Soft and hard ticks (Parasitiformes: Ixodida) on humans: A review of Brazilian biomes and the impact of environmental change

Ticks parasitizing cold-blooded animals from three different Brazilian biomes; with note for males of Amblyomma rotundatum

Ticks parasitize a wide variety of wild animals, including amphibians and reptiles. In addition to the possibility of microorganism transmission to these hosts, ticks can also cause severe bleeding, and high parasitism can lead to death. Therefore, knowing the diversity of ticks parasitizing amphibians and reptiles is important for conservation and preservation measures for these vertebrates. In the present study, we report parasitism by ticks in amphibians and reptiles from different Brazilian biomes (Amazon, Caatinga, Cerrado and Atlantic Forest). Ticks were collected from amphibians and reptiles deposited from the Herpetological Collection of the Federal University of Maranhão (UFMA), São Luís (Maranhão State), the State University Santa Cruz (UESC), Ilhéus (Bahia State), and the Federal University of São Francisco Valley (Univasf), Petrolina (Pernambuco State). Additionally, ticks were collected from amphibians and reptiles captured and road-killed in the Amazon biome, at Maranhão and Amapá States. Specimens of ticks were photographed under a Zeiss stereomicroscope (5.1 zoom). Map with the locations were made using the Qgis program. Overall, 1973 specimens of amphibians and reptiles were examined. A total of 927 ticks were collected: 98 larvae, 421 nymphs and 408 adults. Six species of ticks were identified: Amblyomma rotundatum and Amblyomma dissimile the most frequent, and Amblyomma cajennense sensu stricto, Amblyomma sculptum, Amblyomma nodosum and Amblyomma humerale, occasionally. Surprisingly, a total of twelve males of A. rotundatum were collected. Here we report new records of association between cold-blooded animals and ticks and reinforce the absence of A. dissimile in the Caatinga, Cerrado and Atlantic Forest biomes. Additionally, we report new records of A. rotundatum males on reptiles in the Amazon biome. This last record allows us to speculate about a possible association of A. rotundatum males with reptiles and the Amazon biome.

Isolation and molecular characterization of a novel relapsing fever group Borrelia from the white-eared opossum Didelphis albiventris in Brazil

This study aimed to detect, isolate and to characterize by molecular methods a relapsing fever group (RFG) Borrelia in white-eared opossums (Didelphis albiventris) from Brazil. During 2015-2018, when opossums (Didelphis spp.) were captured in six municipalities of the state of São Paulo, Brazil, molecular analyses revealed the presence of a novel RFG Borrelia sp. in the blood of seven opossums (Didelphis albiventris), out of 142 sampled opossums (4.9% infection rate). All seven infected opossums were from a single location (Ribeirão Preto municipality). In a subsequent field study in Ribeirão Preto during 2021, two new opossums (D. albiventris) were captured, of which one contained borrelial DNA in its blood. Macerated tissues from this infected opossum were inoculated into laboratory animals (rodents and rabbits) and two big-eared opossums (Didelphis aurita), which had blood samples examined daily via dark-field microscopy. No spirochetes were visualized in the blood of the laboratory animals. Contrastingly, spirochetes were visualized in the blood of the two D. aurita opossums between 12 and 25 days after inoculation. Blood samples from these opossums were used for a multi-locus sequencing typing (MLST) based on six borrelial loci. Phylogenies inferred from MLST genes positioned the sequenced Borrelia genotype into the RFG borreliae clade basally to borreliae of the Asian-African group, forming a monophyletic group with another Brazilian isolate, "Candidatus B. caatinga". Based on this concatenated phylogenetic analysis, which supports that the new borrelial isolate corresponds to a putative new species, we propose the name "Candidatus Borrelia mimona".

