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Rocky Mountain or Brazilian spotted fever, caused by Rickettsia rickettsii, is a fulminant, seasonal, and neglected disease that occurs in focal points of North America and South America. Its rapid detection is essential for the better prognosis and survival rate of infected individuals. However, disease diagnosis still faces challenges as the accuracy of many of the available laboratory tests fluctuates. This review aimed to analyze methods for antibody or antigen detection, their gaps, and their evolution over time. A search was conducted to find all studies in the Pubmed database that described the antibody or antigen detection of R. rickettsii infections. Initially, a total of 403 articles were screened. Of these articles, only 17 fulfilled the pre-established inclusion criteria and were selected. Among the different methods applied, the IFA technique was the one most frequently found in the studies. However, it presented varied results such as a low specificity when using the indirect method. Other techniques, such as ELISA and immunohistochemistry, were also found, although in smaller numbers and with their own limitations. Although some studies showed promising results, there is a pressing need to find new techniques to develop a rapid and effective diagnosis of R. rickettssi infection.

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INTRODUCCIÓN: La rickettsiosis, enfermedad potencialmente mortal, es trasmitida por vectores como Rhipicephalus sanguineus, Dermacentor variabilis y D. andersonii, reservorios de Rickettsia rickettsii. En Baja California, México, es endémica, multifactorial, tiene alta letalidad, sus manifestaciones clínicas inespecíficas y ataque multisistémico dificultan el diagnóstico y tratamiento oportuno. OBJETIVO: Identificar los factores de riesgo asociados a la letalidad por rickettsiosis trasmitida por garrapatas en Mexicali, Baja California. PACIENTES Y MÉTODOS : Estudio observacional, analítico, transversal, retrospectivo, de 40 registros de pacientes con diagnóstico confirmado de rickettsiosis, periodo 2014 a 2018. Variables analizadas: sociodemográficas, clínicas, laboratorio clínico, evolución y desenlace. Se reportan frecuencias y medidas de asociación. RESULTADOS: 24 defunciones y 16 vivos. Más de 90% tuvo contacto conocido con garrapatas. Afectó en su mayoría a < 45 años en ambos grupos. La evolución antes del ingreso fue similar y la estancia hospitalaria fue mayor en los pacientes vivos (3,2 ± 4.7 vs 10,62 ± 7,6 p = 0,0002). Fiebre, cefalea, mialgias fueron predominantes. Datos asociados con letalidad: disfunción respiratoria (OR 38,33 IC95% 4,06-361,3 p < 0,0001), creatinina elevada (OR 15,4 IC95% 3,08-76,77 p < 0,0003), retardo del llenado capilar (OR 13,0 IC95% 2,73-61,78 p = 0,0005), dolor abdominal (OR 8,33, IC95% 1,90-36,44 p = 0,0029), AST (OR 7,5, IC95% 1,69-33,27 p = 0,005). CONCLUSIÓN: Esta enfermedad requiere de identificación temprana de factores que se asocian con letalidad para un tratamiento oportuno y adecuado.

BACKGROUND: Rickettsiosis, a potentially fatal disease, is transmitted by vectors such as Rhipicephalus sanguineus, Dermacentor variabilis and D. andersonii, reservoirs of Rickettsia rickettsii. In Baja California, Mexico, it is endemic, multifactorial, has high lethality, its nonspecific clinical manifestations and multisystem attack make diagnosis and timely treatment difficult. AIM: Identify the risk factors associated with lethality due to tick-transmitted rickettsiosis in Mexicali, Baja California. METHODS: Observational, analytical, cross-sectional, retrospective study of 40 records of patients with a confirmed diagnosis of rickettsiosis, period 2014 to 2018. Analyzed variables: sociodemographic, clinical, clinical laboratory, evolution and outcome. Frequencies and association measures are reported. RESULTS: 24 patients died and 16 survived. More than 90% had reported contact with ticks. It mostly affected ≤ 45 years in both groups. The evolution before admission was similar, and the hospital stay was longer in patients who lived (3.2 ± 4.7 vs 10.62 ± 7.6 p = 0.0002). Fever, headache, and myalgia are predominant. Data associated with lethality: respiratory dysfunction (OR 38.33 95% CI 4.06-361.3 p < 0.0001), elevated creatinine (OR 15.4 95% CI 3.08-76.77 p < 0.0003), delayed capillary refill (OR 13.0, 95% CI 2.73-61.78 p = 0.0005), abdominal pain (OR 8.33, 95% CI 1.90-36.44 p = 0.0029), AST (OR 7.5, 95% CI 1.69-33.27 p = 0.005). CONCLUSION: This disease requires early identification of factors that are associated with lethality for timely and adequate treatment.

