1. Chapter 26 - Nematodes: Ascaridids

2. Family Ascarididae Ascaris lumbricoides A large intestinal roundworm of humans; females may attain lengths of 30 cm! In both sexes the mouth is surrounded by one dorsal and 2 ventrolateral lips The posterior end of the female is strait, while that of the males curves ventrally The female is prodigious in egg production, depositing about 200,000 eggs daily! Uterus may contain up to 27 million eggs at one time!!! The anterior end of Ascaris lumbricoides. Notice the three prominent "lips". Female and male Ascaris lumbricoides

3. Life Cycle Adult worms live in the lumen of the small intestine and get nourishment from semidigested food in the host Copulation occurs here and eggs are passed with the feces The outer, albuminous coat of the egg is brown in color due to bile pigment absorbed from the feces The zygote does not begin development until the egg has reached the soil Eggs are fairly resistant to desiccation and low temperatures With proper temperatures and oxygen levels the embryo molts at least once in the shell and develops to an infective larva Eggs can remain viable in the soil for 2 years

4. Ascaris Life Cycle

5. Life Cycle cont. After being ingested, infective eggs hatch in the duodenum Larvae actively burrow into the mucosal lining, enter the circulatory system, and are carried to the liver, through the right side of the heart, and on to the lungs by way of pulmonary arterial flow Larvae remain in the lungs several days, but eventually rupture from the pulmonary capillaries and enter the alveoli From here they move up the lungs and trachea to the epiglottis, are coughed up, swallowed, and passed into the small intestine After molting the worms grow to sexual maturity

6. Epidemiology Distribution of A. lumbricoides is worldwide, but it is prevalent in warmer climates It depends upon poor sanitation for its proliferation It is most prevalent in children; they are exposed to contaminated soil, do not wash before eating, put hands in mouth, etc.

7. Sympatamology Most cases of ascariasis are symptomless The most frequent symptom is upper abdominal discomfort Little damage results from larval penetration of the host’s mucosa However, aberrant larvae migrating in such organs as the spleen, liver, lymph nodes, and brain usually result in an inflammatory response Also, larvae escaping from capillaries in the lungs and entering the respiratory system cause small, hemorrhagic foci accompanied by coughing, fever, and difficulty in breathing Worms sometimes cause mechanical blockage of the intestinal tract Also, worms may penetrate the intestinal wall or appendix causing local hemorrhaging Overcrowding may also lead to wandering; worms can enter the appendix and cause blockage; worms have been known to migrate all he way to the anus Some worms migrate anteriorly and have been known to block pancreatic and bile ducts; others have gotten into the stomach and some even as far as the esophagus and tracheae

8. Toxocara canis Found in the small intestine of dogs and other canines Causes visceral larval migrans among humans (an accidental host); most common among children It usually results from the ingestion of eggs and the subsequent migration of second stage larvae within the internal organs The second stage larvae hatching from the eggs penetrate the intestinal wall and quickly invade the liver Although a majority of these larvae remain in the liver, some pass on to the lungs and, sometimes, the CNS and eyes Although most of the larvae eventually gravitate to a single location and become encapsulated by host tissues, for a period of time they actively migrate through the tissues, leaving long trails of inflammatory reaction cells

9. Visceral Larval Migrans Case Study A previously healthy 37-year-old black man had fever, abdominal cramping, vomiting, and diarrhea. After 1 week of symptoms, a chest radiograph showed multiple noncavitating pulmonary nodules On further questioning, the patient stated that he had acquired a puppy 1 month before onset of the abdominal pain. The puppy was being house- trained, and the patient had had no previous household exposure to dogs. Subsequently, tests for serum antibodies against T canis IgG and IgM were obtained and were positive at 11.5 and 9.3 standard deviations above the mean of a reference group of normal subjects. The Toxocara IgM titer indicated acute infection with T canis. A chest radiograph showing multiple noncavitating pulmonary nodules