Prevalence of Taenia solium porcine cysticercosis in the Eastern, Southern and Western provinces of Zambia

Tongue examination and detection of circulating antigen (Ag-ELISA) were used to establish the prevalence of Taenia solium porcine cysticercosis in free-range pigs in selected districts of Eastern, Southern and Western provinces of Zambia, and to determine if prevalence of porcine cysticercosis was associated with age, breed and sex. Households with pigs were identified using the snowballing technique. A total of 1691 pigs were examined out of which 183 (10.8%) were positive on tongue examination. Ag-ELISA gave a sero-prevalence of 23.3%. When considering the factors in a logistic regression analysis, only breed type was significantly associated with porcine cysticercosis (OR=0.72; 95%CI=0.63-0.81). The crossbred pigs were 72% more likely to have had cysticercosis than the Nsenga (dwarf local) breed as determined by Ag-ELISA. The result that crossbred pigs had a higher prevalence of T. solium cysticercosis suggests that pig breeds may display different susceptibility to cysticercosis. The limited use of latrines in these areas implies that people use the nearby bush for defecation, resulting in pigs having access to human faeces. Therefore, investigation of taeniosis and cysticercosis in humans is warranted to better comprehend the local epidemiology and transmission risks. This should then be followed by extension programs to communities so that the control plans that could be instituted are more sustainable.     

The prevalence of porcine cysticercosis in Eastern and Southern provinces of Zambia

The objective of this study was to determine the prevalence and importance of porcine cysticercosis in rural areas of Zambia. The study involved an abattoir survey of 1316 pigs at a slaughter slab in Lusaka and two field surveys in villages in Southern and Eastern provinces. Lingual examination of live pigs and visual inspection of their carcass as well as blood sampling for measuring circulating parasite antigen by enzyme-linked immunosorbent assay (Ag-ELISA) were used as parameters to measure infection. In the field surveys, a questionnaire was administered to every household whose pigs were examined to obtain information on pig husbandry practices and to study risk factors for the infection. Out of the 1316 pigs examined at the slaughter slab, 143 (10.9%) and 271 (20.6%) were positive by lingual examination and meat inspection, respectively. Most of the pigs were very heavily infected with predominantly live cysts. The field surveys revealed that eight (8.2%) out of 98 pigs from Southern province and eight (5.2%) out of 151 pigs from Eastern province were positive for cysticercosis by tongue palpation. Using the Ag-ELISA 20 (20.8%) and 14 (9.3%) pigs were positive in Southern and Eastern provinces, respectively. The questionnaire survey revealed poor pig husbandry practices, absence of meat inspection and control, poor knowledge of the disease and poor sanitation in the surveyed villages. The prevalence of pig cysticercosis found in this study ranks among the highest in the southern African region, in Africa and in the world. The current study suggests the presence of human tapeworm carriers and a high risk of human cysticercosis in the surveyed areas as well as in urban centres where pigs from rural areas are increasingly sold, slaughtered and consumed.     

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.     

Epidemiological survey of swine cysticercosis in two rural communities of West-Cameroon

To determine the prevalence of porcine cysticercosis, a survey was carried out in 27 villages belonging to two rural communities of West-Cameroon (Bafou and Bamendou). Between January and August, 2000, a total of 707 pigs were examined serologically and by tongue inspection. Serum samples were examined for circulating parasite antigen using a monoclonal antibody-based sandwich enzyme-linked-immunosorbent assay (Ag-ELISA) and for antibodies against cysticerci (Ab-ELISA). Seventy eight samples (11.0%) were found positive in the Ag-ELISA and 154 (21.8%) in the Ab-ELISA, while by tongue inspection on the same animals cysticerci were detected in 43 pigs (6.1%). Gibbs sampling using results of these three tests indicated that the estimated prevalence of porcine cysticercosis was 10.9%. Analysis of the Ag-ELISA results demonstrated that adult pigs showed a significantly higher seroprevalence (15%) than young ones (8.4%). There was no statistical difference in cysticercosis prevalence in pigs raised in households with or without a latrine. Animals that were reported to be usually confined were significantly less infected (9.9%) than free-roaming pigs (16.2%). Infection rates were significantly higher in pigs that had access to human faeces (13.8%) than those which did not have access (9.1%). This study has identified some community behavioural and environmental practices that should be modified to prevent continuous transmission of porcine cysticercosis.     

