RESUMO
Ilheus virus (ILHV) is a mosquito-borne flavivirus circulating throughout Central and South America and the Caribbean. It has been detected in several mosquito genera including Aedes and Culex, and birds are thought to be its primary amplifying and reservoir host. Here, we describe the genomic and morphologic characterization of ten ILHV strains. Our analyses revealed a high conservation of both the 5'- and 3'-untranslated regions but considerable divergence within the open reading frame. We also showed that ILHV displays a typical flavivirus structural and genomic organization. Our work lays the foundation for subsequent ILHV studies to better understand its transmission cycles, pathogenicity, and emergence potential.
Assuntos
Aedes , Culex , Flavivirus , Animais , Flavivirus/genética , América do Sul , Região do Caribe , FilogeniaRESUMO
Cetacean morbillivirus (CeMV) is a global threat to cetaceans. We report a novel morbillivirus from a Fraser's dolphin (Lagenodelphis hosei) that stranded in Maui, Hawaii in 2018 that is dissimilar to the beaked whale morbillivirus previously identified from Hawaii and to other CeMV strains. Histopathological findings included intranuclear inclusions in bile duct epithelium, lymphoid depletion, rare syncytial cells and non-suppurative meningitis. Cerebellum and lung tissue homogenates were inoculated onto Vero.DogSLAMtag cells for virus isolation and cytopathic effects were observed, resulting in the formation of multinucleated giant cells (i.e., syncytia). Transmission electron microscopy of infected cell cultures also revealed syncytial cells with intracytoplasmic and intranuclear inclusions of viral nucleocapsids, consistent with the ultrastructure of a morbillivirus. Samples of the cerebellum, lung, liver, spleen and lymph nodes were positive for morbillivirus using a reverse transcription-polymerase chain reaction. The resulting 559 bp L gene sequence had the highest nucleotide identity (77.3%) to porpoise morbillivirus from Northern Ireland and the Netherlands. The resulting 248 bp P gene had the highest nucleotide identity to porpoise morbillivirus in Northern Ireland and the Netherlands and to a stranded Guiana dolphin (Sotalia guianensis) in Brazil (66.9%). As Fraser's dolphins are a pelagic species that infrequently strand, a novel strain of CeMV may be circulating in the central Pacific that could have additional population impacts through transmission to other small island-associated cetacean species.
Assuntos
Golfinhos/virologia , Infecções por Morbillivirus/virologia , Morbillivirus/isolamento & purificação , Animais , Brasil/epidemiologia , Havaí/epidemiologia , Infecções por Morbillivirus/epidemiologia , Países Baixos/epidemiologia , Irlanda do Norte/epidemiologia , Baleias/virologiaRESUMO
The genus Ehrlichia is composed of tick-borne obligate intracellular gram-negative alphaproteobacteria of the family Anaplasmataceae. Ehrlichia includes important pathogens affecting canids (E. canis, E. chaffeensis, and E. ewingii), rodents (E. muris), and ruminants (E. ruminantium). Ehrlichia minasensis, an Ehrlichia closely related to E. canis, was initially reported in Canada and Brazil. This bacterium has now been reported in Pakistan, Malaysia, China, Ethiopia, South Africa, and the Mediterranean island of Corsica, suggesting that E. minasensis has a wide geographical distribution. Previously, E. minasensis was found to cause clinical ehrlichiosis in an experimentally infected calf. The type strain E. minasensis UFMG-EV was successfully isolated from Rhipicephalus microplus ticks and propagated in the tick embryonic cell line of Ixodes scapularis (IDE8). However, the isolation and propagation of E. minasensis strains from cattle has remained elusive. In this study, the E. minasensis strain Cuiabá was isolated from an eight-month-old male calf of Holstein breed that was naturally infected with the bacterium. The calf presented clinical signs and hematological parameters of bovine ehrlichiosis. The in vitro culture of the agent was established in the canine cell line DH82. Ehrlichial morulae were observed using light and electron microscopy within DH82 cells. Total DNA was extracted, and the full genome of the E. minasensis strain Cuiabá was sequenced. A core-genome-based phylogenetic tree of Ehrlichia spp. and Anaplasma spp. confirmed that E. minasensis is a sister taxa of E. canis. A comparison of functional categories among Ehrlichia showed that E. minasensis has significantly less genes in the 'clustering-based subsystems' category, which includes functionally coupled genes for which the functional attributes are not well understood. Results strongly suggest that E. minasensis is a novel pathogen infecting cattle. The epidemiology of this Ehrlichia deserves further attention because these bacteria could be an overlooked cause of tick-borne bovine ehrlichiosis, with a wide distribution.
