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Study: Most ticks carry disease, Tartu County most dangerous

A nationwide study conducted by the National Institute for Health Development (TAI) shows that most ticks in Estonia carry pathogens of some sort with Tartu, Harju, Viljandi and Valga counties most dangerous in terms of ticks. Nearly a fourth of all ticks sent in carried multiple pathogens.

Last year, TAI opened a "tick-bank" and called on people to register ticks they found on themselves or their pets, freeze them overnight and then mail them to the lab for additional testing. The ticks collected through the campaign have been used to map the spread of tick-borne diseases in Estonia.

The campaign called "Pane puuk posti" ("Mail your tick in") saw 6,400 ticks sent into the "tick-bank". Through summer and fall, the institute registered, sorted, identified species, found samples, analysed pathogens and sent out feedback. The pathogen sample consisted of 3,563 ticks, a little more than half.

"For the study results to be comparable, we created random samples so that a similar number of ticks would reach the sample from each county. When making the sample, we based it off four criteria: location, condition of the tick, stage of development and the sex of the tick," explained Julia Geller, head of the department of virology and immunology at TAI.

The hazard map was redesigned

The sample from each county made up around 6 percent of the complete sample. Only Harju County's sample was considerably larger (12 percent), as more than a third of the ticks sent in originated from the most populated county in Estonia.

Close to two thirds of all ticks sent in turned out to be disease carriers. This means that at least one pathogen was found from the ticks, but 22 percent of all ticks carried multiple pathogens.

Thanks to the public's contribution to the "tick-bank", scientists were able to collect data from across Estonia in a short time, allowing for a first-time comparative tick study.

"Based on current knowledge, Saare County was considered the most hazardous and infectious location. The results of the present study refute this. The most infected ticks were found in Tartu County, Harju County and Viljandi County. Saare County is in the back-end of the list," Geller commented the results.

The least hazardous location in Estonia was discovered to be Ida-Viru County and the county also had the lowest rate of ticks carrying multiple pathogens.

Six different diseases

Ticks were studied in regards to six different pathogens. Estonia registers tick-borne encephalitis Lyme disease and erichiosis. Over the last eight years, only two cases of eclichiosis have been registered in Estonia, according to the Health Board.

The most common pathogen was revealed to be from the Rickettsia family, which 35 percent of studied ticks carried in some form. Rickettsia helvetica was found among more than 50 percent of all ticks sent in from Valga and Tartu counties.

28 percent of the studied ticks were found to carry Lyme disease (Borrelia burgdorferi), the most hazardous are was discovered to be Lääne County, where 41 percent of all ticks carried pathogens. The least dangerous location is Ida-Viru County, with every eighth tick (12 percent) carrying Lyme disease.

According to TAI, a surprising amount (19 percent) of ticks carried Neoehrlichia mikurensis with Viljandi the most common location for ticks carrying the pathogen. Anaplasma phagocytophilum ning Borrelia miyamotoi was found in far less ticks.

In general, the average nationwide anaplasmosis indicator was just under 10 percent. Hiiu County's respective indicator however was 18 percent. The most common causative agents of recurrent fevers were found to be in Lääne County.

Only two of the total 3,563 ticks were carriers of tick-borne encephalitis, one was found in Hiiu County and the other in Võru County. Earlier studies have also shown that there is not much encephalitis in nature and its spread is rather random.

The two ticks carrying encephalitis however could point to potential outbreak locations. Through vaccinations, the disease has been reduced, but the virus has certainly not disappeared.

Going forward

TAI scientists are very thankful to all who sent in ticks and contributed to the study. "We received a lot of knowledge thanks to it, for example the wider spread of neoerlichiosis than expected. Thanks to the numerous material sent in, there is plenty to analyse and research for some time. We are also developing a tick species map that would show which species are most common in Estonian regions. Going forward, we can also calculate the prevalence of ticks in cities or on pets," Geller opened up about TAI's plans going forward.

While the tick collection campaign has wrapped up, the project of tick mapping is still going on puuginfo.ee (link in Estonian). Having found a tick on yourself or your pet, the tick can be registered on the map. The ticks can still be sent in as well to support future studies, but feedback will no longer be given.


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Editor: Kristjan Kallaste

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