Human parasitism by the exotic tick Dermacentor variabilis (Parasitiformes: Ixodida) in Brazil: report of an imported case

In June 2012, a tick was found parasitizing a man in the city of São Paulo, who had recently returned from a visit to Pennsylvania, in the northeast of the United States. The tick was removed and sent to the São Paulo State Department of Health, where it was identified as a male of the species Dermacentor variabilis (Say, 1821), according to the literature and taxonomic keys. The tick was subjected to a PCR test to search for rickettsiae, but the result was negative. The fact that a human entered Brazilian territory unaware that he was parasitized by a hard tick not belonging to the national tick fauna is significant because of the possibility that an exotic species could be introduced and take hold in this country. Another major risk to public health is that this arthropod could be infected with the bacterium Rickettsia rickettsii, as this ectoparasite is the main vector of Spotted Fever on the East Coast of North America.

Aspectos epidemiológicos, diagnóstico e tratamento para febre maculosa brasileira

A febre maculosa é uma doença febril incomum e foi caracterizada pela primeira vez na América do Norte, por volta do final do século XIX. Essa doença é causada pela picada do carrapato-estrela, da espécie Amblyomma cajennense, infectado com a bactéria gram-negativa Rickettsia rickettsii. Esse vetor, o carrapato pertence à família Ixodidae, são artrópodes hematófagos, tendo preferência por animais silvestres, em especial equinos e roedores, como as capivaras. A incidência da febre maculosa é maior durante a estação de inverno e nos primeiros dias da primavera. Portanto, moradores de áreas mais próximas as matas e jardins com presença de animais possivelmente portadores de carrapato devem tomar cuidado para não se contaminarem com a febre maculosa. Para que o contágio por essa bactéria é necessário ocorrer o contato de longa duração entre o carrapato e o homem. Essa doença cursa com vários sinais e sintomas que podem aparecer em um intervalo de 2 dias até 2 semanas depois da picada do carrapato infectado com Rickettsia. O tratamento deve ser iniciado em até 5 dias após o surgimento dos sintomas e é realizado através de antibioticoterapia, com o intuito de evitar complicações mais graves que poderiam surgir sem o início do tratamento. O presente estudo trata-se de uma revisão integrativa sobre a febre maculosa, com objetivo de caracterizar a doença e seus aspectos sobre a epidemiologia, diagnóstico e tratamento.

Determination of NK cell immunophenotype and cytokine profile in patients with Rocky Mountain spotted fever

The intracellular pathogen Rickettsia rickettsii causes tick-borne spotted fever (also called Rocky Mountain spotted fever (RMSF) and is increasingly recognized as an emerging cause of febrile illness in Mexico. However, little is known about the early immune responses to infection. Four RMSF pediatric patients on acute phase and eight healthy controls from Chihuahua, Mexico were recruited. The natural killer cell (NK) immunophenotype and the cytokine profile in peripheral blood were characterized by flow cytometry. The population of cytotoxic NK cells expressing NKG2D was significantly decreased in patients on 3rd day of hospitalization compared to the first sampling on admission. Interleukins IL-6, IL-8, and IL-10 levels were significantly increased in patients upon admission compared to controls. This study shows that circulating NK cells are numerically decreased, while cytokines induce a pro-inflammatory process in patients.

Molecular Detection of Tick-Borne Pathogens in American Bison (Bison bison) at El Uno Ecological Reserve, Janos, Chihuahua, Mexico

American bison (Bison bison) is listed as near-threatened and in danger of extinction in Mexico. Recent studies have demonstrated the presence of several emerging pathogens at the Janos Biosphere Reserve (JBR), inhabited by one wild herd of American bison. Blood samples were collected from 26 American bison in the JBR. We tested for the presence of Anaplasma marginale, Babesia bigemina, B. bovis, Borrelia burgdorferi sensu lato, and Rickettsia rickettsii DNA using nested and semi-nested PCR protocols performing duplicates in two different laboratories. Results showed three animals (11.5%) positive for B. burgdorferi s. l., three more (11.5%) for Rickettsia rickettsii, and four (19.2%) for B. bovis. Two individuals were co-infected with B. burgdorferi s. l. and B. bovis. We found no animals positive for A. marginale and B. bigemina. This is the first report in America of R. rickettsii in American bison. American bison has been described as an important reservoir for pathogens of zoonotic and veterinary importance; thus, the presence of tick-borne pathogen DNA in the JBR American bison indicates the importance of continuous wildlife health surveys.

