Isolation of TBE virus from the tick Ixodes hexagonus

Tick-borne encephalitis (TBE) virus was isolated from a sample of Ixodes hexagonus ticks collected from the hair of the western European hedgehog (Erinaceus europaeus) which had been captured on the edge of a new housing estate in Ceské Bud?jovice at the end of September 1986. This was the first isolation of TBE virus from this vector, supporting the previous experimental results. The virus was identified in immunofluorescent and plaquereduction neutralization tests.     

A contribution to the methods of estimating absolute tick numbers

The method of estimating tick numbers in nature by means of experimental sites and by subsequent determination and comparison of classes of occurrence frequency, originally developed for estimation of the numbers of adult Ixodes persulcatus in the Far East and Udmurtia, was successfully applied to imagoes and nymphs of Ixodes ricinus occurring in typical Central European biotopes.     

Mechanism of action of clenpyrin on the cattle tick Boophilus microplus

Clenpyrin is effective against all stages of development of one-host cattle ticks (Boophilus spp.) including strains resistant to organophosphorus compounds and carbamates. Ticks treated with clenpyrin are quickly immobilised due to a slackening of the muscles. Manometric measurements revealed a marked depression in respiratory gas exchange and a rise in the R Q within 24 h after treatment. Clenpyrin inhibits NADH oxidation and, as a result, all synthesising processes in the tick. The breakdown of proteins taken up with the blood meal is also inhibited. Clenpyrin, however, does not interfere with carbohydrate degradation. These results have been corroborated in detail by determining various substances in treated and untreated ticks: proteins, haematin, guanine, glycogen, glucose, lactate, ATP, lipoids and cuticular wax. Clenpyrin does not inhibit tick proteinase, tick and other acetylcholinesterase, or rat monoamine oxidase; therefore, the mode of action of clenpyrin differs from that of other known tickicides, especially those involving the acetylcholinesterase system.     

Screening techniques for the evaluation of chemicals with activity as tick repellents

Screening techniques are described for the evaluation of the activity of tick repellents in vitro and in vivo, for the control of ticks of veterinary importance. In addition a modification of the in-vitro technique is described whereby the knockdown activity of chemicals may be assessed. There was a lack of correlation between results obtained in vitro and those obtained in vivo. Butopyranoxyl and N, N-diethyl-m-toluamide, which were highly active in vitro, showed only medium to low activity in vivo. Conversely, benzyl benzoate and dimethyl carbate, which were highly active in vivo, showed only low activity in vitro. Chemical breakdown, volatility, the ability of the chemical to bind to hair and skin, and differences in the behaviour and the morphology and physiology of the sense organs between larval and adult Rhipicephalus evertsi evertsi (Neumann 1897) are suggested as likely explanations for these differences in activity. Of the four synthetic pyrethroids tested, cypermethrin, deltamethrin, permethrin and fenvalerate, only the first three were shown to have good knockdown activity but only two, deltamethrin and permethrin, produced significant mortality of the exposed larvae. Further tests would be required to determine whether there is a correlation between knockdown and mortality.     

Formamidine structure and detachment of the cattle tick Boophilus microplus

Evaluation of the effectiveness of topically applied chlordimeform, 14 other formamidines, and 5 sulfur-containing related nonformamidine compounds in causing female Boophilus microplus ticks to detach from mice enabled activity to be related to structure. Five compounds were inactive and 15, including 2 sulfur-containing nonformamidines and 1 sulfur-containing formamidine were active at doses ranging from 0.0005 to 2.0 μg/tick. The most active compounds were the N-monomethyl formamidines, BTS-27271 [N′-(2,4-dimethylphenyl)-N-methylformamidine], and C-8520 (demethylchlordimeform). Among the analogs of chlordimeform tested, those with alkyl substitutions at the amino nitrogen decreased in effectiveness in the order, monomethyl (demethylchlordimeform), monoethyl, mono-n-butyl, mono-i-butyl, mono-i-propyl, dimethyl (chlordimeform), and di-n-propyl. Inactive compounds resulted from the replacement of the chlorine at ring position 4 of the aryl moiety of chlordimeform by bromine or hydrogen or by the conversion of the NCH amidino moiety to the NHCSN < thiourea moiety.Detachment due to chlordimeform was antagonized by piperonyl butoxide but that due to its N-monomethyl analog, a known metabolite of chlordimeform in ticks, was synergized by the same compound. These effects on the detaching response parallel those reported elsewhere concerning synergism and antagonism of toxic responses of B. microplus to formamidines.BTS-27271, which was the most effective formamidine in causing detachment after topical application to ticks was moderately effective when injected into mice but its potency relative to chlordimeform was considerably reduced; when sprayed onto cattle BTS-27271 was somewhat more effective in depressing percentage survival of ticks of all stages than chlordimeform.     