New records of soft ticks (Acari: Argasidae) from caves in Brazil, with a morphological study of Ornithodoros fonsecai and an analysis of the taxonomic status of Antricola inexpectata

In this study, we report soft ticks from bat-inhabiting caves in different areas of Brazil. From 2010 to 2019, we collected 807 tick specimens from nine caves located in four Brazilian states among two biomes. Ticks were morphologically identified as Antricola guglielmonei (282 specimens), Ornithodoros cavernicolous (260 specimens), and Ornithodoros fonsecai (265 specimens). Whereas A. guglielmonei was collected on bat guano in hot caves, O. cavernicolous and O. fonsecai were collected in cracks and crevices on the walls of cold caves, sometimes in the same chamber. Morphological identifications were corroborated by molecular and phylogenetic analyses inferred from tick mitochondrial 16S rRNA gene partial sequences. The sequences of A. guglielmonei, O. cavernicolous and O. fonsecai collected in this study clustered with conspecific GenBank sequences from different localities of Brazil. Remarkably, a clade containing 12 sequences of O. fonsecai was clearly bifurcated, denoting a degree of genetic divergence (up to 5 %) of specimens from Cerrado/Atlantic Forest biomes with the specimens from the Caatinga biome. To further evaluate this divergence, we performed morphometric analysis of the larval stage of different O. fonsencai populations by principal component analysis, which indicated that the larvae from Caatinga populations were generally smaller than the larvae from other biomes. Some of the present A. guglielmonei specimens were collected from the type locality of Antricola inexpectata. Comparisons of these specimens with the type specimens of A. inexpectata and A. guglielmonei indicated that they could not be separated by their external morphology. Hence, we are relegating A. inexpectata to a synonym of A. guglielmonei. This proposal is corroborated by our phylogenetic analysis.

Exotic ticks removed from German travelers

We report the finding of five nymphs and three adult ticks attached to German tourists while traveling the American continents. All eight specimens were morphologically identified and confirmed genetically using the 16S rRNA gene and screened for Rickettsia spp. infections. Five tick species were identified: one Amblyomma mixtum nymph from Ecuador, one Amblyomma varium nymph from Colombia, three Amblyomma coelebs nymphs from Costa Rica, one Amblyomma americanum male from the USA, one Dermacentor andersoni female and one D. andersoni male from Canada. Tick-borne microorganisms screening using the pan-Rickettsia-PCR resulted in two positive and six negative ticks. The A. mixtum nymph was positive for Rickettsia amblyommatis, while the D. andersoni female was positive for Rickettsia peacockii.

Predicting the global potential distribution of two major vectors of Rocky Mountain Spotted Fever under conditions of global climate change

Rocky Mountain spotted fever is a tick-borne disease that is highly dangerous but often overlooked by the public. To prevent the spread of the disease, it is important to understand the distribution patterns of its vectors' suitable areas. This study aims to explore the potential global suitability of areas for the vectors of Rocky Mountain spotted fever, including Dermacentor variabilis and Amblyomma cajennense under both historical and future climate scenarios. The study also seeks to investigate the impact of climatic factors on the distribution patterns of these vectors. Data on species distribution were downloaded from the Global Biodiversity Information Facility, Web of Science and PubMed database. The climatic variables were downloaded from WorldClim Global Climate Database. The Maximum Entropy Model was used to evaluate the contribution of monthly precipitation, monthly maximum temperature, monthly minimum temperature, elevation, and nineteen other climatic variables to vector survival, as well as to predict the suitable area for the vectors. We found that D. variabilis is distributed in North America, while A. cajennense is mainly distributed in South America, but all other continents except Antarctica have a suitable distribution. D. variabilis is more likely to survive in temperate regions, and A. cajennense is more likely to survive in tropical zones. D. variabilis is more sensitive to temperature, whereas A. cajennense is sensitive to both temperature and precipitation, and A. cajennense prefers tropical regions with hot and humid characteristics. The high suitable areas of both vectors were almost expanded in the ssp5-8.5 scenario, but not so much in the ssp1-2.6 scenario. Highly suitable areas with vectors survival should be strengthened with additional testing to prevent related diseases from occurring, and other highly suitable areas should be alert for entry and exit monitoring to prevent invasion and colonization of vectors.

First report of Amblyomma sculptum (Amblyomma cajennense complex) in a Brazilian state classified as a silent area for human rickettsiosis

Background and Aim

Studies on ticks of public health concern in equine husbandry are scarce in the Northeastern region of Brazil. This study aimed to investigate the presence of ticks on horses in the State of Alagoas, which is classified as a silent area for human rickettsiosis.

