What do parasites do?
Parasites suppress the immune system of the host in order to help them survive. They want to carry out their own life cycle and if they cause immunosupression to the host they are less likely to be killed. However, it is a trade off between the host dieing and the parasite being dieing. Parasitism is when an organism lives off another organism, it will be draining its resources.
Types of parasites
There are a number of different types of parasites. Helminths are worms that live in the host. They are often large and need to be well adapted to evade the host’s immune response to prevent them from being killed. They may also adopt host proteins as its own surface protein so it is not recognised as foreign by the immune system. Many have a long life cycle so it is in their interest to keep the host alive for a long time. Helminths are a big problem in livestock and they are often put on worming programs. There are many different types such as strongyles that live in the intestines.
Protozoa are small and will often live inside cells. An example of this type of parasite in the horse is Equine Protozoal Myeloencephalitis (EPM).
Arthropods live on the outside of the animal such as ticks and fleas. They feed off the host through their skin. The well adapted ones have an anaesthetic in their saliva so the host will not feel them drinking their blood and will not scratch them off.
Strongyles vulgaris can be seen in the horse becomes infected by ingesting the larvae. They go through the small intestine and large intestine walls and get into the arteries 7 days after they have been infected. They then carry on developing for the next 3-4 months. Mature worms lay eggs which pass to faeces and pasture.
There are also a number of other methods to control parasites which I will go into in another Science Sunday post.