It's in buffInfectionCatch:
<buff name="buffInfectionCatch" name_key="buff Infection Catch" hidden="true">
<damage_type value="Bashing"/>
<stack_type value="ignore"/>
<duration value=".1"/>
<effect_group>
<triggered_effect trigger="onSelfBuffStart" action="ModifyCVar" cvar="infectionCounter" operation="set" value="25">
<requirement name="!HasBuff" buff="buffInfectionMain"/>
</triggered_effect>
<triggered_effect trigger="onSelfBuffStart" action="ModifyCVar" cvar="infectionCounter" operation="add" value="250">
<requirement name="HasBuff" buff="buffInfectionMain"/>
</triggered_effect>
<triggered_effect trigger="onSelfBuffStart" action="AddBuff" buff="buffInfectionMain"/>
</effect_group>
</buff>
Based on what I see, the buff can be triggered by a bash attack. If you look in the items file, you will see certain items with damage_type as bashing listed.
<property name="Damage_type" value="Bashing"/>
That's from items like the knuckles. So you can try this suggestion below:
In meleeHandAnimalWolf, you can a line like this (place it in the Action0 property class like it is in other instances)
<property name="Damage_type" value="Slashing"/>
This might (might as I don't have the time to test it myself) change the attack from bashing to slashing which wouldn't cause you to catch an infection. Not sure what this would do in regards to other critical buffs though.