Estimating the distribution and abundance of Rhipicephalus appendiculatus in Africa

p67 gene alleles sequence analysis reveals Theileria parva parasites associated with East Coast fever and Corridor disease in buffalo from Zambia

Theileriosis caused by Theileria parva infections is responsible for high cattle mortalities in Zambia. Although infected buffalo are a risk to cattle, the characterization of T. parva parasites occurring in this host in Zambia has not been reported. Furthermore, considering the advances in the development of a p67 subunit vaccine, the knowledge of p67 genetic and antigenic diversity in both cattle and buffalo associated T. parva is crucial. Therefore, blood samples from buffalo (n=43) from Central, Eastern and Southern provinces, and cattle (n=834) from Central, Copperbelt, Eastern, Lusaka, and Southern provinces, were tested for T. parva infection and the parasites characterized by sequencing the gene encoding the p67 antigen. About 76.7 % of buffalo and 19.3 % of cattle samples were PCR positive for T. parva. Three of the four known p67 allele types (1, 2 and 3) were identified in parasites from buffalo, of which two (allele types 2 and 3) are associated with T. parva parasites responsible for Corridor disease. Only allele type 1, associated with East Coast fever, was identified from cattle samples, consistent with previous reports from Zambia. Phylogenetic analysis revealed segregation between allele type 1 sequences from cattle and buffalo samples as they grouped separately within the same sub-clade. The high occurrence of T. parva infection in buffalo samples investigated demonstrates the risk of Corridor disease infection, or even outbreaks, should naïve cattle co-graze with infected buffalo in the presence of the tick vector. In view of a subunit vaccine, the antigenic diversity in buffalo associated T. parva should be considered to ensure broad protection. The current disease control measures in Zambia may require re-evaluation to ensure that cattle are protected against buffalo-derived T. parva infections. Parasite stocks used in 'infection and treatment' immunization in Zambia, have not been evaluated for protection against buffalo-derived T. parva parasites currently circulating in the buffalo population.

A systematic review of ticks and tick-borne pathogens of cattle reared by smallholder farmers in South Africa

Ticks are important ectoparasites of domestic animals, wild animals and humans. They spread a variety of infective agents such as protozoans, viruses, and bacteria. Cattle reared by smallholder farmers are susceptible to ticks and tick-borne pathogens due to the type of production system practiced by the farmers. Hence, this review was focused on the occurrence of ticks and tick-borne pathogens in cattle reared by smallholder farmers in South Africa. The systematic search produced a total of 13,408 articles from four databases, and after screening processes, the review utilized 23 articles published between 1983 and 2023. A total of 26 tick species belonging to seven genera were identified in the reviewed articles, with Rhipicephalus (Boophilus) decoloratus and Rhipicephalus evertsi evertsi being the most frequently reported tick species in South Africa followed by Amblyomma hebreum, Rhipicephalus appendiculatus, Hyalomma marginatum rufipes, Rhipicephalus microplus, Rhipicephalus follis, Rhipicephalus gertrudae and Hyalomma truncatum. The most frequently reported tick-borne pathogens across the provinces included Babesia bigemina, Babesia bovis, and Anaplasma marginale, with Eastern Cape Province accounting for most of the records followed by KwaZulu-Natal and Mpumalanga Provinces. The findings of this review confirm that cattle reared by smallholder farmers harbour various ticks and tick-borne pathogens of veterinary, public health and economic importance, and regular monitoring of tick infestations in South Africa is recommended to avoid disease outbreaks.

