Morphology and development of Anaplasma marginale in midgut of engorged female ticks of Boophilus microplus

Diversity of Rickettsiales in Rhipicephalus microplus Ticks Collected in Domestic Ruminants in Guizhou Province, China

Rhipicephalus microplus ticks are vectors for multiple pathogens infecting animals and humans. Although the medical importance of R. microplus has been well-recognized and studied in most areas of China, the occurrence of tick-borne Rickettsiales has seldom been investigated in Guizhou Province, Southwest China. In this study, we collected 276 R. microplus ticks from cattle (209 ticks) and goats (67 ticks) in three locations of Guizhou Province. The Rickettsia, Anaplasma, and Ehrlichia were detected by targeting the 16S rRNA gene and were further characterized by amplifying the key genes. One Rickettsia (Ca. Rickettsia jingxinensis), three Ehrlichia (E. canis, E. minasensis, Ehrlichia sp.), and four Anaplasma (A. capra, A. ovis, A. marginale, Ca. Anaplasma boleense) species were detected, and their gltA and groEL genes were recovered. Candidatus Rickettsia jingxinensis, a spotted fever group of Rickettsia, was detected in a high proportion of the tested ticks (88.89%, 100%, and 100% in ticks from the three locations, respectively), suggesting the possibility that animals may be exposed to this type of Rickettsia. All the 16S, gltA, groEL, and ompA sequences of these strains are 100% identical to strains reported in Ngawa, Sichuan Province. E. minasensis, A. marginale, and Candidatus Anaplasma boleense are known to infect livestock such as cattle. The potential effects on local husbandry should be considered. Notably, E. canis, A. ovis, and A. capra have been reported to infect humans. The relatively high positive rates in Qianxinan (20.99%, 9.88%, and 4.94%, respectively) may indicate the potential risk to local populations. Furthermore, the genetic analysis indicated that the E. minasensis strains in this study may represent a variant or recombinant. Our results indicated the extensive diversity of Rickettsiales in R. microplus ticks from Guizhou Province. The possible occurrence of rickettsiosis, ehrlichiosis, and anaplasmosis in humans and domestic animals in this area should be further considered and investigated.

Assays to evaluate the transovarial transmission of Anaplasma marginale by Rhipicephalus microplus

The aim of this study was to evaluate the vectorial competence of Rhipicephalus microplus to transmit Anaplasma marginale transovarially, by analyzing the results of three different but complementary assays. First, larvae of R. microplus were fed on a calf infected with the isolate S1P of A. marginale. The engorged females obtained were analyzed by PCR and incubated for oviposition. After hatching, larvae were analyzed by PCR and fed on susceptible splenectomized cattle. Although A. marginale was detected in the females, no A. marginale DNA was amplified from the larvae and transmission of A. marginale to cattle was not recorded. In the second experiment, R. microplus larvae were fed on cattle naturally infected with field isolates of A. marginale and experimentally infected with the isolate S1P of A. marginale. After detachment, engorged females were incubated for oviposition. The offspring were analyzed by PCR, with negative results. Finally, free-living larvae of R. microplus collected from pasture on farms with cattle infected with A. marginale were analyzed by PCR for Anaplasma infection. All samples analyzed were negative for A. marginale. The results of this work indicate that transovarial transmission of A. marginale by R. microplus is unlikely to occur.

Identification of Rickettsia spp., Anaplasma spp., and an Ehrlichia canis-like agent in Rhipicephalus microplus from Southwest and South-Central China

