CATTLE AND THE PARALYSIS TICK IXODES HOLOCYCLUS
B. M. DOUBE, B.Sc., Ph.D. CSIRO, Division of Entomology, Long Pocket Laboratories, Meiers Road, Indooroopilly, Queensland, 4068 Wroduction
Recent thinking on pest-management considers not only pests which affect man’s use of a resource but the entire ecosystem in which the pest occurs (Clark et a1 1967). This approach raises the question whether man, or some section of society is utilising the resource in the best way, taking into account economic, aesthetic and other aspects. The pest-management concept emphasises selectiveness in control, fitting control methods into the biology of the noxious species and the social and economic framework of the problem (Geier 1966). The paralysis tick Ixodes holocyclus has long been recognised as a serious veterinary problem in certain localities along the eastern seaboard of Australia. Research has been concerned chiefly with the biology of the tick in the laboratory (Ross 1924; Oxer and Ricardo 1942; Moorhouse 1966), the toxin (Kaire 1966; Murray and Koch 1969; Koch 1967) and immunity of dogs to the paralysis toxin (Ross 1935; Oxer and Ricardo 1942). Generally the tick is recognised only as a pest of domestic dogs and cats; but paralysis due to I . holocyclus is considered an important disease of domestic stock (Seddon 1967). Tick paralysis is chiefly a disease of young stock, although on occasions large animals succumb (Anon 1961), usually among cattle brought from areas where I. holocyclus does not occur ( S . R. Knott personal communication). The areas which are most troublesome are hilly, high rainfall, coastal districts, for example the Atherton Tableland, the Blackbutt Ranges and Coffs Harbour. Graziers in coastal New South Wales and southern Queensland have claimed that the paralysis problem has worsened in recent years. They attribute this to effective “1080 poisoning campaigns” against dingoes and foxes which have allowed bandicoot and hence tick populations to increase significantly. There is an exciting variety of folk-lore cures for paralysis, for example strong cold tea, “Aspros”, and iodine administered four times daily, but the only proven remedy is injection of canine anti-tick serum. However, con3dering the current depression in the beef market, this treatment is usually uneconomic. There is little pubAustralian Veterinary Journal, Vol. 51, November, 1975
lished ecological or biological information from which one might develop rational management practices to alleviate the paralysis problem of domestic stock. This paper summarises the results of investigations into the ecology and biology of the paralysis tick and the number of ticks required to paralyse cattle, and discusses these in relation to various possible management strategies. Biology and EcoIogy of the Tick
Host Species I . holo~cyclushas a wide host range (Roberts 1960) and has been found on nearly all species of mammals in areas where the tick is abundant. There are few data on the relative abundance of ticks on the different species (Sutherst and Moorhouse 1971), but the bandicoot is considered to be the principal host. Native mammals, birds and reptiles have been trapped regularly at Tamborine Mountain in south-east Queensland and in the suburbs of Brisbane from 1972 to 1974, and the ticks which engorged on the animals were collected and counted. These data (Table 1) revealed that the short-nosed bandicoot Isoodon macrourus was the most favoured host animal and that most other species carried very few ticks. The mountain possum was a favoured host but this animal was rare and so is unlikely to provide a significant host resource for the tick. However, dogs, wallabies and koalas are known, at times, to carry numbers of females similar to those found on bandicoots (N. Trevorow personal communication) and so may also be important host species in some circumstances. Seasonal Incidence Data on the seasonal incidence of the various instars of 1. holocyclus are patchy (Ross 1924; Roberts 1960; Domrow and Derrick 1965; Sutherst and Moorhouse 1971) but all indicate that females are most common in spring and early summer, larvae in summer and autumn, and nymphs in autumn and winter. Collections (Table 2 ) from Tamborine Mountain and Brisbane support this. Nevertheless adults occur in low numbers at all times of the year (Domrow 51 1
TABLE 1 The Occurrence of I. holocyclus on Animals and Birds Trapped from Mt Tamborine, the Suburbs of Brisbane, Bulburin State Forest Queensland and Rockhampton Host Species
Larvae
Mean Number of Ticks per Animal Nymphs
Adults
110.8 13.8 6.0 0.9 119.6 1 .o 0 0.2 0
38.9 45.0 0.2 3.3 19.6 5.0 5.3 0.3 0
0.68 0.20 0 0.6 0.2 0 0 0 0
Number
Short-nosed bandicoot Isoodon macrourus *Longnosed bandicoot Perameles nasuta Rodents Melomys and Rattus spp. Brush-tailed possum Trichosurus vulpecula Mountain possum T . caninus Potooroo Potorous tridactylus Cat Felis catus Birds Reptiles
98 5 13 10 5 2 3 9 3
'Trapped at a time of year when larvae were not abundant.
and Derrick 1965). The host-seeking behaviour of females is said to be more aggressive during warm, moist weather which follows spring storms (D. Johnston personal communication).
