Tick-Borne Bacterial, Rickettsial, Spirochetal, and Protozoal Infectious Diseases in the United States: A Comprehensive Review

Modeling spatiotemporal dynamics of Amblyomma americanum questing activity in the central Great Plains

Ticks represent important vectors of a number of bacterial and viral disease agents, owing to their hematophagous nature and their questing behavior (the process in which they seek new hosts). Questing activity is notably seasonal with spatiotemporal dynamics that needs to be understood in detail as part of mediating and mitigating tick-borne disease risk. Models of the geography of tick questing activity developed to date, however, have ignored the temporal dimensions of that behavior; more fundamentally, they have often not considered the sampling underlying available occurrence data. Here, we have addressed these shortfalls for Amblyomma americanum, the most commonly encountered tick in the central Great Plains, via (1) detailed, longitudinal sampling to characterize the spatiotemporal dimensions of tick questing activity; (2) randomization tests to establish in which environmental dimensions a species is manifesting selective use; and (3) modeling methods that include both presence data and absence data, taking fullest advantage of the information available in the data resource. The outcome was a detailed picture of geographic and temporal variation in suitability for the species through the two-year course of this study. Such models that take full advantage of available information will be crucial in understanding the risk of tick-borne disease into the future.

Human infections with neglected vector-borne pathogens in China: A systematic review

Background

Emerging vector-borne pathogens (VBPs) pose a continuous background threat to the global health. Knowledge of the occurrence, distributions and epidemiological characteristics of VBP are lacking in many countries. Outbreaks of novel VBP are of increasing global interest including those arising in China.

Methods

A systematic review of published literature was undertaken to characterize the spectrum of VBPs causing human illness in China. We searched five databases for VBP-related articles in English and Chinese published between January 1980 and June 2021, that excluded those listed in the National Notifiable Diseases Surveillance System of China. The study is registered with PROSPERO, CRD42021259540.

Findings

A total of 906 articles meeting the selection criteria were included in this study. A total of 44,809 human infections with 82 species of VBPs including 40 viruses, 33 bacteria (20 Rickettsiales bacteria, eight Spirochaetales bacteria, and five other bacteria) and nine parasites, were identified in China. Rickettsiales bacteria were the most common and widely distributed pathogens with 18,042 cases reported in 33 provinces by 347 reviewed articles, followed by Spirochaetales bacteria with 15,745 cases in 32 provinces (299 articles), viruses with 8455 cases in 30 provinces (139 articles), other bacteria with 2053 cases in 19 provinces (65 articles), parasites with 514 cases in 17 provinces (44 articles), and multiple pathogens with 3626 cases in 14 provinces (23 articles). Coxiella burnetii, Bartonella henselae and Rickettsia sibirica were the most frequently reported pathogens. A total of 18 new pathogens were reported in China during this period (these also represented their first identification globally). Based on 419 articles with clinical information, a meta-analysis revealed that flu-like illness was the most common manifestation among infections with VBPs.

Interpretation

This review helps improve the understanding of VBPs in China, demonstrating the need to consider a wider surveillance of VBPs in many different settings, thus helping to inform future research and surveillance efforts.

Funding

Natural Science Foundation of China.

Ecological Niche Models of Four Hard Tick Genera (Ixodidae) in Mexico

Simple Summary

Vector-borne diseases currently represent a significant threat to public health, mainly due to the changes that humans are producing in ecosystems and climates. Analyzing the environmental conditions that allow the establishment and survival of ticks could help determine possible sites for the appearance of infectious outbreaks. In this study, nine ecological niche models were generated from different algorithms to determine the current potential distribution of four tick genera in Mexico. Temperature and moisture have been considered as the main factors limiting tick distribution. However, the analysis of the ecological niche models determined that the four genera exhibited different distribution patterns, which may be associated with their physiological and ecological differences. This type of analysis can improve our understanding of the dynamics of ticks and, therefore, can be very useful in monitoring programs of the diseases they transmit.

