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PubMed2002

Investigation of Bartonella infection in ixodid ticks from California.

A total of 1253 ixodid ticks (254 tick pools) collected between the end of 1995 and the spring of 1997 from six California counties (El Dorado, Los Angeles, Orange, Santa Cruz, Shasta and Sonoma) were examined for the presence of Bartonella DNA by PCR of the citrate synthase gene. Of 1,119 adult Ixodes pacificus ticks tested, 26 (11.6%) of 224 pools, each containing five ticks, were positive (minimum percentage of ticks harboring detectable Bartonella DNA, 2.3%). Bartonella PCR-positive ticks were identified in five counties but none of the ticks from Los Angeles County was positive. Among 47 nymphal I. pacificus ticks collected in Sonoma County, one (10%) positive pool out of 10 pools was identified (minimum percentage of ticks harboring detectable Bartonella DNA, 2.1%). Among the 54 Dermacentor occidentalis grouped in 12 pools from Orange County, one pool (8.3%) was PCR positive for Bartonella and similarly one pool (14.3%) was positive among the 30 Dermacentor variabilis ticks grouped in seven pools. None of the three D. occidentalis from El Dorado County were positive. None of the nine tick pools positive for Ehrlichia phagocytophila were positive for Bartonella. Following our previous findings of Bartonella PCR-positive adult I. pacificus ticks in central coastal California, this is the first preliminary report of the presence of Bartonella DNA in I. pacificus nymphs and in Dermacentor sp. ticks. Distribution of Bartonella among ixodid ticks appears widespread in California.

Animals↗
PubMed1998

Interaction of entomopathogenic nematodes (Steinernematidae) with selected species of ixodid ticks (Acari: Ixodidae).

Entomopathogenic nematodes, currently used for biological control of various insect pests, were tested for their ability to penetrate and kill replete females of several species of ticks including Dermacentor variabilis (Say), Rhipicephalus sanguineus (Latreille), Amblyomma maculatum Koch, and A. cajennense (F.). These species were found to be susceptible to the entomopathogenic nematodes, Steinernema feltiae (Filipjev) or S. riobravus (Cabanillas & Poinar), shown in previous studies in our laboratory to be attracted to and kill replete A. americanum. S. riobravus killed D. variabilis (96%), R. sanguineus (89%), A. maculatum (24%), and A. cajennense (88%), and S. feltiae killed D. variabilis (91%) and R. sanguineus (71%). Of the ticks that survived mean egg mass weights were significantly lower than those of the unexposed controls. When nematode-exposed ticks were examined with light microscopy, nematodes were found to have entered ticks but did not multiply or produce subsequent generations of infective juveniles. The nematodes were separated from surrounding tissues by a clear space, suggesting that they produced protective compounds. Bacteria, thought to be symbiotes released from the nematodes, multiplied initially in the hemocoel of the tick and subsequently were found throughout the degenerating tick tissues. These bacteria eventually filled the tick and appeared to be the cause of tick death. Nematode guts were filled with the bacteria, suggesting that the bacteria were a food source. When ticks were exposed to nematodes while feeding on cattle, partially engorged females were most susceptible to the nematodes. Tick mortality and reduced egg production resulted when the ticks had fed 6 and 9 d before nematode exposure but not when ticks were exposed after 3 d of feeding. Exposure of feeding female ticks demonstrated that the nematodes were able to penetrate tick orifices other than via the hypostome, which was embedded in the bovine epidermis for the duration of the feeding process.

Animals↗
PubMed2000

Acquisition of coinfection and simultaneous transmission of Borrelia burgdorferi and Ehrlichia phagocytophila by Ixodes scapularis ticks.

