Ticks Collected from Selected Mammalian Hosts Surveyed in the Republic of Korea During 2008-2009

In the Republic of Korea (ROK), mammals and their associated ticks are hosts to a number of zoonotic pathogens, such as spotted fever group rickettsiae [1], Ehrlichia and Anaplasma spp. [2], Bartonella spp. [3], Borrelia burgdorferi [4-5], and tick-borne encephalitis virus [6-8]. Humans are incidental hosts as a result of outdoor activities, i.e., agriculture, construction, maintenance, recreation, and military training activities. New information, including retrospective febrile patient surveys, indicates that tick-borne diseases are underdiagnosed in the ROK [9-11].

Outdoor activities, including recreational hiking, agriculture, construction, and military operations, expose large sectors of human populations and their pets to all life stages of ticks, and associated pathogens of mammal [12]. Military populations are at increased risk for acquiring tick-borne infections because they often conduct training operations in unmanaged lands where small mammals (i.e., rodents, soricomorphs, rabbits, and weasels), as well as larger species (i.e., deer, wild pigs, raccoon dogs, badgers, and feral cats) and pathogen-infected ectoparasites are present.

In a large mammal tick survey, Kang (1984) reported 565 ticks to determine baseline susceptibility to selected acaricides of ticks collected from domestic livestock (cows) from 35 cities and counties and 6 provinces from 1982 to 1984. Species collected included, Haemaphysalis longicornis (87.4%), Boophilus microplus (=Rhipicephalus microplus) (8.8%), Ixodes persulcatus (3.4%), Rhipicephalus sanguineus (0.5%), Argas vespertilionis (0.2%), and 1 unidentified tick [13]. Later, Kim et al. (2008) reported 130 H. longicornis and 12 Ixodes nipponensis from 16 wild boars at Dongducheon, Gyeonggi-do (Province), for isolation and detection of tick-borne encephalitis virus [6]. Reports and studies of tick collections from wild large mammals are few, with most surveys limited to small mammals conducted as part of rodent-borne diseases surveillance programs [14-16]. The purpose of the present study was to determine the relative abundance, infestation rates, and geographical distributions of ticks associated with Hydropotes inermis (Korean water deer) and other wild mammals in the ROK.

As part of The 8th US Army, 65th Medical Brigade tick-borne disease surveillance program, the 5th Medical Detachment collaborated with 1) The Conservation Genome Resource Bank for Korean Wildlife, Seoul National University (SNU), 2) National Institute of Biological Resources (NIBR), and 3) The Migratory Birds Center located on Hong Island, National Park Research Institute (NPRI), to collect ticks from wild mammals captured for necropsy under institutional approved animal use protocols (SNU, NIBR, and the NPRI). Ticks were removed from mammals captured from 6 provinces [Gyeonggi-do (Pocheon), Gangwon-do (Chuncheon, Cheorwon, Inje), Jeollanam-do (Goheung, Gokseong, Gwangyang, Gurye, Hampyeong, Suncheon, Yeosu, Hong Island), Chungcheongbuk-do (Cheongwon), Gyeongsangbuk-do (Uljin), and Jeju-do (Jeju, Seogwipo)], and 3 Metropolitan Cities (Seoul, Daejeon, and Ulsan) in the ROK (Table 1). Ticks were carefully removed with a fine forceps from mammals, placed in 2-ml cryovials with 80% ethyl alcohol, and transported to the Entomology Section, 5th Medical Detachment, where they were identified to species and developmental stage under a dissecting microscope using standard keys and current nomenclature [17-20].

Table 1.

Number of ticks and collection sites for each mammal species in the Republic of Korea, 2008-2009

A total of 918 ixodid ticks belonging to 2 genera (Ixodes and Haemaphysalis) were collected from mammals (n=76; 6 families, 9 species) captured for surveillance from 6 provinces and 3 Metropolitan Cities in the ROK. H. inermis (52.6%) was the most frequently collected mammal, followed by Felis catus (feral cat, 27.6%), Capreolus pygargus (roe deer, 5.3%), Nyctereutes procyonoides (raccoon dog, 3.9%) and Tamias sibiricus (Siberian chipmunk, 3.9%) (Table 1). Only 1-2 ticks were collected from each of the remaining 4 species. Of the 6 species of ticks collected, H. longicornis (54.4%) was the most frequently collected, followed by Haemaphysalis flava (28.5%), I. nipponensis (7.6%), Ixodes pomerantzevi (4.8%), I. persulcatus (4.6%), and Haemaphysalis japonica (0.1%). The highest tick indices for selected hosts were recorded from N. procyonoides (38.0), followed by H. inermis (16.4), T. sibiricus (15.0), C. pygargus (9.0), and Meles leucurus (7.0). Tick indices for the remaining mammals were <5.0 (Table 2).

