Prevalence of antibodies to spotted fever group rickettsiae in human beings and dogs from and endemic area of mediterranean spotted fever in Catalonia, Spain

Tick-Borne Rickettsioses in the Iberian Peninsula

Tick-borne rickettsioses (TBR) are caused by obligate, intracellular bacteria of the spotted-fever group (SFG) of the genus Rickettsia (Order Rickettsiales), transmitted by hard ticks. TBR are one of the oldest known vector-borne zoonoses and pose a threat to both human and animal health, as over the years, new SFG Rickettsia spp. have been reported worldwide with the potential to be human pathogens. In Portugal and Spain, the countries that constitute the Iberian Peninsula, reported TB rickettsiae causing human disease include Rickettsia conorii conorii, Rickettsia conorii israelensis, Rickettsia slovaca, Rickettsia raoultii, Candidatus Rickettsia rioja, Rickettsia sibirica mongolitimonae, and Rickettsia monacensis. An allochthonous case of TBR caused by Rickettsia massiliae, described in Spain, points to the need to monitor disease epidemiology, to predict risks of exposure and spread of disease, and taking into account globalization and climate changes. This review aims to provide up-to-date information on the status of TBR in the Iberian Peninsula, as well as to show the importance of a national and international collaborative epidemiology surveillance network, towards monitoring Rickettsia spp. circulation in both Portugal and Spain.

Mediterranean Spotted Fever: Current Knowledge and Recent Advances

Mediterranean spotted fever (MSF) is an emerging tick-borne rickettsiosis of the spotted fever group (SFG), endemic in the Mediterranean basin. By virtue of technological innovations in molecular genetics, it has been determined that the causative agent of MSF is Rickettsia conorii subspecies conorii. The arthropod vector of this bacterium is the brown dog tick Rhipicephalus sanguineus. The true nature of the reservoir of R. conorii conorii has not been completely deciphered yet, although many authors theorize that the canine population, other mammals, and the ticks themselves could potentially contribute as reservoirs. Typical symptoms of MSF include fever, maculopapular rash, and a characteristic eschar (“tache noire”). Atypical clinical features and severe multi-organ complications may also be present. All of these manifestations arise from the disseminated infection of the endothelium by R. conorii conorii. Several methods exist for the diagnosis of MSF. Serological tests are widely used and molecular techniques have become increasingly available. Doxycycline remains the treatment of choice, while preventive measures are focused on modification of human behavior and vector control strategies. The purpose of this review is to summarize the current knowledge on the epidemiology, pathogenesis, clinical features, diagnosis, and treatment of MSF.

Neglected aspects of tick-borne rickettsioses

Rickettsioses are among the oldest known infectious diseases. In spite of this, and of the extensive research carried out, many aspects of the biology and epidemiology of tick-borne rickettsiae are far from being completely understood. Their association with arthropod vectors, the importance of vertebrates as reservoirs, the rarity of clinical signs in animals, or the interactions of pathogenic species with rickettsial endosymbionts and with the host intracellular environment, are only some examples. Moreover, new rickettsiae are continuously being discovered. In this review, we focus on the ‘neglected’ aspects of tick-borne rickettsioses and on the gaps in knowledge, which could help to explain why these infections are still emerging and re-emerging threats worldwide.

Prevalence of antibodies to Rickettsia conorii in human beings and dogs from Catalonia: a 20-year perspective

The incidence of Mediterranean spotted fever (MSF) in Catalonia (Spain) has decreased in the last two decades. The prevalence of antibodies to Rickettsia conorii in human beings and dogs in the region of Vallès Occidental (Catalonia) was assessed by indirect immunofluorescence, and the results compared with those obtained in a similar study from 1987. Nineteen (5·0%) out of 383 human serum samples had antibodies to R. conorii. This seroprevalence was significantly lower (11·5%) (P = 0·003) than that recorded in the 1987 survey. Forty-two out (42·0%) of 100 canine serum samples had antibodies to R. conorii. A high proportion of the studied dogs (91·0%) were receiving anti-tick treatment, mainly with permethrin-imidacloprid spot-on (Advantix, Bayer, Germany). The current canine seroprevalence was not significantly different from that recorded in the 1987 survey (36.9%). In conclusion, this study shows a significant decrease in the prevalence of antibodies to R. conorii in the human population of Catalonia in the last 20 years, which corresponds with a decrease in the number of cases of MSF. We suggest that the widespread use of anti-tick treatment in dogs could limit the introduction of ticks to humans due to a reduction of infestation duration in dogs, thus contributing to the decrease in MSF incidence.