Epidemiological survey of swine cysticercosis using ante-mortem and post-mortem examination tests in the southern highlands of Tanzania

Pig keeping is known to be popular in the regions of the southern highlands zone (Mbeya, Iringa and Ruvuma) of Tanzania where more than 60% of pigs under the small-scale production system are raised. However, no epidemiological surveys on porcine cysticercosis have been conducted in the zone in spite of unofficial reports indicating the disease to be a widespread problem. To estimate prevalence rates and risk factors for porcine cysticercosis in Chunya and Iringa Rural Districts and Ruvuma Region (Songea and Mbinga Districts), 722, 808 and 302 live pigs, respectively, were examined by lingually and the prevalence of swine cysticercosis was found to be 7.6%, 8.4% and 16.9% for Chunya and Iringa Rural Districts, and Ruvuma Region, respectively. Structured observations and questionnaire interviews were used to analyse pig rearing practices and household use of latrines in Chunya and Iringa Rural Districts only. The analysis of effect of pig management practices, lack of a latrine, eating undercooked pork, home slaughter and no inspection of pork and lack of knowledge of T. solium on their association to tongue positivity in pigs was done by means of a contingency table. Odds ratios (OR) with corresponding 95% confidence intervals (95% CI) and p-values were calculated. Structured questionnaire interviews identified factors associated with the disease prevalence in both Chunya and Iringa Rural Districts were free-ranging of pigs, home slaughtering of pigs and pork not being inspected. While in Chunya and Iringa Rural Districts lack of latrine and barbecuing were found a risk factor, respectively. To control the disease in the study areas of the southern highlands there is a need for significant improvements regarding the use of latrines, confinement of pigs, pork inspection and thorough cooking of pork.     

Preliminary evaluation of Community-Led Total Sanitation for the control of Taenia solium cysticercosis in Katete District of Zambia

Taenia solium taeniasis/cysticercosis is a zoonotic disease endemic in sub-Saharan Africa. It is associated with poor sanitary practices, free-range pig husbandry and lack of disease awareness in endemic communities. A comparative research was conducted with pre and post-intervention assessments in nine villages to evaluate Community-Led Total Sanitation (CLTS) as an intervention measure for the control of porcine cysticercosis in Katete District in the Eastern Province of Zambia. Blood samples were collected from pigs for circulating antigen detection and a questionnaire focused on the household was administered to a total of 153 respondents whose pigs were examined (64 pre-intervention, 89 post-intervention), in order to obtain information on general demographic characteristics, pig husbandry practices, sanitation practices and associated knowledge and awareness of T. solium infections. The first sampling was conducted prior to the implementation of the CLTS and second sampling eight months after triggering of CLTS in the selected villages. A total of 379 pig serum samples were examined using the B158/B60 Ag-ELISA to detect T. solium cysticercosis, 104 pre-intervention and 275 post-intervention, of which 14 (13.5%) and 45 (16.4%) were positive, respectively. Wald test p-values were computed to assess significant differences in the variables of interest mentioned above for the pre and post CLTS. The research revealed that CLTS as a control measure did not significantly improve T. solium infections in pigs. The research also revealed that the sanitation practices and awareness of cysticercosis did not change. It is recommended that a longer term evaluation be undertaken when the villages have been declared open defaecation free. In addition, the research recommends that health education, mass drug treatment and pig vaccination be incorporated, as an essential component of prevention and control programmes for T. solium infections.     

