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Home , African tick bite fever, Japanese spotted fever, Lymphangitis, Murine typhus, Rickettsia felis, Rickettsia honei

- and -borne rickettsial emerging zoonoses Philippe Parola, Bernard Davoust, Didier Raoult

To cite this version:

Philippe Parola, Bernard Davoust, Didier Raoult. Tick- and flea-borne rickettsial emerging zoonoses. Veterinary Research, BioMed Central, 2005, 36 (3), pp.469-492. ￿10.1051/vetres:2005004￿. ￿hal- 00902973￿

HAL Id: hal-00902973 https://hal.archives-ouvertes.fr/hal-00902973 Submitted on 1 Jan 2005

HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. Vet. Res. 36 (2005) 469–492 469 © INRA, EDP Sciences, 2005 DOI: 10.1051/vetres:2005004 Review article

Tick- and flea-borne rickettsial emerging zoonoses

Philippe PAROLAa, Bernard DAVOUSTb, Didier RAOULTa* a Unité des Rickettsies, CNRS UMR 6020, IFR 48, Faculté de Médecine, Université de la Méditerranée, 13385 Marseille Cedex 5, France b Direction Régionale du Service de Santé des Armées, BP 16, 69998 Lyon Armées, France

(Received 30 March 2004; accepted 5 August 2004)

Abstract – Between 1984 and 2004, nine more species or subspecies of rickettsiae were identified as emerging agents of tick-borne rickettsioses throughout the world. Six of these species had first been isolated from and later found to be pathogenic to humans. The most recent example is parkeri, recognized as a human more than 60 years after its initial isolation from ticks. A new spotted fever rickettsia, R. felis was also found to be associated with and to be a human pathogen. Similarly, within the family have been considered to be of veterinary importance only, yet three species have been implicated in human diseases in recent years, including , the agent of human monocytic , Anaplasma phagocytophilum, the agent of human (formerly known as “human granulocytic ehrlichiosis agent”, E. equi and E. phagocytophila), and finally , which causes granulocytic ehrlichiosis in humans. We present here an overview of the various tick- and flea-borne rickettsial zoonoses described in the last 20 years, focusing on the ecological, epidemiological and clinical aspects. ticks / fleas / Rickettsia / Anaplasma / zoonoses

Table of contents 1. Introduction...... 470 2. Emerging SFG rickettsioses...... 471 2.1. Tick-borne rickettsioses ...... 471 2.2. Flea-borne spotted fever...... 473 2.3. Specific diagnosis procedures ...... 475 2.4. Treatment ...... 475 3. Human ehrlichioses and anaplasmoses...... 475 3.1. Human monocytic ehrlichiosis (Ehrlichia chaffeensis) ...... 476 3.2. Ehrlichia ewingii granulocytic ehrlichiosis ...... 480 3.3. Human granulocytic anaplasmosis (formerly human granulocytic ehrlichiosis)...... 481 3.3.1. Natural history of Anaplasma phagocytophilum ...... 481 3.3.2. Epidemiological and clinical aspects...... 482 3.4. Specific diagnostic procedures...... 484 3.5. Treatment ...... 484 4. Conclusions and perspectives ...... 485

* Corresponding author: [email protected] 470 P. Parola et al.

1. INTRODUCTION , the agent of Rocky Mountain spotted fever in the USA [126, Rickettsial diseases are zoonoses caused 154]. Interestingly, R. rickettsii was consid- by obligate intracellular bacteria grouped in ered as the only agent of tick-borne rick- the order . Although the bacte- ettsioses in America throughout the 20th ria of this order were first described as short, century. Although other spotted fever group Gram-negative rods that retained basic (SFG) rickettsiae were detected from ticks fuchsin when stained by the method of there, these were considered as “non-path- Gimenez, the of has ogenic” rickettsiae [116, 117]. At the same undergone significant reorganization in the time, other continents were considered to last decade. For example, , have their specific tick-borne pathogenic the agent of has recently been rickettsia such as R. conorii (in Europe and removed from Rickettsiales [117]. To date, Africa), R. sibirica (in the former USSR and three groups of diseases are still commonly China), and R. australis (in Australia) classified as rickettsial diseases. These [117]. However, between 1984 and 2004, include (i) rickettsioses due to bacteria of nine more species or subspecies of tick- the genus Rickettsia, including the spotted borne spotted fever rickettsiae were identi- fever group and the group rickett- fied as emerging throughout the siae, (ii) ehrlichioses and anaplasmoses due world [116, 117]. A new spotted fever to bacteria within the family Anaplasmata- group rickettsia, R. felis was also found to ceae which has been reorganized, and be associated with fleas and to be patho- (iii) due to Orientia tsutsuga- genic to humans [59]. mushi [37, 58, 117, 151]. Since scrub Similarly, bacteria within the family typhus is transmitted by trombiculid Anaplasmataceae have long been consid- in the Asian-Pacific region, it will not been ered to be only of veterinary importance, reviewed here [151]. yet three species have been implicated in The classification within Rickettsiales is human diseases in recent years. The first continually modified as new data become human case of monocytic ehrlichiosis available, particularly those based on molec- (HME) was described in 1987 in the USA ular phylogenetic studies. However, experts and first assumed to be due to Ehrlichia in the field of rickettsiology frequently dis- canis, the agent of canine monocytic ehrli- agree over species definitions. In this review chiosis [81]. The causative agent of HME, we use currently accepted taxa, as well as Ehrlichia chaffeensis, was later isolated in names of species or subspecies proposed 1991 in the USA [34]. In 1994, human gran- recently that are based on polyphasic taxo- ulocytic ehrlichiosis was first described in nomic studies which integrate phenotypic the USA [30] and has subsequently been and phylogenetic data [49]. shown to occur in Europe [110]. The caus- Since the beginning of the 20th century, ative organism, first known as the “HGE ticks and fleas have been implicated as vec- agent” had been found to be closely related tors, reservoirs, and/or amplifiers of some to E. equi and E. phagocytophila (pathogens rickettsial bacteria recognized as agents of of horses and ruminants, respectively). human zoonoses [117]. The flea, Xenop- However, phylogenic studies showed that sylla cheopis, is the main vector of murine insufficient differences exist among these typhus due to , a typhus three to support separate species designa- group rickettsia whereas rodents, mainly tions. Therefore these agents are grouped Rattus norvegicus and R. rattus, act as res- with Anaplasma spp. [37]. Currently, all ervoirs [117]. Ixodids (hard ticks) were first three are considered as a single species, implicated as vectors of spotted fever group Anaplasma phagocytophilum and the dis- rickettsioses in 1906, when the Rocky ease has now been renamed as human gran- Mountain wood tick was shown to transmit ulocytic anaplasmosis. Finally, Ehrlichia Emerging rickettsial diseases 471 ewingii, the agent of canine granulocytic dental hosts when they are bitten by ticks. ehrlichiosis, was found in 1999 to cause dis- When transmitted to people, the pathogenic ease in humans [24]. rickettsiae multiply in endothelial cells Here we present an overview of the var- causing a which is responsible for ious tick- and flea borne rickettsial zoon- the clinical and laboratory abnormalities of oses described in the last 20 years, focusing rickettsioses [117, 150]. Ecological charac- on the ecological, epidemiological and clin- teristics of the tick vectors are keys for the ical aspects. epidemiology of tick-borne diseases [105]. For example, Dermacentor ticks are well known to bite people on the scalp in Europe. As a consequence, the inoculation in 2. EMERGING SFG RICKETTSIOSES R. slovaca , which is transmitted by Dermacentor spp. in Europe, is located 2.1. Tick-borne rickettsioses on the scalp [122]. On the contrary, Ambly- omma hebraeum which are known as vec- Between 1984 and 2004, nine more spe- tors of R. africae in southern Africa, emerge cies or subspecies of tick-borne spotted from their habitats and actively attack ani- fever rickettsiae were identified as emerging mals including people if they enter their pathogens throughout the world, including, biotopes such as the bush during safaris. R. japonica in Japan [6, 46, 65, 71, 72, 82– Numerous ticks can attack a host at the 84, 146]; “R. conorii caspia” in Astrakhan same time and Amblyomma spp. are highly [35, 38, 39, 143], Africa [47] and Kosovo infected by rickettsiae [62, 106]. Thus, [48]; R. africae in sub-Saharan Africa and cases of African tick-bite fever often occur the [62, 63]; R. honei in the as grouped cases among subjects entering Flinders Island, offshore of Australia [9, 57, the bush (safari, raid adventure…) and peo- 140, 141], the Island of Tasmania, Australia ple can suffer several tick bites simultane- [153], Thailand [73], and possibly in the ously [62]. USA [13]; R. slovaca in Europe [29, 74, 101, 122]; “R. sibirica mongolotimonae” in The role of vertebrates as reservoirs of China [157], Europe [44, 118] and Africa rickettsiae is still discussed. In natural ver- [106, 113]; R. heilongjiangensis in China tebrate hosts, could result in a [42, 49]; R. aeschlimannii in Africa [11, rickettsiemia, which enables new lines of 112, 121] and Europe [43]; and finally uninfected ticks to become infected and for R. parkeri in the USA [104]. R. helvetica is the natural cycle to be perpetuated. How- also suspected to be a human pathogen in ever, vertebrates may be rickettsemic for Europe [45] and Asia [46, 61, 107], but this only short periods. In southern Zimbabwe, needs confirmation. Interestingly, out of an endemic area for R. africae infection, the nine tick-borne SFG rickettsiae recently almost 100% of cattle were found to have found to be pathogens for people after 1984, antibodies to SFG rickettsiae. Infection six were first isolated from ticks and later models showed mild clinical manifesta- found to be pathogenic to humans. The tions including regional , delay between their isolation from ticks and dermal erythema, edema, and tenderness at their implication in human diseases ranged the inoculation site. Rickettsiemia was detect- up to 65 years, in the case of R. parkeri able for at least 32 days post infection, sug- which was considered a “non pathogenic gesting that cattle could serve as reservoirs rickettsia” until 2004 in the USA [104]. for R. africae [67]. Other experiments showed Ixodids (hard ticks) may act as vectors, that infection was transmissible to goats reservoirs, and/or amplifiers of spotted through tick-bite, but led to asymptomatic fever group rickettsiae. Humans are inci- infection and short term rickettsiemia [68]. 472 P. Parola et al.

