The role of host behaviour in tick-host interactions: a domestic host-paralysis tick model

The aim of this study was to quantify the infestation densities of Karoo and brown paralysis ticks on sheep and goats and explain it in terms of the etho-ecology of these ticks and their domestic hosts. The Karoo paralysis tick usually quests from a vantage point on the vegetation whereas the brown paralysis tick displays an appetence response from the ground and mainly engages hosts that are prostrate. Both tick species are confined chiefly to hilly areas. Temporal differences in the infestation densities of the hosts within and between tick species were evident. These differences were related to disparities in the spatial distribution of the hosts, their activity patterns and the specific appetence responses of the two tick species. Differential climatological conditions affected the quality of forage in areas with a varied topography and the feeding preferences of hosts influenced tick-host sympatry and hence infestation densities.     

Two seasons of tick paralysis in Victoria yet one season in Queensland and New South Wales,Australia

We studied 22,840 cases of tick paralysis in dogs and cats that were attributable to infestation with the eastern paralysis tick, Ixodes holocyclus. We report that the mortality rates from the holocyclotoxins of the tick or from euthanasia due to complications arising from tick paralysis in dogs and cats were 10% and 8%, respectively. The distribution of cases of tick paralysis among the 52 weeks of 22 years (1999 to 2020, inclusive) in four regions along the eastern coast of Australia revealed much about how the life-cycle of this tick varied among regions. The four regions in our study were: (i) Cairns, Innisfail, and surrounding postcodes in Far North Queensland; (ii) South East Queensland; (iii) Northern Beaches of Sydney in New South Wales; and (iv) the Shire of East Gippsland in Victoria. We found that the season of tick paralysis started earlier in more northerly latitudes than in more southerly latitudes. We also found that Victoria has two seasons of tick paralysis, one from approximately the third week of February to the first week of May, and another from approximately the third week of September to the third week of December, whereas all of the other regions we studied in eastern Australia only had one season of tick paralysis. When we studied the two seasons of tick paralysis in Victoria, we found a statistically significant negative correlation between the number of cases of tick paralysis between the two seasons: the more cases in one season, the fewer the cases in the next season. One possible explanation for the negative correlation may be immunity to I. holocyclus acquired by dogs and cats in the first season.     

A shared epitope found in the major paralysis inducing tick species of Africa

Cross-reactivity between all the paralysis inducing tick species of veterinary relevance in Africa was demonstrated, by using a monoclonal antibody directed against the paralysis inducing toxin of Rhipicephalus evertsi evertsi. Western blot results, together with amino acid composition studies indicated that this monoclonal antibody recognizes protein bands of similar molecular mass and amino acid composition in R. evertsi evertsi and Ixodes rubicundus. This suggests that the Karoo paralysis toxin of I. rubicundus is possibly also a trimer with a high degree of homology to the spring lamb paralysis toxin of R. evertsi evertsi. The conclusive identity of these protein bands of 1. rubicundus could not be shown. Bio-assay studies performed on 1-day-old chickens suggested that the anti-spring lamb paralysis toxin monoclonal antibody also recognizes the paralysis toxin present in Argas (Persicargas) walkerae, by rendering some degree of protection against the effect of this toxin.     

Near-term forecasting of companion animal tick paralysis incidence: An iterative ensemble model

Tick paralysis resulting from bites from Ixodes holocyclus and I. cornuatus is one of the leading causes of emergency veterinary admissions for companion animals in Australia, often resulting in death if left untreated. Availability of timely information on periods of increased risk can help modulate behaviors that reduce exposures to ticks and improve awareness of owners for the need of lifesaving preventative ectoparasite treatment. Improved awareness of clinicians and pet owners about temporal changes in tick paralysis risk can be assisted by ecological forecasting frameworks that integrate environmental information into statistical time series models. Using an 11-year time series of tick paralysis cases from veterinary clinics in one of Australia’s hotspots for the paralysis tick Ixodes holocyclus, we asked whether an ensemble model could accurately forecast clinical caseloads over near-term horizons. We fit a series of statistical time series (ARIMA, GARCH) and generative models (Prophet, Generalised Additive Model) using environmental variables as predictors, and then combined forecasts into a weighted ensemble to minimise prediction interval error. Our results indicate that variables related to temperature anomalies, levels of vegetation moisture and the Southern Oscillation Index can be useful for predicting tick paralysis admissions. Our model forecasted tick paralysis cases with exceptional accuracy while preserving epidemiological interpretability, outperforming a field-leading benchmark Exponential Smoothing model by reducing both point and prediction interval errors. Using online particle filtering to assimilate new observations and adjust forecast distributions when new data became available, our model adapted to changing temporal conditions and provided further reduced forecast errors. We expect our model pipeline to act as a platform for developing early warning systems that can notify clinicians and pet owners about heightened risks of environmentally driven veterinary conditions.     

