Is your friends place in an area that has ticks? If he is then you are supposed to get your horse dipped in a tick bath to kill the ticks when it crosses borders etc. If your horse was in NSW then there are some areas that have a lot of ticks.
And then of coarse there are the odd few ticks you find in tick free areas. If you do find ticks on your horse then pull them out (be careful to get the head out) and then you can either squish them between your finger nails or put them in metho to kill them. You need to kill them! DO NOT drop them on the ground alive!!! You don't want to start a tick farm!!!!!!!!
They will not harm your horse in small numbers and the only damage they can really do to a fully grown horse is to make them itchy and then only in large numbers.
As Ryle said go to your local saddlery and ask if they have any shampoo that you can wash your horse in that may help.