Figure 1. Inoculation eschar (tache noire) at the tick- or flea-bite site, a typical sign of spotted fever group rickettsioses. Note that it may, however, be absent (i.e. Rocky Mountain Spotted fever due to R. rickettsii in America is not associated with eschar).

Each stage of the ixodid tick feeds only such as R. slovaca [123], R. africae [66], once. As a consequence, transstadial trans- and R. parkeri [53], and the suspected path- mission (i.e. passage of bacteria from one ogen R. helvetica [25]. Interestingly, some stage to another, from larvae to nymphs and tick-borne rickettsiae may have a deleteri- adults) is a necessary component for vecto- ous effect on their vectors [94]. Many ques- rial competence. A rickettsia acquired by a tions remain unresolved concerning the tick during feeding on a rickettsiemic ani- ecoepidemiology and life cycle of many mal can then only be transmitted to another tick-borne rickettsiae. host when the tick has moulted to its next The clinical symptoms of spotted fever developmental stage [105]. When rickettsiae group rickettsioses generally begin 6–10 days are transmitted efficiently both transstadi- after the bite and typically ally and transovarially (from one genera- include fever, headache, muscle pain, rash, tion to the next via the female ovaries) in a local lymphadenopathy, and a characteris- tick species, the tick will also be a reservoir tic inoculation eschar (“tache noire”) at the of the bacteria; the distribution of the dis- bite site (Fig. 1) [117]. However, the main ease caused by the bacteria will then be clinical signs vary depending on the rick- identical to that of its tick host [105]. Effi- ettsial species involved, and may allow for cient transovarial transmission has been distinction between several SFG rickettsi- demonstrated for some species of SFG rick- osis occurring in the same location. For ettsiae (but not all), including some of the example, is charac- currently recognized emerging pathogens terized by the high frequency of multiple Emerging rickettsial diseases 473 inoculation and grouped cases. This ments by the group that provided the first is due to the fact that numerous highly description of R. felis [120]. The ELB agent infected Amblyomma ticks may attack and was definitely characterized as a unique bite many people in several places at the spotted fever group rickettsia, and finally same time [62]. In contrast, in cases of Med- the name R. felis was validated [19, 76]. iterranean spotted fever due to R. conorii, a More arguments on the pathogenicity of single eschar is usually due to the low affin- R. felis for humans were provided in 2000 ity of the tick to bite people and a low rate in Mexico, when three patients with fever, of infection of the ticks [117]. The details exanthem, headache, and central-nervous- of emerging pathogen characteristics are system involvement were diagnosed with presented in Table I. Tick-borne SFG rick- R. felis infection by specific PCR of blood ettsioses range from mild to severe and fatal or skin and seroconversion to rickettsial disease. To date, no mortalities or severe antigens [158]. Since then, we found high complications have been reported in patients antibody titers to R. felis in two French with African tick-bite fever caused by R. afri- patients with clinical rickettsial disease and cae [62], whereas severe disease, including one fatal case, has been reported with Jap- 2 of 16 Brazilian patients with febrile rash anese spotted fever rickettsioses [6, 71, 72, 84]. [120]. Moreover, we identified specific sequences of R. felis in the serum of one Brazilian patient [120]. In 2002, two cases 2.2. Flea-borne spotted fever of typical spotted fevers were reported in an adult couple in Germany [125]. Clinical Flea-borne spotted fever (also called features included fever, marked fatigue, flea typhus) is an emerging disease due to headache, generalized maculopapular rash , which is incompletely and a single black, crusted, cutaneous lesion described. This rickettsia was probably first surrounded by a halo (on the woman’s right detected in cat fleas Ctenocephalides felis thigh and the man’s abdomen). The man in 1918 [138]. It was rediscovered in 1990 had enlarged, painful lymph nodes in the when a Rickettsia-like organism was inguinal region. Serologic techniques dis- observed by electron microscopy in midgut criminated R. felis infection among several epithelial cells of C. felis in the USA [1]. rickettsiae for the woman and this was con- This bacterium was characterized by firmed by detection of R. felis DNA in the molecular biology techniques and named woman’s sera. Although no laboratory evi- the ELB agent for the EL Laboratory dence of R. felis infection was obtained for (Soquel, CA, USA). In 1994, ELB agent the man, the simultaneous occurrence of DNA fragments were detected in blood symptoms similar to those observed in his samples obtained from a patient from Texas wife strongly suggests infection with the in 1991 [134]. In 1994 and 1995, isolation same microorganism [125]. Finally, we of the ELB agent was reported [115] and the recently reported the first case of R. felis name Rickettsia felis was proposed [59]. infection documented by serology in Asia Unfortunately, contamination with R. typhi [107]. Rash and/or eschar (6/8) have been has hampered subsequent work. The defin- reported in the few documented cases itive cultivation and characterization of the R. felis has also been recently detected in ELB agent was achieved in 2001 [120]. Par- fleas in Brazil [98], Ethiopia [120], Spain ticularly, we showed that this rickettsia can [85], France [130], the United Kingdom be cultivated at low temperature only [120]. [70], Thailand [109] and New Zealand [69]. We suggested that discrepancies with pre- To date, three species of fleas have been viously reported phenotypic findings may associated with R. felis including C. felis [8, have resulted from contamination of R. felis 85, 98, 109, 130], C. canis [109], and Pulex cultures, which was reported after experi- irritans [8]. Transovarial transmission of 474 P. Parola et al. infection have have infection Documentation c rica (1). Eschar (6/8), Eschar (6/8), (1). rica R. helvetica characteristics Eschar (1 case) Conjunctivitis 34%. with cervical nodes. nodes. Mild. cervical with 43%. No fatal case reported. No fatal 43%. rash (5/8) and (2/8). lymphangitis and (5/8) rash Specific clinical and epidemiological epidemiological and clinical Specific May be severe. One fatal case reported. One fatal May be severe. been reported, but discussed. Few cases Few discussed. but been reported, Eschar and maculopapular rash Eschar and maculopapular (1 case) Eschars: 95% (54% multiple). Rash (49%): (49%): Rash multiple). (54% 95% Eschars: Thailand. Rash and eschar seems to be rare. be seems to eschar and Rash Thailand. with 8% purpuric. Eschar 25%. Nodes 55%. 25%. Nodes Eschar 8% with purpuric. documented by serology only in France and in in and France in only serology by documented has yet to be definitely confirmed. TIBOLA confirmed. has yet to be definitely and July (7) and South Af South and (7) July and Rural. Eschar 23%. Maculopapular rash (94%). Rural. Eschar 23%. Maculopapular Outbreaks and clustered cases 74%. Fever 88%. and clustered cases 74%. Fever Outbreaks sarcoidosis related to related sarcoidosis April to October. Eschar (91%) and rash (100%). rash (91%) and Eschar October. to April maculopapular or vesicular (50%) Regional nodes nodes Regional (50%) vesicular or maculopapular Incompletely described. Fatal perimyocarditis and perimyocarditis Fatal described. Incompletely Rural disease Ecotourism,(safari, Ecochallenges…). Rural. Peak in December and January. Rash (85%) Rash (85%) and January. Rural. Peak in December Cases described in southern France between March between March France Cases in southern described , a a , a a a R. helvetica Africa a a vector has not been definitely proven. proven. has a vector not been definitely Chad Japan bamboo cutting. activities, Agricultural Rural. Africa Europe scalp the eschar on Typical rare. Rash and Fever Thailand Thailand distribution Geographic West Indies Texas (USA) (Indian Ocean) (Indian Reunion Island Island Reunion Inner Mongolia Mongolia Inner Europe, Japan Europe, (China) Southern France Southern Southern Europe Southern SubSaharan Africa SubSaharan Flinders island and and island Flinders South Central USArash. and eschars multiple fever, reported: case One Northeastern ChinaNortheastern case reported. and nodes. No fatal eschar, Rash, Astrakhan, Kosovo Astrakhan, Tasmania (Australia) Tasmania , c d c c c c c c e c d , 2003 , , 2000 d e First First 1992 1992 2003 emalymphadenopathy”. in 1930’s, 1930’s, in definitely in definitely 1999 documentation documentation of human cases of human Note that the pathogenicity of 1982 1996 1992, 1968 1997 1939 2004 19961992 1985 1991 1993 1998 2001 1991 1996 1979 2002 1997 2002 1990 data Preliminary in ticks or/and isolated in this tick, its role as identification -borne--eryth b b b b b b b b b b b b b b spotted fever rickettsioses (1984–2004). (1984–2004). rickettsioses fever spotted Dermacentor “

I. ricinus I. I. ovatus I. Ha. flava Ha. hydrosauri D. silvarum marginatum marginatum Rh. pumilio Rh. H. m. rufipes m. H. D. reticulatus I. granulatus I. D. marginatus D. Ixodes ovatus Ixodes Main vector(s)Main First I. monospinus I. I. persulcatus I. Hy. truncatum Hy. Am. maculatum Am. variegatum Am. Am. cajennense Am. Rh. appendiculatus Rh. Documentation by molecular tools. molecular Documentation by Hyalomma asiaticum Hyalomma e Amblyomma hebraeum Amblyomma Hyalomma marginatum marginatum Hyalomma Dermacentor taiwanensis Dermacentor Rhipicephalus sanguineus Rhipicephalus Bothriocroton (Aponomma) (Aponomma) Bothriocroton Haemaphysalis longicornis Haemaphysalis Although the rickettsia has been detected b (1991) Disease (1970’s) TIBOLA Oriental or Oriental description) fever (1984) fever fever (1934) fever (first clinical clinical (first spotted fever fever spotted Flinders island Flinders Astrakhan fever African tick-bite tick-bite African Unnamed (1996) Unnamed Unnamed (1992) Unnamed Unnamed (1999) Unnamed Unnamed (2004) Unnamed Unnamed (2002) Unnamed Japanese spotted spotted Japanese DEBONEL (1997) Documentation by serology; Documentation by d Characteristics of emerging tick-borne emerging of Characteristics Detection from tick only. Detection from tick only. R. japonica R. honei “R. sibirica sibirica “R. mongolotimonae” R. heilongjiangensis R. helvetica R. slovaca “R. conorii “R. caspia” by culture; by Table I. Rickettsia a R. parkeri R. aeschlimannii R. africae for “tick-borne lymphadenopathy”. DEBONEL for Emerging rickettsial diseases 475

