■cdiiililetion of the tieatiiioiits by the same methods used in tlu' 

 preliminary survey. Such an investigation will make it [los 

 silile to elieek the sanitation and to determine whether the 

 level of infection has retnri\ed to a jioiat where further treat- 

 ment is needed. 



Most important iii .-ittaikint; the hookworm problem is the 

 acceptance of the quantitative point of view and the nsiiij; of 

 (juantitative methods to determine the "hookworm index'' in 

 the preliminary survey and the resiirvey. Much effort and 

 money have been wasted in trying by active treatment cam 

 liaigns to reduce hookworm infection in poi)ulations whi're it 

 ivas already close to the subclinical level. Most fundamental 

 perhaps of all is the changed objective of the modern hook 

 worm campaign, which is to reduce hookworm infection to a 

 subclinical level by treatment and to keep it tlu're by per 

 mauent improvement in sanitation. 



Finally, certain new viewpoints need to be developed on ac- 

 count of the recent ticw information on the significance of ac 

 quired immunity in hookworm infection and its relation to un- 

 dernourishment and other debilitating factors. If the immune 

 respons'- in man to his hookworms proves to be of the same 

 grade as tliat of the dog to .1. en )i i ii ii iii , measures to remove 

 factors that interfere with the normal host responses are just 

 as important in hookworm control as those directed against 

 the spread of infection. In fact, it seems altogether likely that 

 if it were possible to eliniin:ite dietary deficiencies from a 

 population suffering from hookworm disease by furni.shing an 

 adequate food suppl.v, the restoration of the normal host resis 

 tancc would in itself strikingly reduce hookworm infection and 

 disease (Otto and I,andsl)erg, n)40 ; Cort and Otto, 1940). 

 Emphasis in hookworm control, therefore, should be placed not 

 on isolated spectacular treatment campaigns, but on the at- 

 tempt to reduce hookworm infection by all the methods that 

 will improve the sanitation and raise the general economic and 

 health level of the infected populations. 



Ascaris lumbricoides 



W. W. C. 



References to human ascaris are found in the ancient medi- 

 cal literature of the Chinese, Egyptians, and Greeks. Edward 

 Tyson in 1683 and Francesco Redi in l()8-t studied the anatomy 

 of this parasite, distinguished the sexes, and expressed the view- 

 that it reproduced by eggs and not by spontaneous generation. 

 From that time on, ^l.s'ror/.< liimbricnirles became a favorite ob- 

 ject for study, and investigations on its anatomy laid the foun- 

 dation of our present knowledge of nematode structure. Al- 

 though much information on the prevalence, pathology, and 

 geographical distribution of ascaris in man has been long avail- 

 able, it is only recently that much attention has been paid to 

 the epidemiology of ascariasis in relation to control. 



PATHOLOGY AND SYMPTOMATOLOGY 

 In laboratory animals and in pigs the migrations of ascaris 

 larvae are known to produce lesions in the intestinal wall, 

 liver, Ivmph nodes, and especially in the lungs (Ransom and 

 Foster," 1920 ; Yokogawa, 102,S ; Martin, 1926; Roberts, 1S34). 

 The lesions in the lungs consist of petechial hemorrhages and 

 inflammatory processes. In heavy infections the lungs may be 

 very extensively involved, being edematous, hemorrhagic, and 

 even completely consolidated. The picture is that of a multiple 

 lobar pneumonia, which frequently causes the death of experi- 

 mental animals. A disease of young pigs known as "thumps" 

 has been identified as ascaris pneumonia (Ransom, 1920). In 

 man severe pulmonary symptoms may l)e produced by hea^'y 

 infections (Koino, 1922) and in some tropical regions lung sym- 

 toms, especially in children, have been attributed to ascaris in- 

 fection. In most infected populations, however, it is extremely 

 difficult to assign a definite symptomatology to the lung mi- 

 grations of ascaris (Keller, Hillstrom, and Gass, 1932). 



It is not easy to define clearly the symptoms produced by 

 the worms in the intestine. Perhaps the most common com- 

 plaint is an intermittent intestinal colic. Normal digestion 

 may be disturbed and there may be loss of appetite and in- 

 somnia. Nervous sym))toms are particularly common among 

 heavily infected young children. Individuals having a special 

 sensitivity may develop a generalized toxemia or specific ner- 

 vous symptoms. In young children very heavy infections may 

 cause severe illness or even death. Large numbers of ascarids 

 may produce intestinal blockage. Also, the migrations of adult 

 worms sometimes produce penetration of the intestinal wall 

 and severe injury to the appendix, liver, lungs, or other or- 

 gans. However, only a small proportion of infected individuals 

 show symptoms that can be definitely attributed to ascariasis. 



