High-resolution predictive mapping for Rhipicephalus appendiculatus (Acari: Ixodidae) in the Horn of Africa

The brown ear tick Rhipicephalus appendiculatus, vector of East Coast fever (ECF) and related cattle diseases caused by Theileria parva has never been reported from the Horn of Africa. Habitat suitability for this tick species was predicted using Maxent modelling technique based on R. appendiculatus records in Sub-Saharan Africa. Two models were developed: the first is based on the tropical R. appendiculatus distribution and the one is based on the distribution records in the temperate region of Sub-Saharan Africa. The tropical model shows favourable habitat in much of the Ethiopian highlands. The whole Djibouti, the south eastern Ethiopian lowlands, majority of Somalia and Eritrea were found to be not suitable for the survival and development of this tick species. Highly suitable areas occur in areas which have moderate temperature and high precipitation. Introductions of R. appendiculatus into the Horn of Africa probably have been prevented by the natural barrier between the known R. appendiculatus distribution range in East Africa and the Horn of Africa. The effect of an introduction of R. appendiculatus and thereby ECF into the Horn of Africa could be catastrophic since the cattle in this area have no immunity against ECF, and mortality might be considerable in all age groups of cattle.     

Rhipicephalus appendiculatus and R. zambeziensis (Acari: Ixodidae) from Zambia: a molecular reassessment of their species status and identification

The closely related species Rhipicephalus appendiculatus and R. zambeziensis co-occur in a wide area in Zambia. In this area, specimens of both species have been collected on the same individual host at the same time. In addition, specimens that are morphologically intermediate between R. appendiculatus and R. zambeziensis have been found in this area. These observations cast some doubt on the species status of R. appendiculatus and R. zambeziensis. Because the two taxa have varied influences on the epidemiology of East Coast fever (ECF), a cattle disease for which they act as vectors, it is essential that their taxonomic status is clarified and their identification is accurate. Therefore a phylogenetic analysis of nucleotide sequences of the ITS2 and a fragment of the mitochondrial 12S rDNA was performed to reassess the specific status of both taxa. This revealed two well supported clades coinciding with R. appendiculatus and R. zambeziensis as two separate species. In order to facilitate species identification a PCR-RFLP diagnostic assay was developed based on BauI digestion of the ITS2 gene. This assay produced clear diagnostic banding patterns for the two species and is applicable over a wide range of both species’ distribution. Nucleotide sequence data reported in this paper are available in the GenBank™ under the accession numbers DQ849203–DQ849274.     

Inheritance of weight in Rhipicephalus appendiculatus ticks (Acari: Ixodidae) in the laboratory

A selection of the 10% lightest and 10% heaviest males and females of a population of individually weighed Rhipicephalus appendiculatus Neumann adults was made in two experiments. The offspring of homologous pairs were followed until the next adult stage (light x light, control x control and heavy x heavy). The engorged nymphal weights, unfed adult weights, engorged female weights of the parents, egg mass weights, egg weights, larval scutal lengths, engorged larval weights, unfed nymphal weights, engorged nymphal weights and adult weights of the progeny were determined. No significant differences could be demonstrated between the two lines for egg weight, larval scutal length, engorged larval weight and unfed nymphal weight. Significant differences were found between the egg masses, engorged nymphal weights and adult weights of the two lines. The heritability coefficients of body weight determined from adult to adult were 0.14 and 0.10, respectively, during the first and second experiments. Considering females and males separately, the coefficients were 0.10 and 0.18 during the frist experiment and 0.12 and 0.09 during the repeat experiment respectively.     

