A Bayesian approach for estimating values for prevalence and diagnostic test characteristics of porcine cysticercosis

Latent-class methods to evaluate diagnostics tests for Echinococcus infections in dogs

Background

The diagnosis of canine echinococcosis can be a challenge in surveillance studies because there is no perfect gold standard that can be used routinely. However, unknown test specificities and sensitivities can be overcome using latent-class analysis with appropriate data.

Methodology

We utilised a set of faecal and purge samples used previously to explore the epidemiology of canine echinococcosis on the Tibetan plateau. Previously only the purge results were reported and analysed in a largely deterministic way. In the present study, additional diagnostic tests of copro-PCR and copro-antigen ELISA were undertaken on the faecal samples. This enabled a Bayesian analysis in a latent-class model to examine the diagnostic performance of a genus specific copro-antigen ELISA, species-specific copro-PCR and arecoline purgation. Potential covariates including co-infection with Taenia, age and sex of the dog were also explored. The dependence structure of these diagnostic tests could also be analysed.

Principle findings

The most parsimonious result, indicated by deviance-information criteria, suggested that co-infection with Taenia spp. was a significant covariate with the Echinococcus infection. The copro-PCRs had estimated sensitivities of 89% and 84% respectively for the diagnoses of Echinococcus multilocularis and E. granulosus. The specificities for the copro-PCR were estimated at 93 and 83% respectively. Copro-antigen ELISA had sensitivities of 55 and 57% for the diagnosis of E. multilocularis and E. granulosus and specificities of 71 and 69% respectively. Arecoline purgation with an assumed specificity of 100% had estimated sensitivities of 76% and 85% respectively.

Significance

This study also shows that incorporating diagnostic uncertainty, in other words assuming no perfect gold standard, and including potential covariates like sex or Taenia co-infection into the epidemiological analysis may give different results than if the diagnosis of infection status is assumed to be deterministic and this approach should therefore be used whenever possible.

Dogs are a key definitive host of Echinococcus spp; hence, accurate diagnosis in dogs is important for the surveillance and control of echinococcosis. A perfect diagnostic test would detect every infected dog (100% sensitivity) whilst never giving a false positive reaction in non-infected dogs (100% specificity). Since no such test exists, it is important to understand the performance of available diagnostic techniques. We used the results of a study that used three diagnostic tests on dogs from the Tibetan plateau, where there is co-endemicity of E. granulosus and E. multilocularis. In this study opro-antigen ELISA and copro-PCR diagnostic tests were undertaken on faecal samples from all animals. The dogs were also purged with arecoline hydrobromide to recover adult parasites as a highly specific but relatively insensitive third diagnostic test. We used a statistical approach (Bayesian latent-class models) to estimate simultaneously the sensitivities of all three tests and the specificities of the copro-antigen and copro-PCR tests. We also analysed how some determinants of infection can affect parasite prevalence. This approach provides a robust framework to increase the accuracy of surveillance and epidemiological studies of echinococcosis by overcoming the problems of poor diagnostic test performance.

A cross-sectional study of Taenia solium in a multiple taeniid-endemic region reveals competition may be protective

We conducted cross-sectional surveys for taeniasis and cysticercosis in humans, pigs, and dogs in four northern provinces of Laos. Human cysticercosis and taeniasis prevalence was 2.2% (95% confidence interval [CI] = 1.4-3.0%) and 8.4% (95% CI = 6.9-9.9%), respectively. Eating uncooked beef, being male, province of residence, age, and ethnicity were significant risk factors for taeniasis and only province of residence was a significant risk factor for cystiercosis. Thirty-five human tapeworms were recovered during the survey and 33 (94.3%) and 2 (5.7%) were identified as Taenia saginata and T. solium, respectively. Maximum-likelihood adjusted prevalence of T. solium and T. hydatigena in pigs was 4.2% (95% CI = 0.5-7.9%) and 55.9% (95% CI = 47.5-64.3%), respectively, and T. hydatigena taeniasis in dogs was 4.8% (95% CI = 0.0-11.3%). Taenia hydatigena and T. saginata were the most prevalent taeniids in the respective pig and human populations and together may suppress T. solium transmission.

Assessing the burden of human cysticercosis in Vietnam

OBJECTIVES

To describe the occurrence of cysticercosis in patients living in rural areas of Northern Vietnam presenting clinical signs of neurocysticercosis.

METHODS

Serological antigen detection, reflecting current infection with viable larval stages of Taenia solium, was used to estimate the prevalence of active cysticercosis in this patient population.

RESULTS

The seroprevalence in epileptic patient population was <10%. However, antigen detection cannot detect dead cysticerci, which may also cause clinical signs. Therefore, the seroprevalence figures shown here may underestimate the role of neurocysticercosis as a causal agent of epilepsy and headaches in this population.

CONCLUSIONS

Human and porcine cysticercosis remain public and veterinary public health problems in Northern Vietnam and probably in other parts of the country.

A tutorial in estimating the prevalence of disease in humans and animals in the absence of a gold standard diagnostic

Epidemiological methods for estimating disease prevalence in humans and other animals in the absence of a gold standard diagnostic test are well established. Despite this, reporting apparent prevalence is still standard practice in public health studies and disease control programmes, even though apparent prevalence may differ greatly from the true prevalence of disease. Methods for estimating true prevalence are summarized and reviewed. A computing appendix is also provided which contains a brief guide in how to easily implement some of the methods presented using freely available software.

Prevalence of porcine cysticercosis and associated risk factors in Homa Bay District, Kenya

BACKGROUND

Taenia solium is an important zoonosis in many developing countries. Cysticercosis poses a serious public health risk and leads to economic losses to the pig production industry. Due to scarcity of data on the epidemiology of porcine cysticercosis in Kenya, the present study was conducted to determine the prevalence and risk factors for porcine cysticercosis within Homa Bay district. A cross-sectional survey was carried out in 2010, and a total of 392 pigs were recruited in a household survey, with all being tested by ante-mortem lingual palpation (together with questionnaire data on pig production, occurrence and transmission of porcine cysticercosis, risk factors and awareness of porcine cysticercosis collected from the households from which pigs were sampled). Sufficient serum was collected from 232 of the pigs to be tested for the presence of circulating parasite antigen using a monoclonal antibody-based sandwich enzyme-linked immunosorbent assay (Ag-ELISA).

RESULTS

Seventy six pigs were found positive by the Ag-ELISA (32.8%, 95% C.I. 26.8-39.2%), while by tongue inspection cysticerci were detected in 22/ 392 pigs (5.6% 95% C.I. 3.6-8.4%).The most important risk factor for porcine cysticercosis in the Homa Bay area was for pigs to belong to a farm where latrine use by members of the household was not evident (OR = 1.9, 95% CI = 1.13-2.37).

CONCLUSION

The present findings indicate that porcine cysticercosis is endemic in Homa Bay District, and that latrine provision, in conjunction with free-range pig keeping contributes significantly to porcine cysticercosis transmission.

Prevalence of neurocysticercosis among people with epilepsy in rural areas of Burkina Faso

PURPOSE

To estimate the lifetime prevalence of neurocysticercosis (NCC)-associated epilepsy and the proportion of NCC among people with epilepsy in three Burkina Faso villages.