Abstract

Ticks are vectors of a large number of pathogens of medical and veterinary importance, and in recent years, they have participated in the rise of multiple infectious outbreaks around the world. Studies have proposed that temperature and precipitation are the main variables that limit the geographical distribution of ticks. The analysis of environmental constraints with ecological niche modeling (ENM) techniques can improve our ability to identify suitable areas for emergence events. Algorithms used in this study showed different distributional patterns for each tick genera; the environmental suitability for Amblyomma includes warm and humid localities below 1000 m above the sea level, while Ixodes is mainly associated with ecosystems with high vegetation cover. Dermacentor and Rhipicephalus genus presented wider distribution patterns; the first includes species that are well adapted to resist desiccation, whereas the latter includes generalist species that are mostly associated with domestic hosts in Mexico. Ecological niche models have proven to be useful in estimating the geographic distribution of many taxa of ticks. Despite our limited knowledge of tick’s diversity, ENM can improve our understanding of the dynamics of vector-borne diseases and can assist public health decision-making processes.

Emerging tick-borne diseases and blood safety: summary of a public workshop

Tick-borne agents of disease continue to emerge and subsequently expand their geographic distribution. The threat to blood safety by tick-borne agents is ever increasing and requires constant surveillance concomitant with implementation of appropriate intervention methods. In April 2017, the Food and Drug Administration organized a public workshop on emerging tick-borne pathogens (excluding Babesia microti and Lyme disease) designed to provide updates on the current understanding of emerging tick-borne diseases, thereby allowing for extended discussions to determine if decisions regarding mitigation strategies need to be made proactively. Subject matter experts and other stakeholders participated in this workshop to discuss issues of biology, epidemiology, and clinical burden of tick-borne agents, risk of transfusion-transmission, surveillance, and considerations for decision making in implementing safety interventions. Herein, we summarize the scientific presentations, panel discussions, and considerations going forward.

A Molecular Survey for Francisella tularensis and Rickettsia spp. in Haemaphysalis leporispalustris (Acari: Ixodidae) in Northern California

Francisella tularensis and Rickettsia spp. have been cultured from Haemaphysalis leporispalustris Packard, but their prevalence in this tick has not been determined using modern molecular methods. We collected H. leporispalustris by flagging vegetation and leaf litter and from lagomorphs (Lepus californicus Gray and Sylvilagus bachmani (Waterhouse)) in northern California. Francisella tularensis DNA was not detected in any of 1,030 ticks tested by polymerase chain reaction (PCR), whereas 0.4% of larvae tested in pools, 0 of 117 individual nymphs, and 2.3% of 164 adult ticks were PCR-positive for Rickettsia spp. Positive sites were Laurel Canyon Trail in Tilden Regional Park in Alameda Contra Costa County, with a Rickettsia spp. prevalence of 0.6% in 2009, and Hopland Research and Extension Center in Mendocino County, with a prevalence of 4.2% in 1988. DNA sequencing revealed R. felis, the agent of cat-flea typhus, in two larval pools from shaded California bay and live oak leaf litter in Contra Costa County and one adult tick from a L. californicus in chaparral in Mendocino County. The R. felis in unfed, questing larvae demonstrates that H. leporispalustris can transmit this rickettsia transovarially. Although R. felis is increasingly found in diverse arthropods and geographical regions, prior literature suggests a typical epidemiological cycle involving mesocarnivores and the cat flea, Ctenocephalides felis. To our knowledge, this is the first report of R. felis in H. leporispalustris. Natural infection and transovarial transmission of this pathogen in the tick indicate the existence of a previously undocumented wild-lands transmission cycle that may intersect mesocarnivore-reservoired cycles and collectively affect human health risk.

Pattern of tick aggregation on mice: larger than expected distribution tail enhances the spread of tick-borne pathogens

The spread of tick-borne pathogens represents an important threat to human and animal health in many parts of Eurasia. Here, we analysed a 9-year time series of Ixodes ricinus ticks feeding on Apodemus flavicollis mice (main reservoir-competent host for tick-borne encephalitis, TBE) sampled in Trentino (Northern Italy). The tail of the distribution of the number of ticks per host was fitted by three theoretical distributions: Negative Binomial (NB), Poisson-LogNormal (PoiLN), and Power-Law (PL). The fit with theoretical distributions indicated that the tail of the tick infestation pattern on mice is better described by the PL distribution. Moreover, we found that the tail of the distribution significantly changes with seasonal variations in host abundance. In order to investigate the effect of different tails of tick distribution on the invasion of a non-systemically transmitted pathogen, we simulated the transmission of a TBE-like virus between susceptible and infective ticks using a stochastic model. Model simulations indicated different outcomes of disease spreading when considering different distribution laws of ticks among hosts. Specifically, we found that the epidemic threshold and the prevalence equilibria obtained in epidemiological simulations with PL distribution are a good approximation of those observed in simulations feed by the empirical distribution. Moreover, we also found that the epidemic threshold for disease invasion was lower when considering the seasonal variation of tick aggregation.

