Basic information about Ascaris

 The Ascaris

Ascaris lumbricoides is the most common human helminth with low pathogenicity. However, in cases of heavy intensity infection, life threatening complications may occur. This chapter deals with the epidemiology, mode of transmission, life cycle, pathology, clinical manifestations, and complications of ascaris.

What are the general characteristics of Ascaris?

·  Largest intestinal roundworm

·  Most common intestinal helminth in man

The Epidemiology of Ascaris

·  Ascaris is endemic in our country, with prevalence rates of 80-90% in some areas

·  It affects the most vulnerable sector of the population, children age 2-14 years

·  Ascariasis thrives in areas where there is lack of sanitation practices, like slum areas in urban centers

·  Transmission takes place predominantly:

1. In yard/compound contaminated with human feces
2. In field that has been fertilized with human feces
3. By consumption of contaminated vegetables

·  When prevalence rate is high in children and low in adults, it means that the household type of transmission prevails, a case in which the area around the house is heavily contaminated through indiscriminate defecation by young children.

·  Seasonal variations in the incidence of ascariasis show the major peaks for infection:

a. The highest infection rate is from July to August

b. The lowest infection rate is in October and January

·  It appears that ascaris re-infection and transmission are highest when rainfall is minimal and lowest when rainfall is heaviest.

What is the usual mode of transmission of ascaris?

Ascaris is transmitted through the oral-fecal route by ingestion of embryonated egg on its 3rd stage larva

The Life Cycle and Stages of Ascaris

The Egg

The 2 types of eggs recoverable from stool are:

         

The fertilized egg, which is broadly oval, golden brown in color and is in the single cell stage when passed in the feces

· It’s laid by female worm after copulation

· It measures 55-75µm by 35-50 µm

· The egg shell consists of 3 layers:  

1. The inner non-permeable, lipoidal vitteline membrane
2. It is thick transparent middle layer or glycogen membrane
3. The outermost coarsely mamillated, albuminoid layer, which may be occasionally absent

· The egg survives in the environment for as long as 2 years sensitive to heat, being easily killed at = 70ºC.

The Unfertilized egg

·         It’s laid by uncopulated female worm

·         It never undergoes further development

·         It is generally larger, narrower, and elongated

·         It measures 88-94 µm

The Larva

Infective stage which contains the 3rd stage larva

  

The Adult worm

· It is white, creamy, or pinkish yellow when freshly expelled elongated and cylindrical?

· It measures 15-30cm x 3mm with curved posterior end

· It is smaller, shorter and more slender than the female

· It measures 20-45cm x 5mm with straight posterior end

· It lays about 240,000 eggs/day

· 1 female produces approximately 65,000,000 eggs in 9 months

· Its life span of the worm is as long as 18 months

What is the Pathology of Ascaris?

The Larvae

The larvae cause the following damage as they migrate from the liver to the lungs:

1. Petechial hemorrhages in the lungs

2. Massive damage to the lung tissues

3. Initiation of granulomatous reactions should the larvae get lodged in the brain, eyeball, kidney, or spinal cord

The Adult worms

Because adult worms habitate the upper and middle parts of the small intestines, they cause the following disorders:

1. Decreased fat and nitrogen absorption

2. Increased nitrogen loss through the feces

3. Malabsorption of or intolerance to lactose

What are the Clinical Manifestations of Ascaris?

1. There is vague abdominal pain

2. There would be enlarged abdomen

3. There would be Diarrhea

4. There would be Weight loss

5. There would be Vomiting

6. There would be presence of live worms in the stool or vomitus if infection is severe

What are the complications of Ascaris?

1. Loefflers's syndrome is an allergic eosinophilic infiltration of the lung usually seen in hypersensitive individuals.

2. Pathology in the liver, brain, or eyeball as larvae, migrating through the bloodstream, may eventually be lodged in these organs.

3. Wanderlust or erratic behavior of the worms results in erratic migration which, in turn, may lead to: Acute appendicitis when a worm blocks the appendix; Acute pancreatitis when a worm blocks the pancreatic duct; Acute cholecystitis when a worm blocks the ampulla of vater; Multiple liver abscess when a worm invades the liver parenchyma

4. Intestinal obstruction results when there is a bolus of worms or when the worms become entangled.    Peritonitis when a worm causes bowel perforation