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Baseline data from an immuno-epidemiological study of hookworm infection in a rural village in Madang Province, Papua New Guinea are reported. Necator americanus was found to be the commonest helminth infection, with a prevalence of near 100% and intensity of 40 worms per host in adults. Enterobius vermicularis, Ascaris lumbricoides and Trichuris trichiura were also present, at prevalences of 53, 10 and 3% respectively; Ancylostoma duodenale was absent. The frequency distribution of N. americanus was highly over-dispersed, and was well described by a negative binomial distribution with aggregation parameter, k, of 0.370. Intensity of infection was significantly related to host age, but did not differ between the sexes. Haemoglobin levels and haematocrit values were indicative of anaemia in the community, but were unrelated to hookworm infection. Levels of antibodies (IgG, IgA and IgM combined) against adult Necator cuticular collagen and excretory-secretory (ES) products were determined. Serum concentrations of the two types of antibody were significantly correlated with each other. Significant positive correlations were found between anti-ES antibody levels and hookworm egg production, and between anti-collagen antibody levels and host age. It is suggested that the level of anti-collagen antibodies may reflect cumulative exposure to infection, whereas levels of anti-ES antibodies may be more dependent on current worm burden. No evidence was found to suggest that either antibody response is important in regulating parasite population growth. Similarly, the presence of a positive correlation between eosinophil concentration and infection intensity in adults indicates that eosinophilia reflects, rather than determines, the host's worm burden.

Cuticle samples have been prepared from the human parasitic nematode Necator americanus using detergent solubilisation with sodium dodecyl sulphate and subsequent reduction of disulphide bonds using 2-beta-mercaptoethanol. It would appear that N. americanus, like many other nematodes, relies on relatively small collagenous proteins, linked by disulphide bonds, to maintain the integrity of its cuticle. These molecules are normally hidden from the immune system during the course of infection but are potentially immunogenic. It is suggested that waves of antibodies, firstly with specificity against superficial cuticular epitopes followed by antibodies against deeper lying, structural elements, should be induced during vaccination to effectively destroy the nematode at the cuticular level.

Protective immunity is a primary goal in the development of ontiparositic vaccines. Often however, parasite immunologists are faced with chronic infections that apparently do not induce a protective immune response. But although epitopes presented by some parasites may fail to induce protective immunity, there may be other antigens normally concealed from the host that, if revealed, could stimulate the required response. Indeed, there is evidence that some drugs — such as praziquantel — can act in this way, by revealing hidden parasite antigens that then induce the protective response. Vaccination with ‘concealed’ antigens is already being developed to control ectoporasitic ticks (see Parasitology Today 4,196–198). This article suggests a similar approach for hookworm vaccines, by which a ‘first-wave’ attack would be stimulated by surface antigens, followed by a ‘second-wave’ attack directed against the underlying cuticular collagens o f the parasite.