Repellent and acaricidal properties of Ocimum suave against Rhipicephalus appendiculatus ticks

An oil extracted from the leaves of a tropical shrub Ocimum suave was found to repel as well as kill all stages of the tick Rhipicephalus appendiculatus. In an in vitro bioassay for the larvae, the LC₅₀ of the oil in liquid paraffin was 0.024%. A 10% solution was found to kill all immatures and more than 70% of adults feeding on rabbits. Rabbits were protected for 5 days against attaching larvae using a 10% solution. Preliminary experiments undertaken with cattle kept in the field suggest that the oil may have potential in tick control, and a role in integrated tick management.     

Detection of spotted fever group Rickettsia spp. from bird ticks in the U.K.

Migratory birds are known to play a role in the long‐distance transportation of microorganisms. To investigate whether this is true for rickettsial agents, we undertook a study to characterize tick infestation in populations of the migratory passerine bird Riparia riparia (Passeriformes: Hirundinidae), the sand martin. A total of 194 birds were sampled and ticks removed from infested birds. The ticks were identified as female Ixodes lividus (Acari: Ixodidae) using standard morphological and molecular techniques. Tick DNA was assayed to detect Rickettsia spp. using polymerase chain reaction and DNA was sequenced for species identification. A single Rickettsia spp. was detected in 100% of the ticks and was designated Rickettsia sp. IXLI1. Partial sequences of 17‐kDa and ompA genes showed greatest similarity to Rickettsia sp. TCM1, an aetiological agent of Japanese spotted fever‐like illness, previously described in Thailand. Phylogenetic analysis showed that Rickettsia sp. IXLI1 fitted neatly into a group containing strains Rickettsia japonica, Rickettsia sp. strain Davousti and Rickettsia heilongjiangensis. In conclusion, this research shows that U.K. migratory passerine birds host ticks infected with Rickettsia species and contribute to the geographic distribution of spotted fever rickettsial agents.     

Sequential Histopathology at the Rhipicephalus Sanguineus Tick Feeding Site on Dogs and Guinea Pigs

The tick Rhipicephalus sanguineus is a very common parasite of dogs worldwide. Dogs seem unable to acquire resistance against this tick species, whereas guinea pigs demonstrate a very strong resistance following primary infestation. We studied the inflammatory reaction at the R. sanguineus tick feeding site on dogs and guinea pigs during primary and tertiary infestations at different time intervals after attachment. Biopsies were collected after 4, 24, 48 and 96 hours. Changes that were found in all experimental groups included a cone of cement around the mouthparts of the tick, epidermal hyperplasia, edema and inflammatory cell infiltration in the dermis directly underneath the tick attachment site. Dogs reacted to ticks mainly with neutrophils, particularly after repeated exposure. Mast cells and mononuclear leukocytes were also present. Guinea pigs reacted to R. sanguineus mainly with mononuclear cells, eosinophils and basophils. These cells were particularly numerous after repeated exposure to R. sanguineus. Our results suggest that basophils and eosinophils are involved in resistance of guinea pigs to R. sanguineus and that neutrophils in dogs have little effect against this tick species.     

Integrated Control of Acaricide-Resistant Boophilus Microplus Populations on Grazing Cattle in Mexico Using Vaccination with Gavac™ and Amidine Treatments

Throughout most of the twentieth century, tick infestations on cattle have been controlled with chemical acaricides, typically administered by dipping or spraying. This approach can cause environmental and residue problems and has created a high incidence of acaricide resistance within tick populations in the field. Recently we developed a vaccine against Boophilus microplus employing a recombinant Bm86 antigen preparation (Gavac), (Heber Biotec S.A., Havana, Cuba) which has been shown to induce a protective response in vaccinated animals. Here we show for the first time under field conditions a near 100% control of B. microplus populations resistant to pyrethroids and organophosphates, by an integrated system employing vaccination with Gavac and amidine treatments. This method effectively controls tick infestations while reducing the number of chemical acaricide treatments and consequently the rise of B. microplus populations resistant to chemical acaricides.     

