A parasitological, molecular and serological survey of Hepatozoon canis infection in dogs around the Aegean coast of Turkey

Canine hepatozoonosis is caused by the tick-borne protozoon Hepatozoon spp. The prevalence of the infection in the Aegean coast of Turkey was investigated by examination of blood smear parasitology and polymerase chain reaction (PCR) using blood samples from 349 dogs collected from Central Aydin, Kusadasi, Selcuk, Central Manisa, Bodrum and Marmaris within the Aegean coast of Turkey. The indirect fluorescent antibody test (IFAT) for the detection of Hepatozoon canis antibodies was also used to detect the exposure rate to H. canis. PCR amplifying a 666bp fragment of 18S rRNA gene of Hepatozoon spp. was used in the epidemiological survey. The prevalence of Hepatozoon spp. infection was 10.6% by blood smear parasitology and 25.8% by PCR. IFAT revealed that 36.8% of serum samples were positive for antibodies reactive with Hepatozoon spp. The PCR products of 18S rRNA gene of Hepatozoon spp. isolated from six infected dogs, one isolate originating from each of the six different locations, were sequenced. The results of sequence analysis indicate that they are closely related to Indian and Japanese isolates of H. canis. This is the first epidemiological study on the prevalence of H. canis infection in the dog, in Turkey.

Theileriosis in a White-tailed Deer (Odocoileus virginianus) Fawn

A white-tailed deer (Odocoileus virginianus) fawn was collected in Missouri (USA) and submitted for diagnostic evaluation. Necropsy and histologic examination revealed severe Amblyomma americanum infestation, pronounced icterus, and marked hemosiderin deposition in the liver and spleen. Whole blood evaluation revealed a normocytic normochromic anemia and a piroplasm parasitemia of approximately 70%. The piroplasm was identified as Theileria cervi by polymerase chain reaction and sequencing of the V4 variable region of the 18S rRNA gene from a paraffin-embedded section of lung. Although T. cervi parasitemias have been commonly reported in healthy white-tailed deer, the severe parasitemia in this fawn may have contributed to overt clinical disease, perhaps as part of a combined malnutrition and parasitemia syndrome.

Hemorrhagic disease in dogs infected with an unclassified intraendothelial piroplasm in southern Brazil

A hemorrhagic disease affecting dogs in Brazil, referred to popularly as "nambiuvú" (bloody ears) and believed to be transmitted by ticks, has been observed in animals infected with an organism described originally in 1910 as a piroplasm, and known locally as Rangelia vitalii. In this series of 10 cases, the disease was characterized by anaemia, jaundice, fever, spleno- and lymphadenomegaly, hemorrhage in the gastrointestinal tract, and persistent bleeding from the nose, oral cavity and tips, margins and outer surface of the pinnae. The ixodid ticks Rhipicephalus sanguineus and Amblyomma aureolatum infested affected dogs from suburban and rural areas, respectively. Laboratory findings included regenerative anaemia, spherocytosis, icteric plasma and bilirubinuria. Those intracellular organisms were found in bone marrow smears but not in blood smears. Microscopically, zoites were seen within the cytoplasm of blood capillary endothelial cells. Parasitized and non-parasitized endothelial cells were positive immunohistochemically for von Willebrand factor (vWF). Langhans-type multinucleate giant cells were observed in the lymph nodes and choroid plexus. There was prominent erythrophagocytosis by macrophages in the lymph node sinuses and infiltration of the medullary cords by numerous plasma cells. Ultrastructurally, this organism had an apical complex that included a polar ring and rhoptries but no conoid. This parasite was contained within a parasitophorous vacuole that had a trilaminar membrane with villar protrusions and was situated in the cytoplasm of capillary endothelial cells. This organism tested positive by immunohistochemistry for Babesia microti. This pathogen was also positive by in situ hybridization for B. microti. Tentative clinical diagnosis in these cases was based on the history, clinical picture, haemogram and favorable response to therapy, and confirmed through microscopic examination of smears from the bone marrow or histological sections of multiple tissues, especially lymph nodes where zoites were most frequently found. The disease was reproduced by intravenous inoculation of blood from a naturally infected dog into an experimental dog. The authors demonstrate in this study that this organism is a protozoa of the phylum Apicomplexa, order Piroplasmorida. This piroplasm seems to be different from Babesia since it has an intraendothelial stage. Molecular phylogenetic analysis is necessary to better characterize this parasite and clarify its taxonomic status.

