Seroprevalence of Toxocara antibodies in patients with adult asthma.

Abstract: Toxocariasis is a common worldwide infection. Asthma, considered to be one of the most common chronic diseases, is a serious global health problem. Toxocara may be a possible etiologic agent of asthma. The aim of this study was to investigate whether there is an association between adult asthma and Toxocara seroprevalence. Fifty three adult patients with asthma participated in the study. All patients had an age of disease onset of 20 years or older. Blood samples were tested for the presence of Toxocara antibodies using enzyme-linked immunosorbent assay (ELISA).

We found a 13.2% Toxocara seropositivity for asthma. There was a significant difference in the Toxocara seropositivity between adult asthma patients and our healthy cohort populations. There was no significant difference between Toxocara seropositive asthma and Toxocara seronegative asthma in terms of the risk factors for Toxocara infection.

We believe that further research with a large number of asthma patients is warranted and preventive strategies in this patient population are needed.

Key Words: Toxocara, adult asthma, Turkey

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Toxocariasis, a common infection worldwide, is caused by Toxocara canis and Toxocara cati which are common animal nematodes in dogs and cats. Humans acquire the infection by oral ingestion of the Toxocara eggs through contact with larvae contaminating the teats of bitches or by the consumption of a raw or inadequately cooked paratenic host. Infectious Toxocara eggs are ingested and then hatched in the intestines. Larvae migrate through the blood to the liver, lungs, and other organs. As the larvae do not mature during this migration, diagnosis of Toxocara infection is mainly based on antigen-based enzyme-linked immunosorbent assay (ELISA). Toxocariasis in humans causes at least three syndromes: visceral larva migrans, ocular larva migrans, and covert toxocariasis. In addition, toxocariasis may present in several forms, ie, myocarditis, nephritis, idiopathic seizure disorders, prurigo and urticaria, involvement of the central nervous system, epilepsy, a form of eosinophilic arthritis and asthma as well as causes of functional intestinal disorders. (1,2)

Asthma is a serious global health problem and is one of the most common of the chronic diseases. Asthma poses a significant burden, not only in terms of health care costs but also in loss of productivity and reduced participation in family life. Over the last 30 years, asthma has increased worldwide, and its prevalence is up to 10% in adults. There are several risk factors for asthma. It has been suggested that Toxocara may be a possible etiologic agent of asthma. (3,4)

Although some studies have shown an association between toxocariasis and asthma, the role of Toxocara infection in the development of asthma is not well known. Therefore in this study, we investigated the seroprevalance of Toxocara antibodies in adult asthma.

Materials and Methods

Patients

Fifty three patients (12 male, 41 female) with stable asthma living in Eastern Turkey participated in the study. Sixteen of the patients had mild persistent asthma, 14 had moderate persistent asthma, and 23 had severe persistent asthma. Patients that were followed by the Firat University Medical Faculty, Department of Chest Diseases, and who had clinically definite asthma were enrolled. Informed consent was obtained from all of the volunteer participants following a thorough explanation of the nature of the study.

The questionnaire was self-administered and consisted of 16 questions. The questionnaire ascertained the patient's demographic data with regards to asthma, including risk factors, family history, exposure to smoking in the home, allergies to pets, risk factors for Toxocara infection such as ownership of dogs or cats, and history of contamination of sand or soil in playgrounds and sandboxes.

We compared the patient's results with our cohort consisting of 50 healthy subjects (25 male, 25 female) who were living in our urban area. (5)

Enzyme-linked Immunosorbent Assay (ELISA) for Toxocara

Four milliliters of venous blood were drawn under aseptic conditions from each patient. The blood was centrifuged at 3,000 rpm for 10 minutes, and the serum was separated and stored at -20[degrees]C until studied. Toxocara IgG or M antibodies were determined by enzyme-linked immunosorbent assay (ELISA) (Novum Diagnostica, Germany) according to manufacturer's instructions. Briefly, serum was diluted 1/100. Peroxidase-conjugated antibody was then added to react with the bound antibody. Chromogenic substrate for peroxidase was added and the reaction was stopped by stop solution. The intensity of the color was measured at 450 nm in an ELISA reader.

Statistical Analysis

Statistical analysis was performed using Statistical Package for Social Sciences (SPSS) software. [chi square] test was used to evaluate the data. A P < 0.05 was considered statistically significant.