THE EFFECTS OF SOLUBILIZATION PROCEDURES ON THE RELEASE AND MOLECULAR STATE OF ACETYLCHOLINESTERASE FROM ELECTRIC ORGAN TISSUE

Abstract— A study was made of the effect of various solubilization procedures on the release of AChE from electric organ tissue of the electric eel and on the molecular state of the enzyme. The procedures employed included homogenization in different ionic media or in the presence of detergents, etuymic treatment and chemical modification. Studies were performed on intact electroplax, tissue homogenates and membrane fractions. The apparent AChE activity of intact cells, homogenates and membrane fractions was shown to be governed by diffusion-controlled substrate and hydrogen ion gradients, generated by AChE-catalyscd hydrolysis, leading to a lower substrate concentration and a lower pH in the vicinity of the particulate enzyme.
Treatment of homogenates with NaCl solutions or with NaCl solutions containing the nonionic detergent Triton X-100 causes release of the native'molecular forms of the enzyme (primarily the 18 S species) which aggregate at low ionic strength. For optimal extraction both high ionic strength (e.g. 1 M-NaCl) and the detergent are needed AChE is also solubilized by treatment of tissue homogenates with trypsin, bacterial protease or collagenase. The first two enzymes caused its release as an 11 S non-aggregating form, while collagenase also produces a minor non-aggregating - 16 S component. Treatment of tissue homogenates with maleic anhydride causes release of AChE as a non-aggregating 18 S species. On the basis of the solubilization experiments it is concluded that the interaction of AChE with the excitable membrane is primarily electrostatic. The possible orientation of the enzyme within the synaptic gap is discussed.     

Investigations into lymphocyte transformation and histamine release by basophils in sheep repeatedly infested with Rhipicephalus evertsi evertsi ticks

The immune response of a natural host of Rhipicephalus evertsi evertsi to feeding by this tick species was investigated with respect to the effects of tick salivary gland extracts on the transformation of peripheral blood lymphocytes and the release of histamine by basophils obtained from repeatedly infested sheep.The results indicated that there was no stimulation of lymphocyte transformation but that histamine release was elevated 10 fold after four infestations.Although this suggests a hypersensitivity reaction, believed to be a major factor in resistance to tick feeding, it was observed that ticks fed normally even after four infestations with 28 day intervals in between. These results emphasize the adaptation of ticks to feeding on their natural hosts.     

A comparison of Ixodes rubicundus (Acari: Ixodidae) infestations on Friesian and Bonsmara cattle in South Africa

This study was conducted to compare the relative resistance of crossbred Bos indicus X B. taurus Bonsmara and B. taurus Friesian cattle to Ixodes rubicundus (Karoo paralysis tick) infestations. During periods of peak abundance of the ticks, Friesian oxen harboured almost twice or more than twice as many ticks as either Bonsmara oxen or cows. During periods of low tick abundance tick burdens on both cattle breeds were closely similar. It is envisaged that cattle can play an important role in an integrated control strategy against the Karro paralysis tick.     

Tick paralysis: development of a vaccine.

The paralysis tick of Australia, Ixodes holocyclus, causes a severe toxicosis in domestic animals such as dogs and cats, livestock, and in some cases, humans. It is characterised by a rapidly ascending flaccid paralysis. The causative agent of the toxicosis is a neurotoxin(s) produced in the tick salivary glands. The current treatment for tick paralysis is in the form of a polyclonal dog antiserum. This antiserum treatment is expensive and effective only in the early stages of paralysis. The aim of current research is to develop a recombinant veterinary vaccine based on the tick neurotoxin peptide sequence. A successful vaccine would provide cost-effective, long-term protective immunity against tick-induced paralysis.     