R. felis in fleas has also been reported, sug- trol. This technique has been successful gesting that fleas could act as reservoirs of with EDTA-blood, serum, and the rickettsia [8]. All these data suggest that specimens, in the diagnosis of African tick R. felis infection may be endemic world- bite fever and infection due to R. slovaca wide. The role of mammals, particularly [119, 122]. This technique was also applied and dogs, in the life cycle and circula- in our laboratory to DNA from 103 skin tion of R. felis, requires exploration. biopsies from patients with confirmed rick- ettsiosis, 109 skin biopsies from patients who possibly had a , and 2.3. Specific diagnosis procedures 50 skin biopsies from patients with no rick- The specific methods for the diagnosis of ettsial disease. Specificity was 100%. Sen- rickettsioses were reviewed a few years ago sitivity (68%) was 2.2 times higher than [75]. Serologic tests are the most valuable culture and 1.5 times higher than regular tools while is cur- PCR [50]. rently considered as the reference method. One limitation of serology is the cross-reac- 2.4. Treatment tivity that might occur between the antigens of organisms within the same genus and in Early empiric therapy should different genera [105]. Thus, serology be prescribed in any suspected tick-trans- should only be considered as the first step mitted rickettsiosis, before confirmation of towards diagnosing a rickettsial disease, the diagnosis. (200 mg per particularly if no rickettsiae has ever been day) remains the treatment of choice for isolated or detected in the area. This will tick- and flea- transmitted SFG rickettsi- prevent mistakes being made when “emer- oses, including in children [60, 87, 114, 117]. gence” of tick-borne diseases are described. In cases of allergy to , chlo- In order to differentiate infections within ramphenicol or josamycin (a macrolide not rickettsial antigens, difference in dilution as available in the USA) may be administered. well as cross-absorption of sera and West- Fluoroquinolones and newer macrolides ern-blotting can be done when cross reac- may also be used [28, 129, 135]. In pregnant tion is suspected [75, 107]. Isolation in cell women, josamycin or newer macrolides cultures, particularly using the shell vial can be used. In patients with severe disease, technique remains the ultimate diagnostic doxycycline should be administered intra- method but is only available in biosafety venously up to 24 h after apyrexia. The exact level 3 laboratories [75, 148]. Polymerase treatment duration is not fully determined. chain reaction (PCR) and sequencing meth- Usually, therapy should be prescribed for ods are now readily used to detect and iden- up to 2 or 3 days after the patient’s fever has tify rickettsiae in blood and skin biopsies abated. The use of corticosteroids in severe (particularly the eschar). Ticks and fleas forms is controversial [71]. may also be used as epidemiological tools to detect the presence of a pathogen in a spe- cific area, leading sometimes to detect rick- 3. HUMAN EHRLICHIOSES ettsiae of unknown pathogenicity [105, AND ANAPLASMOSES 130]. We recently proposed a nested PCR assay, named “suicide PCR”, which uses Ehrlichioses and anaplasmoses are caused single-use primers targeting a gene never by bacteria within the family Anaplasmata- amplified previously in the laboratory. ceae. These diseases have been known for Such a procedure avoids “vertical” contam- a long time in veterinary medicine [127]. ination by amplicons from previous assays, However, in recent years, three bacteria one of the limitations of extensive use of have been recognized as emerging tick-borne PCR, and does not require a positive con- pathogens in humans: (i) human monocytic 476 P. Parola et al.