The agents of Lyme disease (Borrelia burgdorferi) and human granulocytic ehrlichiosis (Ehrlichia phagocytophila) are both transmitted by the tick Ixodes scapularis. In nature, ticks are often infected with both agents simultaneously. We studied whether previous infection with either Borrelia or Ehrlichia in ticks would affect acquisition and transmission of a second pathogen. Ehrlichia-infected I. scapularis nymphs were fed upon Borrelia-infected mice, and Borrelia-infected I. scapularis nymphs were fed upon Ehrlichia-infected mice. The efficiency with which previously infected nymphal ticks acquired a second pathogen from infected hosts was compared to that of uninfected ticks. An average of 51% +/- 15% of ticks acquired Ehrlichia from infected mice regardless of their prior infection status with Borrelia. An average of 85% +/- 10% of ticks acquired Borrelia from infected mice regardless of their prior infection status with Ehrlichia. Also, we assessed the efficiency with which individual nymphs could transmit either agent alone, or both agents simultaneously, to individual susceptible hosts. An average of 76% +/- 9% of Borrelia-infected ticks and 84% +/- 10% of Ehrlichia-infected ticks transmitted these agents to mice regardless of the presence of the other pathogen. There was no evidence of interaction between the agents of Lyme disease and human granulocytic ehrlichiosis in I. scapularis ticks. The presence of either agent in the ticks did not affect acquisition of the other agent from an infected host. Transmission of the agents of Lyme disease and human granulocytic ehrlichiosis by individual ticks was equally efficient and independent. Dually infected ticks transmitted each pathogen to susceptible hosts as efficiently as ticks infected with only one pathogen.

Animals↗
PubMed2003

Prevalence of granulocytic Ehrlichia and Borrelia burgdorferi sensu lato in Ixodes ricinus ticks collected from Southwestern Finland and from Vormsi Island in Estonia.

Altogether, 343 adult and 111 nymphal Ixodes ricinus ticks collected from parks in Turku and suburban and rural islands of the Turku archipelago, Finland, and 100 adult I. ricinus ticks collected from Vormsi Island, Estonia, were included in this study. Using the polymerase chain reaction the ticks were examined for 16S rDNA of the Ehrlichia phagocytophila genogroup and for Borrelia burgdorferi sensu lato recA and flagellin genes. None of the Finnish ticks was found to be infected with E. phagocytophila, whereas 3% of the Estonian ticks were positive for this organism. The rate of Finnish ticks infected with B. burgdorferi sensu lato varied from 0% to 11.6% (mean 5%; 9% for adult and 4% for nymphal ticks). The corresponding rate for Estonian ticks was 15%. Borrelia afzelii was the most common genospecies in both Finnish (2.6%) and Estonian (12%) ticks. B. burgdorferi sensu stricto was detected in 2.0% of the Finnish ticks, but in none of the Estonian ticks. These results suggest that the E. phagocytophila genogroup is very rare in Finnish ticks, although the ticks were collected from an area endemic for Lyme borreliosis. In Estonia, E. phagocytophila is found in ticks and may cause disease.

Animals↗
PubMed2003

Real-time PCR for simultaneous detection and quantification of Borrelia burgdorferi in field-collected Ixodes scapularis ticks from the Northeastern United States.

The density of spirochetes in field-collected or experimentally infected ticks is estimated mainly by assays based on microscopy. In this study, a real-time quantitative PCR (qPCR) protocol targeting the Borrelia burgdorferi-specific recA gene was adapted for use with a Lightcycler for rapid detection and quantification of the Lyme disease spirochete, B. burgdorferi, in field-collected Ixodes scapularis ticks. The sensitivity of qPCR for detection of B. burgdorferi DNA in infected ticks was comparable to that of a well-established nested PCR targeting the 16S-23S rRNA spacer. Of the 498 I. scapularis ticks collected from four northeastern states (Rhode Island, Connecticut, New York, and New Jersey), 91 of 438 (20.7%) nymphal ticks and 15 of 60 (25.0%) adult ticks were positive by qPCR assay. The number of spirochetes in individual ticks varied from 25 to 197,200 with a mean of 1,964 spirochetes per nymphal tick and a mean of 5,351 spirochetes per adult tick. No significant differences were found in the mean numbers of spirochetes counted either in nymphal ticks collected at different locations in these four states (P = 0.23 by one-way analysis of variance test) or in ticks infected with the three distinct ribosomal spacer restriction fragment length polymorphism types of B. burgdorferi (P = 0.39). A high degree of spirochete aggregation among infected ticks (variance-to-mean ratio of 24,877; moment estimate of k = 0.279) was observed. From the frequency distribution data and previously published transmission studies, we estimated that a minimum of 300 organisms may be required in a host-seeking nymphal tick to be able to transmit infection to mice while feeding on mice. These data indicate that real-time qPCR is a reliable approach for simultaneous detection and quantification of B. burgdorferi infection in field-collected ticks and can be used for ecological and epidemiological surveillance of Lyme disease spirochetes.