Acute febrile illness is associated with Rickettsia spp infection in dogs

BACKGROUND

Rickettsia conorii is transmitted by Rhipicephalus sanguineus ticks and causes Mediterranean Spotted Fever (MSF) in humans. Although dogs are considered the natural host of the vector, the clinical and epidemiological significance of R. conorii infection in dogs remains unclear. The aim of this prospective study was to investigate whether Rickettsia infection causes febrile illness in dogs living in areas endemic for human MSF.

METHODS

Dogs from southern Italy with acute fever (n = 99) were compared with case-control dogs with normal body temperatures (n = 72). Serology and real-time PCR were performed for Rickettsia spp., Ehrlichia canis, Anaplasma phagocytophilum/A. platys and Leishmania infantum. Conventional PCR was performed for Babesia spp. and Hepatozoon spp. Acute and convalescent antibodies to R. conorii, E. canis and A. phagocytophilum were determined.

RESULTS

The seroprevalence rates at first visit for R. conorii, E. canis, A. phagocytophilum and L. infantum were 44.8%, 48.5%, 37.8% and 17.6%, respectively. The seroconversion rates for R. conorii, E. canis and A. phagocytophilum were 20.7%, 14.3% and 8.8%, respectively. The molecular positive rates at first visit for Rickettsia spp., E. canis, A. phagocytophilum, A. platys, L. infantum, Babesia spp. and Hepatozoon spp. were 1.8%, 4.1%, 0%, 2.3%, 11.1%, 2.3% and 0.6%, respectively. Positive PCR for E. canis (7%), Rickettsia spp. (3%), Babesia spp. (4.0%) and Hepatozoon spp. (1.0%) were found only in febrile dogs. The DNA sequences obtained from Rickettsia and Babesia PCRs positive samples were 100% identical to the R. conorii and Babesia vogeli sequences in GenBank®, respectively. Febrile illness was statistically associated with acute and convalescent positive R. conorii antibodies, seroconversion to R. conorii, E. canis positive PCR, and positivity to any tick pathogen PCRs. Fourteen febrile dogs (31.8%) were diagnosed with Rickettsia spp. infection based on seroconversion and/or PCR while only six afebrile dogs (12.5%) seroconverted (P = 0.0248). The most common clinical findings of dogs with Rickettsia infection diagnosed by seroconversion and/or PCR were fever, myalgia, lameness, elevation of C-reactive protein, thrombocytopenia and hypoalbuminemia.

CONCLUSIONS

This study demonstrates acute febrile illness associated with Rickettsia infection in dogs living in endemic areas of human MSF based on seroconversion alone or in combination with PCR.

The role of cats in the eco-epidemiology of spotted fever group diseases

Background

Mediterranean Spotted Fever (MSF), whose etiological agent is R. conorii, is one of the oldest described vector-borne infectious diseases. Although it is endemic in the Mediterranean area, clinical cases have also been reported in other regions. R. massiliae-Bar29 is related to MSF cases. This strain is distributed worldwide. R. conorii and R. massiliae-Bar29 are transmitted by ticks. Dogs are considered the sentinel of R. conorii infection. Cats could also be involved in their transmission. Rickettsia felis, etiological agent of Flea-borne spotted fever, is mainly transmitted by the cat flea, Ctenocephalides felis. Up to now, the role of cats in its transmission is not entirely elucidated. The aim of the study is to analyze the infection in cats by these microorganisms.

Methods

The study was undertaken in Northeastern Spain. Twenty municipalities of seven regions participated in the study. 212 cats (pets and stray cats) were analyzed. Variables surveyed were: date of collection, age, sex, municipality, source, living place, outdoor activities, health status, type of disease, contact with other animals, and ectoparasite infestation. Sera were evaluated by indirect immunofluorescence antibody assay (IFA). Molecular detection (real-time PCR and sequencing) and cultures were performed on blood samples.