intracytoplasmic inclusions in several of the monocytes. The patient had been bitten by ticks in Arkansas. This case was first assumed to be due to Ehrlichia canis, the agent of monocytic canine ehrlichiosis [81], but the causative agent of HME, Ehr- lichia chaffeensis, was isolated in 1991 in the USA [34]. Since that time, several hun- dred cases have been reported. Since a major review on Ehrlichia chaffeensis, was recently published, we refer the reader to this major paper for details [102]. Figure 2. Multiple morulae consistent with Ehr- lichia ewingii in a neutrophil (Giemsa stain, E. chaffeensis is maintained in nature as 100×). Reprinted from [156]. a complex zoonosis, potentially involving many vertebrates serving as reservoirs for the bacterium and/or blood meal sources for tick vectors. Amblyomma americanum, the ehrlichiosis due to Ehrlichia chaffeensis, Lone Star tick, is the primary vector of (ii) Ehrlichia ewingii granulocytic ehrlichi- E. chaffeensis [4]. In the USA, this tick is osis, and (iii) human granulocytic anaplas- distributed in south central, southeastern mosis (formerly human granulocytic ehrli- and mid-Atlantic USA. It usually inhabits chiosis) due to A. phagocytophilum (formerly meadows, woodlands and hardwood for- named the HGE agent, E. phagocytophila ests. Its primary hosts are diverse wild and and E. equi) [37] (Tab. II). Ehrlichioses and domestic mammals, although deer are con- anaplasmoses are tick-borne zoonoses, the sidered to be definitive hosts (hosts upon causative agents being maintained through which the reproductive stage depends). All enzootic cycles between ticks and animals. stages of A. americanum readily bite peo- To date, transovarial transmission of these ple. Adult and nymph activity peaks from agents in ticks appears to be inefficient. April through June and decreases as the Thus, mammals are presumed to play a summer progresses. Larvae are active major role in the maintenance and propaga- through November. E. chaffeensis has been tion of these bacteria in nature. Various detected in A. americanum ticks collected infectious syndromes have been described from 14 states and molecular prevalence in animal species [31] (Tab. II). In vivo, was found to vary between 5–15%, with a these bacteria mainly infect the cells of lower prevalence appearing within nymphs bone marrow origin, in particular leuco- than adults [41, 102]. The tick-bacteria cytes where they occur within membrane- association is, however, poorly known. bound vacuoles. The intraphagosomal bac- Although transstadial transmission of E. chaf- teria divide by binary fission to produce a feensis is known to occur in A. americanum, typical cluster of organisms called a morula there is no data supporting transovarial (Fig. 2). The interaction between members transmission and the absence of transovarial of Anaplasmataceae and the targeted cells transmission has been demonstrated in labo- have been illustrated recently [102, 128]. ratory models [79]. Although PCR has been used to detect E. chaffeensis in other tick species in the USA, their role as a vector has 3.1. Human monocytic ehrlichiosis not been demonstrated [102]. The first HME case was described in To date, the white-tailed deer (Odocoileus 1986, when the examination of a peripheral virginianus) is the sole recognized efficient blood smear of a severely ill man yielded reservoir of E. chaffeensis. Evidence is based Emerging rickettsial diseases 477 on seroprevalence studies, molecular detec- (n = 140), Oklahoma (4.3 cases per million tion and isolation of E. chaffeensis, as well population), and Tennessee (2.5 cases per as experimental transmission studies. Bac- million population). Sporadic cases have teremia has been demonstrated to persist up been reported in the East Coast, most nota- to months after infections [102]. Experimen- bly along the Mid-Atlantic coast plain [52, tal transmission has also been demonstrated 102]. However, differences between the in domestic dogs (Canis familiaris), pre- results of passive and active surveillance senting mild to unapparent disease, and the have been discussed. In general, incidence red fox (Vulpes vulpes). Domestic dogs and based on active surveillance has been esti- wolves (C. lupus) are considered as poten- mated to be 10-fold higher than the highest tial reservoirs because of their numbers, rates reported by individual states for pas- their tick parasitism and the close contact to sive surveillance [102]. For example, a pro- humans, and their susceptibility to E. chaf- spective study in Cape Girardeau, Missouri feensis. Domestic goats were also found to and surrounding counties in southeast Mis- be infected in a single report with a long- souri and southwestern Illinois was con- term bacteremia [102]. Although serologic ducted during a 3-year period (1997–1999). (in the raccoon (Procyon lotor), white- A total of 102 febrile patients with tick- footed mouse (Peromyscus leucopus) and exposure were enrolled during this period, Virginia opossum (Didelphis virginiana)) and 29 (28.4%) of them had either definite or molecular (in coyote (Canis latrans)) or probable HME. As expected, all cases evidence of infection has been reported in occurred between April and mid-August, other mammals, the role of these mammals including 16 (56%) in July. For 1997, 1998, as efficient reservoirs has yet to be demon- and 1999, the calculated incidence for HME strated [102]. was 2, 4.7, and 3 per 100 000 population, From 1986 to 1997, more than 700 pre- respectively (incidence calculations were sumptive cases were reported to the CDC based on the total population of all counties [102]. Data accumulated during the first where the patients lived). According to the five years (1997–2001) of national surveil- authors, HME was even probably underes- lance for human ehrlichioses and anaplas- timated in this