METHODS

Three villages were selected to represent three types of pig-rearing methods: (1) Batondo, where pigs are left to roam; (2) Pabré, where pigs are mostly tethered or penned; and (3) Nyonyogo, where the majority of residents are Muslim and few pigs are raised. In Batondo and Nyonyogo, all concessions (a group of several households) were included. Half of the concessions in Pabré were randomly chosen. All households of selected concessions were included, and one person per household was randomly selected for epilepsy screening and serologic testing for cysticercosis. Self-reported cases of epilepsy were also examined and confirmed cases included in analyses other than the estimate of NCC-associated epilepsy prevalence. Epilepsy was defined as ever having had more than one episode of unprovoked seizures. Individuals with medically confirmed epilepsy had a computerized tomography (CT) scan of the brain before and after contrast medium injection. The diagnosis of NCC was made using a modification of the criteria of Del Brutto et al.

KEY FINDINGS

Thirty-nine (4%) of 888 randomly selected villagers and 33 (94%) of 35 self-reported seizures cases were confirmed to have epilepsy by medical examination. Among the 68 participants with epilepsy who had a CT scan, 20 patients were diagnosed with definitive or probable NCC for a proportion of 46.9% (95% confidence interval [CI] 30.2-64.1) in Batondo and 45.5% (95% CI 19.0-74.1) in Pabré. No cases of NCC were identified in Nyonyogo.

SIGNIFICANCE

All the definitive and probable cases of NCC were from the two villages where pig breeding is common. Prevention policies intended to reduce the burden of epilepsy in this country should include measures designed to interrupt the life cycle of Taenia solium.

Added value of antigen ELISA in the diagnosis of neurocysticercosis in resource poor settings

Background

Neurocysticercosis (NCC) is the most common cause of acquired epilepsy in Taenia solium endemic areas, primarily situated in low-income countries. Diagnosis is largely based upon the “Del Brutto diagnostic criteria” using the definitive/probable/no NCC diagnosis approach. Neuroimaging and specific T. solium cysticercosis antibody detection results are at the mainstay of this diagnosis, while antigen detection in serum has never been included. This study aimed at evaluating the addition of antigen detection as a major diagnostic criterion, especially in areas where neuroimaging is absent.

Methods

The B158/B60 monoclonal antibody-based enzyme-linked immunosorbent assay (ELISA) for the detection of circulating cysticercus antigen was carried out retrospectively on serum samples collected during a hospital-based study from 83 people with epilepsy (PWE) in an endemic area.

Results

The addition of antigen results as a major criterion allowed the correct diagnosis of definitive NCC in 10 out of 17 patients as opposed to 0/17 without antigen results in the absence of neuroimaging. A sensitivity of 100% and a specificity of 84% were determined for the diagnosis of active NCC using antigen ELISA. While the use of a higher cutoff improves the specificity of the test to 96%, it decreases its sensitivity to 83%.

Conclusions

In areas where neuroimaging is absent, NCC diagnosis according to the existing criteria is problematic. Taking into account its limitations for diagnosis of inactive NCC, antigen detection can be of added value for diagnosing NCC in PWE by supporting diagnostic and treatment decisions. Therefore, we recommend a revision of the “Del Brutto diagnostic criteria” for use in resource poor areas and suggest the inclusion of serum antigen detection as a major criterion.

Neurocysticercosis is a parasitic infection of the central nervous system and a common cause of epilepsy in Taenia solium cysticercosis endemic countries. According to the current diagnostic criteria proposed by Del Brutto and colleagues, the diagnosis of neurocysticercosis is mainly based on neuroimaging and detection of specific antibodies. Unfortunately, especially neuroimaging is rarely available in endemic countries. The authors analyzed the value of a test that detects antigens that are excreted by living cysts in people with epilepsy. Different diagnostic scenarios and cut-off values are discussed with the respective sensitivity and specificity of the test. When using the antigen-detecting test, considerably more people with epilepsy were diagnosed correctly with neurocysticercosis. There are some concerns about possible false positive results in other cases. The test was useful for the detection of people with living cysts (active neurocysticercosis), who need further diagnostic evaluation and specific treatment. The authors recommend the addition of this test in the diagnostic criteria for neurocysticercosis.

A combination of the Kato-Katz methods and ELISA to improve the diagnosis of clonorchiasis in an endemic area, China

Background

Examination of feces by light microscopy is widely used for specific parasitological diagnosis of clonorchiasis. However, the true incidence of infection is underestimated owing to the high missing diagnosis rate of this method. The enzyme-linked immunosorbent assay (ELISA) is widely used for the detection and control of clonorchiasis but the practicality of this method is unclear. The purpose of this study was to evaluate the effect of ELISA as a supplementary method for the diagnosis of clonorchiasis.

Methodology/Principal Findings

The present study recruited 2,359 clinically suspected patients from Heilongjiang Province, China. In all, 954 cases were identified as antibody-positive by immunoglobulin (IgG)-ELISA and 495 individuals were diagnosed as egg-positive by the Kato-Katz (KK) method. The seropositive and egg-negative individuals were re-examined by repeated egg counts and/or the number of KK slides and 18 (18.18%) cases were confirmed as clonorchiasis. The 40.44%, antibody-positive rate determined by IgG-ELISA was significantly higher (P<0.05) than the 21.75% egg-positive rate found by examination of feces. A Bayesian approach indicated that the prevalence of clonorchiasis in this region was 22.27% and that the sensitivity, specificity, positive predictive value and negative predictive value of IgG-ELISA were 98.7%, 76.53%, 54.66% and 99.52%, respectively. The agreement between the two methods was moderate (kappa value = 0.564). The clonorchiasis patients lived mainly along the Songhua River. The risk factors, except for ethnic factors, were estimated effectively by both methods.

Conclusions/Significance

The present study suggested that clonorchiasis was widely distributed in Heilongjiang Province, China. The missing diagnosis rate was high using the KK technique alone. The combination of immunological methods and parasitological techniques could improve diagnostic accuracy and reduce the missing diagnosis rate. ELISA used as an auxiliary diagnostic method was realistic and practical for a large-scale screening test, monitoring the prevalence and assessing the risk factors of clonorchiasis.

Prevalence case-control study of epilepsy in three Burkina Faso villages

PURPOSE

To estimate the association between the prevalence of epilepsy and potential risk factors in three Burkina Faso villages.

METHODS

Three villages were selected based on local reports of high numbers of epilepsy cases and pig-rearing practices. One person aged 7 or older was selected at random from all households of selected concessions for epilepsy screening and blood sampling. Epilepsy was confirmed by a physician using the ILAE definition. The cross-sectional associations between epilepsy and selected factors and seroresponse to the antigens of Taenia solium were estimated using a Bayesian hierarchical logistic regression. Prevalence odds ratios (POR) and their 95% Bayesian Credible Intervals (95% BCI) were estimated.

