Skin test to detect resistance of cattle to Rhipicephalus appendiculatus ticks

The evaluation of a skin test to detect acquired resistance to Rhipicephalus appendiculatus Neumann ticks is described. An extract of salivary glands of partially fed female R. appendiculatus was prepared by dissection, sonication and filtration and used for intra-dermal injection. Tests were carried out on twelve calves of known resistance to R. appendiculatus and on twelve naive calves to establish threshold values for positive reactions. Four rabbits naive to ticks were skin tested repeatedly to assess immunogenicity of the test. Reactions to the test at 1 h and at 24 h after injection were significantly correlated with resistance. The correlation was higher with the reactions at 24 h. Rabbits were immunized by the test but the reactions never exceeded the positive threshold. Further development by field testing is recommended.     

The effect of host resistance on the metabolic rate of engorged females of Rhipicephalus evertsi evertsi

Abstract. This study investigated the effect of acquired resistance in guinea-pigs on the metabolic rate of adult females of the tick Rhipicephalus evertsi evertsi. Guinea-pigs were subjected to three successive infestations of ticks and the rate of CO₂ production (Vco₂) measured in first and third infestation engorged females. Ticks which fed on resistant hosts showed a 52% decrease in mass compared to ticks that fed on naive animals. Reduction in mass was accompanied by a decrease in Vco₂ (mlh^-1) per tick but an increase in mass specific Vco₂ (mlg^_1h^_1). However, both groups shared a single allometric relationship between body mass and metabolic rate (Vco₂). We suggest that the differences in size rather than any factor directly relating to the mechanism of acquired resistance account for the differences in metabolic rate between ticks fed on naive and resistant guinea-pigs.     

Development of resistance in laboratory animals to adults of the tick Rhipicephalus evertsi evertsi

Acquired resistance to adults of the two-host tick Rhipicephalus evertsi evertsi Neumann has been demonstrated in guinea-pigs and rabbits. Four infestations of both hosts with R.e.evertsi adults resulted in a significant reduction in the mean weight of the engorged females. A decline in the mean weight of the female ticks was also observed in ticks which fed on a rabbit previously injected with serum taken from a rabbit resistant to R.e.evertsi. This suggests that humoral immunity may have an important role in the acquired resistance to ticks. In both hosts an increase in the level of serum globulins was recorded. In rabbits the level of gamma globulin was affected, while in guinea-pigs an increase was observed in the concentration of alpha 1 and beta globulins. The differences in host responses to the R.e.evertsi adults are discussed.     

Development of resistance in rabbits to immature stages of the Ixodid tick Rhipicephalus appendiculatus

A study of acquired resistance in rabbits to larvae and nymphs of Rhipicephalus appendiculatus Neumann showed a positive correlation between the levels of gamma globulin in the serum and the resistance developed by the host. A negative correlation between the weight of engorged ticks and gamma globulin levels was also demonstrated during this study. Repeated infestations with ticks evoked a typical antibody response to antigenic challenge. The levels of gamma globulin stabilized after three infestations and no further decrease in the weight of ticks was observed. The mechanism of the acquisition of resistance by the rabbits, the production of antibodies and the involvement of complement are discussed.     

Distribution and phenology of ixodid ticks in southern Zambia

Distribution data for epidemiologically important ticks (Acari: Ixodidae) in the Southern Province of Zambia, one of the main cattle areas of the country, are presented. Boophilus microplus (Canestrini) was not recorded in southern Zambia, whereas Boophilus decoloratus (Koch) is present throughout the area. New distribution patterns for less economically important ixodid ticks are also discussed. Southern Zambia is a transition zone because it is the most northern area in Africa where mixed Rhipicephalus appendiculatus Neumann and Rhipicephalus zambeziensis Walker, Norval & Corwin populations were reported. Although a second generation of adult R. appendiculatus/R. zamnbeziensis was encountered, simulations indicated that this phenomenon is very rare in southern Zambia, mainly because of the colder temperatures during the early dry season and lower rainfall. These simulations were supported by a development trial under experimental conditions. Tick body size measurements showed that southern Zambian ticks are larger than eastern Zambian R. appendiculatus. It is hypothesized that body size is related to diapausing intensity in this species. The epidemiological consequences are that a different approach to control Theileria parva (Theiler) (Piroplasmida: Theileriidae) and other tick-borne diseases is needed in southern Zambia, compared to the one adopted in eastern Zambia.     

