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PubMed2000

A state-by-state survey of ticks recorded from humans in the United States.

Based on tick specimens accessioned into the U.S. National Tick Collection, the species of ticks recorded as ectoparasites of humans are documented and compared for 49 U.S. states. A total of 44 tick species was recorded as parasites of humans, consisting of 11 species of soft ticks (Argasidae) and 33 species of hard ticks (Ixodidae). Four of the hard tick species are not native to the U.S. and were removed from travelers returning from foreign destinations. Therefore, we record 40 of the 84 species of U.S. ticks as ectoparasites of humans. Predictably, in the southern U.S. and Atlantic states, all active stages of the lone star tick, Amblyomma americanum (L.), were common ectoparasites of humans. Also, in the eastern U.S., adults of the American dog tick, Dermacentor variabilis (Say), and all active stages (especially adults) of the blacklegged tick, Ixodes scapularis (Say), were commonly recorded. In certain Rocky Mountain and western states, all active stages of the Rocky Mountain wood tick, Dermacentor andersoni (Stiles), predominated, whereas, in most far western states, adults of the western blacklegged tick, Ixodes pacificus Cooley and Kohls, were relatively common parasites of humans. Parasitism by Ornithodoros spp. soft ticks was mainly recorded in the western U.S. These findings, together with records of human parasitism by other tick species in the U.S., are briefly discussed with respect to tick-borne disease risk.

Animals↗
PubMed2000

Performance of female Rhipicephalus sanguineus (Acari: Ixodidae) fed on dogs exposed to multiple infestations or immunization with tick salivary gland or midgut tissues.

This investigation compared the effects of repeated infestations to immunization of dogs with tick salivary gland or midgut extracts on the feeding and fecundity performances of female Rhipicephalus sanguineus (Latrielle). In each immunized group, three tick-naive dogs were immunized three times with tick salivary gland or midgut extracts, and twice challenged at 21-d intervals by allowing 80 female and 40 male adult ticks to feed on each host. The repeated infestation group of three naive dogs was infested five times at 21-d intervals by the same numbers of ticks. The repeated infestation group showed a trend of reduced tick performance after the third infestation, but some of the tick performance parameters had recovered by the fifth infestation. Tick attachment was reduced by immunization with either tick salivary gland or midgut extract. Immunization with tick salivary gland extract had the greatest impact on the feeding period and engorgement weight of the female ticks. Immunization with tick midgut extract resulted in the greatest reduction of tick fecundity parameters, which included preoviposition, oviposition, and egg-incubation periods in addition to reduced egg production and egg viability. These results confirm that dogs can become resistant to R. sanguineus, and demonstrate that immunization with tick salivary gland or midgut extract has different effects on tick feeding and fecundity.

Animals↗
PubMed1990

Strategic tick control in Burundi.

Strategic tick control is an attempt to control ticks and reduce losses in animal production due to tick infestations while decreasing the cost for this control. Tick control is understood as a necessity to achieve maximum animal production from animals raised in tick-infested areas. At the same time, it has become difficult to justify intensive, year-round tick control for local breeds and their crosses. The increasing costs of acaricides, maintenance of the infrastructures, salaries for personnel, etc. have created a tick control programme where the benefits may not be adequate to justify the expense. This has been the case in Burundi. This programme with adequate participation from the cattle owners of Burundi and organizational support from government personnel can help solve this economic problem. The strategic programme reduces the period of tick control to four months each year. Once optimal participation is achieved, this period can probably be reduced to three months (Kaiser et al., 1988). The period of treatment corresponds to when there is maximal feeding activity of adult female ticks on the bovine population within a certain region. Cattle should be treated once each week throughout the four-month period in order to prevent female tick engorgement (based on the life cycle of R. appendiculatus). This will greatly reduce the number of female ticks which are available to recycle the population of ticks in the participating area. At the same time, a certain population of ticks must be maintained in order to assure contact between the cattle, ticks, and tick-borne diseases of this particular region.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed2004

Adaptation of ticks to a blood-feeding environment: evolution from a functional perspective.

