Factors affecting the distributions of the ticks Amblyomma hebraeum and A. variegatum in Zimbabwe: implications of reduced acaricide usage

The ticks Amblyomma hebraeum and A. variegatum are the main vectors of heartwater, a disease of ruminants caused by Cowdria ruminantium, in the agricultural areas of Zimbabwe. At present, A. hebraeum is widely distributed in the dry southern lowveld, and occurs in at least seven foci in the higher rainfall highveld. Amblyomma variegatum occurs in the Zambezi valley and surrounding dry lowveld areas in the northwest. The distribution of A. hebraeum has changed considerably over the past 70 years, while that of A. variegatum appears to have remained fairly static. The distribution patterns of both species in Zimbabwe display anomalous features; the ticks occur in areas of lowest predicted climatic suitability for survival and development and in areas where the densities of cattle, the most important domestic host, are lowest. The only factor favouring the survival of the species in the lowveld habitats in which they occur is the presence of alternative wildlife hosts for the adult stage. Their absence from more climatically favourable highveld habitats appears to have been the result of intensive acaricide treatment of cattle over a long period and a historic absence of significant numbers of wildlife hosts. Eradication of A. hebraeum and A. variegatum by intensive acaricide treatment of cattle can be achieved in the absence of significant numbers of alternative hosts, because of the long attachment and feeding periods of the adults of these tick species. However, eradication becomes impossible when alternative hosts for the adult stage are present, because a pheromone emitted by attached males attracts the unfed nymphal and adult stages to infested hosts. The unfed ticks are not attracted to uninfested hosts, such as acaricide-treated cattle.Regular acaricide treatment of cattle is expensive and so, for economic reasons, the Government of Zimbabwe is no longer enforcing a policy of strict tick control. It is likely that reduced tick control will result in the spread of Amblyomma ticks to previously uninfested areas. Added to this, recent introductions of various wildlife species to highveld commercial farming areas have created conditions in which the ticks could become established in higher rainfall areas. Amblyomma hebraeum is more likely to spread than A. variegatum, because its adults parasitize a wider range of wildlife hosts (warthogs, medium to large-sized antelope, giraffe, buffalo and rhinoceros), whereas adults of A. variegatum appear to be largely restricted to one wildlife species (buffalo) in Zimbabwe, the distribution of which is now confined to very limited areas of the country, as part of foot and mouth disease control measures. A model to predict the rate of spread of A. hebraeum through the highveld is described.Possible control options for dealing with the spread of Amblyomma ticks and heartwater to previous unaffected highveld areas, include (1) continuation of intensive acaricide treatment of cattle to prevent the spread, (2) establishment of a buffer zone of intensive tick control around affected areas to contain the spread and (3) allow the spread to occur and control heartwater by means of immunization. An economic analysis to determine the costs and benefits of the control options, which takes into account the development of Amblyomma-specific tick control technologies and improved heartwater vaccines, is recommended.Deceased.     

Responses of the ticksAmblyomma hebraeum andA. variegatum to known or potential components of the aggregation-attachment pheromone. III. Aggregation

Ten known or potential components of the aggregation-attachment pheromone (AAP) of the ticksAmblyomma hebraeum andA. variegatum, as well as mixtures of these components, extracts of prefed males and live prefed males, were tested as aggregation stimulants. In field assays, laboratory-reared unfed male and female ticks were released 20 cm downwind of CO₂/pheromone release sites; the numbers of ticks that aggregated at the release sites were recorded after 30 min. InA. variegatum, aggregation was induced by methyl salicylate,o-nitrophenol, 2,6-dichlorophenol, phenylacetaldehyde and some mixtures containing these compounds; a strong aggregation response was induced by an extract of five prefed malesA. variegatum and a weak response was induced by an extract of 50 prefed males ofA. hebraeum. InA. hebraeum, aggregation was induced by phenylacetaldehyde, mixtures of compounds that included phenylacetaldehyde, extracts of 50 prefed males ofA. hebraeum orA. variegatum and 50 live prefed males ofA. hebraeum. InA. variegatum, aggregation was inhibited if compounds that do not occur naturally in the AAP of the species were included in mixtures. InA. hebraeum, phenylacetaldehyde appeared to act as an arrestant for ticks that had been attracted to release sites by other compounds.     