RESULTS

Of 888 individuals interviewed, 39 of 70 screened positive were confirmed to have epilepsy for a lifetime prevalence of 4.5% (95% CI: 3.3; 6.0). The prevalence of epilepsy was associated with a positive reaction to cysticercosis Ag-ELISA serology (POR = 3.1, 95% BCI = 1.0; 8.3), past pork consumption (POR = 9.7, 95% BCI = 2.5; 37.9), and being salaried or a trader compared to a farmer or housewife (POR = 2.9, 95% BCI = 1.2; 6.4).

DISCUSSION

Several factors were associated with prevalent epilepsy, with Ag-ELISA suggesting the presence of neurocysticercosis. The association between epilepsy and some occupations may reflect differences in local attitudes toward epilepsy and should be further explored.

Seroprevalence of major bovine-associated zoonotic infectious diseases in the Lao People's Democratic Republic

Bovine-associated zoonotic infectious diseases pose a significant threat to human health in the Lao People's Democratic Republic (Lao PDR). In all, 905 cattle and buffalo serum samples collected in northern Lao PDR in 2006 were used to determine seroprevalence of five major bovine zoonotic infectious diseases that included Taenia saginata cysticercosis, bovine tuberculosis, Q-fever, bovine brucellosis, and bovine leptospirosis. Five enzyme-linked immunosorbent assays (ELISAs) were used to test for the presence of antibodies to the diseases, except Taenia saginata, for which we tested for the presence of Taenia metacestode circulating antigens. The overall highest prevalence was for T. saginata (46.4%), with lower prevalence for Q-fever (4%), leptospirosis (3%), tuberculosis (1%), and brucellosis (0.2%). Although there were no significant differences in the proportion of seroprevalence between sex and age of the animals sampled, there were significant differences between the provincial distributions. Further studies are required to determine the seroprevalence of these infections in other locations in Lao PDR, as well as other animal species including humans, in order to develop effective prevention and control strategies. This is the first study to investigate the prevalence of bovine zoonotic infectious agents in the Lao PDR. Positivity was demonstrated for all diseases investigated, with the highest prevalence for T. saginata antigen and Coxiella burnetti antibodies. For T. saginata, there were significant differences in the provincial distribution. Approximately 16% seroprevalence of Coxiella burnetti was noted in Xayabuly Province; however, there are no clear reasons why this was the case, and further studies are required to determine risk factors associated with this observation.

Use of oxfendazole to control porcine cysticercosis in a high-endemic area of Mozambique

A randomized controlled field trial to evaluate the effectiveness of a single oral dose of 30 mg/kg of oxfendazole (OFZ) treatment for control of porcine cysticercosis was conducted in 4 rural villages of Angónia district, north-western Mozambique. Two hundred and sixteen piglets aged 4 months were selected and assigned randomly to OFZ treatment or control groups. Fifty-four piglets were treated at 4 months of age (T1), while another 54 piglets were treated at 9 months of age (T2) and these were matched with 108 control pigs from the same litters and raised under the same conditions. Baseline data were collected on the prevalence of porcine cysticercosis using antigen ELISA (Ag-ELISA), as well as knowledge and practices related to Taenia solium transmission based on questionnaire interviews and observations. All animals were followed and re-tested for porcine cysticercosis by Ag-ELISA at 9 and 12 months of age when the study was terminated. Overall prevalence at baseline was 5.1% with no significant difference between groups. At the end of the study, 66.7% of the controls were found positive, whereas 21.4% of the T1 and 9.1% of the T2 pigs were positive, respectively. Incidence rates of porcine cysticercosis were lower in treated pigs as compared to controls. Necropsy of 30 randomly selected animals revealed that viable cysts were present in none (0/8) of T2 pigs, 12.5% (1/8) of T1 pigs and 42.8% (6/14) of control pigs. There was a significant reduction in the risk of T. solium cysticercosis if pigs were treated with OFZ either at 4 months (OR = 0.14; 95% CI: 0.05-0.36) or at 9 months of age (OR = 0.05; 95% CI: 0.02-0.16). Strategic treatment of pigs in endemic areas should be further explored as a means to control T. solium cysticercosis/taeniosis.

Taenia solium Infections in a rural area of Eastern Zambia-a community based study

Background

Taenia solium taeniosis/cysticercosis is a parasitic infection occurring in many developing countries. Data on the status of human infections in Zambia is largely lacking. We conducted a community-based study in Eastern Zambia to determine the prevalence of human taeniosis and cysticercosis in a rural community.

Methods and Findings

Stool and serum samples were collected from willing participants. Geographical references of the participants' households were determined and household questionnaires administered. Taeniosis was diagnosed in stool samples by coprology and by the polyclonal antibody-based copro-antigen enzyme-linked immunosorbent assay (copro-Ag ELISA), while cysticercosis was diagnosed in serum by the B158/B60 monoclonal antibody-based antigen ELISA (sero-Ag ELISA). Identification of the collected tapeworm after niclosamide treatment and purgation was done using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP). A total of 255 households from 20 villages participated in the study, 718 stool and 708 serum samples were collected and examined. Forty-five faecal samples (6.3%) were found positive for taeniosis on copro-Ag ELISA while circulating cysticercus antigen was detected in 5.8% (41/708) individuals. The tapeworm recovered from one of the cases was confirmed to be T. solium on PCR-RFLP. Seropositivity (cysticercosis) was significantly positively related to age (p = 0.00) and to copro-Ag positivity (taeniosis) (p = 0.03) but not to gender. Change point analysis revealed that the frequency of cysticercus antigens increased significantly in individuals above the age of 30. Copro-Ag positivity was not related to age or gender. The following risk factors were noted to be present in the study community: free-range pig husbandry system and poor sanitation with 47.8% of the households visited lacking latrines.

Conclusions

This study has recorded high taeniosis and cysticercosis prevalences and identified the need for further studies on transmission dynamics and impact of the disease on the local people.

Taenia solium taeniosis/cysticercosis is a zoonotic infection endemic in many developing countries, with humans as the definitive host (taeniosis) and pigs and humans as the intermediate hosts (cysticercosis). When humans act as the intermediate host, the result can be neurocysticercosis, which is associated with acquired epilepsy, considerable morbidity and even mortality. In Africa, most studies have been carried out in pigs with little or no data in humans available. In this human study, conducted in a rural community in Eastern Zambia, prevalences for taeniosis and cysticercosis were determined at 6.3% and 5.8% respectively, indicating the hyperendemicity of the area. Cysticercosis infection was strongly related with age, with a significant increase in prevalence occurring in individuals from the age of 30 onward. A collected tapeworm was confirmed to be T. solium. Risk factors associated with the transmission and maintenance of the parasite such as free roaming pigs, households without latrines, backyard slaughter of pigs without inspection and consumption of undercooked pork were also present. The findings of this work have identified the need for further research in the transmission dynamics and the burden that this infection has on the resources of poor local people.