Table 2.

Number of mammals captured and number of ticks collected, by stage of development, for each mammal species in the Republic of Korea, 2008-2009

H. japonica (100.0%) was collected only from the Korean water deer, while accounting for 95.2% of I. persulcatus, 91.8% of H. longicornis, 55.7% of H. flava, and 17.1% of I. nipponensis. H. longicornis (69.7%) was the predominant species collected from the Korean water deer, followed by H. flava (22.2%), I. persulcatus (6.1%), I. nipponensis (1.8%), and H. japonica (0.2%) (Table 1).

Tick-borne zoonoses pose a serious health threat to US and ROK military populations throughout Korea [1-9,14-16]. Identification of arthropod ectoparasites and isolation of pathogens provide a descriptive analysis of the relative abundance of ticks, host associations, stages of development found on hosts, and relative distributions. Epidemiological data are critical to identify the prevalence, distribution, and disease risks of endemic and emerging zoonoses affecting animals and humans in the ROK. For US and ROK military populations, these data are central to the development of disease risk assessments and mitigation strategies (e.g., use of insecticide-impregnated uniforms) that reduce the impact of zoonotic diseases while increasing awareness among medical providers of potential arthropod-borne infections. H. longicornis is commonly collected on large mammals and from tall grass habitats with associated herbaceous vegetation and margins of forested hillsides and mountains (unpublished data), while H. flava larvae and nymphs are often associated with small mammals (e.g., rodents and soricomophs) and birds [17]. However, only 1 H. flava nymph was collected from 5,953 rodents and soricomorphs captured from 2004 to 2008 in Gyeonggi-do and Gangwon-do [16].

In our survey, 262 (28.5%) H. flava ticks were collected, with nymphs and adults found on a variety of small and large mammals (Table 3). I. nipponensis, larvae and nymphs, was the predominant tick (98.9%) collected from 5,953 small mammals captured (e.g., rodents and soricomorphs) in Gyeonggi-do and Gangwon-do [16]. In other reports, I. nipponensis was the most frequently collected tick from small mammals captured in Gyeonggi-do, while I. persulcatus was more commonly collected in Gangwon-do [14]. In our survey, this species was predominantly collected from F. catus at Hong Island, Jeollanam-do, and accounted for 96.0% of the total collected from feral cats. Larvae and nymphs of I. nipponensis prefers to blood feed on small mammals, while adults are more commonly found on large mammals.

Table 3.

Total number, percent, and stage of development for ticks collected from mammals, Republic of Korea, 2008-2009

Recent studies indicate that I. nipponensis plays an important role in the transmission of tick-borne pathogens to humans in the ROK, as human tick bites are reported more frequently for this species among patients seen at medical clinics in the ROK [21-24]. However, the number of reports may be not only due to increased propensity to bite humans, but due to greater allergenic reactions to bites by this species than others. Ixodes persulcatus was collected most frequently from H. inermis, which was associated with dense forested habitats in the Taebaek mountain range (20/42; 47.6%) and Sobaek mountain range (13; 31.0%). I. pomerantzevi is an uncommonly collected tick, with all previous collection records of this species collected from small mammals (Myodes regulus, Tscherskia triton, T. sibiricus, and Apodemus agrarius) while conducting routine rodent-borne disease surveillance [18,25,26]. In this survey, T. sibiricus was the primary host of I. pomerantzevi, with 24 larvae, 5 nymphs, and 15 female adults collected from 1 T. sibiricus collected in northern Gyeonggi-do. Only 1 male (0.1%) H. japonica was collected from a Korean water deer, and it has been infrequently recorded in other collections, e.g., tick drags, rodents, and birds.

Adults (57.0%) and nymphs (28.7%) of Ixodes and Haemaphysalis spp. were mostly collected from medium/large mammals in this survey, while larval ticks only accounted for 14.3% of all ticks collected (Table 3). In contrast, larvae (82.8%) and nymphs (17.2%) were collected from small mammals, 5,397 A. agrarius in Gyeonggi-do and Gangwon-do during 2004-2008, while adults accounted for <0.1% of all ticks collected [16].

The changing ecology, particularly reforestation, and associated increases in wildlife populations provide for increased proximal host contact associated with the wide distribution of blood-feeding ectoparasites in the ROK. Further studies of tick-host relationships are necessary to better understand tick species distributions and population dynamics, the distribution and prevalence of tick-borne pathogens, and their potential effects on human and animal health.