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PubMedDate not supplied

[Antibacterial therapy as a means of preventing ixodid tick-borne borreliosis].

A special epidemiological experiment to prevent borreliosis in persons bitten by infected ticks was performed in 1992-1994 in the Russia's Perm region where Borrelia garinii and B.afzelii circulate, and Ixodes persulcatus tick is the sole vector transmitting these pathogens to human beings. Adult ticks were removed from the bodies of persons who had referred to health facilities for first aid. Vital preparations were made from the material obtained from the gut of each tick and examined microscopically (up to 250 microscopic fields per preparation). The patients bitten by infected ticks were divided into experimental and control groups and kept under special medical and serological control for 4-5 months. The patients of the experimental group received doxycycline (100 mg twice daily) for 3-5 days after ticks had bitten. Borreliosis was diagnosed by a combination of clinical and serological data. The control group consisted of 97 patients who took no antibiotics after ticks biting and 12 of them contracted borreliosis. In 823 cases Borrelia were not revealed while microscopically analyzing the ticks removed from the patients' bodies; in this group six patients contracted borreliosis. The morbidity rate (per 100 patients) in the experimental group was 1.1, i.e. 11 times lower than that in control group. Among the patients bitten by infected ticks and untreated with antibiotics, this index was 17.6 times higher than in the group bitten by ticks in which Borrelia were not found. There is no absolute probability of detecting the pathogen during a direct microscopic analysis of the preparation made from the tick removed from the body of a bitten patient. However, this rapid identification of Borrelia, followed by short-term antibiotic treatment for microbiological evidence is an effective tool for preventing patients from contracting borrelioses.

Animals↗
PubMedDate not supplied

Erythema migrans-like rash illness at a camp in North Carolina: a new tick-borne disease?

BACKGROUND: Borrelia burgdorferi, the causative agent of Lyme disease, has never been isolated from a patient thought to have acquired Lyme disease in any southeastern state. OBJECTIVE: To investigate 14 cases of an erythema migrans (EM)-like rash illness that occurred during 2 summers at an outdoor camp in central North Carolina in an effort to determine the etiologic, epidemiological, and clinical aspects of this illness. METHODS: Using active surveillance, we identified cases of clinically diagnosed EM in residents and staff of the camp. We collected clinical and demographic information; history of exposure to ticks; acute and convalescent serum antibodies to B. burgdorferi, Rickettsia rickettsii, and Ehrlichia chaffeensis; and cultures for spirochetes from biopsy specimens of skin lesions. Serum samples from a group of residents and staff who did not develop rashes were tested for the same antibodies. We speciated ticks removed from people and collected from vegetation. RESULTS: We identified 14 cases of EM-like rash illness during the 2 summers. Of the 14 case-patients, 10 had associated mild systemic symptoms and 1 had documented fever. All 14 case-patients had removed attached ticks, and 8 remembered having removed a tick from the site where the rash developed a median of 12 days earlier (range, 2-21 days). One tick removed from the site where a rash later developed was identified as Amblyomma americanum, the Lone Star tick; 97% of ticks collected from vegetation and 95% of ticks removed from people were A. americanum. No spirochetes were isolated from skin biopsy specimens. Paired serum samples from 13 case-patients did not show diagnostic antibody responses to B. burgdorferi or other tick-borne pathogens. CONCLUSIONS: This investigation suggests the existence of a new tick-associated rash illness. We suspect that the disease agent is carried by A. americanum ticks. In the southern United States, EM-like rash illness should no longer be considered definitive evidence of early Lyme disease.

Adolescent↗
PubMed1991

Towards the selection of cattle for tick resistance in Africa.

Half-body tick collections and visual assessment of tick burdens were performed monthly over six months on 100 bulls at the Kenya National Boran Stud, Mutara Ranch, Kenya. Boophilus decoloratus predominated among several tick species infesting the animals. Burdens of B. decoloratus and total tick burdens were highly correlated. Rankings of relative tick resistance among bulls were consistent from month to month. Rankings based on visual assessment were very close to those based on actual tick burdens. Animals with thin skins appeared to carry fewer ticks, but tick burden bore no relationship to coat colour. The results suggest that simple visual inspection of total tick burdens may be a suitable basis for the selection of tick resistance in cattle.

