Abiotic and biotic factors
affecting parasite abundance
Environment of parasites
► 2 components
► host organism (1st level environment) = biotic factors
► external environment of the host (2nd level environment)
= abiotic factors
Host environment
Parasite
Host
►Abiotic vs. biotic factors
1st level environment = host
► Host species
► Age
► Host size
► Sex
► Population density
► Food strategies
► Behaviour
► Hormonal activity
► Physiological conditions
► Immune response
► Stress
► Genetically fixed susceptibility to the parasite
2nd level environment = host
environment
► Temperature
► Light intensity (length of photoperiod)
► Environmental gas concentrations (O2 and CO2)
► Salinity of the environment
► pH of the environment
► Water or air flow
► Size and type of habitat (shape and depth of the water
reservoir)
► Environmental pollution - parasites as bioindicators of
water quality
Epidemiological characteristics of parasitic
infection
► Prevalence - the proportion of infected hosts to all
examined hosts
► Intensity of infection - number of individuals of a given
species of parasite on infected individual of the host
(mean, min-max, median)
► Abundance - number of individuals of a given species of
parasite per host individual (mean abundance ± SD,
median with CI)
Abiotic factors
► 2nd level environment plus annual seasonality and latitude
► Influence on the abundance and intensity of parasite
infection
► In natural ecosystems, the simultaneous influence of
multiple abiotic and biotic factors
e.g. the effect of water temperature
and host body size on the abundance
of fish monogeneans
► Environmental temperature
► The most important abiotic factor
► direct effect – it stimulates the reproduction of the
parasites
indirect effect - effect on the physiology and immunity of
the host (poikilothermic hosts)
► Temperature affects natality and mortality, presence
(Cestoda, Acanthocephala) and abundance, transmission of
parasites (cercariae)
Abiotic factors: temperature
► Different tolerance of species to temperature
Monogenea - genus Gyrodactylus - low temperature
genus Dactylogyrus - higher temperature
Abiotic factors: temperature
► Indirect effect of water temperature on the composition of
parasite communities - temporary absence of competitive
species, release of niches
► The effect of temperature can be confounded by other
abiotic or biotic factors - interspecies interactions in the
case of high population densities induced by temperature
change
► Influence of temperature with seasonal changes - in the
temperate zone → seasonal dynamics of occurrence and
abundance of parasites (temperate zones)
Abiotic factors: temperature
► Temperature, photoperiod
length, seasonal
occurrence of the host,
availability of intermediate
hosts, feeding behavior of
the host
► Seasonal cycles in
occurrence of parasites
► Monogenea, Cestoda,
Nematoda
► Figure: Gyrodactylus
macrochiri on fish Lepomis
macrochirus
Seasonal dynamics of occurrence and
abundance of parasites
Seasonality of parasites
Seasonality of parasite occurrence
e.g. 9 species of the genus Dactylogyrus (Monogenea) on the gills of
the roach
- abundance of 5 species increase with temperature (summer)
- presence of 4 species related to the period with lower temperature
(spring, autumn)
Seasonal variability of morphology
e.g. Gyrodactylus – smaller sclerotized haptor structures in summer
Seasonality of reaching sexual maturity and reproduction
direct effect of temperature, indirect effect of temperature - physiology or
food ecology of the host, occurrence and abundance of intermediate
hosts…
Synchronization of parasite and host reproduction: Proteocephalus in
Leuciscus leuciscus and Squalius cephalus during spawning
Seasonal changes in intensity of infection
Monthly changes in the intensity of infection of 5 species of
leeches in turtles
Seasonal changes in intensity of infection
Ex. Seasonal changes in the abundance of metazoan parasites of common carp
(Cyprinus carpio)
Influence of water temperature on the
occurrence of parasites
► Higher speciation rate
in warm water than in cold ones
► Ex. Ectoparasites of marine fish
Biotic factors
► 1. Biology of the host - host-parasite interactions
► 2. Parasite-parasite interactions
intraspecific
interspecific
► Interconnection of factors
e.g. age of the host with sexual maturity and food ecology
Host size
► The most frequently studied factor
► Larger host = more space for more parasites
