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

Abstract

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. 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 . 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 . 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.