Field evaluation of urine antigen detection for diagnosis of Taenia solium cysticercosis

(Neuro)cysticercosis is an important zoonotic disease caused by infection with Taenia solium metacestode larvae. Existing immunodiagnostic techniques detect antibodies and circulating antigens (Ag) in serum and cerebrospinal fluid (CSF). Blood/CSF collection is an invasive procedure associated with blood-borne infections and is often not well accepted by communities. Detection of circulating Ag in urine has been suggested as an alternative, however this has been evaluated in clinical settings only. The aim of the present study was to evaluate the performance of a urine Ag-ELISA under field conditions. Paired serum and urine samples were obtained from participants in endemic areas of Ecuador (n=748) and Zambia (n=690) and were subjected to a monoclonal antibody-based Ag-ELISA. Calculation of positive and negative agreement indices (AI) showed better agreement in the negative direction both for Ecuadorian and Zambian samples (AI of 93.1 and 86.8, respectively). Using a Bayesian approach to determine the test characteristics, similar sensitivities were obtained for serum and urine Ag detection, whereas a decreased specificity was determined for the urine Ag-ELISA with a lower specificity (78.6%) for Zambian samples than for Ecuadorian samples (88.4%). This study indicates a higher specificity for the serum test under field conditions and promotes further research to improve the urine test.

High prevalence of Taenia solium cysticerosis in a village community of Bas-Congo, Democratic Republic of Congo

Cysticercosis results from tissue infection with the larval stage of the pig tapeworm Taenia solium. Infection of the brain may cause neurocysticercosis, the most frequent cause of acquired epilepsy in developing countries. Information on human cysticercosis in the Democratic Republic of Congo (DRC) is scarce and outdated. We believe this is the first reported study on human cysticercosis and epilepsy in a village community of DRC. The proportion of villagers seropositive by ELISA for T. solium circulating antigen was 21.6%, the highest figure reported to date. The adjusted prevalence of active epilepsy in the community was 12.7 in 1,000.

Human and porcine Taenia solium infections in Mozambique: identifying research priorities

The objective of this paper is to critically review and summarize available scientific and lay literature, and ongoing studies on human and porcine cysticercosis in Mozambique to identify knowledge gaps and direct immediate and long-term research efforts. Data on the spatial distribution and prevalence of the disease in human and swine populations are scarce and fragmented. Human serological studies have shown that 15-21% of apparently healthy adults were positive for cysticercosis antibodies or antigen, while in neuropsychiatric patients seroprevalence was as high as 51%. Slaughterhouse records indicate a countrywide occurrence of porcine cysticercosis, while studies have shown that 10-35% of pigs tested were seropositive for cysticercosis antibodies or antigen. Current research in Mozambique includes studies on the epidemiology, molecular biology, diagnosis and control of the disease. Future research efforts should be directed at better understanding the epidemiology of the disease in Mozambique, particularly risk factors for its occurrence and spread in human and swine populations, documenting the socio-economic impact of the disease, identifying critical control points and evaluating the feasibility and epidemiological impact of control measures and development of local level diagnostic tools for use in humans and swine.

True versus apparent malaria infection prevalence: the contribution of a Bayesian approach

Aims

To present a new approach for estimating the “true prevalence” of malaria and apply it to datasets from Peru, Vietnam, and Cambodia.

Methods

Bayesian models were developed for estimating both the malaria prevalence using different diagnostic tests (microscopy, PCR & ELISA), without the need of a gold standard, and the tests' characteristics. Several sources of information, i.e. data, expert opinions and other sources of knowledge can be integrated into the model. This approach resulting in an optimal and harmonized estimate of malaria infection prevalence, with no conflict between the different sources of information, was tested on data from Peru, Vietnam and Cambodia.

Results

Malaria sero-prevalence was relatively low in all sites, with ELISA showing the highest estimates. The sensitivity of microscopy and ELISA were statistically lower in Vietnam than in the other sites. Similarly, the specificities of microscopy, ELISA and PCR were significantly lower in Vietnam than in the other sites. In Vietnam and Peru, microscopy was closer to the “true” estimate than the other 2 tests while as expected ELISA, with its lower specificity, usually overestimated the prevalence.

Conclusions

Bayesian methods are useful for analyzing prevalence results when no gold standard diagnostic test is available. Though some results are expected, e.g. PCR more sensitive than microscopy, a standardized and context-independent quantification of the diagnostic tests' characteristics (sensitivity and specificity) and the underlying malaria prevalence may be useful for comparing different sites. Indeed, the use of a single diagnostic technique could strongly bias the prevalence estimation. This limitation can be circumvented by using a Bayesian framework taking into account the imperfect characteristics of the currently available diagnostic tests. As discussed in the paper, this approach may further support global malaria burden estimation initiatives.

Factors associated with the prevalence of circulating antigens to porcine cysticercosis in three villages of burkina faso

Background

Little is known about porcine cysticercosis in Burkina Faso. We conducted a pilot study to estimate the prevalence of antigens of Taenia solium cysticercosis and to identify associated factors in pigs of three villages in Burkina Faso, selected to represent different pig management practices: one village where pigs are allowed to roam freely (Batondo), one village where pigs are penned part of the time (Pabré) and one village with limited pig farming (Nyonyogo).

Methods/Principal Findings

A clustered random sampling design was used. Data on socio-demographic characteristics (source of drinking water, presence of latrines in the household, type and number of breeding animals) and pig management practices were collected using a standardized questionnaire. Blood samples were collected from one pig per household to determine the presence of antigens of the larval stages of T. solium by the B158/B60 Ag-ELISA. The associations between seropositivity and socio-demographic and pig management practices were estimated using logistic regression. Proportions of 32.5% (95% CI 25.4–40.3), 39.6% (31.9–47.8), and 0% of pigs, were found positive for the presence of circulating antigens of T. solium in Batondo, Pabré, and Nyonyogo, respectively. The results of the logistic regression analyses suggested that people acquire knowledge on porcine cysticercosis following the contamination of their animals. The presence of antigens in the pigs' sera was not associated with the absence of latrines in the household, the source of drinking water or the status of infection in humans but was associated with pig rearing practices during the rainy season.

Conclusions/Significance

The results suggest that education of pig farmers is urgently needed to reduce the prevalence of this infection.

Taenia solium cysticercosis is a neglected tropical infection transmitted between humans and pigs. This infection is particularly common in areas where sanitation, hygiene and pig management practices are poor, and can sometimes lead to epilepsy in humans. There is very little information about the importance of this infection in Burkina Faso, even though pork meat is widely consumed in many villages. We conducted a pilot study in three villages: two villages where pig rearing and pork consumption are common (Batondo and Pabré) but with different pig management practices, and one village with limited pig farming and pork consumption (Nyonyogo). Blood tests were done on pigs and information on pig raising was collected from farmers. Our study demonstrated that at least one third of pigs are infected with cysticercosis in villages where they are raised, and, particularly when pigs are left to roam some or all of the time. It also demonstrated that farmers may not be aware of this disease until one of their animals is found to be infected. Thus, the study concluded that there is an urgent need for improving education in order to control this tropical disease.

Investigation of an outbreak of Taenia saginata cysts (cysticercus bovis) in dairy cattle from two farms

The paper describes the epidemiological investigation carried out on two dairy farms with cattle infected with Taenia saginata cysts. On the first affected farm it was estimated using Bayesian techniques that approximately 65% of 1400 mixed-age cattle were infected with Taenia saginata cysts. The investigation aimed to determine potential exposure pathways of cattle to Taenia saginata with a view to finding the human source of infection and to describe the epidemiology of the outbreak on the affected farms. In order to determine potential exposure pathways, investigation was centred on how feed or water could have been contaminated with eggs. The plausibility of pathways was determined by examining the spatial and temporal association between factors related to the pathway and the prevalence of infection in cattle strata. We describe the investigation carried out on affected farms.

