- Email: [email protected]
Pyrvinium pamoate in the treatment of pinworm infection (enterobiasis) in the bome
T h e Journal of P E D I A T R I C S
243
Pyrvinium pamoate in the treatment of pimrorm infection (enterobiasis) in the borne Jerro]d A. Turner, M.DP and Paul E. Johnson, Jr., M.D. LOS ANGELES~ CALIF,
T rIE efficient life cycle of the pinworm of man, Enterobius vermicularis, has insured its status as the most prevalent helminthic parasite in the United States. Because of the hand-to-mouth mode of transmission, it is most important in the practice of pediatrics. Although the symptomatology of pinworm infections is not spectacular, anal pruritus may disrupt sleeping habits and cause irritability that affects the entire family. Of particular importance is the psychological impact upon the parents when they discover that their child has "worms." In the past, much attention has been devoted to interrupting transmission by vigorous hygienic measures. The futility of this endeavor was pointed out by Sawitz and associates 1 who showed an increase in incidence over a 6 week period among children in a well-controlled environment under
From the Departments of Infectious Diseases and Pediatrics, University of California School of Medicine, Los Angeles. This study received partial financial support from Parke, Davis and Company, Detroit, Mich. ~Address, Assistant Professor, Department o] InJectious Diseases, Division o] Parasitology and Tropic Diseases, University of Cali[ornla School of Medicine, Los Angeles 24, Call[.
conditions of intense sanitation. The discovery, by Schiiffner and SwellengrebeP of the anaI route of infection by migration of larvae from ova hatched on the perineum, leads to the conclusion that frequent washing of the anus and the perineum is also necessary to prevent infection. Neither of these techniques is satisfactory nor practical in the home environment. Chemotherapy has also been disappointing because of the prolonged treatment required and its relative ineffectiveness. Recently, several reports have appeared which showed that pyrvinium pamoate achieves nearly 100 per cent cures in pinworm infection without unpleasant side effects. Moreover, it was effective in a single dose2 -~ The present study was designed to test the effectiveness of a single dose of pyrvinium pamoate in a large number of children within the family environment. In addition, it was planned to test the usefulness of repeated doses of the drug over a prolonged period in prevention of reinfection and as prophylaxis among noninfected children.
MATERIALS AND METHODS Survey methods. The University of California at Los Angeles provides a limited
244
February 1962
T u r n e r and Johnson
amount of housing for families of students who are veterans. The housing facilities consist of 18 wooden buildings, each containing 14 one-bedroom apartments. There are two adults per apartment and an approximate average of two children per family. The majority of children are under 6 years of age. The families in these units were selected for the study. T h e families were initially contacted by one of four medical students. Meetings of the mothers were held in groups, and a group leader was selected from each apartment building. The distribution and collection of materials and information among the group leaders was carried out by the medical students. The group leaders were responsible for contacting the individual families. In addition to observing demonstrations of the cellulose tape swab technique given by the medical students, each famiIy received a mimeographed set of instructions which could be used as a reference at any later date. Families were requested to obtain swab specimens on 7 consecutive mornings upon arising, prior to bathing or going to the toilet. Each person received a kit which contained (1) a slide box with a data card affixed to its top, (2) seven clean slides, (3) seven tongue depressors, and (4) a roll of N inch cellulose tape. The initial survey included all children and adults who completed the set of 7 swabs. The boxes were collected and the cellulose tape swabs were read by using the following modification of Beaver's 6 technique: (1) The slides were held up to the light
and the portion of the tape which had contacted the anus and perianal skin was Iocated. A definite area of decreased transparency of the tape due to irregularities formed in the adhesive on contact can easily be delineated. (2) This area was marked off on each slide by wax pencil lines made on the underside of the slide. (3) The tape was pulled back from the surface of the slide, exposing the area of contact, and a drop of toluene was placed on the slide. The tape was then smoothed back onto the surface of the slide with the index finger. (The wax pencil marks are soluble in toluene, and, therefore, must be made on the under side of the slide.) (4) The entire area bebetween the marks of the wax pencil was searched in consecutive, low-power fields. It has been suggested that a single positive swab does not necessarily indicate an active infection, but may merely be evidence of the termination of a previous infection. 7 Moreover, an individual who shows only one or two positive swabs during a test period is less likely to be found positive at a later testing than an individual who has a series of positive swabs during the initial test period7 For these reasons, each set of slides was graded for the presence of ova as follows: negative, no ova present on 7 consecutive slides; poor ova-production, ova present but not seen on 3 consecutive slides; good ova-production, ova present on 3 or more consecutive slides. T r e a t m e n t series. Children from the ages of 1 to 12 years were selected for the study. The negative, poor ova-producer, and good ova-producer groups were divided randomly into equal numbers among the following
Table I. A comparison of infection between groups of children considered to be negative, poor, and good ova-producers during a 16 week period Status on initial survey
Negative Poor ova-production Good ova-productlon
.
3 weeks after initial survey Positive I Negative I Total
9 7 14
37 3 2
46 10 16
16 weeks after initial survey Positive f Xeg ative I Total
6 4 6
27 4 4
33 8 10
Volume 60 Number 2
Pyrvinium pamoate and pinworm infection
245
Table II. Results of treatment with a single dose of pyrvinium pamoate compared with a placebo Presence o[ ova Treatment group
Placebo
Prior to treatment Positive I Negative 26 46
Total Pyrvinium pamoate, single dose Total
65 82
I week a#er single dose* Positive I Negative 21 5 9 37 3-0 42 3 1 4
62 81 143
Positive alter treatment (%) 80.8 19.5 41.7 4.6 1.2 2.7
*The 7 consecutive swabs were begun 1 week after the drug or placebo was administered.
treatment groups: placebo, dose repeated every 3 weeks for a total of 5 doses; pyrvinium pamoate, single dose; pyrvinium pamoate, dose repeated every 3 weeks for a total of 5 doses. T h e groups were proportionally distributed by a method of random selection throughout each apartment building. Each child within a single family was placed in a different treatment group whenever possible. With this distribution as m a n y children as possible who were receiving pyrvinium pamoate could be maximally exposed to an environment which contained ova from infected siblings who were taking the placebo. The pyrvinium pamoate was in the form of a flavored suspension containing 10 mg. pyrvinium base per cubic centimeter. ~ It was adiministered in a dosage of 5 mg. per kilogram of body weight. T h e placebo resembled the drug in appearance and flavor.t Six adults who were infected were treated with a single dose of pyrvinium pamoate in coated tablets, each of which contained 100 mg. of pyrvinium base. ~ This was also administered in the dose of 5 mg. per kilogram of body weight. The first dose of pyrvinium pamoate or placebo was administered to the children 2 weeks after the survey. A follow-up series of 7 consecutive daily cellulose tape swabs was begun 7 days after administration of the -"-Supplied as Povan by Parke, Davis and Company. "{'Prepared by the Pharmacy of the University of Callfornia Medical Center.