Responses of the ticksAmblyomma hebraeum andA. variegatum to known or potential components of the aggregation-attachment pheromone. IV. Attachment stimulation of nymphs

Ten known or potential components of the aggregation-attachment pheromone (AAP) of the ticksAmblyomma hebraeum andA. variegatum, as well as a mixture of these components and extracts of prefed males of the two species, were tested as attachment stimulants for nymphs. Unfed nymphs were confined in linen bags on the ears of rabbits that had been treated with the test compounds, mixture or extracts; the numbers attached were recorded after 24 h. InA. hebraeum, attachment was induced by four compounds (2-methyl propanoic acid, methyl salicylate,o-nitrophenol and salicylaldehyde), the mixture and extracts from both species. InA. variegatum, attachment was induced by three compounds (methyl salicylate,o-nitrophenol and salicylaldehyde), the mixture and extracts from both species. Methyl salicylate ando-nitrophenol are primary components of the AAP of bothA. hebraeum andA. variegatum. 2-methyl propanoic acid is a species-specific attachment stimulant forA. hebraeum. Salicylaldehyde, a phenolic compound, is not a naturally occurring AAP component. Nymphs of both species respond to fewer attachment stimulants than the adults and, as shown by their respective host ranges, are less dependent on the AAP in the regulation of attachment than the adults.     

Comparison of known and suspected pheromonal constituents in males of the African ticks,Amblyomma hebraeum Koch andAmblyomma variegatum (Fabricius)

Three low molecular weight compounds were found in hexane: diethyl ether extracts of fed males of the African ticks,Amblyomma variegatum (tropical bont tick) andA. hebraeum (bont tick), namely,o-nitrophenol, methyl salicylate and 2,6-dichlorophenol. These same compounds were also found in a rinse of fedA. variegatum males, but were absent or present in only trace amounts in a rinse of fedA. hebraeum males.o-Nitrophenol and methyl salicylate were present in much higher concentrations (i.e., amounts/tick) inA. variegatum than inA. hebraeum. 2,6-Dichlorophenol was also more abundant inA. variegatum than inA. hebraeum, but the differences were not as great as with the former two compounds. Extraction in hexane over a 3-week period revealed four additional compounds, benzaldehyde, benzyl alcohol, benzothiazole and nonanoic acid. The first three compounds were found in males of both species; nonanoic acid was found only inA. hebraeum males. Published reports consistently show strong attraction byo-nitrophenol and methyl salicylate for both sexes of the two bont tick species; 2,6-dichlorophenol and benzaldehyde have been reported to be attractive to both sexes ofA. hebraeum. The possible roles of these compounds, as well as others occasionally reported fromA. hebraeum andA. variegatum, as components of the aggregation/attachment pheromone or other pheromones is discussed.Supported by Cooperative Agreement No. AFR-0435A-00-9084-00 with the U.S. Agency for International Development to the Department of Infectious Diseases, College of Veterinary Medicine, University of Florida, Gainesville, FL.     

Responses of the ticksAmblyomma hebraeum andA. variegatum to known or potential components of the aggregation-attachment pheromone. II. Attachment stimulation

