Research Article: Ehrlichia species in pond-farmed leeches (Hirudinaria sp.) in Hubei Province, China

Date Published: April 8, 2019

Publisher: Public Library of Science

Author(s): Shu-Han Zhou, Xiao Xiao, Yi-Na Sun, Xiao-Hui Xu, Xin Ding, Si-Yi Zhang, Min Zhang, Wen-Liang Lv, Qing-Hua Gao, J. Stephen Dumler.


Leeches are frequently used in traditional Chinese medicine. However, they are potentially hazardous to human and animal health by transmitting several pathogens. Studies of diseases transmitted by leeches are scarce. The purpose of this study was to analyze the pathogens carried in pond-farmed medicinal leech in China. Leeches were collected from 6 farms in Hubei Province in central China. DNA was extracted from the internal organ of leeches to analyze the origin of blood meal. Leech genera were confirmed through amplification of 18S rRNA and mitochondrial gene cytochrome oxidase I (COI) gene by PCR and host animal species were identified through amplification of mitochondrial cytochrome b gene. Species of Ehrlichia in the leech specimens were screened with PCR using specific primers. PCR amplification and DNA sequencing showed that 620 leeches were Hirudinaria sp. Ehrlichia DNA was detected in 39 specimens from 2 farms. We obtained a total of 65 sequences of the cytB gene from 620 leech internal organ samples including sequences of human (n = 5), rat (n = 1), domestic pig (n = 10), duck (n = 23), goose (n = 12) and buffalo (n = 14). Phylogenetic analysis of the rrs and groEL gene sequences showed that Ehrlichia detected in the study were closely related to Ehrlichia sp. in ticks from Korea and Japan. To the best of our knowledge, this is the first report on Ehrlichia DNA being detected from leeches. Our findings provided new data on Ehrlichia spp. and farmed leech species in China.

Partial Text

Various leech species have been used worldwide in complementary medicine for centuries. Leeches secrete a complex mixture of different pharmacologically and biologically active substances into the wound while feeding[1]. Previous studies indicated that mammalian viruses, bacteria and bacteriophages persisted in the gut of leeches in large numbers for 23 weeks to more than 6 months [2, 3]. Leeches fed on the blood of different wild animals might be expected to bring about severe diseases by transmitting infectious agents that cause erysipelas (Streptococcus sp.), syphilis (Treponema pallidum), tetanus (Clostridium tetani), hog cholera (hog-cholera virus), and hospital wound infection (Aeromonas hydrophila) [2, 4–6]. Both Bartonella sp. and B. grahamii were detected from DNA extracted from terrestrial leeches (Haemadipsa rjukjuana)[7]. Leeches (Haemadipsida spp.) in Laos were reported as further potential vectors for Rickettsia infections[8]. Rickettsia DNA was also detected in field-collected specimens of Torix tukubana, Torix tagoi and Hemiclepsis marginata. Eggs produced by infected females of T. tagoi and H. Marginata were all tested Rickettsia-positive[9]. Ozobranchus (turtle leech) were also reported as a potential mechanical vector for the fibropapilloma-associated turtle herpesvirus[10]. Reports have also been published on experimental infection of leeches by classical swine fever virus, bovine parvovirus, feline calicivirus, equine arteritis virus, equine herpesvirus type 1, and infectious viruses were successfully reisolated from the leeches’ abdominal cavity blood at 23–29 weeks after inoculation[2]. Previous surveys over infectious agents transmitted by leeches in China were very limited. Therefore, the aim of this study was to investigate the prevalence of Ehrlichia in the pond-farmed leeches in the region of Hubei Province, central China.

