Final answer:
In the provided sentence, the verb 'spread' is a transitive verb because it has a direct object, 'West Nile Virus.' There is no intransitive verb in the sentence as all verbs have clear direct objects.
Step-by-step explanation:
The sentence in question is "Mosquitoes spread West Nile Virus, a sometimes-fatal disease that first surfaced in the United States in 1999." In this sentence, the verb 'spread' is the action being performed by the subject 'mosquitoes.'
The direct object of this verb is 'West Nile Virus,' which answers the question of what is being spread. Therefore, 'spread' is a transitive verb as it requires a direct object to complete its meaning.
However, as the question asks to select the intransitive verb, it appears there might be a misunderstanding because this sentence does not contain an intransitive verb since all verbs present have direct objects.