prospective study through- moses have recently been reported [52]. out the rural southeastern and south central During this period, 503 cases of HME were states. In this particular disease-endemic area, reported, including 338 confirmed cases case-patients were identified mainly in one reported from 23 states. Most HME cases primary care-based physician’s office that were reported from south-central and south- cares for a population base of approxi- eastern USA. There, the tick vector A. amer- mately 7 000 persons. Therefore, the real icanum reaches its highest population and incidence of HME is likely to be higher in Cape human exposure is the greatest [102]. HME Girardeau and surrounding counties [97]. is a seasonal disease and incidence is cor- related with tick activity, particularly in Tick-bite or tick-exposure is a common nymphs and adults. Although HME has finding in patients with HME, but this fea- been reported during March through Novem- ture is lacking in 10–30% of the cases. The ber, most of the cases occur during May incubation period is 1 to 2 weeks (median through July. Reports of HME occurring in 9 days). Among the 29 cases reported above the late fall and winter are unusual but may in Missouri, a tick bite was documented in occur particularly in southern states [52, 21 case-patients (72%), and tick exposure 102]. The states with the highest average without a tick bite in 8 case-patients (28%) annual incidence of HME were Arkansas [97]. For all case-patients, tick attachment (6.2 cases per million population), Missouri ranged from 24 to 72 h, except for one case- (5.2 cases per million population) where the patient who experienced tick attachment largest absolute number of cases was reported for 12 h. The incubation period from the 478 P. Parola et al. and South Carolina USA: Missouri, Oklahoma and Tennessee South eastern and south USA central South-central and South- USA eastern Georgia USA Oklahoma, South-central and South- cases USA. Sporadic eastern along the Atlantic Coast plain a, with or without leucopenia rophilic polyarthritis and/or gy (2000). Susceptibility or role festations. Leucopenia ies. Mild-to-moderate 1997), isolation and animal models (1997) Not described Georgia, USA: Kentucky, Fever, headache, thrombocytopeni Fever, 7/8 cases seen in immunocompromised patients Fever and lameness, and/or neut Fever neurologic abnormalit lymphocytes Reactive (2001). Potential reservoir unknown unknown reservoir: as efficient Fever, headache, , , and less frequently rash, Fever, cough, and neurologic mani Thrombocytopenia. May be severe Symptoms and common laboratory findings Geographic area – Serological evidence settings in the USA Various granulocytic granulocytic Molecular detection detection Molecular models animal and (2002) E. ewingii ehrlichiosis (1999) ehrlichiosis (1971) ehrlichiosis (1987) Related diseases (year of recognition) White-tailed White-tailed deer Human Dogs Canine granulocytic DogsGoatsCoyoteRaccoon, white- –footed mouse, possum Virginia – Mild to unapparent disease – Isolation (2000). Susceptibility reservoir: or role as efficient Molecular detection and serolo Oklahoma, USA Virginia, White-tailed deer – Molecular detection ( Human Human monocytic to be infected A. americanum Amblyomma americanum Main vector(s) Animals found Neutrophilc granulocytes Monocytes Typical cell cell Typical tropism

The agents of emerging human ehrlichioses and anaplasmoses. human ehrlichioses The agents of emerging

E. ewingii (1992) (1991) Ehrlichia chaffeensis Table II. Bacteria (year of cultivation) Emerging rickettsial diseases 479 USA Europe Spain, Austria, Norway and the Czech Republic Northern and central Europe Europe Northern central and USA: Northeastern and North Coast. West regions; central Europe Northern central and casesUSA (most in north eastern regions and upper mid-western in of the USA; less frequently California). Northern Europe Northern central and Europe Northern central and Sweden

ticks (1997) Eastern and mid western USA I. trianguliceps I. dentatus (1996) Eastern and mid western USA sal discharge, diarrhea,sal discharge, d in Great Britain (2000) norexia, lower limb oedema, lower norexia, , tachypnea. Neutrophilia, d. Potential reservoir in thed. Potential USA reservoir (2003) and describe woodland vole (2001) Symptoms and common laboratory findings Geographic area Fever, and/or depression, a Fever, petechiae, icterius, ataxia, or reluctance to move febrileUndifferentiated illness occurring in summer or spring arthralgies, , cough, Anorexia, atypical pneumonitis Leucopenia. Thrombocytopenia. May be severe and thrombocytopenia (natural lethargy infection) Fever, anorexia lethargy, Fever, lymphopenia High fever, decrease in decrease milk production, and possibly High fever, depression,anorexia, cough, na abortion, mastitis – Not described. Enzootic cycle involving – Not described. Potential reservoir Related diseases diseases Related (year of recognition) ehrlichiosis (1969) (1994 USA; 1997 Europe) ehrlichiosis (1997) Tick-borne fever fever Tick-borne (1932)

Small mammals mammals Small vole) (mice, shrew, deerRoe boarsWild FoxesBirds – – of infection evidence Molecular characterized Not well – Not described. Molecular of infection evidence (2003) Czech Republic – Not described. Molecular of infection evidence (2003) Austria Not described. Molecular of infection evidence (2003) USA, Europe to be infected Cottontail rabbits – Not described. Enzootic cycle with White-tailed deer White-tailed Human Human anaplasmosis Equines HumanHuman Equine granulocytic DogsCatsWhite-footed mouse Unnamed (1995) Mild to unapparent disease (experimental models). Feline granulocytic – Not describe Cattle, sheeps, goats I. ricinus Main vector(s) Animals found USA: Ixodes scapularis pacificus I. Europe: Typical cell cell Typical tropism Neutrophilc granulocytes ,

