Dataset Information

Detection of Neorickettsia risticii, the agent of Potomac horse fever, in horses from Rio de Janeiro, Brazil.

ABSTRACT: This study aims to report the presence of Neorickettsia risticii DNA in blood samples from naturally infected horses in Rio de Janeiro, provide clinicopathological findings related to the infection, and report the phylogenetic diversity of the 16S rDNA of N. risticii in order to evaluate its heterogeneity. Real-time quantitative polymerase chain reaction (qPCR) was performed to investigate the presence of N. risticii in samples collected from horses (n?=?187). Five positive samples were found in the molecular screening. Hypoalbuminemia and high levels of creatine kinase and lactate dehydrogenase were the predominant findings in the biochemical analysis. The sequences were similar to those of N. risticii. Phylogenetic analysis revealed genotype segregation based on the geographical distribution in the N. risticii sequence clade. Dendrograms constructed with five hypervariable regions revealed that V4 distinguished Neorickettsia at the species level and produced a phylogeny that best represented the phylogeny obtained with the complete 16S rDNA sequence. This is the first report of N. risticii DNA in the blood of Brazilian horses based on sequences deposited in GenBank. Further studies are necessary to clarify the epidemiological chain of this vector-borne parasite in order to determine and establish appropriate preventive measures in the equine trading market.

SUBMITTER: Paulino PG

PROVIDER: S-EPMC7190851 | biostudies-literature | 2020 Apr

REPOSITORIES: biostudies-literature

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Detection of Neorickettsia risticii, the agent of Potomac horse fever, in horses from Rio de Janeiro, Brazil.

Paulino Patrícia Gonzaga PG Almosny Nádia N Oliveira Renata R Viscardi Vanessa V Müller Ananda A Guimarães Andresa A Baldani Cristiane C da Silva Claudia C Peckle Maristela M Massard Carlos C Santos Huarrisson H

Scientific reports 20200429 1

This study aims to report the presence of Neorickettsia risticii DNA in blood samples from naturally infected horses in Rio de Janeiro, provide clinicopathological findings related to the infection, and report the phylogenetic diversity of the 16S rDNA of N. risticii in order to evaluate its heterogeneity. Real-time quantitative polymerase chain reaction (qPCR) was performed to investigate the presence of N. risticii in samples collected from horses (n = 187). Five positive samples were found in ...[more]

PMID: 32350359

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Project description:Neorickettsia (formerly Ehrlichia) risticii is an obligatory intracellular bacterium of digenetic trematodes. When a horse accidentally ingests aquatic insects containing encysted trematodes infected with N. risticii, the bacterium is transmitted from trematodes to horse cells and causes an acute and often fatal disease called Potomac horse fever (PHF). Since the discovery of N. risticii in the United States in 1984, using immunofluorescence and PCR assays, PHF has been increasingly recognized throughout North America and South America. However, so far, there exist only a few stable N. risticii culture isolates, all of which are from horses within the United States, and the strain diversity and environmental spreading and distribution of pathogenic N. risticii strains remain poorly understood. This paper reports the isolation of N. risticii from the blood of a horse with acute PHF in Ontario, Canada. Intracellular N. risticii colonies were detected in P388D1 cells after 47 days of culturing and 8 days after the addition of rapamycin. Molecular phylogenetic analysis based on amino acid sequences of major surface proteins P51 and Ssa1 showed that this isolate is distinct from any previously sequenced strains but closely related to midwestern U.S. strains. This is the first Canadian strain cultured, and a new method was developed to reactivate dormant N. risticii to improve culture isolation.Neorickettsia risticii is an environmental bacterium that lives inside flukes that are parasitic to aquatic snails, insects, and bats. When a horse accidentally ingests insects harboring flukes infected with N. risticii, the bacterium is transmitted to the horse and causes an acute and often fatal disease called Potomac horse fever. Although the disease has been increasingly recognized throughout North and South America, N. risticii has not been cultured outside the United States. This paper reports the first Canadian strain cultured and a new method to effectively culture isolate N. risticii from the horse blood sample. Molecular analysis showed that the genotype of this Canadian strain is distinct from previously sequenced strains but closely related to midwestern U.S. strains. Culture isolation of N. risticii strains would confirm the geographic presence of pathogenic N. risticii, help elucidate N. risticii strain diversity and environmental spreading and distribution, and improve diagnosis and development of vaccines for this dreadful disease.

Project description:Potomac horse fever (PHF), a severe and frequently fatal febrile diarrheal disease, has been known to be caused only by Neorickettsia risticii, an endosymbiont of digenean trematodes. Here, we report the cell culture isolation of a new Neorickettsia species found in two locations in eastern Ontario, Canada, in 2016 and 2017 (in addition to 10 variable strains of N. risticii) from N. risticii PCR-negative horses with clinical signs of PHF. Gene sequences of 16S rRNA and the major surface antigen P51 of this new Neorickettsia species were distinct from those of all previously characterized N. risticii strains and Neorickettsia species, except for those from an uncharacterized Neorickettsia species culture isolate from a horse with PHF in northern Ohio in 1991. The new Neorickettsia species nonetheless had the characteristic intramolecular repeats within strain-specific antigen 3 (Ssa3), which were found in all sequenced Ssa3s of N. risticii strains. Experimental inoculation of two naive ponies with the new Neorickettsia species produced severe and subclinical PHF, respectively, and the bacteria were reisolated from both of them, fulfilling Koch's postulates. Serological assay titers against the new Neorickettsia species were higher than those against N. risticii Whole-genome sequence analysis of the new Neorickettsia species revealed unique features of this bacterium compared with N. risticii We propose to classify this new bacterium as Neorickettsia finleia sp. nov. This finding will improve the laboratory diagnosis of and vaccine for PHF, environmental risk assessment of PHF, and understanding of PHF pathogenesis and Neorickettsia biology in general.IMPORTANCE Despite the detection of Neorickettsia species DNA sequences in various trematode species and their hosts, only three Neorickettsia species have been cell culture isolated and whole-genome sequenced and are known to infect mammals and/or cause disease. The molecular mechanisms that enable the obligatory intracellular bacterium Neorickettsia to colonize trematodes and to horizontally transmit from trematodes to mammals, as well as the virulence factors associated with specific mammalian hosts, are unknown. Potomac horse fever (PHF) is a severe and acute systemic infectious disease of horses, with clinical signs that include diarrhea. Neorickettsia risticii is the only known bacterial species that causes PHF. Ingestion of insects harboring N. risticii-infected trematodes by horses leads to PHF. Our discovery of a new Neorickettsia species that causes PHF and whole-genome sequence analysis of this bacterium will improve laboratory diagnosis and vaccine development for PHF and will contribute to our understanding of Neorickettsia ecology, pathogenesis, and biology.

Dataset Information

Detection of Neorickettsia risticii, the agent of Potomac horse fever, in horses from Rio de Janeiro, Brazil.

Publications

Detection of Neorickettsia risticii, the agent of Potomac horse fever, in horses from Rio de Janeiro, Brazil.

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