Medicinal leech therapy has a long history in complementary medicine. However, studies recently suggested that leeches might be promising candidates as vectors of pathogens. To the best of our knowledge, this is the first report of Ehrlichia DNA being detected from leeches. Previous studies demonstrated that terrestrial leeches feeding on humans and animals contained Bartonella spp. in South Korea, and a woman in Laos was confirmed Rickettsia felis infection after being bitten by a terrestrial leech (Haemadipsida spp.) [7, 8]. These results suggest that leeches may harbor zoonotic bacteria and leech therapy pose potential risks of patients becoming infected with zoonotic agents. The genus Ehrlichia consists of several species of obligate Gram-negative intracellular bacteria that is transmitted to vertebrates by tick bites [21]. E. chaffeensis is the major etiologic agent of human monocytotropic ehrlichiosis (HME), and canine monocytic ehrlichiosis (CME) is a serious and sometimes fatal tick-borne disease in dogs caused by E. canis[22, 23]. E.ewingii, a veterinary pathogen associated with granulocytic ehrlichiosis in dogs was also identified in four patients from Missouri in 1999 and thus became the least known agent of the human ehrlichioses[24]. The spread and maintenance of Ehrlichia involve complex zoonotic systems including vectors and persistently infected vertebrate reservoirs. Severe life-threatening illnesses, such as HME and heartwater, occur mostly in incidental hosts while infections appear to be subclinical in natural hosts. Isolation of E.chaffeensis from wild white-tailed deer (Odocoileus virginianus) confirmed their role as natural reservoir hosts[25]. Previous studies also indicated African ruminants including black wildebeest, African buffalo and eland as proposed reservoirs of E.ruminantium[26]. Rodents are the natural reservoir hosts of E.muris and several carnivores including red fox, may play a role in the epidemiology of canine ehrlichiosis [27–30]. Recently, histopathology and PCR analysis confirmed Ehrlichia infection in goats from Wuhan, Hubei Province, China[31]. Extensive diversity of Rickettsiales bacteria in multiple ticks and mosquito species was also recorded in the same region. Ehrlichia DNA was mainly found in Rhipicephalus microplus and Haemaphysalis longicornis ticks in Hubei Province, and Ehrlichia bacteria has been detected in each life stage of mosquitoes, suggesting that Ehrlichia may be maintained in mosquitoes through both transstadial and transovarial transmission[32, 33]. However, few studies have been conducted to evaluate the infection of Ehrlichiosis in human and wild animals in this region. The number of outdoor leech farms has been increasing in the past few years. However, leech farming in China is unregulated, outdoor farming facilities and environments vary greatly, from natural ponds, cement pool, net cage to net surrounded earthen pond. Live leeches have been freely sold online and shipped alive nationwide. All leeches obtained in this study were identified to be Hirudinaria species, which is a non-native, but commonly farmed genus in central China[34]. Zoonotic bacteria and viruses acquired from previous host via sucking can remain infectious in the leech gut for months [2]. While nested PCR and sequencing of amplified DNA fragments confirmed the presence of Ehrlichia in leeches, detection of Ehrlichia DNA in the leeches may represent residual Ehrlichia DNA from hosts’ blood. Since pond-farmed leeches occasionally feed on the blood of animals that likely carry various pathogens, it is necessary to isolate and characterize Ehrlichia from leeches with macrophage-derived cells to further understand the role of leeches in Ehrlichia ecology. Infection rate of Ehrlichia in leeches in different seasons might be biased due to the limited sample size. Whether leeches obtained Ehrlichia from the feeding animal hosts or they persistently carried Ehrlichia, and the possibilities of vector-host transmission, vertical or horizontal transmission of Ehrlichia in leeches also need to be further confirmed. However, to our knowledge, this is the first report of Ehrlichia DNA being detected from leeches. Our study provided new evidence on the potential role of leeches in the transmission of Ehrlichia. To further assess the prevalence and possible transmission of Ehrlichia by leeches, more extensive research is needed.

We first time detected Ehrlichia DNA in pond-farmed leeches (Hirudinaria sp.) in Hubei Province, China. Phylogenetic analysis based on the rrs and groEL genes showed that Ehrlichia sequences detected from leeches formed a clade together with uncultured Ehrlichia species from ticks in Jeju Island, ROK and Yonaguni Island, Japan. Our findings provided new data on Ehrlichia spp. and farmed leech species in China.