first dose of the drug or the placebo. A repeat series of 7 consecutive swabs was taken daily at the end of the 4 month period of treatment beginning 7 days after the fifth and last dose. Evaluation of side effects. Prior to the commencement of treatment, as m a n y children as possible were evaluated by the following laboratory determinations: hemoglobin (Spencer Hb-Meter, American Optical Company), leukocyte count, urinary protein (sulfosalicylic acid m e t h o d ) ; and urinary sediment (uncentrifuged). Parents were requested to contact the Emergency Service if their child became ill. Members of the Pediatric Staff evaluated any unusual symptoms by examination and appropriate laboratory tests. RESULTS
Survey. A completed series of swabs was received from a total of 277 children. Of these, 120 were found to be positive for pinworm ova (43.3 per cent). There was no sex difference in the prevalence of infection. Ninety-nine adults c o m p l e t e d the series of 7 swabs, and 12 were found to be positive ( 12.1 per cent). The distribution of positive test results among individual families showed that when one member of the family was found to be infected, there was a significant increase in the probability that one or more additional positive tests would be found within that same family. A significantly higher prevalence of infection was found among the
24 6
Turner and Johnson
larger families when a comparison of the results of the survey was made with an expected, random distribution. Treatment series. A reduction in the number of children participating in the study occurred as time passed because of factors such as unrelated illnesses, change in residence, or the development of apathy toward the study. This reduction is seen in the smaller groups recorded at the end of the 4 month period. Table I shows a comparison of good, poor, and the negative ova-production groups which received the placebo over the 16 week period. Some of the children who were initially negative acquired infections, and some of the children in the good and the poor ova-production group became negative. A test of homogeneity showed that both good and poor ova-production groups could be considered as one group. On the basis of their similar responses to the placebo, the "poor" and "good" groups will be considered as a combined group designated "positives" throughout the remainder of this paper. A comparison of the results of a single dose of the placebo with a single dose of pyrvinium pamoate is shown in Table II. In the placebo group there is a marked turnover of infection among the children, although the total number of infected children does not change markedly. Prior to treatment, 36.2 per cent of the placebo group were infected, and after treatment 41.7 per cent. Of those treated with pyrvinium pamoate, only 3 positives failed to respond to the drug and one negative acquired a new infection. With treatment the per cent of positives in the pyrvinium pamoate-treated group dropped from 44.2 to 2.7 per cent. Most studies of therapeutic agents for pinworm infection use the term "per cent cure rate" as a measure of the efficacy of the drug in question. This term has several unfortunate disadvantages in that it takes into consideration only the per cent of positives who bedame negative after treatment and ignores the status of controls both positive and negative, as well as of treated neg-
February 1962
atives. For the sake of comparison, the "per cent cure rate" in 65 positives treated with a single dose of pyrvinium pamoate in this study was 95.4. A simple adjustment for the tendency to spontaneous cures in the positive controls by using the formula per cent treated remaining \ positive _ _ 100 x 1 - per cent controIs r e m a i n i n g ] positive / gives an "adjusted per cent cure rate" of 100
1 - ~
= 94.3.
Table III compares the results of swabs taken at the end of the 4 month treatment period on children who were in the following categories: (1) a dose of placebo every 3 weeks; (2) a single dose of pyrvinium pamoate at the beginning of the 4 month period; (3) a dose of pyrvinium pamoate every 3 weeks. The results show that in 4 months the incidence of infection in the group of children who had received only a single dose of pyrvinium pamoate had again reached a level similar to that of the placebo group. Only 2 infections were acquired by children taking doses of pyrvinium pamoate at intervals of 3 weeks. All the positives who responded to the initial dose of drug maintained their negative status while on the repeat dose schedule. One of the 2 children who acquired a pinworm infection during the repeat dose schedule showed only one ovum on the series of 7 swabs. A chi-square test of the effect of treatment in the 3 groups is presented in Table IV. X~ represents a statistical comparison of all 3 groups and indicates significant differences at a 5 per cent probability level when its value exceeds 5.99. The effect of the drug on infection is definitely significant (17.945 being greater than 5.99). However, children who showed negative test results at the start of treatment showed no statistically significant difference in the incidence of infection among the three categories of treatment. The terms X~ and X~ are introduced to compare the individual treat-
Volume 60 Number 2
Pyrvinium pamoate and pinworm infection
ments. Both X] and X~ indicate a significant difference if their values exceed 3.84. X] provides a comparison of the single dose and placebo groups. The low values of 0.812 and 0.057 show that no significant difference in the incidence of infection existed between the single dose and children treated with placebo at the end of the 4 month period. X22 compares the repeated-dose group with the other two groups. The value of 17.133 substantiates the obvious conclusion that repeated doses were effective in maintaining the negative status of children who had been positive prior to treatment. The X22 calculated for the children who were negative prior to treatment shows no significant difference between the repeateddose and the other two groups. Repeated doses of pyrvinium pamoate failed to prevent the occurrence of 2 infections among the 26 children. The statistical evidence that repeated doses do not afford protection against infection m a y be a misleading consequence of the small size of the sample and requires further investigation. All 6 infected adults were found to be negative on 7 consecutive swabs 1 week after the administration of the coated tablets of pyrvinium pamoate. Side effects. A summary of the results of hemoglobin determinations and leuko-
24 7
cyte counts is presented in Table V. The posttreatment data were obtained at the end of the 4 month period. The values for "t" were computed from the differences between the pretreatment and posttreatment data for each child. Application of the "t" test to hemoglobin concentrations and leukocyte counts showed no significant differences between the groups treated with placebo and with the single dose of pyrvinium pamoate. The group that received repeated doses of pyrvinium pamoate had "t" values which slightly exceed the 5 per cent level. Although this is considered to be significant on a statistical basis, the values are not large and may merely indicate an exaggeration of the tendency to increased hemoglobin levels and a fall in leukocyte counts which occurred to a lesser degree in the groups treated with a placebo and with a single dose of pyrvinium pamoate. To test the possibility that the statistically significant hemoglobin increase and leukocyte decrease were caused by the clearing of pinworm infection in the repeated-dose group, the hematologic data of noninfected children were compared with those of infected children by means of the "t" test. The mean hemoglobin level of 84 children who were positive for pinworm ova was
Table I I I . Results of treatment with pyrvinium pamoate administered at 3 week intervals ~ compared with those of a single dose and of a placebo Presence of ova Prior to treatment Treatment group Placebo at 3 week intervals
Positive
Negative
18
33 Total Pyrvinium pamoate, single dose at beginning of 4 m o n t h period
19 19
Total Pyrvinium p a m o a t e at 3 week intervals
25
26
After 4 month treatment period~
Positive after 4 months
Positive I Negative
(%0
10 6
8 27
16
35
55.6 18.2 31.4
8 3
11 16
42.1 15.8
11
27
28.9
0 2
25 24
0.0 7.7 3.9
Total 2 49 ~Observation period of 4 months. Total of 5 doses of pyrvinmm pamoate given at 3 week intervals. tSeven consecutive swabs begun 1 week after last dose at the end of the 4 month period.