Distribution of Adult Ticks in the Field Flagging pastures and adjacent scrub with a heavy blanket in tick-infested areas has revealed that adult male and female ticks are uncommon on open, well grazed pasture and are abundant in overgrown or regrowth country, especially about the base of small trees or shrubs surrounded by low vegetation (e.g. wild raspberry, crofton weed, lantana). These areas are favoured by bandicoots, Ticks occur on the mat of vegetation and in the lower foliage and leaf litter. The Biobgy of Bandicoots The 2 bandicoot species which are of most importance in the ecology of the paralysis tick (Sutherst and Moorhouse 1971; Ross 1924) are the brindled or long-tailed, short-nosed bandicoot Isoodon macrourus which occurs in Arnhem Land, eastern Queensland and north-eastern New South Wales, and the long-nosed bandicoot Perumeles nasuta which occurs in eastern Queensland, eastern New South Wales and Victoria (Ride
1970). Within these regions the distribution of the two species is patchy. Both species are abundant in areas of northern Queensland, for example Innisfail (Harrison and Emanuel 1960) but the short-nosed bandicoot is the dominant species in south-east Queensland (Table 1) and in the Myall Lakes district of New South Wales (Gordon 1971); yet the long-nosed bandicoot is the dominant species further south, for example Sydney (Ride 1970). The short-nosed bandicoot occurs in areas with dense ground cover (especially regrowth areas) in sclerophyll forests or woodlands but not in rain forest. The long-nosed bandicoot is more cosmopolitan and lives in rain forest, wet and dry sclerophyll forest and sclerophyll woodlands (Ride 1970). In south-eastern Queensland the short-nosed bandicoot is almost completely absent from cleared country, but is abundant in areas with dense ground cover. Gordon ( 197 1) studied populations on islands in the Myall Lakes, New South Wales, where the density ranged from 1 to 2 per ha according to the season; areas near Brisbane supported populations of up to 6 bandicoots per ha (Gordon 1966). Studies at Innisfail (Harrison and Emanuel 1960) showed that bandicoot density varied with habitat. Short-
TABLE 2 *Seasonal Incidence of I. holocyclus on the Short-nosed Bandicoot I. Macrourus Month of Year
J
F
M
A
M
J
J
A
S
No. Bandicoots 4 4 3 9 8 11 6 8 24 Mean no. ticks per host 381 129 270 460 21.5 4.7 5.0 1.0 Larvae 520 1.0 52.4 110 135 44.0 31.5 14.0 3.3 2.5 Nymphs Adult females 0 0.5 0 0.2 0.3 0.7 1.5 1.3 0.1 'Data from Mt Tamborine and Brisbane suburbs for the period September 1972 to September 1974. 512
O 15
7.0 7.7 2.6
N
D
4
10
14.3 0.3 2.8
28.9 4.1 4.6
Australian Veferinary Journal, Vol. 51, November, 1975
TABLE 3 Number of Female I. holocyclus Required to Paralyse Previously Unexposed Calves (Adapted from Uoube and Kemp 1975)
Two to three week old calves 4 34.0 4 35.0 2 38.0 Older Calves 7 111.4 5 7 121.1 20
1 2 10
No No Yes
to 9 to 25
No Yes
nosed bandicoots were absent from rain forest, but there were 2.0 per ha in the borders of the cane fields whereas the comparably densities for the long-nosed bandicoot were 0.6 and 1.0 per ha. Both species are nocturnal and omnivorous with a preference for an insect diet. During the day both hide in well concealed nests which are usually made beneath a mound of grass or leaves (Lyne 1964). At dusk they leave their nests and spend several hours foraging. Bandicoots are relatively solitary animals and occupy exclusive territories and home ranges which overlap extensively (Gordon 1966; Ride 1970). There appear to be significant differences in the behaviour of lsoodon and Perameles bandicoots. Isoodon have more specific habitat preferences, are more territorial and more aggressive (intraspecific) than Perarneles (Heinsohn 1964). These differences may have important consequences when considering ways of regulating populations. Effects of the Tik on Cattle
Number of Ticks Required to Induce Paralysis The susceptibility to paralysis of unexposed cattle is a function of their size/age and the number of ticks engorging on them. Between 3 and 10 females were required to paralyse calves 2-3 weeks of age weighing 30 to 40 kg (Table 3 ) whereas a similar dose failed to paralyse weaner steers weighing between 80 and 160 kg (Doube and Kemp 1975). Twenty to 25 females paralysed the latter. Nine out of the ten calves paralysed subsequently died. In these studies, the females used were reared in the laboratory from engorged nymphs which dropped from bandicoots trapped in the field, but further trials using female ticks collected as adults from the field failed to demonstrate any major differences in toxicity between laboratory moulted and field collected females or between Australian Veterinary Journal, Vol. 51, November, 1975
females from different geographic regions (B. M. Doube and D. H. Kemp unpublished data).
