INTRODUCTION

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Helminthic parasites provide particularly potent stimuli for the synthesis of IgE antibody (1), and the existence of allergic-type reactivity to these organisms is well recognized (2). In addition, immediate hypersensitivity skin-test reactions to extracts of these parasites are very common in situations in which such infections are endemic (3). For a number of years, however, controversy has surrounded both the possible involvement of helminthic infection in the pathogenesis of respiratory disease (4) and its influence on the prevalence of allergic conditions in the tropical environment (3, 7). This may be at least partly due to the ability of these parasites to also cause an interleukin-4 (IL-4)-dependent polyclonal stimulation of IgE synthesis (8, 9). Helminthic infections of low intensity can nonspecifically potentiate the synthesis of IgE antibody against environmental allergens, and thus enhance allergic reactivity (10). In contrast, the excess polyclonal IgE stimulated by more intense helminthic infection can suppress the allergic response by producing mast-cell saturation (14) and inhibition of specific IgE antibody synthesis (3, 7). In previous studies, we have demonstrated a direct relation between helminthic infection and pulmonary function. Thus, bronchial challenge with helminth extracts can induce bronchoconstriction in clinically asthmatic children in areas in which helminthic infection is endemic (15). Also, nonasthmatic children in such areas can respond significantly to bronchodilator inhalation, and this response can be reversed by anthelminthic treatment (16). Moreover, parasite eradication can produce a reactivation of allergic reactivity toward common environmental allergens in children in whom this is suppressed by excessively polyclonal IgE (17).

Considering the complexity of the possible influence of helminthic infection on allergic reactivity, we evaluated in the present study the effect of regular and prolonged anthelminthic treatment on a group of clinically asthmatic patients in a tropical environment in which these parasites are endemic. As the intensity of infection in this group was low to moderate, we hypothesized that such treatment would improve the patients' clinical condition either: (1) by removing the specific allergic stimulus exerted by the parasites at the level of the lung; (2) by decreasing the potentiating effect that helminthic infection might have on the synthesis of IgE antibody against common environmental allergens, such as house-dust mite; or (3) both.

	METHODS

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Asthmatic Patients

The study was performed on a total of 89 asthmatic patients (age: 18.5  ± 14.6 yr [mean ± SD]; 48% male and 52% female), who for a number of years had attended the asthma clinic established by the Fund for the Development of the State of Nueva Esparta (FONDENE) on Coche Island, Venezuela. The patients were all of very low socioeconomic level, being classified as in a condition of "critical poverty" according to the scale in official use in Venezuela (18). Because the clinic belongs to the only medical facility on the island, and provides treatment free of charge, the patients do not seek attention elsewhere. The only criteria applied in the selection of these patients was that they had active asthma, were experienced in the performance of pulmonary function tests, and agreed to participate in the full study program. At the outset of the study, 100 patients were selected, 50 of whom were randomly assigned to the treatment group and 50 to the untreated control group. Of the former, 10 were excluded from the final analysis because of noncompliance with the treatment protocol. In one treated patient, two mild asthmatic episodes closely followed albendazol administration. Although it was uncertain whether this occurred by chance, or was due to the anthelminthic agent, this patient was also withdrawn from the study.

Ethical Considerations

The study protocol was approved by the ethical committee of the Institute of Biomedicine of the Central University of Venezuela and the administrative medical staff of the Coche Island medical dispensary Venezuelan Ministry of Health and Social Assistance, to which the asthma clinic is attached. It was also ratified by the National Council for Scientific and Technological Investigation (CONICIT) of Venezuela. The investigative procedures applied were part of the routine evaluation and follow-up program of the asthma clinic, which up to the time of the study did not include rigorous control of parasitic infection in its patients. In this respect, the control group was not deprived of the right to receive anthelminthic treatment, but rather this was formally implemented in the treated group on a regular basis. Because of the low socioeconomic level and correspondingly limited medical awareness of the patients, the administration of a placebo to the control group was not considered acceptable by the members of the community. Instead, we received ethical permission to inform the treated group of our objective of controlling their helminthic infections without specifically explaining to them the hypothesis of the study that their asthma would also improve with such control.

Anthelminthic Treatment

Albendazol (400 mg) was administered monthly for a period of 1 yr to the treated group. Since the patients were in a situation of endemic helminthiasis, treatment was administered irrespective of the results of the initial fecal examination, and the anthelminthic agent was administered regularly to ensure that reinfection did not occur during the study period. The treatment was personally administered by social workers of the medical dispensary, and any patient who missed two successive doses was withdrawn from the study. The year of treatment was considered as Year 1 of the study, and the subsequent 2 yr, when the anthelminthic agent was not administered, were designated Years 2 and 3. Because of the degree of poverty of the patients, the level of autoadministration of anthelminthic agents is minimal, and we found no evidence of this occurring in the control group.

