Ascariasis is a parasitic disease caused by Ascaris in the human body.
The disease is caused by Ascaris, mostly Ascaris lumbricoides, occasionally Ascaris suum. Ascaris adults are milky white, sometimes light pink. The head and tail are thinner, resembling earthworms. The males are relatively small, with two copulatory spicules at the tail. The females are large and with vertical tail. There are fertilized eggs and unfertilized eggs. Only fertilized eggs can develop and are infective. The eggs can tolerate dryness and cold, and are not sensitive to general disinfectants, but they cannot survive for 15 minutes at 55°C.
Ascaris do not need an intermediate host. After copulation, a female lays 200,000 eggs per day. Fertilized eggs are excreted through feces. If the temperature and humidity are optimal, the eggs are infective in 25 - 26 days. Infective eggs can survive for 1 - 5 years in wet soils. After the eggs are swallowed by humans, most are eliminated by gastric acid. Only few eggs enter the small intestine. The shells can be easily digested by intestinal juice. The larvae shed their shells, invade the intestinal mucosa, enter the portal vein through capillaries, and reach the lungs through liver, inferior vena cava, and right heart. The larvae develop in the alveoli, and migrate upwards to the throat through the small bronchi and trachea. The larvae are swallowed, and reach the small intestine through the stomach, where the larvae develop into adults. It takes about 2 months from infective eggs being swallowed to adults laying eggs. The life span of Ascaris in the human body is 1 - 2 years.
Signs and Symptoms
If Ascaris larvae migrate in the lungs, patients may present symptoms of allergic pneumonia, such as chills, fever, cough, bloody sputum, eosinophilia, and urticaria. If large amounts of infective eggs are swallowed in a short period of time, allergic asthma may occur, and the main symptoms are asthma, dry cough, and foreign body sensation in the throat.
In severe infections, the larvae can enter the systemic circulation through the pulmonary capillaries and left heart, and invade some tissues and organs, such as the thyroid, lymph nodes, thymus, spleen, brain, and spinal cord, resulting in corresponding lesions.
Intermittent periumbilical pain or upper abdominal cramps are the characteristics of intestinal ascariasis. Other symptoms and signs include abdominal distension, abdominal tenderness, indigestion, diarrhea, constipation, anorexia, nausea, and vomiting. Children often present neuropsychiatric symptoms, such as convulsions, night terrors, bruxism, and occasionally allotriophagy.
Biliary ascariasis is caused by intestinal Ascaris entering the bile duct, and is manifested by paroxysmal epigastric boring pain, jactitation, and paleness. Pains radiate to the right shoulder, lower back, or lower abdomen. There are often nausea and vomiting. In the physical examination, the abdominal signs are not obvious, and are not commensurate with the severity of abdominal pain. There are only localized mild point tenderness right under and to the right of the xiphoid process, and there is not abdominal tension. If Ascaris completely enter the bile duct or even the gallbladder, pain is reduced, but the inflammation develops, and the clinical manifestations are prominent fixed point tenderness, muscle tension, rebound tenderness, fever, chills, and jaundice.
Intestinal obstruction caused by Ascaris is characterized by paroxysmal abdominal cramps, particularly periumbilical area or right lower abdomen, vomiting, and absent defecation. After the obstruction is formed, pain can gradually increase, lasting for few minutes, and pains may relapse in a short intermission. In most patients, soft, painless, movable masses or funicular lesions are palpable on the right side of the umbilicus, and the obstruction is more common in the ileum. There may be low-grade fever and leukocytosis in the early stage, and severe dehydration or acidosis, and even shock in the late stage. There is a high morbidity rate in children.
If Ascaris enter the vermiform appendix, appendicitis may occur, and there may be a clinical history of ascaris in the stools or vomitus. When paroxysmal abdominal cramps occur, there are severe pain and frequent vomiting, but when relieved, there is not pain. Pains are initially in the whole abdomen or in the periumbilical area, subsequently migrating to the right lower abdomen. In the early stage, there are severe symptoms and mild signs, and there are only tenderness near McBurney point or tender, funicular lesions in the right lower abdomen. The disease develops quickly, and local muscle tension, tenderness, rebound tenderness, and cutaneous hyperalgesia occur in 8 hours in most patients. If the perforation occurs, there may be secondary peritonitis, and septic shock and systemic failure can occur in the severely ill patients.
Ascaris can perforate the diseased or normal intestinal wall. The diseased intestinal wall includes the lesions caused by duodenal ulcer, intestinal obstruction, enteric typhoid fever, or appendicitis and sutures in appendectomy and gastrectomy. Ascaris can also enter the abdominal cavity through Meckel diverticulum. The clinical manifestations are subacute peritonitis, as well as diffuse or localized peritonitis. There is exudate in abdominocentesis, and the eggs may be detected. There are nausea, vomiting, and abdominal distension, but there is not obvious fever.
If there are Ascaris eggs detected in the stools, or Ascaris adults found in the stools or vomitus, the disease can be diagnosed.
The treatment regimen is albendazole 400mg orally in a single dose, mebendazole 100mg orally twice a day for 3 days or 500mg in a single dose, or ivermectin 150 - 200mcg/kg in a single dose.