RESUMO
Triniti virus (TNTV) has been isolated in Trinidad and Tobago and in Brazil. To date little is known about this virus, which is classified as an ungrouped virus within the family Togaviridae. Here, three isolates of TNTV were characterized both genetically and antigenically. The genome was shown to contain three RNA segments: small (S), medium (M) and large (L). Genome organization, protein sizes and protein motifs were similar to those of viruses in the genus Orthobunyavirus, family Peribunyaviridae. Antigenic reactivity revealed the three TNTV isolates to be closely related, but no serologic cross-reaction with other orthobunyaviruses. Morphological observation by transmission electron microscopy indicated that virus size and symmetry were compatible with those of viruses in the family Peribunyaviridae. Our serological, morphological and molecular results support the taxonomic reclassification of TNTV as a member of the genus Orthobunyavirus, family Peribunyaviridae.
Assuntos
Antígenos Virais/imunologia , Orthobunyavirus/classificação , Orthobunyavirus/isolamento & purificação , RNA Viral/genética , Ordem dos Genes , Genoma Viral , Microscopia Eletrônica de Transmissão , Orthobunyavirus/genética , Orthobunyavirus/imunologia , Sorotipagem , Proteínas Virais/análise , Vírion/ultraestruturaRESUMO
We report here the complete genome sequence of a novel reovirus, designated Chiqui virus (CHQV) strain CoB38d, that was isolated from a pool of unidentified mosquitoes collected in northern Colombia in 2013. CHQV has nine double-stranded DNA (dsRNA) genome segments and has similarity to viruses belonging to the family Reoviridae, subfamily Spinareovirinae.
RESUMO
Three novel insect-specific flaviviruses, isolated from mosquitoes collected in Peru, Malaysia (Sarawak), and the United States, are characterized. The new viruses, designated La Tina, Kampung Karu, and Long Pine Key, respectively, are antigenically and phylogenetically more similar to the mosquito-borne flavivirus pathogens, than to the classical insect-specific viruses like cell fusing agent and Culex flavivirus. The potential implications of this relationship and the possible uses of these and other arbovirus-related insect-specific flaviviruses are reviewed.
Assuntos
Culicidae/virologia , Virologia/tendências , Animais , Flavivirus/genética , Flavivirus/patogenicidade , Florida , Humanos , Malásia , Mosquitos Vetores/genética , Mosquitos Vetores/patogenicidade , Mosquitos Vetores/virologia , Peru , Filogenia , Virologia/métodosRESUMO
The genome and structural organization of a novel insect-specific orthomyxovirus, designated Sinu virus, is described. Sinu virus (SINUV) was isolated in cultures of C6/36 cells from a pool of mosquitoes collected in northwestern Colombia. The virus has six negative-sense ssRNA segments. Genetic analysis of each segment demonstrated the presence of six distinct ORFs encoding the following genes: PB2 (Segment 1), PB1, (Segment 2), PA protein (Segment 3), envelope GP gene (Segment 4), the NP (Segment 5), and M-like gene (Segment 6). Phylogenetically, SINUV appears to be most closed related to viruses in the genus Thogotovirus.
Assuntos
Culicidae/virologia , Evolução Molecular , Orthomyxoviridae/isolamento & purificação , Sequência de Aminoácidos , Animais , Colômbia , Genoma Viral , Modelos Moleculares , Dados de Sequência Molecular , Orthomyxoviridae/química , Orthomyxoviridae/classificação , Orthomyxoviridae/genética , Filogenia , Thogotovirus/química , Thogotovirus/classificação , Thogotovirus/genética , Thogotovirus/isolamento & purificação , Proteínas Virais/química , Proteínas Virais/genética , Proteínas Virais/metabolismoRESUMO
The Rhabdoviridae is a diverse family of negative-sense single-stranded RNA viruses, many of which infect vertebrate hosts and are transmitted by hematophagous arthropods. Others appear to be arthropod specific, circulating only within arthropod populations. Herein, we report the isolation and characterization of three novel viruses from mosquitoes collected from the Americas. Coot Bay virus was isolated from Anopheles quadrimaculatus mosquitoes collected in the Everglades National Park, Florida; Rio Chico virus was isolated from Anopheles triannulatus mosquitoes collected in Panama; and Balsa virus was isolated from two pools of Culex erraticus mosquitoes collected in Colombia. Sequence analysis indicated that the viruses share a similar genome organization to Arboretum virus and Puerto Almendras virus that had previously been isolated from mosquitoes collected in Peru. Each genome features the five canonical rhabdovirus structural protein genes as well as a gene encoding a class 1A viroporin-like protein (U1) located between the G and L genes (3'-N-P-M-G-U1-L-5'). Phylogenetic analysis of complete L protein sequences indicated that all five viruses cluster in a unique clade that is relatively deeply rooted in the ancestry of animal rhabdoviruses. The failure of all viruses in this clade to grow in newborn mice or vertebrate cells in culture suggests that they may be poorly adapted to replication in vertebrates.