Management of Asthma

The strategy for asthma management employed in the asthma clinic is maintenance inhalation of beclomethasone (100 µg twice daily), complemented with inhaled salbutamol (200 µg as needed) when significant symptoms (cough, dyspnea, wheezing) occur. If this treatment was not sufficient to control asthmatic episodes in the patients in the study, they were treated as outpatients in the asthma clinic, receiving intravenous methylprednisolone (1.5 mg/kg) and nebulized fenoterol (250 µg) and ipratropium bromide (125 µg). If asthmatic crises occurred more than twice monthly, the beclomethasone used for maintenance treatment was changed to inhaled budesonide (200 µg twice daily). When a patient was symptom-free for a period of 3 mo, the maintenance treatment was suspended, and was resumed if symptoms reappeared. Because of the cost of the asthma medication, the asthma clinic was the only source of treatment available to the patients, and we were therefore able to accurately monitor the consumption of these drugs over the year prior to the commencement of the treatment period (designated Year 0), and for Years 1 to 3 of the study. We should note here that the day-to-day clinical management of the patients was the responsibility of short-term interns who staffed the medical dispensary, and who were not aware of the objective of the study. They were, however, informed that the patients were receiving albendazol.

Evaluation of Pulmonary Function

As part of the routine clinical management of patients by the asthma clinic, tests of pulmonary function are regularly given by the resident chest physician (Dr. M. Palenque) to all patients in the control program, following the guidelines of the American Thoracic Society (ATS) (19). For the purpose of our study, pulmonary function was measured immediately prior to the beginning of the study (Year 0) and again at the end of Year 1, using a Respiradyne II solid-state spirometer (Sherwood Medical, St. Louis, MO). The values of FVC, FEV₁, peak expiratory flow rate (PEFR), and maximum midexpiratory flow (MMEF) rate were calculated. Because many of the patients were children, the absolute spirometric values at the beginning and end of the study period could not be directly compared. For this reason, they were expressed as percentages of the values predicted according to the height and sex of the patients, using normal values determined for a group of Spanish subjects (20), or as the FEV₁/FVC ratio, also expressed as a percentage. Prior to the study, the bronchial hyperreactivity (BHR) of the patients was confirmed by bronchial provocation with histamine (21), in which 1 ml of histamine base (as dihydrochloride; Sigma Chemical Co., St. Louis, MO) was nebulized in stepwise concentrations from 0.0081 mg/ml to 5.0 mg/ml. Changes in FEV₁ of  20% (PC₂₀) at a histamine concentration  2.5 mg/ml were considered to indicate a state of BHR. This test was repeated at the end of Year 1. All asthma medication was suspended on the day before the testing of pulmonary function. We should point out here that this aspect of the evaluation was not performed in a blind manner, since the chest physician was aware of the objectives of the study.

In a group of 10 asthmatic patients of higher socioeconomic level on a neighboring island (Margarita Island), and in whom helminthic infection was not endemic, pulmonary function tests were performed before and then again at 1 and 24 h after the administration of albendazol, to determine whether this affected their pulmonary function. Although the data for this group are not presented here, we found that this treatment had no bronchodilator effect.

Parasitologic Examination

Three serial fecal samples were collected into preservative solution (40% tincture of merthiolate, 5% formaldehyde, 1% glycerol) and examined microscopically. These tests were performed at the beginning of the study and at regular intervals during the treatment period. Fecal egg counts were not performed on the study group, but in work that is not reported here, we have found that the whole population from which the patients were drawn has a point-prevalence of 40 to 50% for intestinal helminths, and that the intensities of infection are from light to moderate. For example, the median egg count per gram of feces in infected individuals was 1,540 for Ascaris lumbricoides.

Immunologic Evaluation

Skin-prick tests for immediate hypersensitivity were performed with extracts of Dermatophagoides pteronyssinus and A. lumbricoides, and as a positive control, with 1% (wt/vol) histamine. Wheal diameters of  3 mm were considered positive. Total IgE levels were measured with the Phadebas radioimmunosorbent test (PRIST) (Pharmacia, Uppsala, Sweden), and expressed as IU/ml. Levels of IgE for the foregoing allergens were measured with the Phadebas radioallergosorbent (RAST) test, and expressed as Phadebas RAST units/ml (PRU/ml). As suggested by the manufacturers of the test, values  0.7 PRU/ml (RAST Level 2) were considered positive.

