Tick-Borne Rickettsial Pathogens in Ticks and Small Mammals in Korea

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Abstract
In order to investigate the prevalence of tick-borne infectious agents among ticks, ticks comprising five species from two genera (Hemaphysalisspp. andIxodesspp.) were screened using molecular techniques. Ticks (3,135) were collected from small wild-caught mammals or by dragging/flagging in the Republic of Korea (ROK) and were pooled into a total of 1,638 samples (1 to 27 ticks per pool). From the 1,638 tick samples, species-specific fragments ofAnaplasma phagocytophilum(1 sample),Anaplasma platys(52 samples),Ehrlichia chaffeensis(29 samples),Ehrlichia ewingii(2 samples),Ehrlichia canis(18 samples), andRickettsia rickettsii(28 samples) were amplified by PCR assay. Twenty-one pooled and individual tick samples had mixed infections of two (15 samples) or three (6 samples) pathogens. In addition, 424 spleen samples from small captured mammals (389 rodents, 33 insectivores, and 2 weasels) were screened for selected zoonotic pathogens. Species-specific DNA fragments ofA. phagocytophilum(110 samples),A. platys(68 samples),E. chaffeensis(8 samples),E. ewingii(26 samples),E. canis(51 samples), andRickettsiasp. (22 samples) were amplified by PCR assay. One hundred thirty small mammals had single infections, while 4, 14, and 21 striped field mice (Apodemus agrarius) had mixed infections of four, three, and two pathogens, respectively. Phylogenetic analysis based on nucleotide sequence comparison also revealed that Korean strains ofE. chaffeensisclustered closely with those from China and the United States, while theRickettsia(rOmpA) sequences clustered within a clade together with a Chinese strain. These results suggest that these agents should be considered in differential diagnosis while examining cases of acute febrile illnesses in humans as well as animals in the ROK.