Ticks had to adapt to an existing and complex vertebrate hemostatic system from being free-living scavengers. A large array of anti-hemostatic mechanisms evolved during this process and includes blood coagulation as well as platelet aggregation inhibitors. Several questions regarding tick evolution exist. What was the nature of the ancestral tick? When did ticks evolve blood-feeding capabilities? How did these capabilities evolve? Did host specificity influence the adaptation of ticks to a blood-feeding environment? What are the implications of tick evolution for future research into tick biology and vaccine development? We investigate these questions in the light of recent research into protein superfamilies from tick saliva. Our conclusions are that the main tick families adapted independently to a blood-feeding environment. This is supported by major differences observed in all processes involved with blood-feeding for hard and soft ticks. Gene duplication events played a major role in the evolution of novel protein functions involved in tick-host interactions. This occurred during the late Cretaceous and was stimulated by the radiation of birds and placental mammals, which provided numerous new niches for ticks to adapt to a new lifestyle. Independent adaptation of the main tick families to a blood-feeding environment has several implications for future tick research in terms of tick genome projects and vaccine development.

Adaptation, Physiological↗
PubMed2002

Characterization of tick-borne encephalitis (TBE) foci in Germany and Latvia (1997-2000).

Knowledge concerning the prevalence of the tick-borne encephalitis virus (TBEV) in wild living tick populations is very important for understanding the epidemiology of the disease and for immuno prophylactic strategy. In Germany high and low risk areas of TBE exist. In the years 1997-2000, 533 autochthonous clinical TBE cases were recorded, in the high-risk areas of Bavaria and Baden-Wuerttemberg 140 and 363, and in the low risk areas in Hesse (Odenwald) and Rhineland-Palatinate 22 and 8, respectively. Corresponding to these case reports we have measured the virus prevalence in free living ticks in these four risk areas and compared these findings with the situation in high-risk areas in Latvia. In the years 1997-2000, 2,797 clinical TBE cases were recorded in Latvia. For the studies in Germany, a total of 17,398 Ixodesricinus ticks (14,860 nymphs and 2,538 adults) were collected by flagging and examined for TBEV, in Latvia the corresponding numbers were 525 I. ricinus ticks (350 adults and 175 nymphs) and 281 I. persulcatus ticks (adults only). Information concerning annual and seasonal differences of the TBEV prevalence in natural TBE foci is not available in Germany. This paper is a continuation of the study (Süss et al., 1999), starting in 1997. We investigated every year, in May and September, the virus prevalence in ticks in high risk areas of Bavaria (8 foci) and Baden-Wuerttemberg (5 foci). A total of 15,400 ticks (13,100 nymphs and 2,300 adults) were examined for TBEV. The ticks were tested for the presence of TBEV-RNA using a sensitive, nested-RT-PCR. The virus prevalence in the Bavarian foci of the whole tick population ranged from 0.3 to 2.0% during these four years, in adults between 1.2 and 5.3% and in nymphs between 0.1 and 1.4%. In the high-risk areas of Baden-Wuerttemberg, in the Black Forest, the estimated virus prevalence rates of investigated ticks varied from 0.2 to 3.4%, in adults from 0 to 4.8%, and in nymphs from 0.2 to 3.4%. Using the same methods, we have also tested the low risk areas in the Odenwald (840 nymphs, 160 adults) and in Rhineland-Palatinate (920 nymphs, 78 adults). Ticks were collected in those areas where most TBE cases were registered. The virus prevalence in the Odenwald was 0% in adults and 0.5% in nymphs, whereas in ticks from Rhineland-Palatinate we have not found any positive PCR signal. Sequence data of the PCR products have shown that all strains in Germany were closely related to the central European virus prototype Neudoerfl. In I. ricinus ticks, collected in Riga county, the following virus prevalence rates were found: in females 2.4%, in males 3.7%, and in all adults 3.0%, in nymphs 2.4% and in the I. ricinus tick population examined 2.8%. The virus prevalence in I. persulcatus, collected in the eastern parts of Latvia was 6% in females, 4% in males and 5% in all adults. All the PCR products were sequenced and a phylogenetic tree was constructed. Studies in natural foci of TBE in Latvia have shown that I. ricinus carried the central European virus subtype (prototype Neudoerfl) whereas in I. persulcatus two strains have been found, the central European virus subtype (prototype Neudoerfl) and the Siberian virus subtype (prototype Vasilchenko). Sequences of the Far Eastern subtype have not been detected yet.

Animals↗
PubMed2005

Tick prevention in a population living in a highly endemic area.

