T. Junttila et al., Prevalence of Borrelia burgdorferi in Ixodes ricinus ticks in urban recreational areas of Helsinki, J CLIN MICR, 37(5), 1999, pp. 1361-1365
Lyme borreliosis, an infection caused by the tick-borne spirochete Borrelia
burgdorferi, is a major health problem for populations in areas of endemic
ity in the Northern Hemisphere. In the present study we assessed the densit
y of ticks and the prevalence of B, burgdorferi sensu late among ticks in p
opular urban recreational areas of Helsinki, Finland, Altogether 1,688 Ixod
es ricinus ticks were collected from five areas located within 5 km of the
downtown section of Helsinki, and 726 of them (303 nymphs, 189 females, and
234 males) were randomly chosen for laboratory analysis. The midguts of th
e ticks were divided into three pieces, one for dark-field microscopy, one
for cultivation in BSK-II medium, and one for PCR analysis. Ticks were foun
d in all the study areas; their densities varied from I to 36 per 100 m alo
ng which a cloth was dragged. The rate of tick infection with B, burgdorfer
i sensu lato varied from 19 to 55%, with the average being 32%. Borellia af
zelii was the most predominant genospecies in all the areas, and no B. burg
dorferi sensu stricto isolates were detected. Only two ticks were concurren
tly infected with both B. afzelii and Borrelia garinii, Dark-field microsco
py gave more positive results for B. burgdorferi than did cultivation or PC
R analysis. However, the agreement between all three methods was fairly goo
d. We conclude that Lyme borreliosis can be contracted even in urban enviro
nments not populated with large mammals like deer or elk. The disease shoul
d be taken into account in the differential diagnosis of certain symptoms o
f patients from these areas, and the use of measures to improve the awarene
ss of the general population and health care officials of the risk of contr
acting the disease is warranted.