R e v i s ta d a S o c ie d a d e B r a s i l e i r a d e M e d i c in a T r o p ic a l 2 4 ( 4 ) : 2 1 7 - 2 2 1 , o u t- d e z , 1 9 9 1
ASCARIS L UMBR1C01DES
: R E IN F E C T IO N I N C H IL D R E NB E A R IN G A N E S T A B L IS H E D W O R M B U R D E N
F a u s to E . L im a P e r e ir a , A n d r e a P . S a m p a io , C a r lo s M u sso a n d J a n e S . C a ste lo .
T o c la r ify th e e x is ta n c e o f r e in fe c tio n in c h ild r e n b e a r in g a n e s ta b lis h e d A s c a r i s lu m b r ic o id e s in fe c ti o n , th e a u th o r s e v a lu a te d th e w e ig h t a n d th e le n g th o f w o r m s c o l le c te d f r o m te n c a s e s o f a s c a r id ia s is . T h e w o r m b u r d e n w a s g r e a te r th a n 2 7 w o r m s in n in e c a s e s . In s e v e n c a s e s th e w e ig h t a n d th e le n g th o f w o r m s s h o w e d little v a r ia tio n , w ith u n im o d a l d is tr ib u tio n o f v a lu e s , s u g g e s tin g th a t a ll th e w o r m s in e a c h c a s e b e lo n g to th e s a m e p o p u l a ti o n , o r ig in a te d f r o m a s in g l e b r o o d in fe c tio n o r f r o m s u c c e s s iv e in fe c ti o n s o v e r s m a ll tim e in te r v a ls . In th r e e c a s e s th e r e w a s g r e a t v a r ia tio n in w o r m s iz e in d ic a te d b y th e d iffe r e n t v a lu e s f o r th e m e a n s a n d m e d i a n s a n d b y th e h ig h v a lu e s f o r th e s ta n d a r d d e v ia ti o n a n d c o e ffic ie n t o f v a r ia tio n . In t h e s e th r e e c a s e s th e r e w a s a b im o d a l d is tr ib u tio n o f w o r m 's s iz e s u g g e s tin g th e c o e x is ta n c e o f tw o d is tin c t p o p u l a ti o n s : o n e , le s s n u m e r o u s , c o m p o s e d o f m a tu r e w o r m s a n d th e o th e r , m o r e n u m e r o u s , c o m p o s e d o fi m m a tu r e w o r m s , in tw o c a s e s , a n d tw o d is tin c tp o p u la tio n s o f im m a tu r e w o r m s in o n e c a s e . T h e e x is ta n c e o f w o r m s in d iffe r e n t s ta g e s o f m a tu r a tio n in d ic a te s t h a t th e le s s m a tu r e p o p u l a ti o n was a c q u ir e d w h e n th e m a tu r e w o r m s w e r e e s ta b lis h e d in th e g u t. T h e s e r e s u lts in d ic a te th a t th e r e in fe c tio n w ith A s c a r i s in c h ild r e n b e a r in g a n e s ta b lis h e d in fe c ti o n is n o t r a r e a n d r e s is ta n c e in d u c e d b y a p r e e x is tin g in fe c tio n is n o t th e r u le .
K e y - w o r d s : Ascaris lumbricoides. A s c a r ia s is .
Previous reports evaluating the size of
Ascaris
lumbricoides worms expelied after treatment or
collected at autopsy have demonstrated that the size distribution (weight and length) is unimodal in each patient26. This observation suggested the predominance o f a single brood infection or successive infections over small time intervals in human ascariasis. It has been hypothesized that successful development of Ascaris within the host occurs only in the absence of an established infection in the small intestine. The protective effect of an extant worm population against subsequent invaders has been confirmed in experimental infection withAscaridia galli in chickens4 and acquired resistance
against Ascaris larvae has been demonstrated in experimental infections in mice5. Studies of chemotherapeutic elimination of established humanAscaris lumbricolides infection in endemic areas
Departamento de Patologia do Centro Biomédico, Universidade Federal do Espírito Santo e Serviço de Patologia do Hospital Infantil Nossa Senhora da Glória, Vitória, ES.
E n dereço p a r a correspondência: Dr. Fausto E. Lima Pereira. Dept° de Patologia/CBM/UFES. Caixa Postal 780, 29000 Vitória ES.
Recebido para publicação em 02/08/91.
have shown that the clearance o f worms is followed rapidly by reinfection, indicating a loss of reistance against reinfection after elimination of a pre-existing worm burden3.
