Tick-Borne Infections in Humans : Aspects of immunopathogenesis, diagnosis and co-infections with Borrelia burgdorferi and Anaplasma phagocytophilum

Sammanfattning: The tick-borne infectious agents, B. burgdorferi, A. phagocytophilum and the TBE-virus, can all cause clinical disease in humans and may all initially give rise to myalgia, arthralgia, headache and fever. The clinical manifestations of the infections range from subclinical or mild to severe, in some cases with a postinfectious sequel, and mixed infections may occur, confusing the clinical picture.The aim of this thesis was to investigate the occurrence and co-existence of these infections in a Scandinavian context. A further aim was to study aspects of the immunopathogenesis of B. burgdorferi infection and possible effects on the immune response when previously exposed to A. phagocytophilum. Finally, an attempt was made to improve the laboratory diagnosis of Lyme neuroborreliosis (LNB).In a prospective clinical study, patients were recruited based on two independent inclusion criteria; 1) patients with unspecific symptoms or fever, and 2) patients with erythema migrans (EM). Among 206 patients, we found 186 cases of Lyme borreliosis (LB) (174 with EM), 18 confirmed and two probable cases of human granulocytic anaplasmosis (HGA), and two cases of Tick-borne encephalitis (TBE). Thirteen of the HGA cases presented without fever. Furthermore, 22 of the EM patients had a subclinical co-infection with A. phagocytophilum, based on serology. Both TBE cases had co-infections, one with B. burgdorferi and one with A. phagocytophilum.In another investigation, IL-12p70 secretion in patients with current LB was compared in patients with or without previous A. phagocytophilum infection. Patients with serological evidence of previous exposure to A. phagocytophilum had a lower B. burgdorferi-induced IL-12p70 secretion. Since IL-12p70 induces the Th1 response, this finding indicates a reduced Th1 response, possibly caused by A. phagocytophilum. In a separate study, we showed that patients with LNB had increased levels of cytokines associated with cytotoxicity in cerebrospinal fluid (CSF), including the recently described cytokine IL-17.Since it is known that the adaptive immune system, especially the T cells, is activated during an infection with B. burgdorferi, a modified ELISPOT assay using cells from CSF was evaluated to be a useful complementary test in diagnosing LNB. However, we found that the diagnostic performance was too weak in our setting, and we could not recommend it for use in clinical laboratories at this stage.In conclusion, tick-borne co-infections are probably quite common in Sweden. Our HGA cases were most often discovered as co-infections with LB and would probably have been missed during a routine consultation. They presented with mild symptoms and often without fever, which in previous reports has been part of the disease definition.The immune response in LNB was shown to be compartmentalized to the target organ, also in terms of cytokine response. Furthermore, we found indications of possible long-term effects of A. phagocytophilum infection, demonstrated as a reduced IL-12p70 secretion in patients with ongoing LB. This could be a disadvantage when mounting a Th1 response to infection with B. burgdorferi. If this is so, the inter-play of these infectious agents in co-infections or consecutive infections may be of importance to clinical outcome.