Since 2011, there have been numerous anecdotal reports of cattle losses to paralysis ticks (Ixodes spp.) in the Northern and Eastern Fall areas of the New England LHPA. The losses have usually occurred in scrubby uncleared timbered country overgrown with bracken fern, bladey grass and weeds such as blackberry or lantana. These stock losses include introduced and homebred calves and adult cattle and more recently in homebred Poll Dorset sheep.
Initial investigations sought to determine whether other diseases including Theileria infection might be the cause of the losses. Investigations including blood sampling of adult cattle and smear examination showed no evidence of a regenerative anaemia or significant numbers of Theileria organisms present in affected animals or their cohorts. However, levels of <0.5% of organisms are generally seen on blood smears. No tick fever organisms were noted and trace elements such as selenium, copper and vitamin B12 levels were generally within normal ranges.
The presenting clinical signs of affected cattle include an unsteady hunched gait with hind limb ataxia, recumbency and an ascending flaccid paralysis. Death generally occurred from respiratory failure. The adult cattle were often encountered down. They attempted to rise, initially ran a few paces but then fell again. Generally, in the type of country where the losses occurred, extensive management practices are used and recently dead carcases were the presenting signs. If cattle were inspected more frequently, then affected cattle were noted.
Reports of paralysis tick losses generally occurred from September through to March. In all cases clinically examined, there were very large numbers of both attached and unattached bush ticks (Haemaphysalis longicornis) and paralysis ticks (Ixodes spp.) on the cattle and in the surrounding environment.
Most cases of losses due to paralysis tick occurred in cattle. However, cattle are the predominant grazing livestock in the North Eastern New England area with sheep subject to predation from the high numbers of wild dog numbers in adjoining dedicated crown lands under forestry or national park management. However, as mentioned, recent reports also include losses of Poll Dorset sheep.
Case 1: Losses included 20/250 adult Hereford cows and 50 calves in late September 2011 from a property located 30 km North East of Tenterfield. The property had been previously cleared and grassed with native and subtropical pasture and adjoined crown forestry land. In recent years, large areas of the property had been replanted to Tasmanian Blue Gums in a similar manner to many Northern high rainfall properties in an investor and carbon credit driven commercial industry.
Heavy tick burdens were observed on the cattle and several were collected and sent to the Orange Agricultural Institute for identification. The report of 30/9/2011, Ref ON11/0334, identified nine ticks as Haemaphysalis longicornis (Neumann) Acari: Ixodidae, commonly called bush ticks and two as Ixodes cornuatus (Roberts) Acari: Ixodidae, commonly called Tasmanian paralysis ticks.
An adjoining property also reported losses of 70/138 head of purchased cows attributed to paralysis ticks over an 18 month period in 2011 and 2012.
Case 2: A property located 45 km to the North of Tenterfield reported the loss of 6/55 cows introduced on agistment in the preceding 3 months. The cattle had recently been moved into a cleared paddock that adjoined an uncleared scrub paddock. On examination the cattle had Theileria levels less than <1% on blood smear but no anaemia was noted although hemoconcentration was present with a PCV of 39% (normal 23-44%). Large numbers of both bush and paralysis ticks were seen on the recumbent cow with flaccid hindquarter paralysis. Large numbers of bandicoots were reported on the property.
Case 3: A property located 65km North East of Tenterfield with large areas of commercial Tasmanian Blue Gum plantation forestry. A producer reported the deaths of 23/138 adult cows and a newly purchased bull on agistment from the adjoining property with another 39 cows sick and affected. There were no losses of calves reported. The cattle had been moved onto the property 4 weeks prior and all cattle had received a treatment of moxidectin pour-on (Cydectin, Virbac Animal health) on arrival. Of interest, the calves had been inadvertently treated at a much higher dose rate.
Again, Theileria were present at very low levels, tick fever was excluded on smear and PCV hemoconcentration was noted at 43 and 38% (normal range 23-44%). The affected animals sampled had been recumbent and paralysed for at least 24 hours. Ticks were collected and identified by the State Veterinary Laboratory as Ixodes holocyclus and Ixodes cornuatus paralysis ticks.
Case 4: In March 2013, two properties located 60 km North of Tenterfield, adjacent to crown forestry land reported losses in Poll Dorset sheep after grazing blackberry and bladey grass paddocks. Ewes and lambs, found paralysed, were successfully treated post-shearing by removing engorged paralysis ticks and tick antiserum iv. Maremma guardian dogs running with the sheep were also affected and treated although one of these died despite treatment. The owners also reported a resurgence in bandicoot numbers (known hosts for paralysis ticks) after having not previously been recorded on either property, despite a long history of family ownership.
Ixodes cornuatus, the Tasmanian Paralysis Tick, is widely distributed in Victoria, Tasmania and southern New South Wales (Jackson et al 2000 and 2007) and is known to also cause paralysis (Tibballs and Cooper 1986). Jackson et al (2007) proposed that both Ixodes ticks have the ability to extend their geographic range with climatic suitability. Ixodes cornuatus does not appear to have been recorded in northern NSW before but may have always been present.
Historically paralysis ticks (Ixodes holocyclus) have been recorded along the north eastern section of the New England LHPA although major losses have not generally been reported. Paralysis ticks utilise three hosts in the stages of the lifecycle including native marsupials and domestic animals along with the occasional human. There have been more than 20 cases of human deaths recorded in NSW due to paralysis tick in the last century (Tibballs et al 1986).
Both the previous cattle tick treatment eradication programs (involving regular insecticidal treatments) and the clearing and burning of unimproved or hilly areas (to remove undergrowth and stimulate new pasture growth) may have co-incidentally suppressed Ixodes and Haemaphysalis numbers. The convenient and persistent acaricidal product Bayticol Pour-on (Bayer), relied on for many years at the end of the cattle tick program, may have allowed breeder cattle into many paddocks that may not have previously supported this class of stock. Subsequent drought years in early 2000 following the de-registration of Bayticol Pour-on may have delayed the build up of paralysis and bush tick numbers.
Several good seasons in recent years, (or climate change), has seen the exponential rise of paralysis tick numbers in the north eastern New England. It has also been suggested that effective wild dog control programs have contributed to rises in native tick hosts such as northern brown (Isoodon macrourus) and/or long-nosed (Perameles nasuta) bandicoots.
A lack of registered products to aid in the prevention of paralysis tick attachment (apart from the YTex Python Ear Tag) has seen the rise of off-label usage of products such as oil of turpentine, macrocyclic lactones such as Cydectin and Doramectin and the Flurazon cattle tick products Acatak (Novartis Animal Health) and Oztik (Jurox P/L). Deltamethrin (Clout S, Coopers Animal Health) off shears has been suggested as an off label product in sheep. All of these products have residue implications and withholding periods, which need to be observed to minimise residues in meat products.
The significance of the Tasmanian paralysis tick Ixodes cornuatus outside its known range of South Eastern Australia and on properties experiencing significant stock losses in classes not usually reported, warrants further investigation.
Ixodes cornuatus may have benefitted from changing adjacent land use such as Tasmanian blue gum plantations or may have been introduced on stock transported from southern Australia. The tick may have always been present in the area without being identified or may have increased in numbers due to changing climatic conditions that have made the area more suitable to native hosts and the tick. Further monitoring and investigation is warranted on this emerging trend.