Results

All patients with asthma were adult and of white race. Disease onset was at age 20 or older. The mean age of the patients with asthma was 46.3 [+ or -] 12.4 years (min-max: 24-75 years) with a mean disease duration of 10.7 [+ or -] 7.9 years (min-max: 1-30 years). Forty-one patients (77.4%) were female and 12 (22.6%) were male.

We found a 13.2% Toxocara seropositivity in adult asthma patients. There was a significant difference in Toxocara seropositivity between adult asthma patients and our healthy cohort population, [chi square] = 4.51, P < 0.05. (5) Two of 12 male (16.6%) and 5 of 41 female patients (12.1%) were Toxocara seropositive. Demographic data and seropositivity in patients and healthy controls is shown in Table 1.

There was no significant difference between Toxocara seropositive and Toxocara seronegative asthma cases in terms of sex, age, socioeconomic level, or living environment that increased the risk of Toxocara infection. Comparison of seronegative and seropositive cases for Toxocara infection is shown in Table 2.

When Toxocara seropositive and seronegative asthma cases were compared in terms of having asthmatic parents, allergies to pets, smoking, FEV1 and exposure to smoke in the home that increased the risk of asthma, there was no significant difference (Table 2).

Discussion

Toxocara canis is a common parasite and its frequency ranges between 2.6% and 47.5% in the adult urban population. (6) Toxocara seroprevalance had a broad range (2-45.9%) in our country which was considered to be related to different risk factors and within specific disease groups in which the studies were conducted (7-9)

Toxocariasis is related to the lungs as well as other organ systems. It presents as respiratory system symptoms, such as episodes of coughing and dyspnea, fever or persistent eosinophilia. In addition, the lungs are important in the life cycle of the Toxocara parasite. (1,2) Therefore Toxocara seroprevalance has been widely investigated in the etiology of asthma, especially childhood asthma, since children may be exposed to helminth infections on the playground, public field and school garden, and may have other risk factors, as well. (10-13) Due to changes in behavioral patterns, personal hygiene, socioeconomic levels, and climatic conditions, we consider that the association between Toxocara infection and asthma is important in adult asthma as well as childhood asthma. Therefore, the main aim of this study was to investigate whether an association between adult asthma and Toxocara seroprevalance exists or not. Our study showed that Toxocara seroprevalance in asthma patients was significantly higher than in a healthy urban population.

There are several demographical and epidemiologic risk factors affecting Toxocara seroprevalance; socioeconomic level, climatic conditions, dog and cat ownership, contact with soil contaminated by cat and/or dog stool, consuming contaminated food, and personal hygiene. (14-22) In this study, some risk factors for Toxocara infection were investigated. In a recent study, contamination of playgrounds by Toxocara spp. was found to be relatively lower than in other cities in our country. In addition, there is a proper climatic condition for life cycles of Toxocara parasite in this region. Although owning dogs and cats and contamination of soil or sand in playgrounds and public fields are risk factors, there was no significant difference for Toxocara infection between seronegative and seropositive patients with asthma in this study.

Risk factors for asthma may be classified as host factors and environmental factors. Environmental factors include air pollution, smoking, smoke exposure at home, diet, socioeconomic status, family size, and parasitic infections. There is an inverse relationship between asthma and family size; having no sibling or one sibling is associated with an increased risk of asthma compared with having more than one sibling. (4) In our study, the mean family size of patients with asthma was 4.50 [+ or -] 1.80. We showed that the mean family size of the seronegative patients with asthma was 4.36 [+ or -] 1.67, whereas the mean family size of seropositive patients with asthma was 5.42 [+ or -] 1.80. We did not find a significant difference for Toxocara infection between seronegative and seropositive patients as risk factors of asthma in terms of having asthmatic parents, allergies to pets, smoking, and exposure to smoke in the home.

It has been shown that the prevalence of adult asthma is higher in females than in males during puberty especially, and aspirin-induced asthma is more common in females. In our study, all patients with asthma were adult and most of the patients with asthma (77.4%) were female. This was not considered a limitation for the study since it has been shown that gender did not influence Toxocara seropositivity. (23)

Conclusion

Our study revealed higher seroprevalance for Toxocara in adult asthma patient populations as compared with a healthy urban population. Further research with a wide series of asthma patients is warranted.

References

1. Despommier D. Toxocariasis: clinical aspects, epidemiology, medical ecology, and molecular aspects. Clin Microbiol Rev 2003;16:265-272.

