A Case of Illness Following a Bite by a Male Lone Star Tick ( Amblyomma americanum Linnaeus) Infected With Ehrlichia sp. and Rickettsia amblyommatis in Connecticut, United States

ABSTRACT

The lone star tick ( Amblyomma americanum Linnaeus) is a species commonly found in the southeastern U.S., but in recent years its populations have expanded northward, resulting in an increased risk of tick‐borne pathogen transmission in the Northeast. We report a case of local lymphadenopathy and a flu‐like illness in a Connecticut man, following a bite by a male lone star tick infected with Ehrlichia sp. and Rickettsia amblyommatis. It has been documented that Ehrlichia sp. can cause such illness; however, we cannot entirely rule out the potential involvement of R. amblyommatis as a co‐conspirator. Our finding highlights the importance of changing dynamics of pathogen activities and its clinical ramifications in a region with pervasive populations of the blacklegged tick (deer tick, Ixodes scapularis Say) and the recently established presence of at least three non‐native species, including the lone star tick. The case described here with a localized reaction and flu‐like symptoms following a bite by a male lone star tick and subsequent evidence of infection in the tick vector with two unique aforementioned pathogens signifies the need for early detection and treatment of these particular diseases, especially when they have specific or unusual symptoms. These efforts that can be achieved through extensive tick and tick‐borne pathogen surveillance programs will help to reduce possible health hazards, guide diagnosis and treatment, and improve our understanding of the clinical consequences of related illnesses.

A case of local lymphadenopathy and a flu‐like illness in a man, following a bite by a male lone star tick infected with Ehrlichia sp. and Rickettsia amblyommatis.

Summary.

• Reporting a case presentation in areas with changing endemicity and distribution of vectors is important for raising awareness of the causative agents of tick‐borne illnesses.

• We report a disease case following a bite by a male lone star tick infected with Ehrlichia sp. and Rickettsia amblyommatis in the northeastern U.S.

1. Introduction

Tick‐borne diseases continue to pose a major health concern for people, pet animals, livestock, and wildlife in the U.S. Reported tick‐borne disease cases have increased substantially from 22,527 in 2004 to greater than 71,000 in 2022 [1]. Introduction of invasive ticks into new territories has accelerated in recent years due to the frequency of trade and travel, among other factors, and climate change and environmental conditions have facilitated their range expansion, exposing many people to a wider array of tick‐borne pathogens and further complicating the diagnosis and treatment of tick‐borne illnesses.

The lone star tick ( Amblyomma americanum Linnaeus) is a species commonly encountered in the southeastern U.S.; however, recent environmental conditions have promoted its proliferation and geographic advancement in northeastern states including New York, New Jersey, and Rhode Island. More recently, established populations of this tick species have been reported in central New Jersey in 2017, in the coastal regions of southwestern Connecticut (Fairfield and New Haven Counties) in 2018 and 2019, and in the cape and a few nearby islands in Massachusetts in 2019 [2, 3]. Over the years, human encounters with this tick have increased in Connecticut—the number of lone star ticks removed from Connecticut residents and submitted to the Connecticut Agricultural Experiment Station Tick Testing Laboratory (CAES‐TTL) increased substantially between 1996–2006 and 2007–2017, and even more so in recent years [2].

The successful northward expansion of the lone star tick (and a few other tick species) has given rise to the emergence of an unprecedented suite of pathogens in the region, an area already overwhelmed with abundant populations of several tick species and plagued by at least seven tick‐borne diseases. An aggressive human biter, the lone star tick is a known vector of several pathogens of public health concern including Ehrlichia chaffeensis , Ehrlichia ewingii , Panola Mountain Ehrlichia, Heartland virus, Bourbon virus, and the causative agent of Southern tick‐associated rash illness (STARI), which the offending pathogen has yet to be defined. Lone star tick bites are also associated with alpha‐gal syndrome (AGS), commonly referred to as the red meat allergy. This condition is caused by the introduction of alpha‐gal, a sugar found in mammalian cells, to a human host during tick feeding, which can trigger hypersensitivity to this sugar molecule in subsequent exposures. The first human cases of AGS were reported in 2009, and by 2019, 34,000 additional cases had been identified. It is believed that nearly 3% of the U.S. population may have clinical AGS with anaphylactic reactions [3]. The lone star tick is commonly infected with Rickettsia amblyommatis, a species related to the spotted fever group Rickettsia, and some studies have reported infection rates as high as 90% [4, 5]. The clinical relevance of R. amblyommatis to human health is not clearly understood, though some studies have suggested that this Rickettsia species may be responsible for some milder tick‐borne disease cases misdiagnosed as Rocky Mountain spotted fever, a disease caused by the more pathogenic Rickettsia rickettsii [6, 7].