Protectioin A florded by Prior Experience The data in Table 3 show that 20 to 25 female tick will paralyse unexposed cattle of about 120 kg weight. The survivors of this experiment were challenged with 25 to 50 female ticks on 3 occasions subsequent to the primary infestation. Only 2 calves became paralysed and neither died, indicating that prior experience of the tick had afforded protection from a challenge which would have paralysed and killed an unexposed calf (Doube and Kemp 1975). This protection was due, at least in part, to the development of a strong resistance to the tick which slowed or prevented feeding. Most of such ticks failed to finish feeding and died in situ (Doube and Kemp 1975). Db3cl&on
Field experience suggests that the paralysis problem in cattle is limited to young calves born in spring and to unexposed cattle introduced into tick-infested country in spring. Other cattle that are exposed to similar tick challenges have become resistant to the tick or immune to the toxin or both, and thus are protected from paralysis. The author has taken sixty partially engorged female Z. holocyclus from young adult cattle in tick-infested areas, yet they showed no symptoms of paralysis. Although the tick is present in most regions along Australia’s eastern coastline, the calf paralysis problem is serious only in certain areas and particularly in seasons when the tick is abundant. Since unexposed cattle can tolerate low numbers of ticks, the paralysis problem might be solved in some situations by a relatively minor reduction in tick numbers, and in others would be alleviated by a reduction in contact between susceptible cattle and high tick populations. There are four ways one might attempt to alleviate the problem: protection from the toxin, prevention of tick engorgement, avoidance of infestation, and reduction in tick numbers (Wilkinson 1968).
Protection from the Toxin Dogs can develop immunity to the paralysis toxin, but this process is relatively slow and immunity wanes without continuous challenge (Oxer and Ricardo 1942). There is some evidence that immunity can be transferred to puppies through maternal milk (J. Frogley personal communication) and passive immunity can also be conferred by injection of canine anti-tick serum (Ross 1935). There is no similar in513
Reduction in Numbers of Ticks There are two ways one could go about reducing tick numbers: killing the ticks or reducing the number of host animals. Since bandicoots are the principal host of the tick, a reduction in numbers of bandicoots would cause a parallel reduction in tick numbers. Bandicoots could be trapped, shot or poisoned (fauna protection agencies permitting), but such measures are
likely to provide only a temporary reduction in numbers. Furthermore such measures usually only “crop” populations and release the brake of the mechanisms which were previously regulating population size, for example density dependence. A much more satisfactory way to reduce bandicoot populations would be to reduce the area of suitable habitat. The short-nosed bandicoot nests in dense vegetation of regrowth areas and so “cleaning up” paddocks should decrease the density of bandicoots markedly. Burning would also reduce the suitability of such areas for bandicoots because, in addition to shelter, they require grass or leaves to make their nests (Lyne 1964). Newsome et a1 (1975) found a substantial reduction in bandicoot number after a bushfire swept Nadgee Reserve, New South Wales. Burning overgrown areas might have additional benefits in that such areas are favoured tick habitats and so ticks might be killed directly and the subsequent habitat maybe less suitable than previously for survival of the non-parasitic stages. Bandicoots can be a significant food resource of predatory mammals. For example the diet of unmolested dingoes in Nadgee Reserve contained 10.9% bandicoot (A. E. Newsome personal communication). So it is possible that predators could help regulate bandicoot populations in some areas. An encyrtid wasp Hunterellus sp has been found to parasitize the nymphs of 1. holocyclus (Doube and Heath 1975), but it appears to be a poor prospect as an agent of effective biological control. A similar species released in America failed to control Dermacentar undersoni (Cooley and Kolhs 1934). Tick numbers would also be reduced by spraying tick-infested lands with acaricides. However, such treatment would require enormous quantities and may have such undesirable effects as concentration of chemicals in wild life food chains, their storage in soil and endangering of fish. Such treatments have been considered justifiable in the USSR to protect humans from encephalitis carried by Ixodes ticks but have not been as successful as expected (Gorchakovskaya and Korotkov 1973). Recreational areas in Ozark region of Oklahoma, United States of America, have been sprayed with Gardona in an attempt to control the lone star tick Arnblyomma americanum, but these trials have met with mixed success (Hair and Howell 1970). Control of this tick will ultimately involve control of the deerhosts of the tick or the modification of the habitat (Wharton 1974).
