Edit: It has come to my attention that this page is one of the top google hits for “microparasite,” “macroparasite,” and “microparasite vs. macroparasite.” Since dozens of people end up here every day, I’ve remodeled this post to be more informative. I hope this helps! If you can think of something that I should add, let me know in the comments! Thanks for visiting!
Microparasites vs. Macroparasites
The main distinction between microparasites and macroparasites is whether they “multiply” within their definitive host or not. Microparasites do “multiply” in their definitive host, and macroparasites do not “multiply” in their definitive host. This distinction is important because it influences the ecology and epidemiology of micro and macroparasitic infections.
“Multiply” vs. “Reproduce”
Why am I saying “multiply” instead of “reproduce?” Because both microparasites and macroparasites may reproduce in the definitive host. However, in macroparasites, reproduction usually leads to the production of eggs or larval stages that then leave the definitive host. That is, reproduction occurs, but the host does not end up with more parasites. Microparasites use direct reproduction; reproduction leads to an increase in the number of parasites within the host.
Microparasite Infections and Microparasite Examples
Microparasites are tiny!
They tend to have very short generation times in comparison to their hosts. Compare your life span to that of viruses, bacteria, and fungi, which are the main ‘groups’ of microparasites.
In microparasite infections, the intensity of disease/pathology and infectiousness tend to be determined by whether the host is infected or not. (At least, they can usually be modeled that way.) That is, if you are infected, you probably have many, many parasites, because the parasites have high reproductive rates. In other words, the number of parasites per host is not as important as it is in macroparasite infections.
Hosts tend to develop immunity to microparasites.
Here are some good examples of microparasites:
- Malaria (protist)
- Giardia (Protozoan)
- Viruses (influenza, hepatitis)
- Fungi (ringworm)
Macroparasite Infections and Macroparasite Examples
Macroparasites are bigger, and include things like helminths and arthropods.
They have relatively long generation times.
Macroparasite infections tend to be chronic, and they are accumulated relatively slowly.
Hosts don’t usually develop immunity to macroparasites, or else the immunity is short-lived and/or only happens with high parasite burdens.
Here are some good examples of macroparasites:
- Ticks (Arthropod)
- Schistosomes (Flatworm)
- Roundworm (Nematode)
Modeling Microparasites and Macroparasites:
I originally wrote this post because I was reading Anderson and May’s (1991) “Infectious Diseases of Humans.” Early on, they defined microparasites and macroparasites and explained why we model them differently. I’ve basically given you a synopsis of their definitions, and now I’ll briefly touch on modeling.
As with any model, your decisions about what type of model you want to use will depend on a variety of things. But in general, it makes sense to model microparasite infections with ‘compartmental models’ and presence/absence of infection. You’re infected, or you aren’t, and if you are infected, then you have the “average” parasite load. Again, this is because these parasites multiply quickly within the host.
If you’re modeling macroparasite infections, the distribution of parasites becomes more important. In hosts that are infected, most will have very few parasites, and some will have very many parasites. Transmission and pathology will likely depend on the number of parasites per host. Therefore, using a “present and average” type of model may not be useful (depending on your question).
Hope this helps!
Thank you so much! So glad i found this page. Helped alot!
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This is all very interesting but the real question is in eradicating them from the host. Ive read lots that antihelmintic drugs are almost useless, so in what way do the hosts get their lives back? Please assist
I’m not sure that I’d agree that how to eradicate parasites is the “real question.” Certainly we want to be able to treat – either preventatively or reactively – humans, livestock, and pets. And there are certain pathogens of wildlife (e.g., the fungi that cause white-nose syndrome in bats and chytridiomycosis in amphibians) that we would like to be able to treat, due to the widespread extinctions of host taxa that those pathogens cause. But most parasites are healthy, important parts of ecological communities, even though they have detrimental impacts on some individuals in those ecological communities.
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I was wondering if you could possibly repost the image to the Anderson and May compartmental model? (The link isn’t getting me to it and the image isn’t showing up).
Reposted! The link should work now, too. It’s worth checking out!
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Thank for the site and information. When you say that macroparasites do not “multiply” in their definitive host, how about lice since they complete their life cycle on the same host from egg to adult? Please clarify.
Great question! I think this is an important example of how our definitions are a bit wishy-washy. Classically, worms and ectosymbiotic arthropods are considered macroparasites, and that’s still the general consensus. So if you’re just generally trying to lump lice into one category or the other, I’d say that they fall in the macroparasite group. But if you’re trying to model lice epidemics, you’ll need to decide whether lice transmission and pathology will depend on the number of parasites per host. If not, I’d model lice epidemics as if they were microparasites.
I am a PhD student in animal behavior and found your blog post very interesting. Do you have more articles recommendations to explore deeper the difference between macro and microparasites?
Hello! Thanks for visiting! I have one more post about parasite classification schemes that you might be interested in: https://parasiteecology.wordpress.com/2014/02/05/predator-vs-parasite-vs-parasitoid/
Also, Anderson and May (1991) have a great discussion on the topic in their book: Infectious Diseases of Humans: Dynamics and Control. Most university libraries carry the book.
Hope that helps!
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I am a master student in zoology. I am doing research about disease transmission in animal social network. Such a great glob it is!! It helped me a lot on understanding the parasites. Could you please list the references you sited on this article? I am not doubting the veracity of this article. Because I want to cite the article but it is not a published paper. Thank you so much.
Howdy! Most of this is “general knowledge” kind of stuff. But you can check out Anderson and May’s (1991) “Infectious Diseases of Humans” book. Also, there’s this paper by Lafferty and Kuris that talks about the intensity-dependent stuff: https://parasiteecology.wordpress.com/2014/02/05/predator-vs-parasite-vs-parasitoid/
I’m majoring in Ecology and found this site helpful. Thanks!
Glad to hear it!