Nine known or potential components of the aggregation-attachment pheromone of the ticksAmblyomma hebraeum andA. variegatum were tested as attachment stimulants. Unfed adult male and female ticks were confined in linen bags on the ears of rabbits that had been treated with solutions of the test compounds; the numbers attached were recorded after 24 h. In both species, males attached more rapidly and more readily than females. InA. hebraeum, attachment of males was induced by eight compounds (benzaldehyde, benzyl alcohol, 2,6-dichlorophenol, heptadecane, 2-methyl propanoic acid, methyl salicylate, o-nitrophenol and salicylaldehyde) and attachment of females by six compounds (benzaldehyde, benzyl alcohol, 2,6-dichlorophenol, 2-methyl propanoic acid, o-nitrophenol and salicylaldehyde). InA. variegatum, attachment of males was induced by seven compounds (benzaldehyde, benzyl alcohol, 2,6-dichlorophenol, heptadecane, methyl salicylate, o-nitrophenol and salicyladeehyde) and attachment of females by two compounds (methyl salicylate and o-nitrophenol). A mixture of the nine compounds and extracts of prefed males ofA. herbraeum andA. variegatum induced attachment in males of both species and in femaleA. hebraeum; in these tests, attachment of femaleA. variegatum was only induced by extracts of conspecific males.     

A comparison of the attraction of nymphs and adults of the ticksAmblyomma hebraeum andA. variegatum to carbon dioxide and the male-produced aggregation-attachment pheromone

The attraction of nymphs of the ticksAmblyomma hebraeum andA. variegatum to CO₂ alone and CO₂ together with the male-produced aggregation-attachment pheromone (AAP) was investigated. Matching experiments on the attraction of the adults of the two species were run for comparison. Nymphs ofA. hebraeum were strongly attracted to sources of CO₂ and CO₂/AAP at distances of 10 and 15 m. At distances of 20 and 25 m significantly more nymphs were attracted to CO₂/AAP than to CO₂ alone. Adults ofA. hebraeum were not attracted to CO₂ alone at any distance; these ticks were attracted to CO₂ and AAP together for distances of up to 25 m. The patterns of attraction of nymphs and adults ofA. variegatum at 10 m were similar to those recorded inA. hebraeum.     

Responses of the ticksAmblyomma hebraeum andA. variegatum to known or potential components of the aggregation-attachment pheromone. I. Long-range attraction

Nine known or potential components of the aggregation-attachment pheromone of the ticksAmblyomma hebraeum andA. variegatum were tested as long-range attractants. In field assays, laboratory-reared unfed male and female ticks were released 4 m downwind of treated filter-paper targets. Carbon dioxide was used to activate the ticks and the numbers attracted to the targets were recorded. Adults ofA. hebraeum were attracted to six compounds (benzaldehyde, 2,6-dichlorophenol, heptadecane, methyl salicylate, nonanoic acid and o-nitrophenol) and adults ofA. variegatum to four compounds (2,6-dichlorophenol, methyl salicylate, nonanoic acid and o-nitrophenol). The most important attractant forA. hebraeum was o-nitrophenol; methyl salicylate and o-nitrophenol were the most important attractants forA. variegatum. Nonanoic acid and o-nitrophenol attracted significantly more female than maleA. hebraeum. Both species were also attracted by a mixture of the nine compounds.     

Use of carbon dioxide and natural or synthetic aggregation-attachment pheromone of the bont tick,Amblyomma hebraeum,to attract and trap unfed adults in the field

It was determined previously that unfed adults ofAmblyomma hebraeum become active in response to carbon dioxide but are not attracted by it. We have now shown in field experiments that males and females which are activated by carbon dioxide are attracted to the aggregation-attachment pheromone produced by males after a period of feeding on the host. Unfed adults were attracted too-nitrophenol, a component of the aggregation-attachment pheromone ofAmblyomma variegatum, pre-fed males ofA. hebraeum, and extracts of such males. Live males were more attractive than the extracts which, in turn, were more attractive thano-nitrophenol. The ticks were attracted to sources ofo-nitrophenol from as far away as 11 m in 90 min. Simple traps, baited with carbon dioxide and aggregation-attachment pheromone (from pre-fed males or extracts of pre-fed males), were used to capture unfed adults that had been released in the field. The response of unfed adults to carbon dioxide and the aggregation-attachment pheromone presents an obvious host-location mechanism and a means for the ticks to discriminate between suitable hosts (those with males already attached) and potentially unsuitable hosts (those with no males attached).     

