Abstract
BackgroundRickettsiae constitute a group of arthropod-borne, Gram-negative, obligate intracellular bacteria that are the causative agents of diseases ranging from mild to life threatening that impact on medical and veterinary health worldwide.MethodsA total of 6,484 ticks were collected by tick drag from June-October 2013 in the southwestern provinces of the Republic of Korea (ROK) (Jeollanam, n = 3,995; Jeollabuk, n = 680; Chungcheongnam, n = 1,478; and Chungcheongbuk, n = 331). Ticks were sorted into 311 pools according to species, collection site, and stage of development. DNA preparations of tick pools were assayed for rickettsiae by 17 kDa antigen gene and ompA nested PCR (nPCR) assays and the resulting amplicons sequenced to determine the identity and prevalence of spotted fever group rickettsiae (SFGR).ResultsHaemaphysalis longicornis (4,471; 52 adults, 123 nymphs and 4,296 larvae) were the most commonly collected ticks, followed by Haemaphysalis flava (1,582; 28 adults, 263 nymphs and 1,291 larvae), and Ixodes nipponensis (431; 25 adults, 5 nymphs and 401 larvae). The minimum field infection rate/100 ticks (assuming 1 positive tick/pool) was 0.93% for the 17 kDa antigen gene and 0.82% for the ompA nPCR assays. The partial 17 kDa antigen and ompA gene sequences from positive pools of H. longicornis were similar to: Rickettsia sp. HI550 (99.4–100%), Rickettsia sp. FUJ98 (99.3–100%), Rickettsia sp. HIR/D91 (99.3–100%), and R. japonica (99.7%). One sequence of the partial 17 kDa antigen gene for H. flava was similar to Rickettsia sp. 17kd-005 (99.7%), while seven sequences of the 17 kDa antigen gene obtained from I. nipponensis ticks were similar to R. monacensis IrR/Munich (98.7–100%) and Rickettsia sp. IRS3 (98.9%).ConclusionsSFG rickettsiae were detected in three species of ixodid ticks collected in the southwestern provinces of the ROK during 2013. A number of rickettsiae have been recently reported from ticks in Korea, some of which were identified as medically important. Results from this study and previous reports demonstrate the need to conduct longitudinal investigations to identify tick-borne rickettsiae and better understand their geographical distributions and potential impact on medical and veterinary health, in addition to risk communication and development of rickettsial disease prevention strategies.
Highlights
Rickettsiae constitute a group of arthropod-borne, Gram-negative, obligate intracellular bacteria that are the causative agents of diseases ranging from mild to life threatening that impact on medical and veterinary health worldwide
There exists: (i) the spotted fever group Rickettsia (SFGR) (e.g. Rickettsia conorii, R. rickettsii and R. japonica, the causative agents of Mediterranean, Rocky Mountain, and Japanese spotted fever, respectively, that are transmitted by ixodid ticks); (ii) the typhus group (TGR) (e.g. R. typhi, the causative agent of murine typhus transmitted by fleas, and R. prowazekii, the causative agent of epidemic typhus transmitted by the body louse); (iii) the transitional group (TRGR) transmitted by fleas, mites and ticks; (iv) the R. bellii group; (v) the R. canadensis group; (vi) the Helvetica group; (vii) the Scapularis group; (viii) the Adalia group; and (ix) the Hydra group [1,2,3,4]
1/108 (0.93%) and 0/108 (0%) of H. flava were positive for Rickettsia spp. using the partial 17 Rickettsia-specific outer membrane antigen gene (kDa) and ompA genes, respectively, while 7/35 (20.00%) pools of I. nipponensis were positive for R. monacensis
Summary
Rickettsiae constitute a group of arthropod-borne, Gram-negative, obligate intracellular bacteria that are the causative agents of diseases ranging from mild to life threatening that impact on medical and veterinary health worldwide. Rickettsia species are obligate intracellular bacteria in the order Rickettsiales that infect a variety of vertebrate hosts, including humans via arthropod vectors [1]. Ixodid ticks (e.g. Haemaphysalis flava, H. longicornis, Ixodes persulcatus and I. nipponensis in Asia; I. ricinus in Europe; Rhipicephalus sanguineus, Dermacentor andersoni, D. variabilis, Amblyomma americanum and Am. maculatum in America) are the primary vectors/reservoirs of a wide range of rickettsiae of medical and veterinary importance (e.g. R_japonica, R. rickettsii, R. conorii, R. honei, R. sibirica, R. slovaca and R. monacensis) that affect birds, wild and domestic animals, and humans in Japan, Mongolia, South Korea, Russia and China [5,6,7,8,9,10,11]
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