2 4 8
Turner
February 1962
and Johnson
Table IV. Comparison of the results of treatment of single-dose repeated-dose, and placebo-treated groups after a 4 month period Presence of ova Prior to treatment
Positive
Group frequencies
After 4 month period
Placebo every3 Positive i Negative weeks
Euerfl Single dose
3 weeks
x~
x~
x~
44
10 8 18
8 11 19
0 25 25
17.945
0.812
17.133
67
6 27 33
3 16 19
2 24 26
1.380
0.057
1.323
18
Total Negative
Chi squares
Pyrviniura pamoate
11
Total
Table V. Comparison of hematologic studies before and after treatment Examlnation
Group
No. examined
Pretreatment (range)
Posttreatment ~ (range)
Placebo Singledose Repeated doset
38 29
WBC (per c.mm.)
Placebo Single dose Repeated doset
38 29
4,900-20,7503,500-18,100 5,600-25,9005,200-17,000
36
6,600-20,3005,200-18,000
10,421
9,440
10.0-16.5
12.0-16.0
13.4 13.5
Posttreatment ~ (mean)
Hgb. (Gm. %)
36
11.5-16.0 10.5-16.0 11.0-16.0 11.5-16.0
Pretreatment (mean)
Calculated t
tos
13.8 13.6
1.42 2.028 0.625 2.048
13.2
13.8
2.680 2.030
10,421 11,586
9,526 10,957
1.56 2.028 1.64 2.048 2.11
2.030
~At the end of the 4 month period of treatment. t T o ~ l of 5 doses of pyrvlnlum pamoate were given at 3 week intervals.
13.63 Gm. per cent; of 119 who were negative it was 13.60 Gm. per cent. The "t" value calculated for these two groups is 0.153 and indicates no significant difference. Eighty-six infected children with a mean leukocyte count of 10,918 were compared with 120 noninfected children with a mean leukocyte count of 10,728. No significant difference is evident (t = 0.055). This statistical analysis shows that the hemoglobin and leukocyte count values of infected and noninfected children fall in the same range. On the basis of this information, it is clear that the rise in hemoglobin and fall in leukocyte count in the group who received repeated doses of pyrvinium pamoate over the 4 month period cannot be attributed to the loss of pinworm infection. No significant change was detected in the urinary sediment of either placebo-treated or drug-treated children. No proteinuria was detected in any of the children tested.
Of 88 children taking a placebo, i vomited (1.1 per cent), and, of the 166 children taking pyrvinium pamoate, 9 vomited (5.4 per cent). The vomiting occurred from 20 minutes to 2 hours after the administration of the drug and was not preceded by complaints of nausea. Several children who had taken the medicine shortly before bedtime vomited in their sleep. After emesis, the children appeared well and had no complaints of nausea or abdominal pain. One child had transient diarrhea after taking the drug. No diarrhea was reported in the placebo group. DISCUSSION
The therapy of pinworm infection has been frustrating in several aspects because of the lack of a drug which is highly effective. The advent of dithiazanine iodide and pyrvinium pamoate has solved this problem. The fact that pyrvinium pamoate
Volume 60 Number 2
Pyrvinium pamoate and pinworm infection
is effective when administered in a single dose has further simplified treatment. The problems of reinfection and undiscovered infections still remain. The goals of this study were to test the effectiveness of the single dose of pyrvinium pamoate administered to members of a family and to gain additional knowledge concerning reinfection and the means for its prevention. The results obtained substantiate the reports of others concerning the high degree of efficacy of a single dose of pyrvinium pamoate. 3"5 In this study the parents were responsible for the administration of the drug. Although the population was unusual in that one of the parents in each family was a college student, it is likely that similar results can be expected in other groups. Reports by other workers on the use of pyrvinium pamoate in single doses have demonstrated a remarkable lack of side effects. Beck and co-workers 3 reported no complaints from 100 children who received a suspension of pyrvinium pamoate. Bumbalo and associates 4 found one instance of vomiting among 51 children which occurred "under circumstances which suggested that the vomiting was not caused by the medication." Sanders and HalP report vomiting in one child from a group of 25 children and 4 adults. In the present study, 9 of 166 children who were treated with pyrvinium pamoate vomited. Only 1 of the 88 children who were given the placebo vomited. This suggests that a few children who are given a single therapeutic dose of pyrvinium pamoate will vomit the medicine, and parents should be forewarned of this possibility. This is especially important because of the staining property of pyrvlnium pamoate. Results of the leukocyte counts, hemoglobin determinations, and urinalyses in the present study show no clinically significant effect of either single or repeated doses of pyrvinium pamoate. A tendency toward a slight elevation in hemoglobin levels and a slight fall in leukocyte counts over the 4 months probably represents recovery from an epidemic of viral respiratory infections
249
which occurred during the period when the pretreatment specimens were obtained. However, a very slight statistically significant fall in leukocyte count and rise in hemoglobin level occurred only in children receiving 5 doses of pyrvinium pamoate over a 4 month period. This could not be explained on the basis of the loss of pinworm infection in this group. Any further studies utilizing repeated doses of the drug should evaluate the hematologic response to clarify this point. The present attitude toward therapy of pinworm infection is to consider that the entire family is infected, and treatment is recommended for all members simultaneously. The logic of treating those shown to be negative for pinworm ova is based on the possibility that they may have an infection which has not yet matured to the ovipositing stage. Treating isolated cases may clear the infection; but at the end of 4 months, the same proportion of these patients became reinfected as of the untreated control group. This is further support for the technique of treating the entire family. In the past, drug therapy for pinworm infection has required courses of treatment varying in length from 5 days to 2 weeks. These courses may give a period of protection during which the ova in the environment lose their viability. With increased use of single-dose therapy, reinfection from the environment may become a more important factor. Ideally, a second treatment should be administered at a time when all ova in the home have lost their infectivity. The viability of pinworm ova is very dependent upon a suitable temperature and humidity, s Survival of the ova increases with lower temperatures and humidity. Lentze 9 found a loss of infectivity after 9 days during warm, moist, summer weather. Jones and Jacobs s demonstrated the effects of various temperatures and humidity on a short-term survival basis expressed in per cent and found variations among different batches of ova. They also found that optimal conditions of near-freezing temperatures and