<Emphasis Type="Italic">In vitro</Emphasis> splenocyte proliferation responses of BALB/c mice to salivary gland extracts of three ixodid tick species (Acari: Ixodidae)

In vitro proliferation and cytokine production were investigated in BALB/c mice splenic cell cultures that were stimulated with concanavalin A (ConA) and lipopolysaccharide (LPS) and simultaneously exposed to salivary gland extracts (SGE) of unfed and partially fed adult ixodid ticks (Ixodes ricinus, Rhipicephalus appendiculatus, Amblyomma variegatum). Generally, tick SGE enhanced proliferation of unstimulated splenocytes and SGE of unfed ticks suppressed mitogen induced proliferation. Partially fed R. appendiculatus and A. variegatum suppressed ConA responses, while partially fed I. ricinus stimulated both ConA and LPS induced proliferation. A. variegatum and R. appendiculatus females slightly enhanced LPS responses 2 days after attachment but suppressed them at the end of the slow feeding phase. In 72 h ConA induced cell cultures, interferon gamma (IFN-γ) production was suppressed by SGE of all ticks, interleukin (IL)-10 production was enhanced by unfed I. ricinus and partially fed A. variegatum males and IL-5 production was enhanced by feeding R. appendiculatus females and A. variegatum males. The study revealed variability in the responsiveness of murine splenocytes to SGE of different ixodid tick species, whereby patterns of host immunomodulation within one tick species differed between sexes and changed during feeding.     

Monitoring of naturally acquired and artificially induced immunity toAmblyomma variegatum andRhipicephalus appendiculatus ticks under field and laboratory conditions

The ability of rabbits, goats and cattle to acquire immunity to the ixodid ticksAmblyomma variegatum andRhipicephalus appendiculatus was studied under laboratory and field conditions. Rabbits were successfully immunized with crude salivary gland extract (SGE) and midgut extract (ME) obtained from flat or partly fed femaleR. appendiculatus ticks. The lowest numbers of larvae were produced by females fed on rabbits immunized with unfed midgut extract. Similar reductions in larval production could be induced after three infestations of rabbits with adultR. appendiculatus. Also, successive feedings of nymphs ofR. appendiculatus on rabbits resulted in significantly reduced engorgement weights. Skin testing with SGE induced delayed-type hypersensitivity reactions, which could be correlated with immunity toR. appendiculatus in rabbits. Moreover, circulating antibodies were detected in rabbits with an ELISA using SGE ofR. appendiculatus.Immunity toA. variegatum nymphs could be induced in rabbits by repeated infestations, but this failed in goats. Immunization of goats with midgut extract from adultA. variegatum did not protect against subsequent nymphal challenge, but strong skin reactions were noticed when adults ticks fed on immunized goats. Sodium dodecyl sulfate polyacrylamide gel electrophoresis of SGE and ME fromA. variegatum revealed the presence of 48 protein bands in SGE and 29 bands in midgut extract. Western blotting employing serum from a rabbit immune toR. appendiculatus recognized a number of bands in SGE fromR. appendiculatus, but also in SGE ofA. variegatum.Immunity acquired by cattle to ixodid tick infestations under field conditions was monitored by skin testing with SGE and western blot analysis. In general, cattle with the lowest tick numbers manifested the strongest delayed-type hypersensitivity responses. Finally, western blot analysis employing sera from tick-infested and tick-naive cattle could not be related to actual immune status.     

