Survival of unfed Rhipicephalus appendiculatus and Rhipicephalus zambeziensis adults

Two ixodid tick species, Rhipicephalus appendiculatus (Neumann) and Rhipicephalus zambeziensis (Walker et al.) (Acari: Ixodidae), both originating from the southern province of Zambia, were used to study the survival time of adults at a range of different humidities and temperatures. In general, the experiment clearly demonstrates the different survival times of the two species in relation to the climatic conditions tested: survival of R. zambeziensis was better under more extreme conditions of temperature and humidity. These findings offer an explanation for the different distribution ranges of the two tick species. Rhipicephalus appendiculatus is more confined to cooler and wetter conditions, whereas R. zambeziensis is adapted to hotter and drier areas.     

Variation in body size in the tick complex Rhipicephalus appendiculatus/Rhipicephalus zambeziensis.

We examined the relationship between body size and the phenology of the tick complex Rhipicephalus appendiculatus/Rhipicephalus zambeziensis. These ticks transmit Theileria parva in cattle. In Africa, the body size of R. appendiculatus increases with latitude while the body size of the morphologically similar Rhipicephalus zambeziensis is constant at two different latitudes. A larger body size is necessary once survival becomes a constraint. The most plausible explanation for the smaller R. appendiculatus in equatorial Africa is the cost to produce a larger egg. The consequences of these findings for the introduction of R. appendiculatus in new environments are discussed. New field observations from southern Zambia indicate that R. appendiculatus body size does not vary seasonally as compared to eastern Zambia. This is an additional indication of the presence of a single diapausing population of larger ticks.     

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.     

Monthly dynamics of ticks (Acari: Ixodida) infesting N'Dama cattle in the Republic of Guinea

The occurrence of ixodid ticks on N'Dama cattle was studied in the Republic of Guinea between June 1994 and May 1995. Monthly tick collections were performed on 80 animals from 14 villages located in Dabola, Kouroussa and Dinguiraye prefectures. A total of 19,804 ticks was collected and classified using standard taxonomic keys. The following tick species were identified: Amblyomma variegatum, Hyalomma marginatum rufipes, Hyalomma trunctum, Hyalomma nitidum, Rhipicephalus lunulatus, Rhipicephalus muhsamae, Rhipicephalus senegalensis, Rhipicephalus sulcatus, Rhipicephalus turanicus, Boophilus annulatus, Boophilus geigyi. Boophilus spp. were the most numerous adult ticks (57.1%), Am. variegatum adults constituted 27.4%, while 12.4% were Rhipicephalus spp. and 2.5% Hyalomma spp. Rhipicephalus turanicus and Hyalomma nitidum were recorded for the first time in the country. Am. variegatum and Boophilus spp. were present throughout the year, whereas Am. variegatum adults showed a peak during the rainy season between April and September. Immature stages collected belonged exclusively to the genera Amblyomma and Boophilus. Am. variegatum larvae and nymphs showed a peak during the dry season (October-March); no significant variation between seasons was observed for Boophilus immatures. A significantly higher infestation of cattle by Rhipicephalus spp. was found in Dabola and Kouroussa prefectures, located in the southern part of the study area, with similar climatic, vegetation and rainfall characteristics. Possible options for the control of ticks in the study area are briefly discussed.     

Genetic variation in the body weight of ticks of the Rhipicephalus appendiculatus/zambeziensis complex

Sixteen strains of ticks of the Rhipicephalus appendiculatus/zambeziensis complex were created by cross-breeding for one to three generations. The body-weights of adult male ticks of these consanguineous lines were compared. A significant genetic variation was distinguished between the groups. Three classes whose mean weights varied around, respectively, 2, 3 and 4 mg/adult male tick, were found. This variation in weight may be explained by hybridization between R. appendiculatus Neumann and R. zambeziensis Walker, Norval & Corwin. Hybrid ticks were undersized whereas R. appendiculatus and R. zambeziensis groups had significantly higher weights.     

