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PARASITOLOGICAL ASPECTS OF INVASIONS OF ALIEN SPECIES
Bayhanova Nasiba
Andijan State Medical Institute
Abstract.
Biological invasions by alien species present significant challenges not only to native
biodiversity but also to host-parasite dynamics within ecosystems. This article examines the
parasitological dimensions of species invasions, focusing on mechanisms such as parasite release,
spillover, spillback, and parasite-mediated competition. Drawing on empirical examples from
mammalian, amphibian, and aquatic systems, the paper explores how invasive species either
evade or introduce parasitic organisms, and how these interactions impact native species fitness,
community structure, and disease transmission. The analysis underscores the need to integrate
parasitological surveillance into invasive species management and biosecurity policy,
emphasizing that parasites are active ecological agents in the success and consequences of
biological invasions. A deeper understanding of these dynamics is essential for designing
effective conservation and public health interventions.
Kеywоrds:
alien species, biological invasions, parasitology, parasite spillover, parasite release,
host-parasite interaction, zoonosis, ecological disruption, invasive hosts, biosecurity.
INTRОDUСTIОN
Biological invasions by alien species represent one of the major drivers of biodiversity loss and
ecosystem disruption globally. These invasions are not merely ecological events but also complex
parasitological phenomena, as invasive species often interact with local parasite communities in
unpredictable ways. Parasites can act both as mediators and consequences of biological invasions,
influencing the fitness, spread, and ecological impact of alien hosts. The parasitological
dimension of invasion biology therefore warrants critical examination, especially in light of
emerging zoonotic risks, native host-parasite displacement, and the evolution of novel host-
pathogen systems.
MАTЕRIАLS АND MЕTHОDS
A well-documented phenomenon in invasion biology is the parasite release hypothesis, which
suggests that alien species introduced to new habitats often leave behind many of their natural
parasites. This release from parasitic pressure gives invasive species a competitive advantage over
native taxa. For example, the North American grey squirrel (Sciurus carolinensis), when
introduced to the UK, demonstrated reduced parasite load compared to native red squirrels
(Sciurus vulgaris), which contributed to its rapid demographic expansion.
RЕSULTS АND DISСUSSIОN
In contrast, alien species can also introduce novel parasites to naïve ecosystems — a process
known as parasite spillover. These new pathogens may infect native species lacking evolutionary
resistance, resulting in population declines. The introduction of Echinococcus multilocularis
through dog populations in Eastern Europe is a case in point, leading to human alveolar
echinococcosis outbreaks in areas previously free of the parasite.
Spillback occurs when alien species amplify the transmission of native parasites, acting as hyper-
competent hosts. For instance, invasive cane toads (Rhinella marina) in Australia have been
shown to facilitate the proliferation of native helminths such as Rhabdias pseudosphaerocephala,
intensifying parasitic burdens on sympatric amphibian species.
Parasites also influence interspecific interactions via parasite-mediated competition. Native
species suffering higher parasite loads may become ecologically inferior in competition with less
burdened invaders. In some instances, invasive species are co-introduced with their parasites,
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forming tightly linked ecological units. The introduction of Anguillicola crassus, a parasitic
nematode of eels, into Europe along with its Asian host, disrupted native eel populations across
freshwater systems.
The parasitological dimensions of species invasions have profound implications for conservation
biology, wildlife management, and public health. Invasive parasites can destabilize entire trophic
networks and serve as reservoirs for zoonoses. Moreover, they often complicate control strategies,
as parasites may persist even after the removal of their original hosts, or shift to new hosts
altogether. Surveillance and monitoring of parasitic fauna associated with alien species should be
integrated into biosecurity frameworks.
Invasion biology and parasitology intersect not only in ecological disruption but also in
evolutionary dynamics. When alien species enter a novel environment, they often encounter
unfamiliar parasites or are relieved from co-evolved ones. This disturbance in host-parasite
coevolution can catalyze rapid evolutionary change in both the invaders and the native species
they interact with. Notably, invasive hosts may develop increased resistance or tolerance to local
parasites over short timescales, whereas native hosts — when exposed to exotic parasites — may
undergo severe fitness declines due to a lack of evolutionary adaptation [2].
Empirical studies have demonstrated that host-switching events are common in invasion scenarios.
For example, the invasive American mink (Neovison vison) in Europe has acquired native
European parasites such as Echinococcus multilocularis and Trichinella spp., which it may not
have encountered in its native range. Conversely, in certain regions, it acts as a competent vector
of Aleutian mink disease virus, affecting native mustelid populations. Such events illustrate how
host-parasite networks become restructured, often unpredictably, following biological invasions
[3].
While parasites are often viewed as burdens, under certain conditions they can facilitate the
establishment and spread of invasive species. For instance, some parasites manipulate host
behavior in ways that may inadvertently benefit invasive host dispersal. Trophically transmitted
helminths, which increase host predation risk to complete their life cycles, may enhance the
ecological impact of alien prey species by making them more accessible to predators, thus
modifying food web structures.
On the other hand, parasites may also act as biological barriers to invasion. This occurs when
native parasites infect alien species but significantly reduce their survival or reproductive capacity
— a phenomenon observed in some freshwater fish introductions. For example, Gyrodactylus
salaris, a monogenean parasite of Atlantic salmon, limits the establishment of non-native
salmonids in Norwegian rivers [4].
СОNСLUSIОN
Understanding the parasitological aspects of alien species invasions provides critical insights into
their ecological dynamics and consequences. Parasites are not passive participants in invasion
processes but active agents influencing host success, native species decline, and pathogen
emergence. Incorporating parasitological expertise into invasion science is therefore essential for
holistic management strategies and the protection of ecosystem integrity.
RЕFЕRЕNСЕS
1.
Dunn, A. M., & Hatcher, M. J. (2015). Parasites and biological invasions: Parallels,
interactions,
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2.
Dunn, A. M., Torchin, M. E., Hatcher, M. J., Kotanen, P. M., Blumenthal, D. M., Byers, J.
E., ... & Perkins, S. E. (2012). Indirect effects of parasites in invasions. Functional Ecology, 26(6),
1262–1274.
https://doi.org/10.1111/j.1365-2435.2012.02041.xSpringerLink
INTERNATIONAL MULTIDISCIPLINARY JOURNAL FOR
RESEARCH & DEVELOPMENT
SJIF 2019: 5.222 2020: 5.552 2021: 5.637 2022:5.479 2023:6.563 2024: 7,805
eISSN :2394-6334 https://www.ijmrd.in/index.php/imjrd Volume 12, issue 05 (2025)
322
3.
Prenter, J., MacNeil, C., Dick, J. T. A., & Dunn, A. M. (2004). Roles of parasites in
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https://doi.org/10.1016/j.tree.2004.05.002SpringerLink
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Telfer, S., & Bown, K. J. (2012). The effects of invasion on parasite dynamics and
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