Animals↗
PubMed2005

Efficacy of a combination of imidacloprid 10%/permethrin 50% versus fipronil 10%/(S)-methoprene 12%, against ticks in naturally infected dogs.

Preventing tick bites is a fundamental step towards reducing the impact of tick-borne protozoal, bacterial and viral diseases (TBDs) in humans and animals. The aim of this study was to evaluate the efficacy of a combination of imidacloprid 10%/permethrin 50% and of fipronil 10%/S-methoprene 12% against ticks in naturally infected dogs and to assess methodological parameters to calculate drug efficacy on tick immature stages. From July to August 2004, 45 privately owned dogs of various sexes, ages, breeds, coat length and habits were enrolled in a trial carried out in an area (radius approximately 50km) in Southern Italy. Three homogeneous groups (both for dog population and tick population) were formed: 15 dogs treated with imidacloprid 10% and permethrin 50% spot-on (group A), 15 dogs treated with fipronil 10% and methoprene 12% spot-on (group B) and 15 untreated dogs (group C). The dogs in each group were then sub-grouped according to their age and weight. Two different treatments were administered (time 0 and +28 days) to groups A and B, and the dogs were checked weekly for tick infestation until day +56 post-treatment (p.t.). Twenty-four areas distributed on the whole body surface were examined for ticks at each follow-up, while only at time 0 and at day +56 p.t., ticks were collected from the dogs and identified. For the immature stages a semi-quantitative method was adopted and the load of immature stages was evaluated and grouped into four classes up to day +56 p.t. when the mean number of immature ticks (MIT) for each infection class was evaluated. All the adult ticks collected were identified as brown dog ticks (Rhipicephalus sanguineus). Immature stages were first compared at day +28 p.t.. The efficacy of both products used in groups A and B on adult ticks was high and generally very similar. Conversely, the efficacy of imidacloprid 10% and permethrin 50% against immatures was higher than that of fipronil 10% and methoprene 12% throughout the observation period with statistically significant differences (p<0.05) at day +28 p.t. (i.e. group A=98.52%, group B=72.40%). On the whole, in analysing the efficacy of both products against adult plus immature ticks, it was found that the combination of imidacloprid 10% and permethrin 50% was more effective than fipronil 10% and methoprene 12%, with the differences being statistically significant at day +28 p.t. (group A=98.43%, group B=77.56%).

Animals↗
PubMed2002

Field evidence for density-dependent facilitation amongst Ixodes ricinus ticks feeding on sheep.

Engorged Ixodes ricinus nymphs collected from sheep resident in an upland UK field site were significantly lighter than nymphs that engorged on previously tick-naïve sheep, indicating that site-resident sheep continually exposed to ticks acquired anti-tick resistance. The weights of engorged nymphs that fed on naturally tick-resistant sheep increased significantly, however, when increasingly high numbers of adult female ticks fed on the sheep during seasonal peaks of tick activity. This relationship was unaffected by variations in nymph weight amongst individual sheep, between seasons and years, and potential effects of sheep infection with Ehrlichia phagocytophila; this suggests that high adult tick infestations may directly inhibit the expression of acquired anti-tick resistance by sheep. The length, width and weight of adult ticks and the scutum length of adult females were linearly related to their weight as an engorged nymph. The mean scutum length of adult female ticks feeding on sheep in the field site was greater than that of adult females obtained from engorged nymphs collected from sheep of the same site. This suggests that larger ticks have a survival advantage and that I. ricinus ticks exhibit density-dependent intraspecific facilitation at high infestation levels with potential consequences for the transmission of tick-borne diseases.

Animals↗
PubMed1993

Differential recognition of saliva antigens from the ixodid tick Amblyomma hebraeum (Acari: Ixodidae) by sera from infested and immunized rabbits.

