the men in oeeupatioiis that bring thcni into contact with nn- 

 usually intense sources of infectiou. In parts of the southern 

 United States the level of infection rises rapidly from 6 to l.i 

 vears and then declines rapidly until after 20 years the «-orni 

 burden is almost negligible (Smillie and Augustine, 1<J2... 

 Chart 4) Such a situation cau probably be attributed to the 

 wearing of shoes and the greater use of sanitary facilities by 



the adults. , , . j. ■■ i 



Evidence on racial differences m hookworm mteetion and 

 disease is rather conflicting. It does, however, seem clear that 

 negroes in the southern United States have much lighter mtec- 

 tious than whites (Knowlton, Um-. Smillie and Augustine, 

 19-1.) • Keller, Leathers, and Densen, 1940). It seems possible 

 that this difference is due to a true racial immunity m the 

 negro race, although further investigations are needed b 'tore 

 differences in environment and nutrition can be completely 

 ruled out. There is also evidence that suggests that groups 

 with negro and negro-indian blood are more resistant to the iii- 

 iurious effects of the worms than those of the white race 

 (Gordon 192.-> ; Cort, Stoll, Sweet, Riley, and Schapiro, 1919). 

 However', it is difficult to rule out other factors and here also 

 the whole question needs much further investigation. 



CONTROL OF HOOKWORM DISEASE 



Four different methods of preventing the spread of hook- 

 worm infection have been generally recognized, viz., (1) disin- 

 fection of feces or infested soil, (2) the encouraging of wear- 

 ing shoes, (3) anthelmintic treatment, and (4) improvement 

 in sanitation. Extensive experimentation has shown that hook- 

 worm eggs in feces and the larvae in the soil can be killed 

 bv the application of salt, lime, or other chemicals. Such 

 methods are useful in limited areas such as mines (Fisc-lier, 

 19'>8) or in sterilizing human excrement which is to be used as 

 fCTtili'zer (Cort, Grant, and Stoll, 19l2(i). The wearing of shoes 

 has been shown to be a potent factor in keeping hookworm in- 

 fection at a low level (Smillie, 1922; Davis, 192.'.; Chandler, 

 1929 pp. 208-211, 380-3S2). However, attempts to increase the 

 wearing of shoes in hookworm infected populations by propa- 

 ganda or legal requirements do not seem to have been very 

 effective Hookworm control campaigns, therefore, have been 

 organized chieflv around treatment and sanitation. The use of 

 anthelmintics improves the health of the people and reduces 

 soil infestation. The sanitary phase of the program is a fight 

 against soil pollution and involves education and the introduc- 

 tion of latrines. Much work has been done in developing sani- 

 tary conveniences suitable for people of different types. The 

 pit" latrine (privy) has been most widely used in the Western 

 Hemisphere: and the recently developed bored-hole latrine 

 (Teager, 1931 and 1934) seems to be best adapted for the 

 jieoples of certain countries of Asia and Africa. 



In the early hookworm campaigns in Puerto Eico and the 

 southern United States the so-called "dispensary method 

 was used This consisted of the examination and treatment 

 of large groups of people who flocked to the numerous dis- 

 pensaries that were set up. Significant results were attained 

 in the treatment of severe cases and in preliminary education, 

 but only a beginning was made in the reduction of infection 

 and in the improvement of sanitation. 



\s a reaction against the inadequacy of the "dispensary 

 meUiod " the "intensive method" was developed by certain 

 members of the field staff of the International Health Board ot 

 the Rockefeller Foundation. Its ob.ieetive was the complete 

 eradication of hookworm infection by a systematic program of 

 sanitation and treatment to "cure" of all infected individuals 

 (Howard 1919). First, every effort was made to get latrines 

 installed in every house in a given area. Then, after systeinatic 

 stool examinations, the positives were given treatment. Ihey 

 were later reexamined, and those still infected were given a 

 second treatment. Reexamination and retreatment were sup- 

 posed to be continued until the stool samples of all the people 

 of the area were negative for hookworm eggs. Sometimes as 

 many as 9 or 10 treatments were required for "cure." Efforts 

 to improve the sanitation were continued during and after the 

 treatments. Although hookworm infection was never completely 

 eradicated from any area by this method, striking results were 

 obtained in a number of places. Least defensible of the pro- 

 cedures of the intensive method was "treatment to cure" in 

 which much effort and money were wrstcd in treating very 

 light infections and in trying to remove tlie last few worms by 

 retrcatments. On the other hand, the emphasis on intensive 

 sanitation especially before treatment and on a careful follow- 

 ing up of the sanitation after treatment, was an important 

 contribution to hookworm control procedures. 