Recently Baird et al1 reported a fatal Ascaris infection in a child with a massive worm burden composed of two populations: a small number of heavy worms (male and female) and a large number o f lighter worms (male and female). The authors suggested that the heavier worms represented an older pre-existing population, while the smaller, m ore num erous w orm s w ith um im odal size distribution, represented a younger population acquired as a single brood infection. According to the authors, this was the first report o f superimposed Ascaris reinfection in man.
To clarify the existance o f reinfection in children bearing an established
Ascaris lumbricoides infection,
we studied the weight and length of worms colected at autopsy (nine cases) or after surgery (one case) from children with Ascaris infection. The worm burden was greater than 27 worms in nine o f ten cases. Two distinct populations were observed in three cases, indicating that reinfection with AscarisP e r e i r a F E L , S a m p a i o A P , M u s s o C , C a s te lo J S . Ascaris lum bricoides; r e i n f e c t i o n in c h i ld r e n b e a r in g a n e s t a b l i s h e d w o r m b u r d e n . R e v i s ta d a S o c ie d a d e B r a s i l e ir a d e M e d i c in a T r o p ic a l 2 4 : 2 1 7 - 2 2 1 , o u t- d e z , 1 9 9 1
occurs more frequently than previously suspected. RESULTS
MATERIAL AND METHODS
Ascaris collected from nine autopsy and from one surgical case were rinsed in tap water and stored in 10% formalin. The worms were grouped by gender and individually weighed and measured. When necessary a dissecting microscope was used for identification o f males and females. The age and sex distribution o f the ten children are in Table 1.
For each case the mean, the median and the standard deviation were calculated for the weight and length of worms. The “z ” scores were calculated to indicate the largest worm which would be considered a member o f the same population with 99% confidence level (p < 0 .0 1 ). All the worms with “z” scores higher than 2.33 were grouped and compared with the others with “z” scores lower than 2.33. For comparison o f the means the Student “t ” test was used.
The results are shown in Tables 1, 2 and 3 in Figures 1 and 2. Analysis of the distribution of the weight and length (Tables 1 and 2) identified seven cases in which the mean and the median were similar, and in which the standard deviation and the coefficient of variation (Table 3) indicated a relatively small dispersion o f values around the mean. However in four of these seven cases, one or two worms were found with “z” scores above 2.33 (Table 3). The Figure 1 shows clearly the unimodal distribution of w orm 's size in those cases.
In case 10, as showed in Tables 1, 2 and 3, the standard deviation and coefficient o f variation were great but there were not worms with “z” scores above 2 .3 3 . H ow ever th e bim odal distribution of w o rm 's size (Figure 2) showed clearly the existance o f two distinct populations. The stu d en t's “t ” test showed a significant difference between the means o f worm size of these two distinct populations.
Table 1
-Weight (g) of worms colected from children with ascariasis.
Case Age Sex N of worms Mean s Median Range
1 6 m m 51 0.55 0.19 0.54 0.19 - 1.02
f 90 1.34 0.53 1.35 0.23 - 2.93
2 3 f m 32 0.65 0.18 0.64 0.35 - 1.48
f 41 1.71 0.32 1.78 0.92 - 2.56
3 5 f m 82 0.90 0.14 0.90 0.76 - 1.21
f 65 2.76 0.52 ■ 2.80 1.50 - 4.50
4 2 f m 22 0.97 0.17 0.99 0.70 - 1.31
f 22 2.37 0.42 2.53 0.58 - 3.22
5 2 f m 13 0.35 0.11 0.35 0.20 - 0.66
f 14 0.74 0.53 0.71 0.25 - 2.15
6 7 f m 4 1.20 0.14 1.12 1.12 - 1.42
f 4 3.73 0.09 3.73 3.65 - 3.82
7 11 m m 19 1.57 0.23 1.55 1.25 - 2.12
f 13 4.21 0.35 4.12 3.42 - 4.88
8 4 m m 126 0.27 0.23 0.20 0.05 - 1.33
f 229 0.47 0.74 0.30 0.07 - 5.34
9 2 f m 11 0.13 0.12 0.08 0.01 - 0.46
f 32 0.29 0.44 0.07 0.01 - 1.55
10 5 m m 24 0.65 0.54 0.37 0.17 - 1.72
f 32 2.73 1.62 3.47 0.32 - 5.28
Pe r e i r a F E L , S a m p a i o A P , M u s s o C , C a s t e l o J S . As c a r is lu m b r ic o id e s ; r e i n f e c t i o n in c h i l d r e n b e a r i n g a n e s t a b l i s h e d w o r m b u r d e n . R e v i s t a d a S o c i e d a d e B r a s i l e i r a d e M e d i c i n a T r o p i c a l 2 4 : 2 1 7 - 2 2 1 , o u t - d e z , 1 9 9 1
P e r e i r a F E L , S a m p a i o A P , M u s s o C , C a s te lo J S . Ascaris lum bricoides; r e i n f e c t i o n in c h i l d r e n b e a r in g an e s t a b l i s h e d w o r m b u r d e n . R e v i s t a d a S o c ie d a d e B r a s i l e ir a d e M e d i c in a T r o p ic a l 2 4 : 2 1 7 - 2 2 1 , o u t- d e z , 1 9 9 1
Table
2 - Size of worms (cm) collected from children with ascariasis.
