Seroprevalence of Trypanosoma Cruzi Infection in Three Rural Communities in Guatemala
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Seroprevalence of Trypanosoma cruzi infection in three rural communities in Guatemala George J. Greer,1 Nancy A. Nix,1 Celia Cordón-Rosales,1 Beatriz Hernández,1 Charles M. MacVean,1 and Malcolm R. Powell 2 ABSTRACT A systematic, house-based serological survey for Trypanosoma cruzi seroreactivity was con- ducted in three contiguous communities in Olopa municipality, Chiquimula Department, Guatemala. Blood samples from a total of 292 individuals in 63 households were examined by enzyme-linked immunosorbent assay. The seropositive rate ranged from 0% to 20.8% for the three communities, with a mean of 15.1%. Log-linear models showed that seroprevalence was significantly related to age (P < 0.005) but not to sex. However, when the age group with the lowest prevalence (1–9 years) was excluded from the analysis, age was not a significant factor (P = 0.55). Data from a stratified sample collected at the same time were combined with those of the systematic sample to analyze the relationship between seropositivity and possible ex- planatory variables. Log-linear models, based on 586 individuals in 129 households from the two surveys, revealed a significant positive association between seropositivity and thatched roofs (P = 0.01). Guatemala is located in the endemic in Oaxaca State, in the southern part MATERIALS AND METHODS zone of Trypanosoma cruzi, which ex- of Mexico on the country’s Pacific tends from the southern United States coast (2). Reports from Guatemala in- Study area and study sample to southern Argentina and Chile (1). dicate that seroprevalence is highest Humans are rarely infected in the among the departments that border The study was carried out in 1995 northern extreme of this range, but El Salvador, Honduras, or the Pacific and 1996 in three contiguous com- seroprevalence of 51% to 76% was re- Ocean (3). munities in the municipality of Olopa, ported among adults in three villages This is the first report of a systematic, Chiquimula Department, Guatemala: community-based serological study of Tituque, Tuticopote, and Talquezal. T. cruzi infections in Guatemala. The This is an impoverished area near 1 Medical Entomology Research and Training Unit study was conducted in three commu- the border with Honduras, about 125 and the Universidad del Valle, Guatemala City, nities in Chiquimula Department, the km due east of Guatemala City and 10 Guatemala. region of the country with the highest km from the town of Olopa (Fig. 1). 2 U.S. Department of Health and Human Services, Public Health Service, Centers for Disease Control reported T. cruzi seropositive rate (3). The terrain is mountainous and and Prevention, National Center for Infectious Dis- We present prevalence rates and demo- rugged, and the three communities eases, Division of Parasitic Diseases, Immunology Branch. Send correspondence to: Dr. Malcolm R. graphics of persons testing seropositive are at altitudes ranging from about Powell, Division of Parasitic Diseases, Centers for and examine possible associations be- 1 000 to 1 300 meters above sea level. Disease Control and Prevention, 4770 Buford High- way, Atlanta, Georgia, 30341. Telephone: (770) 488- tween seropositivity and potential con- A distinct rainy season occurs from 4115. Fax: (770) 488-3115. E-mail: [email protected] tributory factors. April to November, and the average 110 Rev Panam Salud Publica/Pan Am J Public Health 6(2), 1999 FIGURE 1. Map of Guatemala showing the location of Olopa in Chiquimula Department gia. During the house-to-house visits, information was recorded pertaining to house construction and the presence or absence of dogs, since these features may affect vector populations and/or the prevalence of T. cruzi infections in humans (4–10). With rare exceptions, houses were simple one-room structures with dirt floors. Walls were either earthen, plant material, mixed earthen/plant mater- Belize ial, or cement block. Earthen walls were made of mud-brick (adobe) or mud-stick (bajareque), but were not fin- Mexico ished with plaster, as is common in other regions. Walls of plant material consisted of two basic types. One was Atlantic a tightly spaced lattice of narrow sticks Ocean or strips of bamboo. The other was a similar lattice covered with banana leaves or straw. There were two cate- gories of roofing materials, synthetic and plant. Synthetic roofing materials Olopa included corrugated metal, corrugated cement, tile, and formed cement. Plant Zacapa roofs were either thatched straw or thatched palm. Honduras Guatemala City Serological examinations were per- Jalapa formed on participants from two sam- pling frames. One was a systematic sample that included every seventh Jutiapa Santa household. The other was a stratified Escuintla Rosa sample, taken in conjunction with an entomological study. Houses were El Salvador stratified according to type of wall Pacific Ocean (earthen or plant) and type of roof (synthetic or thatched). A representa- tive sample of houses