514
Australian Veterinary Journal, Vol. 51, November, 1975
formation about cattle, but it may be possible to immunise cattle and calves against the toxin. The prognosis for such a remedy being effective, economically and technically feasible, and acceptable to the farmer, are low.
Prevention of Tick Engorgement Cattle exposed to adult female 1. holocyclus rapidly acquire a significant degree of resistance to the adult (Doube and Kemp 1975). This resistance is also manifest against the larvae and nymphs (Doube unpublished data). It might be possible to induce resistance in cattle by injecting tick antigen so that the ticks do not feed successfully and thereby cattle would be protected from the toxin; again the prognosis is poor. The use of acaricides with a long residual life would provide an initial degree of protection and allow the calves or cattle a low level of tick challenge which would permit acquisition of natural immunity. However, experience in Africa (Barnett 1961) suggests that treatment is required at weekly intervals to be effective against 3 host tick. Thus apart from the risk of poisoning young calves with acaricides, such a program could prove both uneconomic and impractical. Avoidance of Infestation Although all stages of the tick can cause paralysis (Murray and Koch 1969), adult females are responsible for most cases of paralysis in the field. Females are most abundant in spring and so by introducing cattle to ticky areas at other times of the year and by altering calving time away from spring the cattle may well have acquired a degree of natural immunity by spring. Also calving in paddocks which are relatively free of ticks will permit calves to grow and acquire a degree of natural immunity before being exposed to a heavy tick challenge. Cows prefer to calve in scrub and calves are very inquisitive. Both these factors will tend to expose young calves to heavy tick challenge unless “clean” calving paddocks are used.
In conclusion the prospects for control of the tick paralysis problem in cattle by the use of acaricides or inoculations are poor. Ecological manipulation of the tick’s habitat or bandicoot populations by cleaning up “dirty” country and perhaps by burning may provide the most logical way of reducing tick numbers to a level at which they are no longer troublesome. This practice in conjunction with altering calving time to mid winter, calving in “clean” paddocks and careful surveillance of cattle at times of greatest risk, for example in the first few weeks after calving in spring, might well reduce the problem so that cattle owners can “live with the tick” without significant losses. S-arY
Paralysis of domestic stock by the paralysis tick Ixodes holocyclus is chiefly a disease of young animals (especially calves) and of nonhabituated 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 behaviour 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. Ways of reducing the incidence of paralysis of cattle are examined within the context of the ecosystem in which the pest occurs. Four approaches, protection from the toxin, prevention of engorgement, avoidance of infestation and reduction of tick numbers are discussed. It is concluded that the most logical way of alleviating the problem is the ecological manipulation of the habitat to reduce the density of bandicoots, combined with such management practices as altering calving time from spring to winter and calving in “clean” paddocks. Acknowledgment
The Australian Meat Research Committee supplied funds to support this work.
Australian Veterinary Journal, Vol. 5 1, November, 1975
References Anon. (1961)-Rep. Dep. Agric. Qd, 1960-61: 32. Barnett, S. F. (1961)-“The control of ticks on livestock”. F A 0 Agric. Stud. No. 54. Clark, L. R., Geier, P. W., Hughes, R. D. and Morris, R. F. (1967)-“The Ecology of Insect Populations in Theory and Practice”. Methuen; London. 5th Cooley, R, A. and Kohls, S. M. (1934)-Proc. Pacif. Sci. Congr. 1933, 5: 3375. Domrow, R. and Derrick, E. H. (1965)-Aust. J . Sci. 27: 234. Doube, B. M. and Heath, A. J. C. (1975)-J. rned. Ent. (in press). Doube, B. M. and Kemp, D. H. (1975)-Azrsi. 