TickPath Layerplex: adaptation of a real-time PCR methodology for the simultaneous detection and molecular surveillance of tick-borne pathogens

Hard Ticks as Vectors: The Emerging Threat of Tick-Borne Diseases in India

Hard ticks (Ixodidae) play a critical role in transmitting various tick-borne diseases (TBDs), posing significant global threats to human and animal health. Climatic factors influence the abundance, diversity, and vectorial capacity of tick vectors. It is imperative to have a comprehensive understanding of hard ticks, pathogens, eco-epidemiology, and the impact of climatic changes on the transmission dynamics of TBDs. The distribution and life cycle patterns of hard ticks are influenced by diverse ecological factors that, in turn, can be impacted by changes in climate, leading to the expansion of the tick vector's range and geographical distribution. Vector competence, a pivotal aspect of vectorial capacity, involves the tick's ability to acquire, maintain, and transmit pathogens. Hard ticks, by efficiently feeding on diverse hosts and manipulating their immunity through their saliva, emerge as competent vectors for various pathogens, such as viruses, parasites and bacteria. This ability significantly influences the success of pathogen transmission. Further exploration of genetic diversity, population structure, and hybrid tick vectors is crucial, as they play a substantial role in influencing vector competence and complicating the dynamics of TBDs. This comprehensive review deals with important TBDs in India and delves into a profound understanding of hard ticks as vectors, their biology, and the factors influencing their vector competence. Given that TBDs continue to pose a substantial threat to global health, the review emphasizes the urgency of investigating tick control strategies and advancing vaccine development. Special attention is given to the pivotal role of population genetics in comprehending the genetic diversity of tick populations and providing essential insights into their adaptability to environmental changes.

Development of a Syndromic Molecular Diagnostic Assay for Tick-Borne Pathogens Using Barcoded Magnetic Bead Technology

Infectious disease diagnostics often depend on costly serological testing with poor sensitivity, low specificity, and long turnaround time. Here, we demonstrate proof of the principle for simultaneous detection of two tick-borne pathogens from a single test sample using barcoded magnetic bead technology on the BioCode 2500 system. Specific primer sets complementary to the conserved genes of Anaplasma phagocytophilum and Borrelia burgdorferi were used in PCR amplification of the target, followed by the hybridization of the resulting biotinylated PCR products with specific probes tethered to the barcoded magnetic beads for simultaneous detection, using a fluorophore with high quantum yield. The assay has an extremely high signal to background ratio, with a limit of detection (LOD) of 2.81 50% tissue culture infection dose (TCID50)/mL and 1 CFU/mL for A. phagocytophilum and B. burgdorferi, respectively. The observed LOD for gene blocks was 1.8 copies/reaction for both the pathogens. The assay demonstrated 100% positive and negative agreement on performance evaluation using patient specimens and blood samples spiked with 1 × LOD of pathogen stock. No cross-reactivity was observed with other related tick-borne pathogens and genomic DNA of human, cattle, and canine origin. The assay can be upgraded to a sensitive and cost-effective multiplex diagnostic approach that can simultaneously detect multiple clinically important tick-borne pathogens in a single sample with a short turnaround time. IMPORTANCE The low pathogen load in the tick-borne disease test samples and the lack of highly sensitive multiplex diagnostic approaches have impacted diagnosis during clinical testing and limited surveillance studies to gauge prior insight about the prevalence of tick-borne infections in a geographical area. This article demonstrates proof of the principle for simultaneous detection of two important tick-borne pathogens from a single test sample using digital barcoded magnetic bead technology. Using a fluorophore of high quantum yield, the diagnostic approach showed high sensitivity and specificity. The LOD was 1.8 genome copies per reaction for both A. phagocytophilum and B. burgdorferi. The assay can be upgraded for the detection of all clinically important tick-borne pathogens from a single patient sample with high sensitivity and specificity. The assay can provide a diagnostic answer to the clinician in a short turnaround time to facilitate speedy therapeutic intervention to infected patients and implement public health measures to prevent community spread.

Under-diagnosis of vector-borne diseases among individuals suspected of having Scrub Typhus in South Korea