Rhipicephalus microplus is considered to be the most important tick infesting cattle, buffalo, horse, goats as well as other animals. They transmit diseases between domestic animals and act as vectors of a variety of zoonotic pathogens. Although pathogens harbored by R. microplus have been extensively studied, the Rickettsiales pathogens vectored by R. microplus in some areas of China remained largely unexplored. From August to October 2020, a total of 291 R. microplus ticks were collected from goats and cattle in three Southern China provinces, Guangxi (n = 138), Sichuan (n = 120) and Hubei (n = 33) provinces. Phylogenetic analysis based on COI gene sequences shows that these ticks are divided into three distinct clades, indicating the remarkable genetic diversity of R. microplus ticks in China. These samples were subsequently screened for the presence of Rickettsia, Anaplasma and Ehrlichia using conventional PCR and sequencing. Subsequently, five bacterial species were identified. Out of the 120 tick DNA samples from Sichuan province, 35.83% (43/120) were positive for Rickettsia sp. belonging to spotted fever group (SFG), 12.50% (15/120) were positive for Anaplasma marginale and 0.83% (1/120) was identified as A. platys. From the 138 DNA samples from Guangxi province, an Ehrlichia canis-like and Rickettsia sp. were detected, with a positive rate of 11.59% (16/138) and 2.17% (3/138), respectively. A. capra DNA was detected in 4 out of 33 (12.12%) samples from Hubei province. Notably, the 16S, gltA and groEL sequences of the E. canis-like are closely related to the E. canis strain previously identified from China, and form a distinct cluster in the phylogenetic trees. Collectively, our results expand the knowledge on tick-borne Rickettsiales pathogens in China. Because the state of engorgement of ticks was not recorded, it is not clear at this stage whether these pathogens are infecting the ticks or are simply present in the blood meal. Given the public health significance of SFG Rickettsia, A. capra, A. platys and E. canis, a thorough investigation of the diversity and presence of pathogens in R. microplus in areas with tick-associated diseases are needed.

Hard tick factors implicated in pathogen transmission

Ticks are the most common arthropod vector, after mosquitoes, and are capable of transmitting the greatest variety of pathogens. For both humans and animals, the worldwide emergence or re-emergence of tick-borne disease is becoming increasingly problematic. Despite being such an important issue, our knowledge of pathogen transmission by ticks is incomplete. Several recent studies, reviewed here, have reported that the expression of some tick factors can be modulated in response to pathogen infection, and that some of these factors can impact on the pathogenic life cycle. Delineating the specific tick factors required for tick-borne pathogen transmission should lead to new strategies in the disruption of pathogen life cycles to combat emerging tick-borne disease.

Seroprevalence and risk factors for cattle anaplasmosis, babesiosis, and trypanosomiasis in a Brazilian semiarid region

The seroprevalence of Anaplasma marginale, Babesia bigemina, Babesia bovis and Trypanosoma vivax and the risk factors for these infections were investigated in 509 cows on 37 farms in the semiarid region of Paraíba, northeastern Brazil. Cow serum samples were tested by means of immunofluorescence assay (IFA) against each specific antigen. The mean seroprevalence values per farm were 15.0% (range: 0-75%) for A. marginale, 9.5% (range: 0-40%) for B. bigemina and 26.9% (range: 0-73.7%) for B. bovis. All cows tested negative for T. vivax. Higher prevalence for A. marginale was significantly associated with less frequent acaricide spraying per year and with higher use of injectable antihelminthics. Presence of cows positive for B. bigemina was significantly associated with acaricide use and with presence of horse flies on the farm. Both occurrence and higher prevalence of B. bovis were significantly associated with recent observations of ticks on cattle. Overall, the present results indicate that the region investigated is an enzootically unstable area forA. marginale, B. bigemina and B. bovis, since most animals were seronegative to at least one agent.

Transplacental transmission of Anaplasma marginale in beef cattle chronically infected in southern Brazil

In this study, we have investigated the incidence of transplacental transmission of Anaplasma marginale in chronically infected cows with no history of acute anaplasmosis during gestation. In addition, we evaluated various techniques for detection of transplacental transmission ofA. marginale. Blood samples were collected from 30 cows at three different periods: at the time of artificial insemination, at gestational diagnosis, and after calving. Also, blood was collected from the newborn calves, including one sample before colostrum intake, and another three days after birth. A. marginale-specific antibodies were detected in 100% of the cows with an indirect fluorescent antibody test (IFAT), and in 97% of them, using an indirect enzyme-linked immunosorbent assay (ELISA). Also, we observed that all of the three-day-old newborn calves were seropositive by IFAT. According to polymerase chain reaction, 63.3% of the cows were carriers of A. marginale, as well as 6.7% of the newborn calves. This represented a transplacental transmission rate of 10.5%. Furthermore, a correlation of 93.3% was observed between the two serodiagnostic techniques, demonstrating that both ELISA and IFAT can be used in epidemiological surveys of A. marginale. These results confirm the occurrence of transplacental transmission of A. marginale in chronically infected cows and suggest the importance of this transmission route in areas of enzootic instability.

