The importance of synanthropic wild birds in distribution of Borrelia spirochetes: analysis of spring collections of Ixodes ricinus ticks feeding on passerine birds in the Czech RepublicArchived

Dubska L (1), Literak I (1), Kocianova E (2), Taragelova V (3), Sverakova V (1), Sychra O (1), Hromadko M (4) Applied and Environmental Microbiology 2011 Feb; 77(3):1115-7. Epub 2010 Dec 10.

Ixodes ricinus ticks collected from 835 birds and vegetation in the Czech Republic were analyzed. Host-seeking ticks (n=427) were predominantly infected by Borrelia afzelii (25%). Ticks (n=1012) from songbirds (Passeriformes) were infected commonly by B. garinii (12.1%) and B. valaisiana (13.4%). Juveniles of synanthropic birds, Eurasian Blackbirds Turdus merula and Song Thrushes T. philomelos, were major reservoir hosts of B. garinii.

VBORNET comment: 2011-21-02

The authors analyse the infestation rate and the Borrelia prevalence of passerine birds and questing ticks on two sites at two different seasons. Their objective is to see if there is a difference of infestation rate and infection prevalence between seasons and between one site close to human populations (synanthropic birds) and one site at higher altitude. The large sample of bird captures (n=835) is impressive. The study shows that tick infestation rate on birds is lower in spring than in the postbreeding period. Birds from higher altitudes are less infested by Ixodes ticks and infected by Borrelia spirochetes than the ones from lower altitude.

Only few studies have been conducted on birds as hosts of vector-borne diseases. This manuscript confirms that two bird species, Eurasian blackbirds and song trushes, are largely responsible for the distribution of Borrelia genospecies, which are usually found in birds in other European countries (Borrelia garinii and Borrelia valaisiana). Indeed, these two bird species carry more ticks and are more infected than other bird species. Besides, this study highlights the altitude-dependent tick density for birds, which has been already reported for questing ticks. Finally, the difference in infestation rate between seasons shown by this report may be explained by a potential cumulative effect on infestation rate of birds.Identifying reservoir species for Borrelia is important to understand the epidemiology of the disease. We encourage this type of studies. Yet, a more advanced analysis (e.g. by using models) could have strengthen the conclusion.

References:

1. Department of Biology and Wildlife Diseases, Faculty of Veterinary Hygiene and Ecology, University of Veterinary and Pharmaceutical Sciences, Palackeho 1-3, 612 42 Brno, Czech Republic
2. Institute of Virology, Slovak Academy of Sciences, Dubravska cesta 9, 842 45 Bratislava, Slovakia
3. Institute of Zoology, Slovak Academy of Sciences, Dubravska cesta 9, 845 06 Bratislava, Slovakia
4. Halasova 824, 500 09 Hradec Kralove, Czech Republic.