Risk and prevention of transfusion-transmitted babesiosis and other tick-borne diseases

PURPOSE OF REVIEW

Tick-borne diseases have increasingly been recognized in the United States as public health problems. The importance of tick-borne diseases has been accelerated by increases in animal populations, as well as increased human recreation in wooded environments that are conducive to tick bites. Babesiosis, usually caused by the intraerythrocytic parasite, Babesia microti and transmitted by the same tick as Lyme disease, has important transfusion implications. Although Lyme disease has not been reported from blood transfusion, newly identified tick-borne diseases such as ehrlichiosis raise additional questions about the role of the tick in transfusion-transmitted diseases.

RECENT FINDINGS

The risk of transfusion-transmitted babesiosis is higher than usually appreciated and in endemic areas represents a major threat to the blood supply. Furthermore, the geographic range of B. microti is expanding, other Babesia spp. have been implicated in transfusion transmission in the western United States, and the movement of blood donors and donated blood components may result in the appearance of transfusion babesiosis in areas less familiar with these parasites. Consequently, a higher degree of clinical suspicion will allow early recognition and treatment of this important transfusion complication.

SUMMARY

In endemic areas transfusion-transmitted babesiosis is more prevalent than usually believed. The extension of the geographic range of various Babesia spp. and the movement of donors and blood products around the United States has resulted in the risk extending to non-endemic areas. Clinicians should maintain a high degree of clinical suspicion for transfusion-transmitted babesiosis.

[Ixodes ricinus, transmitted diseases and reservoirs]

The tick Ixodes ricinus has been recorded in most Italian regions especially in thermo-mesophilous woods and shrubby habitats where the relative humidity allow the tick to complete its 3 year developmental cycle, as predicted for the European climatic ranges. This tick acts both as vector and reservoir for a series of wildlife zoonotic pathogens, especially the agents of Lyme diseases, Tick borne encephalitis and Human Granulocytic Ehrlichiosis, which are emerging in most of Europe. To assess the spatial distribution of these pathogens and the infection risk for humans and animals within the territory of the Province of Trento, we carried out a long term study using a combination of eco-epidemiological surveys and mathematical modelling. An extensive tick collection with a GIS based habitat suitability analysis allowed us to identify the areas where tick occurs at various density. To identify the areas with higher infection risk, we estimated the values of R0 for Borrelia burgdorferi s.l., TBE virus and Anaplasma phagocytophila under different ecological conditions. We assessed the infection prevalence in the vector and in the wildlife reservoir species that play a central role in the persistence of these infections, ie the small mammals A. flavicollis and C. glareolus. We also considered the double effect of roe deer (Capreolus capreolus) which act as reservoir for A. phagocytophila but is an incompetent host for B. burgdorferi and TBE virus, thus reducing the infection prevalence in ticks of these last two pathogens. Infection prevalence with B. burgdorferi and A. phagocytophila in the vector was assessed by PCR screening 1212 I. ricinus nymphs collected by dragging in six main study areas during 2002. The mean infection prevalence recorded was 1.32% for B. burgdorferi s.l. and 9.84% for A. phagocytophila. Infection prevalence in nymphs with TBE virus, as assessed in a previous study was 0.03%. Infection prevalence in rodents was assessed by screening (with ELISA and PCR) tissues and blood samples collected from 367 rodent individuals trapped extensively during 2002 within 6 main study areas. A. flavicollis (N=238) was found to be infected with all three pathogens investigated, with infection prevalence ranging from 3.3% for TBE virus to 11.7% for A. phagocytophila, and 16.6% with B. burgdorferi s.l. C. glareolus (N=108) showed an infection prevalence of 6.5% with A. phagocytophila and 12.7% with B. burgdorferi s.l., while no individuals were infected with TBE virus. We also screened 98 spleen samples collected from roe deer with PCR, resulting in a mean prevalence of infection with A. phagocytophila of 19.8%. Using a deterministic model we explored the condition for diseases persistence under different rodent and roe deer densities. R0 values resulted largely above 1 for B. burgdorferi s.l. in the vast majority of the areas classified as suitable for I. ricinus occurrence in Trentino, while the condition for TBE persistence appeared to be more restricted by a combination of climatic condition and host densities.

[New distribution of tick-borne diseases in temperate countries]

Since 20 or 30 years, emerging tick-borne diseases are regularly reported. Recent data show that at the same time, we have to expect a change in distribution of some disease as the European tick-borne encephalitis, due to the strong relation between ticks cycle and temperatures for the transmission of this virus.

Problems in the study and prophylaxis of mixed infections transmitted by ixodid ticks

The spread of mixed infections with natural focality transmitted by ixodid ticks is a normal phenomenon attributable to trends in the relationships of different pathogens in the vector organism and ecosystem as a whole. Any disease developing as a result of tick bite should be regarded as a potentially mixed infection. Clinically, tick-borne mixed infections proceed more severely than the corresponding diseases caused by a single agent. The residual course of the disease may sometimes be accounted for by the persistence of two or even several pathogens. This implies the necessity of a comprehensive approach to the study, diagnosis, treatment, management and prophylaxis of infections belonging to this group.

