Strongyloides stercoralis: ultrastructural study of newly hatched larvae within human duodenal mucosa

Aim—To investigate the ultrastructural features of the newly hatched larvae of Strongyloides stercoralis in human duodenal mucosa. Methods—Duodenal biopsies from an AIDS patient were studied by transmission electron microscopy to investigate morphology, location, and host–worm relations of newly hatched larvae. Results—Newly hatched larvae were found in the Lieberkuhn crypts within the tunnels formed by migration of parthenogenic females. Delimiting enterocytes were compressed. Release of larvae into the gut lumen was also documented. It was shown that both a thin and a thick membrane surrounded the eggs and larvae, as a tegument derived respectively from parasite and host. Segmentary spike-like waves, caused by contractures of worm body musculature, were observed on the surface of newly hatched larvae, and their intestinal lumen was closed and empty, with no budding microvilli. Immaturity of the cuticle and some degree immaturity of amphidial neurones were found, but there was no evidence of either immaturity or signs of damage to other structures. Conclusions—Newly hatched larvae of S stercoralis appear to be a non-feeding immature stage capable of active movement through the epithelium, causing mechanical damage. The tegument resulting from the thin and the thick membrane may protect the parasite and reduce any disadvantage caused by immaturity. Key Words: Strongyloides stercoralis • ultrastructure • larvae • immune deficienc

The identification of a species-specific antigen from Necator americanus.

A 17 kD protein of Necator americanus was isolated by SDS-PAGE and used to raise monospecific antisera in rabbits. ELISA and Western blotting against a range of parasite extracts demonstrated the species specificity of this protein. It is expressed at all stages of the life-cycle, appears to be accumulated through the larval stages to adulthood, and can be localized in the oesophageal glands and cuticle of the adult parasite. The possible nature and diagnostic potential of this protein is discussed

Modelling heterogeneity and the impact of chemotherapy and vaccination against human hookworm

There is a growing emphasis on the development of vaccines against helminths (worms), and mathematical models provide a useful tool to assess the impact of new vaccines under a range of scenarios. The present study describes a stochastic individual-based model to assess the relative impact of chemotherapy and vaccination against human hookworm infection and investigates the implications of potential correlations between risk of infection and vaccine efficacy. Vaccination is simulated as a reduction in susceptibility to infection and the model includes population heterogeneities and dynamical waning of protection. To help identify appropriate measures of vaccine impact, we present a novel framework to quantify the vaccine impact on the infection-associated morbidity and introduce a measure of symmetry to study the correspondence between reduction in intensity and reduction in morbidity. Our modelling shows that, in high-transmission settings, the greatest impact of vaccination will be attained when vaccine efficacy is the greatest among individuals harbouring the heaviest worm burdens, and that the decline of morbidity primarily depends on the level of protection attained in the most at risk 8–12% of the population. We also demonstrate that if risk of infection and vaccine protection are correlated, there is not always a direct correspondence between the reduction in worm burden and in morbidity, with the precise relationship varying according to transmission setting