Animals↗
PubMed1993

An evaluation of strategic and short interval tick control in indigenous exotic and crossbred cattle.

The performance of Nguni, Bonsmara and Hereford oxen which were maintained free of ticks by short interval treatment with acaricide irrespective of tick load (tactical) was compared with similar groups which were treated for tick infestation only when the numbers of adult ticks on the cattle increased to moderately high proportions (strategic). Strategically treated Nguni oxen acquired a strong resistance against ticks and showed weight gains comparable with the tick free Nguni group. Weight gains in the Bonsmara group were higher in the strategically treated group suggesting a possible effect of the acaricide on the tick free group. Strategically treated Hereford oxen acquired heavy tick burdens and performed poorly compared with the tick free group. Practical approaches to strategic tick control under African conditions are discussed.

Animals↗
PubMed2005

Reduction of Theileria annulata infection in ticks fed on calves immunized with purified larval antigens of Hyalomma anatolicum anatolicum.

Larval antigen of Hyalonmma anatolicum anatolicum, the vector of Theileria annulata, was purified by two-step affinity chromatography using anti-tick gut-specific rabbit IgG and IgG from immunized cattle. The purified antigen showed the presence of a single polypeptide of 37 kDa (GHLAgP) on SDS-PAGE. Two groups (I and II) of naive crossbred calves (Bos taurus x B. indicus) were immunized with I mg of GHLAgP in three divided doses. Immunized calves of group I were also infected with a sublethal dose of T annulata along with a group of non-immunized calves (group III). Animals in groups I, II, III as well a control group (group IV) were challenged with live nymphs of H. a. anatolicum on the 10th day of immunization. There was a significant reduction in the number of emerging adults of 56.9% +/- 1.67%, in calves of group I (p < 0.01) and 63.09% +/- 1.26% in calves of group II (p < 0.001) compared to the controls. The calves of groups I and II showed antibody responses to tick antigen up to day 70 post immunization. Infection with T. annulata was determined in the salivary glands of adult ticks that developed from the nymphs used for challenge infection. In ticks taken from group I calves, there was a 75.0% +/- 0.00% infection compared with only 85.0 +/- 2.88% infection in ticks taken from calves of group III. Using PCR, a lower infection (83.33% +/- 3.33%) was detected in ticks that developed from calves of group I compared with calves from group III (90.00% +/- 2.88%). The ground-up tick supernatants (GUTS) of the ticks taken from calves of group III yielded higher infection rate and exhibited higher infectivity titre in in vitro infection assay of bovine mononuclear cells than the GUTS of the ticks taken from calves of group I. The results suggest a partial reduction in growth rate of T. annulata in ticks feeding on calves immunized with GHLAgP.

Animals↗
PubMed1994

Tick-induced modulation of the host immune response.

The tick-host-pathogen interface is characterised by complex immunological interactions. Host immune responses to tick infestation and infection with tick-borne pathogens involve cytokines, antibodies, complement and T lymphocyte regulatory and effector pathways. A successful host-parasite relationship is a balance between limiting the parasite by host defenses and the ability of the parasite to modulate, evade or restrict the host response. Hosts acquire immunological based resistance to tick infestation, which reduces engorgement, production of ova and viability. Salivary glands of ixodid ticks produce a complex array of immunogens and pharmacologically active molecules. Tick salivary gland derived material can modulate host cytokine, antibody and cell mediated immune responses. Both immunoregulatory and immune effector pathways of the host are suppressed. Tick feeding impairs the ability to develop a primary immune response to a thymic dependent immunogen. Lymphocytes obtained from tick infested hosts are reduced in their ability to proliferate in vitro to T lymphocyte mitogens, while responses to B lymphocyte polyclonal activators are unaltered. Normal macrophages and lymphocytes were exposed to female tick salivary gland extracts prepared daily during the course of engorgement. All extracts reduced lymphocyte responses to T cell mitogens and enhanced in vitro proliferation in the presence of a B lymphocyte mitogen. Macrophage elaboration of tumour necrosis factor alpha and interleukin-1 are significantly reduced in a differential manner. Production of interleukin-2 and interferon-gamma by T lymphocytes is reduced. Tick modulation of the host immune response could enhance the ability of the arthropod to obtain a blood meal and facilitate pathogen transmission to an immunocompetent host.

