ISSN 1067-4136, Russian Journal of Ecology, 2008, Vol. 39, No. 2, pp. 136–139. © Pleiades Publishing, Ltd., 2008.
Original Russian Text © V.M. Ivanov, 2008, published in Ekologiya, 2008, No. 2, pp. 147–150.
It is known that the species ranges of free-living and
parasitic organisms are not stable but change signiﬁ-
cantly in time and space. The rates of these changes are
different: in some cases, the ranges remain unchanged
for millennia; in other cases, their boundaries may shift
within several years. Most labile are the ranges of those
parasites whose life cycle involves several hosts.
As a rule, the expansion or reduction of a species
range leads to certain changes in the corresponding
ecosystems. The consequences may be either favorable
or detrimental for the environment. In most cases, man
initiates species introduction or creates conditions
facilitating the entry of new species into the ecosystem.
The rate of introduction has abruptly increased in
recent decades, and this process has become global.
A complex interrelation between the spatial distri-
butions of free-living and parasitic organisms is illus-
trated by the example of expansion to the Volga delta of
(Müllend.) (Prosobranchia), intermediate hosts
1899) Lühe, 1909 and
et Lindtrop, 1919 (Heterophyidae). The deﬁnitive hosts
of these trematodes are gulls and two mammals intro-
duced into the Volga delta, the raccoon dog
(Gray, 1839) and the American mink
MATERIAL AND METHODS
The study was performed in the Volga delta from
1976 to 2005. The parasitological material was
obtained from 4500
snails, 38 American minks, 48 rac-
coon dogs, and one jackal. The samples were collected
and processed by standard methods (Skryabin, 1928;
Sudarikov and Shigin, 1965). Trematodes were stained
with carmine acetate, dehydrated in graded alcohols,
clariﬁed in dimethyl phthalate, and embedded in Can-
To estimate the spectrum of supplementary hosts of
trematodes, 4200 ﬁsh of 34 species were examined.
The results were described using the following indi-
ces: invasion prevalence, or the proportion of hosts
infected (IP, %); invasion intensity, or the average num-
ber of parasites per infected host (II, ind.); and the par-
asite abundance index, or the average number of para-
sites per host in the total population studied (AI, ind.).
RESULTS AND DISCUSSION
are now regarded as an essential com-
ponent of parasitocenoses in the Volga delta and the
northern Caspian Sea. They are widespread in temper-
ate latitudes of the Palearctic, from the western Atlantic
coast to Primorye and Kamchatka (Krasnolobova,
1986). The trematodes are characterized by a trixenic
type of the life cycle, with free-living and parasitic
stages alternating during ontogeny.
The parthenitae of trematodes
have been recorded
in the Volga delta only in snails of the genus
. In the initial period after the appearance of these
mollusks in the Volga Delta, the indices of their infesta-
tion (IP) by
did not exceed
0.2–0.3 and 0.1–0.2%, respectively. Favorable ecologi-
cal conditions (optimal temperature and illumination,
Genesis of Epizootics Involving Introduced Species
of Helminths, Mammals, and Mollusks
V. M. Ivanov
Astrakhan State Biosphere Reserve, Naberezhnaya Reki Tsarev 119, Astrakhan, 414021 Russia
Received April 18, 2006
—The functioning of two foci of helminth diseases caused by trematodes
has been studied in the Volga Delta. The origin of these foci is related to the expansion
of species ranges of
snails, intermediate hosts of trematodes. Introduced mammal species, the rac-
and American mink
, are involved in the circulation of the
: trematodes, introduced species, mollusks, mammals, disease foci.