Stage-specific gut proteinases of the cotton stainer bug Dysdercus peruvianus: role in the release of entomotoxic peptides from Canavalia ensiformis urease

Canavalia ensiformis ureases are toxic to insects of different orders. The entomotoxicity of urease is due to a 10 kDa internal peptide released by proteinases in the insect digestive tract. We previously observed that, given orally, urease is toxic to nymphs of Dysdercus peruvianus, but does not affect adults. Here we characterized the major proteolytic activities of D. peruvianus midgut homogenates and investigated their in vitro-catalyzed release of the 10 kDa entomotoxic peptide from urease. Cysteine, aspartic and metalloproteinases are present in both homogenates. Variations in optimal pH and susceptibility to inhibitors indicated differences in the enzyme profiles in the two developmental stages. Only nymph homogenates released approximately 10 kDa fragment(s) from urease, recognized by antibodies against the entomotoxic peptide. Fluorogenic substrates containing urease partial sequences flanking the N-terminal or the C-terminal portion of the entomotoxic peptide were efficiently cleaved by homogenates from nymphs, but much more slowly by the adult homogenate. Different classes of enzymes in the homogenates cleaved both substrates suggesting that in vivo the release of the entomotoxic peptide results from the concerted action of at least two different proteinases. Our findings support the view that a differential processing of ingested urease by the insects explains at least in part the lack of toxicity in adults.     

The relationships between habitat topology, critical scales of connectivity and tick abundance Ixodes ricinus in a heterogeneous landscape in northern Spain

The habitat mosaic was used to quantify connectivity between patches of different tick density of the notorious tick species Ixodes ricinus in an attempt to determine the cause of variations in tick abundance among apparently homogeneous sites in northern Spain. The analysis revealed that patches with high tick abundance are "stepping-stone" territories that, when removed from the landscape, cause large changes in connectivity. Sites with medium tick abundance do not cause such a critical transition in connectivity. Patches with low tick abundance, but optimal abiotic conditions for survival, are located within the minimum cost corridors network joining the patches, while those sites where the tick has been intermittently collected are located at variable distances from this network. Sites where the tick is consistently absent, but where the habitat is predicted to be suitable (old, heterogeneous forests of Quercus spp.) for the tick, are very separated from this main network of connections. These results suggest that tick distribution in a zone is highly affected not only by abiotic variables (vegetation and weather) but also by host movements. Dispersal of the tick is a function of how the hosts perceive the habitat, and the habitat's permeability to host movement. Permanent tick populations seem to be supported by the existence of these critical, high density patches, located at significant places within the habitat network.     

Seasonal patterns of abundance and host relationships of the Australian paralysis tick,Ixodes holocyclus Neumann (Acarina: Ixodidae), in southeastern Queensland

Estimates of seasonal abundance of larvae, nymphs and females of the paralysis tick, Ixodes holocyclus, were obtained by collecting ticks that engorged on small mammals and birds trapped in two localities in southeastern Queensland: Brisbane (wet sclerophyll forest) and Tamborine Mountain (cleared rain forest). The long-tailed short-nosed bandicoot, Isoodon macrourus, was the most common mammal trapped but small numbers of other marsupials, rodents and ground frequenting birds were also captured. Small numbers of five other tick species were also collected. In both habitats there was clearly one dominant generation of I. holocyclus;7er year, although the presence of all stages at most times of the year indicated overlapping of smaller cohorts. Females were most abundant in spring and early summer, larvae in summer-autumn, and nymphs in autumn-winter. I. holocyclus was abundant on I. macrourus and rare on most other mammals and birds captured. At the peak of abundance of each instar, each bandicoot dropped from 500 to 2000 engorged larvae, 100 to 200 engorged nymphs, and four to six engorged females. Life tables were compiled for the tick in both habitats and these indicate that there was relatively high survival from engorged larva to engorged nymph and thence to engorged female and that most mortality occurred between detaching of the engorged female and the detaching of the engorged larva. The tick was more abundant on bandicoots from cleared rain forest and rain forest edge, than on those from sclerophyll woodland. The survival of engorged larvae and nymphs of I. holocyclus and the larval productivity of engorged females were examined in a warm moist climate where the tick was abundant (Tamborine Mountain) and in a hotter dryer climate where the tick was rare or absent (Amberley). In both localities engorged larvae and nymphs survived to the next instar in all seasons of the year. On most occasions engorged females produced eggs which hatched. Mature bandicoots from tick infested areas showed little or no resistance to infestation with larvae or nymphs of I. holocyclus, whereas other small mammals from the same area showed an appreciable degree of resistance to the immature stages of the tick. Feeding larvae and nymphs exposed to normal light-dark cycles in the laboratory detached during the afternoon and early evening. This behaviour and host resistance are discussed in relation to the daily activity cycles of host species, their habitat preferences, and their role as hosts for I. holocyclus.     