AIMS: To describe environmental and personal tick-preventive measures and their predictors, taken by a population living in a highly tick-endemic area. METHODS: Owing to the recent confirmation of human tick-borne encephalitis cases, vaccination against tick-borne encephalitis was offered to the population living in the endemic area through the use of leaflets and media campaigns. At the time of the initial dose, information and enrollment to this cohort study was carried out. Participants' characteristics, frequency of tick-bites and preventive measures were included in questionnaires. Logistic analysis was used to determine behavioural differences in activities taken in order to prevent tick bites. CONCLUSION: In total, 70% of the permanent residents had themselves vaccinated before the next tick season. Of the studied participants 356/517 (69%) regularly took preventive measures in their environment and/or personally. Women in particular, and those previously treated for a tick-borne disease, took significantly more preventive measures. When analysing all variables together, spending less time in a tick-endemic area and being tick-bitten during the latest tick season significantly increased the probability of taking preventive measures. After being tick-bitten, men were more inclined to start taking preventive measures than women. Awareness of the risks caused by living in a high tick-endemic area influenced the participant's daily life through preventive activities. Public health action should be considered, thus encouraging out-of-door activities for the population without anxiety as to the risks of contracting tick-borne disease after being tick-bitten.

Adolescent↗
PubMed1989

Suitability of white-tailed deer as hosts for cattle fever ticks (Acari: Ixodidae).

White-tailed deer (Odocoileus virginianus L.) were evaluated as an alternate host for the cattle fever tick, Boophilus annulatus (Say). The total of adult female ticks recovered and associated reproductive parameters were compared between deer and bovine hosts. Significantly fewer ticks were recovered from deer than from cattle; this was attributed to the grooming behavior of the deer. The mean weight of ticks taken from deer (243.5 mg) was significantly less than that of ticks recovered from cattle (344.5 mg) with about 15% of the ticks from deer prematurely detached. Egg mass weight from the ticks recovered from deer (129.4 mg) was significantly less than that of ticks from cattle (172.1 mg). A significant difference was observed between the percentage hatch of the eggs of ticks from deer (63.1%) and ticks from cattle (76.7%). The index of reproduction was about 20 times greater for the ticks from the cattle than for the ticks from the deer. When the larval progeny of the ticks recovered from deer were reared on cattle, significantly fewer adult females were recovered than when larvae of ticks recovered from cattle were reared on cattle. This indicates a possible reduction in viability. All other parameters were comparable between the two groups. Thus, deer are biologically suitable hosts for B. annulatus, but significantly fewer ticks complete engorgement and those that complete engorgement have reduced fecundity.

Animals↗
PubMed2006

Ixodes frontalis and avian tick-related syndrome in the United Kingdom.

OBJECTIVES: This study aimed to characterise tick species responsible for avian tick infestations in the UK, to analyse various risk factors for tick-related syndrome in tick-infested birds and to test samples for the presence of certain tick-transmitted pathogens. METHODS: Ticks, blood, splenic tissue and tick attachment site tissue from birds with attached ticks were requested from veterinarians and wildlife sanctuaries around the UK. Ticks were identified according to standard keys, and samples were analysed via DNA PCR test for Borrelia burgdorferi sensu lato, Babesia species, Bartonella species and Ehrlichia species. RESULTS: Ixodes frontalis was the most commonly identified tick, and an association of adult female I frontalis with tick-related syndrome in birds was demonstrated. Tick infestation was markedly seasonal. I frontalis was found on 32 species of birds. DNA PCR testing was uniformly negative. Of the birds known to have been treated, 75 per cent (nine of 12) survived. CLINICAL SIGNIFICANCE: Tick-related syndrome is a poorly understood syndrome, with sporadic distribution, both geographically and seasonally. This study confirms I frontalis as the most common cause of this syndrome in the UK and identifies some features of the tick life cycle in this country. The benefit of treatment in affected birds is highlighted. Risk factors for tick-related syndrome are examined and preventive strategies discussed.

Animals↗
PubMed2004

[Ticks and the pediatrician].

