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United States: Recent Trends in Tick-borne Diseases

Since 1999, there has been a striking parallel among rates of reportable tick-borne diseases in the United States – see graph (Lyme disease expressed as cases per 100,000 for fit). [1,2]

1. Berger SA. Infectious Diseases of the United States, 2012. 1089 pages, 467 graphs, 9760 references. Gideon e-books,
2. Gideon graph tool at

Note featured on ProMED

Tick-borne Diseases in the United States

Nine tick-borne infections affect humans in the United States. Data on a national level are available for Lyme disease, Powassan encephalitis, Rocky Mountain spotted fever, Tularemia, Granulocytic ehrlichiosis (Anaplasmosis) and Human monocytic ehrlichiosis. Statistics for three diseases (Babesiosis, Relapsing fever and Colorado tick fever) are not published. The following graph compares reporting trends for tick-borne infections (Lyme disease displayed as cases/100,000 for fit). [1,2]

Note an apparent parallel increase for some diseases during 2000 to 2008, followed by a dip during 2009 to 2010. Assuming a statistical association between these data, explanations might include changes in tick populations as a whole, or trends in human-tick contact over time.

1. Berger SA. Infectious Diseases of the United States, 2012. 1089 pp, 467 graphs, 9760 references. Gideon e-books,
2. Gideon graph tool at

Tick-Borne Encephalitis in Sweden

Rates of tick-borne encephalitis in Sweden are now well beyond those of surrounding countries, and have been increasing significantly since 2000. [1,2] See graph

(outline of Gideon Graph module – see )

1. Berger SA. Infectious Diseases of Sweden, 2011. 427 pp, 133 graphs, 1346 references. Gideon E-books, Berger SA. Tick-borne Encephalitis: Global Status, 2011. 54 pp, 44 graphs, 314 references. Gideon E-books,

Note discussed in ProMED

Anaplasmosis in China

Anaplasmosis has been documented in both humans and animals in China. [1,2] The following background data are abstracted from GIDEON (primary reference available on request).

Time and Place:
– Seropositive ruminants have been documented in Xinjiang Uygur Autonomous Region area.
– Seropositive rodents have been documented in Jilin Province: Japanese field mouse (Apodemus peninsulae), Black-striped field mouse (A. agrarius) and Siberian chipmunk (Tamias sibirica).
– Ehrlichial DNA (Anaplasma phagocytophilum) has been detected in Ixodes persulcatus ticks from the Northeastern (ie, Lyme disease) region – Inner Mongolia and Heilongjiang Province.
– Infected rodents, sheep and ticks (I. persulcatus and Dermacentor silvarum) have been detected in Jilin Province.

Prevalence surveys:
8.82% of forest rodents in Jilin Province, 1.64% in Helongjiang Province and 0% in Inner Mongolia autonomous region (2007 publication)
14.1% of rodents captured from a mountainous area in southeastern China (Zhejiang Province, 2008 publication)
5.5% of rodents from Heilongjiang Province, Inner Mongolia Autonomous Region, Jilin Province, Zhejiang Province, Guizhou Province, and Xinjiang Autonomous Region (2004 to 2006)
1.9% of rabbits captured in southeastern China (2009 publication)
4.6% to 6.8% of I. persulcatus in Jilin Province (2003 to 2005 publications)
7.34% of small mammals in the forest area of Hengduan Mountains, southwestern China (2009 publication)
6.7% of livestock and 14.5% of small rodents (2010 publication)

Seroprevalence surveys:
8.8% of farm workers near Tianjin (2006)
19.8% of persons with animal or tick exposure in central and southeastern China (2007)

Notable outbreaks:
2006 – An outbreak (9 cases) of transmission through blood or secretions was reported in Anhui Province among hospital staff who had treated an index patient.
2008 – An outbreak (5 cases, 3 fatal) was reported in Wanjiakou village in Shandong Province.

1. Berger SA. Infectious Diseases of China, 614 pp. Gideon e-books, 2010.
2. Berger SA. Anaplasmosis: Global Status, 23 pp. Gideon e-books, 2010.

Update: Quoted in ProMED

Tick-borne Encephalitis in Croatia

Although recent reports of Tick-borne encephalitis (TBE) in Croatia belie the fact that this disease has been steadily declining for five decades, the impact of TBE in Croatia is comparable to that of the main form of arthropod-borne encephalitis in the United States. See graph

TBE was first reported in Croatia in 1953, and mandatory reporting was instituted in 1987. There is only one natural focus in the northern part of the country, between the Sava and Drava Rivers. Alleged cases in Zadar and Pula, have not been certified. 75% of cases occur from May to July.