We determined the protein composition and antigenic content of saliva from Amblyomma hebraeum female ticks of different weight classes. The mean protein concentration of saliva of small partially fed ticks (< 100 mg) was 333 +/- 83 micrograms/ml and that of large partially fed ticks (150-420 mg) was 59 +/- 14 micrograms/ml. The reduction in concentration mostly was caused by the significantly higher fluid volume per minute secreted by large ticks. Polypeptide analysis of saliva indicated the presence of a protein (14 kilodaltons [kD]) only in ticks weighing < 60 mg. Other saliva proteins of 21 and 26 kD were present only in ticks weighing < 150 mg, whereas 68-kD protein was absent or very faint in ticks > 100 mg. Immunoblot analysis indicated that sera from rabbits infested with ticks recognized 13 saliva antigens ranging in size from 23 to 200 kD. The antigens were present in detectable quantities in the saliva of small ticks only. In contrast, the sera from rabbits immunized with tick saliva recognized only four antigens from 63 to 200 kD. The 63-kD antigen was not present in the saliva of large ticks. These data indicate that the saliva of A. hebraeum from small ticks is antigenically more complex than that of large ticks and that the route of immunization influences the humoral immune response of the host to the saliva antigens.

Animals↗
PubMed2006

Localized deer absence leads to tick amplification.

Deer support high tick intensities, perpetuating tick populations, but they do not support tick-borne pathogen transmission, so are dilution hosts. We test the hypothesis that absence of deer (loss of a dilution host) will result in either an increase or a reduction in tick density, and that the outcome is scale dependent. We use a complementary methodological approach starting with meta-analysis, followed up by a field experiment. Meta-analysis indicated that larger deer exclosures reduce questing (host-seeking) tick density, but as the exclosure becomes smaller (<2.5 ha) the questing tick density is increased (amplified). To determine the consequences for tick-borne pathogen transmission we carried out a field experiment, comparing the intensity of ticks that fed on hosts competent for tickborne pathogen transmission (rodents) in two small (<1 ha) deer exclosures and their replicated controls. Intensity of larval ticks on rodents was not significantly different between treatments, but nymph intensity, the tick stage responsible for tick-borne encephalitis (TBE) transmission, was higher in deer exclosures. TBE seropositive rodents were found in a deer exclosure but not in the controls. We propose that localized absence of deer (loss of a dilution host) increases tick feeding on rodents, leading to the potential for tick-borne disease hotspots.

Animals↗
PubMed2003

Study of awareness of tick-borne diseases among children and young people in the Czech Republic.

In the 2000 and 2001 years, there was performed a study which has given some insight on the knowledge of youths about ticks and tick-borne diseases. Two thousand seven hundred and sixty-three respondents from 6 to 26 years of age took part in this investigation. More than 98% of respondents knew about the existence of ticks. Almost 93% of children and 97% of adolescents reported that ticks feed on blood. Although the majority of respondents aged 10 to 26 years is convinced that ticks live on vegetation, 23% of them supposed that ticks jump on humans from trees. As many as 93.5% of youths knew that Lyme disease is transmitted by ticks. The main sources of information about Lyme disease for students and pupils older than 10 years of age are television and radio (40.9%) and the press (37.5%). The frequency of contact of young people with ticks is high--90.4% of children younger than 12 years, and 93.7% of youths from 10 to 26 years of age had at least once an attached tick. 56.1% of youths older than 10 years use oil to remove an attached tick. Almost 23.7% remove ticks with bare hands. People used those methods of tick removal although even children younger than 12 years of age knew that it was an incorrect habit. After removing, a tick is most frequently burned.

Adolescent↗
PubMed2002

Foci of tick-borne diseases in southwest Germany.