672. Diagnosis of Rocky Mountain Spotted Fever Using Plasma Metagenomic Next-Generation Sequencing

Background Rocky mountain spotted fever (RMSF), caused by Rickettsia rickettsii, incurs significant morbidity and mortality, especially in children. Early in the course of illness, standard diagnostic tests are of limited sensitivity, and diagnosis is often based on clinical symptoms and local epidemiology. The diagnosis can be missed in areas where RMSF is not endemic, and a delay in initiation of therapy may lead to poor clinical outcomes. Plasma metagenomic next-generation sequencing (mNGS), with turnaround times approaching 48 hours, may be a useful adjunctive tool in the diagnosis of RMSF. Methods We describe four children hospitalized with RMSF between January 1, 2017 to May 15, 2021 at a tertiary children’s hospital in southern California. All had plasma mNGS and rickettsial serologic testing as part of clinical care. Results mNGS detected Rickettsia rickettsii in all 4 patients. Only 2 subjects had positive serologic testing initially and required repeat testing in the convalescent stage to confirm RMSF. The mean turnaround time for mNGS was 2.75 days, which was comparable to serologic testing. Antibiotic therapy was changed in three subjects as a result of the plasma mNGS result. Conclusion Plasma mNGS may be a useful diagnostic modality early in the disease course of RMSF. Disclosures Lauge Farnaes, MD, PhD, Cardea Bio (Advisor or Review Panel member)IDbyDNA (Employee)

Nitric Oxide Inhibition of Rickettsia rickettsii

Rickettsia rickettsii , the causative agent of Rocky Mountain spotted fever, is an enzootic, obligate intracellular bacterial pathogen. Nitric oxide (NO) synthesized by the inducible nitric oxide synthase (iNOS) is a potent antimicrobial component of innate immunity and has been implicated in the control of virulent Rickettsia spp. in diverse cell types. In this study, we examined the antibacterial role of NO on R. rickettsii . Our results indicate that NO challenge dramatically reduces R. rickettsii adhesion through the disruption of bacterial energetics. Additionally, NO-treated R. rickettsii were unable to synthesize protein or replicate in permissive cells. Activated, NO-producing macrophages restricted R. rickettsii infections, but inhibition of iNOS ablated the inhibition of bacterial growth. These data indicate that NO is a potent anti-rickettsial effector of innate immunity that targets energy generation in these pathogenic bacteria to prevent growth and subversion of infected host cells.

Amblyomma aureolatum Genetic Diversity and Population Dynamics Are Not Related to Spotted Fever Epidemiological Scenarios in Brazil

Regional differences in tick-borne disease epidemiology may be related to biological variations between vector populations. Amblyomma aureolatum (Ixodida: Ixodidae), a neotropical tick, is known from several regions in Brazil. However, only in the metropolitan area of São Paulo (SP) state are there studies that establish its role as a vector of a pathogenic rickettsia (Rickettsia rickettsii). The aim of the study was to analyze the genetic diversity, population dynamics, and rickettsia infection in A. aureolatum populations from different spotted fever scenarios in Brazil. Samples were subjected to DNA extraction, amplification and sequencing of 12S rDNA, cytochrome oxidase subunit II and D-loop mitochondrial markers for tick population analyses, and gltA, htrA, ompA, and ompB genes for rickettsia researches. Of the 7–17 tick haplotypes identified, 5–13 were exclusive to each population and 2–12 for each epidemiological scenario, as well as three haplotypes shared by all populations. Amblyomma aureolatum populations are expanding, and do not appear to be genetically structured vis-a-vis the different epidemiological scenarios studied. Rickettsia bellii (in SP) and Rickettsia felis (in Santa Catarina) were identified as infecting A. aureolatum. No relationship between tick haplotypes and rickettsia types were observed.