1. agric. Res. (in press). Geier, P. W. (1966)-A. Rev. Ent. 11: 471. Gorckakovskaya, N. N. and Korotkov, Yu. S. (1973)Proc. 3rd Int. Congr. Acarol 1971; 655. Gordon, G. (1966)-“A Study of the Movements of the Short-nosed Bandicoot Isoodon macrourus Gould”. Honours Thesis, University of Queensland. Gordon, G. (1967)-“A Study of Island Populations of the Short-nosed Bandicoot, Isoodon macrourus Gould”. Ph.D. Thesis, University of New South Wales. Hair, J . A. and Howell, D. E. (1970)-Bu/l. Okla. agric. Exp. Srn B-679. Harrison, J. L. and Emanuel, M. L. (1960)-Rep. Qd Inst. med. Res. 15: 19. Heinsohn, G. E. ( 1964)-“Ecology and Reproduction of the two Species of Tasmanian Bandicoots, Perameles gunni and Isoodon obesula. Ph.D. Thesis, University of California. Kaire (1966)--Toxicon 4. 91. Koch, J. H. (1967)-N.S.W. Vet. Proc. 3: 34. Lyne, A. G. (1964)-Aust. Natur. Hist. 14: 281. Moorhouse, D. E. (1966)-J. med. Ent. 3: 168. Murray, M. D. and Koch, J. H. (1969)--1. Aust. ent. SOC.8: 187. Newsome, A. E., McIlroy, J. and Catling, P. (1975)Proc. Ecol. SOC.Aust. 9. Oxer, D. T, and Ricardo, C. L. (1942)-Aust. vet. J. 18: 194. Ride, W. D. L. (1970)-“A Guide to the Native Mammals of Australia”, Oxford University Press, Melbourne. Roberts, F. H. S. (1960)-“Australian Ticks”, CSIRO: Melbourne. Ross, I. C. (1924)-Parasitology 16: 365. Ross, I. C. (1935)--J. Coun. scient. ind. Res. Arut. 8: 8. Seddon, H. R. (1967)-Serv. Publs Dep. Hlth Aust. vet. H v e . No. 7. Sutheyst, R. W. and Moorhouse, D. E. (1971)--Ausr. J . aaric. Res. 23: 195. Wilkirkon, P. R. (1968)-J. e n [ . SOC.Br. Columb. 65: 3. Wharton, R. H. (1974)-in “Control of Arthropods of Medical and Veterinary Importance”. Ed. R. Pal and R. H. Wharton, p. 35. Plenum Press; New York. (Received for publication 18 February 1975)
515
B. M. DOUBE, B.Sc., Ph.D. CSIRO, Division of Entomology, Long Pocket Laboratories, Meiers Road, Indooroopilly, Queensland, 4068 Wroduction
Recent thinking on pest-management considers not only pests which affect man’s use of a resource but the entire ecosystem in which the pest occurs (Clark et a1 1967). This approach raises the question whether man, or some section of society is utilising the resource in the best way, taking into account economic, aesthetic and other aspects. The pest-management concept emphasises selectiveness in control, fitting control methods into the biology of the noxious species and the social and economic framework of the problem (Geier 1966). The paralysis tick Ixodes holocyclus has long been recognised as a serious veterinary problem in certain localities along the eastern seaboard of Australia. Research has been concerned chiefly with the biology of the tick in the laboratory (Ross 1924; Oxer and Ricardo 1942; Moorhouse 1966), the toxin (Kaire 1966; Murray and Koch 1969; Koch 1967) and immunity of dogs to the paralysis toxin (Ross 1935; Oxer and Ricardo 1942). Generally the tick is recognised only as a pest of domestic dogs and cats; but paralysis due to I . holocyclus is considered an important disease of domestic stock (Seddon 1967). Tick paralysis is chiefly a disease of young stock, although on occasions large animals succumb (Anon 1961), usually among cattle brought from areas where I. holocyclus does not occur ( S . R. Knott personal communication). The areas which are most troublesome are hilly, high rainfall, coastal districts, for example the Atherton Tableland, the Blackbutt Ranges and Coffs Harbour. Graziers in coastal New South Wales and southern Queensland have claimed that the paralysis problem has worsened in recent years. They attribute this to effective “1080 poisoning campaigns” against dingoes and foxes which have allowed bandicoot and hence tick populations to increase significantly. There is an exciting variety of folk-lore cures for paralysis, for example strong cold tea, “Aspros”, and iodine administered four times daily, but the only proven remedy is injection of canine anti-tick serum. However, con3dering the current depression in the beef market, this treatment is usually uneconomic. There is little pubAustralian Veterinary Journal, Vol. 51, November, 1975
lished ecological or biological information from which one might develop rational management practices to alleviate the paralysis problem of domestic stock. This paper summarises the results of investigations into the ecology and biology of the paralysis tick and the number of ticks required to paralyse cattle, and discusses these in relation to various possible management strategies. Biology and EcoIogy of the Tick