Assuntos
Distribuição Animal , Culicidae/virologia , Rhabdoviridae/genética , Rhabdoviridae/isolamento & purificação , Clima Tropical , América , Sequência de Aminoácidos , Animais , Animais Lactentes , Classificação , Regulação Viral da Expressão Gênica , Genoma Viral , Camundongos , Filogenia , Rhabdoviridae/classificação , Proteínas ViraisRESUMO
Viruses in the genus Flavivirus (family Flaviviridae) include many arthropod-borne viruses of public health and veterinary importance. However, during the past two decades an explosion of novel insect-specific flaviviruses (ISFs), some closely related to vertebrate pathogens, have been discovered. Although many flavivirus pathogens of vertebrates have been isolated from naturally infected mosquitoes in Panama, ISFs have not previously been reported from the country. This report describes the isolation and characterization of a novel ISF, tentatively named Mercadeo virus (MECDV), obtained from Culex spp. mosquitoes collected in Panama. Two MECDV isolates were sequenced and cluster phylogenetically with cell-fusing agent virus (CFAV) and Nakiwogo virus (NAKV) to form a distinct lineage within the insect-specific group of flaviviruses.
Assuntos
Culex/virologia , Infecções por Flavivirus/virologia , Flavivirus/classificação , Insetos Vetores/virologia , Animais , Sequência de Bases , Feminino , Flavivirus/genética , Flavivirus/isolamento & purificação , Flavivirus/ultraestrutura , Infecções por Flavivirus/epidemiologia , Humanos , Masculino , Dados de Sequência Molecular , Panamá/epidemiologia , Filogenia , Estudos Retrospectivos , Análise de Sequência de DNARESUMO
The genus Orbivirus of the family Reoviridae comprises 22 virus species including the Changuinola virus (CGLV) serogroup. The complete genome sequences of 13 CGLV serotypes isolated between 1961 and 1988 from distinct geographical areas of the Brazilian Amazon region were obtained. All viral sequences were obtained from single-passaged CGLV strains grown in Vero cells. CGLVs are the only orbiviruses known to be transmitted by phlebotomine sandflies. Ultrastructure and molecular analysis by electron microscopy and gel electrophoresis, respectively, revealed viral particles with typical orbivirus size and morphology, as well as the presence of a segmented genome with 10 segments. Full-length nucleotide sequencing of each of the ten RNA segments of the 13 CGLV serotypes provided basic information regarding the genome organization, encoded proteins and genetic traits. Segment 2 (encoding VP2) of the CGLV is uncommonly larger in comparison to those found in other orbiviruses and shows varying sizes even among different CGLV serotypes. Phylogenetic analysis support previous serological findings, which indicate that CGLV constitutes a separate serogroup within the genus Orbivirus. In addition, six out of 13 analysed CGLV serotypes showed reassortment of their genome segments.