Kinetic properties of toxic protease inhibitors isolated from tick eggs

1. Egg-toxins from Rhipicephalus evertsi evertsi, Boophilus microplus, Boophilus decoloratus and Hyalomma truncatum were found to be inhibitors of trypsin and in two cases also of chymotrypsin. 2. Fast tight-binding and slow-binding inhibition were observed. 3. Immunological identity of the toxins were assessed with Ouchterlony immunodiffusion and ELISA. 4. The protease content of B. decoloratus and Amblyomma hebraeum tick eggs were determined by a linked enzyme assay. 5. The predictive value of the kinetic constants in inferring a possible physiological role was discussed.     

Prevalence of ixodid ticks on cattle in Mazandaran province, Iran

A survey was carried out to investigate the prevalence of hard tick species (Acari: Ixodidae) on cattle in Mazandaran province, Iran. A total of 953 ticks were collected from 86 infested cattle during activating seasons of ticks during 2004-2005. Nine species were identified: Boophilus annulatus (51.3%), Rhipicephalus bursa (16.8%), Haemaphysalis punctata (6.3%), Ixodes ricinus (6.8%), Hyalomma marginatum (12.5%), Hyalomma anatolicum excavatum (5.2%), Hyalomma asiaticum (0.6%), Hyalomma detritum (0.2 %), and Dermacentor spp. (0.1%). The results show that Boophilus annulatus, Rhipicephalus bursa, and Hyalomma species are dominant tick species in the surveyed area.     

The identification of a shared immunogen present in the salivary glands and gut of ixodid and argasid ticks

The identification of a 70-kDa immunogen present in salivary gland extracts of several ixodid species, namelyHyalomma truncatum (sweating-sickness-inducing (SS+) and non-inducing (SS-) strains),Hyalomma marginatum. rufipes andRhipicephalus evertsi evertsi, is reported. The immunogen was identified by Western blots using a monoclonal antibody of the IgM isotype directed against a 70-kDa immunogen present in the salivary glands of (SS-) femaleH. truncatum ticks. Cross-reactivity with the gut of unfed adult ixodid ticks,Amblyomma hebraeum, Rhipicephalus simus simus, R. evertsi evertsi, Rhipicentor nuttali, H.m. rufipes, and salivary glands of adult argasid species,Ornithodoros savignyi andOrnithodoros moubata, was demonstrated using ELISA.     

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.     

Analysis of the systematic relationships among ticks of the genera Rhipicephalus and Boophilus (Acari: Ixodidae) based on mitochondrial 12S ribosomal DNA gene sequences and morphological characters

A portion of mitochondrial 12S rDNA sequences (337-355 base pairs) and 63 morphological characters of 36 hard-tick species belonging to 7 genera were analyzed to determine the phylogenetic relationships among groups and species of Rhipicephalus and between the genera Rhipicephalus and Boophilus. Molecular and morphological data sets were first examined separately. The molecular data were analyzed by maximum parsimony (MP), maximum likelihood, and neighbor-joining distance methods; the morphological data were analyzed by MP After their level of congruence was evaluated by a partition homogeneity test, all characters were combined and analyzed by MP. The branches of the tree obtained by combining the data sets were better resolved than those of the trees inferred from the separate analyses. Boophilus is monophyletic and arose within Rhipicephalus. Boophilus species clustered with species of the Rhipicephalus evertsi group. Most of the clustering within Rhipicephalus was, however, consistent with previous classifications based on morphological data. Morphological characters were traced on the molecular reconstruction in order to identify characters diagnostic for monophyletic clades. Within the Rhipicephalus sanguineus complex, the sequences of specimens morphologically identified as Rhipicephalus turanicus were characterized by a high level of variability, indicating that R. turanicus-like morphology may cover a spectrum of distinct species.     