Approximately 20 cases per year are reported in Koprivnica-Krizevci County, characterized by a relatively mild illness without neurological residua.

1. Berger SA. Infectious Diseases of Croatia, 2010. 356 pp. Gideon e-book series.
2. Berger SA. Tick-borne Encephalitis: Global Status, 2010. 52 pp. Gideon e-book series.

Borreliosis: Lyme or Ljubljana

The first cases of Lyme disease (LD) were recognized in Lyme, Connecticut in 1975. Although many assume that the condition is largely limited to the United States, LD has been reported in 63 countries as of 2010, with cases in Latin America, Asia, Europe and North Africa. Surprisingly, the world’s highest LD rates are reported in Slovenia, followed by the Baltic countries and Czech Republic (see graph). [1,2]

Borrelia burgdorferi was first isolated from patients in Slovenia in 1988, and from ticks in 1993.

Prevalence surveys:
7.7% to 46% of febrile illness following tick bite
45.5% of ticks in the Italy/Slovenia transborder territory (2008 publication)

Seroprevalence surveys:
15.4% of children and young adults in Slovenia (2000 publication)
23.8% of forestry workers (ELISA, 2002)

Infecting species:
– Borrelia burgdorferi, B. afzelii and B. garinii are encountered.
– B. afzelii accounts for the majority of isolates; however, B. garinii predominates among strains cultured from cerebrospinal fluid.
– B. bissettii has been isolated from humans with Lyme disease in Slovenia.
– Borrelia spielmanii (Borrelia A14S) has been implicated in cases of erythema chronicum migrans in Slovenia.

1. Berger SA. Infectious Diseases of Slovenia, 2010, 373 pp. Gideon e-book series.
2. Berger SA. Lyme disease: Global Status, 2010, 66 pp. Gideon e-book series.

Tick-borne Encephalitis in Sweden

Recent reports highlight the fact that Sweden has the highest rate of Tick-borne encephalitis (TBE) in Scandinavia, exceding even those of Russia in 2008. [1,2]

The following background data on TBE in Sweden are abstracted from Gideon. Primary references are available on request.

Time and Place:
Disease rates peak during July to August.
– Natural foci are found throughout the southern and middle parts of Sweden up to the counties of Varmland and Dalarna and further north along the Baltic sea.
– Cases are identified on the Stockholm archipelago, the middle and eastern parts of lake Malaren close to Stockholm, the coastal area of the Baltic sea from Stockholm further south to the city of Kalmar and the islands of Oland and Gotland.
– Highest incidence is found on the East Coast, (particularly on the Stockholm archipelago), the eastern region of Lake Malaren and the Gotland Island region.
– The first cases in Skane were reported in 2001. Six cases were reported in the region to 2006.
– 65.3% of cases reported during 1992 to 1996 were acquired in Stockholm, 15.2% in Sodermanland, 6% from Ostergotland or Gotland, and 4.9% from other countries (primarily Finland).
– 402 cases of TBE were registered during 1955 to 1993, with a case/fatality rate of 0.5%. During this period, the disease rate in Stockholm County was 3.4 per 100,000 per year.
– 71% of cases in 2001 were reported from Stockholm, Uppsala and Sodermanland.
– 56% of cases in 2003 were from Stockholm, 15% from Sodermanland and 6% from Uppsala.
– In 2007, TBE virus was the most common agent of viral meningitis in Sweden, accounting for 37.4% of cases.

The male/female ratio among TBE patients is is 2.1/1; and the median patient age is 41.5 years.

Exported cases:
Tick-borne encephalitis was documented in a Swedish national in England (1991 publication).
An American traveler acquired Tick-borne encephalitis in Sweden in 2006.

Prevalence surveys:
21% of adult aseptic meningitis in Northern Stockholm (1999 and 2004)

Seroprevalence surveys:
4% to 22% in endemic areas, and 5% Stockholm
3.5% on the island of Asp (Southeast Sweden) in 1991; 12% in 2002
0.8% of persons in northeastern Skane are seropositive.

Tick-borne encephalitis virus has been identified in Ixodes ricinus found on migrating passerine birds.


1. Berger SA. Infectious Diseases of Sweden, 2010, 417 pp. Gideon e-book series

2. Berger SA. Tick-borne Encephalitis: Global Status, 2010, 52 pp. Gideon e-book series

Increase in tick-borne diseases, U.S.A.

Rates of tick-borne infections in the United States have been increasing dramatically since 2000. See attached graph (Lyme disease displayed as cases/100,000 to allow fit). Although this phenomenon might reflect changes in human population density and artifacts of reporting and diagnosis, I suspect that these data are related to increasing tick and animal reservoir populations.

Update: Also referenced in ProMED