Risk factors for the prevalence of porcine cysticercosis in Mbulu District, Tanzania

To estimate prevalence of and risk factors for the prevalence of porcine cysticercosis in Mbulu District, Tanzania, 770 live pigs were examined by lingual examination in 21 villages. Structured observations and questionnaire interviews were used to assess pig rearing practices and household use of latrines. Associations between factors were analyzed using a Bayesian hierarchical model to obtain prevalence odds ratio (OR) and 95% Bayesian Credible Intervals (95% BCI). Prevalence was 17.4% (village-specific range 3.2–46.7%). Prevalence of porcine cysticercosis was considerably higher in pigs reared in households lacking latrines than in those reared in households that were using latrines (OR=2.04; 95% BCI=1.25, 3.45). About 96% of the pigs were kept under free-range conditions. This study suggests the need for further studies in order to design and implement effective prevention and control measures for porcine cysticercosis in Mbulu District, Tanzania.     

Evidence that active transmission of porcine cysticercosis occurs in Venezuela

There is a paucity of quantitative data on the status of porcine cysticercosis in Venezuela, information which is essential for understanding the level of disease transmission. This study was, therefore, conducted in a typical small rural community in Yaracuy State, Venezuela, where previous cases of human Taenia solium taeniasis/cysticercosis had been reported and where the free-ranging pig management practices and the lack of rudimentary sanitary facilities indicated an obvious risk for transmission of the disease. Serum samples from 52 village pigs were screened by enzyme-linked immunosorbent assays for anti-cysticercal antibodies (Ab-ELISA), using T. solium cyst fluid as the antigen and the HP10, monoclonal antibody-based, antigen trapping ELISA for parasite antigen (HP10 Ag-ELISA). Significantly, a high proportion of the animals (65.4% for the Ab-ELISA and 42.3% for the HP10 Ag-ELISA) were sero-positive. Five of the pigs, which were selected on that basis of positive tongue palpation, were killed for autopsy, and large numbers of viable cysticerci were found in the carcases. This unequivocal documentation of porcine cysticercosis in Venezuelan pigs presents clear evidence that T. solium is actively transmitted in Venezuela. Further detailed studies and implementation of appropriate control measures are therefore indicated.     

Control of the taeniosis/cysticercosis complex: future developments

Cysticercosis is due to the establishment of the larval stage of the zoonotic cestode parasite Taenia solium. The infection causes substantial human morbidity and mortality, particularly in several Latin American countries and parts of Africa and Asia, as well as economic losses in pig husban dry due to condemnation of infected pork meat. The life cycle of T. solium includes human beings as definitive hosts and pigs as intermediate hosts. Cysticercosis is acquired by the ingestion of eggs released by human tapeworm carriers, who become infected after ingesting pork meat contaminated with cysticerci. Taenia solium transmission has been associated with poverty, lack of sanitary services and practices of rearing backyard pigs with free access to the areas that villagers use as toilets, as well as cultural behaviour. Nonetheless, due to the recent increase of migration and tourism, industrial countries are also reporting cases of human cysticercosis. There are many epidemiological studies that have been conducted mainly in Latin American countries that have evaluated intervention measures for control of cysticercosis including the development and testing of vaccines. Furthermore, the involvement of international agencies and institutions, such as the World Health Organization, the Food and Agriculture Organization and the International Livestock Research Institute, as well as the commitment of policymakers, scientists and field workers, are key means for the sustainable control and, hopefully, eradication of T. solium infections.     

A Slaughter Slab Survey for Extra-Intestinal Porcine Helminth Infections in Northern Tanzania

A survey on extra-intestinal porcine helminths was conducted at three slaughter slabs that receive pigs from Mbulu, a district endemic for porcine cysticercosis in northern Tanzania. Seventy carcases of pigs between 1 and 2 years old were examined between December 1997 and March 1998. The examination involved ante-mortem lingual examination for Taenia solium cysticercosis followed by post-mortem inspection. In addition, a laboratory procedure was performed to determine whether any of these domestic pigs were infected with Trichinella species. Parasites detected were Ascaris suum (44.3%), Echinococcus granulosus (4.3%) and Taenia hydatigena (1.4%). The lack of cases of porcine cysticercosis in this study compared to previous studies suggests that pig traders are conducting their own ante-mortem lingual examinations before purchasing pigs in the rural communities where the parasite is still highly prevalent. It is concluded that improved meat inspection could prove useful in reducing the local population's risk of infection with these parasites. The results of this study have revealed the parasites of agricultral and public health importance in the targeted communities. Further epidemiological investigations are required to better determine parasite prevalence and impact in order to formulate appropriate and cost-effective strategies for control.     