Results

There were 59 (27.8%) cats seroreactive to one or more microorganisms. Considering cross-reactions, the seroprevalences were 15.6%-19.5% (R. massiliae-Bar29), 1.9%-6.2% (R. conorii), and 5.2%-7.5% (R. felis). A weak association was observed between SFG seropositivity and tick infestation. Ticks found on seropositive cats were Rhipicephalus pusillus, R. sanguineus and R. turanicus. DNA of Rickettsia was detected in 23 cats. 21 of them could be sequenced. Sequences obtained were identical to those sequences of SFG rickettsiae similar to R. conorii and R. massiliae. No amplification of R. felis was obtained.

Conclusions

Cats can be infected by SFG rickettsiae and produce antibodies against them. Cats may play a role in the transmission cycle of R. conorii and R. massiliae-Bar29, although the role in the R. felis cycle needs further analysis.

Molecular and serological study of rickettsial infection in humans, and in wild and farm animals, in the province of Burgos, Spain

Limited information is available on the presence of rickettsial infection in humans and animal reservoirs in Spain. Exposure to spotted fever group rickettsia in healthy humans and in farm and wild animals in the Province of Burgos, Spain, was examined by serological methods. Rickettsial DNA was also sought by PCR in animal samples. Of 102 human serum samples examined by indirect immunofluorescence assays (IFA), 5.88% were positive for antibodies against Rickettsia conorii (titers 1/128-1/512). Significant differences were detected in human seroprevalence with respect to age. In further IFAs, 102 out of 375 (27.2%) serum samples from the wild animals reacted with R. conorii antigens (titers 1/64-1/1024); 32 out of 281 (11.38%) samples from farm animals were also positive for R. conorii (titers 1/64-1/2048). The prevalence detected among total wild animals was significantly higher than among total farm animals. No rickettsial DNA was found by PCR in any farm or wild animal sample.

Serological evidence for exposure of dogs to Rickettsia conorii, Rickettsia typhi, and Orientia tsutsugamushi in Sri Lanka

Vector-borne rickettsial infection is a major cause of febrile illnesses throughout the world. Although vertebrates hosting the vectors play a vital role in the natural cycle of rickettsiae, studies have not been conducted on them in Sri Lanka. Therefore, the present study was designed to determine the exposure of dog population in Rajawatta, Thambavita, and areas of the Western Slopes and Unawatuna of Sri Lanka to rickettsial pathogens. A total of 123 dog blood samples were collected from those areas. Samples were tested for antibodies against Rickettsia conorii (RC) of the spotted fever group (SFG), Rickettsia typhi (RT) of the typhus group (TG), and Orientia tsutsugamushi (OT) of the scrub typhus group (ST) of rickettsiae by indirect immunofluorescence antibody test (IFA). Samples with titers ≥ 1:64 were considered as positive in this study. Collectively, 49% dogs were found to have antibodies against the rickettsial agents. Of the dogs, 42%, 24%, and 2% had antibodies against RC, OT, and RT, respectively. The seropositive rate of 100% was observed in areas of the Western Slopes, whereas the lowest rate of 20% was in Unawatuna. Among the positive samples, antibody titers against RC and OT ranged from 1/64 to 1/8192. In contrast, the few dogs that tested positive for RT showed very low titers of 1/64 and 1/128. Results of this study show the extent of exposure to the pathogen and its dispersion in the natural ecology. We suggest that dogs could be acting as reservoirs in the rickettsial transmission cycle or could be effective tracer animals that can be used to detect areas with potential for future outbreaks.