The effects of the brown ear-tick, Rhipicephalus appendiculatus, on milk production of Sanga cattle

Abstract. Lactating Sanga cows of the Mashona breed from Zimbabwe, receiving either a low or a high level of nutritional supplement, were exposed to two levels of infestation of adults of the brown ear-tick, Rhipicephalus appendiculatus in the highveld of Zimbabwe. The effect of the ticks on the milk yield was measured over an 11-week period during the rainy season from January to April 1986. A technique in which calves were weighed before and after suckling was used to estimate milk yield. There were significant treatment effects of ticks (P < 0.05) on milk production but no significant differences in liveweight gain between calves from tick-free and tick-infested dams. The loss in milk production was poorly related to the number of female ticks that engorged, being 9 g (SEM 4) per tick. A Friesian x Hereford (Bos taurus) reference group of cattle carried 50% more ticks than the Mashona cows, illustrating a difference in resistance between the breeds. Thirteen screw-worm (Chrysomya bezziana) strikes were recorded amongst the thirty-two Mashona cows compared with twenty-one amongst the ten Friesian × Hereford animals between January and the end of March.     

The effects of the brown ear-tick, Rhipicephalus appendiculatus, on milk production in dairy cattle

Abstract. The effect is reported of artificially controlled levels of infestation with adults of Rhipicephalus appendiculatus on the milk yield of twenty commercial Bos taurus dairy cattle on a high plane of nutrition and eighteen crossbed B.taurus × Sanga cattle on a lower plane of nutrition in the highveld of Zimbabwe. The results showed no significant effect on milk yield of infestations averaging twenty engorging ticks per animal per day, despite severe ear damage in some animals. They indicate that milk production of dairy cattle under commercial management is not sensitive to infestation with R.appendiculatus. The results have important implications for management of ticks in Africa, but need to be interpreted within the context of the control of tick-borne diseases.     

Comparison of resistance in three breeds of cattle against African ixodid ticks

Tick resistance in three breeds of cattle, two indigenous breeds (Arssi and Boran) and one Boran x Friesian cross-breed, were compared following natural tick infestations at Abernossa ranch in Ethiopia. The local Arssi breed was found to have the highest tick resistance, followed by the Boran breed, whereas the Boran x Friesian was the least resistant. Over a period of 12 months, from October 1991 to September 1992, a total of 32 897 ticks composed of four genera were collected from the animals. The four most abundant tick species were Amblyomma variegatum (61.7%), Boophilus decoloratus (16%); Rhipicephalus evertsi evertsi (16.3%) and Hyalomma marginatum rufipes (3.7%). Furthermore, 63.5% of all ticks were collected from cross-breed cattle, and 26.2% from the Boran, whereas the local Arssi breed carried only 10.3%. The results indicated that cattle resistant to one species of tick were also resistant to other tick species.     

Feeding electrogram studies on the African cattle brown ear tick Rhipicephalus appendiculatus: evidence for an antifeeding effect of tick resistant serum

Abstract. Feeding behaviour of partially engorged Rhipicephalus appendiculatus (Neumann) (Acari: Ixodidae) on rabbit serum held in capillary tubes and placed over the tick mouthparts was studied using the feeding electrogram technique with simultaneous macro video photography. Correlation of electrical events with fluid movement in the vicinity of the tick's mouthparts and the capillary meniscus, permitted the characterization of an orderly sequence of signals, termed the 'Feeding Complex', associated with highest weight gains. This complex consisted of a 3–8 Hz fast-sucking waveform typically lasting 4–5 min, a sharp drop in potential at salivation, and rest lasting 1 or 2 min where no waveform or fluid movements occur. Very high impedence recordings from within the tick capitulum indicate that the fast-sucking waveform coincides with bursts of potentials corresponding to contraction of the pharyngeal dilator muscles, whereas during rest a tonic series of spikes signifies that the floor of the salivarium is actively lowered. Feeding electrograms of ticks fed on serum from tick-resistant rabbits showed significantly fewer feeding complexes. The weight gains achieved by these ticks were reduced correspondingly. This suggests that some of the humoral effectors of immunity have an antifeedant effect on this unusual parasite of rabbits.     