250
Turner and Johnson
100 per cent humidity would allow some ova to survive as long as 14 weeks. Sawitz and associates ~ state that ova remained viable for 19 days when kept "at room temperature and exposed to air." These studies indicate that no precise survival time will fit all conditions. It is doubtful that many ova could survive longer than 3 weeks except under unusual conditions such as cold, rainy weather. Even then, the normal heating of rooms to a comfortable, fairly constant temperature would tend to eliminate the preserving effects of the cold weather. An additional factor which must be considered in a schedule of repeated doses is the capability of mature female pinworms to lay eggs several days after effective therapy. This point was previously made by Jung and Beaver ~ in a study on therapy of pinworm infection. They found that swabs became negative as late as 4 days after termination of therapy. This phenomenon is also evident in the series of Beck and co-workers a in which a single dose of pyrvinium pamoate was used in 100 cases. Only 45 per cent were negative 1 day after treatment, 88 per cent 4 days, and 96 per cent 7 days after treatment. Ninety-six per cent remained free of infection for the remainder of the two week period of the test. Therefore, the possibility must be considered that ova may continue to enter the environment for 7 days after the initial treatment with pyrvininm pamoate. The life cycle of the pinworm in the human being is considered to have a minimum of 15 days from egg to egg-laying adult, x~ Therefore, the minimal time between doses must be less than 15 days. To summarize, the important factors in planning a schedule of dosage in pinworm therapy with pyrvinium pamoate are: (1) egg viability is usually less than 3 weeks, (2) production of ova may continue for as long as 7 days after the initial dose, and (3) the pinworm requires more than 2 weeks to mature from the egg to an egg-laylng adult. It is suggested that an optimal schedule for the administration of pyrvinium pamoate would be a curative dose of 5 rag. per kilo-
February 1962
gram given every 2 weeks for a total of 3 doses. In warm, dry climates, 2 doses would probably be sufficient. Further studies are planned to assess the efficacy of these schedules. Attempted prophylactic treatment of noninfected children by repeated doses of pyrvinium pamoate cannot be justified by the results of this study. The children who were negative at the beginning of the study had a similar low incidence of infection after 4 months whether they received a placebo, a single dose, or repeated doses of the drug. The opportunities for infection during the 4 month period were lessened because a majority of infected children in the population had been treated and, therefore, were no longer sources of infection for the other children. This factor may also be responsible for the over-all drop in the per cent of positives in the placebo-treated group from the first treatment to the end of the 4 month period of observation. Pyrvinium pamoate in the form of coated tablets will be useful with older children and adults who would otherwise need to take unpleasantly large quantities of the drug in a suspension. Six infected adults who were treated with coated tablets of pyrvinium pamoate during the present study became negative and had no gastrointestinal symptoms. A single dose schedule of treatment with pyrvinium pamoate is most convenient, but, as with drugs used in the past, the possibility of reinfection from the home environment shouId be kept in mind. Until this problem is resolved, it is suggested that a dose of pyrvinium pamoate administered 2 or 3 times at biweekly intervals may offer a partial solution. SUMMARY
Pyrvinium pamoate suspension in a dosage of 5 mg. per kilogram was administered to children from a group of families in a university housing project. The results show that a single dose was highly effective initially in controlling infection, but reinfection occurred commonly. Doses repeated at 3
Volume 60 Number 2
Pyrvinium pamoate and pinworm in[ection
week intervals p a r t i a l l y solved the p r o b l e m of r e c u r r e n t infection. T h e d a t a f r o m this study do not justify the use of p y r v i n i u m p a m o a t e p r o p h y l a c t i c a l l y in noninfected children. Factors i m p o r t a n t in reinfection within the family e n v i r o n m e n t are discussed, a n d a dose of 5 mg. p e r k i l o g r a m of b o d y weight a d m i n i s t e r e d 3 times at biweekly intervaIs is suggested.
4.
5.
6. We are indebted to Dr. David G. Hays for statistical advice and to Drs. Janice T. Kayahara, George S. Smith, Rudolph E. Erickson, and Charles H. Schiro for their technical assistance and their help in the collection and distribution of materials. REFERENCES
1. Sawitz, W. G., D'Antoni, J. S., Rhude, K., and Lob, S." Studies on the Epidemiology of Oxyuriasis, South. M. J. 33: 913, 1940. 2. Schiiffner, W., and Swellengrebel, N. I-I.: Retrofection in Oxyuriasis. A Newly Discovered Mode of Infection With Enterobius vermicularis, J. Parasitol. 35: 138, 1949. 3. Beck, J. W., Saavedra, D., Antell, G. J., and
7.
8.
9.
10.
25 1
Tejeiro, B.: The Treatment of Pinworm Infections in Humans (Enterobiasis) With Pyrvinium Pamoate, Am. J. Trop. Med. 8: 349, 1959. Bumbalo, T. S., Plummet, L. J., and Warner, J. R.: A Clinical Evaluation of Four Oxyuricides, A. M. A. J. Dis. Child. 99: 617, 1960. Sanders, A. I., and Hall, W. I-Ix Comparison of Dithiazanine Iodide and Pyrvinium Pamoate in the Treatment of Enterobiasis (Pinworms), J. Lab. & Clin. Med. 56: 413, 1960. Beaver, P. C.: Methods of Pinworm Diagnosis, Am. J. Trop. Med. 29: 577, 1949. Jung, R. C., and Beaver, P. C.: Treatment of Enterobiasls (Pinworm Infestation) With Diphenan, Egressin and Gentian Violet, Pediatrics 11: 611, 1953. Jones, M. F., and Jacobs, L.: Studies on Oxyuriasis. XXIII. The Survival of Eggs of Enterobius vermicularis Under Known Conditions of Temperature and Humidity, Am. J. Hyg. 33: 88, 1941. Lentze, F. A.: Ueber die Verbreitung von Spul- und Madenwilrmern und fiber die Massnahmen zur ihrer Bek~impfung vom Standpunkte der 6ffentlichen Gesundheitspflege, VeriSffentl. a. d. Geb. d. Med.Verwalt. 37: 51, 1932. Cram, E. B.: Studies on Oxyuriasis. XXVIII. Summary and Conclusions, Am. J. Dis. Child. 65: 46, 1943.
