These images show various stages in the development of Ascaris lumbricoides, including an unfertilized egg, a fertilized egg, an infective egg containing a larva, and a larva hatching from an infective egg.
Figure 1 shows an unfertilized egg of Ascaris lumbricoides containing a mass of refractile granules. It has an average length of 90 μm. Figure 2 depicts a fertilized egg. It appears broad and oval in shape with a thick shell that is stained brown by bile. Figures 3 and 4 show an infective egg of A. lumbricoides containing a larva and a larva of A. lumbricoides hatching from an infective egg, respectively. After ingestion, the larvae penetrate the intestinal mucosa where they are subsequently transported by blood circulation to the liver, heart, lungs, and trachea. From the trachea, the larvae are transported to the epiglottis where they are then swallowed (1). When swallowed, they pass down into the small intestine where they develop into adults (Fig. 5, an adult worm of A. lumbricoides showing its blunt and sharp ends). The adults can migrate out of the host by means of the anus, mouth, or nose (2).
All biological structures, such as ova and adult parasite, shown here were found in the feces of children who were approximately 3 years old. The feces were collected in a sterile wide-mouth plastic bottle and processed by a direct wet mount in a 0.85% NaCl solution used as diluent. In Figure 4 the same diluent plus a drop of 0.1% aqueous methylene blue were used. The microscopic examination was done with a DM500 light microscope (Leica Microsystems). The pictures were recorded with a digital camera (Leica) using an oil immersion objective (total magnification of 1,000X), except for Figure 4 (total magnification of 400X). The adult worm of A. lumbricoides was obtained from a fecal sample washed from detritus and preserved in a 10% formalin solution.
Ascaris lumbricoides is one of the most common parasites in the world, transmitted by the fecal-oral route and infecting an estimated 1.2 billion people globally (1, 3). Human hosts infected with A. lumbricoides tend to experience acute lung inflammation, difficulty in breathing, and fever. Abdominal distension and pain, nausea, and diarrhea are also typical symptoms (1). Among school children, the infection is associated with appetite loss, lactose maldigestion, impaired weight gain, and a reduction in cognitive abilities. Large numbers of worms may give rise to allergic symptoms and eosinophils can accumulate in the lungs in response to ascariasis; this is known as Loeffler's syndrome (3).
1. Dold C, Holland CV. 2011. Ascaris and ascariasis. Microbes Infect. 13:632–637.
2. Holland CV. 2009. Predisposition to ascariasis: patterns, mechanisms and implications. Parasitology 136:1537–1547.
3. Neira OP, Pino QG, Muñoz SN, Tobar CP. 2011. Elimination of juvenile stages of Ascaris lumbricoides (Linnaeus, 1758) by mouth. Report of a case and some epidemiological considerations. Rev. Chilena Infectol. 28:479–483. (In Spanish.)