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Asked by $Elean0r$ to Claire, Franco, Koi, Linda, Mark on 13 Jun 2016. This question was also asked by charlie.
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Franco Falcone answered on 13 Jun 2016:
Hi $Elean0r$
parasitism is the most successful strategy of survival and I would state that all animals have parasites, but you tend to have more parasites if your immune system is weak. The important thing is that most parasites will not be able to survive in an animal, because of their immune systems, only the parasites which have adapted to their hosts will survive. That’s why parasites tend to infect specific animals, for example only one species of water snails, or certain mosquitoes. For example malaria is transmitted by Anopheles mosquitoes, but not by Culex mosquitoes or sandflies, or tsetse flies. Parasitism is all about specialisation!
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Arporn Wangwiwatsin answered on 13 Jun 2016:
Hmmm I support Franco’s statement that all animals have parasites … But whether they are heavily infected or not can depends also on how much the animals are exposed to parasites. (like by drinking/eating contaminated water/food or spending time in areas with lots of vectors – things that transmit parasites – like mosquitoes and some biting bugs.)
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Linda Anagu answered on 13 Jun 2016:
@ $Elean0r$, I do not know. But certainly the young of any animal is more prone to any infection as they are encountering most of the parasite for the first time and this give their body the chance to develop the needed immune fighters that will help them kill the parasite, once the parasite comes again.
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Claire Bourke answered on 13 Jun 2016:
Great answers form the other scientists.
Parasites tend to be specialised to infect one or two species (species infected by parasites are also called ‘hosts’) so that they can develop special ways of avoiding detection and expulsion by that species’ immune system. Infecting more species means that the parasite needs more techniques to survive, which takes more energy and adaptation and as a result is a lot harder to achieve. Parasites also compete with one another for space and resources so that if all parasites infected the same animal or the same type of animal there wouldn’t be room for them all. Finally, for thousands of years parasites have interacted with their host species and this has affected their evolution; if any one species was more likely to be infected by parasites and get sick, then it would be less likely to survive and continue to evolve. So today we only have species (both hosts and parasites) that can stand up to infections effectively. For that reason, there isn’t a particular species that is most prone to infections.
I agree with Linda that the age of the host (I.e. The animal that is infected) can play a big factor – for example the heaviest infections from schistosomes (the parasitic worm that I study) are in children, who haven’t developed a protective immune response to these parasites yet; adults tend to have lower infections because their immune systems have learnt how to keep worms out!
Animals (& humans) that are already sick tend to be more likely to become infected with other things too because their immune system is weaker.
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Mark Booth answered on 14 Jun 2016:
Every multi-celled organism has parasites. All animals since the time of the dinosaurs have been affected by parasites. They are part and parcel of the global ecosystem. One of the easiest ways to think about this is to consider that everywhere and everything in and on the planet is a potential habitat for an organism. There are some very hot springs where a certain type of bacteria flourish. Our own blood (a very hostile environment) can support worms that live for 10 years or more.
Most parasites are specialists in the sense of having a well-defined life cycle of specific hosts. But some other parasites are so-called generalists that can inhabit a wide range of hosts. This strategy can help them be more successful in propagating across the planet.
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