A scientific study of wolves in the wild showed infection with the parasite, Toxoplasma gondii, makes them bold, more likely to leave a pack and strike out on their own, express riskier hunting behavior, and become pack leaders. Why would a pathogen seem to improve survival value in making a predator more deadly?

Yours is an interesting question about this peculiar state of affairs but presupposes an evolution-like accommodation, that things are acquired and retained because they have survival value, being dogma of evolutionary theory that happens to be grossly misapplied as it is a very trivial influence on things with respect to so-called "natural selection" favoring the strong over the weak, and so on, having anything to do with inherited characteristics of value to an organism. In this case, the wolves are being heightened in their ferocity, because their body is on higher alert status given there is an internal battle going on, because of the immune system having to contend with a chronic presence of an invading species. The way the animal handles this is a kind of instinctual cue to sense there is a need for ramping things up to be on the offensive, literally, and the animal will, as a consequence, exhibit a number of behaviors that flow in part from the physiology of the physical body trying to generate more energy to use, and directing it in specific ways to muster defenses and an attack on the invading microbes. So this is a kind of blending of responses that cannot be highly specific because there is no conscious awareness on the part of the animal it is infected and needs to reckon with a chronic state of immune system stimulation, and so on. So this is just an interesting example of how animals deal with such problems. They are geared to apply self-help quite powerfully, and there can be an excess of zeal in doing so, and that is what is being observed.