Further evidence for geographic differentiation in R. appendiculatus (Acari: Ixodidae) from Eastern and Southern provinces of Zambia

Studies in the biology, ecology and behaviour of R. appendiculatus in Zambia have shown considerable variation within and between populations often associated with their geographical origin. We studied variation in the mitochondrial COI (mtCOI) gene of adult R. appendiculatus ticks originating from the Eastern and Southern provinces of Zambia. Rhipicephalus appendiculatus ticks from the two provinces were placed into two groups on the mtCOI sequence data tree. One group comprised all haplotypes of specimens from the Eastern province plateau districts of Chipata and Petauke. The second group consisted of a single haplotype of specimens from the Southern province districts and Nyimba, an Eastern province district on the fringes of the valley. This variation provides additional evidence to the earlier observations in the 12S rDNA and ITS2 data for the geographic subdivision of R. appendiculatus from Southern province and Eastern province plateau. The geographic subdivision further corresponds with differences in body size and diapause between R. appendiculatus from these geographic areas. The possible implications of these findings on the epidemiology of East Coast fever (ECF) the disease for which R. appendiculatus is one of the vectors are discussed. Nucleotide sequence data reported in this paper are available in the GenBank^TM under the Accession Numbers DQ859259–DQ859266     

Ecdysteroids in relation to adult development and reproduction in female Rhipicephalus appendiculatus (Acari; Ixodidae)

In view of the paucity of information on ecdysteroids during tick development, the profiles of the free ecdysteroids, together with the polar and apolar conjugates have been established by radioimmunoassay during development of adult females of the hard tick, Rhipicephalus appendiculatus. The free ecdysteroid titre increased sharply to a peak approximately 3 days post-engorgement, a day preceding beginning of oviposition. This titre decreased to a low level, which was maintained throughout oviposition. Although the titre of polar ecdysteroid conjugates was appreciably less than that of the free ecdysteroids during the peak, the general profile of such conjugates was similar to that of the free ecdysteroids. In the case of the apolar ecdysteroid conjugates, the titre increased simultaneously with production of free ecdysteroids, but was maintained at a relatively high level until the end of oviposition, when it sharply declined. The apolar conjugates were the predominant form of ecdysteroids present during most of oviposition. The free ecdysteroids as well as the polar and apolar conjugates were shown to contain 20-hydroxyecdysone accompanied by smaller amounts of ecdysone by high-performance liquid chromatography-RIA (HPLC-RIA) and gas chromatography/mass spectrometry (selected ion monitoring; GC/MS [SIM]). © 1996 Wiley-Liss, Inc.     

Comparison of Preservation Methods of Rhipicephalus appendiculatus (Acari: Ixodidae) for Reliable DNA Amplification by PCR

Five differently preserved groups of adult Rhipicephalus appendiculatus specimens were compared for quality of DNA extracted. Three methods were used to extract DNA from specimens i.e. two simple mosquito validated DNA extraction methods and a tick validated method. Extraction of DNA from tick legs was attempted. The quality of DNA extracted was evaluated by the success of PCR amplification of the ITS2 gene and the mitochondrial COI gene fragment. Fresh specimens (i.e. killed just before extraction) had the highest success of DNA amplification followed by specimens killed in ethanol and subsequently stored in the refrigerator (4 °C). There was no significant difference in amplification success between cryopreserved and 70% ethanol preserved specimens. It was possible to amplify DNA from legs of ticks. Sequenced ITS2 amplicon of template obtained from legs of ticks was as legible as those from whole tick extract. The two mosquito validated DNA extraction methods showed a significantly lower amplification success than the tick validated protocol.     

Population dynamics and density-dependent seasonal mortality indices of the tick Rhipicephalus appendiculatus in eastern and southern Africa

Abstract. Eight sets of previously published data on the seasonal abundance of the tick Rhipicephalus appendiculatus in Burundi, Uganda, Tanzania and Zimbabwe are analysed to yield seasonal mortality indices. Correlations between these indices and abiotic (climatic) and biotic (tick density) variables suggest that it is the stage from females to larvae that is most sensitive to adverse abiotic conditions, specifically low moisture availability. Mortality at the other stages of the tick's life cycle is strongly density-dependent. The precise nature of this density-dependence suggests that it may be caused by acquired resistance to ticks by cattle. Robust correlations between satellite-derived vegetation indices, climatic factors and mortality indices suggest that detailed climatic data, often unavailable, may be replaced by satellite data, now widely available, for use in modelling tick populations.     

