the collar to the dogs. Efficacy was assessed by manually counting ticks on dogs at 24, 48 and 72 h after each infestation. Results Efficacy at the 72‐h count was 96% after the day 14 tick infestation. The 72‐h efficacy remained above 94% from the day 14 to the day 98 infestations, when efficacy was still 99.5%. Efficacy at 72 h was above 90% after the day 112 infestation and was still 93% at 72 h after the day 140 infestation. Conclusions The deltamethrin‐impregnated collar gave greater than 90% control of paralysis ticks for at least 14 weeks.     

The weather determines the number of cases of tick paralysis in dogs and cats in eastern Australia,caused by Ixodes holocyclus,the eastern paralysis tick

We studied over 222,000 cases of emergency veterinary consultations in four regions along the eastern coast of Australia. We found that cases of tick paralysis (TP) caused by the eastern paralysis tick, Ixodes holocyclus, accounted for 7.5% of these cases: >16,000 cases. The season of TP and the number (prevalence) of TP cases varied among regions and over the years. Our study of the association between weather and (i) the start of the season of TP, and (ii) the number of TP cases revealed much about the intricate relationship between the weather and I. holocyclus. We studied the effect of the hypothetical availability of isoxazoline-containing tick-preventative medicines and found that an increase in the availability of these medicines had significantly contributed to the decrease in TP cases. We found that the weather in winter accounted for the time of the year the season of TP starts whereas the weather in summer accounted for the number of TP cases in the TP season. Last, through a study of the effects of shifts in the climate under four hypothetical scenarios (warmer/cooler and drier/wetter than average), we propose that the start of the season of TP depends on how soon the weather in winter becomes suitable for the activity (e.g. host-seeking) and the development of I. holocyclus nymphs, and that the number of TP cases during the TP season depends on how many engorged female ticks and their eggs survive during summer.     

Active surveillance of pathogens from ticks collected in New York State suburban parks and schoolyards

Schoolyards and suburban parks are two environments where active tick surveillance may inform local management approaches. Even in a state such as New York with a robust active tick surveillance programme operated by the state Department of Health, these settings are not routinely covered. The goal of this study was to highlight the importance of active surveillance for tick‐borne pathogens by describing their prevalence in ticks collected from schoolyards and suburban parks and to guide the use of integrated pest management in these settings. Tick dragging was performed in three regions of New York State: Long Island, the Lower Hudson Valley and the Capital Region. A total of 19 schoolyards and 32 parks were sampled. The location, habitat and weather at the time of tick collection were recorded. Ticks were speciated and tested for the presence of 17 pathogens with a novel application of nanoscale real‐time PCR. The causative agents of Lyme disease, anaplasmosis, babesiosis and Powassan virus disease were all detected from Ixodes scapularis in various sites throughout the capital region and south‐eastern counties of New York state. The most common agent detected was Borrelia burgdorferi, and coinfection rates were as high as 36%. This surveillance study also captured the first of the invasive Asian longhorned tick species, Haemaphysalis longicornis, in New York state (collected 2 June 2017). Results from this study highlight the importance of collaborative efforts and data sharing for improvement of surveillance for tick‐borne disease agents.     

Evidence of Powassan/deer tick virus in adult black‐legged ticks (Ixodes scapularis) recovered from hunter‐harvested white‐tailed deer (Odocoileus virginianus) in Pennsylvania: A public health perspective

Studies reporting tick infection rates for Powassan virus (POWV), an emerging zoonotic arthropod‐borne pathogen responsible for POWV disease in the Commonwealth of Pennsylvania, are limited. To determine the presence and ascertain a statewide prevalence of POWV, ticks were collected from 9,912 hunter‐harvested white‐tailed deer (Odocoileus virginianus) heads presented to six regional Pennsylvania Game Commission Chronic Wasting Disease sampling stations in early December of 2013, 2014 and 2015. Of the 2,973 ticks recovered, 1,990 (66.9%) were identified as adult Ixodes scapularis (black‐legged tick). The 1,990 I. scapularis ticks were PCR‐tested for the presence of POWV. The ticks had a statewide Powassan/deer tick virus infection rate of 0.05%, providing evidence of this pathogen in Pennsylvania's adult I. scapularis ticks and supporting the need for more comprehensive pathogen prevalence assessment strategies, as well as increased public health awareness for this emerging zoonotic arthropod‐borne pathogen of public health concern.     

