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A total of 1,618 ticks [420 individual (adults) and pooled (larvae and nymphs) samples], 369 rodents (Apodemus agrarius, Rattus norvegicus, Tscherskia triton, Mus musculus, and Myodes regulus), and 34 shrews (Crocidura lasiura) that were collected in northern Gyeonggi-do near the Demilitarized Zone (DMZ) of Korea during 2004-2005, were assayed by PCR for selected zoonotic pathogens. From a total of 420 individual and pooled tick DNA samples, Anaplasma (A.) phagocytophilum (16), A. platys (16), Ehrlichia (E.) chaffeensis (63), Borrelia burgdorferi (16), and Rickettsia spp. (198) were detected using species-specific PCR assays. Out of 403 spleens from rodents and shrews, A. phagocytophilum (20), A. platys (34), E. chaffeensis (127), and Bartonella spp. (24) were detected with species-specific PCR assays. These results suggest that fevers of unknown causes in humans and animals in Korea should be evaluated for infections by these vector-borne microbial pathogens.

Granulocytic anaplasmosis (GA) and monocytic ehrlichiosis (ME) are maintained in wild rodent reservoirs and tick vectors in the Republic of Korea. This study investigated the prevalence of 2 tick-borne pathogens, Anaplasma phagocytophilum and Ehrlichia chaffeensis, in wild rodents and ticks in central Korea to identify any significant associations with existing or changing climatic conditions. Specifically, the goal of this study was to develop simple models for the probability of occurrence of an epidemic of GA or ME as a function of climate in an area in a given year. Climatic data from 2 regions, Munsan and Dongducheon, Gyeonggi, in central Korea (between the Demilitarized Zone and Seoul, latitude between 37 degrees N-38 degrees N and longitude between 127 degrees E-128 degrees E), were analyzed with respect to the prevalence of GA and ME in Paju, Yoncheon, Pocheon, and Dongducheon for the period from 2001 to 2005. Rates of A. phagocytophilum and E. chaffeensis decreased as the total yearly precipitation levels and daily humidity increased, and as the daily mean sunshine hours decreased. Rates of A. phagocytophilum and E. chaffeensis from rodent ticks and rodents increased in the fall season. Linear regression analyses evaluating the numbers of positive samples by sample type found that rodent ticks were 6.64 times more likely to be actively infected with A. phagocytophilum than grass ticks or rodents, though the likelihood of any samples testing positive for this pathogen decreased by 0.17 as the annual mean level of precipitation increased by 1 mm. For E. chaffeensis, rodents were 15.67 times more likely to be infected than ticks. Logistic regression analyses evaluating each sample separately found that the odds of infection with A. phagocytophilum were nearly 5 times greater for rodents than ticks. In these analyses, precipitation was one potential factor to account for the prevalence of tickborne diseases.

In order to investigate the prevalence of tick-borne infectious agents among ticks, ticks comprising five species from two genera (Hemaphysalis spp. and Ixodes spp.) 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 of Anaplasma phagocytophilum (1 sample), Anaplasma platys (52 samples), Ehrlichia chaffeensis (29 samples), Ehrlichia ewingii (2 samples), Ehrlichia canis (18 samples), and Rickettsia 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 of A. phagocytophilum (110 samples), A. platys (68 samples), E. chaffeensis (8 samples), E. ewingii (26 samples), E. canis (51 samples), and Rickettsia sp. (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 of E. chaffeensis clustered closely with those from China and the United States, while the Rickettsia (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.