2. Garcia LS. Tissue Nematodes. Diagnostic Medical Parasitology. Washington, DC, ASM Press, 2001, pp 256-259.

3. Beyhun NE, Cilingiroglu N. Asthma and cost of illness. Tuberk Toraks 2004;52:386-392.

4. WHO/NHLBI Workshop Report: Global Strategy for Asthma Management and Prevention. Bethesda, MD, National Institutes of Health, National Health, Lung, and Blood Institute Publication No. 95-3659, 1995, pp 27-48.

5. Kaplan M, Bulut S, Godekmerdan A, et al. Toxocara canis seropositivity in epileptic patients. Acta Parasitologica Turcica 2002;4:415-417.

6. Gillespie SH. Toxocara and Toxocariasis. The Clinical Spectrum of Human Toxocariasis. In: Lewis JW, Maizels RM, eds. Birmingham, Birbeck and Sons Ltd, 1999, pp 55-61.

7. Kaplan M, Godekmerdan A, Kalkan A, et al. Toxocara canis seroprevalence in Elazig region. Firat University Journal of Health Sciences 1999;13:51-54.

8. Kaplan M, Kalkan A, Kuk S, et al. Toxocara seroprevalence in schizophrenic patients in Turkey. Yonsei Med J 2006.

9. Oguzturk H, Saygi G. Investigation of infection caused by larvae of Toxocara canis in elementary school students. Acta Parasitologica Turcica 2002;26:409-414.

10. Buijs J, Borsboom G, Renting M, et al. Relationship between allergic manifestations and Toxocara seropositivity: a cross-sectional study among elementary school children. Eur Respir J 1997;10:1467-1475.

11. Buijs J, Borsboom G, van Gemund JJ, et al. Toxocara seroprevalence in 5-year-old elementary schoolchildren: relation with allergic asthma. Am J Epidemiol 1994;140:839-847.

12. Chan PW, Anuar AK, Fong MY, et al. Toxocara seroprevalence and childhood asthma among Malaysian children. Pediatr Int 2001;43:350-353.

13. Sharghi N, Schantz PM, Caramico L, et al. Environmental exposure to Toxocara as a possible risk factor for asthma: a clinic-based case-control study. Clin Infect Dis 2001;32:111-116.

14. Ajayi OO, Duhlinska DD, Agwale SM, et al. Frequency of human toxocariasis in Jos, Plateau State, Nigeria. Mem Inst Oswaldo Cruz 2000;95:147-149.

15. Baboolal S, Rawlins SC. Seroprevalence of toxocariasis in schoolchildren in Trinidad. Trans R Soc Trop Med Hyg 2002;96:139-143.

16. Herrmann N, Glickman LT, Schantz PM, et al. Seroprevalence of zoo-notic toxocariasis in the United States: 1971-1973. Am J Epidemiol 1985;122:890-896.

17. Holland CV, O'Lorcain P, Taylor MR, et al. Seroepidemiology of toxocariasis in school children. Parasitology 1995;110:535-545.

18. Huminer D, Symon K, Groskopf I, et al. Seroepidemiologic study of toxocariasis and strongyloidiasis in institutionalized mentally retarded adults. Am J Trop Med Hyg 1992;46:278-281.

19. Matos M de F, Militao DN, Brum MA, et al. Presence of anti-Toxocara antibodies in children selected at Hospital Universitario, Campo Grande, MS, Brazil. Rev Ins Med Trop Sao Paulo 1997;39:49-50.

20. Overgaauw PA. Aspects of Toxocara epidemiology: human toxocariasis. Crit Rev Microbiol 1997;23:215-231.

21. Radman NE, Archelli SM, Fonrouge RD, et al. Human toxocariasis: its seroprevalence in the city of La Plata. Mem Inst Oswaldo Cruz 2000;95:281-285.

22. Sadjjadi SM, Khosravi M, Mehrabani D, et al. Seroprevalence of Toxocara infection in school children in Shiraz, Southern Iran. J Trop Pediatr 2000;46:327-330.

23. Fan CK, Hung CC, Du WY, et al. Seroepidemiology of Toxocara canis infection among mountain aboriginal schoolchildren living in contaminated districts in eastern Taiwan. Trop Med Int Health 2004;9:1312-1318.

