Eurosurveillance

ECDC

Natural Foci Infections in Republic of Karelia

 Rediger
  Published: 29.04.04 Updated: 12.05.2004 11:10:58

Kovalenko A.I., Rubis L.V., Ekimova O.V., Koloda N.I.
State Center of Sanitary and Epidemiological Surveillance in Republic of Karelia

The Republic of Karelia is situated in the north-western region of the Russian Federation and borders on Murmansk oblast in the north, Leningrad oblast in the south, Arkhangelsk oblast in the east, and Finland in the west.

The whole territory of Karelia is situated in the north and temperate taiga zones. More than half of the territory is covered with forests (mainly coniferous), while 27 % of the territory is covered by marshes and boggy areas, and about 2 % by meadows and plough-land.

A total of 63 mammal species live in the territory of Karelia, among them 22 species of rodents (E.V. Ivanter, 1986). Long standing systematic observations on the size of small mammals has demonstrated that the dominant species throughout Karelia are the bank vole and common shrew.

Overall, six species of Ixodes ticks dwell in Karelia. The area of prevalence of I. ricinus and I. persulcatus is the territory of the Republic to the south of 63° north latitude. I. ricinus dominates mainly in the south-west part of the Republic, and I. persulcatus in the central, south and south-eastern parts (along the coast of the Onezhskoe lake). Occasionally, cases of tick bites (tick attacks on humans) (I. persulcatus) in the territory northwards from these southern areas have been reported.

The epidemic situation in the Republic of Karelia is relatively stable with regard to most of the natural occurring infections. Human cases of tularaemia, anthrax, tetanus, Q fever, rabies and Karelian fever have not been reported in Karelia for many years. Sporadic cases of leptospirosis and haemorrhagic fever with renal syndrome are still being reported.

However, some natural foci for tick-borne encephalitis (TBE), Lyme borreliosis, tularaemia, leptospirosis and haemorrhagic fever with renal syndrome (HFRS) exist in the Republic.

Statistic observation data for tick-borne encephalitis since 1957 give evidence of a significant increase in the incidence of TBE in Karelia during the last decade. The average annual incidence rate for the period 1957-1990 was 1.3 per 100,000 population, while it was 4.8 per 100,000 in the period1991-2001. The highest incidence rate for tick-borne encephalitis was reported in 1995 and was as high as 7.0 per 100,000 population.

The annual incidence of Lyme borreliosis has on average been 2.6 per 100,000 population during the last 11 years (from the outset of registration) (Table 1).

Table 1, Incidence of tick-borne encephalitis and lyme borreliosis in the Republic of Karelia from the beginning of registration.

Year

TICK-BORNS ENCEPHALITIS

LYME BORRELIOSIS

1957

0.1

 

1958

0.4

 

1958

2.0

 

1960

0.4

 

1961

0.1

 

1962

0.2

 

1963

0.2

 

1964

3.2

 

1965

1.4

 

1966

2.2

 

1967

4.5

 

1968

2.1

 

1969

0.2

 

1970

1.1

 

1971

1.6

 

1972

0.9

 

1973

1.3

 

1974

8.0

 

1975

2.0

 

1976

2.1

 

1977

2.0

 

1978

4.2

 

1979

0.6

 

1980

0.5

 

1981

0.5

 

1982

0.1

 

1983

0.2

 

1984

2.0

 

1985

0.9

 

1986

1.6

 

1987

1.6

 

1988

1.6

 

1989

1.3

 

1990

0.6

 

1991

4.6

0.6

1992

5.5

1.8

1993

4.6

3.1

1994

1

0.4

1995

7.2

3.1

1996

5.1

2.8

1997

3.9

1.7

1998

4.6

3.4

1999

4.3

2.6

2000

5.6

5.8

2001

5.9

2.9

 As shown in the graphic (Fig 1), the incidence rates follow the same pattern of increase and decrease with the exception of 2001.

Fig 1. Incidence of tick-borne encephalitis (TBE) and Lyme borreliosis (LB) in Republic of Karelia (per 100 000 population)

It should be noted that the incidence situation for tick-borne encephalitis and Lyme borreliosis in Karelia differs significantly from the situation in north-west Russia as well as in Finland. Incidence rates for tick-borne encephalitis in the Republic are higher and for Lyme borreliosis are lower than in the neighbour territories (Table 2).

Table 2. Incidence of tick-borne encephalitis (TBE) and Lyme borreliosis (LB) among the regions of Russian Federation (per 100 000 population) and Finland. 

 

1998г.

1999г.

2000г.