Our work analyses a 9-year time series of tick co-feeding patterns on Yellow-necked mice. Our data shows a strong heterogeneity, where most mice are parasitised by a small number of ticks while few host a much larger number. We describe the number of ticks per host by the commonly used Negative Binomial model, by the Poisson-LogNormal model, and we propose the Power Law model as an alternative. In our data, the last model seems to better describe the strong heterogeneity. In order to understand the epidemiological consequences, we use a computational model to reproduce a peculiar way of transmission, observed in some cases in nature, where uninfected ticks acquire an infection by feeding on a host where infected ticks are present, without any remarkable epidemiological involvement of the host itself. In particular, we are interested in determining the conditions leading to pathogen spread. We observe that the effective transmission of this infection in nature is highly dependent on the capability of the implemented model to describe the tick burden. In addition, we also consider seasonal changes in tick aggregation on mice, showing its influence on the spread of the infection.

An elective course in differential diagnostics

OBJECTIVE

To design an elective course to teach the principles of differential diagnostics to second-year pharmacy students, critically evaluate the benefits of this approach to self-directed learning, and assess obstacles to implementation that other programs may encounter.

DESIGN

Students attended seven 2-hour class sessions in which the instructor presented a chief complaint, and the class researched and discussed possible causes and arrived at the accurate diagnosis. Each student also was assigned a unique, simulated patient case to work on outside of class. Students asked questions and researched the answers, providing a written rationale for needing the information and the source of the information. Students gave a 10-minute presentation on their diagnosis and treatment recommendations during the last class session.

ASSESSMENT

All students (N = 21) successfully determined their patients' diagnoses and made appropriate treatment recommendations. Fifteen students reported that the most valuable information in solving their case was subjective rather than objective in nature (ie, interviewing the patient rather than reviewing laboratory test results). The majority of the 15 students who completed a post-course survey instrument agreed or strongly agreed that this elective allowed them to practice varied skill sets and integrate past and future curricular content.

CONCLUSION

PharmD students may benefit from instruction in the basic principles of differential diagnostics.

Treatment failure of gentamicin in pediatric patients with oropharyngeal tularemia

Background

Tularemia is a zoonotic infection, and the causative agent is Francisella tularensis. A first-line therapy for treating tularemia is aminoglycosides (streptomycin or, more commonly, gentamicin), and treatment duration is typically 7 to 10 days, with longer courses for more severe cases.

Material/Methods

We evaluated 11 patients retrospectively. Failure of the therapy was defined by persistent or recurrent fever, increased size or appearance of new lymphadenopathies and persistence of the constitutional syndrome with elevation of the levels of the proteins associated with the acute phase of infection.

Results

We observed fluctuating size of lymph nodes of 4 patients who were on the 7^th day of empirical therapy. The therapy was switched to streptomycin alone and continued for 14 days. The other 7 patients, who had no complications, were on cefazolin and gentamycin therapy until the serologic diagnosis. Then we evaluated them again and observed that none of their lymph nodes regressed. We also switched their therapy to 14 days of streptomycin. After the 14 days on streptomycin therapy, we observed all the lymph nodes had recovered or regressed. During a follow-up 3 weeks later, we observed that all their lymph nodes had regressed to the clinically non-significant dimensions (<1 cm).

Conclusions

All patients were first treated with gentamicin, but were than given streptomycin after failure of gentamicin. This treatment was successful in all patients. The results of our study suggest that streptomycin is an effective choice of first-line treatment for pediatric oropharyngeal tularemia patients.