Hold fast to dreams, for if dreams die, life is a broken winged bird
that cannot fly.
--Langston Hughes

Salih Kuk, MD, Eda Ozel, MD, Hakan Oguzturk, MD, Gamze Kirkil, MD, and Mustafa Kaplan, MD, PHD

From the Departments of Parasitology and Chest Diseases, Firat University, Faculty of Medicine, Elazig, Turkey, and the Emergency Departments, Cumhuriyet University, Faculty of Medicine, Sivas, Turkey.

Reprint requests to Dr. Salih Kuk, Firat University, Faculty of Medicine, Department of Parasitology, 23119, Elazig, Turkey. Email: [e-mail]

Accepted March 22, 2006.

RELATED ARTICLE: Key Points

* We believe that the association between Toxocara infection and asthma is important in adult asthma.

* Toxocara may be a possible etiologic agent of asthma.

* We found a 13.2% Toxocara seropositivity for asthma.

* There was a significant difference in Toxocara seropositivity between adult asthma patients and our healthy cohort populations.

Table 1. Demographic data and seropositivity in asthma patients and
healthy controls.

Parameters              Asthma                 Control

Sex (n) (M/F)           (53) (12/41)           (50) (25/25)
Age (mean [+ or -] SD)  (46.3 [+ or -] 12.4)   (31.2 [+ or -] 5.4)
  (min-max)               (24-75)              (20-50)
Disease duration        (10.7 [+ or -] 7.9)      -
  (mean [+ or -] SD)      (1-30)
  (min-max)
Family size              (4.50 [+ or -] 1.80)
  (mean [+ or -] SD)       (2-10)
  (min-max)
Toxocara seropositive    (7) (13.2)             (1)(2)
  (n) (%)
Toxocara seronegative   (46) (86.8)            (49)(98)
  (n) (%)

M, male; F, female, SD, standard deviation.

Table 2. Comparison of Toxocara seronegative (n = 46) and seropositive
cases (n = 7) for Toxocara infection

                                            Toxocara
                                Seronegative  Seropositive
Risk factors                    n   (%)       n  (%)        Total  P (a)

Sex                                                                NS
  Male                          10  (21.74)   2   (28.57)   12
  Female                        36  (78.26)   5   (71.43)   41
Age groups                                                         NS
  [less than or equal to] 35     8  (17.39)   3   (42.86)   11
  35-45                         17  (36.96)   1   (14.28)   18
  45-55                          9  (19.56)   1   (14.28)   10
  55-65                         10  (21.74)   1   (14.28)   11
  > 65                           2   (4.35)   1   (14.28)    3
Socioeconomic level                                                NS
  Low                            2   (4.35)   1   (14.29)    3
  Middle                        37  (80.43)   5   (71.42)   42
  High                           7  (15.22)   1   (14.29)    8
Living environment                                                 NS
  Urban                         40  (86.96)   5   (28.57)   45
  Rural                          6  (13.04)   2   (71.43)    8
Owning dogs and cats                                               NS
  Yes                            6  (13.04)   1   (14.28)    7
  No                            40  (86.96)   6   (85.72)   46
Duration of ownership                                              NS
  In the past one year           -    -       -     -        -
  Longer than a year             6  (13.04)   1   (14.29)    7
  None                          40  (86.96)   6   (85.71)   46
History of contamination        NS                                 NS
  in playgrounds
  0-3 times per month           15  (32.61)   0  (-)        15
  [greater than or equal to] 1  31  (67.39)   7  (100)      38
  times per week
Parent with asthma                                                 NS
  Yes                            8  (17.39)   2   (28.57)   10
  No                            38  (82.61)   5   (71.43)   43
Allergies to pets                                                  NS
  Yes                            9  (19.57)   4   (57.14)   13
  No                            37  (80.43)   3   (42.86)   40
Smoking                                                            NS
  Yes                           13  (28.26)   2   (28.57)   15
  No                            33  (71.74)   5   (71.43)   38
Exposure to smoke at home                                          NS
  Yes                           17  (36.96)   3   (42.86)   15
  No                            29  (63.04)   4   (57.14)   38
FEV1                                                               NS
  [less than or equal to] 60%   19  (41.30)   4   (57.14)   23
  60-80%                        12  (26.09)   2   (28.57)   14
  > 80%                         15  (32.61)   1   (14.29)   16

(a) [chi square] test, seropositive vs seronegative cases.
NS, not significant.