106 Am. J. Trop. Med. Hyg., 62(1), 2000, pp. 106–111 Copyright  2000 by The American Society of Tropical Medicine and Hygiene SEROLOGIC EVIDENCE OF PUUMALA VIRUS INFECTION IN WILD MOOSE IN NORTHERN SWEDEN CLAS AHLM, KJELL WALLIN, A ˚ KE LUNDKVIST, FREDRIK ELGH, PER JUTO, MALIK MERZA, AND ARNE TA ¨ RNVIK Department of Infectious Diseases, and Department of Virology, University of Umea ˚, Umea ˚, Sweden; Department of Applied Environmental Science, University of Go ¨teborg, Go ¨teborg, Sweden; Department of Animal Ecology, Swedish University of Agricultural Sciences, Umea ˚, Sweden; Swedish Institute for Infectious Disease Control and Microbiology and Tumour Biology Centre, Karolinska Institute, Stockholm, Sweden; Department of Microbiology, Division of Nuclear, Biology and Chemistry Defence, Defence Research Establishment, Umea ˚, Sweden; Department of Virology, The National Veterinary Institute, Uppsala, Sweden Abstract. Puumala (PUU) virus is the causative agent of nephropathia epidemica, the Scandinavian form of hemorrhagic fever with renal syndrome. The infection is acquired by airborne transmission of PUU virus from its rodent reservoir, the bank vole. Besides serologic data indicating that the virus may spread also to heterologous rodents, there is little information on the susceptibility of wild living animals to PUU virus. We studied the occurrence of antibodies to PUU virus in serum samples from 427 wild-living moose, of which 260 originated from the PUU virus-endemic northern and central parts of Sweden and 167 originated from the southern, nonendemic part of Sweden. Samples from 5 animals showed reactivity in an ELISA for recombinant PUU virus nucleocapsid protein, an im- munofluorescent assay, and a neutralization test. These 5 animals all originated from the PUU virus-endemic northern part of Sweden. In conclusion, 5 of 260 moose from the endemic region showed convincing serologic evidence of past PUU virus infection. The seroprevalence was low, suggesting that the moose is subjected to endstage infection rather than being part of an enzootic transmission cycle. Members of the genus Hantavirus (family Bunyaviridae) are associated with zoonotic diseases, which are grouped in 2 clinical syndromes. 1,2 Hemorrhagic fever with renal syn- drome (HFRS), which occurs in Europe and Asia, is caused by Hantaan (HTN), Seoul (SEO), Dobrava (DOB), and Pu- umala (PUU) virus. 3 The severity of HFRS varies with the causative agent, with the fatality rate ranging from 5% to 15% in HTN to 0.5% in PUU virus infection. Hantavirus pulmonary syndrome (HPS) occurs in North and South America and is caused by Sin Nombre virus (SNV). This syndrome is a fulminant disease with a fatality rate of 50%. 4 Due to an increased awareness of the heterogeneity of viruses within the genus, new hantaviruses are currently identified and linked to the syndromes. 5–9 Hantaviruses are associated with rodents. The association is strictly regulated insofar as each virus tends to be adapted preferentially to one given species of rodents. The animals are held to be persistently infected with the virus and trans- mission among the animals seems to occur mainly via aero- solized excretions. 10–12 This host restriction suggests that the evolution of hantaviruses is more or less restricted by the evolution of rodents. 13 In addition to its circulation within a rodent reservoir, a hantavirus may also infect heterologous wild living rodents and other mammals. 13–17 However, data on such spread is not yet comprehensive. The information is based largely on sur- veys comprising limited numbers of mammals of various species and less on thorough investigations of specific virus- mammal associations. The obvious exception is humans, in which the spread of hantavirus infection is well elucidated. Human infection is believed to be acquired by inhalation of aerosols containing contaminated rodent secreta. Except for single case descriptions of person-to-person transmission, 18 there is no evidence to indicate that infected humans may contribute to further spread of hantaviruses. In Scandinavia, PUU virus has been the only hantavirus isolated so far. It is the causative agent of nephropathia ep- idemica (NE), the mild form of HFRS. In Sweden, NE oc- curs only in the northern and central parts of the country. During rodent-rich years in the region, the annual incidence may exceed 30 cases per 100,000 inhabitants. 19 In a random- ized and stratified study from northern Sweden, a prevalence of PUU virus antibodies of 9% was found in the adult pop- ulation. 20 The reservoir of PUU virus is the bank vole Clethriono- mys glareolus. This is apparent from successful attempts to isolate virus from tissue samples as well as from serologic investigations. 21–23 Moreover, serologic investigations verify that rodent species other than the bank vole may become infected. In studies of small mammals captured in northern Sweden, bank voles were found to have antibodies to PUU virus much more frequently than did rodents of other spe- cies. 19,24 As is true for hantaviruses in general, there is only limited information on the susceptibility to PUU virus infection of mammals other than humans and rodents. We attempted to find serologic evidence of hantavirus infection in the Swed- ish moose (Alces alces), an animal that is well characterized with regard to living habitat and migration. The study com- prised animals from PUU virus-endemic regions as well as nonendemic regions, and due to the lack of serologic back- ground data in moose, the observations were validated by use of different serologic techniques. MATERIALS AND METHODS Sampling of blood from wild-living moose. During 1995–1997, 427 moose (205 females, 202 males, and 20 sex undetermined) were investigated. As appears from the age distribution (Figure 1), a large proportion of the animals were calves. Six geographically separated areas were rep- resented (Figure 2), each measuring 2,500–5,000 km 2 . The moose were darted from a helicopter (Hughes 500E; The Boeing Company, Seattle, WA) during the winter. They were