Materials and Methods

Ticks infesting horses were collected using anatomical tweezers or a commercial hook and kept in ethanol-labeled tubes for taxonomic identification.

Results

A total of 2,238 ticks were found. Ticks were identified as 2,215 (98.89%, 95% CI: 98.41-99.28) Dermacentor nitens, 19 (0.98%, 95% CI: 0.05-1.38) Amblyomma sculptum, and 4 (0.18%; 95% CI: 0.007-0.46) Rhipicephalus microplus.

Conclusion

This is the first study to report A. sculptum and D. nitens in the State of Alagoas. The presence of A. sculptum should draw the attention of public health managers once Alagoas State is considered a silent area for rickettsial diseases, which means the absence of local surveillance programs for these pathogens.

Tick and flea infestations in captive Tapirus terrestris and Tapirus kabomani (Perissodactyla: Tapiridae) in the Brazilian Amazon

The present study aimed to identify tick and flea species infesting captive tapirs (Tapirus terrestris and Tapirus kabomani) in the Brazilian Amazon. Ectoparasites were collected from tapirs chemically restrained in Zoo-botanical Parks, breeding facilities, conservationists and, environmental compensation areas in the states of Amapá, Amazonas, and Pará. After collection, the tick and flea specimens were placed in plastic pots containing isopropanol and identified according to dichotomous keys. Ectoparasite infestations were observed in 55% (18/33) tapirs, of which 61% (11/18) were single infestations with ticks or fleas, and 39% (7/18) were mixed infestations with different species of ticks and/or fleas. In total, 227 ticks (15 larvae, 107 nymphs, 38 females and 67 males) and 14 fleas (eight females and six males) were collected, identifying four tick species (Amblyomma cajennense sensu stricto , Amblyomma naponense, Amblyomma oblongoguttatum, and Amblyomma pacae) and three flea species and/or subspecies (Ctenocephalides felis felis, Rhopalopsyllus australis australis, and Tunga penetrans). In conclusion, infestations with Ixodidae ticks and Rhopalopsyllidae, Pulicidae and Tungidae fleas were found in captive tapirs in the Brazilian Amazon, and A. cajennense s.s. was the most frequent species. Additionally, the present study reports new associations between A. pacae and R. a. australis with T. terrestris and between A. cajennense s.s. with T. kabomani.

Seasonal dynamics of Amblyomma cajennense (Fabricius, 1787) sensu stricto in a degraded area of the Amazon biome, with notes on Rickettsia amblyommatis infection

BACKGROUND

The tick Amblyomma cajennense sensu stricto (A. cajennense s.s.) frequently parasitizes animals and humans in the Amazon biome, in addition to being a vector of Rickettsia amblyommatis. In the present study, we evaluated both the population dynamics of A. cajennense s.s. in a degraded area of the Amazon biome and the presence of rickettsial organisms in this tick population.

METHODS

The study was carried out in a rural area of the Santa Inês municipality (altitude: 24 m a.s.l.), Maranhão state, Brazil. Ticks were collected from the environment for 24 consecutive months, from June 2021 to May 2023. The region is characterized by two warm seasons: a rainy season (November-May) and a dry season (June-October). We characterized the temporal activity of A. cajennense s.s. on the vegetation by examining questing activity for each life stage (larvae, nymphs, adults [males and females]) in relation to the dry and rainy season. Ticks collected in this study were randomly selected and individually tested by a TaqMan real-time PCR assay that targeted a 147-bp fragment of the rickettsial gltA gene.

RESULTS

Overall, 1843 (62.4%) adults (52.6% females, 47.4% males), 1110 (37.6%) nymphs and 398 larval clusters were collected. All adult females and nymphs were morphologically identified as A. cajennense s.s. Larval activity was observed from April to December, with a peak from June to September (dry season); nymph abundance peaked from September to November (transition period between dry and rainy seasons); and adult ticks were abundant from October to May (spring/summer/early autumn). The infection rate by R. amblyommatis in A. cajennense s.s. ticks was at least 7% (7/99).