Host Species I . holo~cyclushas a wide host range (Roberts 1960) and has been found on nearly all species of mammals in areas where the tick is abundant. There are few data on the relative abundance of ticks on the different species (Sutherst and Moorhouse 1971), but the bandicoot is considered to be the principal host. Native mammals, birds and reptiles have been trapped regularly at Tamborine Mountain in south-east Queensland and in the suburbs of Brisbane from 1972 to 1974, and the ticks which engorged on the animals were collected and counted. These data (Table 1) revealed that the short-nosed bandicoot Isoodon macrourus was the most favoured host animal and that most other species carried very few ticks. The mountain possum was a favoured host but this animal was rare and so is unlikely to provide a significant host resource for the tick. However, dogs, wallabies and koalas are known, at times, to carry numbers of females similar to those found on bandicoots (N. Trevorow personal communication) and so may also be important host species in some circumstances. Seasonal Incidence Data on the seasonal incidence of the various instars of 1. holocyclus are patchy (Ross 1924; Roberts 1960; Domrow and Derrick 1965; Sutherst and Moorhouse 1971) but all indicate that females are most common in spring and early summer, larvae in summer and autumn, and nymphs in autumn and winter. Collections (Table 2 ) from Tamborine Mountain and Brisbane support this. Nevertheless adults occur in low numbers at all times of the year (Domrow 51 1
TABLE 1 The Occurrence of I. holocyclus on Animals and Birds Trapped from Mt Tamborine, the Suburbs of Brisbane, Bulburin State Forest Queensland and Rockhampton Host Species
Larvae
Mean Number of Ticks per Animal Nymphs
Adults
110.8 13.8 6.0 0.9 119.6 1 .o 0 0.2 0
38.9 45.0 0.2 3.3 19.6 5.0 5.3 0.3 0
0.68 0.20 0 0.6 0.2 0 0 0 0
Number
Short-nosed bandicoot Isoodon macrourus *Longnosed bandicoot Perameles nasuta Rodents Melomys and Rattus spp. Brush-tailed possum Trichosurus vulpecula Mountain possum T . caninus Potooroo Potorous tridactylus Cat Felis catus Birds Reptiles
98 5 13 10 5 2 3 9 3
'Trapped at a time of year when larvae were not abundant.
and Derrick 1965). The host-seeking behaviour of females is said to be more aggressive during warm, moist weather which follows spring storms (D. Johnston personal communication).
Distribution of Adult Ticks in the Field Flagging pastures and adjacent scrub with a heavy blanket in tick-infested areas has revealed that adult male and female ticks are uncommon on open, well grazed pasture and are abundant in overgrown or regrowth country, especially about the base of small trees or shrubs surrounded by low vegetation (e.g. wild raspberry, crofton weed, lantana). These areas are favoured by bandicoots, Ticks occur on the mat of vegetation and in the lower foliage and leaf litter. The Biobgy of Bandicoots The 2 bandicoot species which are of most importance in the ecology of the paralysis tick (Sutherst and Moorhouse 1971; Ross 1924) are the brindled or long-tailed, short-nosed bandicoot Isoodon macrourus which occurs in Arnhem Land, eastern Queensland and north-eastern New South Wales, and the long-nosed bandicoot Perumeles nasuta which occurs in eastern Queensland, eastern New South Wales and Victoria (Ride
1970). Within these regions the distribution of the two species is patchy. Both species are abundant in areas of northern Queensland, for example Innisfail (Harrison and Emanuel 1960) but the short-nosed bandicoot is the dominant species in south-east Queensland (Table 1) and in the Myall Lakes district of New South Wales (Gordon 1971); yet the long-nosed bandicoot is the dominant species further south, for example Sydney (Ride 1970). The short-nosed bandicoot occurs in areas with dense ground cover (especially regrowth areas) in sclerophyll forests or woodlands but not in rain forest. The long-nosed bandicoot is more cosmopolitan and lives in rain forest, wet and dry sclerophyll forest and sclerophyll woodlands (Ride 1970). In south-eastern Queensland the short-nosed bandicoot is almost completely absent from cleared country, but is abundant in areas with dense ground cover. Gordon ( 197 1) studied populations on islands in the Myall Lakes, New South Wales, where the density ranged from 1 to 2 per ha according to the season; areas near Brisbane supported populations of up to 6 bandicoots per ha (Gordon 1966). Studies at Innisfail (Harrison and Emanuel 1960) showed that bandicoot density varied with habitat. Short-
TABLE 2 *Seasonal Incidence of I. holocyclus on the Short-nosed Bandicoot I. Macrourus Month of Year
J
F
M
A
