Mild Infections with Multiple Spotted Fever Grouped Rickettsia Species among Forest Rangers with Tick Bites

Abstract

Objectives: Tick-borne rickettsiae are increasingly recognized to cause human infections; however, a complete clinical spectrum is lacking. Thus, surveillance study was conducted among forest rangers with tick bites to describe the clinical manifestations. Methods: One hundred fifty-nine blood samples were obtained from individuals bitten by ticks and 780 tick samples collected in the same endemic region were examined for the presence of Rickettsia. Serum samples were tested for IgM and IgG antibodies against R. heilongjiangensis. Results: Twenty-five (15.7%) individuals were shown to be infected with 5 Rickettsia species, including 14 Candidatus Rickettsia tarasevichiae (CRT), 8 R. raoultii, 1 R. felis, 1 R. heilongjiangensis, and 1 R. massiliae. Five individuals (1 CRT, 1 R. heilongjiangensis, and 3 R. raoultii) had mild illnesses; the other 20 individuals were asymptomatic. CRT was present in 38.4% (274/713) of I. persulcatus and 6.4% (3/47) of Hae. concinna. R. raoultii was demonstrated in 30.0% (6/20) of D. silvarum and 14.9% (7/17) of Hae. concinna. R. heilongjiangensis was detected in 9.5% (2/21) of D. silvarum and 0.3% (2/713) of I. persulcatus. Conclusions: The clinical manifestations of these rickettsioses were non-specific and differed from traditional features, thus supporting the necessity of wider investigations involving individuals with tick bites to develop an early differential diagnosis.