The match between ticks and pediatricians in Italy is usually a seasonal event related to the spring and summer trips and to the increasing of outdoor activity that sun and warm weather allow, both for children and ticks. So cared parents reach emergencies asking for tick removal but more often after the tick has yet been removed by empirical manoeuvres and after the killing and the destruction of the "enemy". We have scheduled, in the years 2002-2003, the 167 children that reached our unit for a tick bite; they where 92 males (mean age four years) and 75 females (mean age five years). Two of them had only a questionable tick bite but one had erythema on the lateral side of the left ankle, fever of obscure origin and weakness with generalised malaise. She was six years old and she lived with a dog on which, in more instances, ticks where found, but she never noticed ticks on her body. The dog had positive levels of anti rickettsial and anti borrelia antibodies but no evidence of conclamate illness. In this girl we found high titers of anti borrelia antibodies that WB testing confirmed to be anti B. burgdoferi. We diagnosed Lyme disease and treated the girl with amoxicillin (50 mg/kg/day) for three weeks achieving the complete relief of symptomatology till today. Three children with conclamate tick bite had positive levels of anti Rickettsia conorii antibodies with increasing levels at a twenty days control; two (aged four and five years) of them had a full symptomatology (tache noire, satellite lymphadenopathy, fever, and maculopapular erythema) for Meditarranean spotted fever; the latter (three years old) had an atypical form with the complete absence of maculopapular erythema. The therapy was clarithromycin (15 mg/kg/day) for three weeks. In Campania, in the years 2002/2003 on 167 children with tick bite that reached our unit, we found only four pathological correlable events; so are our ticks not infected? But we don't know how many children where tick bited and if there were other children with Lyme disease or Rickettsial disease because of the lack of a pediatric reference centre for "tick bite diseases" and the incomplete and late diffusion of knowledge on these diseases. Other Italian regions and such as Trentino Alto Adige, Veneto, and Friuli Venezia Giulia had a remarkable officially notified number of cases of Lyme disease and in Sicilia, Sardegna and Lazio there were numerous officially notified Rickettsial diseases. So we hope that Campania may be an happy island but we also think that a more effective cooperation between pediatricians and veterinarians and the creation of regional reference centres for tick bite diseases may arise a surveillance net to prevent the diffusion of these world wide emerging diseases and so that parents can achieve an univoque and useful information, the only way to defeat the fear of ignorance.

Animals↗
PubMed1984

Seasonal pattern of tick load in Bunaji cattle in the subhumid zone of Nigeria.

The seasonal pattern of tick load on Bunaji cattle under traditional management in northern Nigeria was observed over 12 months to investigate the possibilities of strategic use of acaricide. Ticks were removed 2-3 times weekly by hand from 16 animals, counted and the species determined. Tick load was low in the dry season (2-5 ticks per animal per week), increased after the onset of the first scattered rains, reached a peak (40 ticks per animal per week) 1 month after the beginning of the heavy rains, and declined thereafter. The dominant tick species was Amblyomma variegatum; other species found were Boophilus spp., Rhipicephalus spp. and Hyalomma spp. The low level of tick load compared with data from literature and from crossbred (Friesian-Bunaji) cattle kept in the study area suggests high tick resistance in Bunaji cattle. A biologically feasible method of controlling ticks in indigenous cattle would be twice weekly spraying with acaricide during only 2 months of the year in the early wet season to break the pronounced peak in the tick load. However, hand spraying offers no advantage over hand removal of ticks in terms of saving labour. The main advantage of strategic spraying lies in more thorough removal of ticks and possibly prevention of dermatophilosis at a lower cost than year-round use of acaricide. Knowledge of the seasonal pattern of tick load is also valuable for planning the introduction of selected stock with higher genetic potential, but higher susceptibility to tick-borne diseases than exhibited by Bunaji cattle.

Animals↗
PubMed1998

Studies on host resistance to tick infestations among trypanotolerant Bos indicus cattle breeds in east Africa.