M
J
J
A
S
No. Bandicoots 4 4 3 9 8 11 6 8 24 Mean no. ticks per host 381 129 270 460 21.5 4.7 5.0 1.0 Larvae 520 1.0 52.4 110 135 44.0 31.5 14.0 3.3 2.5 Nymphs Adult females 0 0.5 0 0.2 0.3 0.7 1.5 1.3 0.1 'Data from Mt Tamborine and Brisbane suburbs for the period September 1972 to September 1974. 512
O 15
7.0 7.7 2.6
N
D
4
10
14.3 0.3 2.8
28.9 4.1 4.6
Australian Veferinary Journal, Vol. 51, November, 1975
TABLE 3 Number of Female I. holocyclus Required to Paralyse Previously Unexposed Calves (Adapted from Uoube and Kemp 1975)
Two to three week old calves 4 34.0 4 35.0 2 38.0 Older Calves 7 111.4 5 7 121.1 20
1 2 10
No No Yes
to 9 to 25
No Yes
nosed bandicoots were absent from rain forest, but there were 2.0 per ha in the borders of the cane fields whereas the comparably densities for the long-nosed bandicoot were 0.6 and 1.0 per ha. Both species are nocturnal and omnivorous with a preference for an insect diet. During the day both hide in well concealed nests which are usually made beneath a mound of grass or leaves (Lyne 1964). At dusk they leave their nests and spend several hours foraging. Bandicoots are relatively solitary animals and occupy exclusive territories and home ranges which overlap extensively (Gordon 1966; Ride 1970). There appear to be significant differences in the behaviour of lsoodon and Perameles bandicoots. Isoodon have more specific habitat preferences, are more territorial and more aggressive (intraspecific) than Perarneles (Heinsohn 1964). These differences may have important consequences when considering ways of regulating populations. Effects of the Tik on Cattle
Number of Ticks Required to Induce Paralysis The susceptibility to paralysis of unexposed cattle is a function of their size/age and the number of ticks engorging on them. Between 3 and 10 females were required to paralyse calves 2-3 weeks of age weighing 30 to 40 kg (Table 3 ) whereas a similar dose failed to paralyse weaner steers weighing between 80 and 160 kg (Doube and Kemp 1975). Twenty to 25 females paralysed the latter. Nine out of the ten calves paralysed subsequently died. In these studies, the females used were reared in the laboratory from engorged nymphs which dropped from bandicoots trapped in the field, but further trials using female ticks collected as adults from the field failed to demonstrate any major differences in toxicity between laboratory moulted and field collected females or between Australian Veterinary Journal, Vol. 51, November, 1975
females from different geographic regions (B. M. Doube and D. H. Kemp unpublished data).
Protectioin A florded by Prior Experience The data in Table 3 show that 20 to 25 female tick will paralyse unexposed cattle of about 120 kg weight. The survivors of this experiment were challenged with 25 to 50 female ticks on 3 occasions subsequent to the primary infestation. Only 2 calves became paralysed and neither died, indicating that prior experience of the tick had afforded protection from a challenge which would have paralysed and killed an unexposed calf (Doube and Kemp 1975). This protection was due, at least in part, to the development of a strong resistance to the tick which slowed or prevented feeding. Most of such ticks failed to finish feeding and died in situ (Doube and Kemp 1975). Db3cl&on
Field experience suggests that the paralysis problem in cattle is limited to young calves born in spring and to unexposed cattle introduced into tick-infested country in spring. Other cattle that are exposed to similar tick challenges have become resistant to the tick or immune to the toxin or both, and thus are protected from paralysis. The author has taken sixty partially engorged female Z. holocyclus from young adult cattle in tick-infested areas, yet they showed no symptoms of paralysis. Although the tick is present in most regions along Australia’s eastern coastline, the calf paralysis problem is serious only in certain areas and particularly in seasons when the tick is abundant. Since unexposed cattle can tolerate low numbers of ticks, the paralysis problem might be solved in some situations by a relatively minor reduction in tick numbers, and in others would be alleviated by a reduction in contact between susceptible cattle and high tick populations. There are four ways one might attempt to alleviate the problem: protection from the toxin, prevention of tick engorgement, avoidance of infestation, and reduction in tick numbers (Wilkinson 1968).
