Taenia hydatigena in pigs in Burkina Faso: A cross-sectional abattoir study

Development and evaluation of time-resolved rapid immunofluorescence test for detection of TSOL18 specific antibody in porcine cysticercosis infections

BACKGROUND

Porcine cysticercosis, a serious zoonotic parasitic disease, is caused by the larvae of Taenia solium and has been acknowledged by the World Organization for Animal Health. The current detection methods of Cysticercus cellulosae cannot meet the needs of large-scale and rapid detection in the field. We hypothesized that the immunofluorescence chromatography test strip (ICS) for detecting Cysticercus cellulosae, according to optimization of a series of reaction systems was conducted, and sensitivity, specificity, and stability testing, and was finally compared with ELISA. This method utilizes Eu3+-labeled time-resolved fluorescent microspheres (TRFM) coupled with TSOL18 antigen to detect TSOL18 antibodies in infected pig sera.

RESULTS

ICS and autopsy have highly consistent diagnostic results (n = 133), as determined by Cohen's κ analysis (κ = 0.925). And the results showed that the proposed ICS are high sensitivity (0.9459) with specificity (0.9792). The ICS was unable to detect positive samples of other parasites. It can be stored for at least six months at 4℃.

CONCLUSIONS

In summary, we established a TRFM-ICS method with higher sensitivity and specificity than indirect ELISA. Results obtained from serum samples can be read within 10 min, indicating a rapid, user-friendly test suitable for large-scale field detection.

Concordance between two monoclonal antibody-based antigen detection enzyme-linked immunosorbent assays for measuring cysticercal antigen levels in sera from pigs experimentally infected with Taenia solium and Taenia hydatigena

BACKGROUND

Antigen detection in Taenia solium cysticercosis confirms viable infection in the intermediate host (either pig or human). The reference B158/B60 monoclonal antibody (mAb)-based Ag-enzyme-linked immunosorbent assay (ELISA) has acceptable levels of sensitivity and specificity in human neurocysticercosis with multiple brain cysts, although its sensitivity is lower in cases with single brain cysts, whereas in porcine cysticercosis the assay specificity is affected by its frequent cross-reaction with Taenia hydatigena, another common cestode found in pigs. Our group has produced 21 anti-T. solium mAbs reacting against antigens of the whole cyst, vesicular fluid, and secretory/excretory products, identifying TsW8/TsW5 as the most promising pair of mAbs for an Ag-ELISA.

METHODS

We report the use of the TsW8/TsW5 Ag-ELISA to measure cysticercus antigen levels [expressed as optical density (OD) values] in two panels of sera collected from day 0 (baseline) to day 90 postinfection (PI) from pigs experimentally infected with T. solium (n = 26) and T. hydatigena (n = 12). At baseline and on days 28 and 90 PI, we used Bland-Altman (BA) analysis and Lin's concordance correlation coefficients (CCC) to determine the concordance between the TsW8/TsW5 and the B158/B60 Ag-ELISA.

RESULTS

The TsW8/TsW5 Ag-ELISA was able to efficiently measure circulating antigen levels in T. solium-infected pigs, similar to that obtained with the B158/B60 Ag-ELISA. Almost all paired log-OD differences between assays were within the limits of agreement (LoA) in the BA analysis at baseline and on days 28 and 90 PI (92.3%, 100%, and 100%, respectively), and a high concordance of log-ODs between assays was also found (Lin's CCC: 0.69, 0.92, and 0.96, respectively, all P < 0.001). In pigs infected with T. hydatigena, almost all paired log-OD differences were within the LoA in the BA analysis, whereas the concordance of log-ODs between assays was low at baseline (Lin's CCC: 0.24) but increased on days 28 and 90 PI (Lins' CCC: 0.88 and 0.98, P < 0.001).

CONCLUSIONS/SIGNIFICANCE

The TsW8/TsW5 Ag-ELISA recognizes antigens in pigs with T. solium cysticercosis and is highly concordant with the B158/B60 Ag-ELISA. However, its diagnostic use is hampered by cross-reactions with T. hydatigena, as in other mAb-based Ag-ELISAs.