Sites of attachment and intraspecific infestation densities of the brown paralysis tick (Rhipicephalus punctatus) on Angora goats

Significant differences in the distribution of brown paralysis ticks on various age classes of Angora goats were recorded. In kids, most (>98%) of the ticks attached to the head and ears, whereas in older groups, in addition to the ears, a high proportion (>20%) of ticks also attached to the ventral side of the neck. There were significant differences in the mean infestation densities of both male and femaleR. punctatus in kids and older animals. These differences were, however, only significant for the first two sample dates involving kids, and are probably related to behavioural attributes of the kids which enhance tick/host contact. Newly born Angora goat kids are considered a high-risk group with regard to paralysis caused by the brown paralysis tick. Methods of avoiding mortality amongst kids are suggested.     

Indicators for elevated risk of human exposure to host-seeking adults of the Rocky Mountain wood tick (Dermacentor andersoni) in Colorado

The human-biting adult stage of the Rocky Mountain wood tick (Dermacentor andersoni) can cause tick paralysis in humans and domestic animals and is the primary tick vector in the intermountain west of the pathogens causing Colorado tick fever, Rocky Mountain spotted fever, and tularemia. We conducted drag sampling studies in Poudre Canyon and Rocky Mountain National Park of Larimer County, CO, to determine microhabitat use patterns by host-seeking D. andersoni adults and find environmental factors signaling elevated risk of tick exposure. Big sagebrush (Artemisia tridentata) was found to serve as a general indicator of areas with elevated risk of exposure to host-seeking D. andersoni adults; this likely results from a shared climate tolerance of big sagebrush and D. andersoni. Grass was the favored substrate for host-seeking ticks. Drag sampling of open grass or grass bordering rock or shrub produced abundances of D. andersoni adults significantly higher than sampling of brush. Sampling sites in Rocky Mountain National Park, relative to Poudre Canyon, were characterized by more intense usage by elk (Cervus elaphus) but decreased brush coverage, smaller brush size, and lower abundances of host-seeking D. andersoni adults. There has been a tremendous increase in the population of elk in Rocky Mountain National Park over the last decades and we speculate that this has resulted in an ecological cascade where overgrazing of vegetation by elk is followed by suppression of rodent populations, decreased tick abundance, and, ultimately, reduced risk of human exposure to D. andersoni and its associated pathogens.     

Developmental profile, isolation, and biochemical characterization of a novel lipoglycoheme-carrier protein from the American dog tick, Dermacentor variabilis (Acari: Ixodidae) and observations on a similar protein in the soft tick, Ornithodoros parkeri (Acari: Argasidae)

A novel lipoglycoheme-carrier protein (CP) in the American dog tick, Dermacentor variabilis (Say) has been purified and characterized. CP was purified by native-PAGE from partially fed virgin females. CP has a density of 1.25 g/ml with a molecular weight of 200 K by native-PAGE and 340 K by gel filtration chromatography. CP is comprised of two majour subunits, 98 K and 92 K in molecular weight by SDS-PAGE. Separate amino acid composition of the two subunits indicated high contents of As(x), Gl(x) and leucine. However, the N-terminal amino acid sequence of the two subunits was only 13% identical. The lower molecular weight subunit showed 61% identity to artemocyanin (biliprotein) in fairy shrimps, 46% identity to minor vitellogenin in chickens and 13% identity to vitellin of the black-legged tick. No similarity match was found for the other subunit. CP is a lipoglycoheme-protein as indicated by selective staining of native-PAGE gel for lipids, carbohydrates and heme. Lipid analysis by thin layer chromatography revealed the presence of cholesterol, phospholipids, monoacylglycerides, triacylglycerides and free fatty acids. Heme associated with purified CP demonstrated a lambda(max) of 397.5 nm while the lambda(max) of crude hemolymph plasma was 402.5 nm. The presence of CP in whole body homogenates of eggs, unfed and fed larvae and fed nymphs as well as in the plasma of unfed and fed adults including vitellogenic females was demonstrated by native-PAGE. Although a protein of analogous size was not found in the soft tick, Ornithodoros parkeri Cooley, a high molecular weight protein (500 K) is the predominant plasma protein in both unfed and fed male and female adults of that species as determined by native-PAGE. Also, CP appears to function as a biliprotein which sequesters heme.     

