Prevalence of Toxocara canis antibody among children with bronchial asthma in Klang Hospital, Malaysia

TRANSACTIONS

OFTHE

( Short Report

ROYAL

SOCIETY

OFTROPICAL

MEDICINE

1

Prevalence of Toxocara canis antibody among children with bronchial asthma in Klang Hospital, Malaysia S. Lokman Hakim’, M. Thadasavanthl, R. H. ‘Division of Raden Sham&& and S. Yogeswa& Parasitology, Institute for Medical Research, Jalan Pahang, 50588 KuaIa Lumpur, Malaysia; 2Department of Paediattics, Tengku Ampuan Rahimah Hospital, Klang, Selangor, Malaysia Keywords: toxocariasis,Toxocurucanis,antibody prevalence, asthma,Malaysia

Toxocara canis is a parasitic roundworm of cats and dogs which may infect a wide range of non-compatible hosts, including humans, in whom the larvae do not mature but migrate through the host tissues causing visceral larva miarans WLM). In Malavsia. seronrevalence of toxocari&is ranges from 10.9%-to 35&, the highest rate being among the Indians (~KMAN HAKIM et al., 1992, 1993). Toxocariasis may be a contributory factor in inducine alleraic asthma (DESOWITZ et al.. 198 1; BUUS et al., 1594). we describe here the prevalence ofantiToxocara antibodies among children with bronchial asthma seen at the Klang Hospital, Malaysia. Table. Age and ethnic group asthmatic and non-asthmatic

Age (years)a Ethnic groups Malay Chinese Indian Others

distribution children

among

Asthmatic

Non-asthmatic

3.8(1-g)

3.6(1-10)

13 1

16

4

5 5

0

1

aMean (range in parentheses).

Blood samples were collected from 45 children below the age of 10 years seen at the clinic or admitted to Klang Hospital: Eighteen of the samples were from children with bronchial asthma and the remaining 27 were from children with other medical conditions. The blood samples were centrifuged and sera stored at -20°C until tested. Anti-Toxocara antibody was detected by enxyrnelinked immunosorbent assay-(ELLSA) using excretorysecretory (ES) antigens of cultured L2 larvae of T. canis in serum-free medium as described elsewhere (LOKMAN HAKIM et al., 1992). Briefly, microtitre plates were coated with ES antigen diluted in coating buffer (0.25 pg/mL) at 4°C overnight. After washing, serum samples diluted in phosphate-buffered saline-Tween 2@ (PBST) were added, after blocking non-specific binding sites with 0.1% skimmed milk for one hour, and incubated at room temperature for 2 h. After washing, perimmunoglobul~ - G oxidase-labelled anti-human coniunate (Keonel Lab@) diluted in PBST was added. follow’ed by &ubation for 3 h. After washing again; substrate solution (o-phenylene-diamine) was added

AND

HYGIENE

(1997) 91,528

and after incubation in the dark for 20 min the reaction was stopped using sulphuric acid. The optical density ‘OD,J was read at 490 nm using an ELBA reader (Dynatech ). Each plate had a positive control (pooled sera from patients diagnosed with VLM syndrome and a high antibody level) and a known negative serum sample. Serum samples from 30 healthy blood donors were also tested to determine the negative/positive cut-off OD. Data were tested bv the y2 and Mann-Whitnev U test when appropriate, using &e SPSS@statistical program. The mean OD of the 30 negative control sera was 0.2ofO*15. The positivity cut-off value was therefore arbitrarily taken as 0.625 (mean+3 SD). There was no significant difference in age or ethnic group distribution of asthmatic and non-asthmatic natients (Table). The mean anti-Toxocara antibody t&e was ‘signi&antly higher in bronchial asthma patients (0.6 1!ZtO-514) than in- the non-asthmatic - children (O-343&&276) (-0.025‘1. The nronortion of children witb bronchial &hma whose sekm’ contained anti-Toxocara antibody was also higher (57.8%) than among non-asthmatic children (15.4%) (pZO.04). There appears to be a relationship between exposure to Toxocara infection and bronchial asthma among the children seen at Klang Hospital. The proportion of asthmatic children having significant anti-toxocaral antibodies in this study was much higher than among Hawaiian children (10%; DESOW~~Z et al., 1981) and Netherlands children (19.2%; WS et al., 1994). Pulmonary symptoms are common in toxocariasis (TAYLOR et al., 1988) and repeated exposure to toxocaral infection could trigger allergic manifestations, including bronchospasm, in response to the migrating larvae or their ES products. Cross-reactivity may be of concern, especially in the tropics where polyparasitism is very common. However, the seroprevalence rate of 15.4% in non-asthmatic children in this study falls within the overall seroprevalence rates reported in Malaysia (b3KMAN HAKIM et uZ., 1992, 1993), and therefore cross-reactivity alone could not explain the very high rate found among the asthmatic children. Acknowledgement We thank the Director, Institute for Medical Research,Kuala Lumpnr for permission to publish this paper. References Buijs, J., Borsboom, G., Van Gemmnnd, J. J., Haxebroek, A., Van Dongen, P. A. M., Van Knapen, F. & Neijens, H. J. (1994). Tmocaru seroprevalence in 5 years old elementary school children: relationship with allergic asthma. American Journal of Epidemiology, 140,839-847. Desowitz, R. S., Rudoy, R. & Brnnwell, J. W. (1981). Antibodies to canine hehninth parasites in asthmatic and non-asthmatic children. Znternutrimul Archives of Allergy and Applied Zmmunology, 65,361-366. Lokman Hakim, S., Mak, J. W., Lam, P L. W., Nazrna, S. & Normaxnah,Y. (1992). Seroprevalence ofToxocuru canzs antibodies among Orang Ash (aborigines) in Peninsular Malaysia. SoutheastAsian Journul of Tropical Medicine and Public

Health, 23,493-496.

Lokman Hakim, S., Mak, J. W. & Lam, P L. W. (1993). Seropositivity for Toxocuru canis antibodies in Malaysia 1989-1991. MedicalJournal of Malaysia, 48,303-307. Taylor, M. R. H., Keane, C. T, O’Connor, P., Mulvihill, E. & Holland, C. (1988). The expanded spectrum of toxocaral disease. Luncet, i, 692-694.

Received 29 April 1997; revised 27 May 1997; accepted for publication 27 May 1997