Seroepidemiological aspects of human Strongyloides stercoralis infections in Chile

Aspectos soroepidemiológicos da infecção humana por Strongyloides stercoralis no Chile

BRIEF COMMUNICATION

Seroepidemiological aspects of human Strongyloides stercoralis infections in Chile

Aspectos soroepidemiológicos da infecção humana por Strongyloides stercoralis no Chile

Rubén Mercado^I,II; Maria Isabel Jercic^III; Sergio Alcayaga^IV; Fabiana M. de Paula^V; Marlene T. Ueta^V; Julia M. Costa-Cruz^VI

^IUnidad Docente de Parasitología, Facultad de Medicina, Universidad de Chile

^IIGraduate Program in Parasitology at Instituto de Biologia, Universidade Estadual de Campinas (UNICAMP), Campinas, SP, Brazil

^IIILaboratorio de Referencia de Parasitología, Instituto de Salud Pública de Chile

^IVUnidad de Epidemiología, Servicio de Salud Metropolitano Sur, Chile

^VDepartamento de Parasitologia, Instituto de Biologia, UNICAMP, Campinas, SP, Brasil

^VILaboratorio de Parasitologia, Instituto de Ciencias Biomédicas, Universidade Federal de Uberlândia, Uberlândia, MG, Brasil

^{Correspondence to}

SUMMARY

To determine the frequency of Strongyloides stercoralis antibodies by means of the enzyme linked immunosorbent assay (ELISA) in Chile, in 2001-2003, 675 blood samples of patients of two psychiatric hospitals and 172 of healthy individuals (doctors, nurses and paramedicals) of these institutions, and 1,200 serum samples of blood donors of Northern region (Arica and Antofagasta), Central region (Valparaiso and Santiago) and Southern region (La Union) were collected. ELISA showed positivity of 12.1% in psychiatric hospitalized patients, none (0%) in the health personnel and 0.25% in blood donors (p < 0.05). Only in blood donors of Arica (1%) and La Union (0.5%) the ELISA test was positive suggesting that strongyloidiasis is focalized in determinate zones of the country. In Chile, human infections by S. stercoralis are endemic with very low frequency in apparently healthy individuals and high prevalence in risk groups such as the mentally ill hospitalized patients.

Keywords: Strongyloides stercoralis; Seroepidemiology; Strongyloidiasis; Chile.

RESUMO

Entre os anos de 2001-2003 foram coletadas amostras de sangue de 675 pacientes de dois hospitais psiquiátricos da região central do Chile, 172 de indivíduos sadios (médicos, enfermeiros e paramédicos) destas instituições e 1200 de doadores de sangue de cidades das regiões norte (Arica e Antofagasta), central (Valparaiso e Santiago) e sul (La Union) para determinar a frequência de anticorpos anti Strongyloides stercoralis mediante a reação de enzyme linked immunosorbent assay (ELISA). Foram observadas soropositividade de 12.1% em pacientes de hospitais psiquiátricos e de 0,25% em doadores de sangue (p < 0.05). Todas as amostras dos indivíduos sadios foram não reagentes. Entre os doadores de sangue a soropositividade ocorreu somente nos indivíduos de Arica (1,0%) e La Union (0,5%) sugerindo que a estrongiloidíase poderia estar localizada em determinadas áreas geográficas do país. Conclui-se que no Chile as infecções por S. stercoralis seriam endêmicas, de baixa freqüência e afetando especialmente grupos de risco como os pacientes psiquiátricos.

Human infection by the nematode Strongyloides stercoralis is especially endemic throughout tropical and warm temperate regions of the world^3,11. In other geographical zones or in industrialized countries, strongyloidiasis still represent a clinical-epidemiological problem focalized in institutions for the mentally ill patients¹⁰. Scarce epidemiological information about strongyloidiasis in Latin-American countries is available. Epidemiological studies in selected studied populations of Brazil, Peru, Colombia and Venezuela showed frequency of 13.0%¹⁴, 8.7%²⁰, 2.3%⁸ and 1.4%⁷ respectively. In Chile, in 1983, a mortal case of disseminated strongyloidiasis in a hospitalized psychiatric 53 year-old man was reported¹⁷. Enteroparasitic infections surveys carried out in psychiatric hospitalized patients of the V geopolitical region of Chile in 1985 and 1990 showed percentages of S. stercoralis infections of 11.6 (57/490)⁵ and 7.0 (16/229)⁹ respectively. In 2000, in a psychiatric hospital of Santiago, Chile it was observed that 20 patients presented elevated blood eosinophiles count. Coproparasitological examination of seven stool samples of each patient permits the detection of larvae of S. stercoralis in four of them¹⁵.

The laboratory diagnosis of strongyloidiasis by using commonly stool examination methods such as formol-ethyl acetate techniques - routinely used in Chile - is considered of low sensitivity, so the identification of S. stercoralis infected individuals is difficult⁴. Immunodiagnosis of S. stercoralis infection has been attempted with several serological tests. Enzyme linked immunosorbent assay (ELISA) permits the detection of serum specific IgG¹ , and can be used as an epidemiological tool to determine the prevalence of strongyloidiasis in a given region or population^18,19,20. In Chile, ELISA test to detect S. stercoralis serum antibodies against an alkaline protein extract of the filariform larvae of S. venezuelensis was standardized¹⁶.

