The Entomological and Acarological Situation in Lithuania
Published: 18.11.04 Updated: 18.11.2004 15:40:24
Centre for Communicable Disease Prevention and Control, Lithuania
The spread of blood-sucking anthropodes has been investigated in Lithuania. Ixodes ricinus has spread in administrative regions and the biggest cities, and Dermacentor pictus –in the valley of Nemans River and the biggest tributaries. The mosquito species that most actively attack humans are A.communis, A.cuntans, A.punctor and A.cataphylla, Anopheles maculipennis dominates in town water-bodies. The main blood-sucking fly is Bysson maculatus. Lyme disease and tick-borne encephalitis are the most frequently reported vector-borne zoonosis in Lithuania. Tick-borne encephalitis is spread in Central, Northern and South Lithuania, Lyme disease, throughout Lithuania with fewer cases in the northern part of the country.
An increase in the number of all blood-sucking arthropods has been observed in Lithuania. The abundance of Ixodes ricinus ticks, the principal vector for Lyme disease (LD) and tick-borne encephalitis (TBE) agents, in forests and urban parks of Lithuania was compared with the incidence of Lyme disease and TBE morbidity. Data collected are used to organize preventive activities against infectious diseases transmitted by arthropods.
The objective of this research was to investigate the spread of blood-sucking arthropods and to ascertain the species most aggressive towards human in Lithuanian towns. Ixodes ricinus (L.) are spreading in all administrative regions and the biggest cities. The distribution of Dermacentor pictus (Herm.) in South, South-West and Central Lithuania (the south, southwest and centre of the country) may be associated with the valley of the Nemunas River and the lower parts of the river’s biggest tributaries.
Materials and Methods
The material for this study was collected according to standard zoological methods used for the description and mapping of arthropods. Simuliidae larvae and pupae were collected from leaves of water plants in the Nemunas River. The abundance of ticks was observed annually in various forests and urban parks from different parts of Lithuania, as well as in nine stationary observation points. The stationary sites were established in 1987 and have been observed continually. Ticks were sampled from woodlands by dragging flannel over the vegetation and examined for the presence of B. burgdorferi. Bowel smears were prepared and stained with Giemsa stain and crystal violet.
During the last years 31 species of mosquitoes have been found in Lithuania. The species occurring in towns included: Aedes annulipes (Mg.), A. behningi (Mart.), A. cantans (Mg.), A. caspius (Pallas), A. cataphylla (Dyar), A. cinereus (Mg.), A. communis (De Geer), A. cyprius (Ludl.), A. diantaeus (H., D. & K.), A. geniculatus (Oliv.), A. intrudens (Dyar), A. leucomelas (Mg.), A. nigripes (Ztt.), A. pullatus (Coq.), A. punctor (Kirby), A. riparius (D. & K.), A. rusticus (Rossi), A. vexans (Mg.), Anopheles maculipennis (Mg.), Culex pipiens (L.), Culiseta alaskaensis (Ludl.), and C. ochroptera (Peus). The species that most actively attack humans are A. communis, A. cantans, A. punctor, and A. cataphylla. Thirty six percent of all permanent water bodies in towns are anophelogenic and An. maculipennis species dominate in these areas. The greatest abundance of An. maculipennis larvae was detected in July.
The best known family among small blood-sucking arthropods is the Simuliidae. For almost 10 years we have observed an increase in black flies in the southeastern part of Lithuania. The main blood-sucking black fly is Byssodon maculatus (Meigen). Larvae and pupae of B. maculatus can be found only in the Nemunas and constituted 95% of all the larvae observed in June 1997. In Lithuania B. maculatus has one generation, passes the winter in an egg-stage, and flies exist until the end of June.
Lyme disease and TBE are the most frequently reported vector-borne illnesses in Lithuania. Since the Centre for Communicable Disease Prevention and Control began surveillance for Lyme disease in 1991, the rate of human cases increased from 1.6 to 44.8 per 100 000 in 1997 and 1998, respectively. A similar situation has been observed with TBE. Since 1990 a dramatic increase in TBE morbidity has been recorded, reaching a maximum of 17.4 per 100 000 in 1997. The morbidity of tick-borne zoonosis decreased in 1999: the incidence per 100 000 was 20.7 for Lyme disease and 4.6 for TBE (fig 1). The principal vector for both infections is Ix. ricinus. The increase in reported cases may also display a change in the abundance of ticks. The number of Ix. ricinus registered at stationary observation sites increased annually until 1998 (fig 2). The maximum number of ticks per kilometre during the period of spring activity increased from 20 in 1992 to 38 in 1997 and decreased to 35 in 1999. The period of activity for Ix. ricinus is from April to November, with the greatest activity registered in the second part of August. The mean infection rate of Ix. ricinus ticks by B. burgdorferi in Lithuania was 8%, ranging from 0% to 24% in different locations.
TBE virus was isolated from ticks collected in all administrative regions and in three urban parks. Localities where people had been infected with TBE and LD in 1999 were analysed. Natural foci of TBE were widespread in the central part of Lithuania from north to south. A mosaic picture was obtained after examining localities where people were infected with LD. While Lyme disease occurred throughout the territory of Lithuania, fewer infections were reported from the north of the country.
The acaroentomological situation in Lithuania is similar to the situation in Eastern Europe. Towns are characterised by different natural and geographical environments in which different blood-sucking arthropods prevail. An increase in the number of ticks and possible contact with humans has resulted in an increase in the incidence of tick-borne zoonosis.