Case N o f worms Mean s Median Range
1 m 51 11.6 1.64 12.0 7.5 - 15.5
f 90 16.8 3.05 17.5 7 .0 - 22.5
2 m 32 12.0 1.30 12.0 9.5 - 17.0
f 41 18.9 1.59 19.0 15.0 - 22.0
3 m 82 13.6 1.07 14.0 12.0 - 16.5
f 65 21.9 2.07 22.0 18.0 - 29.5
4 m 22 14.8 1.38 14.5 12.5 - 17.2
f 22 21.8 1.77 21.7 17.0 - 24.0
5 m 13 8.9 1.04 8.8 7.0 - 10.5
f 14 12.5 2.77 12.8 8.3 - 18.5
6 m 4 14.3 2.42 16.2 13.0 - 17.5
f 4 24.5 1.91 23.0 23.0 - 27.0
7 m 19 15.5 1.48 15.5 12.5 - 18.3
f 13 24.0 2.08 24.0 21.9 - 29.0
. 8 m 126 7.9 2.10 8.0 5.5 - 15.5
f 229 10.7 3.03 10.5 6.0 - 28.0
9 m 11 6.5 2.06 6.2 3.5 - 10.5
f 32 7.7 4.61 6.7 3.0 - 18.5
10 TO 24 10.5 2.66 9.5 7.5 - 15.5
f 32 19.5 4.36 20.0 10.6 - 26.0
m = male f = female
DISCUSION
Our results showed that in seven of ten cases of ascariasis in children there was a regular distribution o f worm ’s size. In these cases the variation in size observed was similar to that reported by Jung2 and by Takata et al6 although these authors provided the range o f values and not the standard deviation. Thus in six cases, our observations are in agreement with the concept of a single brood infection in human ascariasis. Althoug we observed in four cases at least one worm with “z” score greaterthan2.33, we believe that these worms are the remnant o f a prev io u s in fection w hich declined through senescenceor, perhaps, in the faceofanew infection. In these four cases it is possible that the apparent reinfection occurred at the end of the life-span of a pre-existing worm burden.
In two cases (cases 8 and 9) the great variation in w o rm 's size indicated by the high value of coefficient o f variation and the great number of
worms with “z” scores above2.33 show clearly the coexistence of two distinct w orm 's populations: one composed of numerous small imature worms and the other of large mature worms in case 8 and composed of two populations o f imature worms in case 9.
In case 10 the standard deviation and coefficient o f variation were great but there were not worms with “z” scores above 2.33: the existance o f two distinct populations was clearly demonstrated by the bimodal distribution o f the values for the weigth and the length. In this case the two populations were composed of imature and mature worms.
P e r e i r a F E L , S a m p a i o A P , M u s s o C , C a s te lo J S . Ascaris lum bricoides; r e i n f e c t i o n in c h i ld r e n b e a r i n g a n e s t a b l i s h e d w o r m b u r d e n . R e v i s ta d a S o c ie d a d e B r a s i l e ir a d e M e d i c in a T r o p ic a l 2 4 : 2 1 7 - 2 2 1 , o u t- d e z , 1 9 9 1
Table 3 -
Coefficient of variation for length and
weigth of worms and number of worms
and number or worms with "z" scores
above
2.33 in ten cases ofascariasis in
children
Case
Length Weight
CV (% ) z > 2.33 C V (% ) z > 2.33
1 m 14 0 36 0
f 18 1 40 1
2 m 10 0 28 1
f 8 0 19 1
3 m 7 1 16 0
f 9 0 19 1
4 m 9 0 19 0
f 8 0 18 0
5 m 11 0 33 1
f 22 0 71 1
6 m 16 0 11 0
f 7 0 3 0
7 m 9 0 14 0
f 9 0 8 0
g m 26 7 90 7
f 31 9 158 10
9 m 31 1 91 1
f 59 7 147 7
10 m 18 0 83 0
f 22 0 56 0
CV = coefficient o f variation
undem utrion in two o f three children with reinfection. It remains possible that other factors are responsible for this phenomenon. In conclusion our results demonstrate that reinfection in ascariasis is not rare, and that the resistance observed with a pre-existing worm burden is not invariable.
