Hiding in plain sight: Leptospirosis and rickettsial disease Unmasking two causes of severe imported infections

Leptospirosis and rickettsial diseases are zoonotic diseases that are increasingly identified worldwide, but the burden of both illness remains largely unidentified. This thesis aimed to add to the knowledge of the epidemiology of both illnesses. We showed that leptospirosis and rickettsial disease are underestimated causes of febrile illness worldwide. Leptospirosis was found to be prevalent in the sub-Saharan African region, but the scale of the problem remains largely unknown due to a lack of epidemiological studies. Travel-related leptospirosis was increasingly observed, both in the Netherlands, as well as in Geosentinel travel clinics worldwide. Geosentinel is a global sentinel surveillance netwerk for infectious diseases in travellers. This was possibly due to increased travelling, and the introduction of polymerase chain reaction (PCR) in the diagnostic algorithm. However, we found that the diagnostic accuracy of these PCR and other nucleic acid and antigen detection tests for the diagnosis of acute leptospirosis has not been firmly confirmed. Because of the high variability between studies performed on this subject, it is hard to draw firm conclusions about the accuracy of these tests, and their position in the testing pathway of leptospirosis.
For rickettsial diseases, despite being a more widely recognised disease entity worldwide, the problem of lack of awareness at a local level was also a problem. We found that especially rickettsial disease presenting without an eschar was vastly underestimated in endemic areas. The same applied to returned travellers with febrile illness that had presented in the travel clinic of the Academic Medical Center. These findings show that rickettsial diseases are a cause of illness that should not be underestimated.