Detection of Rickettsia conorii strains in Portuguese dogs (Canis familiaris)

This study reports a serological and molecular survey on the spotted fever group Rickettsia found in a group of 51 dogs with suspected tick-borne illness from the south of Portugal. Additionally, a prevalence of IgG antibodies to R. conorii was also estimated in a group of 400 healthy dogs from the same region. In the group of healthy dogs, the immunofluorescence test revealed that 154 (38.5%) of the 400 dogs had IgG antibodies reactive with R. conorii. The highest proportion of dogs (45%) with R. conorii antibodies was found in blood samples collected from October to December. Among the group suspected with tick-borne illness, 35 (62%) dogs showed to be seroreactive (IgG≥128) for antibodies against R. conorii, and the analysis of PCR-positive amplicons revealed that 5 dogs were infected with R. conorii Malish and 2 dogs were infected with R. conorii Israeli tick typhus strain. There was a higher prevalence of antibodies to R. conorii in the group of sick dogs, and the detection of R. conorii DNA in blood samples from this group points to their potential role as a reservoir and sentinel host helping to evaluate and characterize the distribution of circulating rickettsial strains.

Epidemiological study of rickettsial infections in patients with hypertransaminemia in Madrid (Spain)

A retrospective analysis was performed to detect anti-rickettsial antibodies in the serum of patients with hypertransaminemia of unknown etiology, and in that of healthy members of the general population of Madrid (Spain). Among 143 patients 16 (11.2%) were positive for anti-R. conorii IgG antibodies and 7% for R. typhi. PCR analysis was performed in patients with IgM antibodies. Among 143 healthy subjects from the general population, seven (4.9%) were positive for anti-R. conorii IgG antibodies, and 2.8% for R. typhi. These results show that anti-rickettsial antibodies are more commonly detected in patients with hypertransaminemia than in healthy people.

Deciphering the relationships between Rickettsia conorii conorii and Rhipicephalus sanguineus in the ecology and epidemiology of Mediterranean spotted fever

Mediterranean spotted fever is the most important tick-borne disease occurring in Southern Europe and North Africa. The first case of this life-threatening zoonosis was reported in 1910. In the 1930s, the role of the brown dog tick, Rhipicephalus sanguineus, and the causative agent, Rickettsia conorii were described. However, basic questions regarding the relationships between the rickettsia and its tick vector are still unresolved, and the life cycle of R. conorii is incompletely known. There is a lack of knowledge associated with the role of Rh. sanguineus in the maintenance and transmission of R. conorii. The infectious rate of Rh. sanguineus ticks with R. conorii has been found low every time it has been tested; usually lower that 1%. The deleterious impact of R. conorii on ticks has been suggested in experimental models as a potential reason to explain a low prevalence in nature. The long-recognized phenomenon known as reactivation has been suggested as a cause of negative effects--that is, the change in temperature and physiology of the tick host induces the agent to emerge from dormancy and attain infectivity with bad effects on ticks. However, naturally infected colonies of ticks have been maintained in laboratory conditions over several generations. We discuss here several aspects that have been recently studied to better understand Rh. sanguineus-R. conorii relationships, including comparison between the fitness of infected and non-infected ticks in laboratory conditions and the role of external factors such as temperature and starvation.

Rickettsia slovaca infection in humans in the northeast of Spain: seroprevalence study

Catalonia is an endemic area of Mediterranean spotted fever. In 1997, A. Lakos described a new tick-borne infectious disease called tick-borne lymphadenopathy. The causative agent is Rickettsia slovaca, which is transmitted by Dermacentor marginatus ticks. We have diagnosed human cases in Catalonia. The objective of this study was to determinate seroprevalence of R. slovaca infection in humans in the northeast of Spain. The population included 217 subjects from Catalonia, northeast of Spain and was stratified by age and living place (rural, suburban, and urban). Age, gender, residence area, contact with animals, occupation, and history of rickettsioses was surveyed. Immunoglobulin G was measured by indirect immunofluorescence assay. Titers >or= 1/40 were considered. Seroprevalence of R. slovaca was 5.5% at titers of 1/40-1/320. Eight (3.7%) sera had antibodies against R. slovaca exclusively. Four sera reacted also against Rickettsia conorii and/or Bar29. Seroprevalence of R. slovaca would range from 3.7% to 5.5%. The only statistically significant association was that between R. slovaca seropositivity and age. We present serologic evidence of R. slovaca infection among population of Catalonia, northeast of Spain.