Continued. Ehrlichia Table II. Bacteria (year of cultivation) and HGE agent) Anaplasma phagocytophilum (1999) (formerly phagocytophila, E. equi 480 P. Parola et al. observed tick bite until the onset of illness 1 308 ticks) [155]. In a recent series of ranged from 1 to 4 weeks. 15 dogs confirmed to have E. ewingii infec- HME appears as an undifferentiated tion by molecular tools, clinical signs included febrile illness. The main clinical signs include fever and lameness, and/or neutrophilic fever (98%), headache (77%), polyarthritis and/or unexplained ataxia, pare- (65%), vomiting (36%), rash (35%) includ- sis or other neurologic abnormalities [56], ing petecchiae, macular, maculopapular or but asymptomatic infection was found in diffuse erythema , cough (25%), neurologic three dogs [56]. Laboratory findings included findings and mental status changes (20%) thrombocytopenia (all dogs), reactive lym- [102]. Malaise (30 to 80%) as well as various phocytes (five dogs). Morulae consistent manifestations including lymphadenopa- with E. ewingii infection were identified in thy, gastrointestinal symptoms, pharyngitis neutrophils in 8 dogs. However, identifica- or less frequently, conjunctivitis, dysuria, tion of granulocytic morulae does not dif- and peripheral edema may occur [102]. ferentiate infections due to E. ewingii from Leukopenia, thrombocytopenia, and ele- infections due to Anaplasma phagocytophilum vated hepatic transaminase levels are the that may occur in dogs [31]. Infection with most common laboratory findings. Hospi- E. ewingii has been reported in 6.2%– talization is required in more than half of the 15.8% of dogs from southeastern Virginia, cases and case-fatality rate has been esti- Oklahoma, and southeastern North Carolina. mated at 3.1% [102]. HME is most com- Recently, by combining data from PCR test- monly diagnosed in adults more than 50 years ing and experimental infection studies in old [52, 102]. Although age has appeared in fawns, at least 8 of 110 white-tailed deer some studies as an independent risk factor (7.3%) from Kentucky, Georgia, and South for severe or fatal HME, many severe or Carolina were shown to be infected with fatal cases have been described in appar- E. ewingii (Fig. 2). These data raised the ently healthy children or young adults. question of white-tailed deer as a potential Severe or fatal HME has also been reported reservoir for E. ewingii [156]. in immunocompromised patients [102]. Human infections with E. ewingii were Asymptomatic infection may occur based first reported in 1999, when blood samples on serologic evidence [102]. Finally, since collected in Missouri from 1994–1998 from A. americanum is also the vector of other tick- 413 patients with possible ehrlichiosis were borne agents, co-infection may occur [136]. retrospectively analyzed [24]. Four tick- exposed patients were shown to be infected 3.2. Ehrlichia ewingii granulocytic with E. ewingii by molecular tools. Further- ehrlichiosis more, morulae were seen in neutrophils from two of them. Clinical signs included Ehrlichia ewingii was recognized in fever, headache, thrombocytopenia, with or 1992 as the agent of canine granulocytic without leucopenia. Three of these patients ehrlichiosis [3], a disease that had been first had underlying diseases and were receiving described in a dog in 1971 in Arkansas [40]. immunosuppressive therapy [24]. More Thereafter the disease was described in sev- recently, four cases were reported in male eral other states in south eastern and south HIV infected patients from Oklahoma and central USA where the recognized vector is Tennessee [103]. The cases were confirmed the Lone Star tick, Amblyomma america- by molecular tools (4/4) and morulae in num (see human monocytic ehrlichiosis for granulocytes were found in one patient out details on this tick) [5, 31]. Field-collected of the two examined. Three were receiving ticks from North Carolina were recently highly active antiretroviral therapy and the tested and the infection rates for E. ewingii median CD4+ cell count was 176/µL (range, were low (< 1% in adults), with a minimum 106–226). The main clinical signs included infection rate for the nymphs at 0.4% (5 of fever (4/4), malaise and myalgia (2/4), Emerging rickettsial diseases 481 headache (1/4), nausea and vomiting (1/4). and cats [31, 144]. The target cells in the Leukopenia, thrombopenia and anemia were organism of A. phagocytophilum are neu- respectively seen in 3/4 patients. Other lab- trophils, although morulae have been oratory findings included an elevated aspar- described in other cells, such as the endothe- tate aminotransferase level (2/4), elevated lium and macrophages [96]. alanine aminotransferase level (1/4), and hyponatremia (1/4). Two patients were hos- 3.3.1. Natural history of Anaplasma pitalized and no fatal case was reported. In phagocytophilum the same study, 13 HIV patients infected with E. chaffeensis were reported and those The life cycle of A. phagocytophilum is infected with E. ewingii developed fewer not fully understood. In the USA, Ixodes disease manifestations and complications scapularis (the black-legged tick) is the than did patients infected with E. chaffeen- principal vector of A. phagocytophilum sis. This should be interpreted carefully [10]. It is distributed in southeastern USA, because of the small number of patients and mid and northeastern USA (where it evaluated [103]. To date, it is still unclear was previously named I. dammini). This whether E. ewingii causes disease primarily exophilic tick inhabits deciduous forests in immunocompromised persons or if it is and maritime forests and favors humid responsible for illnesses in a broader patient microhabitats. In the north of the USA, population. adults are active from March-April through late June, then again between October and December. Nymphs are active in the late 3.3. Human granulocytic anaplasmosis spring and summer. Larvae are active from (formerly human granulocytic late June through October. In the south of ehrlichiosis) the USA, all stages are usually active from The first case of clinically recognized November through May. Primary hosts of human granulocytic anaplasmosis was immatures are small mammals, reptiles and described in the USA in 1994 [30]. Then, birds. Adults feed on large-size mammals the disease emerged in Europe in 1997 (deer, dog). The affinity of this tick species [110]. The causative organism, first named for biting people is high. On the contrary, human granulocytic ehrlichia or HGE I. pacificus (the western black-legged tick) agent, was cultivated in HL 60 Cells in 1996 is the primary vector in the Pacific coast [55] and in tick cell culture in 1999 [91]. states [10]. It is distributed from the south- With the help of molecular phylogenetic ern Pacific coast of Canada through Cali- studies [37], this bacteria has been unified fornia, in shrub forests, coniferous forests, within the single species designation Ana- and deserts. Primary hosts for immature plasma phagocytophilum, with organisms ticks are small mammals, reptiles and birds, formerly known as (i) Ehrlichia equi, whereas adults feed on large sized mam- known as the agent of equine granulocytic mals. Both nymphs and adults readily bite ehrlichiosis in the USA since 1969 and people. Molecular detection of A. phagocy- reported starting in the 1990’s in Europe tophilum in both I. scapularis and I. pacifi- [12, 17, 133] and (ii) E. phagocytophila, cus ticks have been regularly published in known since the 1930’s as the agent of tick- the literature in recent years [78, 105]. borne fever in cattle, sheep and goats in Although other tick species or genera such most European countries where it may con- as Dermacentor spp. have been seldom shown tribute to considerable productivity losses to harbor A. phagocytophilum, their role as [21, 51, 142]. When infected, these animals a vector has not been demonstrated [32]. present various febrile syndromes [21, 93]. In Europe, I. ricinus is the recognized Other animals have been found to be infected vector of human granulocytic anaplasmosis with A. phagocyptophilum, including dogs [18, 21]. It is prevalent from western 482 P. Parola et al.