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The ANESPSAT, a synthetic spilanthol derivative, and its nanoformulation were evaluated against Rhipicephalus microplus and Amblyomma sculptum ticks. ANESPSAT activity was compared with spilanthol and derivatives (ANESPE and others). The compound was synthesized in a gram-scale by a 2-step process, comprising a direct ester amidation and a Horner-Wadsworth- Emmons reaction. The nanoemulsions were produced by coarse homogenization followed by high-energy ultrasonication, in which hydrodynamic diameter, polydispersity index, and zeta potential remained stable. The spilanthol-eugenol hybrid derivatives did not show significant acaricidal activity. ANESPE killed 83% of the R. microplus larvae at 30 mg.mL-1, while ANESPSAT killed 97% at 0.5 mg.mL-1, showing to be the most active compound. Spilanthol and ANESPSAT had similar high mortality rates for tick larvae, with LC50 values of 0.10 and 0.14 mg.mL-1 for R. microplus larvae, and 0.04 and 0.48 mg.mL-1 for A. sculptum larvae, respectively. The efficacy of spilanthol was lower against R. microplus engorged females when compared with ANESPSAT, which was highly effective (>98%) against R. microplus engorged females. The nanoemulsion with ANESPSAT was effective against tick females, preventing egg laying and achieving 100% efficacy at 2.5 mg.mL-1. Spilanthol had only 59% efficacy at 10 mg.mL-1. The results suggest that ANESPSAT, a natural product derivative, could be used in novel formulations for tick management that might be safer and environmentally friendly.

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Rickettsioses have been reported in parts of Mexico since the last century, with Rocky Mountain spotted fever (RMSF) being one of the most prevalent in northern states. Unfortunately, fatality rates for RMSF in Mexico are higher than in other countries, like the USA. The reason for this difference in fatality rates is currently unknown and could be associated with a genotype of the bacterium, but no comparative molecular typing has been conducted in Mexico to date. The purpose of this study was to analyze 47 RMSF samples with different outcomes from several states in northern Mexico to know the genetic variability of Rickettsia rickettsii, as well as to reconstruct its phylogeny, for which the following intergenic regions were sequenced: RR0155-rpmB, cspA-ksgA, RR1240-tlc5, and Spo0J-abc T1, as well as the following partial genes: ompA, ompB, and gltA. We identified 8 genotypes with different distribution and prevalence among the states analyzed, as well as a different association with case outcome; these genotypes were clustered in 2 clades and 5 lineages were revealed, some of them probably exclusive from Mexico.

