Infection by Rickettsia bellii and Candidatus "Rickettsia amblyommii" in Amblyomma neumanni ticks from Argentina

Ticks (Acari: Ixodidae) infesting wild birds in the Atlantic Forest in northeastern Brazil, with notes on rickettsial infection in ticks

A total of 232 individuals representing 46 species of birds were mist-netted and screened for ticks in a region of the Atlantic Forest, State of Bahia, Brazil. Thirty-eight (16.4%) of these birds representing 17 species were found infested by immature stages of Amblyomma ticks, namely, Amblyomma longirostre (Koch, 1844) (15 larvae and seven nymphs), Amblyomma nodosum (Neumann, 1899) (nine nymphs), Amblyomma calcaratum (Neumann, 1899) (five nymphs), Amblyomma cajennense (Fabricius, 1787) (seven larvae), and Amblyomma parkeri (Fonseca and Aragão, 1952) (four larvae). Overall, 21 larvae and five nymphs collected from birds could not be identified to species and were morphologically identified as Amblyomma spp. Among 13 A. longirostre larvae and two A. parkeri larvae, two individuals of A. longirostre (15.4%) were found infected by Rickettsia amblyommii. This study provides some bird species found infested by A. longirostre, A. parkeri, A. calcaratum, A. nodosum, or A. cajennense for the first time and expands the distribution of R. amblyommii-infected A. longirostre ticks.

Detection of "Candidatus Rickettsia sp. strain Argentina"and Rickettsia bellii in Amblyomma ticks (Acari: Ixodidae) from Northern Argentina

Ixodid ticks were collected from vegetation and from humans, wild and domestic mammals in a rural area in the semi-arid Argentine Chaco in late spring 2006 to evaluate their potential role as vectors of Spotted Fever Group (SFG) rickettsiae. A total of 233 adult ticks, identified as Amblyomma parvum, Amblyomma tigrinum and Amblyomma pseudoconcolor, was examined for Rickettsia spp. We identified an SFG rickettsia of unknown pathogenicity, "Candidatus Rickettsia sp. strain Argentina", in A. parvum and A. pseudoconcolor by PCR assays targeting gltA, ompA, ompB and 17-kDa outer membrane antigen rickettsial genes. Rickettsia bellii was detected in a host-seeking male of A. tigrinum. Amblyomma parvum is widespread in the study area and is a potential threat to human health.

Tick-borne rickettsioses in America: unanswered questions and emerging diseases

During most of the 20th century, Rickettsia rickettsii, the agent of Rocky Mountain spotted fever, was considered the only tick-borne rickettsia associated with human diseases in the Americas. This dogma suggested that the other characterized and noncharacterized rickettsiae isolated from ticks were not pathogenic to humans. This concept has been modified extensively in the past 10 years with the identification of at least three additional rickettsial species that cause human tick-borne rickettsioses and that are prevalent in the Americas, including Rickettsia parkeri, Rickettsia massiliae, and Rickettsia africae. Moreover, the genetic variability of R. rickettsii and the milder forms of Rocky Mountain spotted fever reactivate the hypothesis that some circulating genotypes of R. rickettsii may be more virulent than others and may explain the wide variations in fatality rates of the disease.

Ticks (Acari: Ixodidae) infesting wild birds in the eastern Amazon, northern Brazil, with notes on rickettsial infection in ticks

The aim of the study was to report tick infestations on wild birds in a region of the eastern Brazilian Amazon and evaluate the rickettsial infection of these ticks. Wild birds captured by mist nets were examined for the presence of ticks, which were collected and identified to species by morphology or molecular methods. In addition, part of these ticks was individually tested by polymerase chain reaction targeting portions of the rickettsial genes gltA and ompA. Among 331 captured birds, representing 56 species, 133 individuals (40.2%) from 34 species were found infested by 443 ticks, being Amblyomma longirostre (Koch) the most common (103 larvae, 12 nymphs), followed by Amblyomma humerale Koch (15 larvae, 3 nymphs), Amblyomma geayi Neumann (seven larvae, one nymph), Amblyomma calcaratum Neumann (one larva, four nymphs), Amblyomma coelebs Neumann (two larvae), and Haemaphysalis juxtakochi Cooley (one larva, two nymphs). Other 285 larvae and 7 nymphs collected from birds could not be identified to species and were morphologically identified as Amblyomma spp. The species A. humerale and A. geayi are recorded for first time parasitizing birds in the Neotropical region. Among 67 A. longirostre and 7 A. geayi, 38 (56.7%) and 4 (57.1%), respectively, were found infected by Rickettsia amblyommii. In spite of R. amblyommii being not currently recognized as human or animal pathogen, there has been serological evidence for human and canine infection by this agent in the USA and in the Brazilian western Amazon.