A comparison of Chryseobacterium indologenes pathogenicity to the soft tick Ornithodoros moubata and hard tick Ixodes ricinus

A yellow-pigmented Gram-negative bacterium, Chryseobacterium indologenes, was found in the gut contents of about 65% of soft ticks Ornithodoros moubata from a perishing laboratory colony. The isolated putative pathogen, C. indologenes, was susceptible to cotrimoxazol and addition of this antibiotic (Biseptol 480) to the blood meal significantly decreased the tick mortality rate. The artificial infection of healthy O. moubata by membrane feeding on blood contaminated with C. indologenes was lethal to all ticks at concentrations 10(6) bacteria/ml. On the contrary, a similar infection dose applied to the hard tick Ixodes ricinus by capillary feeding did not cause significant mortality. Examination of guts dissected from infected O. moubata and I. ricinus revealed that C. indologenes was exponentially multiplied in the soft tick but were completely cleared from the gut of the hard ticks within 1 day. In both tick species, C. indologenes were found to penetrate from the gut into the hemocoel. The phagocytic activity of hemocytes from both tick species was tested by intrahaemocoelic microinjection of C. indologenes and evaluated by indirect fluorescent microscopy using antibodies raised against whole bacteria. Hemocytes from both tick species displayed significant phagocytic activity against C. indologenes. All O. moubata injected with C. indologenes died within 3 days, whereas the increase of the mortality rate of I. ricinus was insignificant. Our results indicate that hard ticks possess much more efficient defense system against infection with C. indologenes than the soft ticks. Thus, C. indologenes infection has the potential to be a relevant comparative model for the study of tick immune reactions to transmitted pathogens.     

Tick/host interactions forIxodes holocyclus: Role,effects, biosynthesis and nature of its toxic and allergenic oral secretions

The Australian paralysis tickIxodes holocyclus occurs along the eastern coast of Australia. Its interaction with a wide variety of hosts causes a serious toxicosis (tick paralysis) in domestic pets and livestock (occasionally in wildlife and humans) as well as hypersensitivity reactions in humans. Tick paralysis in animals is usually fatal in the absence of speedy antitoxin treatment and human hypersensitivity may result in life-threatening anaphylaxis. The protection of such hosts against toxic or allergic effects by vaccination or desensitisation respectively has been the objective of most of our recent research.The role, biosynthesis and nature of the paralysing toxin (holocyclotoxin) and of the allergens is gradually being elucidated. In this review, some emphasis has been placed on recent research on the interactions of humans with this tick and on the partial characterisation of the allergens.     

Hemolymph proteins in ticks

In comparison to insects and Crustacea, our knowledge of the predominant hemolymph proteins in ticks is minimal. The hemolymph protein most studied in ticks has been vitellogenin (Vg). Vg is synthesized by the tick fat body after female adults obtain a blood meal, is released into the hemolymph and is absorbed by developing oocytes as vitellin (Vn). Much of what we know about Vg is from studies of Vn. In general, the carbohydrate, lipid and amino acid composition is similar to insects except that in the tick, Vg contains heme, most likely from the digestion of host hemoglobin. In the American dog tick, Dermacentor variabilis, Vg is comprised of two native proteins and seven subunits on SDS-PAGE. Vg has been characterized in five tick species but the amino acid sequence is not yet available. Another predominant hemolymph protein, apparently a carrier protein (CP), has recently been studied in two tick species. This protein is found in the hemolymph of both male and females adults, in adult tissues outside of the hemolymph in some tick species, in coxal fluid of soft ticks and in whole body homogenates from eggs, larvae and nymphs. CP from the hard tick, D. variabilis, contains cholesterol, phospholipids, monoacylglycerides, triacylglycerides, free fatty acids, carbohydrate and heme. Under identical assay conditions, the analogous protein in the soft tick, Ornithodoros parkeri, did not contain heme. CP in the American dog tick consists of two subunits, one of which has 61% identity to the biliprotein, artemocyanin, from the fairy shrimp. CP is identical to a heme-lipoprotein (HeLp) from Boophilus microplus. The exact roles of CP and HeLp have not yet been fully determined, but they apparently are important in heme sequestration and as a storage depot for protein and lipid. Macroglobulin, lectin, antimicrobial, JH binding, JH esterase, and other tick hemolymph proteins are also discussed.     