Presently known tick-borne diseases in Germany include Lyme borreliosis, tick-borne encephalitis (TBE-virus, western subtype), Q-fever, babesiosis and presumably ehrlichiosis. Blood samples of 4,368 forestry workers in the State of Baden-Wuerttemberg (B-W), southwestern Germany, were tested for the presence of antibodies against Borrelia burgdorferi sensu lato, TBE-virus and Ehrlichia spp. (genogroup E. phagocytophila). Furthermore 12,327 ticks (Ixodes ricinus) collected in various areas of B-W were analysed by PCR and genotyping for the prevalence of pathogen RNA and DNA. The human seroprevalence rates of antibodies to B. burgdorferi sensu lato ranged from 18% to 52%, for TBE-virus from 0% to 43% and for Ehrlichia spp. from 5% to 16% in various counties of the State. The foci of B. burgdorferi and TBE-virus as indicated by antibody prevalence in humans are only partly overlapping with each other. The highest rates of TBE-virus antibodies are in concordance with available clinical data. However antibody prevalence up to 27% in areas with no reports of clinical cases was found, suggesting that TBE occurs throughout the State of B-W. The prevalence of Ehrlichia spp. antibodies suggests that ehrlichiosis plays a role as a tick-borne disease in Germany, but as long as no clinical data are available, this will remain unclear. Investigations of ticks for TBE-virus (n = 9,189) by nested PCR showed prevalence rates from 0% to 2.3% and for Ehrlichia spp. (n = 1,963) from 2.6% to 3.1%. Examination of ticks (n = 3,138) for the presence of B. burgdorferi sensu lato DNA was performed by PCR and revealed prevalence rates from 13.9% up to 24%. Furthermore 1,106 samples positive for B. burgdorferi sensu lato were used for genotyping. B. afzelii DNA was found in 407 ticks (36.8%), followed by B. garinii (21.9%), B. valaisiana (13.7%), and B. burgdorferi sensu stricto (9.9%). Double infection was found in 6.4% and triple infection in 0.8% of the ticks. 10.5% of the positive samples could not be classified. Prevention of tick-borne diseases has to focus on behavioural intervention to reduce individual tick exposure by proper behaviour in the environment, as a large-scale control of the tick population seems impossible and thus reduction of Lyme borreliosis and TBE through tick control is unlikely. Vaccination against TBE-virus should not only be recommended for high endemic areas but also for persons with a high individual risk.

Animals↗
PubMed2004

Chemical control of ticks on cattle and the resistance of these parasites to acaricides.

Toward the end of the nineteenth century a complex of problems related to ticks and tick-borne diseases of cattle created a demand for methods to control ticks and reduce losses of cattle. The discovery and use of arsenical solutions in dipping vats for treating cattle to protect them against ticks revolutionized tick and tick-borne disease control programmes. Arsenic dips for cattle were used for about 40 years before the evolution of resistance of ticks to the chemical, and the development and marketing of synthetic organic acaricides after World War II provided superior alternative products. Most of the major groups of organic pesticides are represented on the list of chemicals used to control ticks on cattle. Unfortunately, the successive evolution of resistance of ticks to acaricides in each chemical group with the concomitant reduction in the usefulness of a group of acaricides is a major reason for the diversity of acaricides. Whether a producer chooses a traditional method for treating cattle with an acaricide or uses a new method, he must recognize the benefits, limitations and potential problems with each application method and product. Simulation models and research were the basis of recommendations for tick control strategies advocating approaches that reduced reliance on acaricides. These recommendations for controlling ticks on cattle are in harmony with recommendations for reducing the rate of selection for acaricide resistance. There is a need to transfer knowledge about tick control and resistance mitigation strategies to cattle producers.

Animals↗
PubMed1994

Seasonal distribution of Theileria in Hyalomma anatolicum anatolicum ticks of an endemic area of Haryana, India.

The effect of season on the capacity of Hyalomma anatolicum anatolicum ticks to transmit Theileria was studied by detecting Theileria sporoblasts in the salivary glands of 647 adult ticks moulted in winter (November 1990 to March 1991) and 677 adult ticks moulted in the summer-rainy season (June to August 1991). The intensity (number of infected acini per infected tick) and abundance (number of infected acini per tick examined) of Theileria sporoblasts were significantly (P < 0.05) higher in winter moulted ticks (10.75 and 2.23 respectively) than the summer-rainy season moulted ticks (7.31 and 1.77 respectively). The prevalence of infected moulted ticks was not significantly higher in the summer-rainy season (24.22%) than in the winter (20.71%). A higher percentage of winter moulted ticks had high numbers of infected acini (> or = 11/infected tick) than the summer-rainy season moulted ticks, while the trend was reversed for low numbers of infected acini(5/infected tick), being 47.76% for winter and 73.78% for the summer-rainy season. It was concluded that the winter of Haryana is more favourable to the developing theilerial stages in the ticks than the summer-rainy season.