Underwater survival of Rhipicephalus sanguineus (Acari: Ixodidae)

Rhipicephalus sanguineus (Acari: Ixodidae) is a worldwide distributed tick, also due to its adaptability to different environmental conditions. In order to assess its ability to survive and to lay eggs after water immersion, 150 engorged females from southern Italy were water immersed for 1-15 days whereas eggs were flooded for 1-5 days. All females survived water immersion for 48 h, some of them up to 72 h, but egg hatch rate was negatively correlated with female submersion period. All eggs flooded for up to 120 h hatched successfully. These findings suggest that R. sanguineus is able to survive underwater for some days without loosing any biological activity. This feature should be considered in relation to its potential to spread to new areas and to its role as a vector of pathogens also in consideration of changes in climate the Earth is currently experiencing.     

Displacement of Rhipicephalus decoloratus by Rhipicephalus microplus (Acari: Ixodidae) in the Eastern Cape Province, South Africa

The objective of the study was to establish to what extent the native tick species Rhipicephalus decoloratus has been displaced by the invasive introduced tick, Rhipicephalus microplus at two communally grazed areas in the Eastern Cape Province, South Africa. To this end ticks were collected monthly from five cattle over a period of 2 years and from 10 drag-samples of the vegetation over a period of 1 year at each locality. Whereas 10 years previously only R. decoloratus and no R. microplus had been recorded in the vicinity of the two sites, R. microplus now comprised the bulk of collections at both. Furthermore, significantly more R. microplus were collected from cattle at both localities during the 2nd year of the survey than during the 1st. In addition to 83 instances of intraspecific coupling, there were 17 instances of R. microplus males coupled with R. decoloratus females. Collections made from cattle and goats on two farms close to the study sites revealed that R. microplus was present on both host species and that it significantly outnumbered R. decoloratus on one of the farms. Rhipicephalus decoloratus and R. microplus larvae as well as larvae exhibiting characteristics of both species were collected from the vegetation.     

Rhipicephalus appendiculatus (Acari: Ixodidae): dynamics of Thogoto virus infection in female ticks during feeding on guinea pigs

Engorged nymphs (Rhipicephalus appendiculatus) were inoculated parenterally with Thogoto (THO) virus (approximately 1 microl per nymph; 10(6)-10(7) PFU/ml). The adult females which resulted were used as the source of infected ticks for this study. Hemolymph, salivary glands, synganglion, gut, ovary, and Malpighian tubules were collected on each day of the blood meal and titrated for THO virus by plaque assay. The percent of tissues infected with virus was 16% or less on the day of attachment. Percent infection rose for all tissues throughout 6-7 days of feeding, reaching 40-100% infection during the rapid phase of engorgement. For the first 4 days of feeding, virus titer in the synganglion was higher than in salivary glands (means of 6.4-34.7 PFU/synganglion and 1.6-8.8 PFU/salivary gland pair). From days 5-7, virus titer was generally higher in the salivary gland than the synganglion (means of 422, 408, and 817 PFU/gland pair and means of 62, 811, and 9 PFU/synganglion). However, because a salivary gland pair is much heavier than a synganglion, the virus concentration in the synganglion was much higher than in the salivary gland during the slow phase of feeding. During the rapid phase of feeding, the difference in virus titer between the synganglion and salivary gland reduced. This difference between the early and late stages of feeding may explain why a previous study [J. Gen. Virol. 70 (1989) 1093], using immunofluorescence and immuno-gold labelling, failed to detect virus in the salivary gland early in feeding. These data provide evidence to explain that R. appendiculatus can transmit THO virus within 24h of attachment, an important epidemiological finding.     

Gynandromorphism in Amblyomma cajennense and Rhipicephalus sanguineus (Acari: Ixodidae)

During a survey of ticks on horses in November 2000, at the University of S?o Paulo farm in Pirassununga county, S?o Paulo, Brazil, 1 gynandromorph of Amblyomma cajennense was collected from a naturally infested horse. In another survey on dogs in March 2001, in the urban area of Monte Negro, Rond?nia, Brazil, a gynandromorph of Rhipicephalus sanguineus was collected from a naturally infested dog. Both specimens are described and classified as perfect bipartite protogynanders.     