An assessment of host resistance to ticks on cross-bred cattle in Burundi

Abstract. Groups of cattle of four different cross-breeds (Ankole × Friesian, Ankole × Brown-Swiss, Ankole × Guernsey, Ankole × Sahiwal) plus a group of pure Ankole cattle were immunized against tick-borne diseases: East Coast Fever, using a Theileria parva trivalent vaccine, and anaplasmosis, babesiosis and, subsequently, heartwater. With the exception of two small subgroups of Ankole and Ankole × Sahiwal which were treated by weekly spraying using Delnav, all the groups were exposed to natural field challenge of ticks to quantify the development of host resistance to ticks. The results indicate resistance to the most abundant species, Rhipicephalus appendiculatus , as follows: Ankole > Ankole × Sahiwal > Ankole × Brown Swiss > Ankole × Friesian > Ankole × Guernsey. In both Amblyomma variegatum and Rhipicephalus evertsi evertsi , the manifestation of different levels of resistance between breeds is inapparent. Correlations between total ticks and standard female ticks were good for R. appendiculatus (r = 0.73) and R. evertsi (r - 0.51) but poor for A. variegatum (r = 0.31). Correlations between species were reasonably consistent (r = 0.43-0.59). There was no significant correlation between tick burdens and daily liveweight gain (DLWG) over the. whole period of the study. Of the cross-bred groups, Ankole × Sahiwal, which had the highest level of resistance, had the highest DLWG. In contrast, the Ankole × Guernsey which developed the lowest level of resistance had only marginally lower DLWG, the difference being only 8 g/day. During the first period of exposure to ticks, however, the untreated Ankole × Sahiwal group had markedly lower DLWG, which may indicate that the development and manifestation of resistance is at the expense of productivity.     

Resistance and cross-resistance in guinea-pigs and rabbits to immature stages of ixodid ticks

Infestation of guinea-pigs and rabbits with larvae of any one of five species of ticks, Rhipicephalus appendiculatus Neumann, Rhipicephalus evertsi evertsi Neumann, Amblyomma hebrauem Koch, Amblyomma variegatum Fabricius and Ixodes ricinus L., conferred resistance in the animals when exposed to subsequent infestations with the same tick species. Resistance to infestations by other tick species was not observed.     

Phylogenetic analyses of the rhipicephaline ticks indicate that the genus Rhipicephalus is paraphyletic

We inferred the phylogeny of 21 species and subspecies of ticks from the subfamilies Rhipicephalinae and Hyalomminae using cytochrome c oxidase subunit I (COI) and 12S rRNA mitochondrial gene sequences. Two members of the subfamily Haemaphysalinae were used for outgroup reference. The largest rhipicephaline genus, Rhipicephalus, was represented by ticks from six of the species groups, the second largest genus, Dermacentor, by species from two of three of its subgenera, and the genus Boophilus by 3 of its 5 species. We analyzed the 12S and COI sequences separately and together; statistically significant incongruence between the 12S rDNA and the COI sequences was not detected in the combined dataset using the incongruence length difference test. The combined dataset provided greater phylogenetic resolution than the individual datasets, and although the 12S rDNA data had only 25% of the parsimony-informative characters, it provided half of the total partitioned Bremer support for the combined dataset. We present the first hypothesis of phylogenetic relationships among some species groups of Rhipicephalus but our most controversial result was that the genus Rhipicephalus is apparently paraphyletic, unless species of Boophilus are included in it. The species of Rhipicephalus most closely related to Boophilus spp. were from the R. pravus and R. evertsi species groups, which may implicate an African origin for this important group of ticks.     

Factors influencing the distribution of questing ticks and the prevalence estimation of T. parva infection in brown ear ticks in the Tanga region, Tanzania.