Human behaviors elevating exposure to Ixodes pacificus (Acari: Ixodidae) nymphs and their associated bacterial zoonotic agents in a hardwood forest

Epidemiological evidence suggests that the nymph of the western black-legged tick, Ixodes pacificus Cooley and Kohls, is the primary vector of the Lyme disease spirochete, Borrelia burgdorferi Johnson, Schmid, Hyde, Steigerwalt, and Brenner, to humans in northwestern California. In spring 2002, six different human behaviors were evaluated as potential risk factors for acquiring I. pacificus nymphs in a deciduous woodland in Mendocino County, California. Also, the prevalence of B. burgdorferi sensu lato (s.l.) and the causative agents of human granulocytic (Anaplasma phagocytophilum [Foggie] Dumler, Barbet, Bekker, Dasch, Palmer, Ray, Rikihisa, and Rurangirwa) and monocytic ehrlichioses (Ehrlichia chaffeensis Anderson, Dawson, Jones, and Wilson) was determined in nymphs that had been collected from subjects or by dragging leaf litter. Activities involving a considerable degree of contact with wood resulted in greater acquisition of nymphs than those involving exposure solely to leaf litter. Time-adjusted tick-acquisition rates demonstrated that sitting on logs was the riskiest behavior, followed, in descending rank, by gathering wood, sitting against trees, walking, stirring and sitting on leaf litter, and just sitting on leaf litter. The number of ticks acquired appeared to be unrelated to the type of footwear worn (hiking boots, hiking sandals, or running shoes). Overall, 3.4% (n = 234) of the nymphs were infected with A. phagocytophilum, 3.9% (n = 181) with B. burgdorferi s.l., and none (n = 234) with E. chaffeensis. Of 13 nymphs infected with either A. phagocytophilum or B. burgdorferi s.l., 2 (15.4%) were coinfected with both bacteria, as were 1.3% of 158 nymphs obtained from leaf litter, the first report of coinfection in this life stage of I. pacificus. Four unattached, infected nymphs were removed from subjects, including two acquired while sitting on logs that contained A. phagocytophilum, another with the same bacterium obtained while walking, and one acquired while gathering wood that was infected with B. burgdorferi s.l. Despite the use of extreme personal preventive measures by both subjects, two attached, uninfected nymphs were removed from one of them > or = 1-2 d postexposure. The public health implications of these findings are discussed.

Quantitative ecology of ticks as a basis for transmission models of tick-borne pathogens

Tick population ecology is the basis of spatiotemporal variation in the risk of infection by tick-borne pathogens. The continental distribution of tick-borne encephalitis (TBE) in Europe is statistically associated with a specific pattern of the seasonal dynamics of Ixodes ricinus, and a particular characteristic of the seasonal land surface temperature profile. A tick population model would allow us to move from this statistical analysis to a biological, process-based model for TBE virus and the many other pathogens vectored by Ixodes spp. ticks in Europe and the United States. Long-term field data on I. ricinus are analyzed to provide empirical estimates of rates of the major demographic processes, development, questing, attachment to hosts, and mortality.

[Risk of arbovirus transmission by ticks in Thailand]

Ticks are known vectors of transmission for a number of infectious viral diseases from wild or domestic animals to humans. Many tick-borne diseases cause severe clinical syndromes such as encephalitis or hemorrhagic fever. Animal carriers of enzootic diseases are often asymptomatic. Within the framework of a program to monitor emerging viral diseases in Southeast Asia, identification of ticks capable of transmitting diseases from animals to man is a prerequisite for epidemiologic study to assess the risk of tick-borne disease. The purpose of this report is to provide an update on the situation based on a study of tick fauna in the central plain area of Thailand and on current knowledge about tick-borne arboviruses in Asia. In addition to an exhaustive inventory of ticks found in Thailand, this study describes the viruses with pathogenic potential that ticks are known to carry and transmit to man. A perusal of the literature allowed initial assessment of the risk for introduction and spread of ticks by bird hosts in Southeast Asia as well as of associated virus.

Studies on the occurrence of Gram-negative bacteria in ticks: Ixodes ricinus as a potential vector of Pasteurella

A total of 372 Ixodes ricinus ticks (101 females, 122 males, and 149 nymphs) collected by flagging in 6 mixed woodlands of eastern Poland were examined by culture for the presence of internal Gram-negative bacteria other than Borrelia burgdorferi. Adult ticks were examined in pools of 2 specimens each and nymphs were examined in pools of 3-5 specimens each. Ticks were disinfected in 70 % ethanol and homogenized in 0.85% NaCl. The diluted homogenate was inoculated onto 3 kinds of agar media: buffered charcoal yeast extract (BCYE-alpha) for isolation of fastidious Gram-negative bacteria, eosin methylene blue agar (EMB) for isolation of enterobacteria, and tryptic soya agar for isolation of all other non-fastidious Gram-negative bacteria. The Gram-negative isolates were identified with the API Systems 20E and NE microtests. A total of 9 species of Gram-negative bacteria were identified, of which the commonest were strains determined as Pasteurella pneumotropica/haemolytica, which were isolated on BCYE-alpha agar from ticks collected in all 6 examined woodlands. The total number of these strains (49) exceeded the total number of all other strains of Gram-negative bacteria recovered from ticks (30). Of the total number of examined ticks, the minimum infection rate with Pasteurella pneumotropica/haemolytica was highest in females (18.8%), and slightly lower in males (12.3%) and nymphs (10%). Besides Pasteurella pneumotropica/haemolytica, the following species of Gram-negative bacteria were isolated from examined ticks: Pantoea agglomerans, Serratia marcescens, Serratia plymuthica on EMB agar and Aeromonas hydrophila, Burkholderia cepacia, Chromobacterium violaceum, Pseudomonas aeruginosa, and Stenotrophomonas maltophilia on tryptic soya agar. Minimal infection rates with these bacteria were low, ranging from 0.7-5.9%. Of the isolated bacteria, Chromobacterium violaceum, Pasteurella pneumotropica/haemolytica, Pseudomonas aeruginosa, and Serratia marcescens are potentially pathogenic for man and/or animals. In particular, the common occurrence of Pasteurella pneumotropica/haemolytica in Ixodes ricinus ticks poses a potential risk of pasteurellosis for humans and animals exposed to tick bites.

