No 14 - 2011

Neuroborreliosis and tick-borne encephalitis detected in Denmark 2007-2010

Neuroborreliosis 2007-2010

In 2007-2010, a total of 243 cases of neuroborreliosis (NB) were notified, including 89 in 2007, 43 in 2008, 62 in 2009 and 49 in 2010. A reminder of notification was sent out in 11 % of the cases on the basis of a positive SSI lab result.

In 202 (83 %) cases, the diagnosis was made by intrathecal synthesis of antibodies.

A total of 73 (30 %) of the notified cases were below ten years of age, Figure 1.

Information about symptoms was available in 215 (88 %) cases: 112 (46 %) had facial nerve palsy, 21 (9 %) developed pain in the musculoskeletal system, 17 (7 %) headache and five developed aseptic meningitis. The remaining cases stated that they had experienced other neurological or unspecific symptoms.

The majority, 207, were infected in Denmark, while seven were infected in Sweden, 14 in other European countries, one in the USA and one in South America. In 13 cases, the country of infection was unknown.

Symptoms and diagnostics

The infection is caused by the spirochaete Borrelia burgdorferi and is transmitted by the tick Ixodes ricinus.

The clinical manifestations are divided into three stages: Early localized infection typically manifests as erythema migrans 1-2 weeks (3-30 days) after a tick bite. The diagnosis is clinical as serological testing does not provide sufficient sensitivity in the early phase.

Early disseminated infection is observed weeks to months after the initial stage and comprises, among others, multiple erythema migrans, carditis, lymphocytoma and NB.

Late disseminated infection occurs months to a few years after exposure.

The clinical manifestations are chronic atrophic acrodermatitis, chronic arthritis or chronic NB. On suspicion of NB, the diagnosis is corroborated by a positive spinal fluid test for monocytic pleocytosis and intrathecal synthesis of borrelia antibodies.

On suspicion of other manifestations of disseminated borreliosis, the diagnosis is made on the clinical picture in conjunction with detection of borrelia antibodies in serum. It is important to be aware that - depending on the method used - IgG or IgM antibodies may be present in 4-10 % of the healthy adult population. As disseminated borreliosis and NB are rare conditions, the positive predictive value of serology may be limited.

In cases where clinical symptoms persist for more than eight weeks, detection of borrelia IgG antibodies has a high sensitivity.


Over the past four years, the annual number of notified NB cases has varied from 43 to 89 with no signs of an increasing trend. It is assumed that NB is underreported to the SSI. Please note that NB is notifiable on form 1515.

A third of the notified cases occur in children below the age of ten years. Anyone spending time in woods and grass-covered vegetation areas in the period from April to October should make sure to search their skin and scalp afterwards as the tick is particularly active in this period.

(L.K. Knudsen, T.G. Krause, Dept. of Epidemiology, R. Dessau, Slagelse Hospital, S. Villumsen, DBMP)

Tick-borne encephalitis 2010

In 2010 the SSI witnessed a total of 12 cases of tick-borne encephalitis (TBE); three women and nine men aged 9-69 years. In four cases, the patient was presumably infected on the island of Bornholm.

The remaining eight cases were presumably infected in known endemic areas abroad, including six in Sweden, and one in Finland and Lithuania, respectively.

Transmission and symptoms

TBE is caused by a flavivirus (TBE virus) and is transmitted by tick bites within minutes of the bite.

The disease presents as fever and influenza-like symptoms which after approx. 1-2 weeks' absence of symptoms progress into encephalitis in approx. 1/3 of the cases.


The diagnosis is made by PCR for virus in spinal fluid or blood, or by detection of specific antibodies in blood by ELISA. Elevated IgM titres tentatively indicate ongoing or recently overcome infection.

An IgG titre increase of > factor 4 from the initial to the second test supports the diagnosis. The first blood sample should be taken as early as possible in the course of the disease; the second should be taken 1-2 weeks later.

On suspicion of TBE, an extra blood sample should be taken when the patient is discharged from hospital. Antibodies against other flavivirus and previous yellow fever or Japanese encephalitis vaccination may cross-react with TBE virus antigens.

A confirmatory TBE antibody neutralisation test may serve to confirm TBE specificity. Such test is not standard.


Vaccination may be considered in persons who are living permanently or have a fixed summer residence in areas with TBE and who regularly leave the paths of woods and scrubland.

However, in cases of behaviour associated with a particularly great risk of infection, such as forestry work, or when the woods are the fixed location for play, sport or hobby activities, vaccination may also be considered.

For practical purposes, it can be decided to vaccinate only from the age of seven years upwards in circumstances in which TBE vaccination is otherwise indicated.


In 2010, no cases of TBE acquired outside of Bornholm were detected. TBE occurs endemically on Bornholm. Consequently, no cases were found either in North Zealand or other parts of Denmark.

Since 2001 an average of 4.4 annual cases (range 1-12) have been detected, and the increasing number of detected cases in 2010 may be attributed to the increased attention the condition received following the finding of TBE in the area of Tokkekøb Hegn in 2009, EPI-NEWS 35/09 (pdf).

It is estimated that the possible infection area in North Zealand comprises a low risk for humans. Such assessment is underpinned by an offer of complementary TBE diagnosis made by the Department of Virology in the summer of 2010 to the area's physicians.

This active diagnostic effort of relevant fever cases in the area identified no further cases.

In connection with TBE re-testing of 96 blood samples submitted in the summer semesters of 2007, 2008 and 2009 from patients suspected of having Borrelia in North Zealand, a total of three TBE IgG positives were found, all known TBE positives who had been infected on Bornholm and in Sweden.

(P.H. Andersen, K. Mølbak, Dept. of Epidemiology, A. Fomsgaard, Dept. of Virology) 

Individually notifiable diseases and selected laboratory diagnosed infections (pdf) 

6 April 2011