The prevalence of Taenia spp. in pigs slaughtered in Kinshasa

Taenia hydatigena is a non-zoonotic worm that has dogs and wild canids as definitive hosts. Its presence induces cross reactions in certain diagnostic tests for porcine cysticercosis caused by T. solium, the occurrence of which has a considerable public health and economic impact. In the Democratic Republic of the Congo (DR Congo), T. solium is considered endemic, however, the prevalence of T. hydatigena has not been estimated yet. The objective of the study was therefore to estimate the prevalence of T. hydatigena cysticercosis by serological and molecular diagnostic tools in pigs slaughtered in DR Congo. A total of 480 pigs slaughtered in 6 slaughter slabs in Kinshasa, DR Congo, were examined. The thoracal and abdominal cavity organs were inspected for cysts, which were analyzed using PCR-RFLP. Furthermore, 480 sera were collected, and analyzed for the presence of circulating Taenia spp. cysticercus antigens, using the B158/B60 Ag-ELISA. Upon inspection of the carcass, 41 cysts suspected to be metacestodes of Taenia spp. were collected, from the following viscera: spleen (24/41, 59%), liver (13/41, 32%), intestine (3/41, 7%) and lung (1/41, 2%). Molecular analyses revealed a T. hydatigena prevalence of 0.2% (95% CI: 0.0001-0.0116), based on a single lesion (1/480), taken from the spleen. Out of the 480 sera collected, the presence of circulating Taenia spp. cysticerci antigens was detected in 32 (6.7%; 95% CI: 4.5-11.2). The results of this study revealed that T. hydatigena is present in pigs sold in markets in the city of Kinshasa in DR Congo, albeit at a very low prevalence, thus the impact on the interpretation of the B158/B60 seems low in this setting. Detection of circulating antigens in porcine sera by Ag-ELISA, shows that pigs slaughtered in Kinshasa, DR Congo, were infected with viable cysticerci of Taenia spp. which in turn can infect humans.

Prevalence and genetic variance of Taenia hydatigena in goats and sheep from northern Ghana: Preliminary data on a globally neglected livestock parasite

Cysticercosis caused by the larval stages of Taenia hydatigena has a significant global impact on livestock production, particularly of goats and sheep. Despite this, global data on prevalence and genetic variance of this parasite are still scarce. In Ghana, as in most African countries, numerous anecdotal observations agree that it is widespread and frequent. To obtain baseline data, we screened 251 goats and 248 sheep in northern Ghana (Upper East Region) for T. hydatigena metacestode and molecularly characterized the isolates using the mtDNA cox1 gene sequence. Prevalence was 58.57% in goats and 60.48% in sheep, confirming the abundance of this parasite in the region. Gene sequences revealed high diversity (π 0.00346, hd 0.809) and significant negative Tajima D and Fu's Fs values, a characteristic of a population experiencing an expansion after a recent bottleneck. This is the first account of the genetic structure of T. hydatigena in Ghana, intended as a basis for subsequent studies in the region.

Taenia hydatigena in goat and sheep in Ghana: a cross-sectional abattoir survey in Northern and Upper West Regions

Parasitic infections are a major setback to livestock production in Ghana but the disease situation in many localities is poorly understood. A study to determine the prevalence and distribution of Taenia hydatigena in goats and sheep was carried out in two major municipal abattoirs in Tamale and Wa. A total of 538 goats and 256 sheep were screened for cysts during a cross-sectional survey which revealed a prevalence of 22.34% and 33.96% in goats from Tamale and Wa, respectively, and 22.66% in sheep from Tamale. Infection was common in male and female, young and old animals alike. Animals considered in the study originated from various localities within Northern and Upper West Regions and T. hydatigena infection was thought to be autochthonous, depicting a wide distribution of the cestode infection in small ruminants. Our data represent the importance of T. hydatigena infection in goat and sheep production and provide a base for subsequent epidemiological studies in Ghana.

Data-driven analyses of behavioral strategies to eliminate cysticercosis in sub-Saharan Africa

Background

The multi-host taeniosis/cysticercosis disease system is associated with significant neurological morbidity, as well as economic burden, globally. We investigated whether lower cost behavioral interventions are sufficient for local elimination of human cysticercosis in Boulkiemdé, Sanguié, and Nayala provinces of Burkina Faso.

Methodology/Principal findings

Province-specific data on human behaviors (i.e., latrine use and pork consumption) and serological prevalence of human and pig disease were used to inform a deterministic, compartmental model of the taeniosis/cysticercosis disease system. Parameters estimated via Bayesian melding provided posterior distributions for comparing transmission rates associated with human ingestion of Taenia solium cysticerci due to undercooking and human exposure to T. solium eggs in the environment. Reductions in transmission via these pathways were modeled to determine required effectiveness of a market-focused cooking behavior intervention and a community-led sanitation and hygiene program, independently and in combination, for eliminating human cysticercosis as a public health problem (<1 case per 1000 population). Transmission of cysticerci due to consumption of undercooked pork was found to vary significantly across transmission settings. In Sanguié, the rate of transmission due to undercooking was 6% higher than that in Boulkiemdé (95% CI: 1.03, 1.09; p-value < 0.001) and 35% lower than that in Nayala (95% CI: 0.64, 0.66; p-value < 0.001). We found that 67% and 62% reductions in undercooking of pork consumed in markets were associated with elimination of cysticercosis in Nayala and Sanguié, respectively. Elimination of active cysticercosis in Boulkiemdé required a 73% reduction. Less aggressive reductions of 25% to 30% in human exposure to Taenia solium eggs through sanitation and hygiene programs were associated with elimination in the provinces.