Wide dispersal and possible multiple origins of low-copy-number plasmids in rickettsia species associated with blood-feeding arthropods

Plasmids are mobile genetic elements of bacteria that can impart important adaptive traits, such as increased virulence or antibiotic resistance. We report the existence of plasmids in Rickettsia (Rickettsiales; Rickettsiaceae) species, including Rickettsia akari, "Candidatus Rickettsia amblyommii," R. bellii, R. rhipicephali, and REIS, the rickettsial endosymbiont of Ixodes scapularis. All of the rickettsiae were isolated from humans or North and South American ticks. R. parkeri isolates from both continents did not possess plasmids. We have now demonstrated plasmids in nearly all Rickettsia species that we have surveyed from three continents, which represent three of the four major proposed phylogenetic groups associated with blood-feeding arthropods. Gel-based evidence consistent with the existence of multiple plasmids in some species was confirmed by cloning plasmids with very different sequences from each of two "Ca. Rickettsia amblyommii" isolates. Phylogenetic analysis of rickettsial ParA plasmid partitioning proteins indicated multiple parA gene origins and plasmid incompatibility groups, consistent with possible multiple plasmid origins. Phylogenetic analysis of potentially host-adaptive rickettsial small heat shock proteins showed that hsp2 genes were plasmid specific and that hsp1 genes, found only on plasmids of "Ca. Rickettsia amblyommii," R. felis, R. monacensis, and R. peacockii, were probably acquired independently of the hsp2 genes. Plasmid copy numbers in seven Rickettsia species ranged from 2.4 to 9.2 per chromosomal equivalent, as determined by real-time quantitative PCR. Plasmids may be of significance in rickettsial evolution and epidemiology by conferring genetic plasticity and host-adaptive traits via horizontal gene transfer that counteracts the reductive genome evolution typical of obligate intracellular bacteria.

Ecology of Amblyomma neumanni (Acari: Ixodidae)

The life cycle of Amblyomma neumanni was described studying the seasonal distribution of free-living stages and parasitic phases during two consecutive years. Development periods of engorged ticks under different photoperiod conditions were recorded. Larvae of A. neumanni have the peak of abundance in autumn. Nymphs reach the peak in winter. Females were collected on cattle from autumn to late spring. The seasonal distribution pattern of females showed a bimodal curve, with a peak in autumn and other during early and middle spring. The engorged females exposed at shortest photoperiod regimen (10 h light-14 h dark) under both laboratory and field conditions undergo morphogenetic diapause, expressed as a delay in the oviposition. It is concluded that females of A. neumanni that feed and copulate in autumn undergo morphogenetic diapause, and they will lay eggs in spring, simultaneously with the females that feed and copulate in this season. Climate niche analysis shows that adequate suitability for A. neumanni depends mainly from temperature (mean, absolute maximum and minimum, and mean temperature in wettest and driest quarters) as well as from rainfall in warmest and coldest quarters. Sequences of 16S rDNA gene belonging to different populations of A. neumanni, showed no intraspecific genetic differentiation.

Rickettsia parkeri in Argentina

Clinical reports of an eschar-associated rickettsiosis in the Paraná River Delta of Argentina prompted an evaluation of Amblyomma triste ticks in this region. When evaluated by PCR, 17 (7.6%) of 223 questing adult A. triste ticks, collected from 2 sites in the lower Paraná River Delta, contained DNA of Rickettsia parkeri.