Infection with versus exposure to Taenia solium: what do serological test results tell us?

Taenia solium cysticercosis is an endemic zoonosis in many developing countries. Serological tests are the most appropriate diagnostic tools to understand the transmission dynamics of the parasite, but the performances of these methods in such a setting are not known. A south Ecuadorian human population living in an endemic area was tested using three common serological tests. Because none of them is a gold standard, a Bayesian Latent Class analysis was used to estimate the test characteristics. Two definitions of a case were considered to differentiate between prevalence of current infection and prior exposure to the parasite. Differences between the performances of the same test in function of the definition of a case were observed. This study shows that test results and prior information should be interpreted carefully in a Bayesian analysis framework, particularly when the latter is based on clinical studies.

Taenia solium cysticercosis in the Democratic Republic of Congo: how does pork trade affect the transmission of the parasite?

Background

Taenia solium, a zoonotic parasite that is endemic in most developing countries where pork is consumed, is recognised as the main cause of acquired epilepsy in these regions. T. solium has been reported in almost all of the neighboring countries of Democratic Republic of Congo (DRC) but data on the current prevalence of the disease in the country itself are lacking. This study, focusing on porcine cysticercosis (CC), makes part of a first initiative to assess whether cysticercosis is indeed actually present in DRC.

Methods

An epidemiological study on porcine CC was conducted (1) on urban markets of Kinshasa where pork is sold and (2) in villages in Bas-Congo province where pigs are traditionally reared. Tongue inspection and ELISA for the detection of circulating antigen of the larval stage of T. solium were used to assess the prevalence of active CC in both study sites.

Findings

The overall prevalence of pigs with active cysticercosis did not significantly differ between the market and the village study sites (38.8 [CI95%: 34–43] versus 41.2% [CI95%: 33–49], respectively). However, tongue cysticercosis was only found in the village study site together with a significantly higher intensity of infection (detected by ELISA).

Interpretation

Pigs reared at village level are sold for consumption on Kinshasa markets, but it seems that highly infected animals are excluded at a certain level in the pig trade chain. Indeed, preliminary informal surveys on common practices conducted in parallel revealed that pig farmers and/or buyers select the low infected animals and exclude those who are positive by tongue inspection at village level. This study provides the only recent evidence of CC presence in DRC and gives the first estimates to fill an important gap on the African taeniasis/cysticercosis distribution map.

Taenia solium is a parasite that can affect both humans and pigs, causing important economic losses in pig production and being the main cause of acquired epilepsy in endemic areas. However, the parasite has been neglected in many African countries and particularly in the Democratic Republic of Congo (DRC), where recent data are non-existent. The present study is part of a first initiative to assess whether cysticercosis is actually present in DRC and to estimate its potential economic and public health importance. Focusing our work on porcine cysticercosis, we demonstrated high prevalence figures of active infections in villages in a rural area of DRC and in markets in the city of Kinshasa. Moreover, the intensity of infection was higher in pigs sampled in villages as compared to pigs sampled on urban markets. Preliminary surveys conducted in parallel in both study sites suggest an effect of pork trade on the transmission of the parasite selecting highly infected pigs at village level.

Porcine cysticercosis and risk factors in the gambia and senegal

During a stratified cross-sectional survey, 1705 pigs were sampled from 279 randomly selected households, 63 randomly selected communities and villages, from four study areas in The Gambia and Senegal during the period October 2007 to January 2008. Porcine cysticercosis prevalence detected by tongue inspection at animal level per study area ranged from 0.1% to 1.0%. Using an antigen-detection ELISA the seroprevalence of cysticercosis at both community/village and animal levels for the four selected study areas is: Western region 80.0% (95%CI: 52.4%–93.6%) and 4.8% (95%CI: 3.4%–6.5%), Bignona 86.7% (95%CI: 59.8%–96.6%) and 8.9% (95%CI: 5.0%–15.5%), Kolda 82.4% (95%CI: 46.8%–96.1%) and 13.2% (95%CI: 10.8%–16.0%), and Ziguinchor 81.3% (95%CI: 43.5%–96.1%) and 6.4% (95%CI: 4.0%–10.1%), respectively. No risk factors for cysticercosis were found significant in this study. This study proved that porcine cysticercosis is endemic and distributed widely in the study areas though its incidence might be suppressed by the generalised use of toilets and latrines in the study areas.

Spatial clustering of porcine cysticercosis in Mbulu district, northern Tanzania

BACKGROUND

Porcine cysticercosis is caused by a zoonotic tapeworm, Taenia solium, which causes serious disease syndromes in human. Effective control of the parasite requires knowledge on the burden and pattern of the infections in order to properly direct limited resources. The objective of this study was to establish the spatial distribution of porcine cysticercosis in Mbulu district, northern Tanzania, to guide control strategies.

METHODOLOGY/PRINCIPAL FINDINGS

This study is a secondary analysis of data collected during the baseline and follow-up periods of a randomized community trial aiming at reducing the incidence rate of porcine cysticercosis through an educational program. At baseline, 784 randomly selected pig-keeping households located in 42 villages in 14 wards were included. Lingual examination of indigenous pigs aged 2-12 (median 8) months, one randomly selected from each household, were conducted. Data from the control group of the randomized trial that included 21 of the 42 villages were used for the incidence study. A total of 295 pig-keeping households were provided with sentinel pigs (one each) and reassessed for cysticercosis incidence once or twice for 2-9 (median 4) months using lingual examination and antigen ELISA. Prevalence of porcine cysticercosis was computed in Epi Info 3.5. The prevalence and incidence of porcine cysticercosis were mapped at household level using ArcView 3.2. K functions were computed in R software to assess general clustering of porcine cysticercosis. Spatial scan statistics were computed in SatScan to identify local clusters of the infection. The overall prevalence of porcine cysticercosis was 7.3% (95% CI: 5.6, 9.4; n = 784). The K functions revealed a significant overall clustering of porcine cysticercosis incidence for all distances between 600 m and 5 km from a randomly chosen case household based on Ag-ELISA. Lingual examination revealed clustering from 650 m to 6 km and between 7.5 and 10 km. The prevalence study did not reveal any significant clustering by this method. Spatial scan statistics found one significant cluster of porcine cysticercosis prevalence (P = 0.0036; n = 370). In addition, the analysis found one large cluster of porcine cysticercosis incidence based on Ag-ELISA (P = 0.0010; n = 236) and two relatively small clusters of incidence based on lingual examination (P = 0.0012 and P = 0.0026; n = 241). These clusters had similar spatial location and included six wards, four of which were identified as high risk areas of porcine cysticercosis.

CONCLUSION/SIGNIFICANCE

This study has identified local clusters of porcine cysticercosis in Mbulu district, northern Tanzania, where limited resources for control of T. solium could be directed. Further studies are needed to establish causes of clustering to institute appropriate interventions.