A health-education intervention trial to reduce porcine cysticercosis in Mbulu District, Tanzania

We conducted a randomised community controlled trial to estimate the effectiveness of health and pig-management education intervention in reducing the incidence rate of porcine cysticercosis caused by Taenia solium in Mbulu District, northern Tanzania, between April 2002 and July 2004. We included a random sample of 827 pig-keeping households from 42 randomly selected villages in our 27-month study. We collected baseline data on the prevalence of porcine cysticercosis based on lingual examination of live pigs, and pig-management and sanitation knowledge and practices based on questionnaire interviews and observations. We allocated 21 of the villages to the health-education intervention, developed with community participation; we used stratified randomisation to balance the village-level baseline prevalence of porcine cysticercosis. From July 2003 to March 2004 following the intervention, we gave each participant household a sentinel piglet to raise (the timing was balanced between the intervention groups). Knowledge about the transmission and prevention of porcine cysticercosis was improved >42% in both groups when measured 10–12 months post-intervention. There was no improvement in observed practices in either group throughout the study period. However, the intervention had a significant reduction in the reported cases of household consumption of infected pork (a reduction by 20%). The intervention was associated with a considerable decrease in the incidence rate of porcine cysticercosis (incidence rate ratio 0.57) as measured by antigen-ELISA in sentinel pigs. Public education could lead to a reduction of the risk of infection in humans.     

Epidemiologic observations on porcine cysticercosis in a rural community of Michoacan State, Mexico.

The prevalence of and risk factors for Taenia solium infection (cysticercosis) in pigs were studied in a rural community in Michoacan State, Mexico. Visual inspection of the tongues of 216 pigs revealed cysticerci in 14 (6.5%). The prevalence was slightly higher in male (10/105) than female pigs (4/110) (P = 0.06) and increased with age (P less than 0.05). The most important risk factors for infection in pigs were access to human feces at a public washing area (P = 0.004), the presence of an indoor latrine (P = 0.05) and indiscriminate disposal of human feces around the pig owner's household (P less than 0.1). Effective and long-lasting control of the transmission of T. solium from humans to pigs must include measures to deny pigs access to human feces, a change which is likely to be resisted because of the traditional and functional aspects of established pig-rearing practices.     

A pilot study of common health problems in smallholder pigs in Angónia and Boane districts, Mozambique

A pilot survey was conducted in 2 districts in Mozambique to determine the most important health problems facing smallholder pig producers. While African swine fever is the most serious disease that affects pigs at all levels of production in Mozambique, it is likely that productivity is reduced by the presence of mange and gastrointestinal parasites, while in traditional systems the conditions are favourable for the development of porcine cysticercosis caused by the pork tapeworm Taenia solium, which poses a health risk to communities. Results of the pilot survey confirmed that, with the exception of African swine fever, ecto- and endoparasites are probably the most important health risks for producers. Porcine cysticercosis is more prevalent among pigs in traditional, free-ranging systems, while mange becomes a serious factor when pigs are permanently confined.     

Comparative evaluation of an indirect ELISA test for diagnosis of swine cysticercosis employing antigen from Taenia solium and Taenia crassiceps metacestodes