Detecting DNAs of Anaplasma phagocytophilum and Babesia in the blood of patients suspected of Lyme disease

Co-occurrence of granulocytic anaplasmosis, borreliosis and babesiosis in humans is a result of common vectors for the respective pathogens of these diseases, most commonly ticks from the genus Ixodes. Studies on ticks in Europe and also in Poland have shown that several pathogens may co-occur in individuals of I. ricnus. A total of 96 hospitalised patients infected or suspected of being infected with borreliosis were screened for A. phagocytophilum and Babesia sp. DNA. Positive results of PCRs for A. phagocytophilum DNA were obtained for 10 patients, 8 of whom were diagnosed with borreliosis earlier, and 4 of whom were diagnosed with tick-borne encephalitis (on the basis of serological studies of serum and cerebrospinal fluid). None of the 10 patients had clinical or biochemical markers of anaplasmosis, corroborating the existence of asymptomatic anaplasmosis or self-limiting course. in Europe. Similarly, Babesia DNA was not found in the blood of any of the patients. The results of the studies show that in diagnosing tick-borne diseases, clinical examinations should consider infection by two or even three tick-borne pathogens.

Present status of tick-borne diseases in Sudan

Ticks and tick-borne diseases are widespread in the Sudan, cause substantial economic losses and constitute major obstacles to the development of animal wealth. Most important among these diseases are tropical theileriosis, malignant ovine theileriosis, cowdriosis, babesiosis, anaplasmosis and avian spirochaetosis. However, knowledge about ticks and tick-borne diseases is still fragmentary and far from complete. The large number of tick species, the multplicity of transmitted agents and the diverse ecoclimatic zones of the Sudan provide a unique opportunity to host diverse research activities that could benefit other regions in Africa.

Thresholds for disease persistence in models for tick-borne infections including non-viraemic transmission, extended feeding and tick aggregation

Lyme disease and Tick-Borne Encephalitis (TBE) are two emergent tick-borne diseases transmitted by the widely distributed European tick Ixodes ricinus. The life cycle of the vector and the number of hosts involved requires the development of complex models which consider different routes of pathogen transmission including those occurring between ticks that co-feed on the same host. Hence, we consider here a general model for tick-borne infections. We assumed ticks feed on two types of host species, one competent for viraemic transmission of infection, the second incompetent but included a third transmission route through non-viraemic transmission between ticks co-feeding on the same host. Since a blood meal lasts for several days these routes could lead to interesting nonlinearities in transmission rates, which may have important effects.We derive an explicit formula for the threshold for disease persistence in the case of viraemic transmission, also for the case of viraemic and non-viraemic transmission. From this formula, the effect of parameters on the persistence of infection can be determined. When only viraemic transmission occurs, we confirm that, while the density of the competent host has always a positive effect on infection persistence, the density of the incompetent host may have either a positive effect, by amplifying tick population, or a negative ("dilution") effect, by wasting tick bites on an incompetent host. With non-viraemic transmission, the "dilution" effect becomes less relevant. On the other hand, if the nonlinearity due to extended feeding is included, the dilution effect always occurs, but often at unrealistically high host densities. Finally, we incorporated the effects of tick aggregation on the hosts and correlation of tick stages and found that both had an important effect on infection persistence, if non-viraemic transmission occurred.

Study of awareness of tick-borne diseases among children and young people in the Czech Republic

In the 2000 and 2001 years, there was performed a study which has given some insight on the knowledge of youths about ticks and tick-borne diseases. Two thousand seven hundred and sixty-three respondents from 6 to 26 years of age took part in this investigation. More than 98% of respondents knew about the existence of ticks. Almost 93% of children and 97% of adolescents reported that ticks feed on blood. Although the majority of respondents aged 10 to 26 years is convinced that ticks live on vegetation, 23% of them supposed that ticks jump on humans from trees. As many as 93.5% of youths knew that Lyme disease is transmitted by ticks. The main sources of information about Lyme disease for students and pupils older than 10 years of age are television and radio (40.9%) and the press (37.5%). The frequency of contact of young people with ticks is high--90.4% of children younger than 12 years, and 93.7% of youths from 10 to 26 years of age had at least once an attached tick. 56.1% of youths older than 10 years use oil to remove an attached tick. Almost 23.7% remove ticks with bare hands. People used those methods of tick removal although even children younger than 12 years of age knew that it was an incorrect habit. After removing, a tick is most frequently burned.

Aponomma hydrosauri, the reptile-associated tick reservoir of Rickettsia honei on Flinders Island, Australia

Rickettsia honei is the etiologic agent of Flinders Island (Australia) spotted fever. The tick Aponomma hydrosauri is associated with reptiles and is the arthropod reservoir for this rickettsia on Flinders Island. The rickettsia appears to be maintained in the tick via vertical transmission. Of 46 ticks examined, 29 (63%) were positive for spotted fever group rickettsiae by detection of the citrate synthase gene by a polymerase chain reaction (PCR). From the positive tick samples, seven were sequenced and found to be 100% homologous with R. honei. Of 17 reptiles examined, none had evidence of rickettsiae by PCR or culture of blood.