Conclusions/Significance

Despite heterogeneity in effectiveness due to local transmission dynamics and behaviors, education on the importance of proper cooking, in combination with community-led sanitation and hygiene efforts, has implications for reducing morbidity due to cysticercosis and neurocysticercosis.

It is important to consider context-specific behaviors and transmission pathways when designing scalable and sustainable intervention strategies for neglected tropical diseases (NTDs). To reduce the morbidity and mortality associated with cysticercosis, suites of interventions have been recommended but are inconsistently implemented due to cost and feasibility-related constraints. This study investigated the potential of a cooking intervention to interrupt transmission via undercooked pork in marketplaces of Burkina Faso. The sensitivity of Taenia solium parasite to temperatures attainable via improved cooking strategies provides a low-cost, human-centered approach to prevent consumption of infected pork meals. By accounting for differential behavior and the relative role of this transmission route across three provinces, we show how the potential of cysticercosis elimination (as a public health problem) varies across behavior-focused interventions. Further investigation into intervention strategies against human and pig cysticercosis warrants data-driven analyses that account for local variation in transmission behaviors.

Knowledge, practices and seroprevalence of Taenia species in smallholder farms in Gauteng, South Africa

Porcine cysticercosis and associated human infections are endemic in Sub-Saharan Africa, Latin America, and Asia. Poor agricultural practices, sanitary practices, and lack of knowledge increase the burden of the diseases in susceptible populations. This study investigates the seroprevalence of Taenia spp. in township pigs in Gauteng, South Africa and describes knowledge and farming practices of pig farmers regarding T. solium infections. Blood samples were collected from 126 pigs in three Gauteng township areas, and analyzed for active Taenia spp. infection using the B158/B60 Ag-ELISA. Farmer questionnaire surveys were conducted in four township areas to investigate the level of knowledge and practices associated with porcine cysticercosis and neurocysticercosis. Logistic regression models were used to assess the relationship between predictor variables and the outcome variable, knowledge of porcine cysticercosis or knowledge of neurocysticercosis. Overall, 7% of the pigs were seropositive for active Taenia spp. infection. 46% of farmers practiced a free-ranging system, while 25% practiced a semi-intensive system. Latrines were absent on all farms; however, 95% of farmers indicated that they have access to latrines at home. Most farmers had no knowledge of porcine cysticercosis (55%) or neurocysticercosis (79%), and this was not associated with any of the factors investigated. The prevalence of active Taenia spp. infection was reasonably low in this study, yet the knowledge level was also low, thus calling for further educational and training programmes to prevent Taenia spp. transmission in these communities.

Performance of Ag-ELISA in the diagnosis of Taenia solium cysticercosis in naturally infected pigs in Tanzania

Background

Taenia solium is a zoonotic parasite responsible for neurocysticercosis—a major cause of late-onset acquired epilepsy in humans. Lack of affordable, specific and sensitive diagnostic tools hampers control of the parasite. This study assessed the performance of an antigen detection enzyme-linked immunosorbent assay (Ag-ELISA) in the diagnosis of viable T. solium cysticercosis in naturally infected slaughter-age pigs in an endemic area in Tanzania.

Methods

A total of 350 pigs were bled before they were slaughtered and their carcases examined. Serum was analyzed for circulating antigens by using a monoclonal antibody-based B158/B60 Ag-ELISA. Each carcase was examined for the presence of Taenia hydatigena cysticerci and half carcase musculature together with the whole brain, head muscles, tongue, heart and diaphragm were sliced with fine cuts (< 0.5 cm) to reveal and enumerate T. solium cysticerci. Half carcase dissection can detect at least 84% of infected pigs. Prevalence and their 95% confidence intervals (CI) were calculated in Stata 12. Sensitivity, specificity, predictive values and likelihood ratios were determined.

