Francisella tularensis subspecies holarctica occurs in Swedish mosquitoes, persists through the developmental stages of laboratory-infected mosquitoes and is transmissible during blood feeding.

In Sweden, mosquitoes are considered the major vectors of the bacterium Francisella tularensis subsp. holarctica, which causes tularaemia. The aim of this study was to investigate whether mosquitoes acquire the bacterium as aquatic larvae and transmit the disease as adults. Mosquitoes sampled in a Swedish area where tularaemia is endemic (Örebro) were positive for the presence of F. tularensis deoxyribonucleic acid throughout the summer. Presence of the clinically relevant F. tularensis subsp. holarctica was confirmed in 11 out of the 14 mosquito species sampled. Experiments performed using laboratory-reared Aedes aegypti confirmed that F. tularensis subsp. holarctica was transstadially maintained from orally infected larvae to adult mosquitoes and that 25% of the adults exposed as larvae were positive for the presence of F. tularensis-specific sequences for at least 2 weeks. In addition, we found that F. tularensis subsp. holarctica was transmitted to 58% of the adult mosquitoes feeding on diseased mice. In a small-scale in vivo transmission experiment with F. tularensis subsp. holarctica-positive adult mosquitoes and susceptible mice, none of the animals developed tularaemia. However, we confirmed that there was transmission of the bacterium to blood vials by mosquitoes that had been exposed to the bacterium in the larval stage. Taken together, these results provide evidence that mosquitoes play a role in disease transmission in part of Sweden where tularaemia recurs.

Molecular Detection of Persistent Francisella tularensis Subspecies holarctica in Natural Waters.

Tularemia, caused by the bacterium Francisella tularensis, where F. tularensis subspecies holarctica has long been the cause of endemic disease in parts of northern Sweden. Despite this, our understanding of the natural life-cycle of the organism is still limited. During three years, we collected surface water samples (n = 341) and sediment samples (n = 245) in two areas in Sweden with endemic tularemia. Real-time PCR screening demonstrated the presence of F. tularenis lpnA sequences in 108 (32%) and 48 (20%) of the samples, respectively. The 16S rRNA sequences from those samples all grouped to the species F. tularensis. Analysis of the FtM19InDel region of lpnA-positive samples from selected sampling points confirmed the presence of F. tularensis subspecies holarctica-specific sequences. These sequences were detected in water sampled during both outbreak and nonoutbreak years. Our results indicate that diverse F. tularensis-like organisms, including F. tularensis subsp. holarctica, persist in natural waters and sediments in the investigated areas with endemic tularemia.

Salmonella in Black-headed gulls ( Larus ridibundus); prevalence, genotypes and influence on Salmonella epidemiology.

During a period of 3 years, 1998-2000, 1047 faecal swabs from Black-headed gulls were sampled at one location in Southern Sweden. Salmonella spp. was found in 28 individuals (2.7%) and the dominating serotype found was S. Typhimurium (83%). Twenty-five per cent of the Salmonella-infected gulls were later recaptured and re-sampled. We found that Salmonella infection in Black-headed gulls was of short duration, and that infection in this bird species was predominantly expressed as carriage without disease manifestations. All S. Typhimurium isolates were subjected to antibiotic resistance profiling and molecular characterization by pulsed-field gel electrophoresis and IS200 polymerase chain reaction. The S. Typhimurium gull isolates were compared to human and domestic animal isolates of the same serotype and phage type. We found genetic relatedness of S. Typhimurium DT195 isolates from gulls, domestic animals and humans, indicating that Black-headed gulls might play a role in the spread of S. Typhimurium in Sweden.

Clinical studies on multiple sclerosis. I. Presentation of an incidence material from Gothenburg.

Probable and possible MS cases with a debut during the years 1950-1964 within the city of Gothenburg were identified (312 cases). This corresponds to an incidence of 5.3 per 100,000. The material was stratified according to diagnostic probability into three categories. For the final analysis cases with the lowest diagnostic probability were omitted (about 9%). The follow-up was completed during 1977, i.e. 13-27 years from onset. A longitudinal analysis of each case was based upon a mixed prospective/retrospective study in which the authors personally examined the majority of the cases during most of the years. The female/male ratio was 1.5-1.6. The mortality rate was higher for males due in part to an earlier progressive development of multiple sclerosis and in part to a higher trend for acquisition of other mortal diseases. Bouts, as the first manifestation of the disease, were more frequent in young ages than in old, and more frequent among females than in males. The averages bout frequency decreased significantly with the duration of the disease as well as with the age of onset. The opposite trend was characteristic for development of a progressive course. Among symptoms at onset, those indicating lesions of long sensory and/or motor tracts (particularly the sensory) dominated. Such initial symptoms were seen in 30-40% of the younger patients and 70% of the older patients. The rest was divided between cases with optic nerve lesions (20-30% among younger, 12-15% among older patients) and brain stem lesions (approx. 25% among younger, 10-19% among older patients). The occurrence of various symptoms during the first two decades of the disease was also analyzed and the pattern of symptoms presented graphically. These results will be treated further in subsequent studies.

