Fig. 90.—Ancylostoma duodenale (life size). Shows some worms adherent to the intestinal mucosa and some free. (From Jefferys and Maxwell.)
Stiles notes that the more favorable conditions for development are in a porous, sandy soil rather than in a clay one. Where a sewerage system exists there is very little danger of the spread of hookworm disease and the same is true where there is proper disposal of the faeces by burning, boiling or treatment in a septic tank. In rural districts, however, where the stool is often deposited in the shade and retirement of a clump of trees, the soil becomes infested with myriads of larvae, so that one standing with bare feet on such a spot easily becomes infected. It is for this reason that shoes are of protective value. In infected mines with temperatures below 22°C. infection is rare (6%); from 22°C. to 25°C. more common (16.6%), and above 25°C., it may reach high figures (61%).
Those of the negro race do not suffer from the infection as do the whites. They appear to have an immunity but serve as carriers of the disease. There is difference of opinion as to the length of time the parasites may live in man in the absence of reinfection. Some consider this period one of a few months, others of two or three years. We can certainly consider that a case leaving an infested region will get rid of his parasites within seven years.
Pathology
The site of entrance of the larvae is characterized by a dermatitis which is often called “ground itch” or “foot itch” by reason of its frequent location in the foot which has come in contact with the faeces-polluted soil. The dermatitis disappears in about two weeks unless some secondary infection occurs. There are reports of pulmonary irritation which may be explained by the wandering of the larvae through the lungs.
Fig. 91.—Longitudinal section through a hookworm attached to the intestinal mucosa, about 6 hours after the death of the carrier. A portion of the submucous coat is drawn into the buccal cavity and trails along cord-like into the oesophagus, in which 4 small tissue nuclei are still discernible. Section 0.01 mm. thick. (From Mense.)
Pronounced anaemia with yellow, wax-like skin is a feature of severe cases but emaciation is rare, the subcutaneous fat still remaining. There is frequently oedema about the ankles. In the jejunum we find small haemorrhagic spots from the size of a pea to that of a half dollar. A worm may be found in the center of this spot. In sections from the tissues injured by the bite we note an infiltration of eosinophiles. The heart often shows fatty degeneration with dilatation. The liver and kidneys usually show fatty change while the spleen is generally shrunken. Sandwith noted splenic enlargement in many of his autopsies but such enlargement must have been due to other causes.
There are many views as to the manner in which the damage due to the hookworm is brought about. Some think it by bacterial infections occurring through the wounds made by the worms, others that it is due to a haemolytic toxic material excreted by the worms, while Stiles considers the ingestion of the patient’s blood important. Looss thinks it due to the gradual destruction of the intestinal mucosa from the feeding on this, and especially of the submucosa, by the worms. In their feeding the worms move from site to site. When they leave a point bleeding continues and this may account for much of the anaemia.
On the side of the blood we have at first a moderate leucocytosis which disappears with the anaemia. Eosinophilia and Hb. percentage reduction are often observed. In 3 cases I have known a fatal pernicious anaemia to develop.