Pig-farming systems and porcine cysticercosis in the north of Cameroon

A survey was conducted in 150 households owning 1756 pigs in the rural areas of Mayo-Danay division in the north of Cameroon. A questionnaire survey was carried out to collect information on the pig-farming system and to identify potential risk factors for Taenia solium cysticercosis infection in pigs. Blood samples were collected from 398 pigs with the aim of estimating the seroprevalence of T. solium cysticercosis. The results showed that 90.7% of the pigs are free roaming during the dry season and that 42.7% of households keeping pigs in the rural areas have no latrine facility. Seventy-six per cent of the interviewed pig owners confirmed that members of the household used open-field defecation. Enzyme-linked immunosorbent assay (ELISA) for antigen and antibody detection showed an apparent prevalence of cysticercosis of 24.6% and 32.2%, respectively. A Bayesian approach, using the conditional dependence between the two diagnostic tests, indicated that the true seroprevalence of cysticercosis in Mayo-Danay was 26.6%. Binary logistic regression analysis indicated that a lack of knowledge of the taeniasis-cysticercosis complex and the absence of a pig pen in the household were associated with pig cysticercosis.

Prevalence and risk factors of porcine cysticercosis in Angónia District, Mozambique

Taenia solium is an important zoonosis in many developing countries. Cysticercosis poses a serious public health risk and incurs sizeable economic losses to pig production. Because data on the epidemiology of porcine cysticercosis in Mozambique are scarce, the present study was conducted to determine the prevalence and risk factors for porcine cysticercosis. A cross-sectional survey was carried out in 11 villages in Angónia district, Tete province in northwestern Mozambique. Between September and November, 2007, a total of 661 pigs were tested serologically and examined by tongue inspection. Serum samples were tested for the presence of circulating parasite antigen using a monoclonal antibody-based sandwich enzyme-linked immunosorbent assay (Ag-ELISA). In addition, a questionnaire survey to collect information on pig production, occurrence and transmission of porcine cysticercosis, risk factors and awareness of porcine cysticercosis was conducted in the selected households from which pigs were sampled. Two hundred thirty-one samples (34.9%) were found positive by the Ag-ELISA, while by tongue inspection on the same animals cysticerci were detected in 84 pigs (12.7%). Increasing age (OR = 1.63; 95% CI = 1.13–2.37) and free-range pig husbandry system (OR = 3.81; 95% CI = 2.08–7.06) were important risk factors for porcine cysticercosis in the district. The present findings indicate that porcine cysticercosis is endemic in the region, and that increasing pig age and pig husbandry practices contribute significantly to porcine cysticercosis transmission. Further epidemiological studies on the prevalence and transmission of porcine cysticercosis in rural communities in Mozambique are needed to enable collection of more baseline data and implementation of effective control strategies within the country.

Porcine cysticercosis is an infection of pigs caused by the larval stage of Taenia solium, a tapeworm that causes taeniosis in humans. The disease is very common in pigs from many developing countries around the world and poses a serious public health risk and causes significant economic losses in pig production. In Mozambique there is scanty information regarding the occurrence of this disease. Our work conducted in Angónia district, northwestern Mozambique, allowed us to collect important information to evaluate the magnitude and identify the risk factors associated with porcine cysticercosis. This study found that cysticercosis is highly prevalent in pigs and that the free-range husbandry system was by far the main risk factor for the transmission of the disease in the district. These findings should help in the design of control strategies to prevent continuous transmission of this disease in Angónia and in Mozambique.

Seroprevalence to the antigens of Taenia solium cysticercosis among residents of three villages in Burkina Faso: a cross-sectional study

Background

There is limited published information on the prevalence of human cysticercosis in West Africa. The aim of this pilot study was to estimate the prevalence of Taenia solium cysticercosis antigens in residents of three villages in Burkina Faso.

Methods/Principal Findings

Three villages were selected: The village of Batondo, selected to represent villages where pigs are allowed to roam freely; the village of Pabré, selected to represent villages where pigs are usually confined; and the village of Nyonyogo, selected because of a high proportion of Muslims and limited pig farming. Clustered random sampling was used to select the participants. All participants were asked to answer an interview questionnaire on socio-demographic characteristics and to provide a blood sample. The sera were analysed using an AgELISA. The prevalence of “strong” seropositive results to the presence of antigens of the larval stages of T. solium was estimated as 10.3% (95%CI: 7.1%–14.3%), 1.4% (0.4%–3.5%) and 0.0% (0.0%–2.1%) in the 763 participants who provided a blood sample in Batondo, Pabré and Nyonyogo, respectively. The prevalence of “weak” seropositive test results to the presence of antigens of the larval stages of T. solium was 1.3% (0.3%–3.2%), 0.3% (0.0%–1.9%) and 4.5% (2.0%–8.8%) in Batondo, Pabré and Nyonyogo, respectively. The multivariate logistic regression, which included only Batondo and Pabré, showed that village, gender, and pork consumption history were associated with AgELISA seroprevalence.

Conclusions/Significance

This study illustrates two major points: 1) there can be large variation in the prevalence of human seropositivity to the presence of the larval stages of T. solium cysticercosis among rural areas of the same country, and 2) the serological level of the antigen, not just whether it is positive or negative, must be considered when assessing prevalence of human cysticercosis antigens.

Taenia solium cysticercosis is a neglected tropical zoonosis transmitted between humans and pigs. This infection is particularly prevalent in areas where sanitation, hygiene and pig management practices are poor. There is very little information about the importance of this infection in West Africa, even though pork meat is widely consumed in many areas. This pilot study, conducted in three villages of Burkina Faso, demonstrated that people living in areas where pigs are raised were more likely to be infected with cysticercosis than people living in a Muslim village in which there were very few pigs. It also demonstrated variation in the level of infection between the two villages where pigs were raised. Finally, the results suggest that the source of infection in these three villages may differ. These results are significant because they show that there is clustering of infection within villages, even if they are geographically very close to one another. This should encourage future researchers not to combine data from several villages into one summary value. In addition, more work is needed to better describe different potential sources of infection among villages.

Porcine cysticercosis in southeast Uganda: seroprevalence in kamuli and kaliro districts

The recent recognition of neurocysticercosis as a major cause of epilepsy in Uganda and changes in pig demography have lead to a need to better understand the basic epidemiology of Taenia solium infections in pigs and humans. Human exposure is a function of the size of the animal reservoir of this zoonosis. This is the first field survey for porcine cysticercosis to investigate the prevalence of antigen-positive pigs across an entire rural district of south-east Uganda. In our field surveys, 8.6% of 480 pigs screened were seropositive for the parasite by B158/B60 Ag-ELISA. In addition, of the 528 homesteads surveyed 138 (26%) did not have pit latrines indicating a high probability of pigs having access to human faeces and thus T. solium eggs. This study thus indicates the need for better data on this neglected zoonotic disease in Uganda, with a particular emphasis on the risk factors for infection in both pigs and humans. In this regard, further surveys of pigs, seroprevalence surveys in humans and an understanding of cysticercosis-related epilepsy are required, together with risk-factor studies for human and porcine infections.