243
Pyrvinium pamoate in the treatment of pimrorm infection (enterobiasis) in the borne Jerro]d A. Turner, M.DP and Paul E. Johnson, Jr., M.D. LOS ANGELES~ CALIF,
T rIE efficient life cycle of the pinworm of man, Enterobius vermicularis, has insured its status as the most prevalent helminthic parasite in the United States. Because of the hand-to-mouth mode of transmission, it is most important in the practice of pediatrics. Although the symptomatology of pinworm infections is not spectacular, anal pruritus may disrupt sleeping habits and cause irritability that affects the entire family. Of particular importance is the psychological impact upon the parents when they discover that their child has "worms." In the past, much attention has been devoted to interrupting transmission by vigorous hygienic measures. The futility of this endeavor was pointed out by Sawitz and associates 1 who showed an increase in incidence over a 6 week period among children in a well-controlled environment under
From the Departments of Infectious Diseases and Pediatrics, University of California School of Medicine, Los Angeles. This study received partial financial support from Parke, Davis and Company, Detroit, Mich. ~Address, Assistant Professor, Department o] InJectious Diseases, Division o] Parasitology and Tropic Diseases, University of Cali[ornla School of Medicine, Los Angeles 24, Call[.
conditions of intense sanitation. The discovery, by Schiiffner and SwellengrebeP of the anaI route of infection by migration of larvae from ova hatched on the perineum, leads to the conclusion that frequent washing of the anus and the perineum is also necessary to prevent infection. Neither of these techniques is satisfactory nor practical in the home environment. Chemotherapy has also been disappointing because of the prolonged treatment required and its relative ineffectiveness. Recently, several reports have appeared which showed that pyrvinium pamoate achieves nearly 100 per cent cures in pinworm infection without unpleasant side effects. Moreover, it was effective in a single dose2 -~ The present study was designed to test the effectiveness of a single dose of pyrvinium pamoate in a large number of children within the family environment. In addition, it was planned to test the usefulness of repeated doses of the drug over a prolonged period in prevention of reinfection and as prophylaxis among noninfected children.
MATERIALS AND METHODS Survey methods. The University of California at Los Angeles provides a limited
244
February 1962
T u r n e r and Johnson
amount of housing for families of students who are veterans. The housing facilities consist of 18 wooden buildings, each containing 14 one-bedroom apartments. There are two adults per apartment and an approximate average of two children per family. The majority of children are under 6 years of age. The families in these units were selected for the study. T h e families were initially contacted by one of four medical students. Meetings of the mothers were held in groups, and a group leader was selected from each apartment building. The distribution and collection of materials and information among the group leaders was carried out by the medical students. The group leaders were responsible for contacting the individual families. In addition to observing demonstrations of the cellulose tape swab technique given by the medical students, each famiIy received a mimeographed set of instructions which could be used as a reference at any later date. Families were requested to obtain swab specimens on 7 consecutive mornings upon arising, prior to bathing or going to the toilet. Each person received a kit which contained (1) a slide box with a data card affixed to its top, (2) seven clean slides, (3) seven tongue depressors, and (4) a roll of N inch cellulose tape. The initial survey included all children and adults who completed the set of 7 swabs. The boxes were collected and the cellulose tape swabs were read by using the following modification of Beaver's 6 technique: (1) The slides were held up to the light
and the portion of the tape which had contacted the anus and perianal skin was Iocated. A definite area of decreased transparency of the tape due to irregularities formed in the adhesive on contact can easily be delineated. (2) This area was marked off on each slide by wax pencil lines made on the underside of the slide. (3) The tape was pulled back from the surface of the slide, exposing the area of contact, and a drop of toluene was placed on the slide. The tape was then smoothed back onto the surface of the slide with the index finger. (The wax pencil marks are soluble in toluene, and, therefore, must be made on the under side of the slide.) (4) The entire area bebetween the marks of the wax pencil was searched in consecutive, low-power fields. It has been suggested that a single positive swab does not necessarily indicate an active infection, but may merely be evidence of the termination of a previous infection. 7 Moreover, an individual who shows only one or two positive swabs during a test period is less likely to be found positive at a later testing than an individual who has a series of positive swabs during the initial test period7 For these reasons, each set of slides was graded for the presence of ova as follows: negative, no ova present on 7 consecutive slides; poor ova-production, ova present but not seen on 3 consecutive slides; good ova-production, ova present on 3 or more consecutive slides. T r e a t m e n t series. Children from the ages of 1 to 12 years were selected for the study. The negative, poor ova-producer, and good ova-producer groups were divided randomly into equal numbers among the following
Table I. A comparison of infection between groups of children considered to be negative, poor, and good ova-producers during a 16 week period Status on initial survey
Negative Poor ova-production Good ova-productlon
.
3 weeks after initial survey Positive I Negative I Total
9 7 14
37 3 2
46 10 16
16 weeks after initial survey Positive f Xeg ative I Total
6 4 6
27 4 4
33 8 10
Volume 60 Number 2
Pyrvinium pamoate and pinworm infection
245
Table II. Results of treatment with a single dose of pyrvinium pamoate compared with a placebo Presence o[ ova Treatment group
Placebo
Prior to treatment Positive I Negative 26 46
Total Pyrvinium pamoate, single dose Total
65 82
I week a#er single dose* Positive I Negative 21 5 9 37 3-0 42 3 1 4
62 81 143
Positive alter treatment (%) 80.8 19.5 41.7 4.6 1.2 2.7
*The 7 consecutive swabs were begun 1 week after the drug or placebo was administered.
treatment groups: placebo, dose repeated every 3 weeks for a total of 5 doses; pyrvinium pamoate, single dose; pyrvinium pamoate, dose repeated every 3 weeks for a total of 5 doses. T h e groups were proportionally distributed by a method of random selection throughout each apartment building. Each child within a single family was placed in a different treatment group whenever possible. With this distribution as m a n y children as possible who were receiving pyrvinium pamoate could be maximally exposed to an environment which contained ova from infected siblings who were taking the placebo. The pyrvinium pamoate was in the form of a flavored suspension containing 10 mg. pyrvinium base per cubic centimeter. ~ It was adiministered in a dosage of 5 mg. per kilogram of body weight. T h e placebo resembled the drug in appearance and flavor.t Six adults who were infected were treated with a single dose of pyrvinium pamoate in coated tablets, each of which contained 100 mg. of pyrvinium base. ~ This was also administered in the dose of 5 mg. per kilogram of body weight. The first dose of pyrvinium pamoate or placebo was administered to the children 2 weeks after the survey. A follow-up series of 7 consecutive daily cellulose tape swabs was begun 7 days after administration of the -"-Supplied as Povan by Parke, Davis and Company. "{'Prepared by the Pharmacy of the University of Callfornia Medical Center.