Diversities and similarities in PFGE profiles of Campylobacter jejuni isolated from migrating birds and humans.

AIMS: To genetically sub-type Campylobacter jejuni strains isolated from migratory birds, and to compare these with clinical strains collected in the same area and corresponding time period, with the aim to increase our knowledge on sub-types occurring among wild birds and their possible impact on human disease. METHODS AND RESULTS: We sub-typed C. jejuni strains from migrating birds (n = 89) and humans (n = 47), using macrorestriction profiling by pulsed-field gel electrophoresis. Isolates from migrant birds often exhibited sub-types with higher levels of similarity to isolates from birds of the same species or feeding guild, than to isolates from other groups of birds. Likewise, could the vast majority of sub-types found among the migrant bird isolates not be identified among sub-types from human cases. Only two bird strains, one from a starling (Sturnus vulgaris) and one from a blackbird (Turdus merula), had sub-types that were similar to some of the human strain sub-types. CONCLUSIONS: Isolates from one bird species, or feeding guild, often exhibited high similarities, indicating a common transmission source for individuals, or an association between certain sub-types of C. jejuni and certain ecological guilds or phylogenetic groups of birds. Sub-types occurring among wild birds were in general distinctively different from those observed in patients. The two bird isolates that were similar to human strains were isolated from bird species that often live in close associations with human settlements. SIGNIFICANCE AND IMPACT OF STUDY: Wild birds have often been mentioned as a potential route for transmission of C. jejuni to humans. Our study demonstrates that strains isolated from birds most often are different from clinical strains, but that some strain similarities occur, notably in birds strongly associated with human activities.

Salmonella in sub-Antarctica: low heterogeneity in Salmonella serotypes in South Georgian seals and birds.

The number of human visitors to Antarctica is increasing rapidly, and with it a risk of introducing infectious organisms to native animals. To study the occurrence of salmonella serotypes in sub-Antarctic wildlife, faecal samples were collected from gentoo penguins, macaroni penguins, gray-headed albatrosses, black-browed albatrosses and Antarctic fur seals on Bird Island in the South Georgian archipelago during the austral summer of 1996 and 1998. In 1996, S. havana, S. typhimurium and S. enteritidis were isolated from 7% of gentoo penguins and 4% of fur seals. In 1998, however, 22% of fur seals were found to be infected with S. havana, S. enteritidis and S. newport. All isolates, except one, showed identical pulsed-field gel electrophoresis-patterns within each serotype, irrespective of sampling year and animal reservoir. No significant antibiotic resistance was found. The very low heterogeneity in the salmonella isolates found could either indicate a high genetic adaptation of the bacteria to the environment or a recent introduction of salmonella into the area.

Isolation and characterization of Campylobacter jejuni subsp. jejuni from macaroni penguins (Eudyptes chrysolophus) in the subantarctic region.

On Bird Island, South Georgia, albatrosses (n = 140), penguins (n = 100), and fur seals (n = 206) were sampled for Campylobacter jejuni. C. jejuni subsp. jejuni was recovered from three macaroni penguins (Eudyptes chrysolophus). These isolates, the first reported for the subantarctic region, showed low genetic diversity and high similarity to Northern Hemisphere C. jejuni isolates, possibly suggesting recent introduction to the area.

Campylobacter jejuni in black-headed gulls (Larus ridibundus): prevalence, genotypes, and influence on C. jejuni epidemiology.

Campylobacteriosis is a zoonotic disease in which birds have been suggested to play an important role as a reservoir. We investigated the prevalence of Campylobacter jejuni subsp. jejuni in black-headed gulls (Larus ridibundus) in southern Sweden with the aim of examining the nature of C. jejuni infection in this bird species. Birds were sampled in four sampling series each year during 1999 (n = 419) and 2000 (n = 365). Longitudinally sampled C. jejuni isolates from individual gulls were subjected to macrorestriction profiling (MRP) by pulsed-field gel electrophoresis to investigate the genotypical stability during the natural course of infection. Furthermore, a subset (n = 76) of black-headed gull isolates was compared to isolates from broiler chickens (n = 38) and humans (n = 56) originating from the same geographic area. We found a pronounced seasonal variation in C. jejuni carriage, with the highest rates found in late autumn. MRP similarities were higher between isolates of human and broiler chicken origin, than between those of wild bird origin and either of the other two hosts. However, identical MRPs were found in two gull isolates and one human isolate after digestion with two restriction enzymes, strongly indicating that they may have been colonized by the same clone of C. jejuni. The MRPs most prevalent in gull isolates did not occur among isolates from humans and broiler chickens, suggesting the existence of a subpopulation of C. jejuni adapted to species-specific colonization or environmental survival.