Tick-borne diseases in North Carolina: is "Rickettsia amblyommii" a possible cause of rickettsiosis reported as Rocky Mountain spotted fever?

Cases of Rocky Mountain spotted fever (RMSF) in North Carolina have escalated markedly since 2000. In 2005, we identified a county in the Piedmont region with high case numbers of RMSF. We collected ticks and examined them for bacterial pathogens using molecular methods to determine if a novel tick vector or spotted fever group rickettsiae (SFGR) might be emerging. Amblyomma americanum, the lone star tick, comprised 99.6% of 6,502 specimens collected in suburban landscapes. In contrast, Dermacentor variabilis, the American dog tick, a principal vector of Rickettsia rickettsii, comprised < 1% of the ticks collected. Eleven of 25 lone star tick pools tested were infected with "Rickettsia amblyommii," an informally named SFGR. Sera from patients from the same county who were presumptively diagnosed by local physicians with a tick-borne illness were tested by an indirect immunofluorescence antibody (IFA) assay to confirm clinical diagnoses. Three of six patients classified as probable RMSF cases demonstrated a fourfold or greater rise in IgG class antibody titers between paired acute and convalescent sera to "R. amblyommii" antigens, but not to R. rickettsii antigens. White-tailed deer, Odocoileus virginianus, are preferred hosts of lone star ticks. Blood samples collected from hunter-killed deer from the same county were tested by IFA test for antibodies to Ehrlichia chaffeensis and "R. amblyommii." Twenty-eight (87%) of 32 deer were positive for antibodies to E. chaffeensis, but only 1 (3%) of the deer exhibited antibodies to "R. amblyommii," suggesting that deer are not the source of "R. amblyommii" infection for lone star ticks. We propose that some cases of rickettsiosis reported as RMSF may have been caused by "R. amblyommii" transmitted through the bite of A. americanum.

Rickettsia amblyommii infecting Amblyomma americanum larvae

Polymerase chain reaction analysis of Amblyomma americanum adults, nymphs, and larvae from Aberdeen Proving Ground, MD (APG), revealed a very high prevalence of a spotted fever group (SFG) rickettsia. Restriction fragment length polymorphism (RFLP) and sequence analysis identified "Rickettsia amblyommii." This organism is not yet described or well studied, and its pathogenicity is unknown; however, investigations of the organism are warranted because of its high prevalence in A. americanum. This tick is extremely abundant at military training facilities in the south, central, and Mid-Atlantic United States, and many soldiers experience multiple concurrent tick bites. Bites by R. amblyommii-infected A. americanum may account for rates of SFG rickettsia seropositivity that are higher than reported rates of Rocky Mountain spotted fever (RMSF) cases from the same location. Seroconversion to SFG rickettsia following bites of A. americanum may suggest that R. amblyommii is infectious in humans. Subclinical infection in the numerous A. americanum tick bite victims could contaminate donated blood and compromise immunodeficient recipients. Detection of R. amblyommii in questing A. americanum larvae suggests transovarial transmission. The absence of R. rickettsii, the agent of RMSF, in A. americanum may be due to transovarial interference by R. amblyommii. The likelihood of pathogen transmission by larvae is magnified by their habit of mass attack. The very small size of the larvae is also a risk factor for pathogen transmission. High R. amblyommii prevalence in populations of A. americanum presage co-infection with other A. americanum-borne pathogens. A. americanum nymphs and adults from APG were found to be co-infected with R. amblyommii and Borrelia lonestari, Ehrlichia chaffeensis and Ehrlichia ewingii, respectively, and larval pools were infected with both R. amblyommii and B. lonestari. Co-infections can compound effects and complicate diagnosis of tick-borne disease.