first dose of the drug or the placebo. A repeat series of 7 consecutive swabs was taken daily at the end of the 4 month period of treatment beginning 7 days after the fifth and last dose. Evaluation of side effects. Prior to the commencement of treatment, as m a n y children as possible were evaluated by the following laboratory determinations: hemoglobin (Spencer Hb-Meter, American Optical Company), leukocyte count, urinary protein (sulfosalicylic acid m e t h o d ) ; and urinary sediment (uncentrifuged). Parents were requested to contact the Emergency Service if their child became ill. Members of the Pediatric Staff evaluated any unusual symptoms by examination and appropriate laboratory tests. RESULTS
Survey. A completed series of swabs was received from a total of 277 children. Of these, 120 were found to be positive for pinworm ova (43.3 per cent). There was no sex difference in the prevalence of infection. Ninety-nine adults c o m p l e t e d the series of 7 swabs, and 12 were found to be positive ( 12.1 per cent). The distribution of positive test results among individual families showed that when one member of the family was found to be infected, there was a significant increase in the probability that one or more additional positive tests would be found within that same family. A significantly higher prevalence of infection was found among the
24 6
Turner and Johnson
larger families when a comparison of the results of the survey was made with an expected, random distribution. Treatment series. A reduction in the number of children participating in the study occurred as time passed because of factors such as unrelated illnesses, change in residence, or the development of apathy toward the study. This reduction is seen in the smaller groups recorded at the end of the 4 month period. Table I shows a comparison of good, poor, and the negative ova-production groups which received the placebo over the 16 week period. Some of the children who were initially negative acquired infections, and some of the children in the good and the poor ova-production group became negative. A test of homogeneity showed that both good and poor ova-production groups could be considered as one group. On the basis of their similar responses to the placebo, the "poor" and "good" groups will be considered as a combined group designated "positives" throughout the remainder of this paper. A comparison of the results of a single dose of the placebo with a single dose of pyrvinium pamoate is shown in Table II. In the placebo group there is a marked turnover of infection among the children, although the total number of infected children does not change markedly. Prior to treatment, 36.2 per cent of the placebo group were infected, and after treatment 41.7 per cent. Of those treated with pyrvinium pamoate, only 3 positives failed to respond to the drug and one negative acquired a new infection. With treatment the per cent of positives in the pyrvinium pamoate-treated group dropped from 44.2 to 2.7 per cent. Most studies of therapeutic agents for pinworm infection use the term "per cent cure rate" as a measure of the efficacy of the drug in question. This term has several unfortunate disadvantages in that it takes into consideration only the per cent of positives who bedame negative after treatment and ignores the status of controls both positive and negative, as well as of treated neg-
February 1962
atives. For the sake of comparison, the "per cent cure rate" in 65 positives treated with a single dose of pyrvinium pamoate in this study was 95.4. A simple adjustment for the tendency to spontaneous cures in the positive controls by using the formula per cent treated remaining \ positive _ _ 100 x 1 - per cent controIs r e m a i n i n g ] positive / gives an "adjusted per cent cure rate" of 100
1 - ~
= 94.3.
Table III compares the results of swabs taken at the end of the 4 month treatment period on children who were in the following categories: (1) a dose of placebo every 3 weeks; (2) a single dose of pyrvinium pamoate at the beginning of the 4 month period; (3) a dose of pyrvinium pamoate every 3 weeks. The results show that in 4 months the incidence of infection in the group of children who had received only a single dose of pyrvinium pamoate had again reached a level similar to that of the placebo group. Only 2 infections were acquired by children taking doses of pyrvinium pamoate at intervals of 3 weeks. All the positives who responded to the initial dose of drug maintained their negative status while on the repeat dose schedule. One of the 2 children who acquired a pinworm infection during the repeat dose schedule showed only one ovum on the series of 7 swabs. A chi-square test of the effect of treatment in the 3 groups is presented in Table IV. X~ represents a statistical comparison of all 3 groups and indicates significant differences at a 5 per cent probability level when its value exceeds 5.99. The effect of the drug on infection is definitely significant (17.945 being greater than 5.99). However, children who showed negative test results at the start of treatment showed no statistically significant difference in the incidence of infection among the three categories of treatment. The terms X~ and X~ are introduced to compare the individual treat-
Volume 60 Number 2
Pyrvinium pamoate and pinworm infection
ments. Both X] and X~ indicate a significant difference if their values exceed 3.84. X] provides a comparison of the single dose and placebo groups. The low values of 0.812 and 0.057 show that no significant difference in the incidence of infection existed between the single dose and children treated with placebo at the end of the 4 month period. X22 compares the repeated-dose group with the other two groups. The value of 17.133 substantiates the obvious conclusion that repeated doses were effective in maintaining the negative status of children who had been positive prior to treatment. The X22 calculated for the children who were negative prior to treatment shows no significant difference between the repeateddose and the other two groups. Repeated doses of pyrvinium pamoate failed to prevent the occurrence of 2 infections among the 26 children. The statistical evidence that repeated doses do not afford protection against infection m a y be a misleading consequence of the small size of the sample and requires further investigation. All 6 infected adults were found to be negative on 7 consecutive swabs 1 week after the administration of the coated tablets of pyrvinium pamoate. Side effects. A summary of the results of hemoglobin determinations and leuko-
24 7
cyte counts is presented in Table V. The posttreatment data were obtained at the end of the 4 month period. The values for "t" were computed from the differences between the pretreatment and posttreatment data for each child. Application of the "t" test to hemoglobin concentrations and leukocyte counts showed no significant differences between the groups treated with placebo and with the single dose of pyrvinium pamoate. The group that received repeated doses of pyrvinium pamoate had "t" values which slightly exceed the 5 per cent level. Although this is considered to be significant on a statistical basis, the values are not large and may merely indicate an exaggeration of the tendency to increased hemoglobin levels and a fall in leukocyte counts which occurred to a lesser degree in the groups treated with a placebo and with a single dose of pyrvinium pamoate. To test the possibility that the statistically significant hemoglobin increase and leukocyte decrease were caused by the clearing of pinworm infection in the repeated-dose group, the hematologic data of noninfected children were compared with those of infected children by means of the "t" test. The mean hemoglobin level of 84 children who were positive for pinworm ova was
Table I I I . Results of treatment with pyrvinium pamoate administered at 3 week intervals ~ compared with those of a single dose and of a placebo Presence of ova Prior to treatment Treatment group Placebo at 3 week intervals
Positive
Negative
18
33 Total Pyrvinium pamoate, single dose at beginning of 4 m o n t h period
19 19
Total Pyrvinium p a m o a t e at 3 week intervals
25
26
After 4 month treatment period~
Positive after 4 months
Positive I Negative
(%0
10 6
8 27
16
35
55.6 18.2 31.4
8 3
11 16
42.1 15.8
11
27
28.9
0 2
25 24
0.0 7.7 3.9
Total 2 49 ~Observation period of 4 months. Total of 5 doses of pyrvinmm pamoate given at 3 week intervals. tSeven consecutive swabs begun 1 week after last dose at the end of the 4 month period.