Animals↗
PubMed1984

Bovine resistance to Amblyomma americanum ticks: an acquired immune response characterized by cutaneous basophil infiltrates.

Purebred Holstein calves acquired resistance to Amblyomma americanum adult ticks after 1 infestation and expressed resistance during a challenge infestation 26 days later. Tick yields from resistant animals were normal, but mean tick weight and egg-mass weight were reduced significantly (31 and 32%, respectively). Cutaneous cellular responses at tick feeding sites in primary (naive) hosts consisted almost exclusively of mononuclear cells, until 24-h post-infestation when granulocytes appeared. At 48 h, basophils were the most abundant granulocyte and comprised 19% of the total cellular response. Secondary and tertiary hosts expressed significant cutaneous basophil responses as early as 6 h post-tick infestation, indicative of an anamnestic response. Cutaneous basophil levels in tertiary hosts (16-34% of the infiltrate) were increased by 2-fold over secondary hosts (12-16% of the infiltrate). Neutrophils and eosinophils were fairly abundant in secondary hosts (22-33%, and 3-13%, respectively), but decreased significantly in tertiary hosts corresponding to increased basophil levels. Mast cells comprised less than 10% of the cells found in primary hosts, and less than 5% in secondary and tertiary hosts representing a consistent, but insignificant component of the total cells. Basophils were not observed in the blood of hosts during any tick infestation, but a peripheral blood basophilia (0.1-1.1%) marked the end of each tick feeding period. A neutropenia was observed in the blood of tertiary hosts corresponding to a decreased tissue neutrophil response. Blood eosinophil, lymphocyte and monocyte levels remained unchanged during each tick infestation compared to controls. In summary, calves acquired immunity to A. americanum ticks, resulting in significant decreases in feeding and ovipositional success associated with a local cutaneous basophil response and peripheral blood basophilia. These findings suggest that basophils are involved in bovine immunity to ticks as has been established in the guinea pig model.

Animals↗
PubMed2006

Acquisition and transmission of Theileria parva by vector tick, Rhipicephalus appendiculatus.

In order to investigate the transmission dynamics of Theileria parva (T. parva) by the brown ear tick, Rhipicephalus appendiculatus (R. appendiculatus), under experimental conditions, detection of T. parva in ticks and cattle was performed by a quantitative real-time PCR assay. A calf inoculated with a T. parva mixture became PCR-positive for T. parva infection on day 8 post-inoculation, and subsequently, nymphal ticks were introduced and maintained to feed on the infected calf for 6 days. Engorged nymphs were collected daily and allowed to molt into adults, and overall, 70.8% (121/171) of the adult ticks acquired the T. parva infection. Furthermore, the T. parva infection rate in ticks under field conditions was monitored by real-time PCR in R. appendiculatus ticks collected from a traditionally managed pastoral land of Zambia, on which Sanga breed cattle are traditionally reared and the area has endemic East Coast fever (ECF). A total of 70 cattle were randomly selected in the same area and 67 (95.7%) were found to be serologically positive for R. appendiculatus tick antigen (RIM36). Twenty-nine (43.3%) of the 67 serologically positive cattle were real-time PCR-positive for T. parva, although no piroplasms could be detected in the blood smears. Unexpectedly, out of 614 R. appendiculatus nymphal and adult ticks collected by flagging vegetation, 4.1% were positive for T. parva DNA. However, since the rate of transmission of T. parva from infected cattle to ticks and vice versa and the serological evidence of exposure to R. appendiculatus ticks in naturally exposed cattle were relatively high, it would be wise in such a case to consider vector control as well as vaccination against ECF as control measures.

