Ectoparasites 101

Ectoparasites are organisms that live on the surface of its host (e.g., maggots). This is different from other parasites we have learnt so far that live in the tissues, in the intestinal lumen, etc. Most ectoparasites are members of the phylum arthropoda (also known as arthropods) so you will hear the names interchangeably sometimes.

The term “arthropod” refers to invertebrate organisms with a hardened exoskeleton and jointed legs - these include insects (e.g., mosquitos, flies), arachnids (e.g., ticks, mites, spiders), crustaceans (e.g., crabs, crayfish).

We will focus on six arthropods of high medical importance (lice, mites, myiasis, fleas, ticks, and bed bugs). Unfortunately, there are many arthropods that are very high-yield (e.g., mosquitos, triatomines) that will not be covered here. However, they will be mentioned with each disease they are associated with (e.g., Anopheles mosquito in the Malaria module).

These are medically relevant for three main reasons:

1. Some function as vectors for a wide array of infections (e.g., bacteria, viruses, parasites).
2. Some serve as intermediate hosts for parasitic infections (e.g., Hymenolepis, Dipylidium, Paragonimus).
3. Fecal or salivary antigens of the arthropod can induce a hypersensitivity response in the skin and tissues (e.g., mites, fleas, lice), while others can be venomous (e.g., bees, scorpions).