Ecology and phenology of ticks in Zambia: Seasonal dynamics on cattle

A study of the seasonality and infestation rates of ticks was carried out in 11 cattle herds in different ecological habitats in Zambia between 1980 and 1982. Wherever possible supplementary data were obtained from opportunistic collections from cattle and other hosts.Analysis of over 1000 tick collections from cattle indicated that infestation rates of the most important species,Amblyomma variegatum andRhipicephalus appendiculatus vary in different ecological habitats: (i) In Western Province, infestations are much lower than elsewhere; (ii) in Central and Southern Provinces, moderate to high infestations occur; and (iii) in Eastern Province,R. appendiculatus numbers are generally low andA. variegatum numbers are moderate.These two species, however, have similar life cycles throughout their range with one generation per year. Larvae occur mainly from March to May, nymphae from May to September, and adults ofA. variegatum from October to December and ofR. appendiculatus from December to April. Boophilus decoloratus appears to have two to four generations per year but is uncommon during the rainy season. In some areas in central ZambiaRhipicephalus compositus adults are seasonally common in September–October whereasRhipicephalus evertsi is more or less ubiquitous. Low to moderate infestations ofHyalomma truncatum andHyalomma rufipes occur in most areas.At least 14 other less common or rare species ofRhipicephalus, Amblyomma, Haemaphysalis andIxodes were taken infrequently from cattle. These and other host-specific species were also collected from dogs, sheep, various wildlife hosts and the environment.Infestation rates, seasonality and host-relationship of tick species are discussed in relation to their ecology. Relevant biosystematic and disease relationships are reviewed briefly. The baseline data derived from this study are adequate for integrated analysis with those from other ecological and economic investigations to formulate tick control strategies.     

Prevalence of Ehrlichia ruminantium in adult Amblyomma variegatum collected from cattle in Cameroon

Ehrlichia ruminantium, the etiologic agent of the economically important disease heartwater, is an obligate intracellular bacterium transmitted by ticks of the genus Amblyomma, particularly A. hebraeum and A. variegatum. Although serologic and microscopic evidence of the presence of heartwater have been reported in ruminants in Cameroon, knowledge of E. ruminantium infection in the tick vector, A. variegatum, is lacking. In order to determine the infectivity of A. variegatum ticks by E. ruminantium, we analysed 500 un-engorged A. variegatum ticks collected by hand-picking from predilection sites from 182 cattle [115 ticks from 82 cattle at Société de Développement et d’Exploitation des Productions Animales (SODEPA) Dumbo ranch (SDR) and 385 ticks from 100 cattle at the Upper Farms ranch (UFR)] by amplification of the open reading frame (ORF) 2 of the pCS20 region of E. ruminantium. PCR amplification of the 279 bp fragment of the pCS20 region detected E. ruminantium DNA in 142 (28.4 %) of the 500 ticks with a higher infection rate (47/115; 40.9 %) observed in ticks from SDR and 24.7 % (95/385) of ticks collected from cattle at UFR. Twenty five randomly selected PCR products were sequenced and results indicated that some of the isolates shared homology with one another and to sequences of E. ruminantium in the GenBank. This report represents the first molecular evidence of E. ruminantium infection in A. variegatum ticks in Cameroon and suggests possible exposure of cattle to this pathogen in our environment.     

Field sampling of unfed adults ofAmblyomma hebraeum Koch

No methods have previously been available for the field sampling of unfed adults ofAmblyomma hebraeum. We released 2000 unfed adults into a 5-m² area in mopane woodland in southeastern Zimbabwe. The ticks sought shelter beneath the debris on the soil surface but emerged and became active in host seeking when stimulated. Effective stimuli were the odours of cattle and sheep and high concentrations of carbon dioxide from dry ice. The ticks did not respond to low concentrations of carbon dioxide, vibrations generated by stamping the ground with poles, or two volatile components of ox breath known to attract tsetse flies. The presence of humans in the release area also had little or no effect in stimulating the ticks. As adults ofA. hebraeum are large and conspicuous they can easily be collected from the soil surface, either manually or using a vacuum device, after stimulation by cattle or the release of high concentrations of carbon dioxide.     