► Host length (total length, organ length, host weight)
► Ex. The abundance of monogeneans on fish gills increase
with fish size and gill size
Host size
►Ex. Trematode Euhaplorchis californiensis
in the fish brain (Fundulus parvipinnis)
Host size
► Ex. Intensity of infection of an ectoparasite (Argulus
foliaceus) in relation to body weight in different cyprinid
species
Host age
► Correlation with the length and weight of the host
► Difference in parasite infection among age groups
i.e. younger individuals are infected by more helminths
► Link with food strategy
► Difference in the immune system
Host size/age
Ex. Prevalence and intensity of infection of an ectoparasite
(Argulus foliaceus) for different age categories of fish
Host age
► e.g. changes in flea prevalence and aggregation in rodents
(species of Apodemus, Clethrionomys glareolus, two
species of Microtus)
► Assumption: parasite-induced mortality and acquired agedependent
resistance
1. highest aggregation of parasites and prevalence in
middle age categories (Apodemus and C. glareolus)
2. increasing aggregation and prevalence with age
(Microtus)
→ affected by dispersion, spatial distribution and habitat
structure of the hosts
Host sex
► Controversial factor
► Differences in morphology, physiology and behavior
► Influence of steroid hormones
► Possible influence of different food ecology
► Possibly different resistance
e.g. Higher lice abundance in males than females in rodents
Oligoryzomys nigripes – males with higher mobility and
physiological stress - a consequence of the promiscuous
mating system
Host sex
► The effect of host sex on parasite abundance depends on
the biological attributes of the parasite
► Ex. Ectoparasites (ticks, mites, lice and fleas) in rodents
Rhabdomys pumilio
- higher parasitism in males than in females
- influence of host sex on parasitism variable at the level of
parasite species between localities and between species of
a given taxonomic group
Host density and social behavior
► Higher density and social behavior - transmission of
ectoparasites
► Ex. Relationship between population density of 19
mammalian species and abundance of strongylid nematodes
Host social behavior
► Lice Colpocephalum turbinatum in Galapagos Hawk Buteo
galapagoensis
- influence of host sociality on
abundance of parasite
Host population size
► Abundance of Monogenea (Dactylogyrus formosus, D.
wegeneri, D. intermedius a Gyrodactylus carassii) in fish
(Carassius carassius)
- Assumption: increasing abundance with increasing host
population density (density = distances between
individuals)
- density is an insignificant factor
- population size (= total availability of hosts) is a
significant factor
Host population size
Food strategies
► Transmission of endohelminths (complex life cycle)
► Amount of food, proportion of components with parasite
invasive stage
► Influence of seasonal changes in food supply - occurrence
of intermediate host
► Position of the host in the food chain
Host physiology
► Dependent on abiotic and biotic factors
amount of food available
environmental pollution
host age
competition and other interactions
Host immune system
► Genetic factors
► Physiological and hormonal state
► Host age
► Stress
► Previous experience with infection (specific immunity)
Host immune system
► Specific host susceptible, non-specific host resistant
► Break-down of immunity - infection of a non-specific host
► Sensitivity vs. resistance - influence of genetic factors
(genetic compatibility)
► Effect of water temperature on immunity in poikilothermic
hosts
Host genetics
► Eel (Anguilla anguilla), multicellular parasites
► genes implicated in host physiology:
- host response to environmental stress, i.e., heat shock –
protein 70 (HSP70), metallothionein (MT),
- osmoregulation - thyroid hormone receptor (THR), Na /
KATPase
- THR coloration, rhodopsins (FWO, DSO)
► Lower gene expression = digenean infection (7 species)
► Increased trophic activity of eels = nematode infection
(Anguillicola crassus)
Host immune system
► Ex. Cellular immunity (CMI) in response to hematophagous
mobile ectoparasite - fly (Carnus haemapterus) colonizes
birds (Coracias garrulus) during the nesting season
Influence of environmental and host factors
on parasite abundance
► Ex. Epidemiological data from 8 species of coral fish from
two South Pacific islands
Influence of environmental and host factors
on parasite abundance