2 4 8
Turner
February 1962
and Johnson
Table IV. Comparison of the results of treatment of single-dose repeated-dose, and placebo-treated groups after a 4 month period Presence of ova Prior to treatment
Positive
Group frequencies
After 4 month period
Placebo every3 Positive i Negative weeks
Euerfl Single dose
3 weeks
x~
x~
x~
44
10 8 18
8 11 19
0 25 25
17.945
0.812
17.133
67
6 27 33
3 16 19
2 24 26
1.380
0.057
1.323
18
Total Negative
Chi squares
Pyrviniura pamoate
11
Total
Table V. Comparison of hematologic studies before and after treatment Examlnation
Group
No. examined
Pretreatment (range)
Posttreatment ~ (range)
Placebo Singledose Repeated doset
38 29
WBC (per c.mm.)
Placebo Single dose Repeated doset
38 29
4,900-20,7503,500-18,100 5,600-25,9005,200-17,000
36
6,600-20,3005,200-18,000
10,421
9,440
10.0-16.5
12.0-16.0
13.4 13.5
Posttreatment ~ (mean)
Hgb. (Gm. %)
36
11.5-16.0 10.5-16.0 11.0-16.0 11.5-16.0
Pretreatment (mean)
Calculated t
tos
13.8 13.6
1.42 2.028 0.625 2.048
13.2
13.8
2.680 2.030
10,421 11,586
9,526 10,957
1.56 2.028 1.64 2.048 2.11
2.030
~At the end of the 4 month period of treatment. t T o ~ l of 5 doses of pyrvlnlum pamoate were given at 3 week intervals.
13.63 Gm. per cent; of 119 who were negative it was 13.60 Gm. per cent. The "t" value calculated for these two groups is 0.153 and indicates no significant difference. Eighty-six infected children with a mean leukocyte count of 10,918 were compared with 120 noninfected children with a mean leukocyte count of 10,728. No significant difference is evident (t = 0.055). This statistical analysis shows that the hemoglobin and leukocyte count values of infected and noninfected children fall in the same range. On the basis of this information, it is clear that the rise in hemoglobin and fall in leukocyte count in the group who received repeated doses of pyrvinium pamoate over the 4 month period cannot be attributed to the loss of pinworm infection. No significant change was detected in the urinary sediment of either placebo-treated or drug-treated children. No proteinuria was detected in any of the children tested.
Of 88 children taking a placebo, i vomited (1.1 per cent), and, of the 166 children taking pyrvinium pamoate, 9 vomited (5.4 per cent). The vomiting occurred from 20 minutes to 2 hours after the administration of the drug and was not preceded by complaints of nausea. Several children who had taken the medicine shortly before bedtime vomited in their sleep. After emesis, the children appeared well and had no complaints of nausea or abdominal pain. One child had transient diarrhea after taking the drug. No diarrhea was reported in the placebo group. DISCUSSION
The therapy of pinworm infection has been frustrating in several aspects because of the lack of a drug which is highly effective. The advent of dithiazanine iodide and pyrvinium pamoate has solved this problem. The fact that pyrvinium pamoate
Volume 60 Number 2
Pyrvinium pamoate and pinworm infection
is effective when administered in a single dose has further simplified treatment. The problems of reinfection and undiscovered infections still remain. The goals of this study were to test the effectiveness of the single dose of pyrvinium pamoate administered to members of a family and to gain additional knowledge concerning reinfection and the means for its prevention. The results obtained substantiate the reports of others concerning the high degree of efficacy of a single dose of pyrvinium pamoate. 3"5 In this study the parents were responsible for the administration of the drug. Although the population was unusual in that one of the parents in each family was a college student, it is likely that similar results can be expected in other groups. Reports by other workers on the use of pyrvinium pamoate in single doses have demonstrated a remarkable lack of side effects. Beck and co-workers 3 reported no complaints from 100 children who received a suspension of pyrvinium pamoate. Bumbalo and associates 4 found one instance of vomiting among 51 children which occurred "under circumstances which suggested that the vomiting was not caused by the medication." Sanders and HalP report vomiting in one child from a group of 25 children and 4 adults. In the present study, 9 of 166 children who were treated with pyrvinium pamoate vomited. Only 1 of the 88 children who were given the placebo vomited. This suggests that a few children who are given a single therapeutic dose of pyrvinium pamoate will vomit the medicine, and parents should be forewarned of this possibility. This is especially important because of the staining property of pyrvlnium pamoate. Results of the leukocyte counts, hemoglobin determinations, and urinalyses in the present study show no clinically significant effect of either single or repeated doses of pyrvinium pamoate. A tendency toward a slight elevation in hemoglobin levels and a slight fall in leukocyte counts over the 4 months probably represents recovery from an epidemic of viral respiratory infections
249
which occurred during the period when the pretreatment specimens were obtained. However, a very slight statistically significant fall in leukocyte count and rise in hemoglobin level occurred only in children receiving 5 doses of pyrvinium pamoate over a 4 month period. This could not be explained on the basis of the loss of pinworm infection in this group. Any further studies utilizing repeated doses of the drug should evaluate the hematologic response to clarify this point. The present attitude toward therapy of pinworm infection is to consider that the entire family is infected, and treatment is recommended for all members simultaneously. The logic of treating those shown to be negative for pinworm ova is based on the possibility that they may have an infection which has not yet matured to the ovipositing stage. Treating isolated cases may clear the infection; but at the end of 4 months, the same proportion of these patients became reinfected as of the untreated control group. This is further support for the technique of treating the entire family. In the past, drug therapy for pinworm infection has required courses of treatment varying in length from 5 days to 2 weeks. These courses may give a period of protection during which the ova in the environment lose their viability. With increased use of single-dose therapy, reinfection from the environment may become a more important factor. Ideally, a second treatment should be administered at a time when all ova in the home have lost their infectivity. The viability of pinworm ova is very dependent upon a suitable temperature and humidity, s Survival of the ova increases with lower temperatures and humidity. Lentze 9 found a loss of infectivity after 9 days during warm, moist, summer weather. Jones and Jacobs s demonstrated the effects of various temperatures and humidity on a short-term survival basis expressed in per cent and found variations among different batches of ova. They also found that optimal conditions of near-freezing temperatures and
