Hermes Ribeiro Luz

This study evaluated the repellent activity of the botanical compounds thymol, carvacrol, nootkatone, and eugenol (5%), as well as the combination of 2.5% nootkatone + 2.5% eugenol, against Amblyomma sculptum nymphs under laboratory and field conditions. In contact bioassays, carvacrol and nootkatone showed the highest mean repellency rates (94.5% and 93.7%), followed by thymol and eugenol (90.2% and 87.2%). The combination (nootkatone + eugenol) resulted in 92.8% repellency, with 100% efficacy in some evaluation periods. The repellency of 7% DEET (positive control) was 82.2%. Nootkatone 5% and the combination (nootkatone + eugenol) were also tested in a Y-tube olfactometer, showing repellency rates of 86.1% and 72.2%, respectively, both higher than 7% DEET (69.4%). In field trials, volunteers wore treated socks and walked through an area naturally infested with nymphs. A significant reduction (p < 0.05) in tick counts was observed in the treated groups (about five unfed nymphs) compared to the control (about 40 unfed nymphs). Cumulative efficacy exceeded 85% in both treatments. In the cost simulation, the estimated cost of a 100 mL formulation containing 5% nootkatone was USD 50.8, while the combination (nootkatone + eugenol) presented a cost USD 28.6, representing a 44% reduction with no loss of efficacy in field conditions. These results indicate that all compounds tested showed repellent activity in the laboratory. Nootkatone has high repellent activity, and its combination with eugenol is a promising and more economically viable alternative for tick repellency.

Background: In Brazil, spotted fever (SF) is caused by the bacteria Rickettsia parkeri and Rickettsia rickettsii. Seroepidemiological data on Rickettsia spp. in humans are rare in Brazil and nonexistent in the Amazon biome. We sought to quantify antibodies reactive to Rickettsia spp. in serum samples collected from humans in the Amazonia biome, and to detect Rickettsia spp. in ticks parasitizing these hosts. Methods: Human blood samples were collected from three different locations within the eastern Amazon in Maranhão State, northeastern Brazil between 2010 and 2018. Sera generated from those samples were tested for the presence of antibodies reactive to Rickettsia by immunofluorescence assay (IFA) using crude antigens from five Rickettsia isolates from Brazil: R. rickettsii strain Taiaçu, R. amblyommatis strain Ac37, Rickettsia rhipicephali strain HJ5, R. parkeri strain At24, and Rickettsia bellii strain Mogi. Between 2020 and 2025, ticks were manually collected while attached to the skin of humans in seven municipalities in Maranhão State. Adult ticks were randomly selected and individually processed for DNA extraction and examined using a real-time PCR (qPCR) assay targeting a fragment of the rickettsial gltA gene. The qPCR-positive samples were subsequently examined by conventional PCR (cPCR) targeting the ompA gene of SFG rickettsiae. The cPCR amplicons were purified and sequenced bidirectionally using the amplification primers. The resulting sequences were compared with those in GenBank using BLASTn to identify related Rickettsia spp. Results: A total of 341 human serum samples were analyzed, and 145 (42.5%) were recorded as reactive with at least one species of Rickettsia. Among the reactive samples, 68 (47%) were from Imperatriz, 45 (31%) from Açailândia, and 32 (22%) from the municipality of São Luís. Rickettsia rhipicephali was recorded as the possible antigen involved in a homologous reaction (PAIHR) in one individual, R. amblyommatis in five, and R. bellii in three. A total of 187 ticks were collected parasitizing humans in the Amazon biome. Molecular analyses revealed that Rickettsia DNA was present in 44.4% (4/9) of A. cajennense s.s. from Açailândia, 52.4% (22/42) from Centro Novo do Maranhão, and 0% (0/8) from Imperatriz. Among the adults of A. coelebs from Centro Novo do Maranhão, 36.8% (7/19) tested positive. In contrast, all adults of A. oblongoguttatum from the same location tested negative (0/20). Conclusions: This is the first study to detect anti-Rickettsia antibodies in humans and to identify R. amblyommatis in ticks parasitizing humans in the Amazon biome. The detection of R. amblyommatis in human-biting ticks, together with concurrent seropositivity in human sera from the same region, supports the hypothesis that this agent is actively circulating in the Amazon biome and may be responsible for undiagnosed cases of nonlethal spotted fever in the area. Graphical

