Contact with horses is a risk factor for tick-borne lymphadenopathy (TIBOLA): a case control study

Tick-borne lymphadenopathy (TIBOLA) is an emerging infection caused by Rickettsia slovaca. We describe here the seasonal, age and gender characteristics as well as the association with horse contact as risk factors for acquiring TIBOLA in comparison with another, more frequent tick-borne disease, Lyme borreliosis.We analysed a dataset of 855 patients diagnosed with either Lyme (n = 805) or TIBOLA (n = 50) disease using Fisher's exact tests and generalized linear models. Then we performed a matched case-control study in which all TIBOLA patients were paired with one Lyme patient matching in age and gender. We identified the species of ticks collected from the TIBOLA patients (n = 16).We found that horse contact was significantly more frequent among TIBOLA (34/50; 68 %) than among Lyme patients (110/805; 13.7 %) (OR = 13.35, p < 0.001). The younger age and female gender associated with higher risk of acquiring TIBOLA (OR = 3.99, p < 0.001). Ten of the 16 ticks were D. marginatus, six were D. reticulatus suggesting that both species are responsible for transmitting R. slovaca. Two patients acquired the infection from male ticks. TIBOLA is a tick-borne zoonosis, which might have a specific association with horse contact.