Attractivity of cattle infested by Amblyomma variegatum (Acari: Ixodidae) for conspecific adult ticks from the field in Guadeloupe

Four field experiments were conducted with creole cattle in Guadeloupe to study the attractivity for adult ticks of animals previously infested with males of Amblyomma variegatum producing aggregation attachment pheromones (AAPs). In each experiment, two groups of cattle were used; the first group was infested with adult A. variegatum and the second group was kept free of ticks and pheromones by acaricidal treatment and by washing the hair and skin of previously infested sites. Both groups were then exposed to natural infestation by ticks present in the environment or by ticks bred in the laboratory and released on the pasture. The number of additional ticks infesting animals were compared between the treated and control groups. There were no significant differences between both groups in the numbers of new male ticks infesting the animals during the first days following the beginning of the experiment. Thereafter, comparison of the slopes of infestation indicated that infested cattle were no more attractive for male ticks than uninfested hosts. Uninfested cattle were spontaneously and rapidly infested by male ticks. It is concluded that carbon dioxide or another host component was a major attractant for A. variegatum males. Female ticks attached on predilection sites exclusively in the presence of AAP-producing males, i.e. 5–10 days after the attachment of the first males. Based on these results we postulate that slow-release devices impregnated with pheromones have no additional attractive effect on A. variegatum males under Caribbean conditions. However, they may be useful in inducing the attachment of females, but only in the first days preceding the arrival of pioneer AAP-producing males. © Rapid Science Ltd. 1998     

Long-term studies on the economic impact of ticks on Sanga cattle in Zambia

Three different tick control policies were tested in groups of traditionally managed Sanga cattle in the Central Province of Zambia over a period of 3 years. One group was given strategic tick control using 12 pyrethroid acaricide spray applications between the onset and the end of the wet season (October to March). The productivity of this herd was compared with that of a group with no tick control and a group under an intensive tick control regimen of spraying every week in the wet season and every 2 weeks in the dry season (36 applications per year). The highest output was associated with intensive tick control, followed by strategic control and then no tick control policies. However, when the costs of tick control were taken into account, the strategic tick control policy produced the best economic result, followed by the intensive and then the no tick control policies. Neither the strategic nor the intensive tick control policy was sufficient to prevent the transmission of East Coast fever (ECF) infection when this disease was introduced to the area.     

Differential protein expression in ovaries of uninfected and Babesia-infected southern cattle ticks, Rhipicephalus (Boophilus) microplus

We used gel electrophoresis and mass spectrometry to investigate differences in protein expression in ovarian tissues from Babesia bovis-infected and uninfected southern cattle tick, Rhipicephalus (Boophilus) microplus. Soluble and membrane proteins were extracted from ovaries of adult female ticks, and analyzed by isoelectric focusing (IEF) and one-dimensional or two-dimensional (2-D) gel electrophoresis. Protein patterns were analyzed for differences in expression between infected and uninfected ticks. 2-D separation of proteins revealed a number of proteins that appeared to be up- or down-regulated in response to infection with Babesia, in particular membrane/membrane-associated proteins and proteins in a low molecular mass range between 6 and 36 kDa. A selection of differentially expressed proteins was subjected to analysis by capillary-HPLC-electrospray tandem mass spectrometry (HPLC-ESI-MS/MS). Among the ovarian proteins that were up-regulated in infected ticks were calreticulin, two myosin subunits, an endoplasmic reticulum protein, a peptidyl-prolyl cis–trans isomerase (PPIase), a cytochrome c oxidase subunit, a glutamine synthetase, and a family of Kunitz-type serine protease inhibitors. Among the down-regulated ovarian proteins were another PPIase, a hemoglobin subunit, and a lysozyme. This study is part of an ongoing effort to establish a proteome database that can be utilized to investigate specific proteins involved in successful pathogen transmission.     

Population dynamics of ticks on indigenous cattle in a pastoral dry to semi-arid rangeland zone of Uganda

