BORRELIABAKTEERI HELSINGIN PUISTOJEN PUNKEISSA

[Bb]

Lähettäjä: Soijuv Lähetetty: 21.4.2004 10:08

Helsingin puistoalueista Lehtisaaren ja Seurasaaren punkeista jopa 55 % kantoi borreliabakteeria eli borrelioosiin voi sairastua myös kaupungeissa.


Journal of Clinical Microbiology, May 1999, p. 1361-1365, Vol. 37, No. 5
0095-1137/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
Prevalence of Borrelia burgdorferi in Ixodes ricinus Ticks in Urban Recreational Areas of Helsinki

........This study shows that a considerable risk of contracting a borrelia infection can be present in an urban environment, and therefore, a large human population can be at risk. Both the density of vector ticks and the prevalence of borreliae in these vectors were higher than expected in light of previously published studies (1, 3, 9, 21, 27, 30, 33). These observations indicate a need to take Lyme borreliosis into account as one possible differential diagnosis even for patients without a history of a visit to rural areas of endemicity. In addition, the predominance of B. afzelii and absence of B. burgdorferi sensu stricto may affect the clinical picture of Lyme borreliosis in this area.

The presence of large mammals has been considered a prerequisite for Lyme borreliosis in an area of endemicity (7, 8, 32). Our observations are in dispute with these presumptions and confirm the suspicions raised by previously published results (13). None of the study areas was known to be populated by deer or elk. The most numerous mammals are small rodents (Apodemus flavicollis, Apodemus sylvaticus, and Peromyscus leucopus) and insectivores (shrews and hedgehogs), with the largest ones being the hare (Lepus timidus). The areas where ticks were most abundant were also the most capable of supporting a permanent hare population.

Official statistics of the National Public Health Institute of Finland show that the incidence of late manifestations of Lyme borreliosis is twice as high in the district of Helsinki as in the surrounding, more rural areas (13 versus 6.6 cases per 100,000 inhabitants, respectively) (22). These incidence figures may be biased. However, if a bias existed, it should affect Helsinki and its surroundings in a similar manner and should therefore not explain the observed difference. This difference suggests that our findings also have relevance for the occurrence of Lyme borreliosis in the area.

The observed distribution of genospecies is in agreement with the results of earlier studies performed in Finland and Russia (14, 28 ). B. burgdorferi sensu stricto has been detected only in the southwestern parts of Finland, and the prevalence of B. garinii seems to increase toward the eastern border. The untypeable spirochetes could possibly represent new genospecies, but further studies are needed to confirm their identities.

If all reservoir animals were equally and nonexclusively favorable hosts for both B. afzelii and B. garinii, the expected number of mixed infections would be significantly higher than the number observed in this study. The low number of concurrent infections suggests that these two genospecies favor two distinct reservoir animal populations. Because these genospecies did, however, coexist in two adult ticks, significant competition between them in culture media or tick tissues is unlikely. The total lack of B. burgdorferi sensu stricto may indicate that there are no suitable reservoirs for this genospecies in the areas studied.

DF microscopy, culture, and PCR analysis have all been used in studies on the borrelia infestation rates of ticks (35). However, extensive comparisons between these methods have not been available. According to the present study, DF microscopy seems to be the method of choice in surveillance studies, with culture and PCR analysis being complementary in nature.

We conclude that dense populations of I. ricinus ticks heavily infested with B. burgdorferi can exist even in urban environments not populated with large mammals like deer or elk. Inhabitants and health care officials of cities should be made more aware of the risk of contracting Lyme borreliosis in parks or other recreational areas harboring infected ticks.


http://jcm.asm.org/cgi/content/full/37/ ... d=10203487