250
Turner and Johnson
100 per cent humidity would allow some ova to survive as long as 14 weeks. Sawitz and associates ~ state that ova remained viable for 19 days when kept "at room temperature and exposed to air." These studies indicate that no precise survival time will fit all conditions. It is doubtful that many ova could survive longer than 3 weeks except under unusual conditions such as cold, rainy weather. Even then, the normal heating of rooms to a comfortable, fairly constant temperature would tend to eliminate the preserving effects of the cold weather. An additional factor which must be considered in a schedule of repeated doses is the capability of mature female pinworms to lay eggs several days after effective therapy. This point was previously made by Jung and Beaver ~ in a study on therapy of pinworm infection. They found that swabs became negative as late as 4 days after termination of therapy. This phenomenon is also evident in the series of Beck and co-workers a in which a single dose of pyrvinium pamoate was used in 100 cases. Only 45 per cent were negative 1 day after treatment, 88 per cent 4 days, and 96 per cent 7 days after treatment. Ninety-six per cent remained free of infection for the remainder of the two week period of the test. Therefore, the possibility must be considered that ova may continue to enter the environment for 7 days after the initial treatment with pyrvininm pamoate. The life cycle of the pinworm in the human being is considered to have a minimum of 15 days from egg to egg-laying adult, x~ Therefore, the minimal time between doses must be less than 15 days. To summarize, the important factors in planning a schedule of dosage in pinworm therapy with pyrvinium pamoate are: (1) egg viability is usually less than 3 weeks, (2) production of ova may continue for as long as 7 days after the initial dose, and (3) the pinworm requires more than 2 weeks to mature from the egg to an egg-laylng adult. It is suggested that an optimal schedule for the administration of pyrvinium pamoate would be a curative dose of 5 rag. per kilo-
February 1962
gram given every 2 weeks for a total of 3 doses. In warm, dry climates, 2 doses would probably be sufficient. Further studies are planned to assess the efficacy of these schedules. Attempted prophylactic treatment of noninfected children by repeated doses of pyrvinium pamoate cannot be justified by the results of this study. The children who were negative at the beginning of the study had a similar low incidence of infection after 4 months whether they received a placebo, a single dose, or repeated doses of the drug. The opportunities for infection during the 4 month period were lessened because a majority of infected children in the population had been treated and, therefore, were no longer sources of infection for the other children. This factor may also be responsible for the over-all drop in the per cent of positives in the placebo-treated group from the first treatment to the end of the 4 month period of observation. Pyrvinium pamoate in the form of coated tablets will be useful with older children and adults who would otherwise need to take unpleasantly large quantities of the drug in a suspension. Six infected adults who were treated with coated tablets of pyrvinium pamoate during the present study became negative and had no gastrointestinal symptoms. A single dose schedule of treatment with pyrvinium pamoate is most convenient, but, as with drugs used in the past, the possibility of reinfection from the home environment shouId be kept in mind. Until this problem is resolved, it is suggested that a dose of pyrvinium pamoate administered 2 or 3 times at biweekly intervals may offer a partial solution. SUMMARY
Pyrvinium pamoate suspension in a dosage of 5 mg. per kilogram was administered to children from a group of families in a university housing project. The results show that a single dose was highly effective initially in controlling infection, but reinfection occurred commonly. Doses repeated at 3
Volume 60 Number 2
Pyrvinium pamoate and pinworm in[ection
week intervals p a r t i a l l y solved the p r o b l e m of r e c u r r e n t infection. T h e d a t a f r o m this study do not justify the use of p y r v i n i u m p a m o a t e p r o p h y l a c t i c a l l y in noninfected children. Factors i m p o r t a n t in reinfection within the family e n v i r o n m e n t are discussed, a n d a dose of 5 mg. p e r k i l o g r a m of b o d y weight a d m i n i s t e r e d 3 times at biweekly intervaIs is suggested.
4.
5.
6. We are indebted to Dr. David G. Hays for statistical advice and to Drs. Janice T. Kayahara, George S. Smith, Rudolph E. Erickson, and Charles H. Schiro for their technical assistance and their help in the collection and distribution of materials. REFERENCES
1. Sawitz, W. G., D'Antoni, J. S., Rhude, K., and Lob, S." Studies on the Epidemiology of Oxyuriasis, South. M. J. 33: 913, 1940. 2. Schiiffner, W., and Swellengrebel, N. I-I.: Retrofection in Oxyuriasis. A Newly Discovered Mode of Infection With Enterobius vermicularis, J. Parasitol. 35: 138, 1949. 3. Beck, J. W., Saavedra, D., Antell, G. J., and
7.
8.
9.
10.
25 1
Tejeiro, B.: The Treatment of Pinworm Infections in Humans (Enterobiasis) With Pyrvinium Pamoate, Am. J. Trop. Med. 8: 349, 1959. Bumbalo, T. S., Plummet, L. J., and Warner, J. R.: A Clinical Evaluation of Four Oxyuricides, A. M. A. J. Dis. Child. 99: 617, 1960. Sanders, A. I., and Hall, W. I-Ix Comparison of Dithiazanine Iodide and Pyrvinium Pamoate in the Treatment of Enterobiasis (Pinworms), J. Lab. & Clin. Med. 56: 413, 1960. Beaver, P. C.: Methods of Pinworm Diagnosis, Am. J. Trop. Med. 29: 577, 1949. Jung, R. C., and Beaver, P. C.: Treatment of Enterobiasls (Pinworm Infestation) With Diphenan, Egressin and Gentian Violet, Pediatrics 11: 611, 1953. Jones, M. F., and Jacobs, L.: Studies on Oxyuriasis. XXIII. The Survival of Eggs of Enterobius vermicularis Under Known Conditions of Temperature and Humidity, Am. J. Hyg. 33: 88, 1941. Lentze, F. A.: Ueber die Verbreitung von Spul- und Madenwilrmern und fiber die Massnahmen zur ihrer Bek~impfung vom Standpunkte der 6ffentlichen Gesundheitspflege, VeriSffentl. a. d. Geb. d. Med.Verwalt. 37: 51, 1932. Cram, E. B.: Studies on Oxyuriasis. XXVIII. Summary and Conclusions, Am. J. Dis. Child. 65: 46, 1943.