Pheromone/acaricide mixtures in the control of the tickAmblyomma hebraeum: Effects of acaricides on attraction and attachment

Unfed adults and nymphs of the bont tickAmblyomma hebraeum Koch are attracted to hosts on which fed males, emitting an aggregation-attachment pheromone (AAP), are attached. Pheromone/acaricide mixtures have the potential to selectively attract and kill these ticks. We have investigated the effects of three acaricides, amitraz (an amidine), flumethrin (a synthetic pyrethroid) and chlorfenvinphos (an organophosphate), combined with AAP, on the attraction and attachment of the unfed adults. Attraction, measured in field assays involving AAP and CO₂, was not inhibited by any of the acaricides. Attachment was measured over 24 h on the ears of rabbits which had been treated with AAP and mixtures of AAP and the acaricides. None of the acaricides inhibited initial attachment. Flumethrin caused rapid and high mortality in attached and unattached ticks. Chlorfenvinphos caused little mortality in the first 24 h on the ears of the rabbits, but 75% of the exposed ticks died over the next 14 days while held in an incubator. Amitraz caused the ticks to detach after an initial period of attachement; there was little mortality in the detached ticks over the next two weeks and they could later be induced to re-attach to other rabbits. Flumethrin was considered to be the compound of choice for use in pheromone/acaricide mixtures.     

The use of time-series analysis to forecast bont tick (Amblyomma hebraeum) infestations in Zimbabwe

Studying the dynamics of tick infestations on cattle is an essential step in developing optimal strategies for tick control. Successful strategic tick control requires accurate predictions of when tick infestations will reach predetermined threshold levels. In the case ofAmblyomma hebraeum, earlier work has shown that there is no consistent pattern of seasonal activity. This means that a statistical model for predictingA. hebraeum infestations cannot reliably use climatic factors as the only independent variables. An alternative method is to apply time-series, or auto-regressive moving-average (ARMA), analysis which uses only the past population patterns to predict future trends. This technique was applied to a data set consisting of 108 weekly tick counts ofA. hebraeum (adult males, standard females, flat females and standard nymphs), conducted at an experimental station in southeastern Zimbabwe. The ability of the ARMA models to fit and predict actual tick infestations was judged using two sets of criteria. The first set focused on the goodness-of-fit, and used the adjustedR ² values,Q statistic and the Akaike Information Criteria. The second set of criteria measured the forecasting accuracy of an estimated equation, and consisted of regressing a 9-period forecast against an actual out-of-sample data set not used in the estimation process. The root mean square error of the forecast was also considered when comparing several models for the same data set. Using these criteria, the models estimated using the ARMA technique were judged to both fit and forecast with sufficient accuracy to warrant their use in strategic tick control. Although the success of using ARMA to forecastA. hebraeum is partly due to the non-seasonal behaviour of the species, the results presented here suggest that it is worthwhile exploring the use of ARMA techniques to model the dynamics of other tick species. Where independent variables exert considerable influence on the dynamics of a tick species, these variables can be incorporated into an ARMA-style model.     

Resistance of indigenous African cattle to the tickAmblyomma hebraeum

Field collections ofAmblyomma hebraeum Koch adults from six breeds of cattle were conducted on two farms in the Northern Transvaal. The density ofA. hebraeum adults was highest on Simmentaler cows, followed by Santa gertrudis, Africaner, Bonsmara, Brahman and Nguni. Indigenous breeds, namely Nguni, Bonsmara and Africaner, have the highest level of resistance toA. hebraeum. The relationship between tick abundance and the high level of resistance found in the indigenous breeds is discussed.     

Resistance and cross-resistance in rabbits to adults of three species of African ticks (Acari: Ixodidae)

Resistance to Rhipicephalus appendiculatus, Amblyomma variegatum and Amblyomma hebraeum was investigated in the laboratory by infesting rabbits with adults of each of the three species followed by homospecific or heterospecific secondary infestations. Significantly lower female engorged weights and egg mass weights were taken as evidence of protective immunity. Following a single infestation with adults, rabbits developed homospecific protective immunity (resistance) to only R. appendiculatus and A. hebraeum; primary infestation with A variegatum did not protect against secondary infestation with the same species. There was no cross-resistance (heterospecific protective immunity) between the species except for one-way protection between R. appendiculatus and A. variegatum; primary infestation with R. appendiculatus protected against secondary infestation with A. variegatum, but not vice versa. The results from ELISA did not indicate any correlation between serum antibodies to soluble antigens from salivary gland extracts and protective immunity. Post-infestation sera from rabbits infested with each of the three species reacted strongly to their respective salivary gland extracts. Despite the high reactivity of A. variegatum serum with salivary gland antigens from all three species, A. variegatum-infested rabbits did not show any homospecific or heterospecific immunity; on the other hand, although R. appendiculatus serum did not react positively to A. variegatum antigens, infestation with R. appendiculatus protected against a subsequent A. variegatum infestation.     