CONCLUSION

Our data suggest a 1-year generation pattern for A. cajennense s.s., with a well-defined seasonality of larvae, nymphs and adults in the Amazon biome. Larvae predominate during the dry season, nymphs are most abundant in the dry-rainy season transition and adults are most abundant in the rainy season. The presence of R. amblyommatis in adult ticks suggests that animals and humans in the study region are at risk of infection by this species belonging to the spotted fever group of Rickettsia.

Ticks (Ixodida) associated with bats (Chiroptera): an updated list with new records for Brazil

Bats harbor diverse groups of ectoparasites, such as insects and mites like ticks (Ixodida). Some species of ticks with records for bats and humans have already been reported with the occurrence of pathogens. This research article aims to document new geographical and host records of ticks infesting bats in Rio de Janeiro state, Southeastern Brazil, and provides a list of tick species associated with bats in Brazil. We counted 12 argasid ticks and five ixodid ticks associated with six individuals of bats. Larvae of Amblyomma sp., Ixodes sp., Ornithodoros sp., and Ornithodoros hasei and one nymph of Amblyomma sculptum parasitizing Artibeus obscurus, Phyllostomus hastatus, Micronycteris sp., Molossus fluminensis, and Carollia perspicillata in different localities of Rio de Janeiro state were studied. We carried out a systematic review with the descriptors: tick bat Brazil. We considered data from 42 articles in the systematic review. We compiled eleven records of Ixodidae, and 160 records of Argasidae. Ornithodoros cavernicolous were the most recorded tick species. Overall, we registered 171 tick-bat or roost-bat associations with 85 records of these infesting bats. The review also shows the occurrence of tick species associated with bats, and we present new records on ticks parasitizing bats in Brazil.

Phylogenetic relationships of the Amblyomma cajennense complex (Acari: Ixodidae) at mitogenomic resolution

The genus Amblyomma is the third most diverse in the number of species within the Ixodidae, with practically half of its species distributed in the Americas, though there are also species occurring in Africa, Asia, and Australia. Within the genus, there are several species complexes with veterinary and public health importance. The Amblyomma cajennense complex, in the Americas, is represented by six species with a wide distribution, from Texas to northern Argentina. We combined two sequencing techniques to generate complete mitogenomes of species belonging to the Amblyomma cajennense complex: genome skimming and long-range PCRs sequencing methods. Thus, we generated seven new mitochondrial genomes for all species of the Amblyomma cajennense complex, except for Amblyomma interandinum. Genetic distances between the mitogenomes corroborate the clear differentiation between the five species of the Amblyomma cajennense complex. The phylogenetic relationships of these species had previously been evaluated by combining partial nuclear and mitochondrial genes and here these relationships are corroborated with a more robust framework of data, which demonstrates that the conjunction of mitochondrial and nuclear partial genes can resolve close relationships when entire genes or genomes are unavailable. The gene order, structure, composition, and length are stable across these mitogenomes, and they share the general characteristics of Metastriata. Future studies should increase the number of available mitogenomes for this genus, especially for those species from the Indo-Pacific region and Africa, by means of a better understanding of their relationships and evolutionary process.

Analysis of the tick communities associated to domestic mammals in rural areas of the Yungas montane forest from Argentina

