
Zoonosis is an infectious disease that spreads from animals to humans and is classified as bacterial, viral, fungal, and parasitic depending on pathogen. Direct propagation involves transmission from animals to humans without an intermediate vector, whereas indirect propagation involves transmission through intermediate vectors such as mosquitoes and mites. Currently, about 300 types of zoonosis are known, and about 60 types of zoonosis require preventive management. Global warming caused by human activity has resulted in an increase in greenhouse gases such as CO2. As the vectors are sensitive to climate change, recent climate change is mainly caused by global warming. In Korea, temperatures have risen 1.5°C since 1900, with annual precipitation showing a large fluctuation, and more extreme weather (drought and flood) than ever before [1]. Such climate change will change the environment and the ecosystems where vectors live. Because vectors are sensitive to climate change, the distribution of the vectors may be altered, which may also affect the distribution of various infectious diseases.
The class Arachnida includes spiders, scorpions, ticks, mites, harvestmen, and solifuges. Within the Arachnida is the order Acari, which includes ticks and mites, and is reported to have 50,000 species on Earth. Approximately 500 species of ticks and mites are distributed in Korea [2]. Among these, 5 genera and 27 species of ticks are known [3]. Our research included only members of the Acari known as hard ticks.
The tick form is largely divided into the mouthparts and the body. The mouthparts can be uniquely specialized so that ticks can live in various environments. The mouthparts allow ticks to penetrate the host skin and extract a blood meal from the tissue underneath. The upper side of the body consists of a protective plate, called the scutum. The lower side of the body consists of the legs and respiratory, digestive, and reproductive structures. In males, the scutum is large, whereas in females the scutum is much smaller [4].
The life includes a six-legged larva, followed by an eight-legged nymph, followed by an eight-legged adult. Ticks shed their exoskeleton between each of these stages. Hard ticks have a single larval and nymphal stage before becoming adults. The larva and adult have differences in the presence of reproductive cells and the number of bristles. Both sexes of ticks must feed on the blood of a vertebrate host in all of their life stages. Through the blood sucking process, pathogens inside the tick move to the host, causing illness. Ticks detect the host’s movements due to temperature changes, odors, and vibrations of the ground, and then escape from the host to the ground and undergo metamorphosis.
Ticks infect humans and animals with organisms such as viruses, bacteria, and protozoans. Tick-vectored diseases include severe fever with thrombocytopenia syndrome (SFTS), tickborne encephalitis, anaplasmosis, Ehrlichiosis, Lyme disease, and others [5-7].
SFTSV is a
Because the number of infectious diseases caused by vectors is increasing with an increase in global warming and in outdoor leisure activities, it is important to study the influence of climate and environmental changes on the influx and spread of these diseases through long-term monitoring.
Jeju Island is located at the southernmost tip of the Korean Peninsula and corresponds to 33°10′33°34′N and 126°10′127°E east longitude. Recently, with the introduction of warm and humid air in the tropical and subtropical western Pacific, the average temperature has risen 1.31°C over the past decade, especially in Seogwipo City [9].
In this study, we collected ticks and conducted a survey on classification and population density and we determined whether any of the collected ticks were infected with the SFTS virus.
We collected ticks in the Jeju area from April to November 2018. Tombs, mountain roads, copses, and grass fields were selected as tick collection areas. In Jeju, ticks were collected once a month using tick traps, and in Seogwipo, ticks were collected in May and June using the flagging method (Table 1).
Occurrence monitoring of ticks for environment
Survey area | Survey environment | Location | Investigation method |
Time of investigation |
Frequency of investigation | Remarks |
---|---|---|---|---|---|---|
Jeju-city | Glass field | 33°27'20.1"N 126°34‘15.3"E | Trap & flagging | April-November (Trap) May-Jun (Flagging) |
Once a month | Classification identification |
Copse | 33°27‘21.2"N 126°34‘10.5"E | |||||
Mountain road | 33°26'53.2"N 126°34‘35.4"E | |||||
Tomb | 33°26'55.2"N 126°34'42.9"E |
The collected ticks were fixed in 70% alcohol and classified by examination under the microscope (Olympus SZ61, Tokyo, Japan) according to methods of Yamaguti et al [8]. Each tick was identified as larva, nymph, or adult and adults were distinguished as male or female.