Propagation of a Brazilian isolate of Anaplasma marginale with appendage in a tick cell line (BME26) derived from Rhipicephalus (Boophilus) microplus

Anaplasma marginale is a tick-borne pathogen of cattle responsible for the disease anaplasmosis. Data suggest that Rhipicephalus (Boophilus) microplus and R. annulatus may be the major tick vectors of A. marginale in tropical and subtropical regions of the world. In this work we demonstrated the first infection and propagation of a Brazilian isolate of A. marginale (UFMG1) in the BME26 cell line derived originally from embryos of R. (Boophilus) microplus. The establishment of A. marginale infection in a cell line derived from R. (Boophilus) microplus is relevant for studying the A. marginale/tick interface.

Lack of infectivity of a Brazilian Anaplasma marginale isolate for Boophilus microplus ticks

Previous studies have shown that one Brazilian Anaplasma marginale isolate presents an inclusion appendage (tail), while other isolates do not present such inclusion. Studies on tick transmission have been carried out with tailless isolates but little is known about transmission of tailed isolates by Boophilus microplus. Two splenectomized calves were experimentally inoculated with the tailed A. marginale isolate. During ascending rickettsemia, B. microplus larvae, free from hemoparasites, were fed on the calves and the resulting nymphs, adult males and engorged females were examined by optic and electronic microscopy. No A. marginale colonies were observed in the gut cells of engorged females and the larvae originated from them did not transmit A. marginale to susceptible calves. In addition, no colonies of A. marginale were seen in the gut cells or in salivary glands of adult males and nymphs. These results suggest that B. microplus is not the biological vector for this tailed isolate.

Detection ofAnaplasma marginaleDNA in Larvae ofBoophilus microplusTicks by Polymerase Chain Reaction

Boophilus microplus larvae from two different sources were used for the detection of Anaplasma marginale DNA: larvae A, which were collected from a pasture of an endemic farm, and larvae B, which originated from engorged female ticks fed on calves with no clinical signs of disease and with low rickettsemia (approximately 0.01 to 1.0%). Larvae A were collected monthly, from January to May in 2001. Two hundred engorged female ticks fed on calves that provided larvae B were divided into groups of 10 and kept in a controlled environment at either 18 degrees C or 28 degrees C. Fifty larvae were used from each sample for DNA extraction, and 5 muL of DNA were submitted to amplification of the sequence of msp5 gene of A. marginale by polymerase chain reaction (PCR). Seven out of 50 samples of larvae A (14%) were positive for the presence of DNA of A. marginale showing amplified product of 457 bp. Ten out of 91 samples of larvae B (11%) kept at 18 degrees C were positive, and all larvae B at 28 degrees C were negative. Thus, this study confirmed the presence of A. marginale DNA in B. microplus larvae by PCR. The EcoRI restriction enzyme analysis confirmed the specificity of the amplicon, which resulted in two fragments: 265 bp and 192 bp. The sequencing analysis of the amplicon from larvae demonstrated 98% homology with the msp5 sequence from Florida A. marginale strain.