Animals↗
PubMed1998

Trypanosome infections and tick infestations: susceptibility in N'Dama, Gobra zebu and Gobra x N'Dama crossbred cattle exposed to natural challenge and maintained under high and low surveillance of trypanosome infections.

Susceptibility to trypanosome infections and tick infestations was assessed in 51 N'Dama, 48 Gobra zebu and 37 Gobra x N'Dama crossbred (F1) cattle exposed to field-tick infestations and natural high tsetse challenge over more than one year. From these cattle, 12 animals of each breed were randomly selected and examined parasitologically for trypanosome infections and packed cell volume (PCV) twice a week (high surveillance, group HS). In the remaining 100 cattle trypanosome infection and PCV were monitored monthly (low surveillance, group LS). Mortality rates were recorded in both groups. Tick infestation was quantified fortnightly from all animals in group HS and from four to seven randomly selected animals of each breed in group LS. In both HS and LS groups, trypanocidal drug treatment was administered to trypanosome positive animals with PCV equal to or less than 20% or when they showed clinical evidence (dullness, weight loss) of trypanosomosis. In both groups, N'Dama cattle exhibited a superior capacity to control trypanosome infections and limit tick burdens. Particularly, in group HS N'Dama cattle showed lower trypanosome infection rate, higher mean PCV value, lower requirement for trypanocide treatments and lower tick load than crossbred and Gobra cattle in the corresponding group (P < 0.05 or greater). This was also true in N'Damas in comparison with crossbreds in group LS. Unfortunately, the high mortality occurring in Gobra cattle in group LS did not allow within group comparative analysis between N'Dama, Gobra and crossbred cattle overall the study period. No death occurred in N'Dama cattle maintained under high surveillance of trypanosome infection, while approximately 8% of crossbreds and 50% of Gobras died of trypanosomosis. In group LS, all Gobra and more than 70% of crossbred cattle died. In this group, mortality in N'Dama was limited to less than 16%. In both groups, differences in mortality were significantly higher (P < 0.01) in Gobras than in N'Damas. Within breed, animals of the three breeds maintained under high surveillance of trypanosomal infection showed higher mean PCV values, lower tick burdens and required proportionally less trypanocide treatments than corresponding cattle in group LS. The infection rate in N'Dama under high surveillance was lower in comparison with N'Dama cattle in group LS. There was no significant difference in mortality between groups within the N'Dama breed. Conversely, mortality rates were lower in crossbred and Gobra in group HS than in respective cattle in group LS. It was concluded that cattle of the three breeds suffered from trypanosomosis and that trypanosome infections affected tick susceptibility. However, N'Dama showed a superior ability to limit both the pathological effects of trypanosomosis and the level of tick infestations. Therefore, considering the cost of labour and consumable equipment required for a high surveillance, use of multi-disease resistant N'Dama cattle is recommended for the low-input traditional African farming systems in areas where trypanosomosis, ticks and tick-borne diseases are constraints to livestock production. Additional comparative investigations are needed to assess the impact of high surveillance scheme of trypanosome infection in different production systems in trypanotolerant and trypanosusceptible cattle exposed to different gradients of tsetse challenge.

Animals↗
PubMed1991

Biology of ticks.

Ticks are an ancient group of obligate bloodsucking ectoparasites that has evolved over millions of years. Two general types of ticks are evident today: argasid or soft ticks, and ixodid or hard ticks. Each lineage exhibits distinct patterns of host coevolution and preference. However, about 10% of the approximately 850 species are of medical importance because of their indiscriminate host selection and catholic feeding behavior. As a result, a number of diseases have begun to emerge in the temperate zones, including Lyme borreliosis and several others putatively associated with ticks. Ticks may serve as both pathogens and disease vectors. Because of the unique physiology of the salivary glands and the contents in tick saliva of toxins, feeding alone may cause disease. Ticks also transmit a number of different types of pathogens (viruses, rickettsiae, spirochetes and bacteria, fungi, protozoa, filarial nematodes) and even exceed mosquitoes in this regard. Abatement and control of ticks emphasizes a broad approach because of the differing types of habitats in which pest species may be found. The use of repellents and acaricides as well as cultural and management practices are of primary importance. Other approaches (ivermectin) may be beneficial; with the advent of molecular genetics and its usefulness in immunology, the development of tick vaccines for common pest species appears promising.