The role of non-viraemic transmission on the persistence and dynamics of a tick borne virus--Louping ill in red grouse ( Lagopus lagopus scoticus) and mountain hares ( Lepus timidus)

There exist many tick borne infections that are of either economic or public health interest. Mathematical models have previously been used to describe the dynamics of these infections. However it has recently come to light that there is an alternative mechanism for the transmission of these diseases that has not been considered in a modelling framework. This is transmission through ticks co-feeding on non-viraemic hosts. This paper extends a simple mathematical model to include this alternative transmission mechanism. The model is used to describe the dynamics of Louping ill virus in red grouse (the viraemic host) and hares (the non-viraemic host). However, these results are applicable to many other systems. The model is analysed using joint threshold density curves. It is found that the presence of a non-viraemic host allows the virus to persist more readily than it would in the presence of a host that simply amplified the tick population. More importantly, if the level of non-viraemic transmission is high enough the virus can persist in the absence of the viraemic host. This result has important implications for the control of tick borne diseases.

Ecology and epidemiology of spotted fever group Rickettsiae and new data from their study in Russia and Kazakhstan

Rickettsiae represent a wide range of pathogenicity from classic and new pathogens to endosymbionts of eukaryotic cells. Recent studies of rickettsiae have widened the number of representatives of genus Rickettsia, especially in the spotted fever group (SFG). Rickettsiae of SFG are tick-borne microorganisms with effective transovarial and transstadial transmission. The main hosts are ticks (Dermacentor, Rhipicephalus, Haemophysalis, Ixodes, and Amlyomma). Strategy of maintenance of tick microorganisms is vector-type transfer and tropism to endothelial cells or blood cells of animals. The main epidemiological characteristics of SFG rickettsioses are different kinds of anthropogenic activity and connection of morbidity with seasonal tick activity. Two other important characteristics are quantitative and qualitative heterogeneity of its populations (different genotypes of Rickettsia in the same territory and species of ticks, for example) and coexistence of different tick microorganisms (rickettsiae, borreliae, ehrlichiae, tick-borne encephalitis complex viruses, etc.). The role of new rickettsial genotypes in infectious diseases is poorly understood. Simultaneous study of ticks after bites, blood and skin biopsies of patients may be used for detection of spectrum of tick-borne pathogens in mixed natural foci. Interference between rickettsiae with different virulence may affect its populations and levels of morbidity.

Fort Chaffee revisited: the epidemiology of tick-borne rickettsial and ehrlichial diseases at a natural focus

A retrospective cohort study was conducted among troops training at Fort Chaffee, Arkansas, from May through June 1997, to identify infections caused by tick-borne pathogens. Serum samples were tested by IFAs for antibodies to selected Rickettsia and Ehrlichia species and by an investigational EIA for spotted fever group Rickettsia lipopolysaccharide antigens. Of 1,067 guardsmen tested, 162 (15.2%) had antibodies to one or more pathogens. Of 93 guardsmen with paired serum samples, 33 seroconverted to Rickettsia rickettsii or spotted fever group rickettsiae (SFGR) and five to Ehrlichia species. Most (84.8%) of the personnel who seroconverted to SFGR were detected only by EIA, and seropositivity was significantly associated with an illness compatible with a tick-borne disease. In addition, 34 (27%) of 126 subjects with detectable antibody titers reported a compatible illness. The primary risk factor for confirmed or probable disease was finding > 10 ticks on the body. Doxycycline use and rolling up of long sleeves were protective against seropositivity. The risk of transmission of tick-borne pathogens at Fort Chaffee remains high, and use of the broadly reactive EIA suggests that previous investigations may have underestimated the risk for infection by SFGR. Measures to prevent tick bite and associated disease may require reevaluation.

Immunity against Boophilus annulatus induced by the Bm86 (Tick-GARD) vaccine

Friesian cattle were immunized with two inoculations of anti-tick Bm86 (Tick-GARD) vaccine and were challenged 30 or 90 d later with Boophilus annulatus larvae derived from 1.2 g of eggs. No nymphs or adult ticks were found on the immunized cattle during four weeks after challenge. Repeated infestations (2 to 4) with larvae on three other calves during a period of 160 and 390 d after the immunization did not result in development of nymphal and adult stages. In control, non-immunized cattle infested with corresponding batches of larvae 1380 to 4653 replete adult female ticks were collected. Larvae issued from Babesia bovis-infected female ticks transmitted the infection to Bm86-immunized cattle, but the progeny of B. bigemina-infected females did not. Since B. bigemina is transmitted exclusively by nymphal stages of Bo. annulatus these results support the observation that immunity induced by Bm86 affects the larval stage of this tick.

Relationship between tick bites and the seroprevalence of Babesia microti and Anaplasma phagocytophila (previously Ehrlichia sp.) in blood donors

BACKGROUND

Tick-borne diseases, particularly babesiosis and ehrlichiosis, represent recently emerging infections. Despite an increased recognition of the threat tick-borne agents pose to blood safety, our understanding of the prevalence and transmissibility of these agents in blood donors is limited.

STUDY DESIGN AND METHODS

Babesia microti and Anaplasma phagocytophila (previously Ehrlichia sp.) seroprevalence was determined in random Connecticut and Wisconsin donors, and subsequently in Connecticut donors reporting tick bites. In the interim, a postcard survey regarding tick bites during the previous 6 months was sent to 6,000 random donors in six geographically distinct collection regions.

RESULTS

In total, 3 of 999 Wisconsin donors (0.3%) and 6 of 1,007 Connecticut donors (0.6%) had antibodies to B. microti. Of 992 donors tested for A. phagocytophila, 5 Wisconsin donors (0.5%) and 35 Connecticut donors (3.5%) were seropositive. A total of 2,482 donors (41.4%) completed the survey; 103 (4.1%) reported a tick bite. Of 848 Connecticut donors (0.4%) reporting tick bites, 3 had B. microti antibodies, while 8 (0.9%) had A. phagocytophila antibodies. These rates were not significantly different from control donors.