A longitudinal study of sero-conversion to tick-borne pathogens in smallholder dairy youngstock in Tanzania

A longitudinal study of sero-conversion of youngstock to the tick-borne pathogens Theileria parva, T. mutans, Anaplasma marginale, Babesia bigemina and B. bovis was conducted over two years on smallholder dairy farms in Tanga region, Tanzania. There was evidence of maternal antibodies to all tick-borne pathogens in animals less than 18 weeks of age. Seroprevalence increased as expected with age in animals older than this but seroprevalence profiles underestimated the force of infection due to waning antibody levels between samplings. By the end of the 2-year study, less than 50% of study animals had seroconverted to each of the tick-borne pathogens investigated, consistent with the low levels of tick attachment observed on the study animals. Some associations between seroconversion to tick-borne pathogens, and counts of their known tick vectors on the animals, were identified as expected. However, some were not, suggesting that counts of some tick species may act as an index of rates of attachment of other vector species. Variation in acaricide treatment frequencies was not associated with variations in tick-borne pathogen seroprevalence suggesting that acaricides may be used more frequently than necessary on many farms. Most animals were zero-grazed, a management system associated with a significantly lower likelihood that animals seroconverted to any tick-borne pathogen except A. marginale. Seroprevalence varied locally with farm location (particularly for Babesia spp.) but was not well predicted by indices of ecological conditions. Our findings suggest that attempts to achieve a state of 'endemic stability' for tick-borne pathogens may be unreasonable on the smallholder dairy farms studied but reductions in the frequency of use of acaricides may be possible following prospective studies of effects on mortality and morbidity due to tick-borne pathogens.

[Ticks (Acarina: Ixodidae) as vectors and reservoirs of pathogen microorganisms in Spain]

Hard and soft-ticks are obligate haematophagous arachnids of medical and veterinary significance mainly because of the animal disease agents transmitted by them, which include an array of different pathogens (virus, bacteria, protozoa and nematodes). Ticks transmit microbes by several routes including salivary secretions, coxal fluids, regurgitation and faeces. Among the biological factors that contribute to the high vector potential of ticks are their living habits and characteristic properties of their saliva secretions and blood digestion. In the Iberian Peninsula, the prostriata tick Ixodes ricinus, and the metastriata Dermacentor marginatus, Rhipicephalus sanguineus and Hyalomma marginatum are the main species that could bite man, and are involved in the transmission of Borrelia burgdorferi sensu lato, several genoespecies of Rickettsia (R. conorii, R. slovaca, R. aeschlimannii) and Anaplasma phagocytophila.

Tick ecology: processes and patterns behind the epidemiological risk posed by ixodid ticks as vectors

The population ecology of ticks is fundamental to the spatial and temporal variation in the risk of infection by tick-borne pathogens. Tick population dynamics can only be fully understood by quantifying the rates of the demographic processes, which are influenced by both abiotic (climatic) factors acting on the free-living tick stages and biotic (host) responses to the tick as a parasite. Within the framework of a population model, I review methods and results of attempts to quantify (1) rates of tick development and the probability of diapause, (2) the probability of questing for hosts by unfed ticks, (3) the probability of ticks attaching to a host, and (4) tick mortality rates. Biologically, these processes involve the physiological and behavioural response of ticks to temperature, moisture stress and day length that result in specific patterns of seasonal population dynamics and host relationships. Temperate and tropical patterns will be illustrated with reference mostly toIxodes ricinusandRhipicephalus appendiculatus, respectively.

Tick–host interactions: saliva-activated transmission

The skin site at which ticks attach to their hosts to feed is the critical interface between the tick and its host, and tick-borne pathogens. This site is highly modified by the pharmacologically active molecules secreted in tick saliva. For pathogens, it is an ecologically privileged niche that many exploit. Such exploitation is referred to as saliva-activated transmission (SAT) – the indirect promotion of tick-borne pathogen transmission via the actions of bioactive tick saliva molecules on the vertebrate host. Here we review evidence for SAT and consider what are the most likely candidates for SAT factors among the tick pharmacopoeia of anti-haemostatic, anti-inflammatory and immunomodulatory molecules identified to date. SAT factors appear to differ for different pathogens and tick vector species, and possibly even depend on the vertebrate host species. Most likely we are searching for a suite of molecules that act together to overcome the redundancy in host response mechanisms. Whatever they turn out to be, the quest to identify the tick molecules that mediate SAT is an exciting one, and offers new insights to controlling ticks and tick-borne diseases.

Factors that influence the prevalence of acaricide resistance and tick-borne diseases

