Abstract
We present the case summary of the first human recognized to have been bitten by the Haemaphysalis longicornis tick in the United States, which occurred in New York State. Subsequent field studies confirmed that this tick was present in multiple geographic locations near the patient’s residence, including on manicured lawns.
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Tick-borne infections are of increasing concern in the United States [1]. In this location, Lyme disease is transmitted by Ixodes scapularis and Ixodes pacificus ticks [1, 2]. Several other tick-borne infections are also vectored by these species [1, 2]. Additional tick-borne infections in the United States are transmitted by other tick species including but not limited to Dermacentor species, Ixodes cookei, Amblyomma americanum, and Rhipicephalus sanguineus [1]. While a comparatively small proportion of tick bites result in transmitted infections, each bite may cause anxiety and generate health concerns for the person bitten.
Until recently, Haemaphysalis longicornis was limited to Asia, New Zealand, Australia, and certain Pacific Islands [3]. Haemaphysalis longicornis ticks in parts of Asia serve as a vector for the bunyavirus SFTSV (severe fever with thrombocytopenia syndrome virus) [4]. A related tick-borne virus, Heartland virus, is found in the United States [5]. Both of these bunyaviruses may cause potentially fatal human infections. Haemaphysalis longicornis ticks in Asia have also been reported to be infected with spotted fever group rickettsia, Anaplasma species, Borrelia burgdorferi sensu lato, and Babesia species [5, 6], but there is less certainty about whether this tick species is a vector for these microorganisms.
Relatively little is known about H. longicornis in the United States. In 2017, this tick was found on a sheep in New Jersey [7]. This tick species has subsequently been identified in several other states as well [5]. We present the case summary of the first human recognized to have been bitten by this tick in the United States, which occurred in New York State, and the results of subsequent field studies conducted near the patient’s residence.
RESULTS
Case Summary
A 66-year-old man from Yonkers, New York, removed a tick attached to his right leg on 4 June 2018. He had not traveled outside Westchester County, New York, within the prior 30 days, and he had no exposure to farm animals. In the prior 30-day period, his outdoor exposure was restricted to his lawn and 1 other lawn site in Westchester County. He took a single 200-mg dose of doxycycline prescribed by his primary care physician because the tick was presumed to be I. scapularis [8]. Later the same day, the patient brought the tick to the Lyme Disease Diagnostic Center (LDDC) located in Westchester County, New York. The patient was asymptomatic at the time of the encounter and did not develop a clinical illness over the following 3 months.
Tick Identification
As part of a long-term collaborative project on tick bites, the tick (Figure 1) was identified at the New York State Department of Health Regional Medical Entomology Laboratory at Fordham University. It was identified as nymphal stage Haemaphysalis species based on morphological features, although H. longicornis was suspected given the recent finding of this tick in New Jersey [7]. The specimen was sent to the Rutgers University Center for Vector Biology for molecular testing. To leave the majority of the specimen intact for further morphological examination, a single leg was removed and subjected to a rapid extraction procedure (Hot Sodium Hydroxide and Tris), followed by polymerase chain reaction amplification with standard cytochrome c oxidase I barcoding primers. The New York sequence shared 100% identity with sequences of H. longicornis in the National Center for Biotechnology Information’s GenBank from an Australian publication [9] and 99.9% identity with H. longicornis specimens previously identified in New Jersey [7], enabling molecular confirmation as H. longicornis on 22 June 2018. The identification was further confirmed on 25 June 2018 by the National Veterinary Services Laboratory (NVSL, Ames, Iowa). The NVSL made its determination based on morphology and reference specimens in its collection.
Dorsal (A) and ventral (B) views of the blood-engorged Haemaphysalis longicornis nymph found attached to a patient in Westchester County, New York, identified to species by morphological examination and DNA barcoding (photo credit: A. Egizi). Note that 2 legs are missing: 1 was removed to perform DNA barcoding and 1 was missing prior to receipt of the tick.
Field Studies
Tick sampling was conducted near the patient’s home and at a nearby park and trail. The patient resided in a suburban/urban community; his residence was surrounded by a well-manicured lawn and ornamental plantings on 3 sides with a wood patio in the rear. Total lawn area around the house was approximately 321 m2 with an additional 46 m2 of grass adjacent to a front sidewalk. A recreational park was located across the street approximately 150 m from the house. The park consisted mainly of well-maintained fields and grassy areas, both in open sun and adjacent to woods. Directly behind the property, approximately 10 m from the patio, was a public trail. This trail was approximately 5 m wide and consisted of a mowed grass center with taller grass on each edge, leading to narrow wooded strips on either side. Although the patient did not report being in the park or on the trail prior to the tick bite, these areas were sampled for ticks because of their close proximity to the residence and the possibility that H. longicornis ticks were transported to the property, either on their own or via host animals.