Results

Twenty–nine pigs (8.3%, 95% CI: 5.6–11.7%) had viable T. solium cysticerci while 11 pigs had T. hydatigena cysticerci (3.1%, 95% CI: 1.6–5.5%). No co-infection was observed. Sixty-eight pigs (19.4%, 95% CI: 15.4–20%) tested positive on Ag-ELISA; of these, 24 had T. solium cysticerci and 7 had T. hydatigena cysticerci. Sensitivity and specificity were determined to be 82.7% and 86.3%, respectively. Positive and negative predictive values were 35.2% and 98.2%, respectively. Likelihood ratios for positive and negative Ag-ELISA test results were 6.0 and 0.2, respectively. There was a significant positive correlation between the titre of circulating antigens and intensity of T. solium cysticerci (r₍₃₄₈₎ = 0.63, P < 0.001).

Conclusions

The Ag-ELISA test characteristics reported in this study indicate that the test is more reliable in ruling out T. solium cysticercosis in pigs, than in confirming it. Hence, a negative result will almost certainly indicate that a pig has no infection, but a positive result should always be interpreted with caution. Estimates of T. solium prevalence based on Ag-ELISA results should, therefore, be adjusted for test performance characteristics and occurrence of T. hydatigena.

Force-of-infection of Taenia solium porcine cysticercosis: a modelling analysis to assess global incidence and prevalence trends

The World Health Organization (WHO) called, in 2012, for a validated strategy towards Taenia solium taeniasis/cysticercosis control and elimination. Estimating pig force-of-infection (FoI, the average rate at which susceptible pigs become infected) across geographical settings will help understand local epidemiology and inform effective intervention design. Porcine cysticercosis (PCC) age-prevalence data (from 15 studies in Latin America, Africa and Asia) were identified through systematic review. Catalytic models were fitted to the data using Bayesian methods, incorporating uncertainty in diagnostic performance, to estimate rates of antibody seroconversion, viable metacestode acquisition, and seroreversion/infection loss. There was evidence of antibody seroreversion across 5 studies, and of infection loss in 6 studies measured by antigen or necropsy, indicating transient serological responses and natural resolution of infection. Concerted efforts should be made to collect robust data using improved diagnostics to better understand geographical heterogeneities in T. solium transmission to support post-2020 WHO targets.

Performance of a Sandwich Antigen-Detection ELISA for the Diagnosis of Porcine Taenia solium Cysticercosis

The pig is the natural intermediate host of Taenia solium, a parasite causing significant burden of disease in both humans and pigs. Porcine cysticercosis is traditionally detected via tongue palpation and slaughterhouse meat inspection, both with limited sensitivity. Serum antibody detection has a better performance; however, it does not discriminate past from present infection. Serum antigen detection can demonstrate viable infection and gives a good estimate of parasitic load. This study evaluated a sandwich antigen-detection ELISA using monoclonal antibodies (MoAbs) 158C11 and 60H8 for the diagnosis of viable cysticercosis in pigs. Serum samples were used from 35 naturally T. solium cysticerci-infected pigs, 31 cysticercosis-negative pigs, and 22 pigs with Taenia hydatigena infection (to assess cross-reactions). Positive cysticercosis samples were subcategorized at necropsy according to parasitic burden as mild (1-10 viable cysts, n = 10), moderate (11-100 cysts, n = 5), or severe infection (more than 100 cysts, n = 20). This Ag-ELISA showed a sensitivity of 82.9% and a specificity of 96.8% when not considering cross-reactions with T. hydatigena. Hundred percentage of severely infected, 80% of moderately infected, and 50% of mildly T. solium-infected pigs tested positive. Twenty of 22 pigs with only T. hydatigena infections were positive, with 13 reaching saturating levels in the ELISA. The Ag-ELISA revealed the presence of live cysts and is, thus, a fairly reliable test to monitor experimental infection, response to treatment, and follow-up in animal models of cysticercosis. It should, however, be carefully interpreted when used in regions where T. hydatigena is endemic in pigs.

Seroprevalence of circulating taeniid antigens in pigs and associated risk factors in Kongwa district, Tanzania

The aim of this study was to investigate exposure to porcine cysticercosis (PC) and associated risk factors in the Kongwa District, eastern-central Tanzania. For the first time a cross-sectional investigation of the seroprevalence in pigs using a commercial genus specific cysticercosis enzyme linked immunosorbent assay (apDia Ag-ELISA) was undertaken in eastern-central Tanzania. Moreover, the identity of suspected T. solium cysts from pigs in the study area were confirmed by sequencing parasites' mitochondrial cox1 gene. Structured questionnaires and direct observations were used to investigate risk factors associated with parasite transmission. A total of 102 pig-keeping households were surveyed during the dry season between July and August 2017 and 126 households in the rainy season between March and April 2018. Of the 447 examined pigs, 77 (17%, 95% C.I. 14%-20%) tested positive in the ELISA. Seroprevalence was higher in pigs examined during the rainy (21%, 95% C.I. 16%-26%) than dry (12%, 95% C.I. 7%-17%) season (p = 0.019). Eight cyst-positive-pigs were confirmed to be infected with T. solium by sequencing. Risk factors associated with PC seropositivity included origin of piglets or pigs (OR = 0.27, 95% C.I. 0.13-0.42, p = 0.001), socioeconomic factors and pig production system (OR = 0.22, 95% C.I. 0.07-0.37, p = 0.005) and sanitation and hygiene practices (OR = 0.19, 95% C.I. 0.04-0.34, p = 0.014). This study has recorded a high Taenia spp. seroprevalence in pigs in Kongwa suggesting the presence of people in the community carrying the adult parasite, Taenia solium. Our findings also suggest risk of infection by T. solium to people in urban centres and cities consuming pigs from rural areas in Kongwa. The high seroprevalence in Kongwa calls for further studies on taeniasis and cysticercosis in the human population in order to determine suitable control strategies.

