3 research outputs found
Host and Environmental Influences on Development of Disease
While many myxozoan parasites produce asymptomatic infections in fish
hosts, several species cause diseases whose patterns of prevalence and
pathogenicity are highly dependent on host and environmental factors.
This chapter reviews how these factors influence pathogenicity and
disease prevalence. Influential host factors include age, size and nutritional
state. There is also strong evidence for host strains that vary in resistance
to infection and that there is a genetic basis for resistance. A lack of
co-evolutionary processes appears to generally underly the devastating
impacts of diseases caused by myxozoans when introduced fish are
exposed to novel parasites (e.g. PKD in rainbow trout in Europe) or when
native fish are exposed to an introduced parasite (e.g. whirling disease in
North America). Most available information on abiotic factors relates to
water temperature, which has been shown to play a crucial role in several
host parasite systems (e.g. whirling disease, PKD) and is therefore of
concern in view of global warming, fish health and food sustainability.
Eutrophication may also influence disease development. Abiotic factors
may also drive fish disease via their impact on parasite development in
invertebrate hosts
Fish Immune Responses to Myxozoa
Myxozoans evoke important economic losses in aquaculture production,
but there is almost a total lack of disease control methods as no vaccines or
commercial treatments are currently available. Knowledge of the immune
responses that lead to myxozoan elimination and subsequent disease
resistance is vital for shaping the future development of disease control
measures. Different fish immune factors triggered by myxozoan parasites
are reviewed in this chapter. Detailed information on the phenotypic and
underlying molecular aspects of innate and adaptive responses, at both
cellular and humoral levels, is provided for some well-studied fishmyxozoan
systems. The importance of the local immune response, mainly
at mucosal sites, is also highlighted. Myxozoan tactics to disable or avoid
immune responses, such as modulation of immune gene transcription and
immune evasion, are also reviewed. The existence of innate and acquired
resistance to some myxozoan species suggest promising possibilities for
controlling myxozooses through immune-based strategies, such as genetic
selection for host resistance, vaccination, immune therapies and administration
of immunostimulants