The role of wild boar (Sus scrofa) in the eco-epidemiology of R. slovaca in Northeastern Spain

Rickettsia slovaca is considered the etiological agent of tick-borne lymphadenopathy (TIBOLA), an emerging disease transmitted by tick bites. Dermacentor marginatus constitutes the most important vector and wild boar (Sus scrofa) is the main wild host in our area. The epidemiology of this tick-borne rickettsioses has not been completely clarified. During hunting season 2004, wild boar sera sample were collected from northeastern Spain. Ticks were collected both from wild boar and from flagging vegetation in the same areas where wild boar were hunted. Serologic study was carried out using the immunofluorescent antibody (IFA) technique. Ticks were identified as D. marginatus and Rhipicephalus uranicus. Based on sequence analysis on ompA gene, R. slovaca was identified in 30.5% D. marginatus ticks removed from wild boar and in 33.3% D. marginatus collected from flagging vegetation. Rickettsia sp. RpA4 was identified in 4 specimens of D. marginatus removed from wild boar. Twelve of 23 wild boar were seropositive to R. slovaca. Results suggested wild boar are exposed to R. slovaca infection and this pathogen is well established in the wild cycle of D. marginatus in our area.

Febrile illness associated with Rickettsia conorii infection in dogs from Sicily

We report serologic and molecular evidence of acute, febrile illness associated with Rickettsia conorii in 3 male Yorkshire terriers from Sicily (Italy).

Isolation and identification of Rickettsia massiliae from Rhipicephalus sanguineus ticks collected in Arizona

Twenty Rhipicephalus sanguineus ticks collected in eastern Arizona were tested by PCR assay to establish their infection rate with spotted fever group rickettsiae. With a nested PCR assay which detects a fragment of the Rickettsia genus-specific 17-kDa antigen gene (htrA), five ticks (25%) were found to contain rickettsial DNA. One rickettsial isolate was obtained from these ticks by inoculating a suspension of a triturated tick into monolayers of Vero E6 monkey kidney cells and XTC-2 clawed toad cells, and its cell culture and genotypic characteristics were determined. Fragments of the 16S rRNA, GltA, rOmpA, rOmpB, and Sca4 genes had 100%, 100%, 99%, 99%, and 99%, respectively, nucleotide similarity to Rickettsia massiliae strain Bar29, previously isolated from R. sanguineus in Catalonia, Spain (L. Beati et al., J. Clin. Microbiol. 34:2688-2694, 1996). The new isolate, AZT80, does not elicit cytotoxic effects in Vero cells and causes a persistent infection in XTC-2 cells. The AZT80 strain is susceptible to doxycycline but resistant to rifampin and erythromycin. Whether R. massiliae AZT80 is pathogenic or infectious for dogs and humans or can cause seroconversion to spotted fever group antigens in the United States is unknown.

Monitoring of Humans and Animals for the Presence of Various Rickettsiae and Coxiella burnetii by Serological Methods

Serological examination of humans in Slovakia suspected of having rickettsial infections revealed the presence of antibodies to spotted fever group rickettsiae (R. conorii, R. slovaca, and R. typhi). Of interest is the finding of serological positivity to the newly recognized "IRS" agent. Antibodies to these rickettsiae and to C. burnetii were demonstrated also in domestic and hunting dogs and pet animals. These results confirm the occurrence and possible circulation of these rickettsiae and C. burnetii in the Slovak Republic.

Enfermedades producidas por Rickettsia

Species of the genus Rickettsia are small, obligate intracelular, gramnegative bacteria, many of which are considered nowadays a paradigm of emergent pathogens. With the exception of R. prowazekii, they are maintained in the natural environment through a cycle involving different hosts (mainly mammals), and arthropod vectors (in general ticks, and fleas); humans are affected only by incidental transmission due to arthropod bites. The common pathogenesis of these diseases lie on the predominantly infection of endotelial cells, that determines the development of multisistemic small vessel vasculitis, which may affect lungs (interstitial pneumonitis), heart (miopericarditis), skin (rash), central nervous system (meningoencephalitis), as well as liver, and kidneys. They are classified in two groups: spotted-fever group, and typhus group rickettsia. In Spain the most prevalent rickettsioses of both groups are mediterranean spotted fever (caused by R. conorii), and murine typhus (caused by R. typhi), respectively. This review focuses mainly in these two diseases, and also in other rickettsioses of interest due to their recently emergence or reemergence (R. slovaca, R. africae, R. prowazekii, R. felis), or to their high incidence in other areas (R. rickettsii, Orientia tsutsugamushi).