Accurate diagnosis of lesions suspected of being caused by Taenia solium in body organs of pigs with naturally acquired porcine cysticercosis

The definitive method for diagnosis of porcine cysticercosis is the detection of cysticerci at necropsy. Cysts are typically located in the striated muscle and brain. Until recently Taenia solium cysticerci have not been definitively identified in other tissue locations, despite several comprehensive investigations having been undertaken which included investigation of body organs other than muscle and brain. Recently a study conducted in Zambia reported 27% infection with T. solium in the liver of pigs with naturally acquired porcine cysticercosis, as well as some T. solium infection in the lungs and spleen of some animals. We investigated the cause of lesions in sites other than the muscle or brain in a total of 157 pigs from T. solium endemic regions of Uganda and Nepal which were subjected to extensive investigations at necropsy. Lesions which had the potential to be caused by T. solium were characterised by macroscopic and microscopic examination, histology as well as DNA characterisation by PCR-RFLP and sequencing. Lesions were confirmed as being caused by Taenia hydatigena (both viable and non-viable), by T. asiatica and Echinococcus granulosus (in Nepal) and nematode infections. No T. solium-related lesions or cysticerci were identified in any tissue other than muscle and brain. It is recommended that future evaluations of porcine cysticercosis in aberrant tissue locations include DNA analyses that take appropriate care to avoid the possibility of contamination of tissue specimens with DNA from a different tissue location or a different animal. The use of appropriate control samples to confirm the absence of cross-sample contamination is also recommended.

A comparison of Taenia solium and Taenia hydatigena infection in pigs using serological diagnosis and post-mortem inspection methods in Benoué division, North Cameroon

The metacestodes of Taenia solium and Taenia hydatigena are the cause of cysticercosis in pigs. T. solium is also responsible of the taeniosis/neurocysticercosis complex in humans, constituting a main cause of epilepsy cases across endemic countries. T. hydatigena is non-zoonotic, but its occurrence in pigs contributes significantly to false positive reactions should genus-species serological methods be used for diagnosis of T. solium porcine cysticercosis. T. hydatigena is often considered not common in pigs in Africa compared to T. solium. On the basis of the evidence that these two cestodes coexist in Cameroon, we examined the viscera of 305 pigs for the identification of the metacestodes of T. hydatigena in Bénoué division, North Region of Cameroon. Tongue, masticatory muscles and heart were sliced for the identification of T. solium cysticerci (TMH dissection test). Twenty seven (8.85%) and 16 (5.24%) pigs were found infected with the metacestodes of T. solium and T. hydatigena, respectively. The difference between the two rates of infection was not statistically significant (P > 0.05). Serum samples were also collected for the evaluation of an inhibition ELISA (i-ELISA) specific to antibodies anti- T. solium or anti-T. hydatigena cysticerci. After incubation of these sera with cyst fluid of T. solium, T. hydatigena, T. multiceps multiceps, T. multiceps gaigeri and T. saginata to eliminate cross-reactions among cestodes parasites, the i-ELISA indicated that 26.56% and 28.52% slaughtered pigs had predominant specific antibodies to cyst fluid of T. solium and T. hydatigena, respectively. Combination of TMH dissection test, i-ELISA and a standard indirect ELISA in a Bayesian simulation approach revealed a true prevalence of 19.27% (0.7-49.27, CI 95%) and 24.85% (5.17-48.34, CI 95%) of porcine cysticercosis due to T. solium and T. hydatigena, respectively. These results indicated that T. hydatigena is as prevalent as T. solium in pigs in the North of Cameroon.