Due to environmental and ecological changes and suitable habitats, the occurrence of vector-borne diseases is increasing. We investigated the seroprevalence of four major vector-borne pathogens in human patients with febrile illness who were clinically suspected of having Scrub Typhus (ST) caused by Orientia tsutsugamushi. A total of 187 samples (182 patient whole blood and sera samples, including 5 follow-up) were collected. Antibodies to Anaplasma phagocytophilum, Ehrlichia chaffeensis, Borrelia burgdorferi, and Bartonella henselae were tested by using indirect immunofluorescence assays. Molecular diagnoses were performed using real-time PCR. Of the 182 cases, 37 (20.3%) cases were designated as confirmed cases of ST, and the remaining 145 (79.7%) cases as other febrile diseases (OFDs). The seroprevalence of A. phagocytophilum, E. chaffeensis, B. burgdorferi, and B. henselae was 51.4% (19/37), 10.8% (4/37), 86.5% (32/37), and 10.8% (4/37) among the ST group, and 42.8% (62/145), 10.4% (19/145), 57.7% (105/145), and 15.9% (29/145) among the OFD group, respectively. There were no significant differences in the seroprevalence between the ST and the OFD groups. Considering the co-occurrence, 89.0% (162/182) had at least one antibody to tick-borne pathogens, 37.0% (60/162) were positive for two pathogens, 17.3% (28/162) for three pathogens, and 6.2% (10/162) for four pathogens. In real-time PCR, O. tsutsugamushi was positive in 16 cases [15 (40.5%) in ST group and 1 (2.2%) in OFD group], and the four other pathogens were negative in all cases except one confirmed as anaplasmosis. In evaluating the five follow-up samples, the appearance of new antibodies or an increase in the pre-existing antibody titers was detected. Our data highlighted that acute febrile illness and manifestations suggestive of a vector-borne infection must be recognized and further considered for coinfections in clinical practice and the laboratory.

Development and validation of a TaqMan® probe- based real-time PCR assay for detection of Ehrlichia canis

Ehrlichiosis is a potentially fatal zoonotic tick-borne disease, caused by a pleomorphic Gram-negative bacterium. It occurs worldwide and affects humans, domestic and wild animals. Dogs infected with Ehrlichia canis develop canine monocytic ehrlichiosis (CME), a significant infectious disease of canines. TaqMan® based real-time PCR assays to detect Ehrlichia spp. affecting dogs were developed and a real-time PCR assay specific for E. canis validated. The efficiency of the assay was 93% and the 95% limit of detection was 33 E. canis plasmid copies/µl of blood (95% confidence interval: 23 - 58). The assay was specific for E. canis when tested against other haemoparasites. Consistent repeatability was observed, with an inter-run standard deviation (SD) range between 0.33 and 1.29 and an intra-run SD range between 0.04 and 1.14. Field samples were tested in parallel by both the E. canis real-time PCR assay and a reverse line blot hybridization assay. The results were in agreement for the two assays, with an exception of two out of 121 samples. Bayesian latent class analysis was used to calculate a diagnostic sensitivity of the E. canis real-time PCR assay of 90% and a specificity of 92%. This assay is a sensitive and reliable molecular detection method for E. canis and will be a useful tool for early diagnosis and timely treatment for this haemoparasite.

Current and Future Molecular Diagnostics of Tick-Borne Diseases in Cattle

Ticks and tick-borne diseases such as babesiosis, anaplasmosis, ehrlichiosis, Lyme disease, Crimean Congo hemorrhagic fever, and Rocky Mountain spotted fever pose a significant threat to animal and human health. Tick-borne diseases cause billions of dollars of losses to livestock farmers annually. These losses are partially attributed to the lack of sensitive, robust, cost effective and efficient diagnostic approaches that could detect the infectious pathogen at the early stages of illness. The modern nucleic acid-based multiplex diagnostic approaches have been developed in human medicine but are still absent in veterinary medicine. These powerful assays can screen 384 patient samples at one time, simultaneously detect numerous infectious pathogens in each test sample and provide the diagnostic answer in a few hours. Development, commercialization, and wide use of such high throughput multiplex molecular assays in the cattle tick-borne disease surveillance will help in early detection and control of infectious pathogens in the animal reservoir before community spread and spillover to humans. Such approaches in veterinary medicine will save animal life, prevent billions of dollars of economic loss to cattle herders and reduce unwanted stress to both human and animal health care systems. This literature review provides recent updates on molecular diagnostics of tick-borne pathogens and discusses the importance of modern nucleic acid high throughput multiplex diagnostic approaches in the prevention of tick-borne infection to livestock.

Capture Sequencing Enables Sensitive Detection of Tick-Borne Agents in Human Blood

Assay sensitivity can be a limiting factor in the use of PCR as a tool for the detection of tick-borne pathogens in blood. We evaluated the performance of Tick-borne disease Capture Sequencing Assay (TBDCapSeq), a capture sequencing assay targeting tick-borne agents, to test 158 whole blood specimens obtained from the Lyme Disease Biobank. These included samples from 98 individuals with signs and symptoms of acute Lyme disease, 25 healthy individuals residing in Lyme disease endemic areas, and 35 samples collected from patients admitted to the Massachusetts General Hospital or referred to the infectious disease clinic. Compared to PCR, TBDCapSeq had better sensitivity and could identify infections with a wider range of tick-borne agents. TBDCapSeq identified a higher rate of samples positive for Borrelia burgdorferi (8 vs. 1 by PCR) and Babesia microti (26 vs. 15 by PCR). TBDCapSeq also identified previously unknown infections with Borrelia miyamotoi, Ehrlichia, and Rickettsia species. Overall, TBDCapSeq identified a pathogen in 43 samples vs. 23 using PCR, with four co-infections detected versus zero by PCR. We conclude that capture sequencing enables superior detection of tick-borne agents relative to PCR.

