Pia Forsberg

Tick-borne infections - interaction between vector, pathogen and human

Tick-borne infections are increasing probably at least partly, depending on the climate changes

Ticks are often carriers of both bacteria and viruses, which can be transmitted to humans. Several of these microorganisms, Borrelia (B) burgdorferi, Anaplasma (A) phagocytophilum, Rickettsia (R) Helvetica and tick-borne encephalitis – virus (TBEV), are all known to cause disease in human. This is expensive for the healthcare, particularly the worry about the borrelia infection and TBE, that many people feel.

It is not unusual that individuals want antibiotic therapy after a known tick-bite already before a disease is prominent, which might increase the development of resistance among bacteria and other adverse effects in the host.

The risk to be infected by these microbes after a single tick-bite is not known. However, estimations have been done from the occurrence of infected ticks that have been collected from the nature.

Indeed it has been investigated the frequency of infections in ticks which have been BITTEN the humans but as far as we know, the symptoms and the immune-reactivity in the bitten human has never been connected to the confirmed microbe in the tick. Thus, it is unknown how often ticks which have bitten individuals are infected and how the interaction is taking place between the microbial agent and the host (the human).

It is also unknown why the course of the disease is different in different patients, particularly in TBE and borreliosis. It is thus of importance to clarify the risk for disease after the bite of an infected tick.

Specific objectives and questions

We will in this project create better instruments for studies of tick-borne diseases by using newly developed molecular biological techniques for the detection and quantification of the microorganisms. The bitten individuals will be followed up for three months in order to survey the symptoms and their immune-reactivity of their blood. The infected tick will be connected to the individual’s symptoms and disease development and also the development of the host immune-reactivity.

One considerable aim is to reduce the fear of tick-borne diseases in our country.

The objective with the study is to answer the following questions

The interaction between the microbe and tick which has bitten the human:

  • How often are the ticks which bite the individuals in the different study areas infected with B. burgdorferi, TBEV, A. phagocytophilum and/or R. Helvetica?
  • What are the geographical differences?Are there completely new variants of bacteria/viruses which are spread by ticks?
  • Have the new dangerous TBEV already reached Sweden?
  • How often are the ticks co-infected with two or more strains of the pathogen?How often are the ticks co-infected with one or more microbes?

The interaction between the microbe and the bitten individual=human

  • What is the risk to get a disease after a bite of an infected tick with these microbes? Are there asymptomatic infections after a bite by a confirmed infected tick?
  • Is there any connection between the risk of being infected and the time period the tick has been sucking blood?
  • Is there any connection between the number of bacteria/viruses in the tick and the development of disease?
  • Is there any connection between the genetically variant/subtype of Borrelia or TBEV and the clinical prognosis of the infection?
  • How is the immune-reactivity in the bitten individual connected to the clinical prognosis and to the tick?
  • Is there any connection between co-infected ticks and the prognosis of the diseases?


Persons who are interested in participating in the study will be asked, when they were bitten by a tick and to bring the tick to the primary health care centre (PHC). The health care personal will take blood samples from the individual and the individual will be asked to fill in a questionnaire which is related to tick-borne infections.

The person will also be asked to collect any further ticks which bites the person during the study-period (3 months), and come back for a second visit which will take place at the PHC 12+/-2 weeks after the tick-bite. Blood will then be drawn again and the individual will be asked to fill in a new questionnaire regarding the symptoms. If symptoms of a tick-borne infection would appear during the study-period, the patients must contact their PHC for actions.

Then a new blood sample is drawn and a copy of the relevant record is sent to the main investigator (PF). Those who will get tick-borne infections will also be followed up through blood sampling and clinical observations longer than the default study-period until they are healthy.

From the collected ticks RNA will be extracted. For the detection and quantification of infectious agents (B.burgdorferi, TBEV, A.phagocytophilum and R.Helvetica), RNAt will be analysed with real-time PCR (qPCR). Group or species specific primers for these microorganisms will be used.

When primer designing and optimizing has been completed, one must balance specificity contra sensitivity. For typing and epidemiological tracing of different clones of microorganisms, the extracted RNAt will be amplified by conventional PCR followed by electrophoresis analysis of the PCR-products.

Then information will be received if certain clones of microorganisms more often will infect persons than others and if several multiclonal infections are present. These methods are now already established on the Department of Medial Microbiology, University Hospital in Linköping regarding B. burgdorferi and TBEV, and A. phagocytophilum. The next step is to establish methods for R. Helvetica.

The ticks are photographed and scutal-index and coxal index are measured to calculate an approximate time for the duration of the tick bite. Thus, the scutal and coxal index are used to confirm how long time the tick has sucked blood.


Cover of publication ''
Barbro Hedin-Skogman, Stefan Croner, Pia Forsberg, Jan Ernerudh, Pekka Lahdenne, Heidi Sillanpää, Ilkka Seppälä (2008)

The Pediatric Infectious Disease Journal , Vol.27 , s.605-612 Continue to DOI

Cover of publication ''
Ann-Margreth Olinder-Nielsen, Carl Granert, Pia Forsberg, Vanda Friman, Auli Vietorisz, Janne Björkander (2007)

Scandinavian Journal of Infectious Diseases , Vol.39 , s.44-50 Continue to DOI

Publications in DiVA


Nellie Carlströmer Berthén, Eszter Tompa, Susanne Olausson, Clara Nyberg, Dag Nyman, Malin Ringbom, Linda Perander, Joel Svärd, Per-Eric Lindgren, Pia Forsberg, Peter Wilhelmsson, Johanna Sjöwall, Marika Nordberg (2023) The AxBioTick Study: Borrelia Species and Tick-Borne Encephalitis Virus in Ticks, and Clinical Responses in Tick-Bitten Individuals on the Aland Islands, Finland Microorganisms, Vol. 11, Article 1100 Continue to DOI
Paula Gyllemark, Johanna Sjöwall, Pia Forsberg, Jan Ernerudh, Anna Jonsson Henningsson (2023) Intrathecal Th17-driven inflammation is associated with prolonged post-treatment convalescence for patients with Lyme neuroborreliosis Scientific Reports, Vol. 13 Continue to DOI


Ivar Tjernberg, Paula Gyllemark, Henrik Zetterberg, Kaj Blennow, Jan Ernerudh, Pia Forsberg, Johanna Sjöwall, Anna Jonsson Henningsson (2022) Cerebrospinal fluid markers of inflammation and brain injury in Lyme neuroborreliosis - a prospective follow-up study Clinical Chemistry and Laboratory Medicine, Vol. 60, p. 1124-1132 Continue to DOI