This manuscript provides a summary of the results presented at a symposium organized to accumulate information on factors that influence the prevalence of acaricide resistance and tick-borne diseases. This symposium was part of the 19th International Conference of the World Association for the Advancement of Veterinary Parasitology (WAAVP), held in New Orleans, LA, USA, during August 10-14, 2003. Populations of southern cattle ticks, Boophilus microplus, from Mexico have developed resistance to many classes of acaricide including chlorinated hydrocarbons (DDT), pyrethroids, organophosphates, and formamidines (amitraz). Target site mutations are the most common resistance mechanism observed, but there are examples of metabolic mechanisms. In many pyrethroid resistant strains, a single target site mutation on the Na(+) channel confers very high resistance (resistance ratios: >1000x) to both DDT and all pyrethroid acaricides. Acetylcholine esterase affinity for OPs is changed in resistant tick populations. A second mechanism of OP resistance is linked to cytochrome P450 monooxygenase activity. A PCR-based assay to detect a specific sodium channel gene mutation that is associated with resistance to permethrin has been developed. This assay can be performed on individual ticks at any life stage with results available in a few hours. A number of Mexican strains of B. microplus with varying profiles of pesticide resistance have been genotyped using this test. Additionally, a specific metabolic esterase with permethrin-hydrolyzing activity, CzEst9, has been purified and its gene coding region cloned. This esterase has been associated with high resistance to permethrin in one Mexican tick population. Work is continuing to clone specific acetylcholinesterase (AChE) and carboxylesterase genes that appear to be involved in resistance to organophosphates. Our ultimate goal is the design of a battery of DNA- or ELISA-based assays capable of rapidly genotyping individual ticks to obtain a comprehensive profile of their susceptibility to various pesticides. More outbreaks of clinical bovine babesisois and anaplasmosis have been associated with the presence of synthetic pyrethroid (SP) resistance when compared to OP and amidine resistance. This may be the result of differences in the temporal and geographic patterns of resistance development to the different acaricides. If acaricide resistance develops slowly, herd immunity may not be affected. The use of pesticides for the control of pests of cattle other than ticks can affect the incidence of tick resistance and tick-borne diseases. Simple analytical models of tick- and tsetse-borne diseases suggest that reducing the abundance of ticks, by treating cattle with pyrethroids for example, can have a variety of effects on tick-borne diseases. In the worst-case scenario, the models suggest that treating cattle might not only have no impact on trypanosomosis but could increase the incidence of tick-borne disease. In the best-case, treatment could reduce the incidence of both trypanosomosis and tick-borne diseases Surveys of beef and dairy properties in Queensland for which tick resistance to amitraz was known were intended to provide a clear understanding of the economic and management consequences resistance had on their properties. Farmers continued to use amitraz as the major acaricide for tick control after the diagnosis of resistance, although it was supplemented with moxidectin (dairy farms) or fluazuron, macrocyclic lactones or cypermethrin/chlorfenvinphos.

In vitro titration of Theileria parva tick derived stabilates

Immunization against the protozoan Theileria parva by infection and treatment has proved to be very efficient for the control of East Coast fever, an acute and often-fatal lymphoproliferative tick-borne disease of cattle in Eastern, Central and Southern Africa. The immunizing dose of live T. parva sporozoites used in this method is usually determined by in vivo titration. An alternative in vitro method of quantification of sporozoites in whole tick-derived stabilates is proposed. The method consists of incubating serially diluted T. parva stabilates with bovine peripheral blood lymphocytes, the host cell that is infected naturally. Allowing the cultures to incubate undisturbed for the full cultivation period (10 days) reduced the variability among replicate titrations. Fungal contaminations were avoided by centrifuging stabilates at 400 g prior to the incubation, which did not precipitate sporozoites significantly. Fungistatics, Nystatin and Flucytosine, did not appear to interfere with the in vitro development of T. parva but their effect on fungal growth was limited. In vitro titration data were compared to in vivo infection data for 2 stabilates. In vitro titration of T. parva sporozoites should allow more ethical and efficient research on the preparation and storage of T. parva tick-derived stabilates.

[Microscopic diagnosis of tick-borne diseases in Maghreb]

Direct microscopic examination of smears, carried out in the farm, in combination with the clinical symptoms, is in general the quickest and cheapest way to diagnose tick-borne diseases. It is however not always sufficiently specific, as different species of a parasite genus may ressemble each other morphologically. Also, it is not suitable for epidemiological studies. On the other hand, serological and molecular methods may be more sensitive and/or specific, but are not suitable for diagnosing the cause of disease in an individual animal and in any case are not sufficiently rapid. The focus of the paper is on practical details and pitfalls to be avoided in sample taking, smear preparation, fixing and staining, microscopic examination and interpretation of the results

Reverse line blotting: a new technique for the sensitive detection of tick borne pathogens

Recently, a new molecular diagnostic technique for tick borne pathogens has been developed and is called Reverse Line Blotting. This paper outlines the basis of this method and then illustrates its use for the analysis of blood samples obtained from Ugandan cattle and buffalo. The sensitivity and the specificity are discussed in relation to the use of this technique in the Maghreb

Identification of tick vectors of ovine theileriosis in an endemic region of Iran