Europe (with the exception of the Mediter- common shrew Sorex araneus, and the ranean area) through central Asia, in a bank vole Clethrionomys glareolus have humid microhabitat in forests, woods bor- been shown to harbor A. phagocytophilum ders, and pastures. All stages are usually in Switzerland, and have been suggested as active between April and June and in the potential reservoirs [78]. Evidence that A. winter. During the summer, immature ticks phagocytophilum can be maintained in a remain active whereas adults often enter system in which woodland rodents are a diapause until early fall. The primary hosts dominant reservoir host species has also of immature ticks are small mammals, rep- been recently shown in Great Britain by tiles and birds. Occasionally, they feed on molecular tools [20]. Both bank voles and mid-size to large-size mammals. Adults wood mice were positive but restricted to feed on mid-size to large-size mammals. periods of peak nymphal and adult I. trian- The affinity for biting people is high. Many guliceps activity. Most PCR-positive rodents molecular epidemiological studies have were positive only once, suggesting that been conducted and published in recent rodent infections are generally short-lived years, and A. phagocytophilum has been and that ticks rather than rodents may main- detected in I. ricinus throughout Europe tain the infection over the winter [20]. I. tri- [18, 21, 139]. However, the dynamics of anguliceps usually bites small mammals transmission to mammals have not been only, and rarely people [132]. However, completely elucidated [95]. Coinfection of I. trianguliceps–driven endemic cycles may ticks with both A. phagocytophilum and provide an efficient reservoir from which I. other agents transmitted by the same tick ricinus may acquire infections from rodents, species, such as Borrelia burgdorferi, the and transmit the bacteria to another animal agent of are also regularly including people at the next blood meal reported [32], both in the USA and Europe. [20]. Roe deer (Capreolus capreolus) in In the USA, the white-footed mouse Per- Spain, Austria and the Czech Republic, omyscus leucopus and the white-tailed deer wild boars (Sus scrofa) in the Czech Repub- (Odocoileus virginianus), are thought to be lic and foxes (Vulpes vulpes) in Austria the most important reservoirs in the eastern have also been shown by molecular tools to and mid western USA. Recently, an be exposed to this bacteria [99, 111]. Usu- enzootic cycle between cottontail rabbits ally, genetic variants are often identified when and their ticks, I. dentatus was demon- A. phagocytophilum is detected in vectors, strated [54]. This tick has a low affinity for people or animals [86]. biting people and usually feeds on small Interestingly, only sequences determined mammals. However, as suggested by the for part of the GroEL operon of Anaplasma authors, the propensity of I. dentatus to sp. from wild boars in the Czech Republic densely inhabit peridomestic sites, and their were strictly identical to those detected in potential to be transported by birds, a cycle humans with anaplasmosis in Slovenia [111]. of transmission parallel to that of cottontail The role of birds in the circulation of rabbits would facilitate introduction and A. phagocytophilum has also been hypothe- perpetuation of A. phagocyptophilum [54]. sized both in the USA and in Europe [15, 33]. In addition, a cycle involving I. spinipalpis ticks and rodents has been identified in Colorado and California [159]. 3.3.2. Epidemiological and clinical In Europe, in addition to the large mam- aspects mals (horses, cattle, sheep, goats, dogs, cats) described above, small mammals such as Ten years have passed since the first the wood mouse Apodemus sylvaticus, the patient with clinically recognized human yellow-necked mouse A. flavicollis, the granulocytic anaplasmosis was described Emerging rickettsial diseases 483 in Minnesota, USA in 1994 [30]. From surveys have found a prevalence of antibodies 1997 to 2001, 654 confirmed, 434 probable, in a range of 0%–2.9% in blood donors and and 3 suspect/unknown were reported 1.5%–21% of tick-exposed people through- through national surveillance from 21 con- out northern and central Europe [18]. To tinental states in which the cases resided date a total of 20 cases have been reported [52]. This allows for an appreciation of the in Europe including Slovenia [7, 80], the epidemiological aspects of the disease, but Netherlands [147], Spain [100], Sweden is limited by the quality of the surveillance [16, 64], Norway [14], Croatia [90], Poland system [52]. Most cases were reported from [145], Italy [131], Austria [149], and France the states in the north eastern and upper [124]. The majority of cases occurred mid-western regions of the USA. The states between June and August [18]. When cases with the highest annual incidence of the dis- reported in 2001 were reviewed, a history ease were Connecticut (22.3 cases per mil- of tick-bite was recalled in 67% of the lion population), Minnesota (16.2 cases per cases; the median age was 38 years, and less million population), Rhode Island (12.7 cases per million population) and New York than 20% of the patients were under the age (4.7 cases per million population), where of 20 years. the largest absolute number (n = 438) was Human anaplasmosis appears most com- reported [52]. Locally high incidences monly as an undifferentiated febrile illness occur in both Wisconsin (up to 58 cases/ occurring in the summer or spring [96]. The 100 000) and Connecticut (up to 52 cases/ incubation period following the tick-bite is 100 000) (Dumler S., personal communica- 7–10 days. Symptoms include high fever, tion). A few patients have been described in rigors, generalized myalgias, severe headache California. The median age was greater and malaise [10, 96]. Anorexia, , than 50 years, with the highest age-specific nausea and a non-productive cough are fre- incidence occurring among people older quent. A rash is rarely reported (1–11%) than 50. Human anaplasmosis is clearly a and experts in the field do not consider a seasonal zoonosis, since most of the cases rash as part of the clinical picture of human occurred between May and October, linked anaplasmosis [10]. Leucopenia and throm- to the activity of the tick vectors [52]. At bocytopenia are often seen, and less fre- this period, the nymphal stage of I. scapu- quently anemia. Hospitalisation is required in laris, smaller and difficult to see when they approximately one half of the patients. The attach to the human body, are active. Outdoor disease may be severe, particularly in the activities are increased during the summer, elderly, when there is concomitent chronic ill- leading to an increased risk of exposure to nesses, a lack of recognition, or delayed spe- tick-bites [10, 52]. Human behavior in a specific setting have also been shown to cific antibiotic treatment [10]. Fatal cases influence the risk of tick bites. For example, have been reported in the USA, but case when six different human behaviors were fatality rate has been estimated to be about evaluated for acquiring I. pacificus nymphs 1% [10, 102]. In Europe, a few cases have in a deciduous woodland in California, peo- been reported to date. However, the disease ple in contact with wood were at higher risk seems to be less severe than that described when compared to those exposed to leaf litter in the USA and no death has been reported only; sitting on logs was the riskiest behav- [18]. It should also be noted that three cases ior followed by gathering wood, sitting showed atypical pneumonitis [124]. against trees, walking, stirring and sitting Finally, few patients have been shown to on leaf litter, and just sitting on leaf litter [77]. be coinfected with other tick-borne agents The first documented case of human ana- sharing the same Ixodes sp. vectors such as plasmosis in Europe was reported in Slovenia Lyme borreliosis and in Europe in 1997 [110]. Thereafter, seroepidemiologic and the USA [18, 92]. 484 P. Parola et al.