Although in the Northeastern U.S., reports of human disease cases associated with lone star ticks have not been as common as those transmitted by the blacklegged tick, some of these cases are likely misdiagnosed and underreported due to the nonspecific disease symptoms, challenges with patient screening methods, and limited clinical staff awareness of emerging tick‐borne diseases in the region. Here we describe an illness in a Connecticut resident that followed the bite of a male lone star tick, infected with Ehrlichia sp. and R. ambylommatis. This case serves to increase awareness for clinicians and researchers of the many potential human pathogens carried by the lone star tick.

2. Case Report

2.1. Case History and Examination

On June 28, 2024, a 52‐year‐old male resident of Connecticut discovered a tick attached to his left hip. He promptly removed the tick and stored it. He reported that earlier that afternoon, he spent about an hour and a half cutting a tree down in the woods behind his residence. With the help of a family member, a more thorough tick check was carried out during which no additional specimens were found attached to his body. A small, raised erythematous lesion appeared at the bite site (Figure 1), and no other indications of skin abnormality were noticed.

FIGURE 1.

Light microscopy images of a male lone star tick: (A) dorsal; (B) ventral; and (C) the raised erythematous lesion at the tick bite site on the patient's leg.

On July 6, the patient discovered lymphadenitis near the groin area approximately 2 to 3 in. from the bite site and subsequently scheduled an appointment for evaluation at a nearby clinical facility. A complete blood count (CBC) and metabolic panel were done on July 9 and showed a slightly low red blood cell count (3.8 M/μL; references: 4.2–6.1 M/μL), low hemoglobin (12.3 g/dL; references 12.7–17.5 g/dL), low hematocrit values (36.4%; references 38.5%–52.0%), and slightly increased liver function tests—aspartate aminotransferase levels (AST, 43 U/L; references 4–40 U/L) and alanine aminotransferase levels (ALT, 67 U/L; references 4–41 U/L) (Table 1).

TABLE 1.

Blood test results during routine examination, on presentation, and after taking doxycycline.

Component	Values during routine examination (April 18, 2024)	Values on presentation (July 9, 2024)	Values after doxycycline treatment (July 29, 2024)	Normal range
Red blood count	4.3 M/μL	3.8 M/μL	4.3 M/μL	4.2–6.1
Platelet count	N/A	210 K/μL	192 K/μL	150–450
Hemoglobin	13.4 g/dL	12.3 g/dL	14.1 g/dL	12.7–17.5
Hematocrit	40.8%	36.4%	40.8%	38.5–52.0
Mean corpuscular hemoglobin	31 pg	32 pg	33 pg	27–32
Neutrophils	48.5%	38.7%	53.9%	40.0–60.0
Lymphocytes	37.7%	47.8%	35.6%	20.0–40.0
Monocytes	9.5%	10.4%	8.3%	2.0–8.0
Aspartate aminotransferase	33 U/L	43 U/L	27 U/L	4–40
Alanine transaminase	32 U/L	67 U/L	36 U/L	4–41

Abbreviation: N/A, not available.