This study was made to determine the population of ticks in infected sheep and attempting to identify the tick vectors of ovine theileriosis in an endemic area of Iran from 2000 to 2001. A total of 188 suspected cases of ovine theileriosis from 28 flocks were clinically examined and investigated for the presence of Theileria lestoquardi in appropriate blood smears and any tick species on body of sheep. In this study, 36.17% of sheep were infected to T. lestoquardi with a parasitemia of 0.01-15%. There was no significant differences between the rate of parasitemia in sheep and the frequency of infected ticks. We found that 61.1% of the animals harboured Hyalomma a. anatolicum, 33.42% Rhipicephalus sanguineus and 0.05% Hyalomma m. marginatum. The examination of 345 tick salivary glands showed that (15%) of salivary glands of H.a. anatolicum and (4%) of R. sanguineus contained Feulgen positive bodies. Seasonally, the prevalence of Theileria infection and H.a. anatolicum infestation in sheep reached the highest level in July (62.5%) and June (23.6%), while a decrease was observed in September (24.5%) and August (17.39%), respectively. The prevalence of Theileria infection in all age groups and between male and female sheep was statistically non-significant.

Overcoming constraints to meeting increased demand for Babesia bigemina vaccine in Australia

Demand for live trivalent tick fever vaccine containing Babesia bovis, Babesia bigemina and Anaplasma centrale produced by the Department of Primary Industries, Queensland, has increased from less than 10,000 doses in 1988 to 500,000 doses in 2001. This paper describes a series of trials aimed at overcoming certain constraints to obtain B. bigemina parasitised erythrocytes (PEs) on a large enough scale from infected splenectomised calves to meet the demand. Passage through a series of splenectomised calves failed to increase the yield per calf but we showed that the dose rate of infected cells could be reduced from the long-time standard of 1x10(7) to 2.5x10(6) without affecting immunogenicity and still leaving a safety margin of at least 50-fold for infectivity. This change quadrupled the potential yield of doses per calf and allowed the DPI to meet the increased demand for B bigemina in vaccine. Due to the high cost and limited availability of suitable, health tested donors, calves previously infected with B. bovis or A. centrale were used to provide B. bigemina organisms but the practice resulted in red cell agglutination in some batches of prepared vaccine. A trial is described where B. bigemina-infected red cells were washed by centrifugation to remove agglutinating antibodies. Washing had no effect on parasite viability and this method is now in routine use in the production of trivalent vaccine.

Proteolytic enzyme activity and attenuation of virulence in Theileria annulata schizont-infected cells

A field isolate of Theileria annulata (Uzbek strain) was obtained from calves infected by Hyalomma anatolicum ticks collected from an endemic region in Uzbekistan. Schizont-infected bovine cells that had been established and propagated in cell culture were examined for attenuation both in vivo, by inoculating cells from various passages into calves, and in vitro for metalloproteinase activity. During serial subcultivation a gradual reduction in virulence and in enzyme activity in cells infected with the Uzbek strain were observed. Complete attenuation of the Uzbek isolate was obtained at about passage 80, and only traces of proteolysis were detected in gelatin substrate gels. In contrast, there was no direct correlation between virulence and enzyme levels in an Israeli strain. While schizonts of the Israeli strain were completely attenuated at passage 80, proteolysis in the substrate gels was detected up to passage 197. Solid immunity was observed in calves immunized with attenuated T. annulata schizonts of the Uzbek strain upon challenge with the homologous H. excavatum sporozoites. For a strain to be used for vaccine production, it appears that animal inoculation still remains the most reliable method to assess the degree of attenuation and protection.

The impact of tick control on the productivity of indigenous cattle under ranch conditions in Uganda

The impact of tick control on the productivity of indigenous cattle was investigated in three herds of East African shorthorn Zebu and Zebu x Ankole (Nganda) breeds, maintained under three tick management systems practised under ranch conditions: twice-a-week dipping, once-a-month dipping, and no tick control. The milk production and the growth rates of pre-weaned and post-weaned calves were monitored once a month over a period of 34 months. Milk offtake was 23% higher during the heavy rainy seasons than in the long dry seasons. Twice-a-week dipping increased the milk offtake by 21% in the second year of study and prolonged the duration of lactation in cows. Similarly, twice-a-week dipping increased the pre-weaning growth rate by 39% in the second year of study, but had no significant effect on the post-weaning growth rate. Generally, the growth rate of calves were greatest during the heavy rainy seasons and least during the long dry seasons. These results provide a basis for assessing the losses under different tick management systems in the various production systems.

Retrospective seroepidemiological survey for human babesiosis in an area in Japan where a tick-borne disease is endemic

A total of 1,335 archived human sera collected in 1985 from an area in Japan where a tick-borne disease is endemic were examined by indirect immunofluorescence antibody test (IFAT) to estimate seroprevalence against three serologically distinct types of Babesia microti-like parasites; namely, Hobetsu, Kobe, and U.S. types. Eighteen sera (1.3%) were found to be IFAT-positive (titer 1:100-1:6,400), of which 14 and three were ascertained by Western blot analysis to be positive against the Hobetsu and Kobe types, respectively. In addition, four sera showed an IFAT titer of 1:100 against the U.S. type, but they appeared to be false-positive because they were cross-reactive against the Hobetsu and Kobe types, and also because a U.S.-type parasite has not been found in Japan. Our results suggest that human babesiosis in Japan occurred prior to the discovery of the index case in 1999 and that the infections were caused mainly by Hobetsu-type parasites.