CONCLUSION

Blood donors seropositive for B. microti and A. phagocytophila are present in Connecticut and Wisconsin. Donors readily recall previous tick bites, but self-reported bites are not reliable indicators of serologic status. The exposure of blood donors to tick-borne pathogens does suggest a need to better understand the transfusion transmission potential of these agents.

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.

Ticks associated with armadillo (Euphractus sexcinctus) and anteater (Myrmecophaga tridactyla) of Emas National Park, State of Goias, Brazil

This study was conducted in October 1998 and November 1999 in the Emas National Park (131,868 ha), a savanna-type cerrado region situated in the far south of Goias State, Brazil, near the geographic center of South America (15 degrees -23 degrees S; 45 degrees -55 degrees W). Animals were captured with the aid of nets and anesthetized (15 mg/kg ketamine + 1 mg/kg xylasine) in order to collect ticks for identification and to establish laboratory colonies. They included giant anteaters (Myrmecophaga tridactyla) (n = 4) and yellow armadillos (Euphractus sexcinctus) (n = 6). Free-living ticks (larvae, nymphs, and adults) were collected from the field by using a 1 x 2-m flannel cloth. Free-living ticks were identified as Amblyomma sp., A. cajennense, and A. triste. Adult ticks collected from anteaters were identified as Amblyomma cajennense and A. nodosum and from armadillos as A. pseudoconcolor and A. nodosum. The relevance of these host-tick relationships to possible mechanisms underlying emergence of tick-borne pathogens of importance to public health is discussed.

[Tick-borne neurological diseases]

Some microorganisms transmitted to man via tick bite are responsible for infections, which can be associated with neuro-meningeal complications. TBE virus is the most frequent virus associated with potentially severe neurological lesions. No treatment is available so far. The most frequent bacterial diseases in which neurological complications may appear are Lyme borreliosis, Q fever and some rickettsial infections. More recently ehrlichiosis have emerged as new infections that may be associated with neuro-meningeal complications. Appropriate antibiotic therapy may be used for the treatment of these bacterial infections, but no vaccine is available so far.

[New molecular biology detection methods for tick-borne infectious agents]

Tick-borne zoonotic pathogens are well known in many areas all over the world. Among the tick-borne transmitted diseases in Switzerland, Lyme disease caused by Borrelia burgdorferi, ehrlichiosis caused by various species of Ehrlichia and tick-borne encephalitis caused by the tick-borne encephalitis virus (TBEV) are the most important zoonotic diseases. Early diagnosis and treatment is necessary to prevent fatal infections and chronic damage to various tissues. Due to the variety of uncharacteristic clinical signs, tick-borne diseases are not easily recognized. Diagnosis is based on clinical findings, a record of tick exposure, and direct or indirect detection of the pathogen. Here we discuss briefly the most important tick-borne infections and their diagnosis with emphasis on a new molecular diagnostic tool--the real-time TaqMan PCR--and its importance for the diagnosis of tick-borne pathogens.

Diagnostics of tick-borne diseases in the endemic region of Russia

A clinical-laboratory survey of 1952 patients with acute feverish diseases developing after tick bite was carried out in the Pre-Ural region of Russia, which is endemic for tick-borne encephalitis and ixodid tick-borne borreliosis, in 1999-2001. Enzyme-linked immunosorbent assay and indirect immunofluorescence assay were used for the detection of tick-borne encephalitis, ixodid tick-borne borreliosis and ehrlichiosis specific antibodies. Tick-borne encephalitis was diagnosed in 22.8% of patients, ixodid tick-borne borreliosis in 50.5%, ehrlichiosis in 4.5% and mixed infections in 2.9%. For the first time in Russia, a new transmitted disease that appeared to be human monocytic ehrlichiosis was identified and its clinical manifestations were described. The common feature of these infections is the acute course and the marked general infectious syndrome at the early period of the disease. Disorders of the nervous system predominate in tick-borne encephalitis. In ixodid tick-borne borreliosis the development of erythema migrans and organic pathology (disorders of the cardio-vascular system and liver) associated with the involvement of the nervous and locomotor system are pathognomonically significant. The specific characteristics of human monocytic ehrlichiosis include nervous impairments, hepatic lesions, the frequent development of a two-wave course and hemogram changes.

Biology of Ixodes species ticks in relation to tick-borne zoonoses

At least six tick-borne zoonoses are transmitted by members of the Ixodes ricinus species complex in northern hemisphere temperate regions, and include the relatively recently emerged diseases, Lyme borreliosis and ehrlichiosis. An understanding of the biology of these ticks is essential for the prevention and control of the zoonoses they transmit and this review summarises established knowledge in addition to addressing recent work on host specificity of ticks, inter- and intra-specific biological variation and factors affecting tick distribution and abundance.

Detection, characterization, and prediction of tick-borne disease foci

Tick-borne disease (TBD) transmission foci need to be characterized in space and time, and are often discontinuous on both scales. An active TBD focus is dependent on the fulfillment of three conditions: tick survival, pathogen survival and opportunities for human exposure. The essentials for tick survival include food sources, reproduction, and protection from environmental extremes. The pathogen survival kit includes sufficient densities of ticks and suitable reservoir hosts, and opportunities for transmission between them in order to maintain infection. Opportunities for human exposure depend on sufficient number of encounters between ticks and humans. Because tick foci need to be described on a range of spatial and temporal resolutions, data for such characterization include a variety of surveillance data, field and laboratory experimental data, as well as results of statistical and mathematical analysis and modeling. The application of new tools from molecular biology, geographic information systems (GIS), and satellite imagery, in conjunction with appropriate analytical methods allow for detection of unknown foci and prediction of new ones. A long-term multi-scale study of Ixodes scapularis and Lyme disease in the north-central U. S. is reviewed. Diverse surveillance methods of ticks, rodents, deer, canids and humans were coupled with environmental characterization in situ to create a habitat profile for Lyme disease ticks. Incorporating various digitized databases, a statistical model was used to develop a risk map for tick distribution in the region. The process of introduction and establishment of new tick foci along the Illinois River is described in relation to the known tick distribution and predictions of invasion based on the risk model.