Prevalence of tick-borne pathogens in Rhipicephalus species infesting domestic animals in Africa: A systematic review and meta-analysis

Rhipicephalus ticks transmit important tick-borne pathogens (TBPs) such as Anaplasma, Babesia, and Theileria spp. which cause major economic losses in livestock production and contribute to emerging zoonotic diseases. A vast amount of data is available based on the demonstration of these pathogens in various host tissues, with limited information on the prevalence of these TBPs and their vectors. Quantifying TBPs infection rates among Rhipicephalus spp. is essential for the effective control and management of TBDs in domestic animals and surveillance of emerging diseases in humans, as they have close social associations. This review summarizes the prevalence of TBPs in Rhipicephalus spp. from domestic animals of Africa. A thorough search was done in SCOPUS, Web of Knowledge, PubMed, Google Scholar, and library sources from 2000 to 2022. All research in Africa reporting TBPs infection rates in Rhipicephalus spp. were included in the selection criteria. The meta-analysis evaluated publication bias using funnel plots to analyze the observed heterogeneity and applied a quality effects model. Prevalence estimates were based on data from 46 studies reporting TBPs infection rates in Rhipicephalus spp. from northern and sub-Saharan Africa. Sub-group analysis was done by geographic region and tick genus. A total of 12,368 Rhipicephalus spp. collected from domestic animals in Africa were used in the meta-analysis. The quality effects model revealed a high degree of heterogeneity among studies on the various TBPs. The overall prevalence of detected TBPs such as Theileria spp. was 8% (95% CI: 3-15%), Rickettsia spp. 3% (95% CI: 0-9%), Ehrlichia spp. 7% (95% CI: 2-14%), Anaplasma spp. 8% (95% CI: 2-16%), Coxiella spp. 10% (95% CI: 1-26%) and Babesia spp. 6% (95% CI: 2-12%). Northern Africa had the highest prevalence of Anaplasma spp. 12% (95% CI: 3-25%) and Theileria spp. 16% (95% CI: 0-42%). Whilst West Africa had the highest prevalence for Ehrlichia spp. 12% (95% CI: 3-24%) and eastern Africa for Rickettsia spp. 8% (95% CI: 4-12%). This is a systematic and quantitative investigation of the various TBPs detected in Rhipicephalus tick vectors from domestic animal hosts in Africa. The findings demonstrate considerable species variation across the African continent and offer preliminary estimates of infection rates for the continent.

Linking spatial distribution of Rhipicephalus appendiculatus to climatic variables important for the successful biocontrol by Metarhizium anisopliae in Eastern Africa

Cattle production is constantly threatened by diseases like East Coast fever, also known as theileriosis, caused by the protozoan parasite Theileria parva which is transmitted by ticks such as the brown ear tick, Rhipicephalus appendiculatus. To reduce the extensive use of chemical acaricides, fungal-based microbial control agents such as Metarhizium anisopliae have been tested and show promising results against R. appendiculatus both in field and in semi-field experiments in Africa. However, no known endeavors to link the spatial distribution of R. appendiculatus to climatic variables important for the successful application of M. anisopliae in selected East African countries exists. This work therefore aims to improve the successful application of M. anisopliae against R. appendiculatus by designing a temperature-dependent model for the efficacy of M. anisopliae against three developmental stages (larvae, nymphs, adults) of R. appendiculatus. Afterward a spatial prediction of potential areas where this entomopathogenic fungus might cause a significant epizootic in R. appendiculatus population in three selected countries (Kenya, Tanzania, Uganda) in Eastern Africa were generated. This can help to determine whether the temperature and rainfall at a local or regional scale might give good conditions for application of M. anisopliae and successful microbial control of R. appendiculatus.

Models for Studying the Distribution of Ticks and Tick-Borne Diseases in Animals: A Systematic Review and a Meta-Analysis with a Focus on Africa

