Parasitism

Relationship between two organisms, where the parasite benefits at the expense of the host (ant. mutualism)

50% of all living species are parasites

Every organism is susceptible to parasite infection once in its lifetime

Microparasites

Very small, often intracelluar, have short generation times, high rates of reproduction within the host, tendency to induce immunity. Typical infections are of short duration in relation to the normal life-span of the host.

Bacteria, viruses, protozoa, fungi

Borrelia burgdorferi s.l. Staphylococcus aureusHIV

Trypanosoma sp. Candida albicans

Macroparasites

Much larger than microparasites with much longer generation times. Reproduction occurs but reproductive products are shed. Immune response is usually density dependent and of short duration. Such infections are persistent with hosts often being continuously reinfected.

Ectoparasites

On the outside of the host feather, skin, hair, gills (permanent, temporarily)

No complete parasite existence (oxygen from outside the host)

Ticks, fleas, lice, mites, mosquitoes, bugs

Trombidium holosericum

Aedes albopictos

Endoparasites

In the inside of the host Intracellular (microparasites) Intercellular (helminths)

Ascaris lumbricoides Wucheria

bancrofti

Ancliostoma canium

Opisthorchis viverrini

Effect of parasites on their hosts: morbidity and mortality

Microparasites Acute infections over a short term, can have a

major influence on host mortality Macroparasites

More commonly chronic infections, cause less mortality but more morbidity (i.e. pathogenicity leading to reduced fitness)

Mortality in intermediate hosts

Biological invasions – an introduction

Closely connected to human travel and trade (increased by 50% since 1990)

Biggest threat to worldwide biodiversity besides habitat loss and fragmentation

Cause for 40% of historic extinctions

Special danger to island ecosystems

Clavera & García-Berthou 2005

Introduced species: nonindigenous to a given area, transported by human

activity usually localized distribution, possibly rare can include garden and farm animals

Invasive species: non-indigenous species (NIS) that can maintain an

established population causes economic or ecological harm or is likely to do

so in the future

Biological invasions – an introduction

Typical introduction routes: Intentional introductions:

Domestic, farming or hunting animals Farm or ornamental plants Biological control experiments

Unintentional introductions: Transport of plant seeds, small insects and other

invertebrates with other goods Marine organisms via ballast water, fouling Pathogens

Biological invasions – an introduction

Biological invasions – an introduction

100 of the worst invaders, selected by the Invasive Species Specialist Group (ISSG) of the IUCN:

Lowe et al. 2004

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Ecological consequences – Lake Victoria Nile perch (Lates niloticus)

introduction 1954 Massive spread in

1980s Extinction of >200

endemic fish species (mainly cichlids)

Nile perch

Endemic cichlids

Altered fish industry: smoking instead of sun drying

Deforestation, soil erosion, desertification

Increased nutrient levels promoted water hyazinth (Eichhornia crassipes) invasion

Ecological consequences – Lake Victoria

Ecological consequences – Hawaii Avian malaria (Plasmodium

relictum) introduced with pet birds

But: vector necessary for spread

1826: introduction of the southern house mosquito (Culex quinquefasciatus)

Malaria spread among bird populations

Honeycreeper with malaria-transmitting mosquitos

nucleus

Plasmodium

High mortality due to lack of resistance

Contributed to the extinction to >10 native bird species

Limits geographic distribution of birds

Hawaiian honeycreepers

Ecological consequences – Hawaii

Control difficult due to remote habitats

Mosquitos benefit from another invader: feral pigs (Sus scrofa)

Water-filled wallows serve as breeding locations for mosquitos

Ecological consequences – Hawaii

Anguillicoloides crassus

Der Nematode ist der Parasit:Anguillicola crassus

Natürliche Bedingungen: saugt Blut in der Schwimmblase des Japanischen Aals (Anguilla japonica).

Globalisierung: hat Aalarten anderer Kontinente, die mit dem Parasitenkeine Koevolution durchlaufen haben, als naive Neuwirte

kolonisiert. Wurde selbst nicht als Wirt von Parasiten oder Pathogenen beschrieben.

Life-cycle of Anguillicola crassus

Natural and introduced range of A. crassus. Red area: distributional range of Anguilla- species naturally infected by A. crassus (Anguilla japonica) and colonized eel species in Europe, America and Africa

Biogeographical studies: examine native and introduced

populations of invaders

Community studies: compare native and introduced

species within the same community

How is invasion success determined?The enemy release hypothesis (ERH):

Confirmed release from

enemies, impact on invasion

suggested

Invaders do not have less

enemies than the native species

Colautti et al. 2004

Hypotheses opposing the ERH: Propagule/sampling bias Community interactions or abiotic factors

reverse/reduce enemy effects Effects of newly acquired enemies:

NIS are naive hosts Genetic bottleneck leads to higher susceptibility

How is invasion success determined? The enemy release hypothesis (ERH):

Ticks: Acari, Ixodida

About 900 species in two major families: Argasidae (ca. 180 spp.) and Ixodidae (ca.720 spp.)

Almost all species spend much more time free-living in the environment than on their hosts

About 5-10% of species are of medical or veterinary significance

Three families

Argasidae The soft ticks (Lederzecken)

Ixodidae The hard ticks (Schildzecken)

Nuttalliellidae A monospecific family (Nuttalliella namaqua)

The lifecycle of ixodid ticks

Three-host ticks

Larvae Nymphs Adults

Transstadial transmission

Transovarial transmission

Eggs

I. ricinus: larvae, nymphs and adults

Ticks as vectors

Ticks are the most important vectors of pathogens to domestic animals and the second most important to humans

Tick-borne diseases

Viral (e.g. CCHF, TBE) Bacterial (e.g. Borrelia, Ehrlichia,

Rickettsia) Protozoan (e.g. Babesia, Theileria)

Environment and hosts

Tick distribution appears to be largely controlled by the environmental conditions available to the free living stages (eggs, larvae, nymphs and adults), especially temperature and humidity

Host availability may also play a role but many economically and medically important species use a wide variety of hosts (e.g. Ixodes ricinus, Amblyomma variegatum)

Tick distributions and global change Substantial changes in various species, e.g.

I. ricinus in Europe Evidence that these may be due to climatic

changes (e.g. Finland, Czech Republic) Also suggestions that political, social and

habitat changes may be involved (Randolph 2004)

Food-borne trematodes

Opistorchis viverrini, the small liver fluke Mekong area: Thailand, Laos, Cambodia, Vietnam 10 million people infected in Thailand and Laos

alone Infection by eating uncooked freshwater fish from

the cyprinid family

At the taxonomic level: how many species are present?

From: Andrews et al. 2008Trends in Parasitol

Pathogenicity

Causes liver and bile duct problems; blockage

One of the two species classifies by WHO as a carcinogen

Long-term infection can lead to cholangiocarcinoma (bile duct and later liver cancer)

www.stanford.edu

www.nri.org

Road constructionmore pondsstocked with infected fishhigh human prevalence

Problem

Symptoms and disease prevalence in the human population in the northeast of Thailand and southern Laos vary geographically

Does this variation have a population genetic basis: i.e. due to variation in O. viverrini