The "mass treatment" method came as a reaction against 

 the complete ineffectiveness of the intensive method to cope 

 with the situation in a large country such as Brazil. As advo- 

 cated by Darling (1922) mass treatment required first the de 



termination of the index of infection (approximate womi inir- 

 deu) by the examination by worm counts of a representative 

 sample of the population. Later, the development of the Stoll 

 dilution egg counting method (Stoll, 1923a) made it possible 

 with much less effort to obtain a better estimate of infection 

 intensity. Then, wherever incidence was high, a whole group 

 was simultaneously given anthelmintic treatment of known 

 efficacy without a previous diagnostic examination and without 

 reexamination. Thus large groups of people could be rapidly 

 treated. An adequate sanitary program was sometimes com- 

 liined with mass treatment. In many jilaces, however, the great 

 emphasis on treatment and the rapidity with which the cam- 

 paign moved brought about a neglect of sanitation. Whenever 

 this was true reinfection occurred at a rather rapid rate as 

 suggested bv the investigations of a number of workers (Baer- 

 niaiin, 1917b; Sweet, 192.3; Docherty, 1926; Hill, 192.J, 1926, 

 1927b). Mass treatments, therefore, were particularly effective 

 if repeated at intervals of 2 or 3 years (Rice, 1927; Lambert, 

 1928). Perhaps of greatest importance was the emphasis on 

 the quantitative viewpoint ; the object of the campaign was to 

 reduce the worm burden of the population and not to cure 

 cases. Also important was the idea that a preliminary survey 

 was needed to estimate the ' ' index of infection ' ' before control 

 wink was started. 



A campaign against hookworm disease at the present time- 

 can be planned on the basis of the wealth of experience of the 

 last 2.') years. Such a campaign under ideal conditions might 

 include five steps which have actually been utilized in cam- 

 paigns; and to these a sixth might be added. (1) a presurvey 

 to evaluate the problem quantitatively; (2) presanitation to- 

 reduce soil pollution as much as possilile before treatment; (3) 

 mass treatment to reduce the worm burden of the group to a 

 .subclinical level in as short a time as possible; (4) follow-up 

 sanitation to keep soil pollution at a low level; and (5) a post- 

 survey to measure quantitatively the results of the campaign. 

 Finally (6), every effort possible should be made to improve 

 the general health by the correction of dietary deficiences and 

 the elimination of other diseases. 



The central feature of the presurvey should be an examina- 

 tion by the dilution egg-counting method of a representative 

 sample of the population to obtain information on the quanti- 

 tative distribution of hookworm infection in the population 

 and on the extent of true hookworm disease. Investigations of 

 the amount of sanitation present and of soil pollution habits 

 wiU aid in planning the program for sanitar.v improvement 

 which in most situations is by far the most important part of 

 the campaign. In regions where hookworm infection is found 

 to be chiefly at or near the subclinical level, even if its inci- 

 dence is high, control work may well be limited entirely to 

 sanitation. When the preliminary survey shows heavy infec- 

 tion and \videspread disease every effort should be made to re- 

 duce soil pollution to the greatest possible extent before treat- 

 ment is started by the introduction of latrines and education 

 in their use. This is done in order to reduce the amount of 

 reinfection after treatment. 



A course of treatments should be chosen which has been 

 shown by quantitative study on a group of considerable size to 

 reduce the worm burden by at least 90 percent. If the inci- 

 dence of infection shown by the preliminary survey is over 90 

 percent, treatment without diagnostic examination according 

 to the mass treatment method may seem desirable. Such a pro- 

 cedure, however, should not be applied to the youngest age 

 group where infection is almost always least and danger f rom ■ 

 treatment greatest. Mass treatment should be given by popu- 

 lation units so that all the people living in the same environ- 

 ment would be freed of their worms as nearly at the same time 

 as possible. Individual examinations after treatment and re- 

 treatments cannot be justified where the object is to reduce the 

 worm burden as much as possible with a given amount of treat- 

 ment. In tropical regions treatments toward the end of the 

 dry season, when the soil has been unsuitable for a considerable 

 period for the development of the larvae, will have more last- 

 ing value than those given during the rainy season, when rein- 

 fection is very extensive (Chandler, 1929, pp. 40.5-408; Me Vail, 

 1922) ; and in colder regions treatments at the end of the win- 

 ter will be most eft'ective. 



Even in the best organized campaigns a varying percentage 

 of the worm burden will he left after treatment. Whether in- 

 fection will soon return to a high level again depends on the 

 extent to which the people are prevented from returning to 

 their former habits of soil pollution. Real success in hook- 

 worm control, therefore, will be achieved only where efforts to 

 improve sanitation have been permanently organized and effec- 

 tively continued over long periods of time as part of the per- 

 manent public health program. 



The final step in an ideal program for hookworm control 

 would be a resurvey carried out about 2 or 3 years after the 



312 