Ticks and tick-borne diseases (TTBD) are constraints to the development of livestock and induce potential human health problems. The worldwide distribution of ticks is not homogenous. Some places are ecologically suitable for ticks but they are not introduced in these areas yet. The absence or low density of hosts is a factor affecting the dissemination of the parasite. To understand the process of introduction and spread of TTBD in different areas, and forecast their presence, scientists developed different models (e.g., predictive models and explicative models). This study aimed to identify models developed by researchers to analyze the TTBD distribution and to assess the performance of these various models with a meta-analysis. A literature search was implemented with PRISMA protocol in two online databases (Scopus and PubMed). The selected articles were classified according to country, type of models and the objective of the modeling. Sensitivity, specificity and accuracy available data of these models were used to evaluate their performance using a meta-analysis. One hundred studies were identified in which seven tick genera were modeled, with Ixodes the most frequently modeled. Additionally, 13 genera of tick-borne pathogens were also modeled, with Borrelia the most frequently modeled. Twenty-three different models were identified and the most frequently used are the generalized linear model representing 26.67% and the maximum entropy model representing 24.17%. A focus on TTBD modeling in Africa showed that, respectively, genus Rhipicephalus and Theileria parva were the most modeled. A meta-analysis on the quality of 20 models revealed that maximum entropy, linear discriminant analysis, and the ecological niche factor analysis models had, respectively, the highest sensitivity, specificity, and area under the curve effect size among all the selected models. Modeling TTBD is highly relevant for predicting their distribution and preventing their adverse effect on animal and human health and the economy. Related results of such analyses are useful to build prevention and/or control programs by veterinary and public health authorities.

The Unexpected Holiday Souvenir: The Public Health Risk to UK Travellers from Ticks Acquired Overseas

Overseas travel to regions where ticks are found can increase travellers' exposure to ticks and pathogens that may be unfamiliar to medical professionals in their home countries. Previous studies have detailed non-native tick species removed from recently returned travellers, occasionally leading to travel-associated human cases of exotic tick-borne disease. There are 20 species of tick endemic to the UK, yet UK travellers can be exposed to many other non-native species whilst overseas. Here, we report ticks received by Public Health England's Tick Surveillance Scheme from humans with recent travel history between January 2006 and December 2018. Altogether, 16 tick species were received from people who had recently travelled overseas. Confirmed imports (acquired outside of the UK) were received from people who recently travelled to 22 countries. Possible imports (acquired abroad or within the UK) were received from people who had recently travelled to eight European countries. Species-specific literature reviews highlighted nine of the sixteen tick species are known to vector at least one tick-borne pathogen to humans in the country of acquisition, suggesting travellers exposed to ticks may be at risk of being bitten by a species that is a known vector, with implications for novel tick-borne disease transmission to travellers.

Genetic and antigenic variation of the bovine tick-borne pathogen Theileria parva in the Great Lakes region of Central Africa

Background

Theileria parva causes East Coast fever (ECF), one of the most economically important tick-borne diseases of cattle in sub-Saharan Africa. A live immunisation approach using the infection and treatment method (ITM) provides a strong long-term strain-restricted immunity. However, it typically induces a tick-transmissible carrier state in cattle and may lead to spread of antigenically distinct parasites. Thus, understanding the genetic composition of T. parva is needed prior to the use of the ITM vaccine in new areas. This study examined the sequence diversity and the evolutionary and biogeographical dynamics of T. parva within the African Great Lakes region to better understand the epidemiology of ECF and to assure vaccine safety. Genetic analyses were performed using sequences of two antigen-coding genes, Tp1 and Tp2, generated among 119 T. parva samples collected from cattle in four agro-ecological zones of DRC and Burundi.

Results

The results provided evidence of nucleotide and amino acid polymorphisms in both antigens, resulting in 11 and 10 distinct nucleotide alleles, that predicted 6 and 9 protein variants in Tp1 and Tp2, respectively. Theileria parva samples showed high variation within populations and a moderate biogeographical sub-structuring due to the widespread major genotypes. The diversity was greater in samples from lowlands and midlands areas compared to those from highlands and other African countries. The evolutionary dynamics modelling revealed a signal of selective evolution which was not preferentially detected within the epitope-coding regions, suggesting that the observed polymorphism could be more related to gene flow rather than recent host immune-based selection. Most alleles isolated in the Great Lakes region were closely related to the components of the trivalent Muguga vaccine.