Serosurvey among Mediterranean spotted fever patients of a new spotted fever group rickettsial strain (Bar29)

Mediterranean spotted fever is an endemic disease in Catalonia, Spain. A new spotted fever group (SFG) rickettsial strain (Bar29) of unknown pathogenicity for humans was isolated by our group, in 1996, from the dog brown tick, Rhipicephalus sanguineus. Interestingly, Rickettsia conorii was not isolated in this study. The aim of the present study was to assess the possible pathogenic role of the Bar29 strain. To this purpose, serum samples from 15 patients with Mediterranean spotted fever were obtained and tested by immunofluorescence for antibodies against four related rickettsial strains (R. conorii, R. africae, R. massiliae, and Bar29). Eight of the studied sera reacted at high titers with only R. conorii and Bar29 antigens. For five of the eight sera, the titers against Bar29 were clearly higher than for R. conorii. Four of these sera were also studied by Western blot immunoassay to confirm a specific response. Two of these sera reacted with the high-molecular-mass specific proteins of Bar29 as well as with the low-molecular-mass region (LPS antigen) whereas their reactions with R. conorii were located only on bands of the LPS. This specific response would support the possible pathogenic role of the Bar29 strain for humans. According to this finding, spotted fever caused by R. conorii and rickettsial strain Bar29 may be present in our area. The epidemiological implications of spotted fever caused by R. conorii and by rickettsial strain Bar29 in the Catalonia deserve further studies with isolation and characterization of more rickettsial strains.

Prevalence of antibodies to spotted fever group rickettsiae in the region of Split (southern Croatia)

The prevalence of IgG antibodies to spotted fever group rickettsiae (SFG) was investigated by the indirect immunofluorescence assay in a sample of 1207 healthy residents of the central part of southern Croatia (eastern coast of Adriatic Sea). Sera obtained from subjects living in three different places of residency (urban, suburban and rural environs of the region) were tested. Overall 528 (43.7%) persons had significant antibody titers (1:40 or higher), with a significantly higher prevalence in suburban and rural areas. The results show that inhabitants in the area are clearly being exposed to SFG rickettsiae. Risk factors significantly associated with seropositivity to SFG rickettsiae were: living in suburban and rural settlements (odds ratio [OR] = 1.81; 95% confidence interval [CI] = 1.35-2.4), contact with animals (OR: 1.52; 95% CI: 1.15-1.99), and increase of age (OR: 1.18; 95% CI: 1.09-1.26).

Associations between dogs that were serologically positive for Rickettsia conorii relative to the residences of two human cases of Mediterranean spotted fever in Piemonte (Italy)

A geographic information system and K-function analysis were used to evaluate the spatial association of canine serological results for Rickettsia conorii, the causative agent of Mediterranean spotted fever (MSF), and clinical cases of MSF in humans in Piemonte, northwest Italy. The residences of dog owners were clustered in two rural villages in the province of Cuneo, where two human cases of MSF occurred in 1997 and 1998. Eighteen out of 116 dogs examined were positive by indirect immunofluorescent assay (IFA+, titre > or =1:160) for MSF. K-functions were compared for IFA+ dogs and for all dogs sampled. Monte Carlo and bootstrap simulations demonstrated that clustering of IFA+ dogs was significantly greater than clustering of all dogs, at distances of less than 0.6 km from human cases of MSF. Logistic regression analysis indicated that the risk of being IFA+ was highest for dogs residing within the first quartile of distance (0.7 km) from human cases of the disease, and for dogs that were not confined. However, year and season of blood collection were not associated with IFA status. It was concluded that a relatively high dog population density along with a rural or semi-rural environment favours the occurrence of emergent foci of MSF in the province of Cuneo.