Leptospira Status in Sweden during the Past Century, Neglected and Re-Emerging?

Abstract

We compiled data on notified cases of leptospirosis in animals and humans in Sweden. Published studies on leptospirosis in humans and animals from the beginning of the 20th century onwards are summarized. During the Second World War, hundreds of leptospirosis cases in humans were reported in Sweden, but since then, there have been only a few severe cases. Surveillance of leptospirosis in domestic animals demonstrates that the pathogen is still occurring. The occurrence of Leptospira in humans and animals in the other Nordic countries resembles that in Sweden. Leptospirosis is an underdiagnosed and underreported disease globally, both in animals and humans, partly due to the lack of simple, rapid diagnostic tools but possibly also due to the lack of awareness among physicians, veterinarians and nurses. Traditionally, leptospirosis has been mostly diagnosed by serology, but development of molecular methodshas improved the capability for correct diagnosis. As of today, leptospirosis is regarded as a relatively uncommon disease in the Nordic countries, but in some other countries, it is considered a neglected zoonosis or a (re-)emerging disease that may become more common in the future. Possible factors that could contribute to an increase in incidence are discussed in this review. Active surveillance of humans and domestic and wild animals and stringent rodent control in society and animal farms are of outmost importance for prevention.

Keywords: Leptospira; One Health; microscopic agglutination test; surveillance; zoonosis.

Figure 1

Number of reported human leptospirosis cases in Sweden from 1936 to 2022 (for data availability, see the Materials and Methods). Up to 1980, the numbers were based on clinical reports and, for most of the cases, it is unknown if the diagnosis was laboratory-confirmed or not. From 1998 to 2003, leptospirosis was not notifiable. From 2004 onwards, it has been mandatory for the treating physician to report laboratory-confirmed cases.