Animals↗
PubMed1986

Theileria infectivity of Hyalomma ticks in Haryana, India.

Theileria infection of Hyalomma ticks collected from three districts of Haryana was assessed in whole salivary glands by the methyl-green pyronin staining method. Of 1,662 ticks screened, 546 (32.8%) were found Theileria positive. Infection rate in 935 female ticks (36.9%) was more than that of 727 male ticks (27.6%). Density of Theileria infection (number of infected acini per infected tick) was also higher in female ticks. Theileria infection rate of ticks varied greatly in the three districts viz. only 12.0% in Rohtak, 25.8% in Hisar and 48.3% in Karnal. Per cent infection rate was high (63.7%) in ticks from indigenous cattle and low (18.6%) in those collected from buffaloes. However, the intensity of infection in infected ticks from cross-bred cattle was comparatively much higher. Frequency distribution of Theileria positive acini in infected ticks revealed a low density of infection per infected tick. This points to the largely stable endemic situation prevailing in Haryana. Only a single salivary acinus was found infected in 16.6% of the infected ticks, about 70% had up to 10 infected acini while only about 10% had over 25 infected acini per tick. The masses in acini presumed to be Theileria were confirmed by demonstrating parasitic masses on staining one of a pair of salivary glands and inoculating the suspension of the other half of the gland into two cross-bred cow calves which developed clinical signs and lesions typical of theileriosis.

Animals↗
PubMed2005

Efficacy of imidacloprid/permethrin and fipronil/(S)-methoprene combinations against Haemaphysalis longicornis ticks evaluated under in vitro and in vivo conditions.

Haemaphysalis longicornis is one of the most important ticks infesting a wide range of mammals including dogs in Japan. H. longicornis is recorded to be a vector of, for example, Babesia gibsoni. It was the aim of the study presented here to evaluate the efficacy of imidacloprid/permethrin and fipronil/(S)-methoprene against larval, nymphal and adult stages of H. longicornis under in vitro as well as in vivo conditions. In the in vitro part of the study, ticks showed avoidance behaviour to imidacloprid/permethrin-treated filter papers. The onset of acaricidal efficacy in the imidacloprid/permethrin group was recorded earlier than in the fipronil/(S)-methoprene group. In the in vivo experiment three beagles per group were treated with either imidacloprid/permethrin, fipronil/(S)-methoprene or left untreated. Each dog was infested with 30 adult female H. longicornis. Ticks were place on a shaved area of skin of the treated dogs and behaviour of the ticks was recorded as before. After 3 h all ticks were removed and placed in Petri dishes. Ticks were further examined until day 4 post-treatment (p.t.). All ticks recovered from the untreated dogs survived. At 4 h p.t. (1 h post-removal) 40 of the 90 ticks exposed to the imidacloprid/permethrin treatment and 25 of the 90 ticks in the fipronil/(S)-methoprene-treated group were found dead. At day 1 p.t., 61 ticks in the imidacloprid/permethrin- and 81 ticks in the fipronil/(S)-methoprene-treated group were recorded dead. At the final examination day 4 p.t., all 90 ticks were found dead in the imidacloprid/permethrin group, while five ticks remained alive in the fipronil/(S)-methoprene group.

Administration, Topical↗
PubMed1992

Influence of exposure period and management methods on the effectiveness of chickens as predators of ticks infesting cattle.

