Page 91 - Medical Parasitology_ A Textbook ( PDFDrive )

84 10 Nematodes: Roundworms

i = Infective Stage
4 d = Diagnostic Stage
i 7

1 d

3

6

5

Faeces

2 Fertilized egg d 2 Unfertilized egg
will not undergo d
biological development.

Fig. 10.4 Life cycle of Ascaris lumbricoides (Reproduced from https://www.cdc.gov/dpdx/asca-
riasis/index.html)

Pathogenesis and Clinical Features
Clinical manifestations of ascariasis are caused by the migrating larvae and the
adult worms.
The larval migration causes allergic reaction. The initial exposure to larvae dur-
ing the lung migration phase is usually asymptomatic, except when the larval load
is heavy. When reinfection occurs, there may be infiltration of eosinophils and mac-
rophages. Loeffler’s syndrome is characterized by low-grade fever, cough, wheez-
ing, dyspnoea, transient eosinophilia and chest X-ray may show lung infiltration.
The sputum may contain Charcot-Leyden crystals and larvae. Loeffler’s syndrome
seen in ascariasis is also known as ascaris pneumonitis. The pulmonary clinical
features subside in 1 or 2 weeks after infection.