Prevalence of porcine Taenia solium and Taenia hydatigena cysticercosis in Cameroon

Taenia solium, a zoonotic tapeworm species of human and pigs, has been targeted by the World Health Organisation (WHO) for elimination in endemic areas of Africa, Latin America and some parts of Asia. Unfortunately, the assessment of control measures against T. solium is complicated by the lack of specificity of current immunodiagnostic techniques for diagnosis of porcine cysticercosis. Many authors have concluded that the prevalence of T. hydatigena in pigs in Africa is low and extensive epidemiological studies on T. solium cysticercosis in pigs have been carried out using serological tests that cannot differentiate the taeniid species. To estimate and compare the prevalence of T. solium and T. hydatigena in pigs in Cameroon, we examined 416 slaughtered pigs at a pig abattoir in Yaoundé city with the animals originating from several parts of the country. At post-mortem inspection, 35 pigs (8.4%; 95% Confidence Interval (CI), 5.9-11.5 %) were found infected exclusively with T. solium and 27 (6.5%; 95% CI, 4.3-9.3 %) infected exclusively with T. hydatigena metacestodes. One animal was infected with T. solium and T. hydatigena. A stochastic simulation model which took into account the sensitivity of dissection of the tongue, external masseters and heart for diagnosis of T. solium porcine cysticercosis (TMH dissection test) and examination of mesentery, surfaces of the intestines and liver to identify T. hydatigena cysticerci in slaughtered pigs was developed to estimate the prevalence of these taeniid species. The results revealed that the actual prevalence of T. solium and T. hydatigena in Cameroon were 24.8% (95% CI, 20.1-30.5%) and 19.2% (95% CI, 15.1-24.1%), respectively. This study reports the highest porcine T. hydatigena prevalence ever in Africa and adjusted the prevalence of porcine T. solium infection obtained with genus-specific Ag-ELISA (Dorny et al., 2000) in Cameroon due to the presence of T. hydatigena.

Ineffectiveness of meat inspection in the detection of Taenia solium cysticerci in pigs slaughtered at two abattoirs in the Eastern Cape Province of South Africa

Porcine and human cysticercosis, caused by the larval stage of tapeworm Taenia solium, is a zoonosis in southern Africa and known to be endemic in South Africa, mainly in Eastern Cape Province. No efforts to control or eradicate this parasite have been made, despite the increasing occurrence in most Eastern Cape districts, except for routine meat inspection at local abattoirs. The parasite poses a potentially serious agricultural problem, public health risk and economic loss amongst Eastern Cape smallholder pig production communities. The objective of this study was to determine the effectiveness of routine meat inspection for the detection of porcine cysticercosis in pigs from rural smallholder/subsistence production systems in Eastern Cape Province villages. The effectiveness of meat inspection, by registered meat inspectors, in the detection of pigs infected with T. solium cysts was assessed and compared with whole carcass dissection as the "gold standard" method. The commercial antigen enzyme linked immunosorbent assay (B158/B160 Ag-ELISA) kit screened all the slaughtered animals. The proportion of pigs found infected with T. solium cysts, as measured by meat inspection, was lower (5%, 9/180) than with carcass dissection (18.9%, 34/180) and B158/B60 Ag-ELISA test (21.6%, 38/176). Four out of 180 carcasses were heavily infested with T. solium cysts, evenly distributed throughout the carcasses, to a level impossible to enumerate. Of the remaining 176 carcasses, approximately 526 cysticerci, distributed at various anatomical regions of the pig, were counted during carcass dissection. Sites with higher cyst counts, such as the back and hind leg, do not form part of the normal meat inspection regime. The level of agreement (Kappa statistic) between dissection (gold standard) and meat inspection of the two districts was negative (-0.1955). There was a slight agreement in the Kappa statistic (0.0328) between dissection and B158/B60 Ag-ELISA. This study confirms that current meat inspection procedures alone are not sufficiently sensitive to detect all cases of porcine cysticercosis at the abattoirs and require modifications, or should be supplemented by other methods. A risk-based meat safety assurance system, such as HACCP, that considers specific food safety aspects before and after the abattoir (point of slaughter) should be followed. Before slaughter, aspects such as origin, husbandry practices and on-farm animal health control should be considered; after slaughter, the abattoir should inform the next entity in the supply chain of the limitations of meat inspections and the real meaning of an "Approval" stamp. New validated testing methods that can be routinely used should be developed, and government should develop policies and legislation that promotes a risk-based meat safety assurance system throughout the food supply chain.