Conclusions

Our findings suggest that the extensive sequence diversity of T. parva and its biogeographical distribution mainly depend on host migration and agro-ecological conditions driving tick population dynamics. Such patterns are likely to contribute to the epidemic and unstable endemic situations of ECF in the region. However, the fact that ubiquitous alleles are genetically similar to the components of the Muguga vaccine together with the limited geographical clustering may justify testing the existing trivalent vaccine for cross-immunity in the region.

Vasoconstriction induced by salivary gland extracts from ixodid ticks

In their quest for blood, most haematophagous parasites secrete vasodilators in their saliva to counter the host haemostatic response of vasoconstriction. Surprisingly, salivary gland extracts from adult female Dermacentor reticulatus and Rhipicephalus appendiculatus ticks induced constriction in a rat femoral artery model; males induced vasoconstriction or vasodilation depending on the time of feeding. Based on comparative HPLC fractionation, the active compounds inducing vasoconstriction do not appear to be prostaglandins (which ticks normally use as vasodilators). Vasoconstriction may be unique to ixodid ticks, helping them control blood flow during their prolonged blood-feeding of up to 10 days or more.

Assessing the statistical relationships among water-derived climate variables, rainfall, and remotely sensed features of vegetation: implications for evaluating the habitat of ticks

Ticks are sensitive to changes in relative humidity and saturation deficit at the microclimate scale. Trends and changes in rainfall are commonly used as descriptors of field observations of tick populations, to capture the climate niche of ticks or to predict the climate suitability for ticks under future climate scenarios. We evaluated daily and monthly relationships between rainfall, relative humidity and saturation deficit over different ecosystems in Europe using daily climate values from 177 stations over a period of 10 years. We demonstrate that rainfall is poorly correlated with both relative humidity and saturation deficit in any of the ecological domains studied. We conclude that the amount of rainfall recorded in 1 day does not correlate with the values of humidity or saturation deficit recorded 24 h later: rainfall is not an adequate surrogate for evaluating the physiological processes of ticks at regional scales. We compared the Normalized Difference Vegetation Index (NDVI), a descriptor of photosynthetic activity, at a spatial resolution of 0.05°, with monthly averages of relative humidity and saturation deficit and also determined a lack of significant correlation. With the limitations of spatial scale and habitat coverage of this study, we suggest that the rainfall or NDVI cannot replace relative humidity or saturation deficit as descriptors of tick processes.

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.

Modelling the impact of climate change on spatial patterns of disease risk: sheep blowfly strike by Lucilia sericata in Great Britain

Understanding the spatial scale and temporal pattern of disease incidence is a fundamental prerequisite for the development of appropriate management and intervention strategies. It is particularly critical, given the need to understand the elevated risks linked to climate change, to allow the most likely changes in the distribution of parasites and disease vectors to be predicted under a range of climate change scenarios. Using statistical models, the spatial distribution and climatic correlates of a range of parasites and diseases have been mapped previously, but their development into dynamic, predictive tools is less common. The aim of the work described here, was to use a species distribution model to characterise the environmental determinants of the monthly occurrence of ovine cutaneous myiasis (blowfly strike) by Lucilia sericata, the most frequent primary agent of northern European myiasis, and to then use this model to describe the potential spatial changes that might be expected in response to predicted climate change in Great Britain. The model predicts that the range of elevated temperatures predicted by current climate change scenarios will result in an increase in the risk of strike and an elongated blowfly season. However, even for the most rapid warming scenario predictions over the next 70 years, strike is not predicted to occur throughout the winter. Nevertheless, in this latter case, parts of central and southern England are likely to become too hot and dry for strike by L. sericata, to persist in mid-summer. Under these conditions, it is possible that other, more pathogenic Mediterranean agents of myiasis, such as Wolfhartia magnifica, could potentially replace L. sericata. Where the phenology of strike is altered by climate change, as predicted here, significant changes to the timing and frequency of parasite treatments and husbandry practices, such as shearing, will be required to manage the problem. The results suggest that the modelling approach adopted here could be usefully applied to a range of disease systems.