Taenia solium cysticercosis is still a serious public health problem in several countries where poverty and lack of hygiene favor transmission. Because pigs are the primary intermediate hosts, prevalence of porcine cysticercosis is a reliable indicator of active transmission zones. Serological diagnostic methods are important tools for epidemiological studies since they can be applied to living animals on a large scale. Four antigen preparations (cyst fluid and crude) from T. solium and T. crassiceps metacestodes were compared for swine cysticercosis diagnosis by indirect ELISA (IE). Twenty-eight serum samples from swine naturally and experimentally infected by cysticerci of T. solium and 56 serum samples from swine reared in commercial herds were tested. Best results of overall sensitivity were obtained by the use of cyst fluid and crude antigen of T. crassiceps metacestode (100 and 96.4%, respectively). Using homologous antigen preparations we have observed higher specificity percentage (98.2% for cyst fluid and 96. 4% for crude metacestode T. solium antigen). We concluded that sensitivity is of far more importance than specificity for identification of endemic areas in order to prevent transmission to man. We conclude, therefore, that IE performed with cyst fluid antigen of T. crassiceps metacestode is a better tool for that purpose.     

Taenia solium oncosphere antigens induce immunity in pigs against experimental cysticercosis

Immunity to Taenia solium infection was investigated using an experimental intramuscular oncosphere infection assay (IMOA) model in pigs. Three naturally infected pigs with cysticercosis were treated with oxfendazole (OFZ), a drug demonstrated to kill cysts in porcine muscle. These animals were then challenged with oncospheres but did not develop any cysts while three uninfected pigs that were similarly challenged, did develop intramuscular cysts. In another study, two groups of three pigs each were immunized with crude T. solium oncosphere and metacestode antigens, respectively, and tested with the IMOA. Immunization with crude oncosphere antigens (OAs) induced 100% protection, while metacestode antigens provided only partial protection. Immunoblots showed that pigs with complete immune protection to oncosphere intramuscular challenge had antibodies to two OAs at 31.3 and 22.5 kDa, respectively. Antibody to these two antigens was absent in pigs immunized with metacestodes or in uninfected control pigs. This study demonstrated the presence of two antigens that are unique to the oncosphere. Although, antibody to these two antigens is consistently present in pigs that are protected from an oncosphere intramuscular challenge their role in preventing infection by T. solium larval cysts is still hypothetical.     

Evaluation of tongue inspection and serology for diagnosis of Taenia solium cysticercosis in swine: usefulness of ELISA using purified glycoproteins and recombinant antigen

Evaluation of serology using glycoproteins (GPs) purified by preparative isoelectric focusing (pH 8.8) and recombinant chimeric antigen (RecTs) of Taenia solium was carried out using (1) blood samples on filter papers from pigs infected with different doses of eggs of T. solium in Mexico, (2) serum samples from pigs found infected naturally in Vietnam and Ecuador and (3) serum samples from pigs suspected to be infected with T. solium by tongue inspection in Tanzania. Antibody responses (IgG) were detectable in experimentally infected pigs confirmed harbouring 16 or more cysts at necropsy from 30 days after egg inoculation. One of three pigs naturally infected and harbouring 2.5 cysts/kg muscle and most of pigs harbouring=5.0 cysts/kg were also seropositive by ELISA. Although pigs may be infected with other taeniid species such as Taenia hydatigena, pigs harbouring this parasite were negative in ELISA. Approximately, 76 and 78% of sera from pigs having nodule(s) in the tongue (positive tongue inspection) were serologically positive by both ELISA and immunoblot, respectively. Furthermore, approximately 34 and 18% of sera from pigs having no nodules in the tongue (negative tongue inspection) were also seropositive by ELISA and immunoblot, respectively. ELISA using the two antigens was more sensitive than immunoblot and reliable for differentiation of pigs infected with cysticerci of T. solium from those either uninfected or infected with other taeniid species. Pigs without nodule by tongue inspection should be checked serologically in endemic areas.     

Successful immunization of naturally reared pigs against porcine cysticercosis with a recombinant oncosphere antigen vaccine

Taenia solium causes cysticercosis in pigs and taeniasis and neurocysticercosis in humans. Oncosphere antigens have proven to be effective as vaccines to protect pigs against an experimental infection with T. solium. A pair-matched vaccination trial field, using a combination of two recombinant antigens, TSOL16 and TSOL18, was undertaken in rural villages of Peru to evaluate the efficacy of this vaccine under natural conditions. Pairs of pigs (n=137) comprising one vaccinated and one control animal, were allocated to local villagers. Animals received two vaccinations with 200 μg of each of TSOL16 and TSOL18, plus 5mg Quil-A. Necropsies were performed 7 months after the animals were distributed to the farmers. Vaccination reduced 99.7% and 99.9% (p<0.01) the total number of cysts and the number of viable cysts, respectively. Immunization with the TSOL16-TSOL18 vaccines has the potential to control T. solium transmission in areas where the disease is endemic, reducing the source for tapeworm infections in humans.     