The aim of this work was to describe the tick community associated to domestic mammals in rural areas from the Yungas lower montane forest of Argentina. The circulation of tick-borne pathogens was also analyzed. Samples of ticks parasitizing cattle, horses, sheep and dogs were carried out in different seasons, and questing ticks were collected from vegetation and analyzed to detect the presence of Rickettsia, Ehrlichia, Borrelia and Babesia by a battery of different PCRs. The structure of the tick communities was analyzed through the Chao1 species richness estimator, the Shannon-Wiener index and the Horn index of community similarity. Eight tick species were collected in the study area: Amblyomma sculptum, Rhipicephalus microplus, Amblyomma hadanii, Dermacentor nitens, Amblyomma ovale, Haemaphysalis juxtakochi, Ixodes pararicinus and Rhipicephalus sanguineus sensu stricto. However, A. sculptum was by far the dominant species in the tick assemblages analyzed, and this was reflected in the low diversity values obtained. Dermacentor nitens, A. sculptum and R. microplus were the three species associated to horses. The predominance of A. sculptum was also observed in the tick samples obtained from dogs, even on two tick species, namely A. ovale and R. sanguineus s.s., which have dogs as the principal domestic host. Rhipicephalus microplus and A. sculptum were the most abundant ticks on cattle, while few specimens of I. pararicinus, A. hadanii and D. nitens were found on bovines. Dermacentor nitens ticks were found to be infected with B. caballi, which indicate the circulation of this pathogen of horses in the Yungas area. The detection of a strain of Borrelia sp. belonging to the B. burgdorferi s.l. complex in I. pararicinus is consistent with previous findings made in Argentina, but the public health relevance of this vector-microorganism association is far from being similar to that occurs in the northern hemisphere because there are practically no records of these tick species parasitizing humans in South America. The tick community of rural areas of the Yungas lower montane forest is composed by species which are potential vectors of pathogenic microorganism with veterinary and public health importance, circulating in a human-wildlife-livestock interface.

The survival of Amblyomma sculptum ticks upon blood-feeding depends on the expression of an inhibitor of apoptosis protein

BACKGROUND

The tick Amblyomma sculptum is the major vector of Rickettsia rickettsii, the causative agent of the highly lethal Brazilian spotted fever. It has been shown that R. rickettsii inhibits apoptosis in both human endothelial cells and tick cells. Apoptosis is regulated by different factors, among which inhibitors of apoptosis proteins (IAPs) play a central role. In the study reported here, we selected an IAP of A. sculptum that has not yet been characterized to assess its role in cell death and to determine the effects of its gene silencing on tick fitness and R. rickettsii infection.

METHODS

An A. sculptum cell line (IBU/ASE-16) was treated with specific double-stranded RNA (dsRNA) for either IAP (dsIAP) or green fluorescent protein (dsGFP; as a control). The activity of caspase-3 and the exposure of phosphatidylserine were determined in both groups. In addition, unfed adult ticks, infected or not infected with R. rickettsii, were treated with either dsIAP or dsGFP and allowed to feed on noninfected rabbits. In parallel, noninfected ticks were allowed to feed on an R. rickettsii-infected rabbit. Ticks (infected or not with R. rickettsii) that remained unfed were used as a control.

RESULTS

Caspase-3 activity and the externalization of phosphatidylserine were significantly higher in IBU/ASE-16 cells treated with dsIAP than in those treated with dsGFP. The mortality rates of ticks in the dsIAP group were much higher than those in the dsGFP group when they were allowed to feed on rabbits, independent of the presence of R. rickettsii. Conversely, lower mortality rates were recorded in unfed ticks.

CONCLUSIONS

Our results show that IAP negatively regulates apoptosis in A. sculptum cells. Moreover, IAP-silenced ticks experienced higher mortality rates following the acquisition of a blood meal, suggesting that feeding may trigger the activation of apoptosis in the absence of this physiological regulator. These findings indicate that IAP is a potential antigen for an anti-tick vaccine.

Emerging parasites and vectors in a rapidly changing world: from ecology to management

Global changes have influenced our societies in several ways with both positive (e.g., technology, transportation, and food security), and negative impacts (e.g., mental health problems, spread of diseases, and pandemics). Overall, these changes have affected the distribution patterns of parasites and arthropod vectors with the introduction and spreading of alien species in new geographical areas, eventually posing new challenges in public health. In this framework, the Acta Tropica Special Issue "Emerging parasites and vectors in a rapidly changing world: from ecology to management" provides a focus on the biology, ecology and management of emerging parasites and vectors of human and veterinary importance. Herein we review and discuss novel studies dealing with interactions of parasites and vectors with animals in changing environmental settings. In our opinion, a special focus on the implementation of management strategies of parasitic diseases to face anthropogenic environmental changes still represent a priority for public health. In the final section, key research challenges in this rapidly changing scenario are outlined.