The collected ticks were treated as follows for the extraction of the SFTS RNA. Adults (N=5), nymphs (N=30), and larvae (N=50) were put into a 2 mL tube, and the tissues were homogenized twice for 20 sec at 5,000 rpm with an automatic homogenizer. The tick tissues were cooled for 5 min on ice and centrifuged for 1 min at 4°C and 13,000 rpm (13,250 RCF). After taking 140 μL of the upper layer solution and transferring it to a new 1.5 mL tube, RNA was extracted using the QIAamp Viral RNA Mini Kit (Qiagen, Cat# 52906, Hilden, Germany). The solutions were stored in a freezer at −70°C. For the detection of the M-section gene, RT-PCR was performed using a primer set (5'-GATAGGATGTCCATTAA-3' and 5'-CTCATGGGGGGGGGGGGAATGTCAC-3') [10] according to the protocols of the DiaStarTM 2X One-step RT-PCR Pre-Mix (SOLGENT, Daejeon, Korea). PCR products were separated using gel electrophoresis with a 2.0% agarose gel and 0.5 mg/mL ethidium bromide (Table 2). The SFTSV gene amplification product (560 bp) was identified using the standard molecular marker, positive control (480 bp) and SFTSV received from the Centers for Disease Control and Prevention.
Conditions for RT-PCR
A. RT-PCR reaction component | ||
---|---|---|
Component | Volume | |
2X One-step RT-PCR Pre-Mix | 15 μL | |
Primer F (10 pmol/μL) | 12.5 μL | |
Primer R (10 pmol/μL) | 1.25 μL | |
Template RNA | 1.75 μL | |
RNase, DNase-Free water | 1.75 μL | |
Total reaction volume | 25 μL | |
50°C | 30 min. | 1 cycle |
95°C | 15 min. | 1 cycle |
95°C | 20 sec. | |
58°C | 40 sec. | 35 cycles |
72°C | 30 sec. | |
72°C | 5 min | 1 cycles |
In total, 3,090 ticks from the genus
Number of tick collected by environment using tick trap and flagging
Environment | Tick trap | Flagging | Total (%) |
---|---|---|---|
Glass field | 950 | 196 | 1,146 (24.6) |
Copse | 883 | 704 | 1,587 (34.1) |
Mountain road | 847 | 472 | 1,319 (28.3) |
Tomb | 410 | 197 | 607 (13.0) |
Total | 3,090 | 1,569 | 4,659 (100) |
Monthly distributional studies of tick species using tick trap
Month | Total | ||
---|---|---|---|
N (%) | |||
Mar | 85 (2.7) | 21 (0.7) | 106 (3.4) |
Apr | 246 (8.0) | 23 (0.7) | 269 (8.7) |
May | 709 (22.9) | 11 (0.4) | 720 (23.3) |
Jun | 617 (20.0) | 1 | 618 (20.0) |
Jul | 404 (13.1) | 1 | 405 (13.1) |
Aug | 401 (13.0) | 1 | 402 (13.0) |
Sep | 35 (1.1) | 29 (0.9) | 64 (2.1) |
Oct | 141 (4.6) | 0 | 141 (4.6) |
Nov | 306 (9.9) | 59 (1.9) | 365 (11.8) |
Total | 2,944 (95.3) | 146 (4.7) | 3,090 (100) |
Abbreviation:
Monthly distributional studies of
Mar | Glass field | 106 | |||||||||||
Copse | 3 | 2 | 3 | 3 | |||||||||
Mountain road | 32 | 1 | 4 | 1 | 3 | 1 | |||||||
Tomb | 38 | 8 | 2 | 2 | 3 | ||||||||
Apr | Glass field | 155 | 2 | 10 | 13 | 269 | |||||||
Copse | 4 | 3 | 1 | 1 | 4 | ||||||||
Mountain road | 59 | 6 | 4 | 1 | 2 | ||||||||
Tomb | 1 | 1 | 2 | ||||||||||
May | Glass field | 50 | 2 | 720 | |||||||||
Copse | 360 | 1 | |||||||||||
Mountain road | 200 | 4 | 15 | 3 | 29 | 3 | |||||||
Tomb | 34 | 5 | 14 | ||||||||||
Jun | Glass field | 220 | 3 | 8 | 618 | ||||||||
Copse | 120 | 10 | 33 | ||||||||||
Mountain road | 160 | 11 | 1 | 28 | |||||||||
Tomb | 11 | 6 | 7 | ||||||||||
Jul | Glass field | 13 | 71 | 6 | 1 | 405 | |||||||
Copse | 30 | 14 | 15 | 58 | |||||||||
Mountain road | 2 | 11 | 67 | ||||||||||
Tomb | 42 | 22 | 53 | ||||||||||
Aug | Glass field | 11 | 4 | 5 | 40 | 402 | |||||||
Copse | 110 | 3 | 12 | 1 | |||||||||
Mountain road | 13 | 27 | 112 | ||||||||||
Tomb | 11 | 6 | 47 | ||||||||||
Sep | Glass field | 64 | |||||||||||
Copse | 3 | 2 | 7 | 5 | |||||||||
Mountain road | 28 | 2 | 4 | 1 | 4 | 5 | |||||||
Tomb | 2 | 1 | |||||||||||
Oct | Glass field | 141 | |||||||||||
Copse | 50 | 1 | |||||||||||
Mountain road | |||||||||||||
