Parasit. Hung. 6-1973. Population Density of Small Vertebrates and their Role as Hosts of Ticks NOSEK, J. CERNY, V. GULYÁS, M. - MOLNÁR, E. ERNEK, E. KOZUCH, O. LABUDA, M. Institute of Virology SAS, Bratislava National Institute of Public Health, Budapest "Population Density of Small Vertebrates and their Role as Hosts of Ticks" - Hosek, J., Cerny, V-, Gulyás, M., Molnár, E., Ernek, E., Kozuch, 0., Labuda, M. - Parasit. Hung. 6. 239-246. 1973. In Central European TBE foci small mammals, such as bank vole, yellow necked mouse and long-tailed fieldmouse»are the main hosts for Ixodes ricinus larvae. Birds are the main hosts of nymphs in natural foci of the theriodic type; small rodents and insectivores may be the main hosts of nymphs in TBE foci of the therio-boskematic type. As a rule small insectivores contribute less to the level of population density of ticks than do small rodents. Por maintenance of the virus and the tick population in an elementary focus of TBE only those host-populations are of importance which coincide with the seasonal and spatial incidence of ticks. Very high population density of nymphs and adult ticks, over 600 specimens for 100 square meters, was observed in grazing forests and in ecotone pasture-forest in regions with game keeping. In the whole distribution area of natural foci of tick-borne encephalitis (TBE) of Western subtype, of basic importance as very frequent maintenance hosts (reservoirs) of the virus are small insectivores: common shrew Sorex araneus, European mole Talpa europaea and small rodents such as bank vole Clethrionomys glareolus,which are in some places associated with yellow necked mouse Apodemus flavicollis and long-tailed fieldmouse Apodemus sylvaticus. At the same time the range of hosts of the Ixodes ricinus tick, which is considered to be the main
vector of TBE, was found to extend to more than 15 0 species of vertebrates. The mentioned species of mammalian öynusia are not only important as maintenance hosts but also as very frequent and main hosts of larvae of I. ricinus in Central European natural foci of TBE. Prom this point of view"clethrionomys glareolus, Apodemus flavicollis and A. sylvaticus are of primary significance. Small insectivores as a rule play a minor role as hosts of I. ricinus larvae and are less important than small rodents (Pigs. 1 and 2). The population" density of reptiles, birds and insectivores seems to be much more constant than that of small rodents during the year and during the successive years; thus when only a few small rodents are available, birds together with insectivores become an important source of blood for I. r i cinus larvae in natural foci of TBE of theriodic type. However, in the years when the population density of small mammals is normal, only a small percentage of the larvae feeds on birds, most of them parasitizing the mammals. Pig. 1 : Humber of engorged larvae of Ixodes ricinus on small rodents and insectivores. Calculation was made by the formula of Olsufjev (1953): Humber of engorged tick = Density of ho3t per 1 hectare/index of infestation longevity. 1. ábra: Vért szívott Ixodes ricinus lárvák száma kis rágcsálókon és rovarevő gazdákon. A számítás Olsufjev (1953) alábbi formulája alapján történt: Vérszívott kullancsok száma = Gazdaállatok száma 1 hektár területen/a fertőzöttség tartamának indexe. Collection localities in Hungary - Magyarországi gyűjtőhelyek: P = Pertőboz; G = Gic; T = Tómalom; M = Mosonmagyaróvár; D = Debrecen. Time of collection - A gyűjtés ideje: IV = April; V = May; IX = September; X = October. Hosts - Gazdák: I = Insectivora; R = Rodentia; Mm = Mus musculus; Clg = Clethrionomys glareolus; Af = Apodemus flavicoll i s ; As = Apodemus sylvaticus; Aa = Apodemus agrárius; Ma = Microtus arvalis; Ps = Pitymys subterraneus; Sm = Sorex minutus; Ta = Talpa europaea; Sa = Sorex araneus; CI = Crocidura leucodon; Cs = Crocidura suaveolens.