Studies on seasonality and population dynamics of ticks on indigenous cattle and their crosses (calves) were carried out in Buruli Ranching Scheme, Nabiswera, Luwero district of Uganda on three treatment groups of animals: group 1 (twice a week dipping), group 2 (once a month dipping) and group 3 (no tick control). During this study, four major species of ticks of economic importance were recorded in decreasing order of abundance: Rhipicephalus appendiculatus, Rhipicephalus evertsi evertsi, Amblyomma variegatum and Boophilus decoloratus. Of these ticks, a seasonal pattern of activity was only observed in R. appendiculatus ticks, with peak activities occurring during rainy seasons. Greater numbers of ticks were recorded on cows than calves in the three treatment groups, with the exception of A. variegatum where the reverse occurred. The mean numbers of ticks per animal were highly significantly different (p < 0.01) when group 1 animals were compared with group 2 and 3 animals. However, no significant differences (p > 0.05) were observed in mean tick numbers between group 2 and 3 animals. Highly significant differences (p < 0.01) were observed in mean tick numbers on cows and calves (more than 12 months old) in different calving seasons. The state of lactation only affected tick counts on cows in group 1; significantly more ticks (p < 0.01) were observed in lactating than non-lactating cows. Furthermore, significantly greater (p < 0.05) numbers of ticks (with the exception of B. decoloratus) were recorded during the second year of study (March 1992-May 1993) than the first year (January 1991-February 1992), despite lower rainfall during the former period.     

Prevalence and antimicrobial resistance of Campylobacter in US dairy cattle

AIMS: To obtain an overview of the prevalence and antimicrobial resistance of Campylobacter in faeces of US dairy cows in 2002. METHODS AND RESULTS: Faeces from 1435 cows, representing 96 dairy operations in 21 US states, were collected for the culture of Campylobacter. A total of 735 Campylobacter strains were isolated (51.2% positive samples) with 94 operations positive (97.9%) for Campylobacter. From this collection, 532 isolates (473 Campylobacter jejuni and 59 Campylobacter coli) were randomly selected for susceptibility testing to eight antimicrobials: azithromycin, chloramphenicol, ciprofloxacin, clindamycin, erythromycin, gentamicin, nalidixic acid and tetracycline. The C. jejuni isolates exhibited resistance to tetracycline (47.4%), nalidixic acid (4.0%) and ciprofloxacin (2.5%), while the C. coli strains exhibited some resistance to all antimicrobials except chloramphenicol and ciprofloxacin. Only 3.6% of the C. jejuni isolates were resistant to two or more antimicrobials but 20.3% of the C. coli strains were multiresistant. CONCLUSIONS: On most operations, at least one cow was positive for Campylobacter and more than half of the cows sampled were shedding Campylobacter. The C. coli isolates had significantly higher levels of resistance to macrolides and to tetracycline compared with the C. jejuni strains, but were susceptible to ciprofloxacin. SIGNIFICANCE AND IMPACT OF THE STUDY: This study demonstrated a high prevalence of Campylobacter on US dairy operations; however, US dairy cattle have not been recognized as a major source of human infection compared with poultry. Campylobacter coli appears to develop antimicrobial resistance more readily than C. jejuni from the same environment.     

Development of enzyme linked immunosorbent assays to measure Bm86 antigen of Boophilus microplus (cattle tick) and to detect anti-Bm86 antibodies in serum samples

The immunization of cattle with the Boophilus microplus Bm86 antigen has been successful for the control of cattle tick infestations. To monitor the Bm86 production process and to measure the anti-Bm86 antibody titers in vaccinated cattle, mAb-based ELISA were developed and validated. The development of both immunological methods is essential to obtain a product with high quality and immunogenic properties and to monitor the immunological protection induced in vaccinated cattle against B. microplus.     

Attachment kinetics of the adult tick Amblyomma variegatum to cattle

At the beginning of the 1999 rainy season, three traditional cattle herds were monitored for 48 days while grazing in the bushy savannah of southwestern Burkina Faso. Cattle in each herd were caught on several occasions each day and the attached ticks were counted. This confirmed that Amblyomma variegatum Fabricius (Acari: Ixodidae) adults picked up in the pastures mainly attach to the interdigital areas (87% of the 791 ticks captured), and reach the predilection sites later (chest and udder/inguinal area) when the animals lie down. As many females as males attached to the hosts, but the seasonal distribution was very heterogeneous, with only a few females attaching as long as the humidity rate remained low. It is suggested that this prevents eggs from being laid when conditions are not optimal for their survival and that of the larvae. Ticks attached all day but the number picked up hourly and daily varied greatly according to their density on the pasture. As a general trend, confirmed by another study carried out in 2005, the number of ticks picked up daily increased from less than one tick/animal/day, before the onset of the rainy season, to 6.5 (+/- 1.5) ticks/animal/day on average during the infestation peak, which lasted 6-8 weeks, until early or mid-July. The number then decreased to less than one tick/animal/day from the end of July onwards. The infestation on the predilection sites followed the same trend, with a daily tick burden increase of three to five A. variegatum adults, depending on herd and year, during the infestation peak.     