Ticks and tick-borne diseases in Africa: a disease transmission model

A general disease transmission model is developed for a tick-borne disease for cattle. Both the tick and cow are possible hosts for the disease parasite. The two species are therefore classified as infected or uninfected. The tick individual is further classified as sedentary (off-host) or feeding (on-host). First conditions for the persistence of the tick population are investigated. A threshold quantity for the disease is derived which is dependent on both the tick and host population parameters and the two transmission rates: from ticks to cattle and vice versa. From the analysis persistence and non-persistence conditions for both the tick population and the disease are investigated. The effect of the presence of a second host species is introduced as an additional feature in the analysis.

Tick-borne parasitic diseases in cattle: current knowledge and prospective risk analysis related to the ongoing evolution in French cattle farming systems

Parasitic diseases, like babesiosis and theileriosis are transmitted by ticks: their occurrence is therefore linked to the size of the tick stock and the seasonality of the vectors. Babesia divergens bovine babesiosis transmitted by Ixodes ricinus is widespread and often reported in France. Serological prevalence is high, ranging from 20 to 80% according to the farms. Clinical incidence is low: around 0.4% for the whole cattle population. The endemic situation is unstable and clinical cases occur more frequently with farming system modifications. L. ricinus is a tick essentially found in woodlands and so, for the most part, is found in closed rural areas. The situation of the other bovine babesiosis (Babesia major) and theileriosis (Theileria orientalis) is not well documented in France. However, the epidemiology of parasitic diseases is changing, especially because of changes in the environmental characteristics, i.e. both farm and herd management conditions and also climatic conditions. These modifications can provoke an increase in the tick stocks, an increase in the contact rate between cattle and ticks, and an increase in the contact rate between cattle and the wild fauna, especially deer. This results in likely modifications of the endemic situation, with a higher risk of clinical babesiosis in the medium term.

IgG responses to salivary gland extract of Ixodes ricinus ticks vary inversely with resistance in naturally exposed sheep

Enzyme-linked immunosorbent assay (ELISA) was used to investigate the antibody responses of control sheep, and sheep naturally exposed to Ixodes ricinus Linné (Acari: Ixodidae) ticks, to salivary gland extract (SGE) proteins of partially fed, adult I. ricinus. Comparisons between responses of control sheep and naturally infested sheep by Western blot analysis suggested that variations in IgG responses of I. ricinus-exposed sheep were mostly associated with specific responses to I. ricinus SGE antigens. Sheep IgG responses were positively related to the numbers of adult ticks feeding per sheep at the time samples were collected, were greater during the spring than the autumn periods of I. ricinus activity and were inversely related to sheep resistance to ticks measured by the weights of nymphal I. ricinus that engorged on the sheep. These findings suggest that sheep lose their resistance to ticks due to polarization of a Th1 type response to some tick antigens towards a Th2 type response when sheep are exposed to high, natural tick infestations, or to seasonal conditions of relative nutritional stress. Potential consequences for the epidemiology of tick-borne diseases are discussed.

The impact of babesiosis on transfusion medicine

Babesiosis is an emerging zoonotic disease that has begun to have a noticeable impact on transfusion medicine. This is reflected in the growing medical literature on the topic. There has been no review to summarize the various ways in which babesiosis influences transfusion medicine. Babesiosis is the most frequently reported tick-borne pathogen to be transmitted by blood transmission. Until recently, it has been an underrecognized complication of blood transfusion. However, the increased use of blood products for an ever-increasing elderly and immunodeficient patient population has heightened awareness about this disease. Fortunately, the risk of acquiring a symptomatic infection through a blood transfusion is surprisingly low. Nevertheless, babesiosis should be included in the differential diagnosis of a febrile hemolytic illness in recipients of blood transfusions. Infected individuals who become chronic carriers and donate blood during asymptomatic periods pose the greatest risk to the blood supply. The exact risk that this parasite poses to our blood supply remains to be accurately assessed. Reported cases of transmission, to date, have involved only the transfusion of red blood cells (RBCs) and, more rarely, platelets. Transmission of these piroplasms through plasma alone has not been documented. Much of our understanding about this organism evoked host responses and its requirements for in vitro survival has come from studies on non-human vertebrates. These studies have shown that antigenic variation may play a significant role in the development of prolonged parasitemia, that complement-induced changes to erythrocytes are pivotal in facilitating protozoan entry into host RBCs, and that autoimmunity contributes to disease. Severe infections may require lifesaving exchange transfusions and even plasmapheresis. Controlled studies to clearly define specific indications, benefits, and objectives of this therapy are still needed. Despite the development of novel and improved diagnostic tests, these tests are not readily available for the mass screening of blood donors. Improved strategies to assess and prevent transfusion-associated babesiosis are required. Current measures cannot be relied on to identify infected donors with a high degree of sensitivity or to protect susceptible recipients from this parasite.