Seasonal occurrence of the bont tick (Amblyomma hebraeum) in the southern lowveld of Zimbabwe

The seasonal occurrence of the bont tickAmblyomma hebraeum was recorded over 2 years on 20 Brahman cattle held in a 240-ha paddock at Mbizi in southeastern Zimbabwe. The cattle were infested with all life cycle stages throughout the study period, and no clearly defined seasonal patterns were recorded. Males remained attached for up to about 6 months, and consequently accumulated on the cattle and outnumbered females considerably. The cattle did not acquire resistance toA. hebraeum and the abundance of the adults increased steadily over the 2 years of sampling. The occurrence of adults and nymphs on hosts appeared to be largely independent of weather, and these stages were active over the entire range of temperature and relative humidity recorded during the study period. It was concluded that unfed adults and nymphs are able to engage in host-seeking irrespective of weather conditions as they do not await hosts on the vegetation but emerge from protected microhabitats in response to specific stimuli from hosts, notably, carbon dioxide and the aggregation-attachment pheromone emitted by attached males. This behavior may explain the reported absence of a consistent pattern of seasonal occurrence ofA. hebraeum at different locations in southeastern Africa.     

The local effect of hypersensitive or inflammatory reactions to nymphal Amblyomma variegatum on simultaneous infections with Dermatophilus congolensis

Amblyomma variegatum nymphs were applied to sites infected with Dermatophilus congolensis on eight rabbits. Four rabbits were previously sensitized to the fecding of nymphal A. variegatum to produce hypersensitive reactions to the tick feeding; the remaining four rabbits had no previous exposure to nymphal A. variegatum and produced inflammatory reactions to the tick feeding.The resulting dermatophilosis infections were assessed for three weeks and there was a correlation between the position of the inflammatory tick attachment sites and the foci of infection. There was a significant increase in the lesions at sites with inflammatory reactions to the ticks, compared with sites not exposed to tick feeding; these differences appeared to be due to individual variation in the host response and were not sustained throughout the assessment.     

Rickettsia africae infection rates and transovarial transmission in Amblyomma hebraeum ticks in Mnisi,Bushbuckridge, South Africa

Rickettsia africae is a gram-negative bacterium, which causes African tick bite fever (ATBF) in humans. ATBF is a febrile disease mainly affecting travellers to southern Africa. This bacterium is known to be transmitted by Amblyomma hebraeum and Amblyomma variegatum ticks. In southern Africa, the principal vector is A. hebraeum. Febrile disease is a serious issue in the study area. There is a high prevalence of non-malaria illness caused by Rickettsia, so there is a need to have more knowledge on these species. Infection rates and transovarial transmission efficiency of R. africae in A. hebraeum ticks were investigated in a rural area of Mpumalanga province, South Africa. Adult and engorged A. hebraeum female ticks were collected from cattle. Larvae were collected by dragging a cloth at ground level using 100 steps, equivalent to an area of 100 m². Tick identification was performed according to standard taxonomic keys using a microscope. Engorged ticks were incubated to oviposit and egg masses were collected. DNA was extracted from the ticks, larvae and egg masses, and screened for gltA and ompA genes, using quantitative real-time PCR and conventional PCR, respectively. Positive ompA amplicons were sequenced and phylogenetic analysis showed 99.8-100% identity with R. africae. Infection rates were 13.7 and 12.7% for adults and larvae, respectively. Transovarial transmission of R. africae in A. hebraeum from this study was 85.7%. The results provide a clear indication that people living in the study area and travellers that visit the area are at risk of contracting ATBF.