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.

Tick-borne diseases in transfusion medicine

Ticks are effective vectors of viral, bacterial, rickettsial and parasitic diseases. Many of the tick-borne diseases (TBDs) are of significance to transfusion medicine, either because of the risks they pose to the blood supply or the necessity for blood products required in their treatment. The transmission of tick-borne pathogens via blood transfusion is of global concern. However, among transfusion medicine practitioners, experience with most of these microorganisms is limited. Transfusion transmission of TBDs has been documented largely by means of single case reports. A better understanding of the epidemiology, biology and management of this group of diseases is necessary in order to assess the risks they pose to the blood supply and to help guide effective prevention strategies to reduce this risk. Unique methods are required to focus on donor selection, predonation questioning, mass screening and inactivation or eradication procedures. The role of the transfusion medicine service in their treatment also needs to be better defined. This article reviews the growing body of literature pertaining to this emerging field of transfusion medicine and offers some recommendations for transfusionists in dealing with TBDs.

Prevention of tick-borne diseases

Ticks are a part of the landscape where humans live, work, and play. Because ticks carry a wide range of organisms that potentially can cause disease in humans, many studies have focused on ways to reduce risk of these diseases. Ticks have biologically complex interactions with microorganisms and with their vertebrate hosts, on whom they depend for blood meals and survival. To consider ways to reduce the burden of tick-borne diseases in humans, it is necessary to understand the biology and ecology of ticks and their interface with humans. In many areas, changes in land use, reforestation, and patterns of human settlements have led to more abundant tick populations, increasing rates of infections in ticks, and increasing contact with human populations. Warmer winter temperatures in temperate regions may extend the transmission season for some ticks and pathogens. Although much of the discussion in this article has focused on I. scapularis and the Lyme disease spirochete (because they have been studied extensively), other tick-pathogen pairs may differ in risk factors for infection and transmission dynamics. Interventions studied to reduce the burden of tick-borne diseases include changing the environment, controlling vertebrate hosts, killing ticks, altering the behavior of humans, treating tick bites, and trying to protect humans through immunologic means (vaccine). All of these approaches have limitations and drawbacks. From a public health perspective, a plan that employs multiple strategies may be most effective. This article has reviewed what is known about preventive interventions, including the vaccine.

The natural history of ticks

Ticks have evolved to become one of the most important groups of arthropod vectors of human pathogens. One or more of the approximately 840 known species of ticks are found in most terrestrial regions of the earth. Ticks are a highly specialized group of obligate, bloodsucking, nonpermanent ectoparasitic arthropods that feed on mammals, birds, and reptiles. They are classified into two major families, Ixodidae (hard-bodies ticks) and Argasidae (soft-bodied ticks). The Ixodidae is the largest and most important family. There are many taxonomic keys for identifying ticks to assist the serious investigator. Their life cycles are often complex, and even though ticks are associated with their parasitic habits, ticks spend most of their life off hosts and in vegetation or soil. Maintenance of water balance during periods of overhydration while feeding and periods of dehydration while fasting is significant in the distribution, survival, activity, and transmission of disease-causing pathogens to humans and animals. Ticks attach to skin of the host by using their hypostome as an anchor and create a feeding lesion to ingest blood or tissue fluids. Soft-bodied ticks feed relatively rapidly (hours or less) and ingest only blood. Hard-bodied ticks take days to complete feeding and feed on blood, lymph, and lysed tissues from a pool that forms around the mouthparts. Feeding causes direct damage to the skin of the host. Disease-causing organisms may be ingested or expelled during feeding. Ingestion of relatively enormous quantities of blood is characteristic of ticks.

Immunogenicity of Ehrlichia ruminantium grown in tick cell lines

Ehrlichia (previously Cowdria) ruminantium, the pathogen which causes heart-water in domestic and wild ruminants, can now be propagated in cell lines from one vector (Amblyomma variegatum) and five non-vector (Ixodes scapularis, I. ricinus, Boophilus decoloratus, B. microplus and Rhipicephalus appendiculatus) tick species. E. ruminantium isolates from West and South Africa and the Caribbean vary in their cell line preference, growth patterns and immunogenic capability. In laboratory trials, certain combinations of tick cell line and E. ruminantium isolate were highly immunogenic in sheep. These trial vaccines were grown under specific in vitro conditions and administered as a single intravenous dose of freshly harvested whole, live culture. Following immunisation and subsequent exposure to virulent E. ruminantium, protected sheep showed no clinical response and a range of serological responses.

Detection and identification of spotted fever group rickettsiae in ticks collected in southern Croatia

A total of 197 ticks belonging to four species (Haemaphysalis punctata, Hyalomma marginatum, Rhipicephalus bursa and Dermacentor marginatus) collected in October 2000 from domestic animals in southern Croatia were examined for the presence of rickettsiae by molecular techniques. Specific sequences of the rickettsiae were detected in 25 (12.7%) of ticks tested. The prevalence of infection in D. marginatus and H. marginatum ticks was 36.8 and 64.7%, respectively. None of the ticks belonging to the species H. punctata or Rh. bursa were infected. Sequence analysis of amplified products revealed that D. marginatus ticks are infected with Rickettsia slovaca, whereas H. marginatum are infected with R. aeschlimannii. The results of this study extend the knowledge of the geographic distribution of SFG rickettsiae and indicate that at least two of them, with yet uncertain pathogenicity to humans, are present in ticks in southern Croatia.