Tick-borne piroplasmids are apicomplexan protozoa that infect a wide range of vertebrate hosts, with significant implications for animal and human health. This study investigated the occurrence and genetic diversity of piroplasmids in wild mammals, unconventional pets, and associated ticks in Goiás state, midwestern Brazil. Between April 2023 and January 2024, 105 blood samples, 22 tissue samples, and 300 ticks were collected from 21 mammalian species housed in wildlife screening centers, zoos, and veterinary clinics. Molecular screening targeting the 18S rRNA gene of piroplasmids detected a 25.7% (27/105) overall positivity, with gray brockets (Subulo gouazoubira) and South American tapirs (Tapirus terrestris) showing the highest infection rates. Three tick samples tested positive, including two Amblyomma sculptum nymphs and a male of Amblyomma dubitatum collected from a tapir and capybara (Hydrochoerus hydrochaeris). Cytauxzoon brasiliensis was reported, for the first time, in cougars (Puma concolor) from Goiás state, midwestern Brazil, indicating the role of this feline as a host of this parasite. Babesia goianiaensis was confirmed in a capybara, and Theileria terrestris in tapirs. Phylogenetic analyses clustered gray brockets-associated Theileria sequences with Theileria sp. previously detected in Neotropical deer from Brazil and Theileria cervi. While the phylogenetic analysis of amino acid sequences of the cytochrome c oxidase subunit III separated Theileria genotypes detected in S. gouazoubira from T. cervi, hsp70-based phylogenetic inferences clustered the genotypes detected in Tapirus terrestris with Theileria terrestris, suggesting host-specific evolutionary lineages. These findings contribute to the understanding of Piroplasmida diversity and circulation in South American wild mammals, emphasizing the need for enhanced molecular surveillance to elucidate transmission dynamics, assess potential health risks, and contribute to the establishment of wildlife conservation and One Health strategies.

Hyperparasitism has been observed in soft and hard tick species around the world. In Brazil, the phenomenon of hyperparasitism has only been observed conspecifically in hard ticks of the genus Amblyomma. In the present study, we report unprecedented cases of hyperparasitism in soft and hard ticks. Conspecific hyperparasitism is reported for Ornithodoros fonsecai and Ornithodoros tabajara, while interspecific hyperparasitism is reported for Amblyomma sculptum on Rhipicephalus microplus.

This study evaluated the repellent activity of DEET, eugenol, methyl eugenol, 1,8-cineole, and their combinations against Amblyomma sculptum nymphs through laboratory and field tests. Initially, the botanical compounds were tested individually in Petri dish assays to assess repellent activity over various intervals (1 min to 168 h) at concentrations of 2%. Eugenol and methyl eugenol exhibited the highest average repellent percentages (60 to 90%), with significant effects (p < 0.05) across most evaluation periods, in contrast to 1,8-cineole. Therefore, eugenol and methyl eugenol were selected for combination testing with DEET. The combinations of 7% DEET + 1% eugenol and 7% DEET + 2% methyl eugenol showed the best results, with average repellent efficacy exceeding 85%. The first combination was selected for field evaluation. In this test, volunteers wore treated socks and walked for two hours in a naturally infested area. A significant reduction (p < 0.05) in the number of ticks recovered from the socks was observed in the 7% DEET and 7% DEET + 1% eugenol treatments, with efficacies of 82.5% and 88.5%, respectively, after 120 min. Isolated eugenol showed limited field efficacy, with significant repellent activity (p < 0.05) lasting only 20 min. The results highlight the potential of eugenol and methyl eugenol as repellent compounds, especially when combined with DEET. The field study confirmed the efficacy of the 7% DEET + 1% eugenol.

The life-cycle of Amblyomma calcaratum was evaluated experimentally under laboratory conditions using birds (Serinus canaria, Gallus gallus) and rodents (Calomys callosus) as hosts for immatures and a rabbit (Oryctolagus cuniculus) as host for adults. Developmental periods of the non-parasitic stages were observed in an incubator at 27 °C and 90% RH. The passerine S. canaria was the most suitable host for larvae and nymphs whereas the rodent C. callosus was not suitable to both immatures; only one engorged larva was recovered. The suitability of S. canaria for larvae and nymphs of A. calcaratum supports field data regarding passerine birds as main hosts for A. calcaratum immatures. Among the Amblyomma species which life cycle has been evaluated under laboratory conditions, A. calcaratum is one with the longest off-host developmental periods.

Background: Rhipicephalus (Boophilus) microplus is the most important tick species affecting cattle in the world. Under field conditions, the non-parasitic phase of R. (B.) microplus is unknown in the Amazon biome, including Brazil. The present study aimed to evaluate the non-parasitic phase of R. (B.) microplus in field (grass plots) and laboratory conditions. Methods: The study was conducted from September 2020 to April 2022 in an Amazonian region (Maranhão State, Brazil). We evaluated the biological parameters of R. (B.) microplus under laboratory and field conditions. Engorged females were exposed to experimental conditions every 14 days, totaling 20 months of study. The following biological parameters were observed: pre-oviposition period, egg mass incubation period, and maximum larval survival period. Results: Abiotic data (e.g., temperature and humidity) varied little throughout the year. Precipitation was the factor that varied the most throughout the year (dry ~ 30 mm³ and rain 400 mm³), and the parameters of pre-oviposition and pre-hatching are longer during the rainy season. A possible negative effect of the dry season on the percentage of hatched eggs was observed. Larval longevity in the plots of both control and free females was short (mean ~ 50–60 days), below that recorded for larvae under controlled conditions (mean ~ 95 days). Conclusions: Rhipicephalus (Boophilus) microplus was able to complete its non-parasitic phase by producing host-seeking larvae in the pasture during all months of the study. The results indicate that R. (B.) microplus can complete up to six generations per year in biome Amazon. To our knowledge, this is the highest number of annual generations for R. (B.) microplus in Latin America. Graphical