The objective of this communication is to describe some epidemiological aspects of the infections caused by S. stercoralis in two psychiatric institutions of Chile, including the total population of the interned patients and the health personnel of the referred institution. Also, we determined the percentage of positive ELISA test in blood donors of three different geographical regions of Chile: north, central and south to compare it frequency with the observed in the hospitalized psychiatric patients.

A total of 2047 serum samples were collected from Chile individuals, during 2001-2003. In hospital 1 (from the V geopolitical region of Chile) blood samples were taken from 343 patients. According to sex 231 (67.3%) were men and 112 (32.7%) women. Ninety five health personnel (physicians, nurses and paramedical individuals) were studied. In hospital 2 (from Santiago, Metropolitan region) 332 bloods samples were taken, 224 from men (67.5%) and 108 from women (32.5%) psychiatric patients. Health personnel studied in this institution were 77. Serum samples of blood donors were obtained from the northern cities of Arica (n = 200) and from Antofagasta (n = 200), from the central region cities of Valparaiso (n = 100) and Santiago (n = 500) and from the semi-rural southern city of La Union (n = 200). All biological samples were obtained under ethical protocol for epidemiological studies approved by the health institutions involved.

ELISA was performed as we previously described¹⁶ using a filariform larval alkaline extract of Strongyloides venezuelensis and a cut-off value of 0.33 OD. Statistical significance of frequency values observed was determined by using the program STATCALC of EPIINFO 6.0. Results were considered significant at p < 0.05.

Figure 1 shows the seropositivity results for S. stercoralis antibodies in hospitalyzed psychiatric patients and blood donors of the different regions studied. In blood donors a positive ELISA was observed in two serum samples in Arica city (1.0%) and in one in La Union city (0.5%). Positive frequency observed in a total of 1,200 of these serum samples was 0.25% and among 675 psychiatric patients was 12.1% (p < 0.05). Table 1 shows the seroprevalence of S. stercoralis infections according to sex and age detected by means of ELISA in psychiatric patients from hospital 1 of the V geopolitical region and hospital 2 of the Metropolitan region of Chile. A total of 40/343 patients interned in the hospital 1 presented an ELISA positive test (11.7%). By sex, 7.1% of the women studied and 13.9% of the men were positive. This difference was statistically significant (p < 0.05). The most frequent age group affected was those of 21 to 39 year-old in both sexes. Similar results were observed in the hospital 2. A total of 42/332 (12.7%) of the patients presented ELISA positive. By sex, 6.5% of women and 15.6% of men had specific antibodies. This difference was statistically significant (p < 0.05). No positive ELISA test was observed in the health personnel of both Hospitals.

In immunocompetent individuals most infections by S. stercoralis are chronic, however, in some situations hyperinfection or disseminated infection has been found usually associated with host immunosuppression^2,12,13 . CONWAY et al.⁴ considered that there is a typically persistent infection by S. stercoralis over decades in a small fraction of the population of endemic regions.

In Chile, our results of the seroepidemiology of S. stercoralis infections in blood donors of different cities showed that the prevalence of antibodies was 0.25%, suggesting that strongyloidiasis frequency is very low and occurred in determinate geographic areas. Comparison of prevalence percentages observed in hospitalized psychiatric patients (11.7 - 12.7%) and in blood donors (0.25%) indicates that the transmission of S. stercoralis in Chile is facilitated in the closed environment of the psychiatric institution. Geophagy and coprophagy frequently observed among mentally affected or retarded patients probably play important roles in the acquisition and spread of the infection. COSTA-CRUZ et al.⁶ alerted that strongyloidiasis is not only associated with barefoot walking of individuals but with handled soils with unprotected hands and drinking unfiltered waters. Studies performed by CORNEJO et al.⁵ and GARIBALDI et al.⁹ by using formalin-ether techniques to detect larvae of S. stercoralis in the same hospital showed frequencies of 11.6% (57/490) and 7.0% (16/229) respectively. These prevalence rates were similar to those determined in this study using ELISA. S. stercoralis infections are difficult to control in closed institutions, maintaining high frequencies along at least 20 years. In this study of hospitalized mentally ill patients, we observed that ELISA test was a very useful tool to determining the seroepidemiology of infections by S. stercoralis, contributing to define the transmission patterns, which are valuable basic information to apply control measures, such as chemotherapy and improvement of sanitary conditions.

In Chile, human infections by S. stercoralis are endemic with very low frequency in apparently healthy individuals and high prevalence in risk groups such as the mentally ill hospitalized patients.

Received: 29 May 2006

Accepted: 14 December 2006

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Publication Dates

• Publication in this collection
  30 Aug 2007
• Date of issue
  Aug 2007

History

• Received
  29 May 2006
• Accepted
  14 Dec 2006