Duplex real-time PCR methods for molecular detection and characterization of canine tick-borne haemoparasites from Punjab state, India

Background

Microscopy is a routinely used technique for the diagnosis of canine tick-borne haemoparasitic diseases in various clinical laboratories worldwide. In an attempt to provide better diagnostic assay to the clients for effective management of these diseases duplex real-time PCR assays were applied.

Methods and results

Blood samples (n = 338) aseptically collected from suspected dogs of Central Plain Zone of Punjab state, India were subjected to SYBR Green based real-time duplex PCR assays for simultaneous detection of B. vogeli & E. canis and B. gibsoni & H. canis. Results revealed an overall prevalence rate of canine tick-borne haemoparasites as 54.1%, amongst which H. canis was the predominant (25.4%), followed by B. gibsoni (16.3%), E. canis (10.7%) and B. vogeli (1.8%). Sensitivity and specificity of the duplex assays ranged from 59.04 to 100.0% and 58.12 to 92.52%, respectively and their strength of agreement was ″fair″ with kappa value statistics. A significant (p < 0.05) association between prevalence of B. gibsoni, H. canis and E. canis infection with risk factors like sex, breed, season and location was recorded. The ancestral background of the field isolates of haemoparasites was also studied by phylogenetic analysis of their nucleotide sequences.

Conclusions

SYBR Green dye based duplex real-time PCR assays proved to be highly sensitive, specific, rapid and affordable diagnostic tests for use by clinicians to save the life of pets.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11033-022-07286-4.

Gap Analysis of the Habitat Interface of Ticks and Wildlife in Mexico

Mexico is a highly diverse country where ticks and tick-borne diseases (TBD) directly impact the health of humans and domestic and wild animals. Ticks of the genera Rhipicephalus spp., Amblyomma spp., and Ixodes spp. represent the most important species in terms of host parasitism and geographical distribution in the country, although information on other genera is either limited or null. In addition, information regarding the influence of global warming on the increase in tick populations is scarce or nonexistent, despite climate conditions being the most important factors that determine tick distribution. In order to aid in the management of ticks and the risks of TBD in humans and domestic animals in Mexico, an analysis was conducted of the gaps in information on ticks with the purpose of updating the available knowledge of these ectoparasites and adapting the existing diagnostic tools for potential distribution analysis of TBD in wildlife. These tools will help to determine the epidemiological role of wildlife in the human–domestic animal interface in anthropized environments in Mexico.

Challenges in Tick-Borne Pathogen Detection: The Case for Babesia spp. Identification in the Tick Vector

The causative agents of Babesiosis are intraerythrocytic protozoa of the genus Babesia. Babesia parasites are present around the world, affecting several mammals including humans, pets and livestock, hence its medical and veterinary relevance. Babesia spp. detection in its invertebrate host is a main point in understanding the biology of the parasite to acquire more knowledge on the host–Babesia–vector interactions, as increasing knowledge of the Babesia lifecycle and babesiosis epidemiology can help prevent babesiosis outbreaks in susceptible mammals. The aim of the present review is to highlight the newest findings in this field, based on a bibliographic compilation of research studies recently carried out for the detection of the main Babesia species found in tick vectors affecting mammalian hosts, including the different tick stages such as adult ticks, larvae, nymphs and eggs, as well as the detection method implemented: microscopic tools for parasite identification and molecular tools for parasite DNA detection by conventional PCR, nested-PCR, PCR-RFLP, PCR-RLB hybridization, real time-PCR, LAMP and RAP assays. Although molecular identification of Babesia parasites has been achieved in several tick species and tissue samples, it is still necessary to carry out transmission experiments through biological models to confirm the vectorial capacity of various tick species.