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Rickettsia rickettsii is the etiological agent of Rocky Mountain spotted fever, which is an important tick-borne zoonosis and, in Brazil, it causes Brazilian spotted fever, which has high lethality rate. This study aimed to evaluate a synthetic peptide corresponding to a segment of the outer membrane protein A (OmpA) as an antigen in a serological test for the diagnosis of rickettsial infections. The amino acid sequence of the peptide was selected by predicting B cell epitopes using B Cell Epitope Prediction (Immune Epitope Database and Analysis Resource) and Epitopia and OmpA sequences of Rickettsia rickettsii strain 'Brazil' and Rickettsia parkeri strains 'Maculatum 20' and 'Portsmouth'. A peptide with amino acid sequence common to both Rickettsia species was synthesized and arbitrarily named OmpA-pLMC. To evaluate this peptide in enzyme-linked immunosorbent assay (ELISA), serum samples of capybara (Hydrochoerus hydrochaeris), horse (Equus caballus), and opossum (Didelphis albiventris) that had been previously tested by indirect immunofluorescence assay (IFA) for rickettsial infection were separated into IFA-positive and IFA-negative groups and used in the assay. There were no significant differences in ELISA optical density (OD) values between IFA-positive and IFA-negative groups with horse samples. The mean OD values were significantly higher in the IFA-positive capybara serum samples (IFA-pos vs. IFA-neg = 2.389 ± 0.761 vs. 1.760 ± 0.840). However, receiver operating characteristic (ROC) curve analysis did not show significant diagnostic parameters. On the other hand, 12 out of 14 (85.7%) opossum samples of the IFA-positive group showed reactivity in ELISA, and this was significantly higher than of the IFA-negative group (0.7196 ± 0.440 vs. 0.2318 ± 0.098, respectively; 85.7% sensitivity, 100% specificity). Therefore, our results show that OmpA-pLMC has a potential to be used in immunodiagnostic assays to detect spotted fever group rickettsial infections.

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We report an isolated outbreak of Rickettsia rickettsii in the Ngäbe-Buglé indigenous region, located 750 m (tropical wet) above sea level, in a jungle and mountainous area of Western Panama. Seven members of a family were infected simultaneously, resulting in four deaths. Family outbreaks have been previously described and are responsible for 4-8% of the cases described [1-4]. The simultaneous onset of symptoms in the affected population group is extremely unusual [1,5], but it should not dissuade the clinician from considering the possibility of Rickettsia rickettsii infection.

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BACKGROUND: In recent years, promising vaccination strategies against rickettsiosis have been described in experimental animal models and human cells. OmpB is considered an immunodominant antigen that is recognized by T and B cells. The aim of this study was to identify TCD4+INF-γ+ and TCD8+INF-γ+ lymphocytes in an autologous system with macrophages transfected with the vaccine candidate pVAX1-OmpB24. Lymphocytes and monocytes from 14 patients with Rickettsia were isolated from whole blood. Monocytes were differentiated into macrophages and transfected with the plasmid pVAX1-OmpB24 pVax1. Isolated lymphocytes were cultured with transfected macrophages. IFN-γ-producing TCD4+ and TCD8+ lymphocyte subpopulations were identified by flow cytometry, as was the percentage of macrophages expressing CD40+, CD80+, HLA-I and HLA-II. Also, we analyzed the exhausted condition of the T lymphocyte subpopulation by PD1 expression. Macrophages transfected with pVAX1-OmpB24 stimulated TCD4+INF-γ+ cells in healthy subjects and patients infected with R. typhi. Macrophages stimulated TCD8+INF-γ+ cells in healthy subjects and patients infected with R. rickettsii and R. felis. Cells from healthy donors stimulated with OmpB-24 showed a higher percentage of TCD4+PD1+. Cells from patients infected with R. rickettsii had a higher percentage of TCD8+PD-1+, and for those infected with R. typhi the larger number of cells corresponded to TCD4+PD1+. Human macrophages transfected with pVAX1-OmpB24 activated TCD4+IFN-γ+ and CD8+IFN-γ+ in patients infected with different Rickettsia species. However, PD1 expression played an important role in the inhibition of T lymphocytes with R. felis.