Tick sampling was conducted using drag cloths, during which a 1 m2 corduroy cloth is dragged over the vegetation, collecting host-seeking ticks in the process. The cloth was checked for ticks every 5 m. Sampling was conducted in 2018 on 2 July and 9 July for the patient’s residence, on 9 July and 18 July for the nearby park, and on 10 July for the trail.
At the residence, the entire lawn, including ornamental plantings, was sampled on each date. On 2 July, a total of 4 H. longicornis (3 nymphs, 1 female) ticks were collected, all on manicured lawn and with 2 of the nymphs and the female found in direct sun. No ticks were collected from the property on 9 July.
In the park, a total of 1675 m2 was sampled on 9 July and 1000 m2 on 18 July. A total of 11 H. longicornis (4 nymphs, 7 females) were collected on the first date and 14 H. longicornis (7 nymphs and 7 females) were collected on the second date. Ticks were collected both in open, cut grass exposed to direct sun, as well as in shade and taller grass adjacent to woods. On the trail, 1080 m2 was sampled, resulting in the collection of 61 H. longicornis (25 nymphs and 36 females). Ticks were collected in mowed short- to mid-length grass near the trail edges, in both full sun and partial shade. At the time these ticks were discovered, they were the first known collections of H. longicornis in New York State.
DISCUSSION
Haemaphysalis longicornis ticks have been identified in New Jersey and in several other states including West Virginia, Virginia, Arkansas, North Carolina, Connecticut, Maryland, Pennsylvania, and New York State [5, 7]. In June 2018, a patient from New York State was bitten by a H. longicornis tick in Westchester County, which was discovered when he presented it to the LDDC. Prior to June 2018, no human in the United States was known to have been bitten by this tick species, but it is difficult to be certain that human bites had not previously occurred, as patients do not always find or save the tick that bit them, and when they do, the option of expert identification by an entomologist may not be available. A recent analysis of human-biting ticks worldwide considers H. longicornis a “frequent” parasite of humans, although less so than A. americanum, I. scapularis, I. cookei, and Dermacentor variabilis [10].
This tick species poses a risk for farm animals due to blood loss and transmission of certain infectious agents such as Theileria orientalis [3, 5]. Unlike I. scapularis, which usually do not feed for >7 days, H. longicornis may feed for up to 19 days [3], possibly providing greater opportunity to find this tick on a host. Whether H. longicornis will pose a health risk for humans in the United States is unclear [5]. If future introductions of this tick species should occur and if some of the introduced ticks were infected with SFTSV, this could indeed pose a public health concern, particularly because recent data suggest that the tick itself may serve as a reservoir for the pathogen [4]. Another concern is whether H. longicornis might be able to transmit local US pathogens such as the Heartland virus [5, 11]. In addition, there is some evidence that bites from H. longicornis ticks may lead to red meat allergy [12].
Finding H. longicornis nymphs and females on manicured lawns in open sun may be significant. Ixodes scapularis, the most common human-biting tick in New York State, is typically found in wooded areas or shaded grass, and public education efforts have stressed this point. Indeed, in the original sampling conducted for this case study, I. scapularis ticks were not collected in any of the areas sampled in which H. longicornis was found. The presence of H. longicornis on manicured lawns may result in an increase in tick exposure for residents who are more familiar with the landscape habits of I. scapularis. Thus, the findings of this investigation suggest that public health messages may need to be changed, at least in certain geographic areas, to emphasize a wider range of potential tick habitats.
In conclusion, this investigation reinforces the public health importance of collaborations between clinicians and entomologists with regard to emerging tick-borne infections.
Notes
Acknowledgments. The authors thank Lisa Giarratano, Julia Singer, Shana Warner, Thomas Mistretta, Denise Bonilla, Dr James Mertins, and Dr Thomas Daniels for assistance.
Disclaimer. The contents of this work are solely the responsibility of the authors and do not necessarily represent the official views of the Centers for Disease Control and Prevention (CDC) or the Department of Health and Human Services.
Financial support. The work presented in this publication was partially supported by the CDC (cooperative agreement number U01CK000509).
Potential conflicts of interest. G. P. W. has received research grants from Immunetics, the Institute for Systems Biology, Rarecyte, the National Institutes of Health/Tufts, and Quidel Corporation; owns equity in Abbott/AbbVie; has been an expert witness in malpractice cases involving Lyme disease; and is an unpaid board member of the American Lyme Disease Foundation. All other authors report no potential conflicts of interest. All authors have submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest. Conflicts that the editors consider relevant to the content of the manuscript have been disclosed.