Microbiome Composition and Borrelia Detection in Ixodes scapularis Ticks at the Northwestern Edge of Their Range

Lyme disease-causing Borrelia burgdorferi has been reported in 10–19% of Ixodes ticks from Alberta, Canada, where the tick vector Ixodes scapularis is at the northwestern edge of its range. However, the presence of Borrelia has not been verified independently, and the bacterial microbiome of these ticks has not been described. We performed 16S rRNA bacterial surveys on female I. scapularis from Alberta that were previously qPCR-tested in a Lyme disease surveillance program. Both 16S and qPCR methods were concordant for the presence of Borrelia. The 16S studies also provided a profile of associated bacteria that showed the microbiome of I. scapularis in Alberta was similar to other areas of North America. Ticks that were qPCR-positive for Borrelia had significantly greater bacterial diversity than Borrelia-negative ticks, on the basis of generalized linear model testing. This study adds value to ongoing tick surveillance and is a foundation for deeper understanding of tick microbial ecology and disease transmission in a region where I. scapularis range expansion, induced by climate and land use changes, is likely to have increasing public health implications.

Apparent Ixodes tick paralysis in a cat from North America

Case summary

A 2-year-old castrated male domestic longhair cat presented for acute, diffuse, flaccid paralysis. Thoracic and abdominal radiographs, biochemistry panel and complete blood count were unremarkable. Titers to Toxoplasma gondii, myasthenia gravis radioimmunoassay testing and creatinine kinase levels were within normal limits. The most likely differentials included acute toxicity (coral snake envenomation, organophosphate toxicity), botulism and, less likely, acute polyradiculoneuritis. A thorough physical examination revealed a single engorged tick attached to the ventral neck of the cat, which was later identified as an adult female Ixodes species. Topical fipronil and (S)-methoprene was administered. Over the next 48 h, the cat recovered full motor function and at 5 days post-tick removal the cat had resumed all normal activities.

Relevance and novel information

Tick paralysis is considered endemic in Australia by bites from, most commonly, the Ixodes holocyclus tick. However, this phenomenon is rarely reported in the USA. This is the first report of a domestic cat suffering from acute tick paralysis in North America.

Prevalence of common tick-borne pathogens in white-tailed deer and coyotes in south Texas

Determining which wildlife hosts are involved in the enzootic cycles of tick-borne diseases (TBD) enables enhanced surveillance and risk assessment of potential transmission to humans and domestic species. Currently, there is limited data to indicate which tick-borne pathogens (TBP) can infect coyotes. Additionally, limited surveillance data for white-tailed deer (WTD) in south Texas is available. The purpose of this study was to detect current infections of common TBP in coyotes and WTD in south Texas, which represents a transboundary region and common site for animal migrations across the U.S.-Mexico border. A patent pending real-time PCR assay, the TickPath layerplex test, was used to screen whole-blood samples for species from Borrelia, Rickettsia, Ehrlichia, Anaplasma, and Babesia genera. Conventional PCR and subsequent sequencing of positive samples confirmed the pathogen species. Of 122 coyote samples, 11/122 (9.0%) were positive for Babesia vogeli and 1/122 (0.8%) was positive for Borrelia turicatae. Of 245 WTD samples, 1/245 (0.4%) was positive for Anaplasma platys, 4/245 (1.6%) were positive for Ehrlichia chaffeensis, and 18/245 (7.3%) were positive for Theileria cervi. All positive samples from both species, except for one coyote, were collected from counties located in south Texas along the U.S.Mexico border. One coyote positive for B. vogeli originated from a county in northern Texas. The results from this study depicts the first known molecular detection of B. turicatae in a coyote, and demonstrates that coyotes and WTDs can potentially serve as sentinels for several zoonotic TBD as well as TBD that affect domestic animals.

Prevalence of protozoan parasites in small and medium mammals in Texas, USA

Wildlife interaction with humans increases the risk of potentially infected ticks seeking an opportunistic blood meal and consequently leading to zoonotic transmission. In the United States, human babesiosis is a tick-borne zoonosis most commonly caused by the intraerythrocytic protozoan parasite, Babesia microti. The presence of Babesia microti and other species of Babesia within Texas has not been well characterized, and the molecular prevalence of these pathogens within wildlife species is largely unknown. Small (e.g. rodents) and medium sized mammalian species (e.g. racoons) represent potential reservoirs for specific species of Babesia, though this relationship has not been thoroughly evaluated within Texas. This study aimed to characterize the molecular prevalence of Babesia species within small and medium sized mammals at two sites in East Texas with an emphasis on detection of pathogen presence in these two contrasting wild mammal groups at these sites. To that end, a total of 480 wild mammals representing eight genera were trapped, sampled, and screened for Babesia species using the TickPath layerplex qPCR assay. Two sites were selected for animal collection, including The Big Thicket National Preserve and Gus Engeling Wildlife Management Area. Molecular analysis revealed the prevalence of various Babesia and Hepathozoon species at 0.09% each, and Sarcocystis at 0.06% . Continued molecular prevalence surveys of tick-borne pathogens in Texas wild mammals will be needed to provide novel information as to which species of Babesia are most prevalent and identify specific wildlife species as pathogen reservoirs.