Questing ticks from various districts and agro-ecological zones (AEZ) in the Tanga Region of Tanzania were studied for a two-year period between September 1999 and July 2001. Collections of both nymphal and adult ticks occurred at 29 sites using a blanket or white cloth dragging technique. The species recorded in the order of decreasing abundance were Rhipicephalus appendiculatus, Boophilus spp., and Ambylomma variegatum. Rhipicephalus appendiculatus field infestation levels varied across administrative districts and seasons, with Amani and the cool-to-dry season having lower tick counts ( = -2.09, SE = 0.71, P < 0.001 and = -1.54, SE = 0.56, P = 0.006 for Amani and cool to dry season, respectively). Based on the polymerase chain reaction technique, Theileria parva infection prevalence in adult R. appendiculatus was estimated to be 2.6%. Implications of these findings in light of the spatial and temporal distribution of ticks are discussed for the accurate diagnosis of multiple tick-borne diseases, the infected vector tick, the endemic status of T. parva in the region, and the implemention of control strategies.     

Immune suppression induced by the brown ear tick Rhipicephalus appendiculatus Neumann, 1901

The brown ear tick Rhipicephalus appendiculatus suppressed in vivo and in vitro immune responses in the rabbit. Humoral responses were suppressed during infestation; however, suppression was transient and was unrelated to previous exposure of hosts to similar tick infestations. Immune suppression was caused by putative lymphocytotoxic factor(s) in tick salivary secretions as evidenced by in vitro lymphocytotoxicity assays. In an identical study of Rhipicephalus zambeziensis, a closely related rhipicephalid, the immune response was not suppressed, indicating that immune suppression is not common to the genus Rhipicephalus.     

The localization of a paralysis toxin in granules and nuclei of prefed female Rhipicephalus evertsi evertsi tick salivary gland cells

A monoclonal antibody directed against a paralysis toxin of Rhipicephalus evertsi evertsi ticks was used to localize the toxin in cytoplasmic granules and, surprisingly, chromatin of the nuclei of cells which resemble the b cell type in the salivary glands of Rhipicephalus appendiculatus, Boophilus microplus and Ixodes holocyclus. The association of toxin with chromatin indicates that the toxin may have a regulatory function. Evidence is provided to support the view that the toxin is made up of three identical sub-units, with only the trimeric form being toxic.     

Evidence to show that an agent that cross-reacts serologically with Cowdria ruminantium in Zimbabwe is transmitted by ticks

The serological diagnosis of heartwater based on reactions to the immunodominant Cowdria ruminantium major antigen protein-1 (MAP-1) is impaired by the detection of false-positive reactions. In this study, the prevalence of false-positive reactions on seven heartwater-free farms in Zimbabwe was determined to be 8-94% by immunoblotting against C. ruminantium antigens. The highest prevalence of false-positives on Spring Valley Farm correlated with the presence of Rhipicephalus evertsi evertsi ticks. The other tick species found on these seven farms were Hyalomma truncatum and Hyalomma marginatum rufipes. Rhipicephalus evertsi evertsi ticks collected from Spring Valley Farm and fed on seronegative sheep caused seroconversion in one of two sheep. This sheep developed a mild febrile reaction and C. ruminantium MAP-1 antigen reactive antibodies 3 weeks after the ticks started feeding. Polymerase chain reactions (PCRs), conducted using C. ruminantium-specific primers on ticks collected from the seven farms and on some of the R. e. evertsi ticks that had caused seroconversion in one sheep, were negative. However, some of these ticks gave positive PCRs with DNA primers which amplify a 350 bp DNA fragment of the 16s rRNA gene from all ehrlichial agents indicating the presence of infection with one or more Ehrlichia species. Although attempts to isolate the cross-reacting agent from the sheep were unsuccessful, this study demonstrates that false-positive reactions with the MAP-1 C. ruminantium antigen are associated with agents transmitted by ticks.     

Genetic variation in Rhipicephalus appendiculatus (Acari: Ixodidae) from Zambia: correlating genetic and ecological variation with Rhipicephalus appendiculatus from eastern and southern Africa.