OBSERVATIONS ON DISEASES OF FREE-LIVING AND CAPTIVE KOALAS (PHASCOLARCTOS CINEREUS)

SUMMARY During 1975–1978, pathological examination of 15 free-living and 11 captive koalas from Queensland revealed the following conditions: Bordetella bronchiseptica-associated pneumonia (6 cases), Pseudomonas aeruginosa-associated pneumonia (1), idiopathic chronic interstitial pneumonia (1), severe alveolar emphysema (3), ulcerative stomatitis (1), intestinal blockage (3), urinogenital lesions (3), Ixodes holocyclus paralysis (1), chlamydial keratoconjunctivitis (2), neoplasia (3), trauma/shock (2).     

Seasonality and anatomical location of human tick bites in the United Kingdom

Tick bites on humans can occur in a variety of habitats and may result in the transmission of tick‐borne pathogens, such as the causative agent of Lyme borreliosis (LB), Borrelia burgdorferi sensu lato. As the risk of transmission of this pathogen to the host increases with the duration of tick feeding, the recognition and removal of ticks as soon as possible following attachment is important for reducing the risk of infection. Performing a thorough body examination for ticks following potential exposure is recommended by tick awareness campaigns. Knowledge of where on the body feeding ticks are frequently found, and at which times of year peak tick exposure occurs, provides important information for public health messaging and may aid those bitten by ticks to engage more effectively with tick‐checking behaviour. This paper summarizes human tick bites in the United Kingdom (UK) during 2013–2018 reported to Public Health England's passive Tick Surveillance Scheme and further examines the anatomical location and seasonality of bites from the most commonly encountered tick and LB vector Ixodes ricinus. A total of 1,328 tick records from humans were received of which 93% were I. ricinus. Humans were most commonly bitten by I. ricinus nymphs (70% bites). Tick bites were recorded on all parts of the body, but there were significant differences in their anatomical location on adults and children. Most tick bites on adults occurred on the legs (50%), whereas on children tick bites were mostly on the head and neck (43%). Bites from I. ricinus were recorded throughout the year but were most numerous during May to August. This study adds to the body of research on the seasonality and anatomical location of human tick bites in temperate Europe and highlights the importance of data collected through passive surveillance in addition to research and epidemiological studies.     

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.     

In this issue – May 2012

Breech‐strike in Merinos in south‐eastern Australia · Risk factors for clinical mastitis in dairy cows · Tick (Ixodes holocyclus) envenomation in horses · Attitudes to and use of analgesia by Queensland veterinarians · Treatment of anoestrus in bitches · Risk of arboviruses following waterbird movement     

Study of general practitioner consultations for tick bites at high,medium and low incidence areas for Lyme borreliosis in England and Wales

Lyme borreliosis (LB) is a tick‐borne disease caused by Borrelia burgdorferi sensu lato complex. In Europe, it is predominately transmitted by the sheep tick, Ixodes ricinus. Compared with other European countries, the United Kingdom (UK) is considered to have a low incidence of LB, although this varies regionally. To determine whether an association exists between tick bite consultations and LB incidence in the UK, retrospective questionnaires were sent to general practitioners (GPs) in high (Wiltshire), medium (Cumbria) and low (Wales) incidence areas. During 2011, the greatest incidence of consultations for tick bites was reported by GPs in Cumbria (204 consultations per 100,000 inhabitants), followed by Wiltshire (160 per 100,000 population) and Wales (54 per 100,000 population). In Wiltshire and Cumbria, GPs predominantly provided advice on tick removal, whilst Welsh GPs mostly advised patients on tick bite prevention. Focusing on Cumbria during 2011–2013, 72.5% of GPs removed ticks from patients (incidence of 101 consultations per 100,000 population), and more GPs diagnosed LB based on clinical features than laboratory‐confirmed diagnoses. To date, this is the first study to investigate the incidence of tick bite consultations and LB in England and Wales.     

THE ESTABLISHMENT OF A LABORATORY COLONY OF IXODES HOLOCYCLUS

SUMMARY A laboratory colony capable of producing annually 3000 female Ixodes holocyclus was maintained for 3 years. Guinea-pigs were used for larval feeding and bandicoots for nymphs and adults. The methods and equipment employed are described in detail.     

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.     

