HOOKWORM, parasitism caused by the hookworms Necator americanus, Ankylostoma duodenale, and, more rarely, Ankylos toma braziliense, which inhabit a relatively small portion of man's small intestine. A single healthy female hookworm passes daily several hundred eggs which leave man in his excrement. Under favourable conditions, such as its deposit on suitable soil, larvae form therein, develop to an infective stage, and enter the soil. Infection ordinarily occurs through the piercing by infective larvae of the skin, commonly of one who walks barefoot over infected soil. Carried by the circulation from the skin to the lungs, larvae reach the air passages and, like all foreign bodies, are driven up these to the throat, are swallowed, and so finally reach the small intestine. Man's normal mechanisms are thus subverted to the hookworm's use.
The treatment of ankylostome infestation involves, firstly, dis infestation by a vermifuge or anthelmintic, and, secondly, neutralization of the consequences of infection. To increase their concentration in the bowel, and presumably their efficacy, anthel mintics have customarily been preceded by purging and fasting. Accumulating evidence, however, suggests that purging lessens effectiveness. Starvation, beyond the ordinary nightly fast, in creases, for some drugs, risk of poisoning the host. Anthelmintics are best given in the early morning. The ideal vermifuge, with a dosage which poisons all hookworms without endangering the host, is non-existent. The dosage employed for any drug should give the greatest efficiency compatible with safety, and may be termed the optimum dose. Attainment of increased safety is attempted by dividing the optimum dose into fractions, usually 3 or 4, given with intervals of one or two hours, by which means treatment can be stopped at any stage should ill effects appear, while efficacy is apparently increased; nevertheless, supervising costs of mass treatment are thereby increased. Subsequent removal of the drug by purgation lessens risk of poisoning.
The many millions of persons infected throughout the tropics necessitates mass treatment, the essentials of which, namely safety, efficacy, cheapness, and palatability, are varyingly com bined in the five anthelmintics in present or recent use. These are eucalyptus-chloroform, betanaphthol, thymol, oil of chenopo dium, and carbon tetrachloride. By some they have been ad ministered promiscuously to whole communities in which examina tion of a few individuals has shown a high rate of infection. Eucalyptus-chloroform has been almost completely abandoned as inefficient. Pure betanaphthol, in optimum dosage of two grammes, is inefficient; in larger doses it has caused deaths in India and Brazil. Thymol and oil of chenopodium, in their respec tive optimum doses of 4 grammes and 1.2 cubic centimetres or mils (the latter dose equalling 48 drops or 20 minims) have for N. americanus equal efficiency and minimal risk; contrary state ments emanate from the use of oil of chenopodium in excessive dosage of 3 mils, due apparently to considering a drop of this liquid as equivalent to a minim. For A. duodenale chenopodium appears the better drug, and is, in London, the cheaper. Its active principle is ascaridol. Unfortunately the oil contains markedly varying quantities of this substance, and its amount lessens on keeping Ascaridol, extracted and administered in place of the whole oil, is effective but relatively costly. Carbon tetrachloride, recently introduced, has been taken by many thousands of per sons in dosage of three mils, and has proved most efficient. The medicinally pure drug produces in large doses, in dogs, extensive fatty degeneration, followed by necrosis of the liver, and, appar ently, of the kidneys ; changes aggravated by starvation and fatty food, and lessened by glucose. Extensive similar change has been present in man when death has followed the 3-mil dose. A number of such deaths have been recorded. Clearly this dose required reduction, so that the efficacy of carbon tetrachloride under optimum dosage has still to be ascertained. It is the cheapest of all advocated treatments. A combination of this drug with ascaridol is being tested.
Hygienically viewed, treatment of whole unsanitated communi ties lessens the risk of further infections ; since destruction of female worms diminishes the seeding of egg-containing material upon the soil, and, on the whole, the number of infective larvae originating therefrom. Nevertheless, an imperfectly treated, and still lightly infected, person, seeding a favourable spot, is a danger to the community.
Individually viewed, disinfestation, by treatment, of the obvi ously ill and presumably heavily infected, restores health, always provided damaged tissues be still reparable. In the case of ap parently healthy, but infected, persons, comparison of their con dition of general health, wage-earning capacity, blood state and, in children, development of body and mind, before, and again a sufficient period after, disinfestation shows that they are often markedly improved by disinfestation ; so that a light infection definitely handicaps the apparently healthy. Whether the lightest infections do, or may, penalize the individual is questioned. If, as now appears likely, we can detect infection by a single female worm, treatment producing complete disinfestation of such cases, combined with critical observation of conditions before and after effecting this, will doubtless shortly settle this point, so vital to the individual and community.
Iron and arsenic, ineffective before, may be essential for com bating anaemia after disinfestation. Treatment of skin lesions at the site of infection varies with the condition present. (See