Diagnosis and treatment of tick infestation and tick-borne diseases with cutaneous manifestations

Hard and soft ticks may be associated directly or indirectly with a number of dermatoses, both infectious and inflammatory in origin. Morbidity may occur as a result of tick bites, tick toxicosis, and even infestation. These arthropod vectors may transmit life-threatening protozoan, bacterial, rickettsial, and viral diseases with systemic and cutaneous findings. Additionally, ticks may transmit more than one pathogen with subsequent human coinfection. This article reviews the presentation of tick-borne illnesses and the medical management of these diseases. Among others, diseases such as ehrlichiosis, anaplasmosis, babesiosis, tularemia, borrelioses, tick-borne encephalitides, rickettsial spotted fevers, and tick typhus are discussed in this article. The recognition of skin manifestations associated with these diseases is paramount to early diagnosis and treatment initiation.

Tularemia type A in captive Bornean orangutans (Pongo pygmaeus pygmaeus)

In 2003, tularemia was suspected to be the cause of severe illness in two orangutans (Pongo pygmaeus pygmaeus) and the cause of death in a third orangutan at an urban zoo. The two sick orangutans were treated two times under chemical immobilization with i.v. doxycycline, fluids, and antipyretic drugs, followed by a sustained course of oral doxycycline. The rest of the orangutan group was treated prophylactically with oral doxycycline. Postmortem diagnosis was obtained via immunohistochemistry and bacterial culture that revealed Francisella tularensis type A. Tularemia was also confirmed in the two surviving orangutans via paired serology testing. In addition, F. tularensis was identified in two wild rabbit carcasses submitted during a die-off, several weeks prior to the tularemia outbreak in the apes, indicating that rabbits were possibly a reservoir for tularemia within the zoo premises.

Inhibition of neutrophil function by two tick salivary proteins

The saliva of hematophagous arthropods contains potent anti-inflammatory and antihemostatic activities that promote acquisition of the blood meal and enhance infection with pathogens. We have shown that polymorphonuclear leukocytes (PMN) treated with the saliva of the tick Ixodes scapularis have reduced expression of beta(2) integrins, impaired PMN adherence, and reduced killing of Borrelia burgdorferi, the causative agent of Lyme disease. Here we describe two Ixodes proteins that are induced upon tick feeding and expressed predominantly in the salivary glands. Using saliva harvested from ticks with reduced levels of ISL 929 and ISL 1373 through targeted RNA interference knockdown, as well as purified recombinant proteins, we show the effects of these proteins on downregulation of PMN integrins and inhibition of the production of O(2)(-) by PMN in vitro. Mice immunized with ISL 929/1373 had increased numbers of PMN at the site of tick attachment and a lower spirochete burden in the skin and joints 21 days after infection compared to control-immunized animals. Our results suggest that ISL 929 and ISL 1373 contribute to the inhibition of PMN functions shown previously with tick saliva and support important roles for these inhibitory proteins in the modulation of PMN function in vivo.

Tick-Borne Bacterial, Rickettsial, Spirochetal, and Protozoal Diseases

Approximately 900 tick species exist worldwide, parasitizing a broad array of mammals, including humans, and thereby playing a significant role in the transmission of infectious diseases (1). In the United States, tick-borne diseases are generally seasonal and geographically distributed. They occur mostly during the spring and summer but can occur throughout the year.

Ulceroglandular Tularemia in a Nonendemic Area

Two patients present with the abrupt onset of fever, malaise, anorexia, fatigue, progressive skin lesions and lymphadenitis. These patients represent two of the six cases of tularemia reported in Alabama over the last decade. The cases illustrate how mode of acquisition (direct versus vector-mediated) influences the clinical manifestations of ulceroglandular tularemia. In addition, a brief review of the epidemiology, differential diagnosis, clinical manifestations, and treatment of tularemia is provided.

Orally active acaricidal peptide toxins from spider venom

Numerous species of ticks and mites (collectively known as acarines) are serious pests of animals, humans, and crops. There are few commercially available acaricides and major classes of these chemicals continue to be lost from the marketplace due to resistance development or deregistration by regulatory agencies. There is consequently a pressing need to isolate new and safe acaricidal compounds. In this study, we show that two families of peptide neurotoxins isolated from the venom of the Australian funnel-web spider Hadronyche versuta are lethal to the lone star tick Amblyomma americanum. These toxins, which are specific blockers of arthropod voltage-gated calcium channels, induce a pronounced phenotype characterized by an unusual gait that is rapidly followed by paralysis and death. Remarkably, one of these toxins, the calcium channel blocker omega-atracotoxin-Hv1a, is virtually equipotent whether the toxin is injected or fed to A. americanum.