The documents includes chapter 7 of the course ecology, epidemiology and control of infectious diseases taught by prof. Leirs. The document does not contain the exercises, as these were made in an excel document.
CHAPTER 7: BIODIVERSITY AND
INFECTIONS
INTRODUCTION
All organisms living in a certain area are part of both an abiotic and biotic environment:
- Biotic environment: living part of an environment
- Abiotic environment: non-living part of an environment that shapes the environment where the
organism is living in (e.g. light, water, temperature, humidity, soil, …)
- Parasite: affected by abiotic factors inside and outside the host
o In the host: factors are fairly constant (? -> small variations)
o Outside the host: factors immediate affect the parasite
Depending on the conditions the parasite can have a higher/lower fitness
Parasite has to adapt to the conditions (especially when free-living) resulting in
evolutionary adaptations
Example: characteristics adapted to the abiotic conditions of where they live
Trichinella spiralis: sensitive to heat and to cold
o Found in Europe
Trichinella nativa: can withstand freezing T but is sensitive to heat
o Found in arctic conditions
Trichinella nelsoni: can withstand boiling T but is sensitive to cold
o Found in sub-Saharan Africa (tropical areas)
Note: the environment affects the parasite also via indirect effects through the effects on their host (e.g.
malaria, if T differs then the duration for the sporogonic cycle will change so T has no effect directly on
plasmodium)
ECOSYSTEM-DIVERSITY
The world is distributed in a large variety of different ecosystems. These different ecosystems each has their
consequences for the presence of different organisms (different T, latitudinal gradient, vegetation, humidity …)
- The environment is largely determined by the ecosystem and the ecosystem depends on where on
the globe it is located: other areas will have different conditions (T, vegetation, humidity ..)
- The ecosystem is dependable on the movement of the continents
o Example: India
At the time of Pangea it was almost at the South Pool and now it is above the equator. So
during this move the organisms living there had to adapt to survive
DISPERSION OF SPECIES
Conditions for establishment of a species in a new area:
- compatible physiology that matches local conditions
- ecological potential for establishment
o open niche: ecological place is not yet taken by another organism
o area must be large enough: population must be large enough to avoid extinction
- physical opportunity to reach the area: movement of the species (active or passive)
These aspects determine whether species can disperse to other areas
, Island biogeography
- more immigration on islands near to a source continent
- lower probability of extinction on larger islands
the rate of immigration and extinction will determine how many species are established on the island
Note: island can be a true geographical island but can also be a part of the population that is in another habitat
(e.g. forest with grass land around it).
ZOOGEOGRAPHIC PROVINCES
= areas around the world that had a similar type of evolution and where there has been contact between the
organisms that are living over such a whole area
result: 1) within one area there will be the potential to be the habitat for similar species
2) the more far away the areas from each other, the less related the species between the
areas, this also counts for parasites
Distribution of parasites and infectious diseases
- Host of the parasites are disturbed in the provinces: limit the spreading of the parasite
o Even though the climate between provinces might be the same, the parasite might be present
in one and not in the other because they could not reach the area (e.g. America and Asia)
- Exception: parasites of the human host we have successful inhabited in all the different province
o Human travel = global transport of infections
o Example: schistosomiasis
S. haematobium + S. mansoni: Africa
Due to slave trade:
o S. mansoni also in S-America because found a good snail host
o S. haematobium not in America because never found a good
snail host
S. japonicum: East-Asia
Distribution of infectious diseases depends on:
- Host/vector distribution: host/vector needs to be suitable for the parasite
- Host/vector abundance: needs to be above the threshold to avoid extinction of the infection
- Abiotic conditions for free-living stages
- Host behaviour and health interventions
HOST SPECIFICITY
Parasites are going to adapt to the environmental conditions but also to the conditions in the hosts (and
biotopes within a host (different organs)) that are available (evolutionary adaptations). Therefore a large
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