Recent epidemiological studies carried out in East Africa have indicated that some Bos indicus cattle breeds such as the Orma Boran and Maasai Zebu have a degree of trypanotolerance worth exploitation by their introduction into trypanosomosis endemic areas where other cattle breeds cannot survive. However, in most areas of East Africa, trypanosomosis, ticks, and tick-borne diseases occur together. It is therefore important to obtain information on the susceptibility of these breeds to tick infestation and tick-borne diseases. This study was therefore designed to determine the susceptibility of these cattle breeds to tick infestations. They were compared with the Galana Boran (trypanosusceptible) and the Friesian (susceptible to tick infestations, tick-borne diseases, and trypanosomosis). The four breeds of cattle were exposed to natural tick challenge for a period of seven months and whole body weekly tick counts were done on each animal. Significant differences to tick infestations among the four breeds were observed. For both Rhipicephalus appendiculatus and Boophilus decoloratus, susceptibility to infestation increased in the order, Maasai Zebu, Orma Boran, Galana Boran and Friesian. The results generated by this pilot study so far suggest that variation in susceptibility to tick infestations exists among the four breeds. The Orma Boran and Maasai Zebu showed greater resistance to tick-infestations than the Galana Boran and Friesian. This suggests that utilization of these trypanotolerant cattle breeds could be feasible even in the face of tick challenge and should therefore be considered when planning integrated trypanosomosis and tick control strategies.

Africa, Eastern↗
PubMed1996

Importance of localized skin infection in tick-borne encephalitis virus transmission.

Arboviruses are transmitted to vertebrates by the "bite" of infected arthropods. Events at the site of virus deposition are largely unknown despite increasing evidence that blood-sucking arthropods immunomodulate their skin site of feeding. This question is particularly relevant for ixodid ticks that feed for several days. To examine events under conditions mimicking tick-borne encephalitis (TBE) virus transmission in nature (i.e., infected and uninfected Ixodes ricinus ticks feeding on the same animal), infected adult and uninfected nymphal ticks were placed in one retaining chamber (skin site A) and uninfected nymphs were placed within a second chamber posteriorly (skin site B) on two natural host species, yellow-necked field mice (Apodemus flavicollis) and bank voles (Clethrionomys glareolus). Virus transmission from infected to uninfected cofeeding ticks was correlated with infection in the skin site of tick feeding. Furthermore, virus was recruited preferentially to the site in which ticks were feeding compared with uninfested skin sites. Viremia did not correspond with a generalized infection of the skin; virus was not detected in an uninfested skin site (C) of 12/13 natural hosts that had viremia levels > or = 2.0 log10 ic mouse LD50/0.02 ml blood. To characterize infected cells, laboratory mouse strains were infested with infected ticks and then explants were removed from selected skin sites and floated on culture medium. Numerous leukocytes were found to migrate from the skin explants of tick feeding sites. Two-color immunocytochemistry revealed viral antigen in both migratory Langerhans cells and neutrophils; in addition, the migratory monocyte/macrophages were shown to produce infectious virus. The results indicate that the local skin site of tick feeding is an important focus of viral replication early after TBE virus transmission by ticks. Cellular infiltration of tick feeding sites, and the migration of cells from such sites, may provide a vehicle for transmission between infected and uninfected cofeeding ticks that is independent of a patent viremia. The data support the hypothesis that viremia is a product, rather than a prerequisite, of tick-borne virus transmission.

Animals↗
PubMed1993

Ticks (Acari: Ixodidae) infesting the Arabian camel (Camelus dromedarius) in the Sinai, Egypt with a note on the acaricidal efficacy of ivermectin.

In this study, tick burdens on camels (Camelus dromedarius) were determined in the vicinity of the St. Catherine monastery, Sinai, Egypt. In total 2,545 ticks (1,491 adults and 1,054 nymphs) were collected and identified. Mean tick burdens were relatively heavy and the range in number of ticks per camel was very broad (6-173). Hyalomma dromedarii was the predominant tick species and accounted for 95.6% of the adult ticks. Other ticks found were H. marginatum subspp. and H. anatolicum excavatum. All nymphs collected were Hyalomma spp. In addition, the effect of ivermectin (Ivomec MSD AGVET) on tick burdens, when given subcutaneously at 0.2 mg/kg-1, was evaluated in nine camels in the date-palm plantation of Kibbutz Yahel in the Arava valley, Israel. Initial tick burdens on these camels (half-body tick counts) ranged from 20-105 ticks per camel. Seven camels from the same herd with half-body tick counts ranging from 40-107 ticks per camel were not treated and served as a control group. Ivermectin was not effective against Hyalomma tick infestation in camels under these conditions.

Animals↗
PubMed1989

The effect of the bont tick (Amblyomma hebraeum) on the weight gain of Africander steers.