Tomb | 90 | ||||||||||||
Nov | Glass field | 280 | 13 | 18 | 10 | 1 | 14 | 365 | |||||
Copse | 2 | 3 | 9 | 2 | 8 | ||||||||
Mountain road | 3 | ||||||||||||
Tomb | 1 | 1 | |||||||||||
Total | 610 | 0 | 1,556 | 52 | 230 | 44 | 548 | 50 | 3,090 |
In total 1,569 ticks from the genus
In May, the distribution of
Distributional studies of ticks based on the developmental stages collected from the four environments in Jeju
Month | Environment | Tick number | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Larva | Nymph | Male | Female | Total | Larva | Nymph | Male | Female | Total | ||||
N (%) | |||||||||||||
May | Mountain road | 262 | 1 | 2 | 265 | 6 | 3 | 5 | 14 | 279 (17.8) | |||
Tomb | 41 | 2 | 43 | 6 | 2 | 1 | 9 | 52 (3.3) | |||||
Copse | 323 | 8 | 30 | 361 | 11 | 8 | 13 | 32 | 393 (25.1) | ||||
Glass field | 126 | 1 | 4 | 131 | 2 | 4 | 3 | 9 | 140 (8.9) | ||||
Jun | Mountain road | 184 | 5 | 4 | 193 | 193 (12.3) | |||||||
Tomb | 2 | 140 | 2 | 1 | 145 | 145 (9.2) | |||||||
Copse | 305 | 1 | 306 | 5 | 5 | 311 (19.8) | |||||||
Glass field | 44 | 1 | 7 | 52 | 4 | 4 | 56 (3.6) | ||||||
Total | 2 (0.1) |
1,425 (90.8) |
19 (1.2) |
50 (3.2) |
1,496 (95.3) |
2 (0.1) |
27 (1.7) |
13 (0.8) |
31 (2.0) |
73 (4.7) |
1,569 (100) |
We monitored 3,090 ticks (Trap) and 1,569 ticks (Flagging method) in pooled samples for the presence of SFTSV using RT-PCR. 235 Pools (Trap) and 129 Pools (Flagging method) consisted of 50 larvae, 30 nymphs, and 5 adult ticks per pool were set up at each collected site. All the ticks tested were confirmed to be negative for SFTSV (Figure 2).
Infectious-disease vectors, such as mosquitoes and ticks, are sensitive to climate change. Rising temperatures and increased precipitation may lead to increased lifespans, increased metabolic rates, and increased reproductive rates. These changes in ecological factors may result in higher incidence and greater spread of infectious diseases, emergence of new allergens, and genetic mutations [1].
Ticks are usually collected along the boundary of a forested area, a hillside with copses of trees, and burial sites. These environments provide opportunities for population growth and proliferation while using wild animals as hosts. In these situations, common infectious diseases vectored by external parasites can take hold.
When using tick traps, we collected the most ticks in grass fields, followed by copses, mountain roads, and tombs, in descending order. When using the flagging method, we collected the most ticks in copses, followed by mountain roads, tombs, and grass fields, again in descending order (Table 6). Therefore, continuous monitoring for SFTSV will be required in all collection environments. Ticks were collected monthly using tick traps. Ticks were collected in May and June using the flagging method.
Thirty-two species of ticks have been reported in Korea. In this survey,
Ticks consist of the steps of egg-larva-nymph-adult. When hatching from an egg, a tick becomes a larva with three pairs of legs, adhering to the host during the larval and nymph infestation period, and then molting to develop into an adult. Differences in the developmental stages occur according to the season. In the case of the widely distributed
As a way to diagnose SFTSV, Yun et al [14] examined the medium segment gene, a specific gene of SFTSV, using RT PCR for
제주지역의 4개 환경(초지, 잡목림, 산길, 무덤)에서 2018년 3월부터 11월까지 진드기 채집을 통하여 진드기의 분포 특성 및 SFTSV 병원체 보균 여부를 조사하였다. Tick trap을 이용해 채집된 3,095마리와 flagging을 이용하여 채집된 1,569마리를 채집하였다. 총 4,664마리의 채집된 진드기 중에서
This study was supported by fund (code: 4851-304) of the Korea Centers for Disease Control.
None
Chung KA, Professor; Song HJ, Professor; Lee HJ, Professor; Park C, Professor; Seo MY, Professor.