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Background and objectives: we investigated the existence of a historical geographic overlap between the location of spotted fever group rickettsiosis human cases, a disease caused by the gram-negative bacterium Rickettsia sp., and that of mammalian reservoirs, specifically domestic horses and capybaras, in the urban perimeter of the city of Juiz de Fora, Minas Gerais, Brazil. Methods: cases of human rickettsiosis that occurred during a period of 17 years (2003-2020) were geolocated and the distribution of cases in time and geographic space was assessed using 1st and 2nd order geospatial association indicators. We also analyzed the overlap between the locations of human rickettsiosis cases and the area of occurrence of domestic horses and capybaras. Results: men were diagnosed more often than women, but a large proportion of affected women died. The results indicate an aggregation of human rickettsiosis cases in time (cases tend to occur close to each other at each epidemic event) and in geographic space (cases are concentrated in a specific geographic region of the urban perimeter). Human cases seem to be more associated with city regions with: i) higher local frequency of domestic horses and not capybaras; ii) lower rates of family development. Conclusion: it is suggested that, in the local epidemiological scenario, domestic horses appear to be the main sources of the rickettsia infecting humans, not capybaras.(AU)

Justificativa e objetivos: foi investigada a existência de uma sobreposição geográfica histórica entre a localização dos casos de riquetsiose humana do grupo da febre maculosa, um grupo de doenças causadas pela bactéria Gram-negativa Rickettsia sp., e dos reservatórios mamíferos, especificamente cavalos domésticos e capivaras, no perímetro urbano do município de Juiz de Fora, Minas Gerais, Brasil. Métodos: foram geolocalizados os casos de riquetsiose humana ocorridos durante um período de 17 anos (2003-2020), sendo avaliada a distribuição dos casos no tempo e espaço geográfico através de indicadores de associação geoespacial de 1a e 2a ordem. Também analisamos a superposição dos locais dos casos de riquetsiose humana com a área de ocorrência de cavalos domésticos e capivaras. Resultados: homens foram diagnosticados mais frequentemente que as mulheres, mas grande proporção das mulheres acometidas faleceu. Os resultados indicam uma agregação dos casos de riquetsiose humana no tempo (os casos tendem a ocorrer próximos entre si a cada evento epidêmico) e no espaço geográfico (os casos se concentram em uma região geográfica específica do perímetro urbano). Os casos humanos aparentam ser mais associados às regiões da cidade com: i) maior frequência local de cavalos domésticos e não das capivaras; ii) menores índices de desenvolvimento familiar. Conclusão: sugere-se que, no cenário epidemiológico local, são os cavalos domésticos que aparentam ser as principais fontes da riquétsia infectando os humanos, não as capivaras.(AU)

Justificación y objetivos: investigamos la existencia de una superposición geográfica histórica entre la localización de casos de rickettsiosis exantemáticas humana, enfermedad causada por la bacteria gramnegativa Rickettsia sp., y la de mamíferos reservorios, específicamente caballos domésticos y capibaras, en el perímetro urbano de la ciudad de Juiz de Fora, Minas Gerais, Brasil. Métodos: se geolocalizaron los casos de rickettsiosis humana ocurridos durante un período de 17 años (2003-2020), y se evaluó la distribución de casos en el tiempo y espacio geográfico utilizando indicadores de asociación geoespacial de 1er y 2do orden. También analizamos la superposición entre las ubicaciones de los casos de rickettsiosis humana y el área de ocurrencia de los caballos domésticos y capibaras. Resultados: los hombres fueron diagnosticados con más frecuencia que las mujeres, pero una gran proporción de mujeres afectadas fallecieron. Los resultados indican una agregación de casos de rickettsiosis humana en el tiempo (los casos tienden a ocurrir cerca uno del otro en cada evento epidémico) y en el espacio geográfico (los casos se concentran en una región geográfica específica del perímetro urbano). Los casos humanos parecen estar más asociados con regiones urbanas con: i) mayor frecuencia local de caballos domésticos y no de capibaras; ii) menores tasas de desarrollo familiar. Conclusión: se sugiere que, en el escenario epidemiológico local, los caballos domésticos parecen ser las principales fuentes de la rickettsia que infecta a los humanos, no los capibaras.(AU)