Remotely sensed correlates of phylogeny: tick-borne flaviviruses

Vector-borne pathogen systems are limited by climate, principally through its impact on the distribution, abundance and population dynamics of the vectors and on the interaction of vectors with their hosts. This leads to the prediction that climate has been a significant factor in the evolution of these pathogens and, by implication, will be important in future events on both evolutionary and ecological time-scales. New phylogenetic trees of organisms, that describe their evolutionary history, are routinely available, but explanations for the driving force and constraints that have shaped the evolutionary origin of new pathogen strains are rare. Under the force of environmental pressures that change in space and time, which pathogens are likely to emerge in new places and where will this be? To answer such questions, data from molecular biology can be linked with data from satellites that allow us to characterize environmental conditions on a global scale. Broad-scale patterns in the satellite imagery are consistent with the pattern of new tick-borne flaviviruses having evolved sequentially in a cline across the world. So far, the distribution of three tick-borne flaviviruses from western Europe have been captured simultaneously by the same 10 satellite-derived seasonal climatic variables. Once this procedure is extended to the remaining viruses in this clade, we shall test for significant matches between their phylogenetic tree and an independent tree derived from quantitative descriptions of the viruses' 'eco-space'. This will indicate the extent of key ecological drivers for specific evolutionary events, whose biological basis can then be explored in detail.

Progress toward molecular characterization of ectoparasite modulation of host immunity

Ectoparasitic arthropods and vector-borne infectious agents are global medical and veterinary public health concerns. Economic impact due to direct effects of infestation and disease transmission are significant. These problems are increased by development of arthropod resistance to insecticides/acaricides; drug resistance of vector-borne pathogens; and, lack of effective vaccines to prevent many of these diseases. There is much to be gained from understanding the complex array of immunological interactions occurring at the arthropod-host-pathogen interface. One application of that knowledge is the development of novel vaccines for the control of both ectoparasitic arthropods and the diseases they transmit. We now realize that blood-feeding arthropods are not simply flying or crawling hypodermic needles and syringes. Ectoparasitic arthropods are not passive partners in their relationships with the immune systems of their hosts. These clever invertebrates produce numerous pharmacologically active molecules that help them migrate through tissues of their hosts or to successfully obtain blood meals. Arthropod parasites stimulate a spectrum of host immune responses that could potentially impair development, reduce feeding success, or kill the ectoparasite. Not unexpectedly, arthropods have developed sophisticated arsenals of countermeasures that modulate or deviate host immune responses. Not only does arthropod modulation of host immunity facilitate survival in tissues or increase the likelihood of obtaining a blood meal, but it is increasingly recognized as a critical factor in pathogen transmission. Those countermeasures to host immune defenses are the topics of this review. Emphasis is placed on our current understanding of the molecular bases of those changes; the molecules responsible for host immunomodulation; contemporary approaches for studying these complex relationships; and, the potential for using this information to develop innovative vaccine-based control strategies.

Seroprevalences of vector-transmitted infections of small-holder dairy cattle in coastal Kenya

A cross-sectional study was carried out from July to September 1989 in Kaloleni Division, Coast Province, Kenya to estimate the prevalence of vector-transmitted diseases in small-holder dairy cattle and to identify the risk factors associated with different management systems. One hundred and thirty of the 157 herds with dairy cattle in Kaloleni Division were surveyed. These were from three agro-ecological zones (coconut-cassava, cashew nut-cassava and livestock-millet), comprised two management systems (stall-feeding and herded grazing) and were herds with either dairy cattle only or with Zebu and dairy cattle. A formal questionnaire sought answers to questions on cattle health and management practices. A total of 734 dairy and 205 Zebu cattle in 78 dairy and 52 mixed (dairy and Zebu) herds were sampled and screened for haemoparasites (Trypanosoma, Anaplasma, Babesia, and Theileria infections). Sera were tested for antibodies to Theileria parva, using the schizonts-antigen indirect fluorescent-antibody (IFA) test and to antibodies for Babesia bigemina and antigens to Anaplasma marginale by enzyme-linked immunosorbent assay (ELISA). Packed-cell volume (PCV) also was measured. Tick-control measures were practised by all except three of the farmers. Despite this, overall seroprevalence to T. parva was >70%--suggesting either that control practices were not strictly implemented or they were ineffective. The seroprevalence of T. parva in adult cattle kept in stall-feeding systems in the coconut-cassava zone was significantly lower (57+/-8% (S.E.)) than in herded-grazing systems (79+/-3%) and there was no association between antibody prevalence and age of cattle in this zone. Antibody prevalences in cattle in the cashew nut-cassava and the drier livestock-millet zone increased with age. Cattle in herded-grazing systems had an overall lower seroprevalence of T. parva infection in the livestock-millet zone (45+/-6%) than in the other two zones. Analysis was confined to the coconut-cassava zone for B. bigemina and to the coconut-cassava and cashew nut-cassava zones for A. marginale. Mean prevalences of B. bigemina were 40.9+/-9 and 73+/-6% for dairy cattle under stall-feeding and herded-grazing systems, respectively, and increased with age. Antigen prevalences of A. marginale were over 80% in all age groups of cattle in the coconut-cassava and cashew nut-cassava zones. Overall trypanosome prevalence in cattle was <1%. Trypanocidal treatment was uncommon. The variations in antibody prevalence associated with risk factors such as feeding system, agro-ecological zone and age of animal suggest that management system influenced exposure to tick-borne infection (particularly, T. parva infections) in small-holder dairy cattle in coastal Kenya.