Assuntos
Genoma Viral , Orbivirus/genética , Orbivirus/fisiologia , RNA Viral/genética , Análise de Sequência de DNA , Animais , Brasil , Análise por Conglomerados , Eletroforese , Ordem dos Genes , Humanos , Insetos , Microscopia Eletrônica , Dados de Sequência Molecular , Orbivirus/química , Orbivirus/ultraestrutura , Filogenia , Proteínas Estruturais Virais/análise , Vírion/ultraestruturaRESUMO
Arboretum virus (ABTV) and Puerto Almendras virus (PTAMV) are two mosquito-associated rhabdoviruses isolated from pools of Psorophora albigenu and Ochlerotattus fulvus mosquitoes, respectively, collected in the Department of Loreto, Peru, in 2009. Initial tests suggested that both viruses were novel rhabdoviruses and this was confirmed by complete genome sequencing. Analysis of their 11â482 nt (ABTV) and 11â876 (PTAMV) genomes indicates that they encode the five canonical rhabdovirus structural proteins (N, P, M, G and L) with an additional gene (U1) encoding a small hydrophobic protein. Evolutionary analysis of the L protein indicates that ABTV and PTAMV are novel and phylogenetically distinct rhabdoviruses that cannot be classified as members of any of the eight currently recognized genera within the family Rhabdoviridae, highlighting the vast diversity of this virus family.
Assuntos
Culicidae/virologia , Genoma Viral , RNA Viral/genética , Rhabdoviridae/classificação , Rhabdoviridae/isolamento & purificação , Análise de Sequência de DNA , Animais , Análise por Conglomerados , Feminino , Microscopia Eletrônica de Transmissão , Dados de Sequência Molecular , Fases de Leitura Aberta , Peru , Filogenia , Rhabdoviridae/genética , Homologia de Sequência , Proteínas Virais/genética , Vírion/ultraestruturaRESUMO
Pools of mosquitoes were tested for insect-specific viruses using cytopathic effect (CPE) assays on Aedes albopictus (C6/36) cells. Illumina sequencing of RNA from pool TR7094, which produced extensive CPE 2 days post-infection, yielded the complete genome sequences of a previously unknown Bunyavirus, designated Cumuto virus (CUMV), and a second virus designated Wallerfield virus (WALV). WALV shared highest amino acid identity (60.1 %) with Dezidougou virus from Côte d'Ivoire, a positive-sense, single-strand RNA, insect-specific virus belonging to the newly proposed genus Negevirus associated with mosquitoes and phlebotomine sandflies. The S, M and L segments of CUMV were most closely related to those of Gouleako virus, also from Côte d'Ivoire (amino acid identities of 36 %, 38% and 54 % respectively). Neither virus produced CPE on vertebrate cells, or illness in newborn mice. Isolation and characterization of these viruses increase our knowledge of the geographical distribution, diversity and host range of mosquito-specific bunyaviruses and negeviruses.
Assuntos
Bunyaviridae/classificação , Bunyaviridae/isolamento & purificação , Culex/virologia , Animais , Bunyaviridae/genética , Linhagem Celular , Efeito Citopatogênico Viral , Dados de Sequência Molecular , RNA Viral/genética , Análise de Sequência de DNA , Trinidad e TobagoRESUMO
Enterotoxigenic Escherichia coli (ETEC) is an important cause of diarrhea, mainly in developing countries. Although there are 25 different ETEC adhesins described in strains affecting humans, between 15% and 50% of the clinical isolates from different geographical regions are negative for these adhesins, suggesting that additional unidentified adhesion determinants might be present. Here, we report the discovery of Coli Surface Antigen 23 (CS23), a novel adhesin expressed by an ETEC serogroup O4 strain (ETEC 1766a), which was negative for the previously known ETEC adhesins, albeit it has the ability to adhere to Caco-2 cells. CS23 is encoded by an 8.8-kb locus which contains 9 open reading frames (ORFs), 7 of them sharing significant identity with genes required for assembly of K88-related fimbriae. This gene locus, named aal (adhesion-associated locus), is required for the adhesion ability of ETEC 1766a and was able to confer this adhesive phenotype to a nonadherent E. coli HB101 strain. The CS23 major structural subunit, AalE, shares limited identity with known pilin proteins, and it is more closely related to the CS13 pilin protein CshE, carried by human ETEC strains. Our data indicate that CS23 is a new member of the diverse adhesin repertoire used by ETEC strains.
Assuntos
Adesinas Bacterianas/metabolismo , Antígenos de Bactérias/metabolismo , Escherichia coli Enterotoxigênica/metabolismo , Proteínas de Escherichia coli/metabolismo , Regulação Bacteriana da Expressão Gênica/fisiologia , Adesinas Bacterianas/genética , Sequência de Aminoácidos , Antígenos de Bactérias/genética , Antígenos de Superfície/genética , Antígenos de Superfície/metabolismo , Aderência Bacteriana/fisiologia , Sequência de Bases , Células CACO-2 , Escherichia coli Enterotoxigênica/genética , Proteínas de Escherichia coli/genética , Humanos , Dados de Sequência Molecular , Mutação , FilogeniaRESUMO
Real-time PCR of Amblyomma imitator tick egg masses obtained in Nuevo Leon State, Mexico, identified a Rickettsia species. Sequence analyses of 17-kD common antigen and outer membrane protein A and B gene fragments showed to it to be R. rickettsii, which suggested a potential new vector for this bacterium.