Protection from the Toxin Dogs can develop immunity to the paralysis toxin, but this process is relatively slow and immunity wanes without continuous challenge (Oxer and Ricardo 1942). There is some evidence that immunity can be transferred to puppies through maternal milk (J. Frogley personal communication) and passive immunity can also be conferred by injection of canine anti-tick serum (Ross 1935). There is no similar in513
Reduction in Numbers of Ticks There are two ways one could go about reducing tick numbers: killing the ticks or reducing the number of host animals. Since bandicoots are the principal host of the tick, a reduction in numbers of bandicoots would cause a parallel reduction in tick numbers. Bandicoots could be trapped, shot or poisoned (fauna protection agencies permitting), but such measures are
likely to provide only a temporary reduction in numbers. Furthermore such measures usually only “crop” populations and release the brake of the mechanisms which were previously regulating population size, for example density dependence. A much more satisfactory way to reduce bandicoot populations would be to reduce the area of suitable habitat. The short-nosed bandicoot nests in dense vegetation of regrowth areas and so “cleaning up” paddocks should decrease the density of bandicoots markedly. Burning would also reduce the suitability of such areas for bandicoots because, in addition to shelter, they require grass or leaves to make their nests (Lyne 1964). Newsome et a1 (1975) found a substantial reduction in bandicoot number after a bushfire swept Nadgee Reserve, New South Wales. Burning overgrown areas might have additional benefits in that such areas are favoured tick habitats and so ticks might be killed directly and the subsequent habitat maybe less suitable than previously for survival of the non-parasitic stages. Bandicoots can be a significant food resource of predatory mammals. For example the diet of unmolested dingoes in Nadgee Reserve contained 10.9% bandicoot (A. E. Newsome personal communication). So it is possible that predators could help regulate bandicoot populations in some areas. An encyrtid wasp Hunterellus sp has been found to parasitize the nymphs of 1. holocyclus (Doube and Heath 1975), but it appears to be a poor prospect as an agent of effective biological control. A similar species released in America failed to control Dermacentar undersoni (Cooley and Kolhs 1934). Tick numbers would also be reduced by spraying tick-infested lands with acaricides. However, such treatment would require enormous quantities and may have such undesirable effects as concentration of chemicals in wild life food chains, their storage in soil and endangering of fish. Such treatments have been considered justifiable in the USSR to protect humans from encephalitis carried by Ixodes ticks but have not been as successful as expected (Gorchakovskaya and Korotkov 1973). Recreational areas in Ozark region of Oklahoma, United States of America, have been sprayed with Gardona in an attempt to control the lone star tick Arnblyomma americanum, but these trials have met with mixed success (Hair and Howell 1970). Control of this tick will ultimately involve control of the deerhosts of the tick or the modification of the habitat (Wharton 1974).
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formation about cattle, but it may be possible to immunise cattle and calves against the toxin. The prognosis for such a remedy being effective, economically and technically feasible, and acceptable to the farmer, are low.
Prevention of Tick Engorgement Cattle exposed to adult female 1. holocyclus rapidly acquire a significant degree of resistance to the adult (Doube and Kemp 1975). This resistance is also manifest against the larvae and nymphs (Doube unpublished data). It might be possible to induce resistance in cattle by injecting tick antigen so that the ticks do not feed successfully and thereby cattle would be protected from the toxin; again the prognosis is poor. The use of acaricides with a long residual life would provide an initial degree of protection and allow the calves or cattle a low level of tick challenge which would permit acquisition of natural immunity. However, experience in Africa (Barnett 1961) suggests that treatment is required at weekly intervals to be effective against 3 host tick. Thus apart from the risk of poisoning young calves with acaricides, such a program could prove both uneconomic and impractical. Avoidance of Infestation Although all stages of the tick can cause paralysis (Murray and Koch 1969), adult females are responsible for most cases of paralysis in the field. Females are most abundant in spring and so by introducing cattle to ticky areas at other times of the year and by altering calving time away from spring the cattle may well have acquired a degree of natural immunity by spring. Also calving in paddocks which are relatively free of ticks will permit calves to grow and acquire a degree of natural immunity before being exposed to a heavy tick challenge. Cows prefer to calve in scrub and calves are very inquisitive. Both these factors will tend to expose young calves to heavy tick challenge unless “clean” calving paddocks are used.
In conclusion the prospects for control of the tick paralysis problem in cattle by the use of acaricides or inoculations are poor. Ecological manipulation of the tick’s habitat or bandicoot populations by cleaning up “dirty” country and perhaps by burning may provide the most logical way of reducing tick numbers to a level at which they are no longer troublesome. This practice in conjunction with altering calving time to mid winter, calving in “clean” paddocks and careful surveillance of cattle at times of greatest risk, for example in the first few weeks after calving in spring, might well reduce the problem so that cattle owners can “live with the tick” without significant losses. S-arY
Paralysis of domestic stock by the paralysis tick Ixodes holocyclus is chiefly a disease of young animals (especially calves) and of nonhabituated 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 behaviour 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. Ways of reducing the incidence of paralysis of cattle are examined within the context of the ecosystem in which the pest occurs. Four approaches, protection from the toxin, prevention of engorgement, avoidance of infestation and reduction of tick numbers are discussed. It is concluded that the most logical way of alleviating the problem is the ecological manipulation of the habitat to reduce the density of bandicoots, combined with such management practices as altering calving time from spring to winter and calving in “clean” paddocks. Acknowledgment
The Australian Meat Research Committee supplied funds to support this work.
Australian Veterinary Journal, Vol. 5 1, November, 1975
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