This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Microbiology
Most common presenting symptom of threadworm infection amongst the following is - 
Select and explain. 
A. Abdominal pain, B. Rectal prolapse, C. Urticaria, D. Vaginitis
A: Abdominal pain
Answer: A: Abdominal pain 
Explanation: Most patients infected of thread worm/pin worm/seat worm /Enterobius vermicularis are asymptomatic.
Most common complaint: Perianal and perineal pruritus (pruritus ani)- nocturnal/early morning.
Other complaints: Abdominal pain, irritability and restlessness.
All these symptoms caused by the female worms laying eggs on anal area.
Severe infections: Sleep disturbances, neurosis, nail bite, grinding teeth at night.
Adult worms can cause appendicitis.