Statistical Analysis

Owing to a high degree of dispersion of the values of most of the continuous variables measured, nonparametric statistical tests (one-way analysis of variance [ANOVA], Wilcoxon's test) were applied, using the InStat program of Graphpad Software (San Diego, CA). For convenience of presentation, the means ± SEM are shown in the tables. Frequency analyses of discrete variables were performed with the chi-square test.

	RESULTS

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Parasitologic Evaluation

At the beginning of the study, 41% of the entire group of patients were found to be infected with helminths. The predominant parasites were Trichuris trichiura (26%) and Ascaris lumbricoides (23%). Infections were detected at some time in six of the anthelminth-treated patients during Year 1 of the study.

Clinical Status

Owing to the low level of literacy and medical awareness of the study group, we chose three criteria, that depended directly or indirectly on the asthma clinic, to estimate the clinical status of the patients. These were: (1) the number of months per year that maintenance therapy with beclomethasone was administered; (2) the number of metered-dose inhalers (MDI) of salbutamol that were used electively by the patients to control symptoms; and (3) the number of times the patients required attention in the asthma clinic for episodes that did not respond adequately to the ₂-agonist. The results of this analysis are presented in Table 1, where it can be seen that during the year of anthelminth treatment (Year 1), there were statistically significant decreases in the number of months of maintenance treatment (p < 0.01), the number of asthmatic crises (p < 0.001), and the number of MDIs used (p < 0.001) as compared with the year prior to the study (Year 0). In contrast, no significant changes were found in these parameters in the untreated control group. Of the 39 anthelminth-treated patients, 35 were followed for a further 2 yr (Years 2 and 3), during which time the anthelminth was not administered. Table 1 shows that the severity of the asthma continued to decline during Year 2, but that it reverted to the initial levels in Year 3. We should note here that the four patients who were lost to long-term follow-up were not remarkable in the severity of their asthma during Year 1. In Table 2 we present the frequency distribution of asthmatic crises in the 35 anthelminth-treated patients who were evaluated over the entire 4-yr period. It can be seen that before the anthelminth treatment (Year 0), the therapeutic regimen used by the asthma clinic resulted in the symptoms being well controlled in 60% of the patients, moderately controlled in 28%, and poorly controlled in 12%. For the year following the period of anthelminth administration (Year 2), these percentages were 80%, 17%, and 3%, respectively (p < 0.01).

Pulmonary Function

The pulmonary function of the anthelminth-treated and control groups was measured immediately prior to the beginning of the study (Year 0) and at the end of Year 1. The spirometric results were expressed as percentages of the predicted values, and in Table 3 it can be seen that no significant changes were detected in either group. The FEV₁/FVC ratios were also unchanged (mean ± SD of the treated group: 76 ± 8% in Year 0 and 80 ± 10% in Year 1). We should note here that patients who at the beginning of the study were positive for helminths in the fecal examination showed no significant differences in spirometric values from those who were negative (results not presented). Comparing the BHR to histamine before and after anthelminth treatment, the PC₂₀ values were increased in 38% of the patients, remained unchanged in 44%, and decreased in 18%. Of particular interest is the observation that after treatment five of the patients did not react to histamine concentrations as high as 2.5 mg/ml. In fact, these patients became crisis-free, and were able to stop taking maintenance beclomethasone for essentially the whole of Years 1 and 2. 

Immunologic Evaluation

As no clinical changes were found in the control group, total and specific IgE levels were measured only in the treated patients, before (Year 0) and after (Year 1) the period of anthelminth administration (Table 4). The total serum levels of IgE, which were initially elevated, decreased significantly (p < 0.001), and significant decreases also occurred in positivity to Dermatophagoides as reflected both by specific IgE antibody measured by RAST (p < 0.05) and skin-test results (p < 0.025). Such decreases did not, however, occur in specific IgE antibody levels or skin-test positivity to Ascaris. In fact, there was a tendency toward an increase in these measures. It is relevant to point out here that at the beginning of the study patients who were found to be positive for helminths in fecal testing showed no significant differences in these immune parameters from those who were negative (results not presented). In addition, in the initial evaluations, the spirometric results were comparable for patients who had negative skin-test results for both Dermatophagoides and Ascaris (26% of the group), those who had positive results for Dermatophagoides alone (28%) or Ascaris alone (31%), and those who had positive results for both Dermatophagoides and Ascaris (15%).