The effects of the bont tick Amblyomma hebraeum on the productivity of cattle need to be quantified in order to design economically optimal control programs. Liveweight gains (LWGs) of three groups of Africander steers, maintained in the same pasture and exposed to zero, medium or high numbers of larvae, nymphs and adults of the tick, were measured. Larvae and nymphs had no significant effect on LWG but adults had a large, statistically significant effect (P less than 0.05). The tick-free group had an average LWG of 20 kg more than the heavily infested group after 3.5 months. No mortality was recorded from ticks or tick-borne diseases during the experiment. There was no relationship between the number of engorging adult female ticks counted and loss of LWG of individual animals. The latter suggests that exposure to ticks as well as engorgement by female ticks causes losses. The loss per adult female that completed engorgement was estimated, by relating the LWGs of individual animals to their tick infestations, to be 4 +/- 2 g per adult female tick. An alternative estimate, made by comparing the average LWG and tick infestations of each treatment group, was equal to 10 +/- 4 g. This latter estimate includes the effect of challenge (and rejection) as well as tick feeding and so was accepted as giving the best estimate. Screw-worm fly (Chrysomya bezziana) struck an average of 7.5% of the cattle infested with ticks in any week but the effects on the productivity of the cattle were minimized by immediate treatment. There was a significant, positive correlation between the incidence of screw-worm fly strike and the numbers of adult ticks counted on the experimental animals. The results provide data for calculating losses caused by A. hebraeum in different parts of its geographical range.

Animals↗
PubMed2004

Tick-borne viruses.

At least 38 viral species are transmitted by ticks. Virus-tick-vertebrate host relationships are highly specific and less than 10% of all tick species (Argasidae and Ixodidae) are known to play a role as vectors of arboviruses. However, a few tick species transmit several (e.g. Ixodes ricinus, Amblyomma variegatum) or many (I. uriae) tick-borne viruses. Tick-borne viruses are found in six different virus families (Asfarviridae, Reoviridae, Rhabdoviridae, Orthomyxoviridae, Bunyaviridae, Flaviviridae) and at least 9 genera. Some as yet unassigned tick-borne viruses may belong to a seventh family, the Arenaviridae. With only one exception (African swine fever virus, family Asfarviridae) all tick-borne viruses (as well as all other arboviruses) are RNA viruses. Tick-borne viruses are found in all the RNA virus families in which insect-borne members are found, with the exception of the family Togaviridae. Some tick-borne viruses pose a significant threat to the health of humans (Tick-borne encephalitis virus, Crimean-Congo haemorrhagic fever virus) or livestock (African swine fever virus, Nairobi sheep disease virus). Key challenges are to determine the molecular adaptations that allow tick-borne viruses to infect and replicate in both tick and vertebrate cells, and to identify the principal ecological determinants of tick-borne virus survival.

African Swine Fever↗
PubMed2003

Serological evidence of exposure to tick fever organisms in young cattle on Queensland dairy farms.

OBJECTIVES: To compare the features of farms on which the exposure of young cattle to tick fever organisms is sufficient to ensure that immunity is high and the risk of clinical disease is low (endemic stability) with those of farms on which exposure is insufficient to induce widespread immunity (hence without endemic stability); to examine the relationships between the management of ticks and tick fever, and endemic stability to Babesia bovis, B. bigemina and Anaplasma marginale. DESIGN: Cross-sectional study of 874 cattle between the ages of 6 and 15 months on 64 dairy farms, from three centres in south-eastern Queensland (Mutdapilly, Dayboro and Kenilworth) and one centre in far-north Queensland (Malanda). PROCEDURE: Blood samples collected from between 5 and 20 calves from each farm were submitted for serological assay to determine exposure to B. bovis, B. bigemina and A. marginale. A questionnaire about the farm characteristics and the management of ticks and tick fever was completed with each farmer. RESULTS: On 73% of farms, confirmed clinical cases of tick fever were recalled by the farmer, indicating that tick fever was a threat on most farms. The majority of herds in the study (54 of 64) did not have sufficient numbers of seropositive animals aged between 6 and 15 months to have a low risk of tick fever. Region had an effect on the likelihood of endemic stability for all tick fever organisms. Cattle near Malanda in Far-north Queensland were more likely to be seropositive to B. bovis and B. bigemina. The method, strategy and intensity of tick control were not related to the likelihood of endemic stability when the effect of region was considered. The decision to leave a few ticks on cattle in an effort to induce endemic stability did increase the likelihood of endemic stability to A. marginale. However, in practical terms, it was ineffective, because only 26% of these farms had endemic stability against all three organisms. CONCLUSIONS: Given the low proportion of farms that have endemic stability to the tick fever organisms and the high likelihood of clinical disease, vaccination is recommended to protect dairy cattle from tick fever throughout the tick infested area of Queensland. However, further work is required to determine the economic value of vaccination, taking into account the costs of vaccination, of outbreaks and the protective value of vaccination.