In addition, on July 6 and 9, the patient's white blood cell counts and platelet counts were normal. His red blood cell counts and liver function tests were within normal range earlier in April 2024 when the patient completed bloodwork for his annual physical exam. Serological testing for IgG/IgM antibodies against Borrelia burgdorferi (the causative agent of Lyme disease) was negative with an index of 0.04 (references: < 0.90). PCR screening for Anaplasma phagocytophilum (the causative agent of anaplasmosis), E. chaffeensis (the causative agent of ehrlichiosis), and Babesia microti (the causative agent of babesiosis), as well as microscopic observation for malaria/babesia/other blood parasites, were also negative. On July 10, the patient was prescribed a 14‐day course of doxycycline, which he started on July 13. On July 26, the patient experienced nausea (which may have been from his illness or a side effect of the doxycycline), loss of appetite, and fatigue in addition to the persisting swollen lymph nodes. A follow‐up CBC and metabolic panel done on July 29 was basically normal (Table 1) and at this time he was clinically well and remained well over the next 3 months of follow‐up.

2.2. Investigation and Follow‐Up

The tick was submitted to the CAES‐TTL on July 8, and initial examination of the specimen on July 11 using a dissecting microscope and standard taxonomic key [8] revealed that it was an A. americanum male. After the patient called the CAES‐TTL on July 29 and reported persisting swollen lymph nodes and the decision by his healthcare provider to put him on doxycycline, the tick was screened for common pathogens associated with the lone star tick. DNA was extracted from the whole specimen using DNAzol BD (Molecular Research Center, Cincinnati, OH, USA) according to the manufacturer's recommendations with some modifications. Briefly, the tick was placed in a 1.5‐mL tube containing 400 μL of DNAzol BD and a copper BB and homogenized in a MM 300 Mixer Mill (Retsch, Newtown, 116 PA, USA). The homogenate was incubated at 70°C for 10 min followed by centrifugation at 14,000 RPM for 10 min. DNA was precipitated by adding 200 μL 100% EtOH and 3 μL Poly Acryl Carrier (Molecular Research Center). DNA pellets were then washed twice with 75% EtOH and resuspended in 30 μL diH₂O. For pathogen screening, isolated DNA from the tick was used in PCR reactions to amplify a portion of the outer membrane protein A (ompA) gene to detect Rickettsia species [9]. For Ehrlichia screening, two sets of primers were used to amplify the 16S rRNA region: one universal primer pair targeting all Ehrlichia species [10] and the other primer pair to search for E. chaffeensis [11]. Successful amplification was observed only for the ompA and 16S rRNA gene using the universal Ehrlichia primer pair, and no amplification was observed using E. chaffeensis ‐specific primers. PCR products were purified and sequenced using the Sanger sequencing method at the Keck Sequencing Facility, Yale University (New Haven, Connecticut, USA). Comparison of the obtained sequences to those in the NCBI GenBank DNA sequence database revealed their identity as Ehrlichia sp. and R. ambylommatis. Sequences were later submitted to GenBank (accession numbers: PQ315658 for Ehrlichia sp., and PQ333016 for R. ambylommatis). Amplification and sequencing of the mitochondrial 16S region [12] corroborated with the result of morphological identification of the tick as A. americanum (GenBank accession number PQ331226).

3. Discussion

We describe a patient who presented to his primary care office with swollen lymph nodes following the bite by a male lone star tick which tested positive for Ehrlichia sp. and R. ambylommatis. Subsequent laboratory testing ordered by a clinician revealed that the patient had slightly low red blood cell count, hemoglobin, and hematocrit values, and elevated AST and ALT levels. Test results for common vector‐borne pathogens in the region were negative.

Considering the clinical and laboratory findings reported here, it is possible that this patient contracted ehrlichiosis caused by Ehrlichia sp. found in the removed male lone star tick. Although some signs and symptoms of ehrlichiosis can be nonspecific, some studies have highlighted elevated AST and ALT as important laboratory manifestations in patients afflicted with the disease [13, 14]. In fact, heightened hepatic aminotransferase levels could be an indication of infection caused by all types of human ehrlichioses, including those caused by the well‐characterized pathogens E. chaffeensis , E. ewingii , and the related A. phagocytophilum [14, 15]. A meta‐analysis study reported elevated AST or ALT levels in 83% (n = 276) and 71% (n = 177) of patients diagnosed with ehrlichiosis and anaplasmosis, respectively [14, 16]. The laboratory findings of the patient in this study are therefore consistent with those in previous disease reports and lend support to the possibility that he became ill with ehrlichiosis caused by Ehrlichia sp.