The disease burden of Taenia solium cysticercosis in Cameroon

Background

Taenia solium cysticercosis is an important zoonosis in many developing countries. Human neurocysticercosis is recognised as an important cause of epilepsy in regions where the parasite occurs. However, it is largely underreported and there is a lack of data about the disease burden. Because a body of information on human and porcine cysticercosis in Cameroon is becoming available, the present study was undertaken to calculate the impact of this neglected zoonosis.

Methods

Both the cost and Disability Adjusted Life Year (DALY) estimations were applied. All necessary parameters were collected and imported in R software. Different distributions were used according to the type of information available for each of the parameters.

Findings

Based on a prevalence of epilepsy of 3.6%, the number of people with neurocysticercosis-associated epilepsy was estimated at 50,326 (95% CR 37,299–65,924), representing 1.0% of the local population, whereas the number of pigs diagnosed with cysticercosis was estimated at 15,961 (95% CR 12,320–20,044), which corresponds to 5.6% of the local pig population. The total annual costs due to T. solium cysticercosis in West Cameroon were estimated at 10,255,202 Euro (95% CR 6,889,048–14,754,044), of which 4.7% were due to losses in pig husbandry and 95.3% to direct and indirect losses caused by human cysticercosis. The monetary burden per case of cysticercosis amounts to 194 Euro (95% CR 147–253). The average number of DALYs lost was 9.0 per thousand persons per year (95% CR 2.8–20.4).

Interpretation

This study provides an estimation of the costs due to T. solium cysticercosis using country-specific parameters and including the human as well as the animal burden of the zoonotic disease. A comparison with a study in South Africa indicates that the cost of inactivity, influenced by salaries, plays a predominant role in the monetary burden of T. solium cysticercosis. Therefore, knowing the salary levels and the prevalence of the disease might allow a rapid indication of the total cost of T. solium cysticercosis in a country. Ascertaining this finding with additional studies in cysticercosis-endemic countries could eventually allow the estimation of the global disease burden of cysticercosis. The estimated number of DALYs lost due to the disease was higher than estimates already available for some other neglected tropical diseases. The total estimated cost and number of DALYs lost probably underestimate the real values because the estimations have been based on epilepsy as the only symptom of cysticercosis.

Taenia solium cysticercosis is a zoonotic disease occurring in many developing countries. A relatively high prevalence in humans and pigs has been reported in several parts of the world, but insufficient data are available on the disease burden. Disease impact assessment needs detailed information on well-defined epidemiological and economic parameters. Our work conducted in West Cameroon over several years allowed us to collect the necessary information to estimate the impact of the parasite on the human and animal populations in this area using both cost and Disability Adjusted Life Year (DALY) estimations. This study identified the professional inactivity caused by the disease as the major loss factor in comparison to the cost of health care and losses due to infected pigs. These findings should allow a simpler estimation of the global disease burden based on information on salary levels and human cysticercosis prevalence in endemic areas of the world. In addition, the number of DALYs lost was higher than estimates already available for some other neglected tropical diseases in sub-Saharan Africa.

Use of ProteinChip technology for identifying biomarkers of parasitic diseases: the example of porcine cysticercosis (Taenia solium)

Taenia solium cysticercosis is a significant public health problem in endemic countries. The current serodiagnostic techniques are not able to differentiate between infections with viable cysts and infections with degenerated cysts. The objectives of this study were to identify specific novel biomarkers of these different disease stages in the serum of experimentally infected pigs using ProteinChip technology (Bio-Rad) and to validate these biomarkers by analyzing serum samples from naturally infected pigs. In the experimental sample set 30 discriminating biomarkers (p<0.05) were found, 13 specific for the viable phenotype, 9 specific for the degenerated phenotype and 8 specific for the infected phenotype (either viable or degenerated cysts). Only 3 of these biomarkers were also significant in the field samples; however, the peak profiles were not consistent among the two sample sets. Five biomarkers discovered in the sera from experimentally infected pigs were identified as clusterin, lecithin-cholesterol acyltransferase, vitronectin, haptoglobin and apolipoprotein A-I.

Frequentist and Bayesian approaches to prevalence estimation using examples from Johne's disease

Although frequentist approaches to prevalence estimation are simple to apply, there are circumstances where it is difficult to satisfy assumptions of asymptotic normality and nonsensical point estimates (greater than 1 or less than 0) may result. This is particularly true when sample sizes are small, test prevalences are low and imperfect sensitivity and specificity of diagnostic tests need to be incorporated into calculations of true prevalence. Bayesian approaches offer several advantages including direct computation of range-respecting interval estimates (e.g. intervals between 0 and 1 for prevalence) without the requirement of transformations or large-sample approximations. They also allow direct probabilistic interpretation, and the flexibility to model in a straightforward manner the probability of zero prevalence. In this review, we present frequentist and Bayesian methods for animal- and herd-level true prevalence estimation based on individual and pooled samples. We provide statistical methods for detecting differences between population prevalence and frequentist methods for sample size and power calculations. All examples are motivated usingMycobacterium aviumsubspeciesparatuberculosisinfection and we provide WinBUGS code for all examples of Bayesian estimation.

Prevalence of Taenia solium cysticercosis in swine from a community-based study in 21 villages of the Eastern Cape Province, South Africa

The pork tapeworm, Taenia solium, causative organism of porcine cysticercosis and human neurocysticercosis is known to occur in areas of South Africa including Eastern Cape Province but, despite increasing reports of its occurrence throughout the subregion, the prevalence is yet to be clearly established. The parasite presents a potentially serious agricultural problem and public health risk in endemic areas. The human populations considered to be at highest risk of infection with this zoonotic helminth are people living in rural areas most of whom earn their livelihood wholly or partially through livestock rearing. Here we report on initial results of a community-based study of pigs owned by resource-poor, emerging pig producers from 21 villages in the Eastern Cape Province. Lingual examination (tongue palpation) in live pigs, two enzyme-linked immunosorbent assays (ELISAs), which detect parasite antigen (B158/B60 Ag-ELISA and HP10 Ag-ELISA) and an enzyme immunotransfer blot (EITB) assay, which detects antiparasite antibody, were used to verify endemicity and estimate apparent prevalence. In the absence of a gold standard true prevalence was obtained, using a Bayesian approach, with a model that uses both available data and prior information. Results indicate that the parasite is indeed present in the study villages and that true prevalence was 64.6%. The apparent prevalences as measured by each of the four tests were: 11.9% for lingual examination, 54.8% for B158/B60 Ag-ELISA, 40.6% for HP10 Ag-ELISA and 33.3% for EITB. This base-line knowledge of the prevalence of T. solium in pigs provides information essential to the design and monitoring of sustainable and appropriate interventions for cysticercosis prevention and control.