 

TBE

LB

TBE

LB

TBE

LB

Russian Federation

5.1

5.9

6.8

5.8

4.1

5.4

Republic of Karelia

4.7

3.4

4.3

2.6

5.6

5.7

Arkhangelsk oblast

2.3

1.3

1.9

2.9

2.3

2.3

Leningrad oblast

1.7

11.3

0.9

4.4

2.6

8.4

City of Saint-Petersburg

1.6

11.7

1.1

5.6

2.5

11.6

Finland

n.a

n.a

0.2

7.8

0.8

17.2

This situation needs further investigation. The average rate for ticks bearing TBE-infection during the 11 year period in Karelia was 7.2 % and increased to 9.6% in 2001, the data being obtained from Virus Laboratory of the Karelian Center of State Sanitary and Epidemiological Surveillance. The investigation conducted in 2001 of one of the cases of tick-borne encephalitis confirmed that the tick bite had occurred near the city of Ioensu in Finland.

Today, haemorrhagic fever with renal syndrome (HFRS) is the leading natural foci infection besides tick-borne encephalitis and Lyme disease in Karelia. At least 1 to 3 cases are reported every year, but more than 10 to 20 cases of the disease have been reported in some years. The main carrier of the HFRS virus in Republic of Karelia is the bank vole. The examination of small mammals for the presence of HFRS virus antigens has been conducted since 1996 in Karelia. The prevalence among those tested has fluctuated from 1.3% (in 2000) to 16.3% (in 1996). Epizooties of HFRS are closely associated, as a rule, with the years of large bank vole populations, but local epizooties are also noted when the number of rodents is not high. (Table 3)

Table 3. The results of examination for HFRS, tularaemia and leptospirosis in the laboratory of special dangerous infections and in the laboratory of virology at the Center of State Sanitary and Epidemiological Surveillance in Republic of Karelia during 1999-2001. 

   

Number of samples examined

Rate of detection (%)

   

1999

2000

2001

1999

2000

2001

tularaemia

rodents

376

480

752

0

0

0

faeces of birds of prey

160

95

143

8.1

2.1

33.6

open water reservoirs

179

223

134

0

0

0

other environmental objects

51

481

413

0

0

0

leptospirosis

rodents

by culture

211

138

73

0.5

0

0

serological methods

337

314

444

0.3

0.3

0.7

HFRS

rodents

286

236

516

4.9

1.3

4.0

Tularaemia in Karelia has been registered since 1945 when the first outbreak of the disease (45 cases) was noted among the residents of one of the regions previously belonging to Finland. The source of the infection was rodents but they failed to ascertain the species. Hypothetically, the carriers of the disease were two-wing insects. The measures timely carried out made it possible to prevent the further spread of the disease. During the following 15 years, cases of the disease were reported in the south-west part of Karelia. In the years 1960 to 1982 the incidence was sporadic. No cases of the disease among humans have been registered since 1983. At the same time, circulation of the agent of disease in nature still continues in rodent populations. These facts are supported by the results of the laboratory investigations. The size of water rat populations, the natural reservoir for the infection, have remained low in Republic of Karelia for more than 10 years, and thus provides the basis for predicting a favourable view of the situation.

Both natural and economic foci of leptospirosis are revealed in the Republic. One to three cases of the disease are reported every year. Small moisture liking mouse-like rodents such as voles, field mice and grey rats are the main reservoir of leptospirosis in nature. The detection of leptospiras by culture and antibody detection in field material is reported every year as single instances. The leptospiras cultures were obtained from water samples (3 positive from 56 total) in1999. During the last years the disease has been registered more often among people from cities than from rural areas.

Epidemic outbreaks of Karelian fever (Pogost disease) were reported in 1981 in several regions of the central part of Karelia (Lvov D.K. The atlas of prevalence of natural foci viral infectious agents on the territory of Russian Federation. 2001). In 1982-1983 and later only single cases of the disease were noted. The discovery of a high immunity among the population of Karelia (up to 54 % in data of 1982 -1984) testifies to the fact that the real incidence rate for Karelian fever is higher than that reported. Effaced and inapparent forms of the disease that are not apparent by clinical features explain the lack of reported cases. Also, laboratory analyses on Karelian fever virus are not performed. The Karelian fever virus is transmitted to man mainly by mosquitoes of the Aedes genus. The activating of foci of Karelian fever occurs comparatively rarely in conjunction with several natural and anthropogenic factors.

Zooparasitologic monitoring of natural foci of zooanthroponostic diseases conducted in Karelia allows the forecasting and timely, highly reliable detection of their increase in activity along with elaborating of measures of disease prevention in human population.

Literature

  1. E. V. Ivanter "Mlekopitaioshchie ", 2nd edition, Petrozavodsk 1986.
  2. Lvov, D. K. Deryabin, P. G. Aristova, V. A. et al. "Atlas rasprostraneniya vozbuditelei prirodno-ochagovykh infektsij na territorii Rossijckoj Federatsii" Moscow, 2001

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