Animals↗
PubMed2005

Tick-borne Great Island Virus: (II) Impact of age-related acquired immunity on transmission in a natural seabird host.

Tick-borne pathogen transmission is dependent upon tick number per host and the physical and temporal distribution of each feeding stage. Age-related acquired immunity to tick and pathogen may also be important but has received less attention. In this study we evaluate which of these parameters has the greatest impact on Great Island Virus (GIV) transmission between Ixodes uriae ticks and common guillemots (Uria aalge). The study system is well suited to investigate age-related effects because the guillemot population is naturally divided into 2 groups, older breeding and younger pre-breeding adult birds. The physical distribution and timing of adult and nymphal tick feeding was similar for both guillemot age groups. However, breeding birds were parasitized by significantly more ticks (mainly nymphs). Calculations based on tick number predict virus prevalence should be higher in ticks that have fed on breeding rather than pre-breeding birds. However, empirical evidence indicates the reverse. Protective acquired immunity to GIV infection may be the reason why GIV prevalence is actually significantly lower in ticks that have fed on breeders. Far more breeding (74%) than pre-breeding (12%) guillemots had antibodies that neutralized 1 or more GIV strains. Estimates of the force of infection support the view that pre-breeding birds experience higher rates of virus infection than breeding birds. The results indicate age-related acquired immunity is a key factor in GIV transmission and highlight the need to consider age-related effects and host immunity when undertaking quantitative studies of tick-borne pathogen transmission.

Age Factors↗
PubMed1999

Efficiency and cost of strategic use of acaricide for tick control in N'Dama cattle in The Gambia.

The efficiency of strategic and strategic/selective applications of flumethrin spray formulation for controlling ticks were assessed, respectively, in two groups of fourteen N'Dama cattle (Group S and Group S/S) by comparison of the number of feeding ticks with thirteen untreated N'Dama cattle (Group U) over a period of 11 months (June 1996 to April 1997). During the expected peak of tick abundance, acaricide was applied fortnightly on the whole body in animals in Group S and only on the most infested body areas in cattle in Group S/S. Weight changes and skin lesions, directly associated with tick attachment, were recorded in cattle in the three groups. The costs of the two tick control schemes were estimated. Maximum level of ticks, all species together, feeding on cattle was observed in the rainy season. Both in Group S/S and Group S, cattle carried a lower (P < 0.001) number of feeding ticks than animals in Group U over the whole study period. Percentage of tick control, over the entire period of tick investigation, was satisfactory in both acaricide-treated groups, reaching 61.2 and 75.2% in Groups S/S and S, respectively. However, the proportion of control varied according to tick species or genus. Significantly lower prevalence of skin lesions was observed on the ano-genital and udder region in cattle in Group S/S (P < 0.05) and Group S (P < 0.01) in comparison with cattle in Group U. Mean amount of acaricide solution used and relative estimated cost of treatment in cattle in Group S/S were, respectively, 25- and 14-fold lower than those in cattle in Group S. At the end of the study, animals in Groups S/S and S were, respectively, 7.2 and 15.9 kg heavier than animals in Group U. The difference was statistically significant (P < 0.02) only between Groups S and U. However, the efficiency, low cost and derived benefits of the strategic/selective acaricide application scheme indicated that it might be the most cost effective.

Animals↗
PubMed2004

The prevalence of serum antibodies to tick-borne infections in Mbale District, Uganda: the effect of agro-ecological zone, grazing management and age of cattle.