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Rickettsial diseases have seen a re-emergence in the Americas in the last few decades, with concerning morbidity, mortality and economic implications that result from loss of productivity, income, curbs in liberal trade agreements, and reduction in agricultural practices. The aim of this study is to determine the socioecological determinants and seroprevalence for Rickettsia typhi and Rickettsia rickettsii among residents of Teabo, a rural community of Yucatán, Mexico. Sociodemographic data and serum samples were obtained from 180 consenting participants. Antibody titers for R. typhi and R. rickettsii were determined by indirect immunofluorescence assay (IFA). Participants also submitted tick samples collected from their residential area. We conducted logistic regression models to evaluate the association between exposure variables and seroprevalence. Rhipicephalus sanguineus s.l. (37%; n = 65), and Amblyomma cajennense Fabricius (17%; n = 29) were the predominant tick species in peri-domestic areas. Out of the 180 participants, there was significantly higher seroprevalence of R. typhi (n = 77; 46%) compared to R. rickettsii [n = 27, 15%, (p < 0.05)]. Pearson's chi-square test of independence revealed significant differences in R. rickettsii seroprevalence by gender (X2 [n = 175, df = 4, (p < 0.001)] = 180.26), level of education, (X2 [n = 180, df = 4, (p < 0.001)] = 44.0), and by tick species found in residential area, (X2 [n = 180, df = 4, (p = 0.050)] = 9.48). After adjusting for other variables in a logistic regression model, for each unit increase in the number of dogs present in the residential area, there was a 27% increase in the odds of human seroprevalence for R. typhi IgG (AOR = 1.27, 95% CI: 1.01-1.63). Compared to study participants living in residential areas with a 'low' height of vegetation, those living in residential areas with a 'medium' height of vegetation had 2.5 times greater odds of human seroprevalence for R. typhi IgG (AOR = 2.51, 95% CI: 1.19-5.40). Potentially modifiable existing factors in the peri-domestic area may constitute a high-risk source of seroprevalence for rickettsial antibodies among residents of the rural community of Teabo, Yucatán, Mexico.

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Resumen | Introducción. Las rickettsiosis son enfermedades zoonóticas transmitidas por artrópodos que cumplen el papel de vectores y reservorios, y cuyos síntomas son inespecíficos, por lo que su diagnóstico clínico es difícil. La inmunofluorescencia indirecta (IFI) es el método de referencia para el diagnóstico. En Colombia, ha resurgido el interés por su estudio por los casos de rickettsiosis detectados en el norte del departamento de Caldas a partir del 2001. Objetivo. Establecer la frecuencia de anticuerpos y la seroconversión contra Rickettsia spp. en pacientes atendidos en instituciones de salud del departamento de Caldas, Colombia, entre 2016 y 2019. Materiales y métodos. Se hizo un estudio de diseño cuantitativo, observacional y descriptivo, con una muestra no probabilística de 175 pacientes atendidos en diferentes municipios de Caldas, a quienes se les realizó IFI para la detección de anticuerpos en fase aguda y convaleciente contra Rickettsia rickettsii, R. typhi y R. felis. Resultados. El promedio de edad de los pacientes fue de 31 años. Los municipios con mayor proporción de seropositivos fueron Belalcázar, Chinchiná, Filadelfia, La Dorada, La Merced y Manizales. El 66 % tenía mascotas y el 12 % reportó picaduras por artrópodos. Los signos y síntomas más frecuentes fueron cefalea (69,7 %), artromialgia (60 %), y fiebre (58,2 %). La seroprevalencia por IgG fue de 60 % para R. rickettsii, 47,9 % para R. typhi y 24 % para R. felis. Ocho pacientes presentaron seroconversión. Conclusión. Se encontró evidencia de la circulación de rickettsias del grupo de las fiebres manchadas y del grupo del tifus asociada con casos humanos en el departamento de Caldas.