Understanding the Relationships between Landscape Connectivity and Abundance of Ixodes ricinus Ticks

The density of Ixodes ricinus ticks in a heterogeneous landscape of northern Spain was determined and associated with some aspects of habitat topology. The habitat mosaic was used to quantify connectivity between patches of different tick density. The analysis revealed that patches with high tick abundance are ‘stepping-stone’ territories that, when removed from the landscape, cause large changes in connectivity. Sites with medium tick abundance do not cause such a critical transition in connectivity. Patches with low tick abundance, but optimal abiotic conditions for survival are located within the minimum cost corridors network joining the patches, while those sites where the tick has been intermittently collected are located at variable distances from this network. These results suggest that tick distribution in a zone is highly affected not only by abiotic variables (vegetation and weather) but also by host movements. Whether these high-density ‘stepping-stone’ patches occur in other tick species needs to be evaluated because of the potential implications of these foci for human health. This revised version was published online in July 2006 with corrections to the Cover Date.     

Mutagenicity of some dialkylnitrosamines, cyclic nitrosamines and N,N-diethanolnitrosamine in Salmonella typhimurium with rat and rabbit nasal, lung and liver S9 homogenates

6 nitrosamines, 5 of which cause rat nasal cancer, were tested for mutagenicity in the TA100 strain of S. typhimurium with rat and rabbit nasal, lung and liver S9 homogenates. The TA98 strain also was used with rabbit tissue homogenates. The two cyclic nitrosamines tested, N-nitrosopiperidine and N-nitrosopyrrolidine, were substantially mutagenic with all rabbit tissue homogenates in TA100, but in the rat only nasal homogenate was effective in activating them. N-Nitrosodi(n)propylamine also was activated by rat nasal tissue homogenate but not by the other rat or rabbit tissue homogenates. Diethanolnitrosamine was a direct mutagen in both TA100 and TA98. N-Nitrosodimethylamine and N-nitrosodiethylamine were not mutagenic under any test conditions. The results indicate that some nitrosamines that cause nasal cancer can be activated by nasal enzymes and that possibly important differences in activating capabilities occur among respiratory tract and hepatic tissues and among animal species.     

Host community structure and infestation by ixodid ticks: repeatability,dilution effect and ecological specialization

Abundance of a species in a location results from the interplay between the intrinsic properties of that species and the extrinsic properties, both biotic and abiotic, of the local habitat. Intrinsic factors promote among-population stability in abundance, whereas extrinsic factors generate variation among populations of a species. We studied (a) repeatability and (b) the effect of abundance and species richness of small mammals on the level of their infestation by larvae and nymphs of Ixodes ricinus (ecological generalist) and Ixodes trianguliceps (ecological specialist). We asked if tick infestation parameters are characteristic (=repeatable) for a particular host species or a particular stage of a particular tick species. We also asked how abundance and diversity of hosts affect the level of tick infestation on a particular host species. We predicted that the dilution effect (decrease in tick infestation levels with an increase of host abundance and/or species richness) will be better expressed in an ecological generalist, I. ricinus, than in an ecological specialist, I. trianguliceps. We found that (a) tick abundance, prevalence and aggregation were generally repeatable within tick species/stage; (b) tick abundance and prevalence, but not the aggregation level, were repeatable within host species; (c) the proportion of variance among samples explained by the differences between tick species and stages (as opposed to within-tick species and stage) was higher than that explained by the differences between host species (as opposed to within host species); and (d) the relationship between tick infestation parameters and host abundance and diversity revealed the dilution effect for I. ricinus but not for I. trianguliceps.