3.4. Specific diagnosis procedures sion or ≥ 4-fold change in serum antibody titers, or positive PCR result with subse- Laboratory confirmation of human mono- quent sequencing of the amplicons demon- cytic ehrlichiosis and human granulocytic strating Anaplasma-specific DNA in the anaplasmosis is based on several tests that blood, or isolation of A. phagocytophilum are not to date widely available for routine in blood culture. A probable human granu- use. Indirect immunofluorescence serology locytic anaplasmosis definition corresponds remains the most widely available test. to (i) a febrile illness with a history of a tick However, limitations include delay for sero- bite or tick exposure, and (ii) the presence conversion (early sera will often return neg- of a stable titre of A. phagocytophilum anti- ative), as well as possible false positive bodies in acute and convalescent sera if titre detection due to cross-reacting bacteria. > 4 times the cut off, or a positive PCR result Diagnostic procedures have been recently without a sequence, or presence of intracy- reviewed including serology, detection of toplasmic morulae in a blood smear [23]. morulae in leukocytes, molecular methods, immunohistochemistry and isolation in cell cultures [36, 102]. 3.5. Treatment Laboratory criteria for the diagnosis of both diseases have been defined by the Tetracyclines appear to be very effective Council of State and Territorial Epidemiol- in treating human ehrlichioses and anaplas- ogists [102]. They include demonstration of mosis. E. chaffeensis has been found to also a fourfold or greater change in antibody titer be susceptible to rifampin in vitro (without to E. chaffeensis or A. phagocytophilum in vivo evidence) but resistant to aminogly- antigen by IFA in paired serum samples, or cosides, macrolides and ketolides, cotri- a positive PCR assay and confirmation of moxazole, penicillin, cephalosporin, chlo- E. chaffeensis or A. phagocytophilum DNA, ramphenicol and quinolones [102]. It was or identification of morulae in leukocytes demonstrated in vitro, that fluoroquinolone and a positive IFA titer, or immunostaining resistance in E. chaffeensis is strongly cor- E. chaffeensis or A. phagocytophilum anti- gen in a biopsy or autopsy sample, or culture related to the presence of a specific amino of E. chaffeensis or A. phagocytophilum from acid variation in a portion of the protein a clinical specimen [102]. A confirmed case sequence of the A subunit of (GyrA) [88]. When the antibiotic susceptibilities of eight of human monocytic ehrlichiosis and human anaplasmosis requires a patient to have a strains of A. phagocytophilum collected in clinically compatible illness that is labora- various geographic areas of the United States tory confirmed. A probable case requires a were recently tested in vitro, doxycycline and rifampin were the most active drugs patient to have a clinically compatible ill- ness with either a single IFA titer at or above [89].However, levofloxacin was also active. Interestingly, no natural gyrase-mediated the cutoff dilution or the visualization of morulae in leukocytes. Recently, case def- resistance to fluoroquinolones was demon- initions were also adopted in Europe by the strated for A. phagocytophilum [88]. study group for Coxiella, Anaplasma, Rick- The optimal duration of doxycycline ettsia and of the European Society treatment in human ehrlichioses and ana- of Clinical Microbiology and Infectious Dis- plasmosis has yet to be determined. It is rec- eases [23]. Confirmed human granulocytic ommended that treatment be anaplasmosis definition requires (i) febrile continued for 7–10 days, or for at least 3– illness with a history of a tick bite or tick 5 days after defervescence. Most patients exposure, and (ii) demonstration of A. become afebrile within 1–3 days following phagocytophilum infection by seroconver- treatment [96, 102]. Emerging rickettsial diseases 485

4. CONCLUSION documented only in the USA. However, AND PERSPECTIVES there has been an increasing number of pub- lications suspecting its occurrence else- What are the factors influencing the where in the world in recent years. Patients emergence and recognition of tick- and flea with antibodies reactive to E. chaffeensis or borne rickettsial diseases in recent years? antigenically related to ehrlichiae have First, the major role of primary physicians been reported in Europe, Asia, South Amer- should be emphasized, including their care- ica, Central America and even Africa [102]. ful case history recording as well as their As discussed elsewhere, these results have complete physical and laboratory examina- to be considered with caution since serosur- tions, since it was essential for the description vey results can be due to different bacteria of some emerging SFG rickettsioses, such but cross-reacting with E. chaffeensis, leading as Flinders Island spotted fever, Japanese to misinterpretation [105]. DNA fragments spotted fever and Astrakhan fever. Second, closely related to those of E. chaffeensis the recent availability of molecular biology have been detected by PCR in ticks from techniques have been shown to greatly Russia [2], China [26, 152], Japan [137], facilitate the description of emerging human and Vietnam [108]. This fact neither con- rickettsioses and the investigation of their clusively incriminates the corresponding epidemiology all over the world. Third, ticks as efficient vectors nor is it evidence improved culture systems have also allowed of the prevalence of the agent of HME out- for incrimination of a new rickettsial spe- side the USA. Also, three different sequences cies in human diseases. Finally, people are of A. phagocytophilum have been recently more involved in outdoor activities and detected by molecular tools in Ixodes per- there is an increased in the development of sulcatus ticks from northeastern China and tourism in rural and/or remote areas result- are identical to the published sequences of ing in increased contact with ticks and tick- A. phagocytophilum responsible for human borne pathogens, as for the African tick-bite disease [27, 152]. fever. Finally, numerous Rickettsia spp., Ehr- For human monocytic ehrlichioses, Pad- lichia spp. or Anaplasma spp. have been dock and Childs [102] recently presented identified in ticks throughout the world [22, several factors influencing the emergence 108, 117, 152]. Although their pathogenic- of human monocytic ehrlichiosis (HME), ity for people has yet to be demonstrated, particularly changes in the host-vector ecol- they are good candidates to be involved in ogy. These include an increase in A. amer- human diseases since many of them have icanum density and geographic distribution, been detected in ticks that readily bite peo- an increase in vertebrate-host populations ple. Therefore, more worldside studies (wild turkeys, white-tailed deer) for this could lead to the description of emerging tick, an increase in the reservoir host pop- human ehrlichioses and anaplasmoses in ulation for E. chaffeensis (i.e. white-tailed the future. deer), an increased human contact with nat- ural foci of infection through recreational and occupational activities, an increased REFERENCES frequency or severity of disease in aging or immunocompromised people, an increas- [1] Adams J.R., Schmidtmann E.T., Azad A.F., ing size and longevity of the population Infection of colonized cat fleas, Ctenocephal- older than 60 years of age and immunocom- ides felis (Bouche), with a rickettsia-like microorganism, Am. J. Trop. Med. Hyg. 43 promised populations in regions of enzootic (1990) 400–409. infection, available diagnostic procedures [2] Alekseev A.N., Dubinina H.V., Semenov and improved surveillance and reporting A.V., Bolshakov C.V., Evidence of ehrlichi- [102]. To date, HME has been definitely osis agents found in ticks (Acari: Ixodidae) 486 P. Parola et al.

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