Cattle ticks of the genera Rhipicephalus and Amblyomma of economic importance in Tanzania: distribution assessed with GIS based on an extensive field survey

In order to implement a robust integrated tick and tick-borne disease control programme in Tanzania, based on ecological and epidemiological knowledge of ticks and their associated diseases, a national tick and sero-surveillance study was carried out in all 21 regions of the mainland, as well as on Mafia Island, between 1998 and 2001. The current distributions of Rhipicephalus appendiculatus, R. pravus, Amblyomma variegatum, A. gemma, and A. lepidum are illustrated and discussed. Tick distribution maps were assessed using the Weights-of-Evidence method (WofE), and employing temperature, humidity, NDVI, rainfall, and land-cover predictive data. Ground-truthing was done to check correspondence both of the data employed in prediction with land-cover characteristics discerned in the field as well as of the surveyed and predicted tick distributions. Statistical methods were used to analyse associations of the tick species with their environment, cattle density, and other ticks. Except for R. appendiculatus, no appreciable changes were demonstrated in the predicted and observed tick distributions compared to the existing maps that originated in the 1950-1960s. Cattle density influenced the distribution of A. variegatum and, to a certain extent, of A. lepidum, but had no appreciable influence on the distribution of any of the other ticks discussed in this paper, neither did livestock movement. Distinct differences for environmental requirements where observed between different tick species within the same genus. The predictive maps of R. appendiculatus and R. pravus suggest their mutually exclusive distribution in Tanzania, and simultaneous statistical analysis showed R. pravus as a greater specialist. Of the three Amblyomma species, A. variegatum is the most catholic tick species in Tanzania, while both A. gemma and A. lepidum belong to the more specialized species. Despite dissimilar habitat preferences, all three Amblyomma spp. co-exist in central Tanzania, where very heterogeneous habitats may simultaneously satisfy the environmental requirements of all three species. The current study, conducted about 4 decades after the last major survey activities, has shown that changing livestock policies, unrestricted livestock movement and a continuous change in climatic/environmental conditions in Tanzania have brought about only limited changes in the distribution patterns of R. appendiculatus, R. pravus and the three Amblyomma species investigated. Whether this observation indicates a relative indifference of these ticks to environmental and/or climate changes allows room for speculation.

GIS tools for tick and tick-borne disease occurrence

Geographic information systems (GIS), their fundamental components and technologies are described. GIS is a computer-based system enabling the storage, integration, query, display and analysis of data using information on data location. Further, remote sensing (RS) methods and their application in landscape characterization are described. Landscape pattern analysis, combined with statistical analysis, allows the determination of landscape predictors of disease risk. This makes RS/GIS a powerful set of tools for disease surveillance, enabling the prediction of potential disease outbreaks and targeting intervention programs. The 'pre-GIS era' is briefly described including the early mapping of tick distribution, analyses and the display of biogeographical and medical data. The theory of natural focality of diseases (NFD) is explained and its significance in tick-borne diseases (TBD) research is discussed. Many problems of tick ecology and TBD epidemiology and epizootology have been addressed by means of GIS and examples of these studies are presented and discussed.

Distribution of tsetse and ticks in Africa: past, present and future

The current concern over the effects of global warming has rekindled interest in the neglected topic of vector distribution. In order to predict the future, however, we must first comprehend the past and present. In this review, David Rogers and Sarah Randolph discuss the alternative biological and statistical approaches to understanding the present-day distributions of vectors, and make predictions about how these might change with global warming.