Detecting Resistance to Organophosphates and Carbamates in the Cattle Tick Boophilus Microplus, with a Propoxur-based Biochemical Test

Rapid and sensitive detection of resistance to insecticides in arthropods is needed. In the cattle tick, Boophilus microplus, resistance to a variety of acaricides is widespread. The most commonly used assay for resistance, the larval packet test, takes at least two, but generally six weeks for a one-host tick like B. microplus to complete and may take up to three months to complete for three-host ticks. Here we describe a test for resistance to organophosphate acaricides that can be used on larvae and adult ticks which takes less than 24 hours. The test measures the difference in acetylcholinesterase (AChE) activity in homogenates of ticks in the presence and absence of propoxur, a carbamate acaricide. We found clear discrimination of organophosphate-susceptible and organophosphate-resistant adults with 100 M propoxur. AChE from susceptible ticks had almost no activity at this concentration of propoxur whereas AChE from resistant ticks had 67% of its potential activity. AChE from heterozygote ticks could also be distinguished from AChE from homozygous-susceptible and homozygous-resistant ticks. This is the first biochemical test for resistance to an acaricide. Rapid, sensitive tests like ours will allow resistance to organophosphates to be detected soon after it develops in the field, thus, the spread of resistance might be slowed and the useful life of acaricides extended.     

Assessment of temporal changes in haem and protein levels in Ixodid ticks following blood engorgement, and their use as age-grading parameters

Nymphs of Rhipicephalus appendiculatus and Hyalomma anatolicum anatolicum were fed on rabbits and maintained in the laboratory to allow moulting and further development. At specified time intervals from 0 to 500 days after engorgement, samples of ticks were ground individually in distilled water within the wells of an agglutination plate. A 0.1 ml aliquot was removed from each and levels of haemin and protein assessed from optical density values at specific wavelengths in a spectrophotometer.

Both protein and haemin levels showed an initial rapid decrease after engorgement; values did not fall to zero in either case but showed marked fluctuation throughout the study period. These fluctuations combined with the high standard errors of the results, made assessments of the physiological age of individual ticks impossible.

Such fluctuating values, however, suggested the possibility that haem biosynthesis might be taking place, and this was tested by injecting the radioactively-labelled haem precursor [4-¹⁴C]δ-amino laevulinic acid into engorged nymphs, immediately following their detachment. Both tick species revealed an incorporation of this compound into their haematin content, although neither incorporated the non-haem precursor [1-¹⁴C]2-amino isobutyric acid. These results indicate an ability of ticks to synthesize haem in vivo, although the underlying reasons for such a mechanism remain unknown.     

An assessment of opportunities to dissect host genetic variation in resistance to infectious diseases in livestock

This paper reviews the evidence for host genetic variation in resistance to infectious diseases for a wide variety of diseases of economic importance in poultry, cattle, pig, sheep and Atlantic salmon. Further, it develops a method of ranking each disease in terms of its overall impact, and combines this ranking with published evidence for host genetic variation and information on the current state of genomic tools in each host species. The outcome is an overall ranking of the amenability of each disease to genomic studies that dissect host genetic variation in resistance. Six disease-based assessment criteria were defined: industry concern, economic impact, public concern, threat to food safety or zoonotic potential, impact on animal welfare and threat to international trade barriers. For each category, a subjective score was assigned to each disease according to the relative strength of evidence, impact, concern or threat posed by that particular disease, and the scores were summed across categories. Evidence for host genetic variation in resistance was determined from available published data, including breed comparison, heritability studies, quantitative trait loci (QTL) studies, evidence of candidate genes with significant effects, data on pathogen sequence and on host gene expression analyses. In total, 16 poultry diseases, 13 cattle diseases, nine pig diseases, 11 sheep diseases and three Atlantic salmon diseases were assessed. The top-ranking diseases or pathogens, i.e. those most amenable to studies dissecting host genetic variation, were Salmonella in poultry, bovine mastitis, Marek's disease and coccidiosis, both in poultry. The top-ranking diseases or pathogens in pigs, sheep and Atlantic salmon were Escherichia coli, mastitis and infectious pancreatic necrosis, respectively. These rankings summarise the current state of knowledge for each disease and broadly, although not entirely, reflect current international research efforts. They will alter as more information becomes available and as genome tools become more sophisticated for each species. It is suggested that this approach could be used to rank diseases from other perspectives as well, e.g. in terms of disease control strategies.