The degree of infestation and host preference by ticks of vertebrates in an area will determine their potential importance in maintaining natural foci of infection. The importance of vertebrates as hosts to the ticks will depend on the average seasonal total number of ticks per individual specimens for each species as well as on species population densities. Indirect correlation exists between the population density of hosts and tick-load.the tick-load for individual species would appear to be related to host size. Further, the tick-load on vertebrate hosts may be related to their home range. We have observed that more isolated wide-ranging yellow necked mouse and long-tailed fieldmouse acquires much more ticks than hosts which move ( Fig. l ). The higher infestation of male mice is also attributable to their greater mobility. For maintenance of virus and tick population in a natural focus only those populations of host are of importance,which coincide with the seasonal and spatial incidence of ticks. I t is necessary to add that the significance of a given species as tickhost in different habitats may be quite different. Spatial coincidence of tick and host (ecological niche) comes here into consideration, e. g., the European mole in forests of Central Europe may be heavily infested with larvae and nymphs of I. r i - Fig. 2: Relative incidence of larvae, nymphs and female imagoes of Ixodes ricinus on various host species. 2. ábra: Ixodes r i c i n u s lárvák, nymphák és nőstény imágók v i szonylagos előfordulása különféle gazdafajokon. [~J = Small L = larvae - lárvák; 0- Birds - Madarak N = nypmhs - nymphák. rodents and insectivores - Kisrágcsálók és rovarevők [*~\ - Bigger rodents and insectivores - Nagytermetű rágcsálók és rovarevők ^jj = Free living ungulates - Vadon élő patások ~*~ = Carnivora - Ragadozók = Reptilia - Hüllők P] = Grazing goats - Legelőn tartott kecskék
cinus, while in meadows this species is non-infested. Another example is given from pastures of Scotland^ where the population density of ticks is very high but the mole is very scarcely infested because i t lives in deep layer of humus soil (VARMA, I960). The limited home range of small mammals, such as the common shrew, is one of the factors in maintaining natural foci of infection (NOSEK et al., 1972). Conversely, on the basis of marked animals and their virological and serological examination i t is possible to find so called "microfoci". Birds, as hosts of the ticks or the virus, may be capable of establishing new foci of infection in areas in the same landscape outside the home range of a particular population of small mammals. Birds may also be able to introduce ticks into areas from which ticks have been eradicated or their number greatly reduced. The population density of ticks in an overflowed Danube region regained its normal value in a 4 year period. The population density per 1 hectare of small mammals in the TBE focus Topol'cianky (Tribec Mountain),assessed by means of the mark-release-recapture method 7 has been estimated: 1966 1967 1968 Spring 45 50 20 Autumn 75 90 42 The average population density for 1 hectare of ticks,assessed by means of carbon dioxide technique in mid-april 1969, was of 46,000 nymphs and 50,000 adults, while at the beginning of May i t was 760,000 larvae, 16,000 nymphs and 3,300 adults only 7 being in indirect correlation with the population density of hosts (MOSEK and KOZUCH, 1970). The protection and preservation of hunting games, such as red deer, roe deer, fallow deer, wild boars, which are usually heavily parasitized by I. ricinus, first of all with adult ticks,
as well as the grazing of farm animals contribute substantially to the increase of tick population. The optimum condition for increasing population density of ticks exists in grazing forests or in ecotone pasture-forest i f parallelly a high population density of small rodents occurs. In the area of tick distribution, natural foci of TBE will be indicated by the presence of viruliferous ticks. A low infection rate, though difficult to detect, could s t i l l effectively maintain virus activity in an elementary focus. Amplifying factor s f such as unusually large populations of small mammals due to cyclical changes 7 could result in increased populations o? ticks and an increased rate of infection. NOSEK, J. - CERNY, V. - GULYÁS, M. - MOLNÁR, E. - ERNEK, E. - KOZUCH, O.-LABUDA, M. : Kisemlősök populáció-sürusége és szerepük a kullancsok közvetítésében Az ún. kullancs-encephalitis közép-európai természeti gócaiban a Rodentia és az Insectivora rendbe tartozó kisemlősök, elsősorban az erdei pocok, az erdei egér és a sárga nyakú erdei egér az Ixodes ricinus lárvák legfontosabb gazdái. E kisemlősfajok nagy egyedszámban való előfordulása egybeesik a kullancsok aktivitási idejével. A kisebb rovarevők kevésbé jelentős szerepet töltenek be a kullancsok terjesztésében, mint a kisrágcsálók. A kullancsok elszaporodására a vadgazdálkodási körzetekben azokon az erdőkön és bozótos legelőkön találhatók a legkedvezőbb feltételek, amelyeken háziállatokat is legeltetnek. Ilyen helyeken a kullancs nymphák és imágók száma meghaladhatja a 100 négyzetméterenkénti 600 példányt is.
References NOSEK, J. - KOZUCH, 0-: New aspects in the ecology of tick vectors. - Folia Par. (Praha) 17. 327-329. 1970. NOSEK, J. - KOZUCH, 0. - CHMELA, J.: Contribution to the knowledge of home range in common shrew Sorex araneus L - Oecologia (Berlin) 9_. 59-63. 1972. VARMA, M. G. R.: I960. Personal communication. Received: 30. 1. 1973- Dr. NOSEK, I. Inst. Vir. SAS Bratislava Ulinska Dolina 9 Czechoslovakia