Abstract | Introduction: Rickettsioses are zoonotic diseases transmitted by arthropods acting as vectors and reservoirs. Disease symptoms are nonspecific and, therefore, their clinical diagnosis is difficult. Indirect immunofluorescence (IFA) is the gold standard assay for diagnosis. The interest for conducting studies on these pathologies has resurfaced in Colombia since 2001; besides, previous studies have evidenced cases of rickettsiosis in the north of the department of Caldas. Objective: To establish the frequency of antibodies and seroconversion against Rickettsia spp. In patients consulting health institutions in Caldas, Colombia, from 2016 to 2019. Materials and methods: We conducted a quantitative, observational, and descriptive study on a non-probabilistic sample of 175 patients with symptoms compatible with rickettsiosis who consulted in different municipalities of Caldas, Colombia; IFA was performed to detect antibodies in the acute and convalescent phases against Rickettsia rickettsii, Rickettsia typhi, and Rickettsia felis. Results: The average age of the patients was 31 years. The municipalities with the highest proportion of seropositive cases were Belalcázar, Chinchiná, Filadelfia, La Dorada, La Merced, and Manizales; 66% of patients owned pets and 12% reported arthropod bites. The most frequent signs and symptoms were headache (69.7%), arthromyalgia (60%), and fever (58.2%). IgG seroprevalence was 60% for R. rickettsii, 47.9% for R. typhi, and, and 24% for R. felis. Eight patients presented seroconversion. Conclusion: We found evidence of the circulation of Rickettsia species from the spotted fever group and the typhus group associated with human cases in Caldas.

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Amblyomma patinoi ticks infected with Rickettsia rickettsii are present in Colombia, but its vector competence is unknown. Hence, we evaluated the vector competence of A. patinoi with R. rickettsii under laboratory conditions. Experimental guinea pigs and rabbits (males and females) were separated in the infected group (IG) and the control group (CG). In the IG, the filial 1 (F1) larvae (R. rickettsii-free) from Colombian A. patinoi engorged female specimens were exposed to R. rickettsii (ITU strain) by feeding on infected guinea pigs. Next, F1 nymphs and adults, and F2 larvae were allowed to feed on uninfected guinea pigs or rabbits and tested by qPCR targeting the gltA rickettsial gene. All animals used to feed the IG F1 ticks became febrile and had R. rickettsii infection (89% fatality rate) detected through serological or molecular techniques. After the F1 larvae ticks became R. rickettsii infected, subsequent IG tick stages were able to maintain the rickettsial infection by transstadial maintenance to all infested animals, indicating A. patinoi vector competence. Subsequently, almost 31% of the F1 female egg masses and only 42% of their F2 larvae were infected. Less than 50% of the infected females transmitted R. rickettsii transovarially, and only a part of the offspring were infected. This study demonstrated that A. patinoi might not be able to sustain R. rickettsii infection by transovarial transmission for successive tick generations without horizontal transmission via rickettsemic hosts. This condition might result in low R. rickettsii-infection rates of A. patinoi under natural conditions.

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Background and Objectives:Rickettsia rickettsii is a pathogen that is known to cause spotted fever, a zoonosis that is endemic in several regions of the Americas. However, no systematic review and meta-analysis has been conducted to estimate the prevalence of this rickettsial disease in the Americas. Therefore, the objective of this study was to estimate the prevalence of R. rickettsii in ticks in the Americas. Methods: The Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines were followed and data were retrieved from four electronic databases: MEDLINE/PubMed, SciELO, ScienceDirect, and Directory of Open Access Journals. The pooled prevalence and heterogeneity were determined using a random-effects model and using Cochran's Q test and I2 index, respectively. Publication bias was assessed using a funnel plot and Egger's method. Results: The pooled prevalence of R. rickettsii in ticks was highest in Colombia (17.00%; confidence interval [95% CI]: 7.01-30.24), followed by Mexico (9.89%; 95% CI: 2.03-22.74), Panama (2.76%; 95% CI: 0.45-6.93), Brazil (2.03%; 95% CI: 0.66-4.14), and the United States (0.50%; 95% CI: 0.15-1.05). The tick species most frequently infected by R. rickettsii were Rhipicephalus sanguineus sensu lato (6.23%; 95% CI: 2.79-10.92) and Amblyomma mixtum (4.36%; 95% CI: 0.25-13.14). Interpretation and Conclusion: It can be suggested that studies aiming to identify the potential vectors of R. rickettsii should be conducted more intensively to better understand the epidemiology of spotted fever in the Americas.