A simulation model for environmental population densities, survival rates and prevalence of Boophilus decoloratus (Acari: ixodidae) using remotely sensed environmental information

A simulation model for the African tick Boophilus decoloratus is presented. This model is based on the use of a dynamic life table that is driven by abiotic variables (temperature and vegetation status) remotely sensed (AVHRR sensor of the NOAA series of satellites) over time. The model incorporates temperature-dependent rates of egg production and development, climate-driven density-independent mortality rates, and density-dependent regulation of on-host stages. The model successfully describes both the seasonality and annual variation in the numbers of questing larvae and engorging females observed in eight sites throughout sub-Saharan Africa. Climate data from 1983 to 1999 in 10-day intervals are used as the basic input for modelling the dynamic patterns of activity at four different sites in Africa and to understand how abiotic factors can modulate the long-term life cycle of B. decoloratus.

Rickettsia africae, a tick-borne pathogen in travelers to sub-Saharan Africa

BACKGROUND

African tick-bite fever occurs after contact with ticks that carry Rickettsia africae and that parasitize cattle and game. Sporadic reports suggest that this infection has specific clinical and epidemiologic features.

METHODS

We studied patients who were tested for a rickettsial disease after returning from a visit to Africa or Guadeloupe. To assess the value of the microimmunofluorescence assay, Western blotting, and cross-adsorption assays, we compared the results of these tests in 39 patients in whom African tick-bite fever had been confirmed by the polymerase-chain reaction assay, cell culture, or both; 50 patients with documented R. conorii infection; and 50 blood donors. These diagnostic criteria were then applied to 376 additional patients who had returned from southern Africa and 2 who had returned from Guadeloupe and whose serum was being tested for rickettsial disease.

RESULTS

In the 39 patients with direct evidence of R. africae infection, the combination of microimmunofluorescence assay, Western blotting, and cross-adsorption assays showing antibodies specific for R. africae had a sensitivity of 0.56; however, each test had a positive predictive value and a specificity of 1.0. An additional 80 patients were found to have an R. africae infection on the basis of these serologic criteria. Infections with R. africae were acquired by visitors to 11 African countries and Guadeloupe. The illness was generally mild and was characterized by a rash in 46 percent of the patients; the rash was usually maculopapular or vesicular and rarely purpuric. Ninety-five percent of patients had an inoculation eschar or eschars, and 54 percent of these patients had multiple eschars, a finding that is unusual in patients with rickettsial infection.

CONCLUSIONS

In this series, R. africae was the cause of nearly all cases of tick-bite rickettsiosis in patients who became ill after a trip to sub-Saharan Africa.

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.

[Meningitis and encephalitis in 1998]

In 1998--3,024 cases of meningitis and 581 cases of encephalitis were reported. It was 1,436 cases less then in 1997. A significant decrease of enteroviral meningitidis was observed and strains of ECHO30 was not dominant, it was Cox B5. Among bacterial factors the most common was N. meningitidis. 131 sporadic cases of meningitis caused by this bacteria were reported with serotype B dominating (96%). There were 103 cases of bacterial meningitis caused by S. pneumoniae and 101 cases caused by H. influenzae b among those with confirmed diagnosis. There were 208 cases of tick-borne encephalitis, diagnosed mainly in endemic areas of Białystok and Suwałki voivodeships.

Molecular characterization of ticks and tick-borne pathogens

Ticks and their vertebrate hosts often carry several pathogens simultaneously, which either belong to different or to the same genera. Conventional methods (such as blood smear examination or tick salivary gland staining) are often unable to discriminate between pathogens. Therefore, molecular methods for the detection and differentiation of tick-borne pathogens are increasingly used. Technical problems still remain to identify pathogens within tick tissues, or within host animals when infection rates are very low. Recently we developed an integrated approach to identify several pathogens with only one molecular test. This approach, the reverse line blot hybridization (RLB) reduces costs of analysis, gives quicker results. and allows standardized inter-laboratory comparisons. Finally, this paper also focuses on the molecular diagnostic techniques currently used in the laboratories of the Mediterranean countries.

Protective immune mechanisms to ticks and tick-borne diseases of ruminants

A workshop of the European Union (EU) Concerted Action Project on the Integrated Control of Ticks and Tick-borne diseases (CA-ICTTD) recently assessed protective immune mechanisms to ticks and tick-borne diseases. The consensus achieved there is summarized here by Patricia Preston and Frans Jongejan. The current understanding of this field is expanded upon by the accompanying articles, and Poster, in this special issue of Parasitology Today.

