**8.1 Acute infection**

The obligate pulmonary phase of the parasite's life cycle typically occurs within hours after infection. During larval passage through the lungs, the parasite induces haemorrhage in the alveolar spaces, inflammatory infiltrate, and, occasionally, granuloma (Kinjo et al., 1998).

Histopathological analyses of human intestines have shown that *S. stercoralis* eggs and adult females colonise the duodenum and upper jejunum. Studies have also demonstrated the presence of oedema, duodenal villous atrophy, and crypt hyperplasia with disrupted epithelium due to the inhibition of cell proliferation and apoptosis (Coutinho et al., 2006; Werneck-Silva et al., 2006). Surface damage, ulceration, an increase in mucus secretion and functional changes in the intestine have also been reported. In many cases, the eosinophil infiltrates are associated with the intensity of the infection (Rivasi et al., 2006; Kishimoto et al., 2008).