Inhibition of oviposition in the cattle tick Boophilus microplus by certain acaricides

Doses of ten acaricides, ranging from 2.5 to 10 μg, induced about 10-60% mortality and inhibited oviposition in engorged Boophilus microplus as well as preventing larval hatching from the eggs. The effects of the acaricides were dose dependent. The efficacy of acaricides in reducing the reproductive potential (inhibition of oviposition × inhibition of hatching/100) was in the following order: dimethoate > dioxathion > naled > diazinon > chlordimeform > carbaryl > trichlorphon > phosphamidon > gamma-HCH > fenitrothion. Most of the acaricides also retarded the oviposition cycle, delaying the peak activity by 4-8 days. The ovarian development in control ticks reached its peak between the 5th and 7th days before decreasing gradually and ceasing completely between the 16-20th days after engorgement. The protein content of the ovaries and the rate of incorporation of [¹⁴C]glycine into the tissues followed a similar pattern. Carbaryl, fenitrothion and naled inhibited these activities. Chlordimeform stimulated [¹⁴C]glycine incorporation and increased the ovarian protein content up to the 13th day before resorption of the oocytes. The eggs from treated ticks were mostly non-viable and contained more protein; those from dioxathion, carbaryl and chlordimeform treatments had a higher dry weight than the control.     

Occurrence of the tick Ixodes ricinus (L.) under the conditions of anthropopressure

The authors report on their findings of the tick Ixodes ricinus under urban conditions of Prague. The concrete data were taken as a basis for a general scheme of possible occurrence of this species in various town parts, determined by the state of vegetation and presence of large mammals. Discussed are also conditions for I. ricinus maintenance in another type of anthropogenous landscape, the spoil banks resulting from brown coal exploitation.     

Cypermethrin inhibits egg development in the ixodid tick, Amblyomma hebraeum

The pyrethroid insecticide, cypermethrin (CyM), stimulates vitellogenesis in Ornithodoros moubata (an argasid tick) by stimulating the release of the normal vitellogenesis-inducing factor (a neuropeptide) and subsequent release of the vitellogenic hormone [19]. Here we examine the effects of CyM on egg development in the ixodid tick, Amblyomma hebraeum. Ovary weight, oocyte size, and vitellin content of the ovary were measured after CyM treatment; in partially fed ticks, none of these parameters were affected significantly. However, CyM treatment caused an inhibition of ovary development, as well as reduction of both hemolymph 20-hydroxyecdysone (20E; the vitellogenic hormone in this species) and vitellogenin (Vg)-concentrations in engorged ticks. In addition, the degree of salivary gland degeneration (which is triggered by 20E) was slightly reduced in CyM-treated engorged ticks. These results indicate that CyM acts differently in Amblyomma compared to Ornithodoros. Instead of stimulating vitellogenesis, CyM inhibits egg development perhaps in part as a result of inhibiting release of 20E.     

Effect of tick salivary gland extract on the cytokine production by mouse epidermal cells

Previous studies have demonstrated that both tick saliva and Borrelia burgdorferi sensu lato antigens modulate the cytokine response of the host. In this paper, the effect of salivary gland extract (SGE) from Ixodes ricinus (L., 1758) ticks on cytokine production by primary cultures of mouse epidermal cells stimulated with Borrelia afzelii Canica, Nato, du Merle, Mazie, Baranton et Postic, 1993 spirochetes was analysed. Epidermal cells were derived from C3H/HeN mice, susceptible to Lyme disease, and BALB/c mice, which are resistant. In cultures from C3H/HeN mice, SGE down regulated production of tumour necrosis factor alpha (TNF-alpha) and up regulated Th2 cytokine, interleukin 4 (IL-4). Cultures from BALB/c mice produced higher basal levels of monitored cytokines, but their production was affected by SGE a different way. While Th2 cytokines IL-6 and IL-10 were down regulated, the effect on TNF-alpha and IL-4 was ambiguous. These results indicate that the effect of tick saliva on the epidermal cells of Lyme disease-susceptible C3H/HeN mice mirrors its effect on other cells of the immune system.     