Spontaneous bilateral ankylosis of the carpometacarpal joint in a Paint Horse

An 8‐year‐old Paint Horse gelding was evaluated for a persistent left forelimb lameness (grade 4/5), with a hard swelling at the dorsomedial aspect of the carpometacarpal joint, due to osteoarthritis. Previous systemic and local anti‐inflammatory therapy had only a temporary effect. Partial carpal arthrodesis was suggested, but the owner elected for conservative treatment. The horse was confined to a small paddock and received phytotherapeutic supplementation with Harpagophytum procumbens. The lameness gradually resolved but a similar hard swelling developed on the right carpus. Radiographic follow‐up 1.5 years later revealed a spontaneous bilateral ankylosis of the carpometacarpal joint.     

Antidiuretic response of a horse affected with pituitary pars intermedia dysfunction to desmopressin acetate

Central diabetes insipidus (DI) was diagnosed in a 20‐year‐old American Quarter Horse gelding that was concomitantly affected with pituitary pars intermedia dysfunction (PPID). The diagnosis of DI was supported by a positive response to administered desmopressin acetate. Diagnosis of PPID was supported by physical appearance and elevated plasma adrenocorticotropic hormone concentration following domperidone administration. The horse's physical condition improved following treatment with pergolide but long‐term treatment with desmopressin was not undertaken and severe polyuria and polydipsia persisted. Desmopressin acetate appears to be useful for the diagnosis of DI in mature horses concomitantly affected with PPID.     

Septic funiculitis caused by Streptococcus equi subspecies equi infection with associated immune‐mediated haemolytic anaemia

A 2‐year‐old Quarter Horse gelding presented for anaemia, icterus, depression and intermittent colic 2 weeks after routine castration. Bilateral septic funiculitis with Streptoccocus equi ssp. equi with secondary immune‐mediated haemolytic anaemia were diagnosed. A blood transfusion was required to facilitate general anaesthesia for surgical excision of the septic funiculitis. Antibiotic therapy was provided initially with chloramphenicol and later enrofloxacin. Immunosuppressive therapy was provided with dexamethasone and later azathioprine. The horse responded well to treatment and was discharged 8 weeks after presentation. Streptococcus equi ssp. equi should be considered in cases with septic funiculitis and the potential for a secondary immune‐mediated haemolytic anaemia exists with this bacterial species.     

Discrepancies between self‐reported tick bites and evidence of tick‐borne disease exposure among nomadic Mongolian herders

Twenty‐six per cent of Mongolians live pastoral lifestyles, increasing their likelihood of exposure to ticks and placing them at a higher risk for contracting tick‐borne diseases (TBDs). Anaplasma spp. and Rickettsia spp. have been identified in ticks, livestock and humans in Mongolia, but no known qualitative research has been conducted investigating the association between nomadic herder characteristics, tick bite history and exposure to TBDs. To better understand the association between self‐reported tick bites and symptoms versus actual exposure to TBDs, this study paired serological data with 335 surveys administered to Mongolian herders, ages 12–69, from 2014 to 2015. Logistic regression results identified no significant associations between reported tick bites or symptoms with serological evidence of Anaplasma spp. and Rickettsia spp. controlling for age, gender and aimag. Among the 335 respondents who were seropositive to either Anaplasma spp. or Rickettsia spp., 32.9% self‐reported experiencing abnormal symptoms such as redness, inflammation, headache, arthritis or fever after being bitten. Alternatively, 17.3% (58/335) of individuals reported experiencing symptoms following a tick bite in instances where serological results indicated no exposure to Anaplasma spp. or Rickettsia spp. Results also identified inconsistencies in reporting and seroprevalence among different age groups, with children having the highest reporting and treatment seeking rates but low levels of exposure in comparison with other groups. While survey results showed that individuals were aware of peak tick seasons and tick species that inhabit specific areas, 58% of heads of households (49/84) were unaware that ticks can cause disease in livestock or dogs. This study suggests that herders are an at‐risk population in Mongolia with gaps in awareness of TBD risk. Increased surveillance paired with focused outreach to prevent TBDs targeted to the herder population is encouraged.     