Implementation of a practical and effective pilot intervention against transmission of Taenia solium by pigs in the Banke district of Nepal

Taenia solium is a zoonotic cestode parasite which causes human neurocysticercosis. Pigs transmit the parasite by acting as the intermediate host. An intervention was implemented to control transmission of T. solium by pigs in Dalit communities of Banke District, Nepal. Every 3 months, pigs were vaccinated with the TSOL18 recombinant vaccine (Cysvax, IIL, India)) and, at the same time, given an oral treatment with 30mg/kg oxfendazole (Paranthic 10% MCI, Morocco). The prevalence of porcine cysticercosis was determined in both an intervention area as well as a similar no intervention control area, among randomly selected, slaughter-age pigs. Post mortem assessments were undertaken both at the start and at the end of the intervention. Participants conducting the post mortem assessments were blinded as to the source of the animals being assessed. At the start of the intervention the prevalence of porcine cysticercosis was 23.6% and 34.5% in the control and intervention areas, respectively. Following the intervention, the prevalence of cysticercosis in pigs from the control area was 16.7% (no significant change), whereas no infection was detected after complete slicing of all muscle tissue and brain in animals from the intervention area (P = 0.004). These findings are discussed in relation to the feasibility and sustainability of T. solium control. The 3-monthly vaccination and drug treatment intervention in pigs used here is suggested as an effective and practical method for reducing T. solium transmission by pigs. The results suggest that applying the intervention over a period of years may ultimately reduce the number of tapeworm carriers and thereby the incidence of NCC.

Neurocysticercosis is a disease caused by a parasitic infection of the brain. The parasite responsible, Taenia solium, is transmitted by pigs where human sanitation is poor and pigs roam freely. Neurocysticercosis is responsible for many cases of epilepsy in people living in poor, developing countries. The feasibility and sustainability of implementing control measures have been major impediments to reducing the incidence of neurocysticercosis. Recently, two new commercial products have become available which together offer the possibility of interrupting the parasite’s transmission by pigs–the TSOL18 vaccine (Cysvax, IIL, India) and an oxfendazole formulation (Paranthic 10%, MCI, Morocco) licensed for use in pigs for the treatment of cysticercosis. Here we describe the impact of implementing vaccination plus drug treatment of pigs in the Banke district of Nepal. The intervention eliminated the risk of transmission of T. solium by the animals vaccinated and treated during the trial. Application of the vaccination and drug treatment program used here, possibly with strategic use of anthelmintics also in the human population, is an effective option for reducing the incidence of neurocysticercosis in Nepal and elsewhere.

Detection of circulating antigens for Taenia spp. in pigs slaughtered for consumption in Nairobi and surroundings, Kenya

Background & methods

Taenia solium a zoonotic tapeworm, responsible for neurocysticercosis in humans is a major public health threat, being a leading cause of acquired epilepsy in endemic regions. Eastern and southern African nations have experienced a recent rapid growth in pig production, including small-scale, free-range systems, with an accompanying increased risk of T. solium transmission. Seven hundred blood samples were collected from randomly selected pigs presented for slaughter at one of the largest porcine abattoir supplying unprocessed pork to Nairobi city and its surroundings. The samples were tested using an antigen ELISA to determine the prevalence of infection with Taenia spp.

Results

The prevalence, adjusted for diagnostic test characteristics, was estimated to be 4.4% (95% CI: 1.9–7.1) with no significant statistical difference by pig sex or age. Infection with Taenia spp. was detected in pigs from all regions of the country supplying pigs to this slaughterhouse. Official post-mortem inspection did not detect cysticercosis in the duration of the study. Therefore, all the carcasses entered the food chains of Nairobi (70%), or neighboring counties (30%).

Conclusions

Circulating antigens of Taenia spp. were detected in pigs slaughtered in one of the largest porcine slaughterhouses in Kenya, which receives pigs from several regions in the country. This is an indication that pigs entering the value chain are raised under poor husbandry conditions and that pork consumers in Nairobi and its surroundings may be exposed to the important zoonotic parasite. Whilst further research utilizing full carcass dissection is required to confirm T. solium positive cases, interventions to improve food-safety throughout the pork value chains in Kenya should be seriously considered.

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Taenia spp. were detected in pigs (4.4%) slaughtered for Nairobi’s pork market.

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Taenia spp. infections were present in pigs from each region in Kenya supplying pork to Nairobi during this study

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A comprehensive risk assessment is necessary to identify exposure to food-safety hazards in pork value chain

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Proper cooking of pork is recommended, as a way of reducing the risk of transmission of Taenia spp. to consumers

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Interventions to improve food-safety should consider the full pork value-chain