Anaplasma marginale↗
PubMed1999

African swine fever virus replication in the midgut epithelium is required for infection of Ornithodoros ticks.

Although the Malawi Lil20/1 (MAL) strain of African swine fever virus (ASFV) was isolated from Ornithodoros sp. ticks, our attempts to experimentally infect ticks by feeding them this strain failed. Ten different collections of Ornithodorus porcinus porcinus ticks and one collection of O. porcinus domesticus ticks were orally exposed to a high titer of MAL. At 3 weeks postinoculation (p.i.), <25% of the ticks contained detectable virus, with viral titers of <4 log(10) 50% hemadsorbing doses/ml. Viral titers declined to undetectability in >90% of the ticks by 5 weeks p.i. To further study the growth defect, O. porcinus porcinus ticks were orally exposed to MAL and assayed at regular intervals p.i. Whole-tick viral titers dramatically declined (>1,000-fold) between 2 and 6 days p.i., and by 18 days p.i., viral titers were below the detection limit. In contrast, viral titers of ticks orally exposed to a tick-competent ASFV isolate, Pretoriuskop/96/4/1 (Pr4), increased 10-fold by 10 days p.i. and 50-fold by 14 days p.i. Early viral gene expression, but not extensive late gene expression or viral DNA synthesis, was detected in the midguts of ticks orally exposed to MAL. Ultrastructural analysis demonstrated that progeny virus was rarely present in ticks orally exposed to MAL and, when present, was associated with extensive cytopathology of phagocytic midgut epithelial cells. To determine if viral replication was restricted only in the midgut epithelium, parenteral inoculations into the hemocoel were performed. With inoculation by this route, a persistent infection was established although a delay in generalization of MAL was detected and viral titers in most tissues were typically 10- to 1,000-fold lower than those of ticks injected with Pr4. MAL was detected in both the salivary secretion and coxal fluid following feeding but less frequently and at a lower titer compared to Pr4. Transovarial transmission of MAL was not detected after two gonotrophic cycles. Ultrastructural analysis demonstrated that, when injected, MAL replicated in a number of cell types but failed to replicate in midgut epithelial cells. In contrast, ticks injected with Pr4 had replicating virus in midgut epithelial cells. Together, these results indicate that MAL replication is restricted in midgut epithelial cells. This finding demonstrates the importance of viral replication in the midgut for successful ASFV infection of the arthropod host.

African Swine Fever↗
PubMed2006

Synergistic effect of silencing the expression of tick protective antigens 4D8 and Rs86 in Rhipicephalus sanguineus by RNA interference.

Tick proteins have been shown to be useful for the development of vaccines which reduce tick infestations. Potential tick protective antigens have been identified and characterized, in part, by use of RNA interference (RNAi). RNAi allows for analysis of gene function by characterizing the impact of loss of gene expression on tick physiology. Herein, we used RNAi in Rhipicephalus sanguineus to evaluate gene functions of two tick protective antigens, 4D8 and Rs86, the homologue of Bm86, on tick infestation, feeding and oviposition. Silencing of 4D8 alone resulted in decreased tick attachment, survival, feeding and oviposition. Although the effect of Rs86 RNAi was less pronounced, silencing of this gene also reduced tick weight and oviposition. Most notably, simultaneous silencing of 4D8 and Rs86 by RNAi resulted in a synergistic effect in which tick survival, attachment, feeding, weight and oviposition were profoundly reduced. Microscopic evaluation of tick tissues revealed that guts from dual injected ticks were distended with epithelial cells sparsely distributed along the basement membrane. These results demonstrated the synergistic effect of the silencing expression of two tick protective genes. Inclusion of multiple tick protective antigens may, therefore, enhance the efficacy of tick vaccines.

Animals↗