Assuntos
Insetos Vetores/microbiologia , Rickettsia rickettsii/isolamento & purificação , Febre Maculosa das Montanhas Rochosas/transmissão , Carrapatos/microbiologia , Animais , Proteínas da Membrana Bacteriana Externa/química , Proteínas da Membrana Bacteriana Externa/genética , Sequência de Bases , DNA Bacteriano/química , DNA Bacteriano/genética , Feminino , Humanos , Insetos Vetores/ultraestrutura , Masculino , México , Microscopia Eletrônica , Dados de Sequência Molecular , Reação em Cadeia da Polimerase , Rickettsia rickettsii/genética , Análise de Sequência de DNA , Carrapatos/ultraestruturaRESUMO
Recent reports indicate that flaviviruses similar to the cell fusing agent virus (CFAV) naturally infect a wide variety of mosquito species. These newly recognized insect-specific viruses comprise a distinct CFAV complex within the genus Flavivirus. Here, we describe the isolation and characterization of nine strains of Culex flavivirus (Cx FV), a member of the CFAV complex, from mosquitoes collected in the United States (East Texas) and Trinidad. Phylogenetic analyses of the envelope protein gene sequences of these nine mosquito isolates with those of other CFAV complex flaviviruses in GenBank indicate that the U.S. isolates group with CxFV isolates from Asia (Japan and Indonesia), while the Trinidad isolates are more similar to CxFV isolates from Central America. A discussion follows on the possible biological significance of the CFAV complex flaviviruses.
Assuntos
Culex/virologia , Flavivirus/genética , Flavivirus/isolamento & purificação , Animais , Linhagem Celular , Análise por Conglomerados , Ordem dos Genes , Produtos do Gene env/genética , Dados de Sequência Molecular , Filogenia , Análise de Sequência de DNA , Homologia de Sequência , Texas , Trinidad e TobagoRESUMO
Primary cultures of embryonic murine neurons and newborn mouse astrocytes were inoculated with West Nile virus (WNV) strain NY385-99 to compare the pathogenesis of WNV infection in these types of CNS cells. Two different outcomes were observed. WNV infection in the neurons was rapidly progressive and destructive; within 5 days, all of the neurons were destroyed through apoptosis. WNV infection in the astrocytes evolved more slowly and did not seem to be highly lethal to the cells. The infected astrocytes continued to produce infectious virus (10(4.6)-10(6.5) PFU/mL) for 114 days, in a permissive, persistent infection. During this period, WNV antigen could be shown in the cytoplasm of the infected astrocytes by immunocytochemical assay, transmission electron microscopy of ultrathin sections, and in the cell culture medium by complement fixation test. Our results with this in vitro experimental murine cell model indicate that astrocytes can develop chronic or persistent infection with WNV, suggesting that these cells may play a role in the maintenance of WNV in the CNS.
Assuntos
Astrócitos/virologia , Neurônios/virologia , Vírus do Nilo Ocidental/fisiologia , Animais , Antígenos Virais/análise , Apoptose , Astrócitos/ultraestrutura , Células Cultivadas , Testes de Fixação de Complemento , Efeito Citopatogênico Viral , Testes de Hemaglutinação , Imuno-Histoquímica , Marcação In Situ das Extremidades Cortadas , Camundongos , Camundongos Endogâmicos ICR , Neurônios/ultraestrutura , Replicação Viral , Vírus do Nilo Ocidental/imunologia , Vírus do Nilo Ocidental/patogenicidade , Vírus do Nilo Ocidental/ultraestruturaRESUMO
The state of Nuevo Leon, Mexico has had outbreaks of typhus group rickettsiosis, most recently recognized in 1997. Evaluation of the sera of 345 patients with a dengue-like illness revealed that 25.5% had antibodies reactive with typhus group rickettsiae and 16% had antibodies to Rickettsia parkeri. Rickettsiae were detected by PCR and shell-vial isolations in the field-collected Amblyomma ticks. Molecular characterization by DNA sequence analysis of the gltA, ompB, and 17-kDa gene identified the organisms to be R. prowazekii.