	DISCUSSION

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There exists considerable evidence that helminthic infection can either increase or decrease the allergic reactivity of infected populations (3, 6, 7). First, helminthic parasites can stimulate the production of large amounts of specific IgE antibody against their own antigens, which sensitizes the mast cells of the host (1). This, coupled with the fact that many of these parasites have lung-migratory phases, and that soluble parasite antigens circulate in the blood (22), suggests that such infections could affect pulmonary physiology (6, 7). Helminths also cause a polyclonal stimulation of IgE synthesis, which at low intensities of infection results in enhanced allergic reactivity toward environmental allergens (10). In contrast, heavy parasite loads provide such a strong polyclonal stimulus that the excess IgE blocks the allergic response (3, 7, 14). In view of these considerations, the effect of anthelminthic treatment on the allergic reactivity of endemic populations will depend, at least in part, on the initial intensity of the infection and the allergic condition of the subjects. In accord with the complexity of this situation is our demonstration in previous studies that the anthelminthic treatment of nonallergic children with a high degree of exposure to these parasites increased their allergic reactivity in immunologic terms (17), but decreased the degree of bronchoconstriction associated with the infection (16). For these reasons we evaluated the effect of sustained anthelminthic treatment on the clinical condition of asthmatic patients in an area in which intestinal helminths are endemic. The group that we chose to study belongs to the population of an island close to the coast of Venezuela, which has a high prevalence of asthma (23), and is served by a single medical facility that provides attention and treatment free of charge to a community that does not have the financial resources to obtain these services elsewhere. The prevalence of intestinal helminthiasis on the island is about 50%, and is of mild to moderate intensity. We should note here that although only 41% of our patients were found to be infected at the beginning of the study, this does not mean that the rest are not exposed to helminthic parasites, as the human and worm populations in the study area are in dynamic equilibrium situation. In fact, the present study found no significant differences in the immunologic parameters investigated in those patients who were positive and those who were negative for helminths in the initial fecal examination.

During the year of regular albendazol administration, the control of asthma in the treated patients was significantly better than that in both groups the previous year and that in the control group of untreated patients. This improvement was even more marked in the year following treatment, but by the second posttreatment year the clinical condition of the patients had deteriorated to its initial level. This accords with results that we obtained in another study on the island (unpublished data), which showed a relatively low level of reinfection during the first year after prolonged treatment, but significant reinfection toward the second year. These results indicate that the beneficial effect of albendazol is related to its anthelminthic activity, and not to a direct effect of the drug on the respiratory system. Although we were not permitted to use a placebo-control in our study, neither the patients nor the medical staff directly involved in their routine clinical management were aware of the hypothesis of the study that anthelminth treatment would improve the patients' asthmatic condition. Moreover the criteria used for characterizing the clinical state of the patients were selected for the maximum possible objectivity in a study of this nature. Possibly because at the beginning of the study the pulmonary function of the patients, as determined by spirometry, was not profoundly abnormal, the clinical improvement of the treated group was not accompanied by evident changes in measurements of pulmonary function. In this respect, other studies have also shown that asthmatic patients in remission do not necessarily have normal spirometric values (24). Of possible relevance here is a tendency that we observed in the treated group toward a lower pulmonary sensitivity to histamine challenge, which is an indicator of BHR. As can occur in viral infection (25), the presence of helminth-derived products, either in the blood or occurring during larval migration, may produce inflammation and thus increase airway irritability (26, 27). Another factor to be considered is that the tables of predicted values for spirometric parameters commonly used in Venezuela, which are based on a Spanish sample group (20), may not have been the most suitable for our study population. Because "normal" values have not been determined for persons of low socioeconomic level in developing countries, where concurrent infections and nutritional problems could be important variables, we are unable to make firm statements on this point.

From the immunologic viewpoint, because the intensity of helminthic infection in our study population is relatively low, we can predict that these parasites would cause both significant increases in total IgE levels and a potentiation of the allergic response to environmental allergens. The effects of the anthelminthic treatment in our study indicated that this is indeed the case, as the total serum IgE levels, which at the beginning of the study were moderately elevated, decreased significantly, as did the allergic reactivity to Dermatophagoides, one of the predominant allergens in the tropical environment. Further studies will, however, be required to determine the degree to which this change contributed to the clinical improvement of the treated patients. Of interest is our observation that the specific response to Ascaris, one of the most common intestinal helminths on the island on which our study was conducted, was maintained during the year of anthelminth administration. This probably occurred because: (1) the patients received continual immunologic stimuli in the intestine through the ingestion of infective eggs; and (2) because the specific response to parasite antigens is relatively independent of the polyclonal stimulus, particularly in persons with an atopic disposition (unpublished observations). In fact, as the IgE response can participate in protective mechanisms against helminthic infection (6, 28, 29), it can be proposed that the allergic genotype has been conserved in evolution because of the more effective antiparasitic IgE response that it confers.

In conclusion, the results of this study are consistent with the possibility that helminthic infection can contribute to the symptomatology of asthma in an endemic situation, and that this could occur both through a direct effect of the parasite and through the nonspecific potentiation of allergic reactivity toward environmental allergens.