Between August and October 2000, a cross-sectional study was conducted in smallholder dairy farms in Mbale District, Uganda to assess the prevalence of ticks and tick-borne diseases under different grazing systems and agro-ecological zones and understand the circumstances under which farmers operated. A questionnaire was administered to obtain information on dairy farm circumstances and practices. A total of 102 farms were visited and sera and ticks were collected from 478 animals. Sero-prevalence of tick-borne diseases was determined using an enzyme-linked immunoassay. Acaricides were used indiscriminately but the intensity of their use varied with the grazing system and zone. Cattle from different farms mixed for various reasons. During the dry seasons farmers have to get additional fodder from outside their farms that can result in importation of ticks. The prevalence of ticks and serum antibodies to tick-borne infections differed across the grazing systems and zones. The highest serum antibody prevalence (>60%) was recorded in the lowland zone under the free range and tethering grazing systems. The lowest tick challenge and serum antibody levels (<50%) were recorded in the midland and upland zones under a zero-grazing system. These findings suggest that endemic stability to East Coast Fever, babesiosis and anaplasmosis is most likely to have existed in the lowland zone, particularly, under the tethering and free-range grazing systems. Also, endemic stability for babesiosis existed in the upland zones. Endemic instability for East Coast Fever existed in the midland and upland zones. These structured observational studies are instrumental in planning of control strategies for ticks and tick borne diseases since production systems and the cattle population at high risk of the diseases in the district have been identified.

Aging↗
PubMed1990

Computer simulation of management strategies for American dog ticks (Acari: Ixodidae) and Rocky Mountain spotted fever.

Computer models were developed to simulate the effects of management technologies on populations of the American dog tick, Dermacentor variabilis (Say), principal vector of Rocky Mountain spotted fever (RMSF) in eastern North America. The technologies modeled were area-wide acaricide application, acaricide-food-baited tubes for self-treatment by small mammals, dipping of dogs in acaricides, acaricide-impregnated plastic dog collars, reduction of small mammal host populations (host management), and removal of vegetation that protects free-living tick stages (vegetative management). Submodels for each of these technologies were incorporated into a model (ADTSIM) for the population dynamics of the tick and RMSF transmission. Comparisons of simulated and observed data were used to verify reasonable accuracy of the submodels. Repetitive simulations were made to identify levels and timing of each control method (alone or combined) required to reduce tick populations below a RMSF transmission threshold of 252 unfed adults/ha. Eight to 30 acaricide applications, depending on acaricide and percentage of population treated, were needed during a 10-yr period to reduce densities of ticks below the threshold. The baited-tube method, host management, and vegetative management (depending on level and frequency of treatment) also were capable of reducing tick density below the threshold. However, acaricide-impregnated plastic dog collars did not reduce tick density below the threshold unless at least 50% of the hosts of adult ticks were domestic dogs. Integrated strategies were developed for management of ticks and RMSF in six selected states. These strategies reduced numbers of human cases of RMSF 90% or more by year 20 by maintaining tick densities between 100 and 252 unfed adults/ha.

Animals↗
PubMed1996

Ticks (Acari: Ixodidae) in Bulloch County, Georgia.

An 18-mo study was conducted in Bulloch County, Georgia, to determine tick species composition, seasonal activity of individual tick species, and host-tick associations. The following 7 methods of tick collection were included: (1) live trapping of potential host animals, (2) checking wild game, (3) drag sampling, (4) carbon dioxide attraction, (5) checking livestock, road kills, nests, and burrows, (6) samples submitted from veterinarians, and (7) ticks collected by local residents and submitted for identification. Twelve tick species (Ixodidae) were identified. Blacklegged tick, Ixodes scapularis Say, and American dog tick, Dermacentor variabilis (Say), had the widest host ranges and were the most numerous. White-tailed deer, Odocoileus virginianus (Zimmermann), supported 5 tick species, the greatest number on any host. Of 55 animal species examined, 16 mammal, 5 bird, and 3 reptile species were parasitized by ticks. Opossums, Didelphis virginiana Kerr, and cotton mice, Peromyscus gossypinus (LeConte), were the most commonly examined wild animals.

Animals↗
PubMed1996

Control of Karoo paralysis ticks through vegetation management.