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We report new cases of Rocky Mountain spotted fever in patients from Kinkantu, Ngäbe-Bugle indigenous comarca, Panama. We isolated Rickettsia rickettsii in cell culture after intraperitoneal inoculation of guinea pigs with tissues from a deceased patient. Our results indicate that Rocky Mountain spotted fever is emerging in this region.

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A febre maculosa brasileira (FMB), causada pelabactéria Rickettsia rickettsii, é a zoonose transmitida porcarrapatos mais importante no Brasil. No estado de SãoPaulo, onde a doença apresenta letalidade ao redor de50%, os carrapatos Amblyomma aureolatum e Amblyomma sculptum são os principais vetores. O primeiro, associado a cães domésticos e fragmentos de Mata Atlântica,transmite a doença na Região Metropolitana de São Paulo.Já A. sculptum, é vetor no interior do estado, especialmente nas regiões de Campinas, Piracicaba e Marília, onde oscarrapatos infectados são mantidos principalmente porcapivaras. O período de incubação da FMB em humanosvaria de 2 a 14 dias, sendo febre, mialgia e cefaleia os principais sintomas. Posteriormente, podem aparecer exantema, insuficiências respiratória e renal, lesões neurológicase icterícia. A letalidade da doença depende do retardo doinício da terapia com antibióticos específicos, tais comodoxiciclina e cloranfenicol. O cão também adoece, porémcom taxa de letalidade abaixo de 20%. Não existem vacinas disponíveis para proteção contra a FMB. A prevençãose baseia primariamente no controle e prevenção das infestações por carrapatos nas áreas endêmicas da doença.Práticas de controle reprodutivo de capivaras estão sendoaplicadas para diminuir os riscos de transmissão da FMB nointerior do estado de São Paulo. (AU)

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A febre maculosa brasileira (FMB), causada pelabactéria Rickettsia rickettsii, é a zoonose transmitida porcarrapatos mais importante no Brasil. No estado de SãoPaulo, onde a doença apresenta letalidade ao redor de50%, os carrapatos Amblyomma aureolatum e Amblyomma sculptum são os principais vetores. O primeiro, associado a cães domésticos e fragmentos de Mata Atlântica,transmite a doença na Região Metropolitana de São Paulo.Já A. sculptum, é vetor no interior do estado, especialmente nas regiões de Campinas, Piracicaba e Marília, onde oscarrapatos infectados são mantidos principalmente porcapivaras. O período de incubação da FMB em humanosvaria de 2 a 14 dias, sendo febre, mialgia e cefaleia os principais sintomas. Posteriormente, podem aparecer exantema, insuficiências respiratória e renal, lesões neurológicase icterícia. A letalidade da doença depende do retardo doinício da terapia com antibióticos específicos, tais comodoxiciclina e cloranfenicol. O cão também adoece, porémcom taxa de letalidade abaixo de 20%. Não existem vacinas disponíveis para proteção contra a FMB. A prevençãose baseia primariamente no controle e prevenção das infestações por carrapatos nas áreas endêmicas da doença.Práticas de controle reprodutivo de capivaras estão sendoaplicadas para diminuir os riscos de transmissão da FMB nointerior do estado de São Paulo.