Genetic diversity and molecular phylogeny of Anaplasma marginale isolates from Minas Gerais, Brazil

Anaplasma marginale (Rickettsiales: Anaplasmataceae), a tick-borne pathogen of cattle, is endemic in tropical and subtropical regions of the world, and many isolates of A. marginale may occur in a given geographic area. Phylogenetic relationships have been reported for A. marginale isolates from the US using gene and protein sequences of MSP1a and msp4. These studies demonstrated that msp4 sequences, but not MSP1a DNA or protein sequences, provide phylogeographic information and also that MSP1a sequences are highly heterogeneous among A. marginale populations. However, little information is available on the genetic diversity of A. marginale isolates from other regions of the world. The present study was undertaken to examine genetic variation among 10 isolates of A. marginale obtained from infected cattle in the State of Minas Gerais, Brazil, where A. marginale is endemic. Neighbor-joining analysis of msp4 sequences of Brazilian and New World isolates of A. marginale from Argentina, Mexico and the US provided bootstrap support for a Latin American clade. The sequences of the MSP1a repeats of four Brazilian isolates of A. marginale were compared to sequences of Latin American and US isolates. The MSP1a repeated sequences of Latin American isolates of A. marginale had nine repeat forms, alpha-phi, which have not been reported previously in North American isolates of A. marginale. Furthermore, the repeated forms tau, sigma and mu were only present in the Brazilian isolates. The results demonstrated that the genetic heterogeneity observed among isolates of A. marginale is common in endemic areas, independent of the predominant tick vector and is consistent with previous studies in which msp4 provided phylogeographic information about A. marginale isolates, while MSP1a was found not to be a useful marker for phylogeographic characterization of A. marginale isolates.

Transmission of Anaplasma marginale by Boophilus microplus: retention of vector competence in the absence of vector-pathogen interaction

Whether arthropod vectors retain competence for transmission of infectious agents in the long-term absence of vector-pathogen interaction is unknown. We addressed this question by quantifying the vector competence of two tick vectors, with mutually exclusive tropical- versus temperate-region distributions, for genetically distinct tropical- and temperate-region strains of the cattle pathogen Anaplasma marginale. The tropical cattle tick Boophilus microplus, which has been eradicated from the continental United States for over 60 years, was able to acquire and transmit the temperate St. Maries (Idaho) strain of A. marginale. Similarly, the temperate-region tick Dermacentor andersoni efficiently acquired and transmitted the Puerto Rico strain of A. marginale. There were no significant quantitative differences in infection rate or number of organisms per tick following feeding on cattle with persistent infections of either A. marginale strain. In contrast, the significantly enhanced replication of the Puerto Rico strain in the salivary gland of B. microplus at the time of transmission feeding is consistent with adaptation of a pathogen strain to its available vector. However, the transmission of both strains by B. microplus demonstrates that adaptation or continual interaction between the pathogen and vector is not required for retention of vector competence. Importantly, the results clearly show that reestablishment of acaricide-resistant B. microplus in the United States would be associated with A. marginale transmission.

Development of an ELISA system for detection of anti-Anaplasma marginale antibodies in cattle in Brazil

An ELISA test was developed for detecting antibodies against Anaplasma marginale in bovine sera. Four antigenic preparations were produced from infected red blood cells. Some aliquots of this preparation were stored at -70 degrees C with 30% DMSO in phosphate-buffered saline (PBS) and others were lysed with 0.9% NH4Cl and stored at -20 degrees C. Typical anaplasmal structures were seen by electron microscopy in the antigenic preparations containing the erythrocytes that had been stored with DMSO. The performance of the ELISA test was evaluated by testing 298 positive serum samples collected from immunized cattle, 39 negative serum samples collected from cattle imported from areas free of A. marginale and 50 samples collected from cattle naturally infected in the field. The test gave a specificity of 94.87% and a sensitivity of 100%.

Ultrastructure of Anaplasma marginale with an inclusion appendage, isolated in Minas Gerais State, Brazil

This is the first report on the occurrence and isolation of a strain of Anaplasma marginale with an inclusion appendage in Brazil. The inclusion appendage presented longitudinal electron-dense striations and did not originate directly from the body of the rickettsia but from an electron-dense complex located at the junction of the inclusion membrane and inclusion appendage. The inclusion appendage remained in the host cell after the Anaplasma inclusion appeared to be leaving the red blood cell. Other ultrastructures of this rickettsia are described and its epidemiological importance is discussed.