Short summary

The tick, Ixodes ricinus, is the most important vector of emerging zoonotic pathogens in Europe.

Ticks host-seeking, is highly dependent on local climatic conditions. The density of host-seeking ticks is influenced by the local abundance of hosts, while infection prevalence depends on the pattern of tick infestation on these hosts. In many areas in Europe these basic requirements have been changing in favour of the tick population, including Denmark. Many vector-borne human pathogens have been found in Danish ticks, but only a few, has been described in Danish patients and the populations at risk. This study aims to increase the knowledge on vector-borne pathogens in Denmark.

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Rationale

It has been well established that many infectious diseases - especially those which are vector-borne - have seasonal patterns and a geographic range that are influenced by environmental variables such as climate and vegetation, both being interrelated. Therefore, the impending changes in climate may affect distribution, seasonality and severity of these infectious diseases.

Danish vectors:

The tick, Ixodes ricinus, is the most important vector of emerging zoonotic pathogens in Europe.

Ticks host-seeking, called questing, is highly dependent on local climatic conditions, especially temperature and humidity. The density of questing ticks is influenced by the local abundance of hosts, while infection prevalence depends on the pattern of tick infestation on these hosts. In many areas in Europe these basic requirements have been changing in favour of the tick population. This is also the case in Denmark.

A variety of Mosquitos in Denmark are competent of transmitting human pathogens, as an example there are several Anopheles species known for their capability of transmitting Malaria. New species not previously found in Denmark are closing in from southern Europe, bringing with them the possibility of new pathogens. The newest on this list is Culex modestus, with the potential to transmit West Nile virus. To the best of our knowledge, no mosquito-borne human pathogens have yet been found in Danish mosquitos.

Our knowledge of the vector-borne pathogens in Danish patients and populations at risk is very limited, when compared with our neighbouring countries. Vector-borne diseases are emerging in Europe, and the previous boundaries of diseases requiring a milder climate are shifting. This brings forth the risk of new emerging pathogens in Denmark and the need for increased vigilance.

Study aim:

This study aims to increase the knowledge on vector-borne pathogens in Denmark, by investigating the presence of vector-borne pathogens using roe deer as sentinels and in the groups of individuals under increased risk of tick bites. We will further try to identify and characterize substances in sweat that may repel or attract primarily the tick I. ricinus. Futhermore we will collect ticks in collected locations in Denmark to try to establish if a new emerging tick-born pathogen may be established in a certain area.

Perspective:

It is expected that this study will contribute with new knowledge on tick-borne infections in all of Denmark. This knowledge can be utilized to improve risk assessments and prevention methods, and contribute to public health education. For some of the pathogens it may provide information to form the basis for a possible vaccination strategy as well as more timely diagnosis and treatment. More over this study could deliver information on vector-borne human pathogens not seen before in Denmark. 

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Description of the cohort

Roe deer
Approximately 800 roe deer culled in the regular hunting season of 2013-2014.

Ixodes ricinus
Aproximately 8000

Persons in risk of tick bite
Inclusion criterion:

1. Age >18-<90.
2. At least one of the following:
1. Hunter who has participated in the collection of roe deer blood
2. Partner/spouse living with hunter living up to criterion a
3. Hunter who has his/hers own hunt/ or hunt renting and with more than 4 active hunting days each year.
4. Partner/spouse living with hunter living up to criterion c.
5. Limer Huntsman (på dansk Schweisshundefører)
6. Partner/spouse of a Limer Huntsman (på dansk Schweisshundefører).
7. Employed as a butcher of game for more than 3 years
8. Administrative employee at a butcher of game, for more than 3 years.
9. Working in a forest area, primarily outdoor, for more than 1 year.
10. Partner/spouse of a person living up to inclusion criterion i.
11. Recreational activities in a forest area more than once a week for more than 3 years.
12. Partner/spouse of a person living up to inclusion criterion k.

The participants can decline to deliver a sweat sample and still participate in the study.

Number of participants:

665 people representing the people at risk (criterion 2a; 2c; 2e; 2g; 2i, 2k).

665 representing parred samples and with the possibility of domestic or work related cross-infection (criterion 2b; 2d; 2f; 2h; 2j; 2l)

665 participants in the Danish Blood Donor Study will serve as represents of the general population.

Data and biological material

Roe deer (has been collected)
Biological material: 4 ml of EDTA blood
Information on: age, sex, tick infestation, address/GPS-location of where the roe deer were bagged.

Ticks (some have been collected):
Pooled in up to 10 ticks pr. pool in MEM + 5% Fetal Calf Serum with antibiotics.
Information on: Time of day duration of collection and GPS-location.    

Persons in risk of tick bite
Biological material: 15 ml of blood and one sweat sample.
Questionnaire: Risk behaviour regarding tick exposure. Previous tick-borne infections. Vaccination status. Travel.
Clinical data: If relevant data from clinical medical records are collected.   

Collaborating researchers and departments

Clinical Center for Emerging and Vectorborne Infections, Odense University Hospital

• Clinical Associate Professor Sigurdur Skarphédinsson

Research Department of Clinical Microbiology, University of Southern Denmark

• Professor Hans Jørn Kolmos

Department of Plant- and Environmental Sciences, University of Copenhagen

• Associate Professor Per Moestrup Jensen

Applied Wildlife Research, Danish Hunters' Association

• Head of Research Carsten Riis Olesen

Institute of Microbiology, Munich, Germany

• Dr. Gerhard Dobler