In the U.S., E. chaffeensis ehrlichiosis cases increased ten‐fold from roughly 200 cases in 2000 to over 2000 cases in 2019 [17]. However, a smaller subset of ehrlichiosis cases was associated with E. ewingii and Ehrlichia muris eauclairensis (transmitted by the blacklegged tick) during that period. Ehrlichiosis cases are most frequently reported from the southeast and southcentral U.S., overlapping with the known range of the lone star tick, the primary vector of E. chaffeensis and E. ewingii . Similar to other tick‐borne diseases, ehrlichiosis is associated with fever, headache, malaise, nausea, and vomiting, and a rash can occasionally be present. The CDC suggests doxycycline as the antibiotic of choice for treatment of adults and children of all ages.

Although Ehrlichia sp. has been reported to be capable of causing illness consistent with the reported symptoms and laboratory findings in this case report, we cannot entirely rule out the potential involvement of R. ambylommatis found in the removed tick as a co‐conspirator. Rickettsia ambylommatis has undefined pathogenicity, and its public health significance remains to be fully ascertained; however, in recent years, there has been increasing evidence describing its association with clinical illness and potential to cause symptoms including rash, anemia, fever, and headache in infected patients [18, 19]. A relatively higher prevalence of Rocky Mountain spotted fever (RMSF) cases in the southeastern U.S. despite the rarity of ticks infected with R. rickettsii, the known etiologic agent of RMSF, has provided reasons for some studies to implicate R. ambylommatis as the likely cause of milder, potentially misdiagnosed cases [6, 7]. One such study conducted in North Carolina observed a fourfold or greater increase in titers to R. ambylommatis antigens in three of six probable RMSF cases [6]. Rickettsia ambylommatis has been identified in several tick species; however, it is primarily associated with the lone star tick, and infection prevalence in this tick species can be as high as 90% [4, 5]. Given that the lone star tick is an aggressive and dominant human‐biting species in the southeastern U.S. and its range overlaps with a large number of RMSF cases, it is plausible that R. ambylommatis transmitted by this tick species contributes to rickettsial disease cases in the U.S.

There exist ongoing challenges associated with clinical and laboratory diagnoses of ehrlichiosis and spotted fever group rickettsioses. Clinician awareness of and suspicion for ehrlichiosis and rickettsioses may be lower in nonendemic areas where nonnative tick vectors are only beginning to emerge. Moreover, it is often the case that patients afflicted with these diseases initially present with nonspecific symptoms, which physicians may attribute to a wide array of health conditions. The methods used to screen for ehrlichiosis have several limitations. Serology using indirect fluorescent antibody (IFA) assays has been frequently utilized to diagnose ehrlichiosis; however, acute‐phase sera is typically nonreactive as evidence of infection does not become apparent until convalescent sera is analyzed, thereby delaying diagnosis to several days to weeks after symptom onset [20]. Cross‐reactivity of antigens can also impede an effective diagnosis by displaying false positives. Conversely, molecular methods such as PCR can better detect pathogens during early infection [21]. While serology can be non‐specific and can cross‐react with pathogens closely related to the target, PCR can more accurately detect and differentiate pathogens within the same genus. A drawback of PCR is that available assays usually target a limited number of important and prevalent species, and it is likely that some less common or entirely unknown species of Ehrlichia remain undetected. This may be evident in the current study as the patient was screened for E. chaffeensis by PCR, and results indicated that he was not infected with this pathogen; however, it is entirely possible that the patient was infected with the Ehrlichia sp. which was later identified in the tick. These limitations in testing methods and/or detection of an Ehrlichia species other than E. chaffeensis and E. ewingii might explain the lack of an identifiable etiologic agent for > 2400 cases with known clinical and laboratory signs consistent with ehrlichiosis/anaplasmosis from 2008 to 2021 reported by the CDC [17].