constructed with these materials was selected systemat- ically using house numbers. Serological methods annual rainfall is between 1 000 and The purpose of the serological study 2 000 mm. was explained during the house-to- We collected finger prick blood Farming is the principal occupation house visits, including the require- samples on individually labeled strips in the area. Corn and beans are the ments and benefits of participation. All of Whatman No. 1 filter paper (Fisher main staple crops, and coffee is the occupants, except for infants less than 1 Scientific, Pittsburgh, PA, United States main cash crop. At the time of the year old, were invited to participate. A of America), which were air dried and study, neither electrical nor telephone consent form was read aloud and par- returned to the main laboratory in service was available in the communi- ticipants were asked to sign or finger- Guatemala City. Dried samples were ties. We conducted a house-to-house print individual forms, with parents or maintained at 4 oC until processed. A census and recorded the name, age, guardians providing consent for those modification of Voller et al. (11) was and sex of all individuals. Each indi- below 10 years of age. The project was used to perform the enzyme-linked vidual was assigned an identification approved by the Institutional Review immunosorbent assay (ELISA) (12). number based on the community, Board of the U.S. Centers for Disease The antigen used was a crude extract household, and order in the family. Control and Prevention, Atlanta, Geor- of T. cruzi (Brazil strain) culture forms Rev Panam Salud Publica/Pan Am J Public Health 6(2), 1999 111 prepared as described by McCormick and stratified samples could be com- tants, respectively), but Talquezal was and Rowland (13). Antiparasite anti- bined (14). Hierarchical log-linear smaller (236 inhabitants). Of the popu- bodies were detected using peroxi- models were used to test for relation- lation, 46.5% were below the age of 15, dase-conjugated goat antihuman im- ships between seroreactivity (depen- which is typical of rural populations in munoglobulins (gamma and light dent variable) and factors believed to developing countries (16). Sex distri- chains) (Biosource International, Ca- be associated with T. cruzi infections bution was essentially equal, 50.6% marillo, California, United States of (explanatory variables). In this type of male and 49.4% female. America) followed by 3,3′,5,5′-tetra- analysis, chi-square contingency tables Table 1 gives a breakdown, by sam- methylbenzidine with 0.01% H2O2 test the null hypotheses of indepen- pling frame and community, of the (Kirkland & Perry Laboratories, Gai- dence between the dependent and ex- participation and seroprevalence rates. thersburg, Maryland, United States). planatory variables. Significant effects Although every seventh house was The enzyme reaction was developed (nonindependence) arise when the ob- targeted, only 63 (11%) of the house- in the dark at ambient temperature served frequency of seropositive per- holds were included in the systematic and was stopped using a 2M solution sons is significantly lower or higher sample. Houses were excluded be- of H2SO4. The optical density (OD) of than expected from the null model for cause the inhabitants refused to par- each well was determined at 450 nm a particular combination of the ex- ticipate, the residents were not home using an automated ELISA reader planatory variables (15). In those during the survey, or the house was (Titertek Multiskan, Flow Laboratories, cases, the null hypothesis of indepen- unoccupied. Seventy-five houses par- McLean, Virginia, United States). dence is rejected. Partial chi-square ticipated in the stratified sample. The A 6-mm-diameter circle, made with associations generated by log-linear participation rate among households an ordinary paper punch, was taken analysis were used to determine included in the study was 76% (292 of from a completely saturated area of which explanatory variables had sig- 382 persons) for the systematic sample each dried blood sample. The punches nificant effects. Materials used for and 78% (349 of 445 persons) for the were eluted for at least 1 hour in 0.25 house construction and the presence of stratified sample. The overall sero- mL of phosphate buffered saline con- dogs were tested as explanatory vari- prevalence rate was 12.3%. Seropreva- taining 0.5% Tween 20 (Sigma Chemi- ables in our log-linear model. lence differed significantly between cal Co., St. Louis, MO, United States). the two sampling frames (2 = 3.74, Eluates were tested in duplicate on df = 1, P = 0.05) and among the three 96-well PVC microtiter plates. Positive RESULTS communities (2 = 11.3, df = 2, P = and negative controls were included 0.004). Even when Talquezal, which in duplicate on each plate. The OD val- At the time of our census in 1995, had an overall seroprevalence of 2.4%, ues obtained for positive and negative the combined population of the three was excluded, the difference between controls were analyzed to define the communities was 2 890.