The sensitivity of PCR and serology in different Theileria parva epidemiological situations in Rwanda

Theileria parva is the causative agent of a lethal tick-borne disease of cattle occurring in eastern, central and southern Africa. Variations in the sensitivity of the serological and molecular tests with seasonal vector occurrence and discrepancies between low PCR prevalence and high T. parva vector density are a setback to estimate true prevalences. Therefore, the objectives of the present studies were to evaluate (1) the sensitivity of three serological tests (IFAT, ELISA and SELISA) and one molecular test (PCR) in the diagnosis of chronic T. parva infections in four different agro-ecological zones of Rwanda and (2) the effect of tick challenge and animal's age on the sensitivity of PCR. Blood samples from 635 bovines were collected in four agro-ecological zones of Rwanda. All sera were screened using the IFAT, ELISA, SELISA and PCR. The binary results of the four diagnostic tests were introduced separately for each agro-ecological zone in a Bayesian model to estimate the prevalence of T. parva infections and the sensitivity of the four diagnostic tests. All test specificities were set to 100%. The estimated T. parva prevalence was much higher (83-85%) than estimations based on single diagnostic tests. The estimated sensitivity of serological tests was relatively constant and ranged from 57 to 75% in the various areas. The sensitivity of PCR showed more pronounced variations, ranging from 66% in the low T. parva transmission (high land) zones compared to 24% in the highly vector infested (low land) zones. Calves and adult cattle (n=194) were also sampled in regularly and irregularly dipped herds in the low land region. The apparent T. parva prevalence detected by PCR was significantly higher in calves than in adult cattle and in herds regularly treated with acaricides, while no significant differences were found with IFAT. The conditional probability that a sample was positive at PCR while it was positive at IFAT was significantly lower in adults. The implication of these findings in the use of diagnostic assays for epidemiological studies is discussed.

Serological responses in porcine cysticercosis: a link with the parasitological outcome of infection

An oral infection model with Taenia solium whole proglottids was used to study host-parasite relationships and the mechanisms underlying resistance to infection in pigs. In addition, an attempt was made to link the parasitological findings to serological data. Groups of six piglets aged 1, 3 and 5 months were infected and slaughtered 3 months p.i. Circulating antibody and antigen levels were monitored weekly. At autopsy total cyst counts were performed. Although the detailed carcass dissection at necropsy revealed a high variation in the number of cysts, the trend was that the number of viable cysts decreased with the age at which the animals were infected. The kinetics of the antigen levels throughout the course of the infection differed markedly between the three age groups of the experimental infection model. In the younger animals, a fast increase in titres of circulating antigen was observed in most animals, reaching a plateau as early as 2 weeks p.i. Besides its faster increase, antigen levels in pigs infected at younger ages also reached higher levels than in older animals and were associated with weaker antibody responses. Results also demonstrated that a relationship exists between the number of cysts and the titre of circulating antigen. This is promising in view of the development of an assay to quantify the progress of an active T. solium infection and would be a useful tool in epidemiological studies to assess the infection burden and the risk of transmission of the disease. The use of specific antibody-detection assays combined with circulating antigen detection could improve our understanding of this relationship.

Contribution of immunodiagnostic tests to epidemiological/intervention studies of cysticercosis/taeniosis in Mexico

Cysticercosis is acquired when swine ingest human faeces contaminated with Taenia solium eggs. Humans become tapeworm carriers when they ingest infected pork meat. They can also develop cysticercosis after inadvertently swallowing T. solium eggs. Human neurocysticercosis (NCC) is considered as a public health problem in Mexico and in several countries around the world, mainly developing ones. The development of immunodiagnostic techniques has promoted the conduct of seroepidemiological studies. This review provides insight into the evolution of these techniques, their predictive values and their use in field studies, and summarizes evidence supporting health care practice and policy related to cysticercosis/taeniosis in Mexico. Serological studies in rural and urban settings have demonstrated that close proximity with a tapeworm carrier is the main risk factor for acquiring cysticercosis. Research focusing on the tapeworm carrier generated an ELISA for the detection of Taenia coproantigens and facilitated the evaluation of intervention measures. Health education and self-identification of tapeworm carriers were shown to be successful. However, cestodial treatment as a community-based intervention was not as successful. Current immunodiagnostic techniques can be used to pinpoint transmission foci so that appropriate and effective interventions can be applied. In this way, sustainable control, and even eradication of T. solium may be envisioned.

Foot-and-mouth disease non-structural protein serology in cattle: use of a Bayesian framework to estimate diagnostic sensitivity and specificity of six ELISA tests and true prevalence in the field

The diagnostic performance of six foot-and-mouth disease (FMD) assays for detection of antibodies to the non-structural proteins (NSP) of the FMD virus (FMDV) was estimated using a Bayesian analysis on field sera from cattle of unknown infection status originating from post-FMDV outbreak situations in Israel and Zimbabwe. Estimations of the disease prevalence in both populations were also obtained. The diagnostic sensitivity estimates did not differ between both field studies, although overall Bayesian estimates were markedly higher than those previously reported based on sera from comparable experimentally infected (vaccinated) cattle populations. All NSP-based assays demonstrated a lower diagnostic specificity when applied to the Zimbabwean sera compared to both published specificities and similar Bayesian specificity estimates derived for the Israeli dataset. In Israel, the disease prevalence was estimated at 23.9% (95% credibility interval: 19.5-28.8%), whereas 65.4% (59.0-72.5%) was found in Zimbabwe. The need for reliable diagnostic test performance estimates and the benefits of Bayesian analysis in obtaining them are also addressed.

Bayes and diagnostic testing

Interpretation of the result of a diagnostic test depends not only on the actual test result(s) but also on information external to this result, namely the test's sensitivity and specificity. This external information (also called prior information) must be combined with the data to yield the so-called updated, posterior estimates of the true prevalence and the test characteristics. The Bayesian approach offers a natural, intuitive framework in which to carry out this estimation process. The influence of the prior information on the final result may not be ignored. Guidance for the choice of prior information not in conflict with the data can be obtained from a set of statistics and indices (DIC, p(D), Bayes-p).

Combined use of an antigen and antibody detection enzyme-linked immunosorbent assay for cysticercosis as tools in an epidemiological study of epilepsy in Burundi

OBJECTIVE

To evaluate the benefits of the detection of both circulating antibodies (Ab) and antigens (Ag) for the diagnosis of cysticercosis in people with epilepsy. Neurocysticercosis is a cause of neurological diseases world-wide, especially epilepsy. The clinical symptoms of neurocysticercosis are non-specific and diagnosis is often difficult.

METHODS

Serum samples were collected from subjects in a matched case-control study for epilepsy in the Kiremba area, Burundi, between March and April 2001 (epileptic cases=303; controls without epilepsy=606). The enzyme-linked immunosorbent assay (ELISA) was used for the detection of antibodies (Ab-ELISA) and circulating Ag (Ag-ELISA).

RESULTS

The Ab-ELISA revealed 58.7% positivity in epilepsy cases and 31.4% in healthy controls; and Ag-ELISA revealed 38.3% positivity in epilepsy cases and 20.0% in controls. The matched odds ratios were 3.6 (95% CI: 2.5-4.9) for Ab-ELISA, and 2.9 (95% CI: 2.1-4.3) for Ag-ELISA.

CONCLUSION

Both Ag- and Ab-ELISA detected a significantly higher number of seropositives among people with epilepsy than among controls. The risk of epilepsy was high in cases with a positive Ag-ELISA, although less important than in cases with positivity for Ab-ELISA. Dead or degenerating cysticerci appear to be more frequently associated with epilepsy than living cysts. The high number of people with circulating Ag of Taenia solium suggests that the study area is a focus of active transmission of the parasite.