This is an interesting phenomenon, I think, because you often find that tick infestation is greatest on animals who are sick or have weak immune systems. With the dry conditions we had earlier this year, there were quite a few animals who were weak from not getting enough quality food.
When an animal is sick or weak, it probably lies down and stands still for longer period, allowing ticks more of a chance to climb onto its body. These ticks, in turn, can cause other diseases in the animal, further weakening it or even leading to its death.
Another interesting case was the problems caused by ticks when we first introduced lions to the Park:
The lions came from the Kgalagadi where there are not many ticks and so were not used to being infested with ticks. The ticks caused sores on the lions which were a cause for concern. Our conservation manager invented a system to spray the lions with anti-tick spray. A kraal (small enclosure) was made with a pressure-sensitive plate at the entrance. when the lion stepped on this, it triggered a spray aimed at their body. The lions were attracted to the kraal with a warthog carcass and a recording of hyena calls. This worked well for the male lions and allowed the sores to heal so that they had time to adapt to the onslaught of ticks. The two lionesses ran in the opposite direction to the hyena calls, showing how lionesses rely on male lions to defend them from hyena clans at kills/during confrontations (as they did not have other lionesses to support them at the time).