We were very interested in the discovery and comprehensive investigation by Dieme et al. (1) of mosquitos as potential vectors for Rickettisa felis. We would like to draw attention to another ectoparasite that we encountered as a possibly overlooked potential vector for rickettsial infections: the leech. In 2008, a 39-y-old diabetic woman was admitted to a hospital in Northern Laos with a 7-d history of fever, headaches, limb pains, chills, and 2 d of nausea and vomiting. She had a typical eschar on her right anteromedial thigh (7 × 4 mm) (Fig. 1). She remembered being bitten by a terrestrial leech (Haemadipsida spp.), while working in a rice field, exactly at the eschar site 5 d before onset of fever. No tick or other ectoparasite was observed at this site until eschar manifestation. Molecular characterization of eschar biopsy revealed amplicons of 100% identity to the Rickettsia felis-URRWXCal2 strain (2). The patient responded promptly to treatment with oral doxycycline.

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Fig. 1.

Typical eschar at the right anteromedial thigh at the site of a leech bite in the patient with R. felis infection.

Balcells et al. (3) reported rickettsiosis from Chile with a characteristic eschar at the site of a bite by a terrestrial leech (Xerobdellidae). Molecular analysis of eschar and skin biopsy revealed 97% sequence similarity with isolates of Orientia tsutsugamushi. Closely related Rickettsia species have been described in leeches (Glossiphoniidae) of frogs and fish in Japan with nearly 100% vertical transmission (4).

Leech bites are uncommon in urban environments but might play a considerable role in endemic rural areas. In a household survey in the patient’s village in 2010, 146 (75.3%) of 194 villagers aged ≥15 y reported that they had been bitten by leeches in the previous year. Leech bites were associated in multivariate analysis with being a farmer and younger age (both P < 0.001), and correlated with frequency of field visits (Pearson’s correlation coefficient r = 0.15, P = 0.04). Bites were noted mainly during the raining season (Haemadipsida spp.: 5.17 bites per month vs. 0.58 per month during the dry season, P < 0.001). Of the villagers, 113 of 194 (58.2%) associated health problems with leech bites; 85 (43.8%) had itching, 30 (15.5%) a rash, 25 (12.9%) bleeding, 16 (8.2%) scratches/wounds, 8 (4.1%) pain, and 7 (3.6%) infection, including 2 (1.0%) with febrile illnesses. Three villagers (1.5%) reported seeking hospital treatment after leech bites.

No data of Rickettisa spp. within Laos leeches are yet available. So far, global research has focused mainly on nosocomial Aeromonas infections by medicinal leeches. Recent studies of leeches’ digestive tract microbiota suggest more diverse potential infection transmission by leeches (5). Transmission might not only occur via the bite per se, but could be exacerbated during removal by human manipulation, such as squeezing, dropping salt solutions on leeches, or burning them. The wound could also be inoculated with regurgitated blood from previous hosts. Further parasitological and microbiological research is needed to clarify the role of leeches as potential vectors for infectious diseases.