The object of verbs having the sense of ruj 'to afflict', with the exception of the Causative verb jvaraya 'to be feverish', takes the 6th-Case-affix, when the verb expresses a condition (i.e. when the subject is an Abstract noun).,
Ex. चौरस्य रुजति रोगः 'the disease afflicts the thief' चौरस्यामयति आमयः ।
Why do we say 'when the subject is an Abstract noun'? Observe नदी कूलानि रुजति 'the river breaks the banks.' So also not here चौरं ज्वरयति ज्वरः 'the fever burns the thief.' So also when the verb संताप is used, चौरं संतापयति तापः ।
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The word शेष is also understood here. Thus चौरं रुजति रोगः ॥,