Experiments undertaken on Rusinga Island, Kenya, indicated that Rhipicephalus appendiculatus (Neumann) was the predominant tick consumed on tick-infested cattle by chickens, followed by Amblyomma variegatum (Fabricius), Boophilus decoloratus (Koch) and Rhipicephalus evertsi evertsi (Neumann). The number of ticks consumed by chickens released with cattle in a 3 h release period was not significantly different from ticks consumed in a 4 h release period. In a free management system, chickens 1-3 months of age consumed more ticks than older ones; in a confined management system however, chickens 4-6 months of age consumed more ticks than younger birds. Although the numbers of ticks consumed by local and exotic breeds of chickens were not significantly different, a period of 8-10 weeks was necessary for the exotic breeds to become behaviorally adapted to tick predation on cattle. Local chickens bred in environments where cattle were absent took a shorter period of 4-6 weeks to adapt. It was concluded that the relatively large number of ticks consumed by each chicken during the 3 or 4 h release period is an indication that a good reduction of ticks on cattle can be achieved through tick predation by chickens. The preponderance of R. appendiculatus over other tick species consumed was a reflection of its relative abundance on cattle on the island rather than a selective preference for tick species.

Animal Husbandry↗
PubMed2005

RNAi-mediated gene silencing to assess the role of synaptobrevin and cystatin in tick blood feeding.

In addition to being the conduit for pathogens into hosts, tick saliva contains a broad array of secretory products that facilitate prolonged tick attachment and blood feeding. Proteins found in tick saliva modulate host hemostasis and immune responses. However, it is not clear whether ticks manipulate the immune responses of their hosts by disrupting the antigen-processing pathways of the hosts. Protein secretion into tick saliva from the salivary glands is due to exocytosis of vesicular membrane-bound granular material regulated by SNARE complex proteins. Proteins associated with vesicles (v-SNAREs) are essential components of the exocytotic process. In this study, we assessed the functional significance of synaptobrevin, a SNARE protein, and cystatin, a cysteine protease inhibitor to blood feeding success, in the lone star tick, Amblyomma americanum, using in vivo RNA interference. In separate experiments, tick salivary cystatin and synpatobrevin genes were silenced by injecting adult ticks with 500 ng of dsRNA complementing each gene sequence. Silencing was demonstrated by reduced transcript in midguts and salivary glands. Additionally, disrupting expression of cystatin and synaptobrevin by RNAi reduced the ability of ticks to feed successfully, as demonstrated by feeding inhibition and reduced engorgement weights. Moreover, normal ticks exposed to a rabbit previously exposed to cystatin-silenced ticks exhibited significant resistance to tick feeding. Based on these findings, ticks appear to skillfully evade the host immune system by secreting cystatin, which disrupts normal antigen processing in antigen-presenting cells of hosts.

Animals↗
PubMed2001

Major surface protein 1a effects tick infection and transmission of Anaplasma marginale.

Anaplasma marginale, an ehrlichial pathogen of cattle and wild ruminants, is transmitted biologically by ticks. A developmental cycle of A. marginale occurs in a tick that begins in gut cells followed by infection of salivary glands, which are the site of transmission to cattle. Geographic isolates of A. marginale vary in their ability to be transmitted by ticks. In these experiments we studied transmission of two recent field isolates of A. marginale, an Oklahoma isolate from Wetumka, OK, and a Florida isolate from Okeechobee, FL, by two populations of Dermacentor variabilis males obtained from the same regions. The Florida and Oklahoma tick populations transmitted the Oklahoma isolate, while both tick populations failed to transmit the Florida isolate. Gut and salivary gland infections of A. marginale, as determined by quantitative PCR and microscopy, were detected in ticks exposed to the Oklahoma isolate, while these tissues were not infected in ticks exposed to the Florida isolate. An adhesion-recovery assay was used to study adhesion of the A. marginale major surface protein (MSP) 1a to gut cells from both tick populations and cultured tick cells. We demonstrated that recombinant Escherichia coli expressing Oklahoma MSP1a adhered to cultured and native D. variabilis gut cells, while recombinant E. coli expressing the Florida MSP1a were not adherent to either tick cell population. The MSP1a of the Florida isolate of A. marginale, therefore, was unable to mediate attachment to tick gut cells, thus inhibiting salivary gland infection and transmission to cattle. This is the first report of MSP1a being responsible for effecting infection and transmission of A. marginale by Dermacentor spp. ticks. The mechanism of tick infection and transmission of A. marginale is important in formulating control strategies and development of improved vaccines for anaplasmosis.

Anaplasma↗