Characterization of rickettsial infection in Amblyomma americanum (Acari: Ixodidae) by quantitative real-time polymerase chain reaction

Several species of the spotted fever group Rickettsia (SFGR), with considerable variation in vertebrate host pathogenicity, are present in ticks in the United States. In this study, quantitative real-time PCR (qPCR) was used to characterize the growth and the distribution of Rickettsia amblyommii in selected tissues (salivary glands, gut, and ovaries) of naturally infected Amblyomma americanum (L.) (Acari: Ixodidae), during bloodmeal acquisition and throughout vertical transmission to eggs and postembryonic life cycle stages (larvae and nymphs). R. amblyommii was identified in the samples at ratios of < or = 1 rickettsiae per tick cell. Significant variability in the ratio of rickettsial to tick gene copy numbers between the tissues was identified; however, no single tissue was consistently observed to have the greatest rickettsial burden throughout the feeding event. Furthermore, the ratio of rickettsial to tick gene copy numbers did not significantly differ between eggs, immature ticks, and feeding events. This is the first study to use qPCR to enumerate rickettsial growth and distribution in the tick host during bloodmeal acquisition. Deciphering SFGR tissue distribution and transmission mechanisms is necessary for the development of novel approaches to control tick-borne rickettsial diseases.

Detection of a novel spotted fever group rickettsia in Amblyomma parvum ticks (Acari: Ixodidae) from Argentina

The present study evaluated the rickettsial infection in Amblyomma parvum ticks collected in Northwestern Córdoba Province, Argentina. Each tick was subjected to DNA extraction and tested by polymerase chain reaction (PCR) targeting fragments of the rickettsial genes gltA and ompB. Nine (69.2%) out of 13 adult ticks yielded expected PCR products for the two rickettsial genes. Products from the ompB PCR were sequenced, generating DNA sequences 100% identical for the nine PCR-positive ticks. Three of these ticks were tested in another battery of PCR targeting fragments of the rickettsial genes gltA, htrA, and ompA. Products from the gltA, htrA, and ompA PCRs were sequenced generating DNA sequences 100% identical for the three PCR-positive ticks. The rickettsia detected in the A. parvum ticks was designated as Rickettsia sp. strain Argentina. Phylogenetic analyses performed with partial sequences of the rickettsial genes gltA, htrA, ompB, and ompA showed that Rickettsia sp. strain Argentina belonged to the spotted fever group, being distinct from all known Rickettsia species and genotypes available in GenBank, representing possibly a new Rickettsia species. This was the first evidence of rickettsial infection in the tick A. parvum, and the third report of rickettsial infection among the Argentinean tick fauna. The role of Rickettsia sp. strain Argentina as a human pathogen is unknown. Further studies are needed to obtain tissue-cultured isolates of Rickettsia sp. strain Argentina, in order to better characterize it and to determine its taxonomic status as a new species.

Isolation of Rickettsia rhipicephali and Rickettsia bellii from Haemaphysalis juxtakochi ticks in the state of São Paulo, Brazil

In the present study, attempts to isolate Rickettsia in cell culture were performed individually in seven specimens of Haemaphysalis juxtakochi ticks collected in the state of São Paulo (southeastern Brazil). Rickettsia was successfully isolated by the shell vial technique and established in Vero cell culture from six ticks (six isolates). DNA extracted from infected cells of these isolates was tested by PCR and DNA sequencing, using genus-specific Rickettsia primers targeting the genes gltA, htrA, ompA, and ompB. After the generated sequences were compared with available sequences in GenBank, five out of the six isolates were identified as Rickettsia bellii (isolates HJ#1, HJ#2, HJ#3, HJ#4, and HJ#7). The sixth isolate (HJ#5) was closest to Rickettsia sp. strain R300, previously detected in H. juxtakochi in northern Brazil, and to Rickettsia rhipicephali, isolated from ticks in the United States. Following recent gene sequence-based criteria proposed for the identification of Rickettsia isolates, both isolate HJ#5 and strain R300 were identified as South American strains of R. rhipicephali, which was confirmed in this continent for the first time. Isolation of R. bellii from H. juxtakochi ticks, added to eight other tick species that have been reported to be infected with this bacterium in Brazil, indicates that R. bellii is indeed the most frequent Rickettsia species infecting ticks in Brazil. Currently, the role of both R. rhipicephali and R. bellii as human pathogens is regarded as unknown.