In this case report, we describe the possible role of a male lone star tick in pathogen transmission to humans. Although infections of male ticks have been reported, for most tick species, they occasionally engage in blood feeding and therefore play an insignificant role in pathogen transmission. Conversely, female ticks feed more frequently and for longer durations as nutrients obtained from blood are necessary for vitellogenesis, a critical process in tick reproduction involving the generation of yolk proteins. Despite this, a small portion of ticks attached to humans are male. For example, from 2014 to 2024, 3532 male ticks were found on humans and submitted to the CAES‐TTL, of which 333 (9.4%) were lone star ticks; however, the extent of their engagement in blood feeding is unclear. Several studies have also described the capability of male ticks to transmit pathogens to humans and other animals. For instance, it has been postulated that because male Amblyomma ticks are highly motile on hosts and stay on for longer periods of time compared to females, they are more likely to infect humans with R. rickettsii [22]. The result of the aforementioned investigation showed that unfed adult male Amblyomma aureolatum (Pallas) ticks needed to be attached to a host for at least 10 h to successfully transmit R. rickettsii . It is worth noting that for most tick species, males are naturally intermittent feeders and engage in interrupted blood feeding as a result of having to seek out a female for mating on a host [23]. This phenomenon of partial feeding has been illustrated to promote pathogen transmission in male ticks. For instance, the study discussed above also documented that male ticks that initially fed on rabbits for 48 h before being transferred to a guinea pig were able to infect the second host with R. rickettsii within only 10 min of attachment [22]. In another study, pre‐fed male Dermacentor reticulatus (Fabricius) ticks infected dogs with Babesia canis within 8 h of attachment, a substantially shorter time required for successful pathogen transmission compared to unfed ticks [24]. The results of these studies are compatible with our findings suggesting the role of a male lone star tick in causing infection with Ehrlichia sp. and/or R. amblyommatis.

4. Conclusion

We describe a Connecticut resident who likely experienced a tick‐borne illness shortly after a bite from a male lone star tick with evidence of infection with Ehrlichia sp. and R. ambylommatis. Our finding highlights the occasional involvement of male ticks in pathogen transmission and the importance of these two pathogens in causing illnesses in areas where ehrlichiosis and rickettsioses are emerging. Our report also illustrates the changing dynamics of tick‐borne pathogen transmission and its public health ramifications in the Northeast, a region with pervasive populations of blacklegged ticks and recently established populations of lone star ticks. It is crucial to raise awareness among clinicians of the range expansions of invasive tick species and pathogens, as well as the clinical and laboratory manifestations of associated diseases, particularly in areas where current changing climatic factors have created conducive environments for these ticks and pathogens to thrive. Considering these challenges, it is also pivotal to not only test for known and prevalent pathogens but also include those that have not been commonly attributed to tick‐borne illness in the region, such as the ones described in this case report. Moreover, because of limitations in screening, multiple types of tests might be considered for proper diagnosis and to further elucidate the epidemiology of Ehrlichia and Rickettsia infections in areas where lone star ticks are becoming established.

Author Contributions

Noelle Khalil: data curation, formal analysis, investigation, methodology, visualization, writing – original draft, writing – review and editing. Abigail Chang: data curation, investigation, methodology, software, visualization, writing – original draft, writing – review and editing. Lorelei Sandland: data curation, investigation, methodology, software, visualization, writing – original draft, writing – review and editing. Henry M. Feder Jr.: data curation, investigation, methodology, visualization, writing – original draft, writing – review and editing. Goudarz Molaei: conceptualization, data curation, formal analysis, funding acquisition, investigation, methodology, project administration, resources, software, supervision, validation, visualization, writing – original draft, writing – review and editing.

Ethics Statement

All the procedures were performed in compliance with relevant laws and institutional guidelines.

Consent

Written informed consent was obtained from the patient to publish this report in accordance with the journal's patient consent policy.

Conflicts of Interest

The authors declare no conflicts of interest.

Khalil N., Chang A., Sandland L., Feder H. M. Jr., and Molaei G., “A Case of Illness Following a Bite by a Male Lone Star Tick ( Amblyomma americanum Linnaeus) Infected With Ehrlichia sp. and Rickettsia amblyommatis in Connecticut, United States,” Clinical Case Reports 13, no. 9 (2025): e70825, 10.1002/ccr3.70825.

Data Availability Statement

The data that support the findings of this study are available on request from the corresponding author. The data are not publicly available due to privacy or ethical restrictions.