Based on their ecology, Rhipicephalus appendiculatus ticks from eastern and southern Africa have been divided into three groups. We investigated how two geographic genetically differentiated stocks of R. appendiculatus from the southern and the eastern provinces of Zambia, representing two ecological groups, i.e., southern African and transition groups, respectively, genetically compare to stocks from east Africa (Rwanda) and southern Africa (Zimbabwe and South Africa). The ITS2 and two mitochondrial genes segments, 12s rDNA and COI, were used in the investigations. The ITS2 tree did not show support for differentiation into any groups, while the two mitochondrial genes trees (12s rDNA and COI) showed two genetically differentiated groups: an east African genetic group which included specimens from Rwanda and the plateau area of the eastern province of Zambia, and a southern African genetic group represented by specimens from South Africa, Zimbabwe and specimens collected on the fringes of the eastern province plateau in the Nyimba district of Zambia. This suggests that the two geographically differentiated stocks of the southern and eastern provinces of Zambia might be part of two wider geographic genetically differentiated R. appendiculatus groups that extend beyond Zambia. Stocks of "transition" ecology (eastern province) belong to the east African genetic group and the differences in ecology within this genetic grouping may be due to genetic polymorphism, phenotypic plasticity, and other local factors.     

Morphological identification of ticks (Acari: Ixodidae) infesting donkeys (Equus asinus) in Maputo Province,Mozambique

Donkeys (Equus asinus) are rustic animals, but in Africa’s poorest regions, they can present multiple health problems, including tick infestation. The study’s objective was to determine the species composition of ticks that infest donkeys in Maputo Province (Mozambique). Ticks were collected in five conveniently selected southern districts of Maputo Province (Moamba, Matutuíne, Marracuene, Boane, and Matola) and were identified to species level using a stereoscopic microscope with the aid of dichotomous identification keys. In total, 500 ticks were collected from all 88 selected donkeys. Three genera of ticks were identified, namely Rhipicephalus (97.2%; 486/500), Amblyomma (2.2%; 11/500), and Hyalomma (0.6%; 3/500). Seven species were identified, of which Rhipicephalus evertsi evertsi with 50.4% (252/500) was the most prevalent, followed by Rhipicephalus appendiculatus (27.4%; 137/500), Rhipicephalus turanicus (11.6; 10/500), Rhipicephalus (boophilus) microplus (6.8; 20/500), Amblyomma hebraeum (2.2%; 11/500), Rhipicephalus sanguineus (1%; 5/500) and Hyalomma truncatum (0.6%; 3/500). Rhipicephalus evertsi evertsi occurred in all locations, whereas Hyalomma truncatum occurred only in the Boane district. Males were the most prevalent (67.2%; 336/500). The study revealed that donkeys in Maputo Province were infested with seven tick species of which R. evertsi evertsi was the main species.

     

An update on the ecological distribution of Ixodid ticks infesting cattle in Rwanda: countrywide cross-sectional survey in the wet and the dry season

As part of the epidemiological studies aimed at developing an East Coast fever (ECF) immunisation control strategy, which combines an infection and treatment method with strategic tick control, a countrywide tick survey was carried out in both the dry and the wet season to determine the abundance and the dynamics of the tick populations infesting cattle in Rwanda. Six Ixodid tick species where identified from a total of 12,814 tick specimens collected. Rhipicephalus appendiculatus, the main vector of ECF was the most abundant (91.8%) followed by Boophilus decoloratus (6.1%) and Ambyomma variegatum (1.2%). Few ticks from the three other less economically important Ixodid species (Rhipicephalus compositus, R. evertsi evertsi and Ixodes cavipalpus) were recovered. Both adult and immature stages of the most dominant tick species were found to be widespread with a year round presence. The numbers of ticks were high in low land and medium zones and declined markedly in the higher regions of Rwanda. The geographical distribution of various tick species throughout the country and their epidemiological implications are discussed.