Assuntos
Rickettsia prowazekii/imunologia , Carrapatos/microbiologia , Tifo Endêmico Transmitido por Pulgas/diagnóstico , Tifo Epidêmico Transmitido por Piolhos/diagnóstico , Animais , Humanos , Imunoglobulina G/sangue , México/epidemiologia , Rickettsia prowazekii/isolamento & purificação , Rickettsia typhi/imunologia , Rickettsia typhi/isolamento & purificação , Carrapatos/genética , Tifo Endêmico Transmitido por Pulgas/epidemiologia , Tifo Endêmico Transmitido por Pulgas/transmissão , Tifo Epidêmico Transmitido por Piolhos/epidemiologia , Tifo Epidêmico Transmitido por Piolhos/transmissãoRESUMO
This study evaluates the rickettsial presence in Amblyomma ticks from eight areas of the Amazon forest in Rondônia, Brazil. The following tick species (number in parentheses) were examined: Amblyomma ovale Koch (121), Amblyomma cajennense (F.) (41), Amblyomma naponense (Packard) (36), Amblyomma scalpturatum Neumann (35), Amblyomma oblongoguttatum Koch (30), Amblyomma incisum Neumann (27), Amblyomma rotundatum Koch (16), Amblyomma coelebs Neumann (10), and Amblyomma humerale Koch (6). Ticks were examined individually or in pools (2-10 ticks) by polymerase chain reaction (PCR) targeting the gltA gene. The PCR-determined minimal infection rate for each tick species was A. ovale 28%, A. cajennense 27%, A. naponense 0%, A. scalpturatum 11%, A. oblongoguttatum 3%, A. incisum 0%, A. rotundatum 87%, A. coelebs 10%, and A. humerale 50%. Partial sequences of the gltA gene of Rickettsia from A. ovale, A. scalpturatum, A. oblongoguttatum, A. rotundatum, and A. humerale were 99.9% (349/350) identical to Rickettsia bellii. DNA sequences of PCR products from A. cajennense and A. coelebs were 100% (350/350) identical to Rickettsia amblyommii. R. bellii organisms were isolated in Vero cells from A. scalpturatum, A. ovale, A. rotundatum, and A. oblongoguttatum, but only one of the isolates, cultured from A. scalpturatum, was established in continuous cell culture passage. R. amblyommii was isolated from A. cajennense and was successfully established in continuous passage in cell culture. R. amblyommii infection of Vero cells was analyzed by transmission electron microscopy. This study adds South America to the known geographic distribution of R. amblyommii and reports rickettsiae in six Amblyomma species for the first time.
Assuntos
Ixodidae/microbiologia , Rickettsia/isolamento & purificação , Animais , Sequência de Bases , Brasil , Chlorocebus aethiops , Primers do DNA , Geografia , Rickettsia/classificação , Rickettsia/genética , Células VeroRESUMO
Owing to the potential role of the tick Amblyomma cooperi in the enzootic cycle of Rickettsia rickettsii, the etiologic agent of Brazilian spotted fever (BSF), this study evaluated infection by Rickettsia species in A. cooperi ticks collected from an area in Brazil where BSF is endemic. Among a total of 40 A. cooperi adult ticks collected in an area of BSF endemicity in the state of São Paulo, PCR analysis detected DNA of Rickettsia bellii in 16 ticks (40%), and 3 other ticks (7.5%) were positive for a previously unidentified spotted-fever-group (SFG) rickettsia. Cultivation in Vero cell cultures by the shell vial technique with individual A. cooperi ticks resulted in two isolates of R. bellii and one isolate genotypically characterized as an SFG rickettsia. The two R. bellii isolates were established in Vero cell cultures in the laboratory and were confirmed to be R. bellii by molecular analysis of the gltA and 17-kDa protein-encoding genes and by electron microscopic analysis. The SFG rickettsial isolate could not be stably passaged in cell culture in the laboratory, but molecular analysis of early passages suggested that it was closely related to Rickettsia parkeri, Rickettsia africae, and Rickettsia sibirica. These results do not support the role of A. cooperi in the ecology of R. rickettsii in the area studied, but they add two more species of rickettsiae to the poorly developed list of species occurring in ticks in South America.