Vaccination of pigs with the S48 strain of Toxoplasma gondii – safer meat for human consumption

As clinical toxoplasmosis is not considered a problem in pigs, the main reason to implement a control strategy against Toxoplasma gondii (T. gondii) in this species is to reduce the establishment of T. gondii tissue cysts in pork, consequently reducing the risk of the parasite entering the human food chain. Consumption of T. gondii tissue cysts from raw or undercooked meat is one of the main sources of human infection, with infected pork being considered a high risk. This study incorporates a mouse bioassay with molecular detection of T. gondii DNA to study the effectiveness of vaccination (incomplete S48 strain) in its ability to reduce tissue cyst burden in pigs, following oocyst (M4 strain) challenge. Results from the mouse bioassay show that 100% of mice which had received porcine tissues from vaccinated and challenged pigs survived compared with 51.1% of mice which received tissues from non-vaccinated and challenged pigs. The presence (or absence) of T. gondii DNA from individual mouse brains also confirmed these results. This indicates a reduction in viable T. gondii tissue cysts within tissues from pigs which have been previously vaccinated with the S48 strain. In addition, the study demonstrated that the main predilection sites for the parasite were found to be brain and highly vascular muscles (such as tongue, diaphragm, heart and masseter) of pigs, while meat cuts used as human food such as chop, loin, left tricep and left semitendinosus, had a lower burden of T. gondii tissue cysts. These promising results highlight the potential of S48 strain tachyzoites for reducing the number of T. gondii tissues cysts in pork and thus improving food safety.     

Taenia solium porcine cysticercosis: viability of cysticerci and persistency of antibodies and cysticercal antigens after treatment with oxfendazole

The aim of this study was to assess the effect of treating Taenia solium infected pigs with oxfendazole (OFZ) on viability and clearance of cysticerci and the corresponding persistence of specific antibody isotypes (IgG(total), IgG1, IgG2 and IgA) and circulating cysticercal antigen (CCA). Antibody isotypes and CCA responses were measured by antibody-ELISA (Ab-ELISA) and antigen ELISA (Ag-ELISA), respectively. Correlations were made between antibodies, CCA and the total number of cysticerci enumerated at necropsy. Forty pigs with cysticercosis were randomly allocated into two groups: Treatment group (n=20) was treated with OFZ at 30 mg/kg orally while the treatment control group (n=20) was not treated. Five uninfected pigs served as negative controls. Pigs were killed at 1, 4, 8 and 26 weeks post-treatment (wkpt). Overall, the mean total cyst count in treated pigs was 2904+/-5397 (mean+/-S.D.) while in the controls it was 6235+/-6705. Mean cyst viability was 5+/-11% (mean+/-S.D.) and 97+/-4% in treated and control pigs, respectively. Results showed that OFZ killed muscular cysticerci over a period of 4 weeks but failed to kill cerebral cysticerci. Antibodies, CCA responses and clearance of dead cysts from the meat, depended on the cyst intensity of individual pigs at time of treatment since both antibody and CCA correlated with intensity of cysticerci at necropsy (r=0.441, P=0.005; r=0.654, P<0.001), respectively. IgG1 responses were the best indicator of treatment efficacy because they were predominant in both infected treated and control pigs and disappeared early after treatment. Both Ab/Ag-ELISA failed to detect cysts in the brain. Though dead cysticerci took some time (26 wkpt) to clear from the meat, treatment of porcine cysticercosis with OFZ should, in combination with other intervention measures be considered as an important, cost-effective measure in the control of taeniosis/cysticercosis.