Manifestations of tick-borne illness. Incidence and variety are increasing worldwide

The incidence and variety of diseases associated with tick bites have continued to grow worldwide. Lyme disease, the most common tick-borne disease in the United States, has received extensive media coverage because of its protean manifestations and propensity for causing chronic disease. Our ability to prevent, identify, and effectively treat Lyme disease and other tick-borne diseases has significantly improved in the last decade. Tick-borne illnesses should be one of the differential diagnostic considerations in patients with consistent clinical findings and exposure history. In addition, the prudent use of laboratory testing ensures an accurate diagnosis while avoiding the cost and risk of inappropriate diagnostic tests and antibiotic therapy.

Assessing the association between the geographic distribution of deer ticks and seropositivity rates to various tick-transmitted disease organisms in dogs

OBJECTIVE

To determine whether the geographic distribution of deer ticks (Ixodes scapularis) was associated with the distribution of dogs seropositive for various tick-transmitted disease organisms (ie, Borrelia burgdorferi, Rickettsia rickettsii, the human granulocytic ehrlichiosis [HGE] agent, Ehrlichia canis, and Bartonella vinsonii subsp berkhoffii).

DESIGN

Serologic survey.

SAMPLE POPULATION

Serum samples from 277 dogs in animal shelters and veterinary hospitals in Rhode Island.

RESULTS

Overall, 143 (52%) dogs were seropositive for B burgdorferi, 59 (21.3%) were seropositive for R rickettsii, 40 (14.4%) were seropositive for the HGE agent, 8 (2.9%) were seropositive for E canis, and 6 (2.2%) were seropositive for B vinsonii. Regression analysis indicated that the natural logarithm of nymphal deer tick abundance was correlated with rate of seropositivity to the HGE agent and to B burgdorferi but not to rate of seropositivity to R rickettsii, E canis, or B vinsonii. Percentages of samples seropositive for B burgdorferi, R rickettsii, the HGE agent, and E canis were significantly higher for samples from the southwestern part of the state where ticks in general and deer ticks in particular are abundant than for samples from the northern and eastern portions of the state, where ticks are relatively rare.

CONCLUSIONS AND CLINICAL RELEVANCE

Results suggested that all 5 disease agents are in Rhode Island and pose a risk to dogs and humans. Knowledge concerning tick distributions may be useful in predicting the pattern of disease associated with particular tick species and may aid diagnostic, prevention, and control efforts.

Transmission of Theileria parva in the traditional farming sector in the Southern Province of Zambia during 1997-1998

The incidence of first contact with the protozoan Theileria parva was determined in two traditional cattle herds in the Southern Province of Zambia during a period of average rainfall in 1997 and 1998, following a drought in the previous two years. Compared to that period, there was a marked increase in the number of rainy season first contacts attributable to transmission by Rhipicephalus appendiceulatus adults. However, there were still more dry season contacts that resulted from nymphal transmission. These results highlight the important role that climate plays in the transmission of theileriosis in the Southern Province of Zambia.

[Molecular tools in the epidemiology of tick-borne bacterial diseases]

Molecular tools have been used to detect rickettsiae in ticks. In Ixodes ricinus ticks collected in France, we detected for the first time there an emerging pathogen, Rickettsia helvetica, and an Ehrlichia sp, closely related to the agent of human granulocytic ehrlichiosis. In Guadeloupe (French West Indies), we described the occurrence of African tick-bite fever due to Rickettsia africae, which had been previously reported in sub-Saharan Africa only. In Africa, we completed our knowledge about the distribution of R. africae (Mali, Niger, Sudan, Burundi), and detected for the first time Rickettsia mongolotimonae, an emerging pathogen. Anaplasma marginale the agent of bovine anaplasmosis was detected in Mali. Rickettsiae of unknown pathogenicity were detected in Mali and Niger.

[Prevelance of the etiological agent of human ehrlichiosis (HGE) in ticks from west-north Poland]

Ehrlichias occur in ticks in the cells of their haemolymph-hematocytes. They enter the vertebrate host organism with the saliva of the tick, during a blood meal. Humans can also be the hosts for this pathogen. Two pathogens cause a humane disease-monocytic ehrlichiasis (E. chaffensis) or granulocytic ehrlichiasis (HGE factor). The above disease units are difficult to diagnose because of their non-specific symptoms. A preliminary study has been conducted on the prevalence of the HGE factor in the ticks, Ixodes ricinus in the recreational areas of the West-Pomeranian Province. All forms of I. ricinus were collected from 3 sites. All the sites are known to be frequented by hikers and gatherers of forest mushrooms and berries. The site selection involved also careful consideration of the tree- and underbrush type. The ticks were collected twice a year in spring (May/June) and in autumn (August\September), which was associated with the biological activity of the collected acarines. A total of 1159 Ixodes ricinus ticks were collected, in this number 172 females, 167 males, 597 nymphs, and 223 larvae. Using the PCR technique, the 16SrRNA-gene fragment was amplified using primers specific for the HGE factor: EHR 790 and EHR 521. The studied population contained 3.7% infected females in spring and 2.7% in autumn, 0.68% infected males in spring, no infected in autumn. The nymphs were infected in spring (2.17%) and in autumn too (0.73%), but the larvae were not infected in both seasons. Analysing the above-mentioned results it can be concluded that the decisive majority of the individuals transmitting the HGE factor are the adult forms. The present study was only a preliminary one. In the future much more sites will be monitored, in the recreational areas of both the city of Szczecin and the entire province.