Karoo paralysis, caused by feeding Ixodes rubicundus females, is a major disease of small stock in South Africa. Control methods currently practised are almost exclusively chemical based. To limit overdependance on chemicals, vegetation management was investigated as a possible method for control, to be incorporated in an integrated tick management system. Laboratory and field experiments were conducted to determine, firstly, the extent of vertical migration and survival of ticks on long and short copper rods which simulated grasses as questing substrates; secondly, the infestation burdens of sheep exposed to similar tick challenges in pens with long and short grass; and thirdly, the effect of trimming the lower crown line of wild olive trees, simulating the browsing effect of goats, on tick density in the immediate environment of the trees. When ticks were exposed to optimal ( > 45 cm) and sub-optimal ( < 10 cm) length rods on which to quest, the extent of vertical migration over extended periods of time (up to 87 days) was significantly higher (P < 0.001) for the ticks exposed to long rods. Also, almost 3 times as many ticks exposed to long rods survived compared to those exposed to short rods. Sheep exposed to long grass were infested by twice as many ticks compared to those exposed to short grass. Tick density at modified wild olive trees (Olea europaea africana) (0.027 ticks/m2) differed significantly (P < 0.05) from that at control trees (0.088 ticks/m2). It is recommended that coarse grazers such as cattle and horses should be used to graze down long grasses before sheep are introduced into camps known to be infested with I. rubicundus. Similarly, domestic goats can, through their browsing effect on shrubs and trees, modify the vegetation and as such play an important role in an integrated tick management system.

Animals↗
PubMed1997

The effects of the bont tick, Amblyomma hebraeum, on milk production of Sanga and Sanga x Brahman cattle.

The effects of adults on the bont tick, Amblyomma hebraeum on the milk production of Sanga and Sanga x zebu (Brahman) cattle were measured over a period of 11 weeks in the low veld of Zimbabwe in the summer of 1986. Four groups of lactating cows, consisting of two breeds, each divided into a high and low tick treatment, were exposed to very low or high challenges of ticks and their milk production measured by weighing their calves before and after suckling. The liveweight gains (LWG) of the calves were also measured. Tick burdens on the infested groups averaged around fourteen engorging females of A.hebraeum per day, which amounted to infestations of about 150 adult ticks. This is greater than most observed field infestations. This caused no significant reduction in milk yield or calf growth over the whole period, provided the teats of the dams had not been damaged by ticks. Mismothering occurred when teats were damaged. No breed differences were observed so all data was pooled for further analysis. Average calf LWGs of the high tick groups were reduced by 2.2 kg (P < 0.01) during one 4-week period but overall the 3.9 kg difference in LWG of the tick treatment groups was not quite significant (P < 0.10). Although there was a poor relationship between tick numbers and reduced milk yield or calf LWG, the effects were always in the direction expected. The effects averaged 6 +/- 10 g reduction of milk and 2.6 +/- 1.8 g loss of LWG of calves for every female tick that engorged. it was concluded that milk production is not an important consideration when estimating the losses in production caused by A.hebraeum on Brahman x Sanga or Sanga breeds of cattle. Losses due to teat or udder damage could be much more important and need to be quantified.

Animals↗
PubMed2000

Biocontrol of ticks by entomopathogenic nematodes. Research update.

Entomopathogenic nematodes (EPNs) are lethal to ticks even though they do not use their normal propagation cycle within tick cadavers. The tick Boophilus annulatus was found to be far more susceptible to EPNs than Hyalomma excavatum, Rhipicephalus bursa, or Rhipicephalus sanguineus. Ticks seem to be less susceptible to nematodes when feeding on a host. Preimaginal tick stages were less susceptible to nematodes than adult ticks. The mortality rate of unfed females was highest, followed by unfed males, and engorged females. The virulence of nematodes to ticks varied greatly among different nematode strains. In most cases, the Heterorhabditis sp. strains were the most virulent strains tested in petri dishes. In buckets containing sandy soil sprayed with 50 nematodes/cm2 and engorged B. annulatus females, the LT50 of the ticks was less than five days. The addition of manure to soil or a manure extract to petri dishes reduced nematode virulence. Since ticks spend most of their life cycle in the upper humid layer of the ground, and many nematode strains share this same ecological niche, the use of EPNs for biocontrol of ticks appears promising.

Animals↗