Distribution, abundance, and habitat preferences of Ixodes ricinus (Acari: Ixodidae) in northern Spain

Ixodes ricinus (L.) was collected by standard dragging in 2,082 different sites in 18 broad vegetation categories in northern Spain to explore the influence of vegetation on its abundance. Of these, 785 sites were surveyed in 1995, 636 in 1996, and 661 in 1997. The impact of habitat features on differences in tick numbers is addressed. The tick was present in low numbers in areas of old, heterogeneous coniferous forests. Ticks appeared to prefer sites that had substantial secondary plant growth such as river canopies, heterogeneous Pinus uncinata forests, mixed forests, and deciduous heterogeneous woods. Highest tick abundance was recorded for sites that contained Quercus spp., as well as for mixed old forests that had many ecotones. I. ricinus was absent in open habitats, homogeneous young coniferous forests, and open hillsides. These differences were attributed to greater shrub cover and litter depth, which created more favorable microclimatic conditions for tick survival. The abundance of I. ricinus nymphs was not homogeneous in sites within the same habitat category and vegetation physiognomy at these sites did not appear to cause differences in tick abundance. Analysis of variance (ANOVA) indicated that variation in tick abundance could be explained by the exposure of the sampled site, at least for some zones within deciduous forest categories. However, this factor did not explain the variation observed in other habitats. Temperature and vegetation (normalized derived vegetation index) features were recorded daily by remotely sensed imagery throughout the study period and the data were used to obtain long-term mean and maximum values of the physical parameters considered. Multiple regression analysis performed between these long-term abiotic factors and nymphal abundance in positive sites showed high relationship (R2 coefficients) for every habitat category and explained >50% of the variation in tick abundance.

Ticks and tick-borne disease systems in space and from space

Analyses within geographical information systems (GISs) indicate that small- and large-scale ranges of hard tick species (Ixodidae) are determined more by climate and vegetation than by host-related factors. Spatial distributions of ticks may therefore be analysed by statistical methods that seek correlations between known tick presence/absence and ground- or remotely-sensed (RS) environmental factors. In this way, local habitats of Amblyomma variegatum in the Caribbean and Ixodes ricinus in Europe have been mapped using Landsat RS imagery, while regional and continental distributions of African and temperate tick species have been predicted using multi-temporal information from the National Oceanic and Atmospheric Administration-Advanced Very High Resolution Radiometer (NOAA-AVHRR) imagery. These studies illustrate ways of maximizing statistical accuracy, whose interpretation is then discussed in a biological framework. Methods such as discriminant analysis are biologically transparent and interpretable, while others, such as logistic regression and tree-based classifications, are less so. Furthermore, the most consistently significant variable for predicting tick distributions, the RS Normalized Difference Vegetation Index (NDVI), has a sound biological basis in that it is related to moisture availability to free-living ticks and correlated with tick mortality rates. The development of biological process-based models for predicting the spatial dynamics of ticks is a top priority, especially as the risk of tick-borne infections is commonly related not simply to the vector's density, but to its seasonal population dynamics. Nevertheless, using statistical pattern-matching, the combination of RS temperature indices and NDVI successfully predicts certain temporal features essential for the transmission of tick-borne encephalitis virus, which translate into a spatial pattern of disease foci on a continental scale.

Spatial statistics and geographical information systems in epidemiology and public health

This chapter surveys the principles behind spatial statistics and geographic information systems (GIS), and their application to epidemiology and public health. Like the other introductory chapters, it is aimed mainly to facilitate understanding in the chapters specific to certain diseases that follow, and to provide a short introduction to the field. A brief overview of spatial statistics and GIS is provided in the introduction. The sections that follow explore the ways in which we can map the distribution of disease, ways in which we can look for spatial patterns in the distribution of disease, and ways in which we can apply spatial statistics and GIS to the problem of identifying the causal factors of observed patterns. In the last section I discuss some of the ways in which these techniques have been applied to assist decision making for disease intervention, and conclude by discussing future developments in the field, and some of the issues surrounding the integration of spatial statistics and GIS.

Environmental information systems for the control of arthropod vectors of disease

Over the last decade, remote sensing technologies and geographical information systems have moved from the research arena into the hands of vector control specialists. This review explains remote sensing approaches and spatial information technologies used for investigations of arthropod pests and vectors of diseases affecting humans and livestock. Relevant applications are summarized with examples of studies on African horse sickness vector Culicoides midges (Diptera: Ceratopogonidae), malaria vector Anopheles and arbovirus vector culicine mosquitoes (Diptera: Culicidae), leishmaniasis vector Phlebotomus sandflies (Diptera: Psychodidae), trypanosomiasis vector tsetse (Diptera: Glossinidae), loaiasis vector Chrysops (Diptera: Tabanidae), Lyme disease vector Ixodes and other ticks (Acari: Ixodidae). Methods and their uses are tabulated and discussed with recommendations for efficiency, caution and progress in this burgeoning field.