DI.'!TRIBI'T10X .^XD EPIDEMIOLOGY 

 Doling tlie last 1." years our knowledge of the factors in- 

 fluencing the dissemination of ascaris has been very greatly in- 



creased by a number of siiecific epidemiologic studies in differ 

 ent i)arts of the world. The distribution of the worm burden 

 has been studied by the StoU dilution egg counting method, 

 and attempts have been made to get at the sources of infec- 

 tion liy the observation of soil pollution habits and by the iso 

 lation of eggs from the soil (Spindler, 1929a; Majilestone and 

 Mukerji, 193(i). Data from these investigations and infornm 

 tion on the factors influencing tlie«development and viability 

 of ascaris eggs outside the body of the host have given a fairly 

 good body of ei)idcmiological knowledge on wliich to base con- 

 trol measures. In addition, recent studies indicate that host 

 relations may be of importance in determining the distribution 

 of ascaris in populations. 



DISTRIBUTION 



.1. Iiimbricoidffi in man has a world wide distribution and 

 appears to rival Eiitcrohiiis rcniiinilnri.': for the distinction of 

 being the commonest of all human parasites. It has been found 

 within the Arctic Circle and in regions where almost desert 

 conditions i)revail. It is most abundant in tropical countries 

 with a heavy rainfall and is especially widespread in the Orient, 

 although extensive endemic centers are also present in Europe 

 and in the United States (Otto and Cort, 1934a; Denecke, 1937; 

 Girges, 1S34). 



Recently the information on the distribution of ascaris within 

 population groups has been greatly increased. The family is 

 almost always the unit of infection (Cort, Stoll, Sweet, Rih'v, 

 and Schapiro, 1929; Cort, Otto, and Spindler, 1939; Otto, Cort, 

 and Keller, 1931). This is true in urban as well as rural areas 

 (Headlee, 1936; Winfield and Chin, 1938). Only in Egypt 

 (Scott, 1939) and In certain special institutional situations 

 (Caldwell, Caldwell, and Davis, 1930) was a larger group in- 

 dicated as the unit. In numerous situations negative or lightly 

 infected families are found living close to those that are heav- 

 il.v infected. With few exceptions (Scott, 1939) about •")n per- 

 cent of the total worm burden of any population group is con- 

 centrated in about .5 percent of the infected individuals. These 

 heavy cases are largel.v found in a small number of families, 

 the so called "ascaris families." Usually the peak of the in- 

 fection curve comes early in life, sometimes even in the o to 9 

 age group, and the worm burden in adults is only a fraction 

 of that in children. Also, women of child-bearing age are fre- 

 quently more heavily infected than men of the same age groups. 

 However, heavy infections are sometimes found in adults, es- 

 pecially in certain places in the Orient (Cort and Stoll, 1931). 



Ascaris is in general a parasite of people on a low economic 

 and social level. "Ascaris families" are usuall.v among the 

 poorest and most degraded of the population. Not infrequently, 

 however, infections in children, sometimes rather heavy, are 

 found in families of a higher type living under favorable en- 

 vironmental conditions. In the Orient, also, ascaris is often 

 widespread in people of the better classes (Mills, 1927). It is 

 not primarily a parasite of rural districts since in many jjarts 

 of the world it is present and sometimes very common in cities 

 of various sizes. The reasons for most of the pecularities in 

 the distribution of ascaris which have just been summarized 

 become clear when the knowledge available on the various fac- 

 tors that influence dissemination is considered. These factors 

 may be grouped under (1) host relations, (2) general environ- 

 mental factors, and (3) human habits. 



HOST RELATIONS 

 In this connection one of the important problems is the re- 

 lation of the ascaris of pig to human infection. Extensive 

 investigations have shown no differences between the ascarids 

 of these two hosts in morphology or in physiological and bio- 

 chemical relations (Schwartz, 1920; Bakker, 1921; Barker, 

 1923). Almost all attempts to infect pigs with eggs from hu- 

 man sources have been unsuccessful fPayne, .\ckert, and Hart- 

 man, 192."); Martin, 1926). Also, the attempts to infect man 

 with the pig ascaris have given negative results (Koino, 1922; 

 Payne, Ackert, and Hartman, 292.'i; Buckley, 1931). Several 

 workers have expressed the view that the human and pig as 

 carids are physiological or host varieties which have each lost 

 their infectivity for the other host. As Lane (1934) has sug 

 gested, however, the evidence from these experimental infections 

 is not very conclusive because of the lack of adequate controls 

 and because of the difficulty reported by a number of workers 

 of infecting pigs with the pig ascaris (see also Roberts, 1934). 

 Also, de Boer (193."ia & b) reported that he succeeded in infect- 

 ing suckling pigs with eggs from both pig and human sources 

 and Hiraishi (1928) and others in .Japan have infected pigs 

 deficient in vitamin .\ with human ascaris. It is difficult, how- 

 ever, to escape the conclusion that under field conditions in- 

 fection of man with pig ascaris is at least very infrequent. In 

 fact, no evidence has been found in the reports of epidemiologi- 

 cal studies of undoubted human infection from pig sources. At- 

 tention has also been called to areas in which differences in the 



313 