RESUMO
P a r a t e n t a r e s c l a r e c e r a e x i s tê n c ia d e r e i n f e c ç ã o e m c r i a n ç a s p o r t a d o r a s d e a s c a r i d í a s e j á e s t a b e le c id a , f o r a m a v a l i a d o s o p e s o e o c o m p r i m e n t o d o s v e r m e s c o l h i d o s e m l O c a s o s d e a s c a r i d í a s e , e m n o v e d o s q u a is a c a r g a p a r a s i t á r i a f o i m a i o r d o q u e 2 7 v e r m e s . E m s e t e c a s o s o p e s o e o c o m p r i m e n t o d o s v e r m e s a p r e s e n t a r a m p o u c a v a r i a ç ã o , c o m d i s t r i b u i ç ã o u n im o d a l d o s v a l o r e s , s u g e r i n d o a s s i m p e r t e n c e r e m t o d o s a u m a m e s m a p o p u l a ç ã o o r ig i n a d a d e u m a ú n ic a
in f e c ç ã o o u d e i n f e c ç õ e s r e p e t id a s c o m i n t e r v a l o s m u ito c u r to s . E m t r ê s c a s o s , o p e s o e o c o m p r i m e n t o d o s v e r m e s m o s tr a r a m g r a n d e v a r ia ç ã o , in d i c a d a p e l o s v a l o r e s d if e r e n t e s p a r a a s m é d i a s e a s m e d i a n a s e d o s a lto s v a lo r e s d o s d e s v i o s p a d r ã o e d o s c o e fic ie n te s d e v a r ia ç ã o . N e s s e s c a s o s , a d i s t r ib u i ç ã o d o s v a l o r e s p a r a o c o m p r im e n to e p a r a o p e s o f o i b im o d a l, s u g e r in d o a c o e x is tê n c ia d e d u a s p o p u l a ç õ e s d if e r e n t e s d e v e r m e s : u m a , m e n o s n ú m e r o s a , c o m p o s ta d e v e r m e s j á m a d u r o s e o u tr a , m a is n u m e r o s a c o m p o s t a d e v e r m e s im a tu r o s e m d o is c a s o s e d u a s p o p u l a ç õ e s d e v e r m e s im a t u r o s e m u m c a s o . A p r e s e n ç a d e p o p u l a ç õ e s d is t i n t a s d e v e r m e s , c o m d i f e r e n t e s g r a u s d e m a tu r i d a d e , i n d i c a q u e a p o p u l a ç ã o m a is im a t u r a f o i a d q u i r id a q u a n d o a p o p u l a ç ã o m a is d e s e n v o l v i d a j á e s t a v a e s t a b e l e c i d a n o in te s tin o . E s s e s r e s u lta d o s d e m o n s tr a m q u e a r e in fe c ç ã o c o m A s c a r i s e m c r i a n ç a s p o r t a d o r a s d e a s c a r i d í a s e e s t a b e l e c i d a n ã o é r a r a e q u e a r e s is t ê n c i a in d u z i d a p o r u m a in f e c ç ã o p r é - e x i s t e n t e n ã o é u m f a t o in v a r iá v e l.
P a la v r a s - c h a v e s : Ascaris lumbricoides. A s c a r ía s e .
REFERENCES
1. Baird JK, Mistrey M, Pimsler M , Connor DH. Fatal human ascariasis following secondary massive infection. The American Journal of Tropical Medicine and Hygiene 35:314-318,
1988.
2. Jung RC. The predominance o f single brood infection in human ascariasis. Journal of Parasitology 48:405-407, 1984.
3. Otto GF.
Ascaris lumbricoides
: treatment and loss of worms and reinfection. Journal of American Medical Association 95:194-195, 1930.4. Sadun EH. Resistance induced in chickens by infection with the nematode Ascaridia galli. The American Journal o f Hygiene 47:282-289,
1948.
5. Sprent JFA, Chen HH. Immunological studies in mice infected w ith larvae o f Ascaris lumbricoides.