Separation and characterization of the pyrethroid-hydrolyzing esterases of the cattle tick, Boophilus microplus

The principal esterases present in homogenates of cattle tick larvae have been separated by gel filtration and preparative isoelectric focusing. Substrate specificities have been determined using trans-permethrin, trans-cypermethrin, p-nitrophenyl butyrate, and the pyrethroid analog, p-nitrophenyl-(1R,S)-3-(2,2-dichlorovinyl)-2,2-dimethylcyclopropanecarboxylate (t-NPDC). One of the esterases, with pI = 4.6, and molecular weight ～67,000, hydrolyzed the α-cyano-substituted pyrethroid, trans-cypermethrin, but not permethrin. The major esterase activity was found in the pI 5.6–5.8 region, and corresponded to a molecular weight of ～89,000. Small differences in substrate specificity and differences in the banding pattern after isoelectric focusing were detected between esterases of ticks of a pyrethroid-resistant strain (Malchi) and a pyrethroid-susceptible strain (Yeerongpilly). Rate constants were determined for the inhibition of the different esterases by the organophosphate coroxon and by naphthyl N-propylcarbamate, using p-nitrophenyl butyrate and t-NPDC as substrates.     

Studies on the transovarial transmission of Borrelia burgdorferi sensu lato in the taiga tick Ixodes persulcatus

The possibility of vertical transmission of Borrelia burgdorferi sensu lato in Ixodes persulcatus Schulze, 1930 ticks was studied in the progeny of 20 females collected from the vegetation in an active focus of ixodid tick-borne borrelioses (ITBB) located in the Perm oblast, Russia, where Borrelia garinii and B. afzelii are circulating. The presence of Borrelia DNA was detected by the PCR method after feeding and egg laying in 16 engorged females (80.0%), as well as in 36.5 +/- 7.2% samples containing 20 eggs each and in 21.4 +/- 4.2% samples containing 10 eggs each. The respective rates of individual egg infection were 0.4-8.0% and 0.5-23.0%. PCR analysis of 370 eggs (one egg per sample) and 781 unfed larvae hatched from the same egg masses (1, 10, 20, 40, and 50 larvae per sample) failed to reveal the presence of Borrelia DNA. Negative results were also obtained in experiments on inoculating the BSK II medium with the egg and larval materials. Microscopic analysis of 1,683 smear preparations of eggs and 1,416 preparations of unfed daughter larvae revealed spirochete-like cells in 7 (0.4 +/- 0.3%) and 13 (0.9 +/- 0.5%) preparations, respectively; typical Borrelia cells were found in seven preparations of larvae (0.5 +/- 0.4%). Only 1 out of 16 infected females transmitted Borrelia vertically, through the eggs to the larval progeny. The infection rate in this progeny was about 7%, and the prevalence of Borrelia in individual larvae was 0.4-0.8 cells per 100 microscopic fields. These data do not allow the conclusion that transovarial transmission of B. burgdorferi sensu lato in the I. persulcatus tick is an established fact. However, they show that, even if such transmission is possible, its probability is very low.     

Choline acetyltransferase in organophosphorus-resistant and -susceptible strains of the cattle tick, Boophilus microplus

Choline acetyltransferase was demonstrated in homogenate extracts of larvae and adult brains of the cattle tick. The enzyme activity was approximately 15 and 100 μmol of acetylcholine synthesized/g of tissue/hr for larvae and adult brains, respectively. Comparisons of five strains showed that, despite organophosphate selection for acetylcholinesterases with wide differences in activity and inhibition kinetics, the choline acetyltransferase activity was statistically uniform between strains. it is concluded that the two enzymic components of the cholinergic system are controlled independently.     

Nymphal diapause and its photoperiodic control in the tick Ixodes scapularis (Acari: Ixodidae)

It is shown experimentally that the option between developmental diapause and non-diapause development in nymphs of Ixodes scapularis Say, 1821 (Middle Atlantic population) is determined by photoperiodic conditions according to a two-step photoperiodic reaction of short-day long-day type. Diapause arrest of development is induced by an impact of either long day upon unfed nymphs, or short day upon engorged nymphs, while non-diapause development completed in 2-2.5 months at 20 degrees C needs the change from short-day to long-day conditions. Some ecophysiological aspects of mechanisms controlling seasonal development of ticks belonging to Ixodes ricinus complex are discussed.