Detection and typing of Borrelia burgdorferi sensu lato genospecies in Ixodes persulcatus ticks in West Siberia, Russia

The prevalence of Borrelia burgdorferi sensu lato (s.l.) genospecies in West Siberia as well as in many other regions of Russia remains insufficiently investigated. In the present study a total of 151 adult female ticks Ixodes persulcatus Schulze, collected at three localities in eastern regions of West Siberia, where Lyme disease is endemic, were examined for the presence of the spirochete B. burgdorferi s.l. by polymerase chain reaction targeting the 23S-5S rRNA intergenic spacer regions. Spirochetal DNA was detected in on average 15.2+/-3.0% of the ticks examined. The infection rate of adult ticks with B. burgdorferi s.l. at various localities ranged from 8.6+/-3.4% to 29.0+/-7.6%, being greatest in the northernmost site studied and decreasing southwards. The restriction patterns obtained after MseI digestion of the 23S-5S rRNA intergenic spacer amplicons assigned 23 DNA samples to the following genomic groups: 19 to B. garinii (12 to group NT29 and seven to group 20047(T)), three to B. afzelii, and one to mixed B. afzelii and B. garinii NT29. We have not detected other genospecies, which were found in ticks in Europe, the Russian Far East and Japan. Thus, the ticks examined were associated only with two genospecies of Borrelia burgdorferi s.l. pathogenic to humans (B. garinii and B. afzelii), and B. garinii was the major genospecies infecting adult I. persulcatus in eastern regions of West Siberia.     

Phylogenetic analysis of spotted fever group rickettsiae based on gltA, 17-kDa, and rOmpA genes amplified by nested PCR from ticks in Japan

In order to understand the natural situation of rickettsiae in the ticks in Japan, the rickettsial genes, gltA gene, rOmpA gene, and 17-kDa gene, were amplified from the ticks by nested PCR. The prevalences of rickettsial gltA genes among Haemaphysalis formosensis, H. longicornis, H. megaspinosa, Ixodes ovatus, H. flava, H. kitaokai, and I. persulcatus were 62, 57, 24, 24, 19, 13, and 10%, respectively; 26% (186/722) being the average. The gltA genes amplified from the ticks were classified into 9 genotypes (I to IX) by the difference in nucleotide sequences. Genotype I was detected from 7 species of ticks. Genotype II mainly was detected from H. longicornis and H. formosensis. Genotypes III and VII mainly were detected from H. flava and I. ovatus. The polarization in the distribution of genotypes among regions where the ticks were collected was not clear. Based on the phylogenetic analysis of the three genes presented here, genotypes I, III, and IV (detected from H. formosensis, H. hystricia, and I. ovatus ) are genetically close with each other, but rickettsiae of the same property still have not been isolated from ticks anywhere in the world. These genotypes should be considered as new species among SFG rickettsiae. Genotype II was identical with strain FUJ-98, genetically close to R. japonica which has been isolated from ticks in China. Genotype V was identical with R. felis and strain California 2 isolated from the cat flea. This is the first report on the detection of R. felis from ticks. Genotype VI detected from Ixodes sp. did not seem to belong to genus Rickettsia. Based on the previous antigenic data and the phylogenetic analysis presented here, Genotype VII should be considered a variant of R. helvetica and genotype VIII detected from I. ovatus and I. persulcatus were identical with R. helvetica. Genotype IX detected from I. nipponensis was genetically close to the strains IRS3, IRS4, and IrR/Munich isolated from I. ricinus in Slovakia and German.     

In vitro efficacy of extracts of Melia azedarach against the tick Boophilus microplus