Canine hepatozoonosis: comparison of lesions and parasites in skeletal muscle of dogs experimentally or naturally infected with Hepatozoon americanum

We report previously undescribed, early lesions in skeletal muscle of dogs experimentally infected with Hepatozoon americanum by ingestion of laboratory-reared, infected Amblyomma maculatum. The earliest muscle lesion was recognized at the first interval of examination 3 weeks following exposure. The lesion consisted of a large, modified host cell whose cytoplasm frequently contained a demonstrable parasite. In skeletal muscle, the cell was consistently located between muscle fibers or in loose connective tissue adjacent to those fibers. Evidence suggesting that the parasite arrives in muscle and other tissue within the host cell cytoplasm is presented. Mucopolysaccharide encystment of the host cell, absent at this early stage, was acquired gradually and approached maximal development 26 weeks post exposure. Completion of the asexual cycle as evidenced by the presence of parasites entering vascular lumens within granulomas and also by the presence of gamonts in peripheral blood leukocytes, occurred within 28-32 days postexposure. Progression of the parasite cycle from meront to passage of zoites into vessel lumens of granulomas can occur in 11 or fewer days. The density with which parasitic lesions occur in one named skeletal muscle compared to other named muscles, although somewhat variable, was not significantly different in either experimentally induced or natural infections. The distribution of developmental stages of the parasite/lesion in four experimental infections (969 lesions) is compared with those in eight dogs with natural infections (557 lesions).

[The biodiversity dynamics of the causative agents of diseases transmitted by ticks in the genus Ixodes: an analysis of multiyear data]

Fauna of pathogen's met in the organism of the primary tick-borne disease vectors--Ixodes persulcatus Schulze and Ixodes ricinus (L.) was observed. Prevalence of Borrelia mono- and poly-infection in the I. persulcatus ticks within a season of the vector activity was analyzed and increase of the number of the dual infected specimens during the season was demonstrated. The first determination of Ehrlichia infected I. ricinus and I. persulcatus collected in the Baltic region of Russia was stated. The triple infection of Ixodes ticks in was proved: infection by the two species of Borrelia and Ehrlichia; infection by the three species of Borrelia and infection by the tick-borne encephalitis virus and two species of Borrelia. The first determination of the tick-borne encephalitis virus in I. ricinus in the recreational zone of Kaliningrad Province (Courland [correction of Curonian] Spit) was described. Dipetalonema sp. was detected in the St. Petersburg population of I. persulcatus. The prevalence of poly-infection among I. persulcatus ticks was stated.

Naturally occurring hepatozoonosis in coyotes from Oklahoma

Nine of 16 free-ranging coyotes (Canis latrans) from central Oklahoma (USA) had naturally acquired infections of Hepatozoon americanum. Infections were confirmed by recognition of tissue stages closely resembling H. americanum in skeletal and cardiac muscle. At the time coyotes were collected they were infested with a variety of ticks, including adult Gulf Coast ticks (Amblyomma maculatum). We propose that the high prevalence of H. americanum in this small sample of free-ranging coyotes and the ability of these same animals to harbor adult populations of A. maculatum is an important component of the epizootiology of canine hepatozoonosis in North America.

[A review of the types of parasite-host relations in ixodid ticks]

In the first type of mutual relationships the ixodid ticks expose an evident pathogenicity to vertebrate hosts (tick toxicoses) and in the second type the hosts expose a resistance on a base of organism immune system activisation in a response to blood sucking. In the third type of relationships an interaction between the ticks and hosts have a dynamic character (tolerability of host). The first type of relationships leading to a selective elimination of hosts according to our opinion means a comparatively youth of relationships. The third type represent ancient and long term relationships. The second type probably having been widely spread in a historical past occupies an intermediate position. Depending upon areal the ticks of the same type expose different degree of the pathogenicity. Even an acquired resistance of the host does exist in natural conditions, it is a transient phenomenon.

Antibody response to Hepatozoon canis in experimentally infected dogs

Canine hepatozoonosis is a disease caused by the tick-borne protozoan Hepatozoon canis. Five puppies were inoculated by ingestion of Rhipicephalus sanguineus ticks experimentally infected with H. canis, and all became infected with H. canis: gametocytes were detected in blood smears from four dogs and schizonts were observed in the spleen and bone marrow of the fifth. Antibodies reactive with H. canis gametocytes were detected by the indirect fluorescent antibody test (IFA), with IgM detected initially in all dogs 16 to 39 days post infection (PI) and IgG 22 to 43 days PI. The presence of gametocytes was first observed within peripheral blood neutrophils in Giemsa-stained blood smears between days 28 and 43 PI. Gametocyte-reactive antibodies were detected before the appearance of blood gametocytes in three of the four parasitemic dogs and also in a dog with no observed parasitemia. The detection of serum antibodies prior to the detection of blood gametocytes, or without apparent parasitemia, suggests that antibodies reactive with gametocytes may be formed against earlier forms of the parasite developing in the parenchymal tissues. Sera of dogs experimentally infected with Babesia canis, Babesia gibsoni and Ehrlichia canis exhibited no reactivity when tested with H. canis antigen. Additionally, sera positive for H. canis were not reactive with antigens of Toxoplasma gondii, Neospora caninum, Leishmania donovani and E. canis. In conclusion, incoculation of dogs with ticks infected with H. canis results in production of antibodies reactive with peripheral blood gametocytes. Detection of IgG titres would be beneficial for the diagnosis of progressive infections with undetectable parasitemia, for seroprevalence studies, and as an adjunct to IgM titres in early infections.