Suspected case of hypersplenism as a cause of anaemia,thrombocytopenia and leucopenia in a Miniature Horse gelding

A 23-year-old Miniature Horse gelding was presented to the Lloyd Veterinary Medical Center with a 3-week history of decreased appetite, lethargy and mild intermittent colic. A complete blood count revealed leucopenia, characterised by neutropenia and lymphopenia, as well as anaemia, thrombocytopenia and hyperproteinaemia whereas hypertriglyceridaemia was noted on serum biochemistry profile. Bone marrow evaluation was nondiagnostic and the horse was negative for antiplatelet antibody testing, Coombs test, equine infectious anaemia virus and Anaplasma phagocytophilum. The horse was hospitalised for 36 days and received supportive care, antibiotics, corticosteroids, dextrose-containing fluids and a whole blood transfusion. Following initial improvement and stabilisation, the horse became severely anaemic and acutely recumbent on Day 36 and was subjected to euthanasia. Post-mortem examination provided a diagnosis of hypersplenism with a markedly enlarged spleen along with histiocytic phagocytosis of erythrocytes and platelets. Examination of bone marrow showed appropriate erythroid hyperplasia and no evidence of myelopthisis or neoplasia. This report describes the first presumptive case of primary hypersplenism in an equid as a cause of pancytopenia.     

Prospective survey of tick paralysis in dogs

OBJECTIVE: To obtain information on tick paralysis in dogs, including the nature of disease, host signalment, tick-host relationship, treatment, disease progression and recovery, and preventive measures. DESIGN: A prospective survey of 577 dogs affected by tick paralysis was conducted during 1998. Forty-two veterinary clinics along the eastern coast of Australia were instructed to complete survey forms for the first 15 dogs that presented with tick paralysis during September to November. RESULTS: Five percent of dogs died from tick paralysis. Younger dogs were more likely to survive. Long coat length was associated with a greater tick burden but not greater tick size, whereas coat thickness had no bearing on either. Dogs with mild disease recovered more quickly from tick paralysis. Respiratory and gait scores reflected disease severity and were good prognostic indicators. The size of the tick did not reflect the severity of the clinical condition it induced in the host. No method of tick removal or in situ treatment improved recovery time or reduced mortality. However, the time spent in hospital was significantly less for dogs from which the live tick was manually removed. Inspiratory stridor, evident in some dogs with tick paralysis, was not related to tick attachment on the neck. The use of acepromazine maleate or dexamethasone did not reduce recovery time or mortality. Increasing the dose of tick antitoxin serum (TAS) above 0.1 mL/kg had no effect on mortality or recovery time. Dogs with severe disease that received an additional dose of TAS were significantly less likely to survive. Subcutaneous use of TAS at the site of tick attachment was of no benefit in reducing mortality or time to initial clinical improvement. A registered preventative product had not been used on the majority of dogs. Clipping the coat to search for ticks did not reduce mortality. CONCLUSIONS: Therapy needs to address cardiopulmonary dysfunction that may be due directly to the effect of tick toxin and not just respiratory compromise caused by progressive respiratory muscle failure.     

COMPARISON BETWEEN PROTON MAGNETIC RESONANCE SPECTROSCOPY FINDINGS IN DOGS WITH TICK‐BORNE ENCEPHALITIS AND CLINICALLY NORMAL DOGS

In vivo diagnosis of tick‐borne encephalitis is difficult due to high seroprevalence and rapid viral clearance, limiting detection of antibodies in blood and cerebrospinal fluid. Magnetic resonance imaging (MRI) characteristics of tick‐borne encephalitis have been reported, however MRI studies can also be negative despite the presence of neurologic signs. Magnetic resonance spectroscopy (¹H MRS) is an imaging method that provides additional information about the metabolic characteristics of brain tissues. The purpose of this retrospective cross‐sectional study was to describe brain metabolites using short echo time single‐voxel ¹H MRS in dogs with confirmed tick‐borne encephalitis and compare them with healthy dogs. Inclusion criteria for the affected dogs were neurological symptoms suggestive of tick‐borne encephalitis, previous endemic stay and tick‐bite, diagnostic quality brain MRI and ¹H MRS studies, and positive antibody titers or confirmation of tick‐borne encephalitis with necropsy. Control dogs were 10, clinically normal beagles that had been used in a previous study. A total of six affected dogs met inclusion criteria. All dogs affected with tick‐borne encephalitis had ¹H MRS metabolite concentration alterations versus control dogs. These changes included mild to moderate decreases in N‐acetyl aspartate and creatine peaks, and mild increases in glutamate/glutamine peaks. No lactate or lipid signal was detected in any dog. Myoinositol and choline signals did not differ between affected and control dogs. In conclusion, findings supported the use of ¹H MRS as an adjunctive imaging method for dogs with suspected tick‐borne encephalitis and inconclusive conventional MRI findings.