The efficacy of ripe fruit extracts of Melia azedarach L. (Rutales: Meliaceae) was evaluated against the tick, Boophilus microplus (Canestrini) (Acari: Ixodidae). Ripe fruits of M. azedarach dried and powdered were extracted by Soxhlet apparatus successively using hexane, CHCl3 and 96% aqueous ethanol. Larvae and engorged females were immersed in decreasing concentrations from 0.25% to 0.015% of each extract. The mortality of larvae was evaluated 24, 72 and 168 h after treatment. The effectiveness of treatment against engorged females was assessed by measuring egg production. All tested extracts caused mortality of B. microplus larvae, with higher mortality rates observed in CHCl3 (100%) and hexanic extract (98%) than in ethanolic extract (50%) 168 h after treatment. The mortality was dependent on concentration and on time after treatment. Similarly hexanic and CHCl3 extracts showed higher effectiveness (varying from 14% to 100%) against B. microplus engorged females than ethanolic extract (varying from 0% to 46%). Melia azedarach extracts did not kill the adult females, but inhibited partially or totally egg production and embryogenesis. These results show that the less polar the extract of M. azedarach ripe fruits the more its effectiveness against larvae and engorged females of B. microplus. This plant may therefore be useful in the control of resistant B. microplus populations.     

In vitro assays for repellents and deterrents for ticks: differing effects of products when tested with attractant or arrestment stimuli

Most in vivo and in vitro tests with repellents or deterrents against ticks have not considered which sensory channel is being targeted. We have recorded the responses of two hard tick species (Acari: Ixodidae) in vitro to determine if such products can disrupt the perception of an attractant in a repellent assay or the perception of an arrestment stimulus in a deterrent assay. Ethyl butylacetylaminopropionate (EBAAP), N,N-diethyl-methyl-benzamide (deet), permethrin and indalone were chosen to test their capacity to inhibit the attraction of Amblyomma variegatum Fabricius to its aggregation-attachment pheromone. Vapours of each test product plus those from a synthetic blend of the pheromone were delivered to the walking tick in an air stream on a locomotion compensator. Neither EBAAP, deet, permethrin nor indalone could inhibit attraction of A. variegatum even when each of the test products was delivered at 106 times the pheromone. Indalone did decrease the attraction of A. variegatum to the pheromone and induced repulsion of A. variegatum when presented on its own in the air stream. The effect of permethrin, a sodium channel blocker, was also tested in a deterrent assay measuring the arrestment of Ixodes ricinus (L.) adults on its own faeces and faecal constituents. Permethrin deterred arrestment at doses of 670 fg/cm2 to 67 ng/cm2, i.e. at levels five times lower than the dose of chemostimuli present in the arrestment stimulus. This sensitivity to permethrin suggests that it acts via the contact chemoreception channel.     

IgG responses to salivary gland extract of Ixodes ricinus ticks vary inversely with resistance in naturally exposed sheep

Enzyme-linked immunosorbent assay (ELISA) was used to investigate the antibody responses of control sheep, and sheep naturally exposed to Ixodes ricinus Linné (Acari: Ixodidae) ticks, to salivary gland extract (SGE) proteins of partially fed, adult I. ricinus. Comparisons between responses of control sheep and naturally infested sheep by Western blot analysis suggested that variations in IgG responses of I. ricinus-exposed sheep were mostly associated with specific responses to I. ricinus SGE antigens. Sheep IgG responses were positively related to the numbers of adult ticks feeding per sheep at the time samples were collected, were greater during the spring than the autumn periods of I. ricinus activity and were inversely related to sheep resistance to ticks measured by the weights of nymphal I. ricinus that engorged on the sheep. These findings suggest that sheep lose their resistance to ticks due to polarization of a Th1 type response to some tick antigens towards a Th2 type response when sheep are exposed to high, natural tick infestations, or to seasonal conditions of relative nutritional stress. Potential consequences for the epidemiology of tick-borne diseases are discussed.     

Kinetics of Experimental Infection of Sheep with Ehrlichia ruminantium Cultivated in Tick and Mammalian Cell Lines

Inoculation of sheep with Ehrlichia (previously Cowdria) ruminantium which has been cultivated in mammalian endothelial cell cultures is almost always followed by a severe clinical reaction, whereas inoculation of the agent cultivated in tick cell lines usually does not provoke a clinical response, but may result in seroconversion and/or protection against subsequent challenge with virulent stabilates. A quantitative, real-time PCR assay was developed to determine the kinetics of infection (rickettsaemia) in sheep inoculated with tick cell- and mammalian cell-derived E. ruminantium (Gardel isolate). The method and initial results are described, and the significance of the findings is discussed in relation to the clinical responses of the sheep. This revised version was published online in July 2006 with corrections to the Cover Date.