Evidence for a mounting sex pheromone in the brown ear tick Rhipicephalus appendiculatus,Neuman 1901 (Acari: Ixodidae)

The presence of a mounting sex pheromone was demonstrated on the surface of fed female Rhipicephalus appendiculatus. This pheromone, which is present on the female cuticle, allows the male to recognise the female. The pheromone was removed by cleaning the female in hexane, resulting in the loss of male mating behaviour in in vitro experiments. Male mating behaviour was resumed when extract made from fed female cuticle was replaced on cleaned females. When the extract was transferred to innanimate objects typical male mating behaviour was released. Preliminary chemical analyses indicated that the active component of the extract was contained in the sterol ester fraction of the extract.     

First detection and genetic identification of Rickettsia infection in Rhipicephalus sanguineus (Acari: Ixodidae) ticks collected from Southern Taiwan

Experimental and Applied Acarology - The prevalence and genetic identity of Rickettsia infection in Rhipicephalus sanguineus sensu lato (s.l.) ticks were determined in Taiwan. In total 1153 ticks...     

Resistance in cattle againstRhipicephalus appendiculatus with an assessment of cross-resistance toR. pulchellus (Acari: Ixodidae)

A comparison of the yield of engorged nymphs ofRhipicephalus appendiculatus andR. pulchellus was carried out between cattle highly resistant toR. appendiculatus but susceptible toR. pulchellus, and cattle and rabbits susceptible to both species.Resistant cattle yielded fewer and smallerR. appendiculatus nymphs than either susceptible cattle or rabbits. More nymphs of both tick species dropped from susceptible cattle but no differences were detected in the mean weight of engorgedR. pulchellus nymphs fed onR. appendiculatus-resistant and susceptible cattle, although resistant animals yielded more nymphs ofR. pulchellus than ofR. appendiculatus.An acute inflammatory reaction, accompanied by intense pruritus and grooming, was observed in the ears of the resistant cattle infested withR. appendiculatus, but no reaction was detected in the opposite ears whereR. pulchellus was feeding.The low cross-resistance between these two closely related tick species suggests that different antigens may be involved in the development of resistance in cattle to different tick species.     

Ultrastructural characterization of cultured embryonic cells of Rhipicephalus appendiculatus neumann (Acarina : Ixodidae)

Cultured embryonic cells of Rhipicephalus appendiculatus (Acarina : Ixodidae) have been studied by electron microscope. Two major cell types, an epithelial-like cell and the fibroblast-type cell, are described. A possible third cell type, a muscle cell, which occurs rarely in the cell culture, is also described. The different phases of development, namely the growth, maturation, and aging of the cells are described and discussed.     

Differentiation of Rhipicephalus ticks (Acari: Ixodidae) by gas chromatography of cuticular hydrocarbons.

Gas chromatography of the cuticular hydrocarbons of 4 species of ticks belonging to the genus Rhipicephalus (R. sanguineus, R. turanicus, R. pusillus, and R. bursa) showed a unique pattern for each taxon. The hydrocarbon fractions were composed of a mixture of straight-chain, terminally methylated, and internally branched alkanes; however, only a small quantity of alkenes was detected. Freshly collected, dried, and alcohol-stored specimens of R. sanguineus were analyzed and their patterns found to be nearly identical. Collection of specimens from separate localities demonstrated a species-specific pattern for Spanish material.     

Detection of new Francisella-like tick endosymbionts in Hyalomma spp. and Rhipicephalus spp. (Acari: Ixodidae) from Bulgaria

We report on the identification of two new Francisella-like endosymbionts (FLEs) found in three different tick species from Bulgaria. The FLEs were characterized by 16S rRNA and tul4 gene sequencing and seem to lack the molecular marker RD1. These two new taxa seem to be facultative secondary endosymbionts of ticks.