Some epizootiological and clinical aspects of ovine babesiosis caused by Babesia ovis--a review

The study shows a close relationship between incidence of ovine babesiosis caused by Babesia ovis and the activity period and distribution area of the vector tick Rhipicephalus bursa. The most important factor limiting the distribution of this tick is a decrease in humidity. In general, it is absent from areas with an average annual rainfall of less than about 300 mm. The rate of parasitaemia and the degree of anaemia were not correlated. Decrease of the packed-cell volume ranged from 30 to 40%. Parasitized erythrocytes were not observed to block capillaries in the brain, which explained the absence of nervous symptoms in acute babesiosis. The kidney was the most severely affected organ, exhibiting acute glomerulonephritis. The lesions observed were suggestive of vascular alteration and vascular stasis, leading to anoxia of the tissues. A disseminated intravascular coagulation (DIC) syndrome was recorded in sheep infected with babesiosis. Biochemical studies revealed possible damage to the liver and kidneys. Most of the lambs (85%) that were infested with larvae, and all lambs infested with adult R. bursa ticks reacted serologically to B. ovis antigen. The serological reactions following infestation with the larvae occurred much later than those following infestation with the adult stage. Both transovarial and transstadial transmission of the parasite were demonstrated. A study of antibodies to B. ovis using IFAT in hoggets and ewes revealed high serological prevalence, i.e., 88.9% in ewes and 84.5% in hoggets. No marked seasonal fluctuation was observed. The serological findings, in addition to the fact that one splenectomised lamb reacted to larval infestation with acute ovine babesiosis, show that the preimaginal stages of R. bursa occurring in the winter can transmit B. ovis, usually causing a sub-clinical disease. This might play a major role in pre-immunizing and strengthening the premunition of the sheep against the main spring challenge by the adult ticks. The sub-clinical reactions are probably due to the low infection rate of the preimaginal stages of R. bursa by B. ovis parasites.

Hepatozoon canis: the prevalence of antibodies and gametocytes in dogs in Israel

A survey for the prevalence of antibodies to Hepatozoon canis and for intraneutrophilic H. canis gametocytes in the peripheral blood neutrophils of dogs in Israel showed that 33.1% were seropositive, while only 1% of the dogs sampled had detectable parasites in their blood smears. Exposure to H. canis is widespread but it appears that most infected dogs undergo a subclinical infection and only a small proportion develop clinical disease.

East Coast fever as a continued constraint to livestock improvement in Tanzania: a case study

An investigation was carried out into the cause of deaths in a recently established dairy farm with 211 animals. Clinical examination revealed that 14 out of 15 sick animals were depressed, pyrexic, anorexic and had variable degrees of respiratory distress and enlarged lymph nodes. These clinical signs were suggestive of East Coast fever (ECF). This was confirmed on positive demonstration of piroplasms and macroschizonts in blood and lymph node smears respectively, and on post-mortem examination. Parasites were also demonstrated in smears taken from 5 other animals which were pyrexic and had enlarged lymph nodes. Epidemiological investigation revealed that the occurrence of the disease was associated with contact with tick-infested pastures and unsatisfactory tick control due to improper dipping of the herd. The use of pasture by pastoral cattle which are rarely dipped also increased tick infestation. It is concluded that, unless effective disease control is applied ECF will continue to be a major killer disease of cattle in Tanzania.

[The probable utilization of the protective properties of the vector's saliva by the causative agents of specifically tick-borne infections]

It is proved that in the tick fluid saliva and in the cement plug produced by Rhipicephalus appendiculatus there are bactericidal substances very similar in their activity to the egg lysozyme. The possible role in the transmission and conservation of the specific tick-borne, insensitive to the lysozyme pathogens such as rickettsiae, tick-borne encephalitides virus and borreliae (pathogen of Lyme disease) is discussed. It is supposed, that bactericidal substances in the cement plug protect accumulated in it the tick-borne pathogens (TBE virus, borreliae) from the compete and destructive influence of the vulgar, mainly coccal microflora and from the purulent inflammation, which hinders not only tick feeding but probably specific tick-borne pathogens spreading in the vertebrate host.