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Rocky Mountain spotted fever (RMSF) is a life-threatening tick-borne disease caused by Rickettsia rickettsii, which is widely distributed throughout the Americas. Over 4000 cases of RMSF are recorded annually in the United States, while only around 100 cases are reported in Brazil. Conversely, while case fatality rates in the United States oscillate around 5%, in Brazil they can surpass 70%, suggesting that differences in tick vectoring capacity, population sensitivity, and/or variability in virulence of the rickettsial strains may exist. In this study, we compared the susceptibility of C3H/HeN mice to two highly virulent strains of R. rickettsii, one from the United States (Sheila Smith) and the other from Brazil (Taiaçu). Animals inoculated with the Taiaçu strain succumbed to infection earlier and exhibited severe histological lesions in both liver and spleen sooner than mice infected with the Sheila Smith strain. These differences in survival and signs of the disease are not related to a greater proliferation of the Taiaçu strain, as there were no significant differences in the rickettsial load in mice tissues inoculated with either strain. The present study is the first step to experimentally assess differences in fatality rates of RMSF in two different regions of the American continent.

RESUMO

Brazilian spotted fever (BSF) is a highly lethal disease in southeastern Brazil. BSF is caused by the bacterium Rickettsia rickettsii and is transmitted by the bites of the tick of the genus Amblyomma. The spatial distribution of BSF risk areas is not well known in the country given the complexity of the transmission cycle. This study used the ecological niche modeling (ENM) approach to anticipate the potential distribution of the etiological agent (Rickettsia rickettsii), vectors (Amblyomma sculptum and A. dubitatum), and hosts (Hydrochoerus hydrochaeris, Didelphis aurita, and D. marsupialis) of BSF in Brazil. We compiled occurrence records for all vectors, hosts, and BSF from our own field surveillance, online repositories, and literature. ENM identified BSF risk areas in southeastern and southern Brazil, and anticipated other dispersed suitable areas in the western, central, and northeastern coast regions of Brazil. Tick vectors and mammalian hosts were confined to these same areas; however, host species showed broader suitability in northern Brazil. All species ENMs performed significantly better than random expectations. We also tested the BSF prediction based on 253 additional independent cases identified in our surveillance; the model anticipated 251 out of 253 of these independent cases. Background similarity tests comparing the ENMs of R. rickettsii, tick vectors, and mammalian hosts were unable to reject null hypotheses of niche similarity. Finally, we observed close coincidence between independent BSF cases, and areas suitable for combinations of vectors and hosts, reflecting the ability of these model pairs to anticipate the distribution of BSF cases across Brazil.

Assuntos

RESUMO

The systematics of several ticks species (Acari: Ixodidae) remains controversial. Many species, including those of the Amblyomma cajennense complex and Rhipicephalus sanguineus s.l., are given special attention since they are cryptic species complexes and are also important in human and veterinary medicine. The A. cajennense complex was recently reorganized into six valid species, among which Amblyomma patinoi and Amblyomma mixtum have been confirmed in Colombia. On the other hand, the taxonomic status of R. sanguineus s.l. is controversial since it is a cosmopolitan cryptic species complex with a high reproductive capacity and a broad range of hosts (including man). To address this challenge, the germ cells of male ticks display a diverse morphology that offers novel opportunities for taxonomy. This study describes the events of spermatogenesis in A. mixtum and R. sanguineus s.l. individuals collected during active feeding on domestic hosts in the department of Caldas, Colombia. The individuals were identified using dichotomous keys and through PCR amplification of a fragment of the mitochondrial 16S ribosomal DNA gene. The male reproductive systems of A. mixtum and R. sanguineus s.l. were fixed in 2.5% glutaraldehyde for 48 h and dehydrated in increasing dilutions of ethanol. The samples were then embedded and mounted in historesin to obtain sections of 3 µm that were stained with hematoxylin-eosin (HE), photographed, and visualized through optical microscopy. The results show that the morphology of mature germ cells displays excellent diagnostic traits that can be used for tick taxonomy.

Assuntos