Cysticercosis is a significant public health problem in countries where pigs are raised for consumption and remains an important cause of neurological disease worldwide. The Philippines is considered an endemic area for cysticercosis because cases in both humans and pigs have been reported; however, epidemiologic information stays limited. We conducted a pilot survey of the seroprevalence of human cysticercosis in a village in Leyte, the Philippines, by measuring antibody specific for
Human cysticercosis is caused by infection with the larvae (cysticerci) of
Cysticercosis is endemic in Africa, Asia, and Latin America [
At present, epidemiological surveys of cysticercosis have not been conducted in many endemic areas due to the lack of availability and cost of the diagnostic methods [
The Philippines is a developing country whose economy relies mainly on agriculture and is considered an endemic area because both human [
The study was approved by Institutional Review Board at Brown University and at the Philippines Research Institute of Tropical Medicine. Written, informed consent was obtained from each adult participant or from the parents of minors.
This study was conducted in Macanip, a
Prior to treatment for schistosome infection, blood was collected into Vacutainer tubes (Becton Dickinson and Company, Franklin Lakes, NJ) for all subjects. Serum was prepared, aliquoted, and stored at
All serum samples were tested by indirect ELISA assay to quantify the level of antibody reacting with
The ELISA assay was performed following the instructions and using the diluents supplied with the kit. Briefly, serum samples were diluted 1 : 8 in kit diluent and transferred into wells (100
The serum sample of each study subject was assayed in triplicate. All control sera were run on each plate in duplicate. One negative control serum provided by the kit was diluted 1 : 8 while a standard reference serum prepared using pooled sera from ten cysticercosis patients was diluted serially 2-fold from 1 : 8 to 1 : 1024. Based on the ODs of standard reference sera on each ELISA plate, a standardization method I-STOD (improved-optical density standardization) was used to transform the OD value of all serum samples into standardized antibody concentration as arbitrary units for analysis of antibody level in the population [
All statistical analysis was performed using STATA 7.0 software. Because the distribution of specific antibody concentration in the study population was right skewed, natural logarithm transformation (ln(concentration + 1)) was performed for each concentration value before multivariate regression analysis. Multivariate linear regression analysis was used to detect the influence of sex, age, and coinfection status for four different helminths (
The study sample consisted of 497 individuals, of which, 310 were males and 187 were females. The mean age of this sample was 14.9 years with a standard deviation of 6.0 years. Most subjects were infected with one or more helminths. The prevalences of the four helminths infections determined by stool examination (
The prevalence of the four helminth infections in the study sample.
Category | Variable | Number of | Percent | 95% CI* |
positives | Positive (%) | (%) | ||
Helminth infected | 422 | 84.9 | 81.5−88.0 | |
353 | 71.0 | 66.8−75.0 | ||
460 | 92.6 | 89.9−94.7 | ||
Hookworm | 259 | 52.1 | 47.6−56.6 | |
Multiple helminth infections | None | 2 | 0.4 | 0.5−1.5 |
One | 31 | 6.2 | 4.3−8.7 | |
Two | 100 | 20.1 | 16.7−23.9 | |
Three | 193 | 38.8 | 34.5−43.3 | |
Four | 171 | 34.4 | 30.2−38.8 |
The distribution of
Multivariate linear regression analysis between
Variable | Coefficient | 95% CI | |
---|---|---|---|
Age | .350 | ||
Sex | .623 | ||
.402 | |||
.529 | |||
.019 | |||
Hookworm infection | .431 |
The distribution of
The overall seroprevalence of cysticercosis in this study sample was 24.6% (95% CI: 20.8%
Multivariate logistic regression analysis between seroprevalence of cysticercosis and potential confounders.
Variable | Coefficient | 95% CI | |
---|---|---|---|
Age group | .803 | ||
Sex | 0.1249 | .578 | |
.972 | |||
.551 | |||
.900 | |||
Hookworm infection | .199 |
Seroprevalence of cysticercosis in different sex-age groups. The numbers of subjects in different groups are as follows. Male: age 7–10 (
Cysticercosis is a long-standing problem in Latin America, a growing problem in Africa and Asia, and an emerging problem in developed countries [
In recent years, several epidemiological surveys of cysticercosis using both antigen and antibody detection methods have been carried out in endemic areas in Asia. These studies reported a seroprevalence of cysticercosis ranging from 2% to 48% in different districts in Indonesia, 5%–7% in Bac Ninh province of Vietnam, 0.02%–11.2% in different areas of China [
In the Philippines, to date, there have been only 15 published cases of neurocysticercosis [
To our knowledge, ours is the first community-based study examining the seroprevalence of human cysticercosis in the Philippines. The seroprevalence of cysticercosis in our study sample was 24.6%, although comparable with other surveys in Asia [
We did not identify any subjects excreting
Clinically, schistosomiasis japonica has been a main concern in the study area and has been implicated in the neurological complications of the residents [
While our data supports an unexpectedly high estimate of cysticercosis prevalence in the study population, several study limitations merit discussion. First, our study population has a higher prevalence of
Second, the immunodiagnostic method employed in our study is based on indirect ELISA to detect specific IgG using
Third, anticysticercal antibody may persist long after the parasite has been eliminated by either immune mechanisms or drug therapy [
Fourth, the age range of our study sample was restricted to 7–30 years, which may have decreased our ability to detect a relationship between cysticercosis seropositivity and host age (Figure
Despite the limitations of antibody detection using cyst-fluid antigen, a high community seroprevalence for cysticercosis identifies a “hot spot” where preventive and control measures should be targeted. The high seroprevalence of human cysticercosis in the present study sample suggests that cysticercosis may be a significant, yet unrecognized problem in the Philippines. These pilot data in a selected sample underscore the need for community and school based surveys of cysticercosis as well as studies identifying risk factors for cysticercosis in rural areas of the Philippines. In addition, our results support a reexamination of pigs as a sentinel indicator for human cysticercosis in the same area [
This study was funded by Natural Science Foundation of China no. 30671836 and the NIH Grant no. AI48123. The authors thank the villagers in Macanip for their participation in this study and the field team workers for their help in sample collection and microscopic analysis. They also thank Dr Feng Chen at the Department of Statistics of Nanjing Medical University for assistance with data analysis, and Dr. Paul Knopf at Brown University for constructive discussions.