Taenia solium cysticercosis in West Africa: status update

Cysticercosis is caused by the larvae of the cestode Taenia solium. Few data are available on the prevalence of this disease in pigs and humans in West African countries. The aim of this study was to provide an overview of existing data concerning the spread of this parasitosis in the countries of the Economic Community of West African States (ECOWAS) on the basis of the literature published over the last five decades. Systematic searches for publications were carried out on PubMed and Google Scholar, as well as in certain regional and local journals. From a total of 501 articles initially retrieved concerning T. solium cysticercosis in West African countries, only 120 articles were relevant for this review and therefore finally retained. For pigs, only eight out of sixteen countries of the region have reported porcine cysticercosis. Post-mortem examination of carcasses at slaughterhouses, meat inspection at butcheries or tongue inspection in herds have been the main source of data, but may not entirely reflect actual parasite distribution. For humans, only five out of sixteen countries reported epidemiological data on neurocysticercosis. Most data referred to neurocysticercosis prevalence among epileptic patients or isolated clinical cases. Furthermore, existing data are often old. Overall, T. solium cysticercosis remains largely neglected in West Africa, and its prevalence appears not to be affected by any religion in particular. There is an urgent need to promote and implement health partnerships and programs on this disease in order to collect more data and identify sensitive populations in the countries of the ECOWAS area.

Co-occurrence of swine cysticercosis due to Taenia solium and Taenia hydatigena in ethnic minority villages at the Thai-Myanmar border

As part of the international joint projects working towards the control of taeniosis/cysticercosis in Asia Pacific, epidemiological studies on Taenia solium cysticercosis have been carried out in high-incidence populations, such as minority groups in Thailand. To assess the epidemiology of cysticercotic infections in pigs in the hill-tribe minority villages (Karen) in Tak province, Thailand, we conducted serological screening and necropsies. The patterns of antibody response to T. solium antigens were then investigated using immunoblot assays. Of the 188 pig serum samples tested for antibody responses to partially purified low-molecular-weight antigens of T. solium cyst fluid, positive responses were detected in 37 samples (19.7%). Based on these results, 16 pigs (10 seropositive and 6 seronegative) were necropsied for investigation of cysticerci and intestinal parasites. All seropositive pigs were coinfected with both T. solium and Taenia hydatigena cysticerci, except one, which was infected with T. hydatigena alone. Three of the six seronegative pigs were confirmed to be infected with T. hydatigena. Pigs infected with T. solium showed much stronger antibody responses than those infected with T. hydatigena. Our results demonstrate the co-occurrence of two swine cysticercoses due to T. solium and T. hydatigena in the studied areas. This study also reveals the importance of direct confirmation of the presence of cysticerci by necropsy after serological screening. In addition to the prevalence of swine cysticercosis in these endemic areas, our findings also reveal potential implications for the development of serological diagnostic assays for swine cysticercosis.

Re-visiting the detection of porcine cysticercosis based on full carcass dissections of naturally Taenia solium infected pigs

Background

Taenia solium is a neglected zoonotic parasite. The performances of existing tools for the diagnosis of porcine cysticercosis need further assessment, and their shortcomings call for alternatives. The objective of this study was to evaluate the performance of tongue palpation and circulating antigen detection for the detection of porcine cysticercosis in naturally infected pigs of slaughter age compared to full carcass dissections (considered the gold standard). Additionally, alternative postmortem dissection procedures were investigated. A total of 68 rural pigs of slaughter age randomly selected in the Eastern Province of Zambia were dissected. Dissections were conducted on full carcasses (or half carcass in case cysticerci were already detected in the first half), including all the organs. Total cysticercus counts, location and stages were recorded and collected cysticerci were identified morphologically and molecularly. All sera were analysed with the B158/B60 antigen detecting ELISA (Ag-ELISA).

Results

Key findings were the high occurrence of T. solium infected pigs (56%) and the presence of T. solium cysticerci in the livers of 26% of infected animals. More than half of the infected carcasses contained viable cysticerci. Seven carcasses had T. hydatigena cysticerci (10%), out of which five carcasses were co-infected with T. hydatigena and T. solium; two carcasses (3%) had only T. hydatigena cysticerci. Compared to full carcass dissection, the specificity of the Ag-ELISA to detect infected carcasses was estimated at 67%, the sensitivity at 68%, increasing to 90% and 100% for the detection of carcasses with one or more viable cysticerci, and more than 10 viable cysts, respectively. Tongue palpation only detected 10% of the cases, half carcass dissection 84%.

Selective dissection of the diaphragm, tongue and heart or masseters can be considered, with an estimated sensitivity of 71%, increasing to 86% in carcasses with more than 10 cysticerci.

Conclusions

Depending on the aim of the diagnosis, a combination of Ag-ELISA and selective dissection, including investigating the presence of T. hydatigena, can be considered. Full carcass dissection should include the dissection of the liver, kidneys, spleen and lungs, and results should be interpreted carefully, as small cysticerci can easily be overlooked.