Reducing a spatial database to its effective dimensionality for logistic-regression analysis of incidence of livestock disease

Large databases with multiple variables, selected because they are available and might provide an insight into establishing causal relationships, are often difficult to analyse and interpret because of multicollinearity. The objective of this study was to reduce the dimensionality of a multivariable spatial database of Zimbabwe, containing many environmental variables that were collected to predict the distribution of outbreaks of theileriosis (the tick-borne infection of cattle caused by Theileria parva and transmitted by the brown ear tick). Principal-component analysis and varimax rotation of the principal components were first used to select a reduced number of variables. The logistic-regression model was evaluated by appropriate goodness-of-fit tests.

Sustainable tick and tickborne disease control in livestock improvement in developing countries

Tick and tickborne disease (TTBD) control is a major component of animal health programmes protecting livestock, thereby enhancing global food security. The present methods for TTBD control are reviewed and an integrated use of the tools is recommended with a broader view of how to link TTBD control to the control of other parasitic diseases. The work of FAO in this field is presented and it is advocated that, although there are still areas that need further investigation, a stage has been reached where robust integrated TTBD control schemes, based on ecological and epidemiological knowledge of ticks and their associated diseases, can be promoted and implemented. Major challenges are the implementation of these policies in the field through the continuation of the present on-going programme in Africa and support to Latin America and Asia. The importance of involving all parties, governments, international and private organisations and the agrochemical industry in developing sustainable, cost-efficient control programmes is stressed and a global strategy is proposed. The main thrust should now be to convince policy makers on the adoption of the strategies and veterinarians and farmers on their implementation.

Climate, satellite imagery and the seasonal abundance of the tick Rhipicephalus appendiculatus in southern Africa: a new perspective

Recent predictive models for the distribution of the African tick Rhipicephalus appendiculatus Neumann, based on the computer packages CLIMEX and BIOCLIM and data derived from meteorological satellites, and for the seasonal dynamics of the same tick using the computer simulation models ECFXPERT and T3HOST, all have their limitations. Statistical analysis of the relationships between the seasonal abundance of all three life stages of this tick and climatic and satellite-derived data from five sites in southern Africa, taken from the literature, supports a new perspective that it is the timing of the questing activity of the desiccation-vulnerable larvae that determines the pattern of the tick's seasonal dynamics. The timing of the activity of nymphs and adults is determined by temperature-dependent development rates plus the delaying phenomenon of photoperiod-sensitive diapause, the timing and duration of which have evolved to achieve maximum generation survival by ensuring the occurrence of eggs and larvae during periods of optimal climatic conditions. The most important environmental factor appears to be night-time minimum temperature, determining condensation and saturation deficit and thus the tick's ability to replenish moisture lost during the daytime and so to survive while questing for hosts. It is the larvae whose numbers are correlated most closely with these factors, consistent with earlier experimental results showing larvae to be most susceptible to desiccating conditions. There is a statistical linkage between larval tick numbers and satellite imagery, arising from the correlation between larval numbers and minimum temperature and saturation deficit conditions, and in turn the relationship between these climatic conditions and the subsequent vegetational changes monitored by the satellites. Moisture availability to larvae is likely to be the critical factor throughout the geographical range of R. appendiculatus, but the precise combination of climatic conditions that optimize moisture availability and questing tick survival can be expected to vary geographically. The relationships between ticks, temperatures and satellite data in parts of equatorial Africa have yet to be established. These correlative patterns highlight both the critical life stage and environmental factors when trying to understand temporal, and ultimately spatial, variations in tick abundance.